Talk:Bipolar junction transistor/Archive 1

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Archive 1

Voltage or current?

"very sensitive to the current passing through the base."

I've heard it's actually the voltage that does it, in BJTs *and* FETs. current is just a byproduct in BJTs. - Omegatron 20:37, Jul 28, 2004 (UTC)

You can't have one without the other. Whether you see it as current-sensitive or voltage-sensitive just depends on which model you use. As a first approximation, a BJT can be modelled as a current-controlled current source. The proportionality constant between the base current and the collector current is β or h_FE. This is taught in many lower-level electronics courses, since it is often sufficient for circuits operating in the forward-active mode. The Ebers–Moll and Gummel–Poon models use diode-like equations relating voltage to current. When using the current-controlled model, it's useful pedagogically to assign causation to the current, and when using the Ebers-Moll model it may be more useful to assign causation to the voltage. -- Tim Starling 01:02, Jul 29, 2004 (UTC)

Math models obscure the question as they simplify the concepts. Look to the full-blown details in order to understand how transistors actually work. As with any diode junction, the B-E junction contains an insulating "depletion layer" whose thickness is controlled by applied voltage. Make this insulating layer thicker, and the diode turns off (reverse biased), or make the layer thin enough, and charges are able to get across; the diode turns on. E.g. the diodes's current is controlled by the voltage applied to the diode's terminals. Now in a BJT there essentially are two currents in the same B-E diode junction: the base current and the Collector current, and... both are controlled by the thickness of the insulating B-E depletion layer. And the thickness of the B-E depletion layer is controlled by the applied voltage Vbe. THEREFORE, both the collector current Ic and the base current Ib are controlled by the Base-Emitter voltage Vbe. Things only SEEM confusing because Ib happens to be proportional to Ic. In reality Ib cannot affect Ic, instead both are affected by a third variable: the B-E voltage. Weird, eh? At the most fundamental level, BJTs and FETs are both controlled by voltage. However, in a BJT the main current must cross an insulating layer of variable thickness, while in an FET the main current remains in the conductive regions while the insulating regions encroach from the side. If a BJT acts like the dark lens in a pair of variable-density sunglasses, then an FET is more like a variable-aperature optical shutter or iris: a variable-sized empty hole. --Wjbeaty 21:29, Mar 20, 2005 (UTC)

Can't agree with this. Whether a BJT is a current or voltage controlled device depends upon whether the base-emitter junction is current or voltage fed. If we use a current source, then the b-e voltage will float to whatever is appropriate to allow that current to flow. If we use a voltage source, then a current appropriate to the voltage will flow. So, in truth, the collector current is dependent on *both* the base-emitter voltage and current. However, given that beta (the current gain) is relatively constant, then it's easier to consider a BJT as a current controlled device: increase the base current by x, and the emitter current increases by beta times X. Phil Holmes 15:45, 19 August 2005 (UTC)

I agree in principle with what you are trying to say here but I am uncomfortable with how you have said it. Specifically, the manner in which a two-port is driven does not in any way affect it's fundamental nature. Further, claiming that the collector current is dependent on both the base-emitter voltage and current is misleading. I am not aware of an equation for collector current that, to first order, has independent terms for both base-emitter voltage and current. But, you have also said in effect (and correctly) that the base-emitter voltage and base current are not independent. Thus, the collector current equation can be written as a function of base-emitter voltage OR base-emitter current.

Now, consider an ideal transconductance amplifier. By definition, the input current is zero so driving this amplifier with a current source is, let us say, a problem. In the non-ideal case however, the input current may be non-zero and is related to the input voltage (linearly in the case of a resistive input or more generally, non-linearly as in the case of BJT). Thus, by solving for the input voltage in terms of the input current, one can look at the non-ideal transconductance amplifier as a non-ideal current amplifier. This has nothing to do with the way the amplifier is driven - it is simply an alternate perspective on the transfer equations.

If the base-emitter of a BJT is driven directly by a current source, it is reasonable to adopt the current amp perspective. Since the voltage developed at the input is relatively small and nearly constant over a wide range of input current, the BJT is an (approximately) ideal linear current amplifier from this perspective. If a voltage source is used instead, it is reasonable to adopt the transconductance amp perspective. However, since the source current varies greatly and non-linearly over a small range of input voltage, the BJT is a highly non-linear non-ideal transconductance amplifier from this perspective. Alfred Centauri 20:57, 19 August 2005 (UTC)

I think the only difference between what you've said and what I said is that I said *both* and you, in effect, replaced that with *either*. On reflection, I'd go along with that. Phil Holmes 08:30, 22 August 2005 (UTC)

It all boils down to whether we want to teach how transistors work, or whether we only want to solve some design equations. Never lose sight of the fact that the collector current is never directly controlled by the base current. If we drive the base with a constant current source, this creates a certain value of BE voltage. This BE voltage then determines the thickness of the depletion layer, which then controls the collector current. Yet if we could somehow hold Vbe constant while changing Ib, we'd find that Ib cannot control Ic. Be careful not to confuse the simplified "black box" mathematical model with the physics-based explanation of transistor behavior. Yes, simplified engineering equations say that Ic is determined by Ib, and these equations are incredibly useful... but these equations are "wrong" because they mislead us into believing that Ib directly affects Ic. It does not. Instead, Ib determies Vbe, and Vbe determines Ic, which shows that a transistor is a voltage-controlled device which pretends to be a current-controlled device. Many people seem to hate this fact, and try to talk themselves into believing that Ib directly affects Ic. But unfortunately there's no escaping the well-known transistor physics. If we want to know how transistors work, we have to confront the fact that the flow of Ib charges has no affect on the flow of Ic charges. Yet for simplified introductory classes where nobody cares how transistors actually work, it's fine to say that Ic is controlled by Ib... and then to never mention any complexities such as the fact that the control relies indirectly upon Vbe. On the other hand, if a more advanced textbook never mentions the Eber-Molls model, or worse, tries to use semiconductor physics concepts to "prove" that Ib affects Ic, then that author has a serious misconception, and is doing their readers a disservice. --Wjbeaty 20:02, 4 April 2006 (UTC)

mnemonic

i can't ever remember from the schematic symbol which side is emitter/collector and whether it is npn/pnp. any silly mnemonics for remembering or should i make one up? - Omegatron 16:21, Oct 18, 2004 (UTC)

It's not much of a mnemonic, but the terminal with the arrow is the emitter, and the arrow points in the direction of current flow. So if the arrow points from emitter to base, it implies the emitter is injecting positive charge into the base. Emitter positive, base negative, therefore pnp. -- Tim Starling 03:45, Oct 19, 2004 (UTC)

yeah, not much of one. something like e is for arrow and the N in the middle of PNP stands for "pointing iN". it has to be something you can just remember without thinking about it. but that is a really stupid attempt. ummmm... i dunno. i'll just stare at them until i remember i guess. :-) - Omegatron 13:41, Oct 19, 2004 (UTC)

Never Points iN and Points iN Proudly. that is a good one. and a bow/archer "emits" arrows? i guess that works. - Omegatron 14:50, Oct 19, 2004 (UTC)

The one I used was Not Pointing iN for NPN, and you could use Pointing iN Permanently for PNP if you need to remember both. This assumes you can remember that the emitter is the one with the arrow on. This last could'nt be more obvious really- its a bit like the symbol for a male! (who is normally the 'emitter' in sexual relations! --Light current 00:55, 5 February 2006 (UTC)

doping

In the illustration, there seems to be 4 types of semiconductor - p+, p-, n+, n-. What does this signify? The diagram looks to be more informative than the usual NPN or PNP layer discription. Where can I find more info? Thanks.

p⁺ means strongly doped with acceptor impurities, p^- means weakly doped with acceptor impurities, n⁺ and n^- mean strongly and weakly doped with donor impurities, respectively. The region of very strong doping leading up to the metal is called an ohmic contact. Strong doping reduces the diodic effect of touching metal and semiconductor, see Schottky barrier. As for more information, a google search didn't turn up much for me. You might want to try a textbook, e.g. ISBN 0471333727. -- Tim Starling 00:03, Nov 23, 2004 (UTC)

I've beefed up the sections on doping in the semiconductor article - this explains the n+, p+ nomenclature. --Phil Holmes 21:26, 29 August 2005 (UTC)

models

this should have some small- and large- signal models and such. - Omegatron 02:24, Mar 4, 2005 (UTC)

I'll draw up some diagrams for ones that we decide to use. Actually, this could be a good test for Wikipedia:Modular electronics diagrams. I'm going to start working on it. (Since I need to re-learn this for a project anyway). - Omegatron 16:44, Mar 6, 2005 (UTC)

Here are two active-mode models:

		C
		αi_E
B
	i_E ↓	I_s/α
		E

B				C
	i_B ↓		βi_B

		E

What do you think? - Omegatron 18:09, Mar 6, 2005 (UTC)

Uses and possible technical details

Well I was thinking that a uses section for BJTs could be added to the article.

Uses - Current sources - TTL, transistor transistor logic

Technical Detail

-Low input impedance when compared to FETs and MOSFETs. Input impedance depends on amplifier configuration. - Output impendance is low. Also is dependent on amplifier configuration.

Amplifier configurations

Links to the following configurations maybe.

- Common collector - Common emitter - Common base

How gain works

Please see that I've changed the sentence that used to say "The proportion of electrons able to run the base "gauntlet" and make it to the collector is very sensitive to the current passing through the base." That's not correct - I've now clarified that this is fairly constant, but that gain occurs as a result of the emitter being more highly doped. Phil Holmes 08:47, 22 August 2005 (UTC)

Good catch. I was just reading that paragraph a day or to ago and the word 'proportion' didn't jump out at me at all. But don't forget that the light doping and the thinness of the base is also important to the gain. What is required is that the the diffusion length is long compared to the thickness of the base. This ensures that the odds of a charge carrier from the emitter recombining in the base region before reaching the base-collector junction are small. The smaller the odds, the greater the 'gain'.

One thing that I don't see mentioned in the article is that once the charge carrier reaches the base-collector junction, it is the electric field within the depletion zone that sweeps the charge carrier into the collector region. In a way (this is sure to raise some eyebrows!), it can be said that the role of the forward biased base-emitter junction is to increase the reverse bias 'leakage' current through the base-collector junction.

On another note, there is a statement in the opening paragraph that I'm concerned about but that I'm hesitant to change. This statement is: "BJTs can be thought of as current-controlled resistors". This is really wrong technically yet if it helps newcomers grasp the concept I'm not going to bother with it. Alfred Centauri 20:41, 22 August 2005 (UTC)

I've always been in favor of the "controlled resistors" analogy for newcomers, but it's perfectly acceptable to add "this is only a crude analogy" or whatever you want to make it accurate. — Omegatron 21:33, August 22, 2005 (UTC)

I'm not sure there is a better analogy at the newcomer level. I've thought about something like "the BJT is to electric current what power brakes are to pedal pressure" but I not sure if that even makes sense. Is there any way that an analogy can be made between a BJT CE amplifier circuit and a power brake system? Alfred Centauri 21:53, 22 August 2005 (UTC)

You can make a good analogy to a Globe valve where the plunger is controlled by a diaphragm. EGR valves work this way. There is a big flow that is stopped by the plunger, and then you can control the plunger by applying a constant pressure or vacuum to a diaphragm (FET) or a small, constant current to a diaphragm with small holes in it (BJT). I've been meaning to draw a picture of this for hydraulic analogy. — Omegatron 23:57, August 22, 2005 (UTC)

I just visited the hydraulic analogy page. I've often thought about this analogy so it is good to see you working on this. I have a suggestion for resistor. A small diameter pipe sounds like higher gauge wire. But a resistor is like an obstacle course for moving electrons so maybe a water resistor is like a restrictor plate. I'm picturing a disk with holes in it that fits inside the pipe. I doubt if such a thing is actually found in a hydraulic system but maybe it would help create a picture of electrical resistance in a resistor Alfred Centauri 03:06, 23 August 2005 (UTC)

The analogy of a BJT to a current controlled resistor is very poor. Alfred's comment towards the top of this page reminded me of how much that grated when I read the article for the first time. To explain. The resistor we would be refering to would be between the collector and emitter terminals. With no base current, we put a voltage varying between 1 and 5 volts (say) between those terminals, and see what current flows. In this state, it would be negligible. We now apply some base current and do the same. The result we will see is that beta times the base current will flow at 5 volts, and there will be very little difference at 1 volt. (The Early effect means there is some difference). This is very different behaviour from a current controlled resistor. With one of those, I'd expect to see "infinite" resistance with no base current, and a current at 1 volt that is 1/5 the current at 5 volts with base current applied. My suggestion would be to delete the analogy. Phil Holmes 11:44, 23 August 2005 (UTC)

We already agreed it's a poor analogy. I still think it's helpful for someone who has no concept of what it is. It's better than saying "a controlled current source" or "an amplifier". Do you have a better suggestion? — Omegatron 14:06, August 23, 2005 (UTC)

Frankly stuck for a good analogy. Perhaps it would be best not to bother with analogy and simply say that a BJT is a device that controls current flow between the collector and emitter by using a control signal between base and emitter? Incidentally, and you're probably aware of this, I found a useful reference when searching for source information to validate my memory on some of this. [1] Phil Holmes 15:52, 23 August 2005 (UTC)

The physical reason for gain

I was wondering if much more could be said on how current and voltage gain are obtained in a transistor. I have no idea myself, and i couldn't find any good explanation of it. I too think of a transistor as a variable resistance, but that analogy obviously breaks down when applied to an amplifying transistor circuit. I would greatly appreciate it if anyone could explain how gain is physically obtained. Fresheneesz 21:12, 10 February 2006 (UTC)

Does this not explain it ?

In normal operation, the emitter-base junction is forward biased and the base-collector junction is reverse biased. In an npn-type transistor for example, electrons from the emitter wander (or "diffuse") into the base. These electrons in the base are in the minority and although there are plenty of holes with which to recombine, the base is always made very thin so that most of the electrons diffuse over to the collector before they recombine with holes. The collector-base junction is reverse biased to prevent the flow of holes, but electrons are swept into the collector by the electric field around the junction. The proportion of electrons able to cross the base and reach the collector is approximately constant in most conditions. The heavy doping (low resistivity) of the emitter region and light doping (high resistivity) of the base region mean that many more electrons are injected into the base, and therefore reach the collector, than there are holes injected into the emitter. The base current is the sum of the holes injected into the emitter and the electrons that recombine in the base - both small proportions of the total current. Hence, a small change of the base current can translate to a large change in electron flow between emitter and collector. The ratio of these currents Ic/Ib, called the current gain, and represented by β or Hfe, is typically 100 or more.

--Light current 21:44, 10 February 2006 (UTC)

mm.. not really. I mean, it does indeed explain the general operation of a transistor, but the way its written is a bit hard to understand. On top of that, gain takes a huge backseat in this description. After reading that paragraph perhaps for the 4th time or so, I still can't imagine how gain would occur. Obviously small changes in the base voltage produce large changes in the amount of current allowed throgh the transistor - thats the whole point of the device. However, gain requires that *more* current or *more* voltage come out than comes in, which seems 120% unintuitive to me and I think is *so* important that it should have its own section on this page. Also I'm pretty sure that the base *current* is more of a byproduct than a cause, and that the base *voltage* is really what produces the transistor changes. Fresheneesz 22:25, 10 February 2006 (UTC)

OK then, does this explain it any better:

Math models obscure the question as they simplify the concepts. Look to the full-blown details in order to understand how transistors actually work. As with any diode junction, the B-E junction contains an insulating "depletion layer" whose thickness is controlled by applied voltage. Make this insulating layer thicker, and the diode turns off (reverse biased), or make the layer thin enough, and charges are able to get across; the diode turns on. E.g. the diodes's current is controlled by the voltage applied to the diode's terminals. Now in a BJT there essentially are two currents in the same B-E diode junction: the base current and the Collector current, and... both are controlled by the thickness of the insulating B-E depletion layer. And the thickness of the B-E depletion layer is controlled by the applied voltage Vbe. THEREFORE, both the collector current Ic and the base current Ib are controlled by the Base-Emitter voltage Vbe. Things only SEEM confusing because Ib happens to be proportional to Ic. In reality Ib cannot affect Ic, instead both are affected by a third variable: the B-E voltage. Weird, eh? At the most fundamental level, BJTs and FETs are both controlled by voltage. However, in a BJT the main current must cross an insulating layer of variable thickness, while in an FET the main current remains in the conductive regions while the insulating regions encroach from the side. If a BJT acts like the dark lens in a pair of variable-density sunglasses, then an FET is more like a variable-aperature optical shutter or iris: a variable-sized empty hole. --Wjbeaty 21:29, Mar 20, 2005 (UTC)

--Light current 22:36, 10 February 2006 (UTC)

It does explain a transistor better. But I must be missing something fundemental, because I see no mention of gain in that description, nor can I see how gain arrises from that description. All of these descriptions seem to follow the variable-resistor analogy, while the concept of gain doesn't. Sorry if i'm being a pain in the ass, but I really think this is important. Fresheneesz 23:22, 10 February 2006 (UTC)

Well you do understand that current gain is the ratio of Ic/Ib ? Also, if you can control a variable resitor with a voltage or current, you can get gain , yes? --Light current 23:28, 10 February 2006 (UTC)

That must be what I don't understand. I understand the mathematics of Ic/Ib, but I don't understand why that it is the case. What I think I don't understand is that you can get gain with a voltage-based variable resistor. I would have thought that that is impossible. If the variable resistor analogy is held, then by, say, increasing the voltage in the base, the resistance through the CE junction goes down. But no matter how much one varies a resistor, it seems to me that the limits are a gain of 1 and a gain of 0 (when the resistance is infinity and 0 respectively). It seems to me that the resistance would have to be negative for one to get gain out of it (ie a battery or something). Fresheneesz 00:28, 11 February 2006 (UTC)

OK. If you have a variable resistor connected between a voltage supply and a load, then suppose somehow, you could alter the value of that variable resistor in sympathy with the input signal. Do you see how that will change the voltage across the output resistor?--Light current 01:00, 11 February 2006 (UTC)

Perhaps it might help if a sentence were added at the end of the paragraph originally quoted by Light Current. Put simply, this feature of the high doping of the emitter and low doping of the base means that a small change in current flowing between the base and emitter causes a larger change in current flowing between the collector or emitter: gain. --Phil Holmes 15:37, 11 February 2006 (UTC)

I think Fresheneesz must be thinking that the gain is happening from C to E or something, when in fact it is happening between B and C. But he is correct in thinking that it is the base emitter voltage that controls the collector current and the base currrent is just a by product!.--Light current 16:52, 11 February 2006 (UTC)

OH! Gain from B to C. That makes perfect sense. I've never thought of it like that. But looking back at the problem that confused me, It seems like the emitter and base get the same magnitudes of voltage. Heres a picture:

In my book this is labeled as "common-base" configuration

I can see how one would get gain using two different voltage sources (one at the emitter end, and one at the base end), but I can't see how gain could happen when the emitter and base voltages have the same magnitude. Fresheneesz 21:47, 11 February 2006 (UTC)

Well E and B have nearly (but not quite) the same voltages on them. Remember that there is an exponential dependence of the collector (or emitter) current on Vbe.--Light current 22:53, 11 February 2006 (UTC)

I didn't read the whole thing (and didn't understand transistors neither) but I'll try to help anyway, corrections are welcome:

gain is a mathematical concept that arises from equations. In the physical world we have lots of electrons (in the npn) pushing to enter the emitter and cross base's ultra thin layer (since the depletion (insulating) layer has been removed by direct polarization.) Then electrons are projected to the collector's layer since the ultra thin base layer has not as much holes to capture every electron. In the collector an electromagnetic field attracts the 99% of electrons and "collects" them to the collector's exit. A negligible amount of charges goes to the base "forming" a little current (that can be seen as an unwanted side-effect, hence the MOSFETs.) The whole process can be modelled mathematically as an amplifier with a gain of quasi 100 (the 1 electron that goes out the base against the 99 that go out the collector.)

BJT transistors are made in order to work this way efficiently. That's why they have a thin base layer (otherwise there would be no transistor effect) and an emitter more doped than the collector and very different surfaces (otherwise they would have been symmetrical and with major power losses.) --Zimbricchio 13:09, 7 June 2006 (UTC)

Here is another perspective of the bjt gain: For a well constructed transistor when a single carrier (hole for an NPN) is injected from the base into the base-emitter space charge layer, you will get approximately beta times as many carriers (electrons for an NPN) injected from the emitter into the space charge layer. The reason for the larger number of carriers from the emitter is the higher doping of the emitter. Once the carriers injected from the emitter reach the base most will diffuse through and end up at the collector. You get more than beta injected from the emitter because you lose a few due to recombination in the base, hence the requirement for a thin base. The imbalance of carriers from the base compared to the emitter is the primary cause for current gain. This explanation covers the case for an upside down transistor (where you try to use the collector as the emitter) where the beta is about one because the base and collector doping is comparable.

This explanation also is relevant to the current control vs voltage control discussion because it shows that the factor that controls the emitter current is the base current, the number of carriers injected from the base to emitter.

Volts must exist? Two majority carriers?

Light current - Your change of 'a voltage must be applied' to 'a voltage must exist' is interesting but rather opaque. What is your reasoning for making this change?

Also, isn't it true that a PN junction necessarily 'employs' both types of majority carriers? It might be misleading to make this statement especially in the opening paragraph. It is usually said that the BJT is a minority carrier device for the reason that the charge carrier current making the greatest contribution to the total electric current is the minority carrier in the base of the BJT. Alfred Centauri 13:52, 25 August 2005 (UTC)

a) I changed it to 'volts must exist' to remove the impression that you can just put any old battery across the BE junct. as the diagram shows. Because of the exponential relationship of current to voltage, current can vary tremendously with a few mV change. I admit its not the best wording! But I cant alter the diag to include a base resistor.

b) I mentioned 2 types of charge carrier to try to explain the name Bipolar Junction Transistor (as opposed to FET which has only one type of charge carrier) Again this may need rewording if you think its not clear.

See here for instance [2] Light current 15:52, 25 August 2005 (UTC)

Perhaps stating that current is carried by both holes and electrons would be a good wording? Phil Holmes 16:11, 25 August 2005 (UTC)

I've changed some wording related to my first question but I guess I got auto-logged out before I finished my edit. Alfred Centauri 18:35, 25 August 2005 (UTC)

Anybody know what is meant by 'high' doping and 'low' doping? Is the writer trying to differentiate between the majority carrier types in the base(P region) and the emitter(N region). If so, it is not explained very well. Light current 23:04, 25 August 2005 (UTC)

If I were to use those terms, I would be refering to high or low doping densities. The base region is lightly doped which means that the mobile hole and electron densities are relatively similar. That is, the majority carriers aren't that great of a majority. On the other hand, the emitter is highly doped meaning that there are very few minority carriers compared to the majority carriers. BTW, I like your addition of the word 'appreciable' but I would suggest that you parenthetically add what appreciable is in this context. I would think that something in the neighborhood of 1mA would be about right. Regarding your change of 'emitter' to 'base' - if it makes you feel better then so be it. Both are correct as long as $\beta$ is finite. Here's a question for you to ponder though. Let $\beta$ go to infinity and ask what current does $V_{BE}$ control? Alfred Centauri 01:44, 26 August 2005 (UTC)

I was thinking of the case when the collector current is small - but in that case, Ib = ~ Ie, so I'm not sure now! I guess I was thinking of the B-E junction alone.Light current 20:21, 26 August 2005 (UTC)

I'm not sure what your notation is here. Are these small-signal currents? Actually, it looks like the notation used on the original schematic that I have now modified. That is, for DC (constant) voltages and currents, the letter and subscripts should both be capitalized. So given that, you are correct that $I_{B}$ is proportional to $I_{E}$ as long as $\beta$ is finite and the BJT is in the active region of operation. So, it is equally correct to say that $V_{BE}$ controls $I_{B}$ or $I_{E}$ or $I_{C}$ . However, if you let $\beta$ tend to infinity (which is not so farfetched - the small signal model for a JFET 'looks' like the small signal model of a BJT with $\beta$ set to infinity), $I_{B}$ is zero. In this limit, it is clear that fundamentally, $V_{BE}$ controls $I_{E}$ I'm teaching a junior level class on small signal modeling of transistor circuits this semester. It's good to clear out the cobwebs and review this stuff. It's amazing how much more sense it makes when you have to explain to someone else. I remember reading somewhere that a prominent theoretical physicist would, whenever he was stumped on some difficult problem, explain the problem to his dog. His dog would just sit there and look at him without interrupting and, as he would try to explain the problem to his dog, he would invariably see the resolution to his difficulty. Alfred Centauri 20:52, 26 August 2005 (UTC)

Yes, I was intending DC currents, but I've always been sloppy about the capitalisation I use (I just cant remember them all (any?). The problem does not practically occur in JFETs in that most reasonable voltages applied between gate and source won't cause a large current to flow and blow up your transistor junction( unless you apply the wrong polarity).-- that is the point I was tring to make. PS I must get a dog!!(or is WP just as good?):-) Light current 21:22, 26 August 2005 (UTC)

Text from Transistor

I did not know why I'm putting so much info on transistor, slaps forehead. The transistor page can get smaller if I link to bjt and fet. The following paste will be highly edited on transistor now. It is here for future use.

The bipolar junction transistor (BJT) was the first type of transistor to be commercially mass-produced. Bipolar transistors are so named because the main conduction channel uses both electrons and holes to carry the main electric current. Two p-n junctions exist inside the BJT, colector-base junction and base-emitter junction. When the BJT is not powered, the junctions are in unbiased thermal equilibrium with a depletion region formed at each junction. The arrangement of greatest interest is when the B-E junction is forward biased and the C-B junction is reverse biased because this makes amplification possible. Applying a forward bias voltage to the B-E junction unbalances the thermal equilibrium of the junction. In an NPN type BJT, the p-type base begins to inject surplus holes (holes not required to maintain thermal equilibrium) into the emitter where they quickly recombine in the n-type material at the emitter contact. Similarly, the emitter injects surplus electrons into the base. If not for the close proximity of the reverse-biased C-B junction, the B-E junction would behave like a diode–injected emitter electrons would recombine in the base and transistor action would not occur. However, in the NPN BJT, the electrons which are injected from the emitter into the base diffuse across the very narrow base region before most of them have time to recombine within the base region. The depletion region of the nearby reverse biased C-B junction contains an electric field, which sweeps any electrons close to it into the n-type collector, where they recombine with holes at the collector contact. Through this action, only a small amount of carriers in the base (holes) are needed to cause a large amount of carriers in the emitter (electrons) to flow through to the collector.

diagram

that diagram looks like its meant to represent a particular highly complex process but it doesn't specify which one and really serves more to confuse then inform. imo the first diagram in the article should show a minimal bjt and possiblly have diagrams of more complex processes further down. Plugwash 03:15, 7 January 2006 (UTC)

Dopant concentrations

At the moment, part of the article reads "By varying the voltage across the base-emitter terminals very slightly, the current allowed to flow between the emitter and the collector, which are both heavily doped and hence low resistivity regions, can be varied." AFAIK, this is incorrect. The emitter region of the BJT is the highest doped region, whilst the collector region has a relatively low dopant concentration --Rspanton 00:22, 28 January 2006 (UTC)

Correct. I've deleted the reference to doping at this point to correct this. (The author probably meant that the bulk collector is highly doped to minimise collector resistance, which is true, but it's confusing to state that here). --Phil Holmes 16:41, 28 January 2006 (UTC)

The transistor models

I think the article should include the transistor's signal models, including the reference to the model's components such as gm, r0, rπ, Cμ, Cπ, etc... It should represent the transistor model to a full range of frequencies, from DC to the infinite. Afonso Silva 21:49, 3 February 2006 (UTC)

You are talking about a particular transistor model (the hybrid-pi model). Would it be best to start a new page about that model, or add it to this one? I am unsure about the relevant wikipedia policies. Rspanton 00:01, 5 February 2006 (UTC)

I think a new page on hybrid pi woud be appropriate.--Light current 00:50, 5 February 2006 (UTC)

Yes, that was an example, I think the article should include a section with a brief description of the models, with a picture and the description of the main parameters on every type of signals. Those models include not only the hybrid pi model but also the Ebers-Moll model or the T Model (I don't know more), that section would later include links to the main articles and also explain the advantages and applications of each model. The article lacks that kind of information and much more. By the way, Rspanton, what policies are you talking about? Afonso Silva 23:41, 7 February 2006 (UTC)

Yes . One page on Transistor 'hybrid pi' model, one page on Transistor 'T' model. (I think Ebers Moll is the same as the T model). I dont think there are any more common models!--Light current 00:42, 8 February 2006 (UTC)

Maybe I'm wrong, but I think the Ebers Moll and the T Model are separate models, the Ebers Moll model is used to predict the operation of the BJT in all modes (active and saturation). The T model is mainly used to analyze the BJT behaviour in AC operation. Afonso Silva 21:22, 15 February 2006 (UTC)

High-frequency behaviour

The article should also include a reference to the transistor behaviour at high frequencies, and the existance of parasite capacitances that influence the device behaviour. Afonso Silva 21:50, 3 February 2006 (UTC)

Alpha

In my ECE book, it says that alpha is different during DC operation and AC operation. It defines α_DC to be I_C / I_E and α_AC to be ΔI_C / ΔI_E. It goes on to say that the ac alpha is formally called the "common-base, short-circuit, amplification factor". This seems to be inconsistant with the article's "α_F. Fresheneesz 20:46, 9 February 2006 (UTC)

Forgive me if you already know this, but if you're ECE, you should get comfortable with the small signal model concept. In analog design, you have steady-state (DC) and small-signal (AC) models. You need DC and AC versions of each parameter, because each one is used for different purposes. DC is needed to find the operating point, output range, etc. AC is needed to find the gain. In reality AC and DC operation are happening at the same time; it's just more convenient to analyze them separately. - mako 21:33, 9 February 2006 (UTC)

picture of the structure section

I've replaced the original picture by a much more simple one, that illustrates the contant of the section much better. If someone disagrees with that, just revert the change.

Thank you! It looks fine. I wanted to do that but I don't have drawing skillz Snafflekid 23:40, 15 February 2006 (UTC)

Ebers-Moll Model

Great article! I'm not overly familiar with the Ebers-Moll model, but in the diagrams, the emitter dependant current source refers to I_CD - which doesn't appear to be present in the model. Should the I_ED on the collector side be changed to I_CD?

I believe so too, I_ED is the current from Emitter to Base, it has no place between the Collector and Base. Also, Why are these currents not named I_EB and I_CB? Sounds more logic since we're talking about the Base, not the Drain. -Pelotas 09:58, 9 July 2006 (UTC)

I think there is a slight error in the unapproximated Ebers-Moll equation for iB, looks like VBC and VBE are swapped.

image

most top image has in npn transistor arrow denoting thats npn but pnp lacks it, and its often used on schematics, maybe some info about or image update could solve that? 193.238.17.211 (talk · contribs · WHOIS)

I've just reverted back to the png images. TBH i'm getting mighty pissed off with people replacing well done pngs with poor SVGs. Plugwash 22:52, 2 May 2006 (UTC)

Can you tell us ignoramuses what the difference is please? 8-)--Light current 23:25, 2 May 2006 (UTC)

The arrow was missing on the NPN transistor. Plugwash 23:34, 2 May 2006 (UTC)

There is also the blurry grayness but thats probablly a result of mediawikis SVG renderer and not something you can do much about Plugwash 23:35, 2 May 2006 (UTC)

So png's are prefereable?--Light current 23:39, 2 May 2006 (UTC)

Well for web use a png designed for the size it will be displayed at beats everthing else. However apparently the svg pushers have convinced the powers that be that svg is better as it scales better for other output formats.

In an ideal world, SVG would be best, because it is a vector format. But for whatever reason, mediawiki's rastering process leaves out the arrows. I discovered this when editing Image:Photomultipliertube.svg; the arrows do show up in Inkscape. - mako 21:29, 3 May 2006 (UTC)

http://bugzilla.wikimedia.org/show_bug.cgi?id=5163 says it's a bug in librsvg. - mako 21:38, 3 May 2006 (UTC)

using alpha and beta

Hello. The parameters alpha and beta appear before any explanation about them is given. Could anyone please write some info about it..? Thanks, 132.68.145.85 19:27, 23 June 2006 (UTC)

Ive changed page now to explain alpha, beta and their relationship. Is it any better now? 8-|--Light current 19:39, 23 June 2006 (UTC)

I've added that there is a big difference between the Beta in forward or reverse operation mode, however I am not entirely sure of the numbers. I believe the ideal forward operation current gain is mostly about 300, but the 100...1000 region is probably correct. In reverse the gain is surely smaller than 1? Also, should not be mentioned that another reason for that big gain in forward operation is the extremely small dimension of the base? - Pelotas 10:02, 9 July 2006 (UTC)

Logarithms

I'd like to know more about using bjts to compute logarithms.

The base-emitter voltage is proportional to the log of the base-emitter or collector-emitter current. A diode can do the same things, as shown in this book: [3].

Current or voltage control - that is the question

Moved here from my talk page;--Light current 19:54, 1 August 2006 (UTC)

Bipolar transistors are fundamentally current-controlled devices, notwithstanding the hobbyist page you cite. I'll sit back and let someone else correct it back for now. Dicklyon 19:14, 1 August 2006 (UTC)

There has been a detailed and exhaustive discussion on this topic well before you joined. The consensus of opinion was that the BJT is voltage controlled. I dont think anyone will revert it. but we'll see ! 8-)--Light current 19:54, 1 August 2006 (UTC)

OK, I read that discussion, but I don't agree that a consensus was reached. I think we need to add a section to the article about voltage- and current-control views. The current-control view is most commonly used in circuit engineering, since beta is a simple linear parameter that describes the transistor well. Dicklyon 19:38, 1 August 2006 (UTC)

I agree that the current control explanation appears to work and describe things, but is it the truth of the matter? I think not! 8-|--Light current 19:54, 1 August 2006 (UTC)

I think the issue of truth is a bit misplaced here. It's all about description of physical processes, in which no part of the situation can be called the cause as opposed to the effect. A better model, if you want truth, is the charge-controlled model, since it explains collector current as a function of minority charge concentration in the base region, and therefore contains photo-transistor effects, turn-off recovery-time effects, etc. Voltage and current are just the terminal properties we use to explain charge in the base region. Maybe we should write that up, too. Dicklyon 19:59, 1 August 2006 (UTC)

Yes the charge control expalnation would be good addition. 8-)--Light current 20:03, 1 August 2006 (UTC)

OK, I added it, to the section on current control and voltage control, as you noticed and already mutilated. Please don't think that the current-control and voltage-control models should be associated with driving the base from a current source or voltage source (the latter being a ridiculous thing to attempt with a BJT, notwithstanding the funny diagram that shows it that way). In general, the transistor is in a circuit that needs to be analyzed as a whole, and the current-control model almost always makes that job easier if the circuit is intended to be approximately linear. Dicklyon 21:24, 1 August 2006 (UTC)

Dick, I would truly enjoy watching you present this view at a design review of 20 professional analogue i.c design engineers of a mainstream i.c. manufacture. There are those that actually routinely design 10,000 transistor analogue circuits, and actually understand what they are doing, and there are those that don’t. There are also those that don’t know that they don’t.

Kevin aylward (talk) 16:16, 22 February 2009 (UTC)

Kevin, I would truly enjoy seeing you act like a mature contributor to wikipedia; what are the chances? Dicklyon (talk) 23:39, 22 February 2009 (UTC)

Sorry Dick. I do not mutilate. I either improve or delete. Misleading info must be exterminated.--Light current 21:26, 1 August 2006 (UTC)

Apology accepted, as Stephen Colbert likes to say. When you changed "(current control)" to "(if unusually driven by a current source)", you destroyed the parallel explanatory structure of the sentence to insert your irrelevant opinion of what kind of base drive might be usual. It makes no sense anyway, as it seems to imply that you think maybe the base would be driven by a voltage source. As I said, how the base is driven is not relevant to the alternative ways of modeling the transistor action. Dicklyon 21:33, 1 August 2006 (UTC)

Yes I can see you are going to be a worty adversary! I look forward with relish!--Light current 23:11, 1 August 2006 (UTC)

I believe it's spelled 'warty'; and there's no need to be advesarial here, just open up your mind to the alternate points of view. That's what I've done by allowing the voltage-control view to stay. Dicklyon 23:54, 1 August 2006 (UTC)

Sorry I missed out the 'h'. my spelling is always terrible . Ask anyone here!--Light current 00:14, 2 August 2006 (UTC)

The Gummel–Poon charge control model subsection is just a stub, but let's leave it and maybe someone who understands it better or has time will elaborate it. Dicklyon 00:36, 3 August 2006 (UTC)

Anyone disagree with this?

See what's happening here? THE TRANSISTOR IS NOT CONTROLLED BY CURRENT. Instead it is controlled by the base/emitter voltage.

   7. THE P-TYPE AND N-TYPE ARE CONDUCTORS BECAUSE THEY CONTAIN MOVABLE CHARGES.

   8. A LAYER OF INSULATING MATERIAL APPEARS WHEREVER P-TYPE AND N-TYPE TOUCH.

   9. THE INSULATING LAYER CAN BE MADE THIN BY APPLYING A VOLTAGE.

(extracted from Bill Beatys pages at amasci.com)

If so , why? --Light current 23:06, 1 August 2006 (UTC)

If by conductors you mean semiconductors with free majority carriers in them, then yes, 7 is OK. If by a layer of insulating material you mean a depletion region, in which the majority carriers are absent, then yes, 8 is OK. And 9 is OK; you can make the depletion region thin or nil by forward biasing the junction. So yes, that's all fine. However, it does not make a case for "THE TRANSISTOR IS NOT CONTROLLED BY CURRENT". Anyone who uses BJTs knows that you control the collector current by the base current, and that you get a current gain of beta, and that the base–emitter junction has to be forward biased to get such a current.

Oh dear.. .Dicky… err... anyone that is a professional analogue i.c design engineer knows, from trivial inspection of this text, that you are not.

Kevin aylward (talk) 16:28, 22 February 2009 (UTC)

That's my comment you're responding to, not someone named Dicky. But you're right I'm not a professional IC designer at this time, and when I was doing IC design I didn't do a lot of bipolar. And I realize the current-control and voltage-control views are both used. I'm not sure why I stated it above as strongly as I did, three years ago; but the point is that the collector current is based on base charge, which is has its own dynamics, influenced by the B–E junction I and V among other things. Don't push one view to the exclusion of the other, OK? Dicklyon (talk) 17:48, 22 February 2009 (UTC)

As I said in the article, the voltage-control and current-control views are related to each other by the b–e junction V–I curve, and these are both simplifications of the internal processes of the transistor. It is not necessary to deny one to use the other. Dicklyon 23:52, 1 August 2006 (UTC)

If you agreee with 8 & 9, why is a transistor not voltage controlled? PS Pls use my proper name which is 'Light current'. or if you wish to be less formal you can call me 'LC'. Thanks! --Light current 00:19, 2 August 2006 (UTC)

Light voltage, I mean LC, I did not disagree that you can consider a transistor to be voltage controlled. I thought I had stated this clearly; please re-read. I believe it is you who is saying a transistor is NOT CURRENT CONTROLLED. I say it is. Still not clear? Consider re-writing 9 as "the depletion region becomes thin when a forward current is flowing across the junction." Dicklyon 01:01, 2 August 2006 (UTC)

How do you get a current to flow if not by applying a voltage. BTW Dont make fun of my name. You cant afford to with a name like Dick! Think of the fun i could have with that!--Light current 01:05, 2 August 2006 (UTC)

Actually, Dick IS my name. If Light is yours, I'll tred more gently as you must be sensitive about it. How else do you get a voltage on the junction except by putting a current through it? See the symmetry? Dicklyon 01:19, 2 August 2006 (UTC)

Which is more fundamental: current or voltage(emf). ie which comes first?--Light current 09:00, 2 August 2006 (UTC)

I see a bit of confusion here, and it seems to be caused by semantics. People can argue forever over whether the transistor is "voltage controlled" or "current controlled." And each side means something different by that. And each side is trying to win an argument, not trying to clarify matters. (They already know the truth. In any religious battle, the first rule is to never question the viewpoint you're defending.)

Instead, what if we ask a different question: how do transistors work?

In explaining the transistor effect, if we drill down through various ideas, we find a central concept: when the base terminal injects charged particles into the base region, there is no way for the motion of those particles to influence the other charged particles being sent out by the emitter. There is no mechanism by which the base charge-flow can directly affect the emitter's charge-flow. Yet if we inject a tiny base current, we obtain a huge emitter current! The hfe parameter is no illusion. Base current obviously does control emitter current. How? It's because any change in Ib absolutely requires a change in Vbe... and Ie is determined by Vbe because Vbe determines the thickness of the depletion layer. Base current can control emitter current through a multi-step process involving Vbe and the depletion layer. Charged particles injected by the base do in fact influence the charged particles sent out by the emitter. They just can't do it directly.

So is a transistor controlled by current? Yes, if by "controlled," we mean that the emitter current can be changed by changing the base current. Is it "controlled" by voltage? Yes, if by "controlled" we mean that the emitter current can be changed by changing the value of Vbe. And those people who choose one side or the other can fight forever about the "right answer." They'll almost come to blows over the One True Path to transistor enlightenment, since their own viewpoint is obviously good and true and right, while the opposing side are all a bunch of worshippers of Darkness and Confusion whose blasphemy must be ridiculed. After all, young students could be misled from the One True Path! Think of the children! :)

On the other hand, it's hard to become a victim of either meme if you laugh at religious wars. But that's a very difficult habit to teach. Instead, it's easier to take some devout "Current Believers" and shatter mental grip of that meme by demonstrating an alternate religion. So some become outspoken "Voltage Worshippers." With luck they'll eventually see the folly in either viewpoint, and be immunized against both, yet accept both. The "Transistor Zen" practitioner views BJTs from both viewpoints, switching back and forth as needed, while also seeing the duality as an illusion and rejecting the notion that a single best answer can exist. --Wjbeaty 03:03, 2 August 2006 (UTC)

Very nicely articulated, Bill. But then weren't you the guy with the all-caps denial of the current-control view, who LC quoted? Confess it! Dicklyon 05:26, 2 August 2006 (UTC)

Of course! The voltage-control view is "right" because it gives us a deep grasp of the transistor effect. If we watch the impact that the depletion layer has upon transistor currents, then we can figure out how transistors work. But while designing circuitry, unfortunately the voltage viewpoint is far less useful than the current-control viewpoint, because current-control gives us a powerful rule of thumb called hfe.--Wjbeaty 06:10, 16 August 2006 (UTC)

It is an extract from Bills pages and I should have credited it to him. I omitted to do so. Apologies 8-( --Light current 08:52, 2 August 2006 (UTC)

It seems to me the debate can be settled if we can agree whether the voltage controls the current in a resistor, or whether current controls voltage. If we can sort that out, we can apply the same logic to a diode, and then to the transistor base-emitter junction. :-) --Phil Holmes 16:34, 5 August 2006 (UTC)

In resistor physics at the micro level, the e-field accelerates the charge carriers, and they in turn start moving. Isn't this a one-way causation? After all, the acceleration of the charge carriers does not create the e-field. (And... while gravity causes dropped rocks to fall, a falling rock does not magically create a strong gravity field.)

On the other hand, transistors are less akin to resistors and more akin to diodes. Perhaps the real question is: are diodes turned on by forcing charges forward through the depletion layer, or are they turned on by applying a forward voltage across the depletion layer? --Wjbeaty 06:10, 16 August 2006 (UTC)

There's no real answer to the question, though. You're very comfortable with voltage as cause and current as effect, but they're both just a relaxation to the conditions imposed by the external circuit. At the electron level, you can think about a field accelerating the electrons, or about the electron distribution creating a field. Don't think it can only be one way. Dicklyon 06:24, 16 August 2006 (UTC)

Its probably energy flow between the wires that causes the effects (current and voltage) at the terminating resistor.--Light current 17:12, 5 August 2006 (UTC)

Does a wheelbarrow accelerate because you push it, or does the accelerating wheelbarrow cause you to be pushing it? Surely the whole point is whether "control" means "physically control" (i.e. a belief of cause and effect) or "mathematically control" (i.e. apply this function to that value). It is very hard to comprehend a transistor being "physically" controlled by current, because our bodily experience tells us that force causes motion/acceleration; therefore voltage causes current, and so transistors are (physically) voltage-controlled. However the mathematics is not tied to a physical interpretation, and by rearranging equations you can model transistors as current-controlled or voltage-controlled; however this is completely detached from a physical interpretation.

I don't really have much bodily experience with pushing via alteration of electric potentials, so they're both abstract to me. It seems foolish to limit our conception of quantum phenomena (electrons) to things that match our bodily experience. Dicklyon 15:28, 30 August 2006 (UTC)

2007 Revival of argument

The BJT is VOLTAGE CONTROLED, period. It works according to generalised Newton’s laws, to wit, F=qE. That is, to make a charge move in the collector circuit, requires a *force*. It is the *electric field* that makes charges move. Current (ignoring magnetic effects), can not make charges move, so the idea that base current causes collector current is simply daft. It has no basis in physics. We can argue that all voltage is due to charge, so charge is the real cause, but this misses the point. We apply a voltage to the base emitter, and the collector current is caused. Whatever base current exists, just comes in the wash.

For those of you that claim that base current causes collector current, please supply a mathematicall derivation of such effect. Additionally, please explain, why base current does not appear in the 1st order expression, Ic=Io.exp(Vbe/Vt) —Preceding unsigned comment added by Kevin aylward (talk • contribs) 12:06, 7 September 2007 (UTC)

Kevin, such strong statements must come with a strong source. What you're saying makes very little sense, since the field the moves charges to the collector has little to do with the physics of charge injection at the B–E junction. The physics of current control is more based on emitter current (which is where the collector current comes from), not base current, but they happen to be nearly lienarly related so they get used interchangeably in models. And since first-order expression omitting any current or voltage are easy to write, that's no kind of argument. In any case, we should not argue, but cite sources for viewpoints. Dicklyon 15:16, 7 September 2007 (UTC)

That is, to make a charge move in the collector circuit, requires a *force*. Nonsense. You've made a serious error in reasoning, my friend, and an ironic one at that since you invoked Newton. The electric field accelerates a charge. The mere movement of charge does not require any electric field (force) at all. Alfred Centauri 23:36, 7 September 2007 (UTC)

Now why did I just *know* that someone would say that. Yeah, so I am ignorant of basic F=ma. Try getting a current in a resister without a force. —Preceding unsigned comment added by Kevin aylward (talk • contribs) 11:52, 10 September 2007 (UTC)

There's some truth on both sides; in a semiconductor, electrons tend to give up their momentum in collisions, so you need a field to make a net drift current, according to the Einstein relation (kinetic theory). But none of this is particularly relevant to the point being argued, which is whether the transistor can be equally well described as voltage-controlled, current-controlled, or charge-controlled. They all work, and to try to make just one variable be the cause and the others the effect is very contrary to everything we know about physical systems. Dicklyon 00:30, 8 September 2007 (UTC)

so you need a field to make a net drift current. Rather, associated with a net drift current in a semiconductor is an electric field. It really can't be argued that this field makes the drift current because it can be equally well argued that the collisions due to the current cause a charge density gradient that in turn causes the field. But, that's precisely the point you made when you said that "to try to make just one variable be the cause and the others the effect is very contrary to everything we know about physical systems", right? Alfred Centauri 01:49, 8 September 2007 (UTC)

Not precisely the point I was trying to make, but OK, close enough; I won't argue. Dicklyon 03:48, 8 September 2007 (UTC)

OK, precisely was a poor choice. But, I do think we're on the same page. The bottom line, IMHO, is that this question of whether the BJT is a voltage-controlled device or a current-controlled device is a false dichotomy. Regards, Alfred Centauri 14:50, 8 September 2007 (UTC)

Grammatical structure

It seems to be conventional to write the terms such as base–emitter incorrectly with a hyphen instead of an en dash. But shouldn't we strive to do it right here, instead of following the typical error, so that the meaning of the terms become more clear at least to those who understand English punctuation? I've made a start in various sections, but it's a pain to fix throughout since my browser's editor won't find and replace. Dicklyon 21:09, 1 August 2006 (UTC)

Why bipolar?

LC reverted my claim that the term BJT comes from requiring junctions of both semiconductor polarities. I found the current claim not credible, because "the main conduction channel employs both electrons and holes" is not true; only minority carriers flow through the base to the collector; or there some other notion of "main conduction channel" that I'm missing. So I'm trying to find a reference, and having trouble. I found this one [4] that says the BJT is a current-controlled resistor, but that sure won't fly with LC.

I'm willing to believe I got it wrong, but it's also wrong as written. Perhaps it can be corrrected to say that both types of carriers are involved, since there is a small component of the opposite type in the base–emitter current. Dicklyon 02:15, 2 August 2006 (UTC)

Ah, I see where it came from. LC references [5] which says "The device is called “bipolar” since its operation involves both types of mobile carriers, electrons and holes." But somewhere along the way the meaning got distorted to "the main conduction channel employs both". Let's fix it. Dicklyon 02:20, 2 August 2006 (UTC)

Just to keep you going, Dick, Ive found a ref that may interest you:

The main difference between field effect transistors and normal junction transistors is that in FETs the current is only carried by the majority charge carriers. Field effect transistors are thus "unipolar" transistors, ie only one type of charge carrier is responsible for their actio, unlike normal transistors, which are "bipolar"

Page 1 para 1, Field effect transistors,(multiple authors) Mullard Ltd, 1972, ISBN 0 901232 42 4.--Light current 10:36, 2 August 2006 (UTC)

However, it's not totally on point, as in BJTs the collector current is only carried by the minority carriers. Still, this may be the right reason, if we just phrase it right. It would be nice to see it in a book on BJTs. Dicklyon 18:48, 2 August 2006 (UTC)

Dont forget that the term Bipolar Junction Transistor is a relatively recent term. Originally they were just called 'normal' transistors or perhaps 'junction' transistors to diff them from point contact types (perhaps). THe term 'bipolar' in this usage aint been around too long!--Light current 21:26, 2 August 2006 (UTC)

Good point. I was able to look through my old transistor books today, including Shockley's Electrons and Holes in Semiconductors with applications to transistors, and all seven editions of the GE transistor manual, and didn't find bipolar in any of them. I wonder who coined it. I seem to remember a book on BJTs I used in college in the 1970s, but it's missing. Dicklyon 23:55, 2 August 2006 (UTC)

Aha! I have that classic book also! Must get round to reading & digesting it sometime. The term must have been coined when FETs became popular I would think 8-)--Light current 23:58, 2 August 2006 (UTC)

Looks like we're wrong about how recent the term is. I found this from 1958 in Google Book Search:

"The operation of the field-effect transistor depends essentially on the presence of just one type of carrier, the majority carrier. For this reason it may be called a unipolar transistor. The junction transistor, however, depends for its operation on both types of carrier and is hence a bipolar transistor."

p. 520, vols 2-3 (unclear if this means two volumes bound as one?)

Biondi, F.J., H.E. Bridgers, J.H. Scaff and J.N. Shive (eds.) Transistor Technology, 1958.

Dicklyon 00:27, 3 August 2006 (UTC)

Interesting. What I was saying tho was that common usage of the term is relatively recent (say last 20 yrs). Im sure we didnt use this term when I was studying.--Light current 13:24, 3 August 2006 (UTC)

More like 35 years and I would agree. I studied from a book entitled something like "BJTs, FETs, and Microcircuits" around 1971. I just looked it up, and it's by E. James Angelo, 1969. Perhaps that started the common use of the term, by teaching it to college students. Dicklyon 18:33, 3 August 2006 (UTC)

I studied from a book called 'Integrated electronics' by Millman and Halkias pub. 1972. THey do mention the term BJT in the introduction to the transistor chapter, but everywhere else, its just 'transistor'. --Light current 22:40, 3 August 2006 (UTC)

I have referred a Book called "Solid State Electronics Fundamentals - Chih Tang Sah " here he has explicitly mentioned that Bipolar is because of conduction in BJT is due to "Majority"(In collector and Emitter) & "Minority"(In base) charge carriers and not anything else.

Suggestions for this article

In scanning over this article, it seems that it is very heavy on BJT usage in circuit topology and general application, but extremely light on the actual device operation and the various processes that govern its behavior. For example, the sadly short "Explanation" section discusses an NPN BJT in forward active mode but never makes it lucid to the reader that this is the case. I think this section should be rewritten and generalized into something better. I'd propose bringing in a simple energy band diagram as well as one or two figures showing carrier distributions under the common operation modes (active, saturation, and cutoff; inverted mode is rarely used). Personally, I find it highly useful to visually show the six or so significant current components within an active-mode BJT when explaining its operation.

Speaking of which, this article is nearly totally about BJTs in active mode (as it probably should be), but never makes it clear that this is the only mode that really provides useful current gain or why. That seems to be a fundamental failure since the primary use of BJTs in modern devices is as a high gain amplifier. The article seems often guilty of making statements without explaining them. For example, the section about the Ebers Moll model mentions "normal" operation but doesn't define what "normal" is. From the rest of the article, the reader might be led to assume that "normal" means "forward active". We also have very brief mention of junction breakdown without any explanation of the basic breakdown mechanics. These should at least be briefly summarized, perhaps with a nod to the PN junction article (assuming there's a decent explanation of breakdown mechanics there... I haven't looked).

Then too, there is the discussion of the hybrid parameter BJT model. Therein it is explained that the model is useful for "small signal" analysis, but never what small signal conditions are or why they must be maintained to keep the transistor in forward active mode (it also neglects to mention that the H-parameter model is only useful in active mode). Maybe a simple common-emitter single-BJT amplifier with a resistor biasing network would be good for illustrative purposes here? I dunno; I'm admittedly more keen on device operation and design than circuit topology. A full discussion of a single transistor amplifier might be too far out of this article's scope anyway.

Anyway, I just wanted to vent some of my complaints with this article before I messed with it too much. I made a few changes here and there and decided I should check in on the talk page before going much further. I don't want to step on anyone's toes or anything, just make some needed improvements to the article. If nobody has any objections, I'll probably try to write a decent explanation of BJT operation in terms of carrier concentrations and movement. Of course, I'm far from an expert on semiconductor physics (just a humble research student), so your feedback is greatly appreciated! -- uberpenguin @ 2006-08-22 05:49Z

Go for it. But if it gets real technical, try to keep that in subsections such that a more general audience can still find the article useful. Dicklyon 06:23, 22 August 2006 (UTC)

Okay, I threw together a simple energy band diagram for an NPN BJT under equilibrium. If you like the style, I'll also make one for active mode and use these and perhaps a minority carrier concentration diagram to help illustrate things. I don't plan to include all this in the top section, but in a subsequent section that goes into a little more detail about the device's operation. Anyway, let me know what you think. -- uberpenguin @ 2006-08-22 23:54Z

Any correct diagram is a worthwhile addition to an article. So, yes please!--Light current 00:19, 23 August 2006 (UTC)

Cool... Here's the diagram for forward-active mode. These should help a lot in explaining the device operation. The only thing I'm concerned about is that a lot of the terminology that must be used to describe BJT operation is heavily rooted in semiconductor physics, and I'm not sure whether there are any decent articles on Wikipedia that explain the transport mechanics and current components in semiconductors or the specifics of PN junction operation. Is it okay for the purposes of this article to just link where possible and hope that those articles get improved eventually? -- uberpenguin @ 2006-08-23 01:58Z

Yes I would say so.--Light current 02:09, 23 August 2006 (UTC)

I know nothing about transistors and I didn't find this page as useful as I had hoped. The non-technical section really needs some help in order to be useful for the general audience (maybe put it in terms of when this wire is 'on' the other wire is 'off' or something). The explanation makes this idea more complicated than it has to be. Thanks everyone!

Proposed merge of PNP and NPN

I see no reason for there to be two articles that should at most be a couple of sentences in this one. -- mattb @ 2006-09-11T03:31Z

Support. I agree, merge them in here. Dicklyon 03:37, 11 September 2006 (UTC)
Support — Omegatron 04:44, 11 September 2006 (UTC)
Support. I felt rather silly making the NPN article, even though it was requested. — Matt B. 05:20, 11 September 2006 (UTC)
Support CyrilB 12:13, 12 September 2006 (UTC)
Support Lincher 03:13, 17 September 2006 (UTC)
Support --Light current 23:03, 29 September 2006 (UTC)

Done. -- mattb @ 2006-09-29T23:10Z

Regions of operation

This whole section is sort of a mess, and I thought we might as well talk about it since there seems to be a disagreement. The section is very confusing and, on the whole, misleading because it sort of combines an explanation of operation regions with small signal modeling. In reality there are four well defined regions of operation (or biasing modes) for a BJT:

Forward active — EB junction forward biased, BC junction reverse biased
Reverse active (inverted) — EB junction reverse biased, BC junction forward biased
Saturation — Both junctions forward biased
Cutoff — Both junctions reverse biased

"Linear" is NOT a BJT operation region (it is for the MOSFET). I can only assume that whomever wrote that was combining or confusing small and large signal models. Operation mode of a BJT depends on nothing but the biasing of the two junctions; things like external current limiting circuitry do not directly affect the operation region (unless they change the biasing of one of the junctions). Most of the time BJTs will be biased squarely into the forward active region, wherein the common small signal models later described in the page actually apply. -- mattb @ 2006-09-29T22:49Z

Cut-off region

While it is true that a transistor is in cut-off region when both junctions are reverse biased, that is not as strictly necessary condition. Furthermore, it is not even typical. Consider, for example, the grounded-emitter switch configuration. When the base is at or near ground, it is in cut-off; it is not possible to reverse bias the base–emitter junction in a circuit that can't pull the base below ground. So let's just say what's true and verifiable, OK? Dicklyon 20:53, 30 September 2006 (UTC)

As I stated in my edit comment, your view seems to reflect a simplified CVD model of the junctions in a bipolar transistor, not the actual physics of the device. If you'd like, I would be happy to provide references from three modern semiconductor physics textbooks and one modern microelectronic circuits textbook that verify exactly what I asserted. I think this is merely a conflict of terminology understanding, since some googling confirmed that a few sources claim that cutoff exists for small forward bias on either junction. However, this isn't correct usage of terminology and is not claimed by any semiconductor device design book I'm aware of.

Taking the example you gave (if I understand you correctly, and assuming an NPN device), the transistor is actually in forward-active mode for small input voltage. Since

V_{BE}

is very small (as you said, close to ground potential), very little electron current diffuses across the EB junction, and there is therefore a relatively small minority carrier perturbation in the base to provide carriers to be swept over the BC junction to the output. Now, once the potential at the base becomes larger than a few multiples of the thermal voltage (

{kT}/q

), the current through the EB junction quickly becomes significant. This current is amplified and a larger current is pulled through the collector and load. Obviously this causes a voltage drop at the collector, which quickly ends up at a lower potential than the base as the collector current rises. When this occurs, the device goes from forward active to saturation and the collector current doesn't change much with increasing

V_{BE}

. So you see, the simple emitter-grounded BJT switch is in forward-active when "off" and saturation when "on". The "turn on" voltage of such a switch is a few times the thermal voltage, which is approximately where diffusion current starts to dominate over the small R-G current in the EB junction.

I encourage you to look at how TTL works; it uses transistors primarily in saturation and reverse-active mode, but not cut-off. Anyway, to show good faith, I will not make any further changes to the section until we've talked things out to your satisfaction. Please let me know if you'd like me to cite those textbooks I mentioned. I'd also be happy to sketch some potential diagrams to illustrate what I have explained if that will help. I realize that you have much more electronics experience than myself, and I mean no disrespect to you. However, semiconductor device research and physics is my area, I think I've provided a clear enough explanation, and I'd be happy to cite some sources that confirm proper usage of the four BJT biasing regions' terms. -- mattb @ 2006-09-30T23:30Z

Matt, since in your first couple of rounds you left the statement "the base–emitter voltage is too small for any significant emitter current to flow. In typical BJTs manufactured from silicon, this is the case below 0.5 V or so," I assumed you had no quarrel with that; your additions narrowed the scope of cut-off a lot from there. So, which is it? I do understand semiconductor physics well enough, but there may be a disagreement over the terminology, among various texts. I can see the logic of what you're saying, which is that it's in forward active region even when the current is too small to measure, by far. Please do show me the references. I showed a couple that disagreed, and didn't find any that defined cut-off the way you want to. I did find some that said the transistor is in cut-off when the junctions are reversed biased, which is obviously true, but they did not specifically say that the cut-off region is limited to that condition. That is, reverse bias is sufficient, but perhaps not necessary, for cut-off. Who is the authority on such terminology? Furthermore, if we decide to define cut-off that way, should we then change the part about transistors used as switches, since in many cases (e.g. H-bridge drivers) they will never be in cutoff by that definition? Dicklyon 23:42, 30 September 2006 (UTC)

Dick, I cited my four references in the below section. If you'd REALLY like, I'll try to make some photocopies of relevant pages from the texts, but that will take some time (two of the books are lent out to friends right now and I don't own a scanner) and I'd rather not have to do it if possible. I don't have any quarrel with the statement you quoted, but the magnitude of current flow does not determine the biasing modes of the BJT in any semiconductor physics text I have seen. A quick google search found numerous online documents that confirm my voltage-only definition of biasing modes, but I hate referencing online documents, which is why I mentioned the text books. It seems that the only sites which agree with the current-related definition of biasing/operation regions are those that use a CVD-like simplification for the transistor. There's nothing wrong with that, of course, because that's a useful simplification for small signal modeling, and obviously small signal models are what we typically use for real electronics design, not the full mathematical models. However, I have never seen operation modes defined with anything but the signs of

V_{EB}

and

V_{BC}

. Personally, I think these definitions make the most sense because they directly define the positioning of quasi fermi levels within a device, which ultimately is what determines the rates of drift, diffusion, and R-G current. Of course, at a circuit level potential and current are so closely related that it's a difficult distinction to make, so I certainly acknowledge that there's a fine line to tread here. Anyway, I'm sticking with my definition as being backed up by a number of semiconductor physics texts, and I will provide copies of my references if that's what it will take to change your mind. -- mattb @ 2006-09-30T23:57Z

P.S. - I'm not contesting at all that the transistor is being used as a switch in the described configuration, just how we define the device biasing regions. There's obviously no perfect solid-state switch (especially with a bipolar device), and the small "off" base current is negligible regardless of what we choose to call the transistor's biasing mode at that point. -- mattb @ 2006-10-01T00:03Z

P.S. (again) - Perhaps we can strike a balance between the voltage/current definitions. The more I think about it, the more it seems to me that the voltage explanation makes slightly more sense and is easier to quantify, but the current definition has more to do with the operation of the device within a circuit and is therefore equally valid. Would it be acceptible to you if I added something like "the biasing regions overlap for very small applied voltages" and briefly explain that this has to do with the exponential nature of the I-V relationships? -- mattb @ 2006-10-01T00:26Z

Proposed "regions of operation" section

I was going to change the regions of operation section to the following, but I won't do it if I'll just be reverted on the spot, so I'll leave it here until we work this out. I reference "Semiconductor Device Fundamentals" by R.F. Pierret, "Physics of Semiconductor Devices" by S.M. Sze, "Semiconductor Physics and Devices" by D.A. Neaman, and "Microelectronc Circuit Design" by R.C. Jaeger and T.N. Blalock. All of these quite clearly agree with my proposed text. I also reference google, which will quickly verify the biasing conditions for the four BJT operation regions. I can provide photocopies from some of these books upon request, if necessary, but I encourage you to just google it since a quick search for "bjt biasing modes" will verify all of this (ignoring the handful of sites that use a CVD model simplification for teaching transistors in circuits without bothering with actual device physics... a pox on them for the "lie to students" method of simplification).

Anyway, the proposed text follows my signature. -- mattb @ 2006-09-30T23:40Z

Bipolar transistors have four distinct regions of operation:

Forward-active (or simply, active): The emitter-base junction is forward biased and the base-collector junction is reverse biased. Most bipolar transistors are designed to afford the greatest common-emitter current gain, $\beta _{f}$ in forward-active mode. If this is the case, the collector-emitter current is approximately proportional to the base current, but many times larger, for small base current variations.
Reverse-active (or inverse-active or inverted): By reversing the biasing conditions of the forward-active region, a bipolar transistor goes into reverse-active mode. In this mode, the emitter and collector regions switch roles. Since most BJTs are designed to maximise current gain in forward-active mode, the $\beta _{f}$ in inverted mode is very small. This transistor mode is seldom used, usually being considered only for failsafe conditions and some types of bipolar logic.
Saturation: With both junctions forward-biased, a BJT is in saturation mode and facilitates high current conduction from the emitter to the collector. This mode corresponds to a logical "on", or a closed switch.
Cutoff: In cutoff, biasing conditions opposite of saturation (both junctions reverse biased) are present. There is very little current flow, which corresponds to a logical "off", or an open switch.

While these regions are well defined for sufficiently large applied voltage, they overlap somewhat for small (less than a few hundred millivolts) biases. For example, forward active mode may be alternatively viewed as cutoff mode for very small biasing of the emitter-base junction or as saturation mode for very small biasing of the base-collector junction. However, transistor behavior in these regions is usually only considered in transient analysis and is avoided for principle device operation.

I cant see anything wrong with the above statements. 8-)--Light current 00:18, 1 October 2006 (UTC)

I added a little bit about region overlap, which will hopefully address Dick's concerns as raised above. -- mattb @ 2006-10-01T00:32Z

That all looks good and fine, provided you show me the refs where that's how cut-off is defined. Dicklyon 00:45, 1 October 2006 (UTC)

Cut off (or the off state) is defined in the Motorola switching transistor handbook (1973) as where there is minimum current flowing through the transistor (C to E) and there is maximum voltage (Vce) across the transistor. Is that a satisfactory defn?--Light current 00:55, 1 October 2006 (UTC)

That's a mixture of both definitions, which is equally valid. I'm still voting for the applied junction voltage sign definition (with the note about region fuzzyness), however, if only because it's valid and it's a very simple and methodical way of explaining things. -- mattb @ 2006-10-01T01:03Z

Very valid, simple, and methodical is nice, if you're writing your own text. But here we need to document the actual use of the term in the field, not clean it up to suit. So we need those refs. Dicklyon 01:10, 1 October 2006 (UTC)

On the one hand, you're right, but on the other there is a balance to be struck here. This is (supposedly) an encyclopedia article, and is therefore an overview and summary of the topic. Simple and methodical (as long as its correct) is often preferable to a full explanation for obvious reasons. The biggest thing I've gotten out of this dialogue is that the definitions of the operation regions are less universal than I had originally thought, so I don't really see a problem with us picking a simple explanation as long as it is a correct one. Industry usage? I learned analog electronics from a guy who was a senior analog engineer at TI for several years. He never indicated that there is any other way to reference biasing regions than the voltage-sign method. I learned semiconductor device operation and physics from the guy who I now work for, someone whose research is all about semiconductor devices (HBTs, APDs, MEMS). Same story. If you have alternative experiences to relate, I'm all for hearing them. I'm certainly not suggesting that alternative definitions of the biasing regions are less valid, far from it. I'm merely asserting that for two equally correct explanations, the simpler one is preferable. -- mattb @ 2006-10-01T01:49Z

Okay, after a hunt for a cable that can only be described as "epic" in scale (stupid proprietary connector), I took some pictures of the two of my four references that I have on hand. I apologize for the bad flash, but this is a really terrible camera. You should still be able to read the important parts of the text. Pierret: [6], Jaeger: [7] [8]. If you really want to make me work hard, I can try to hunt down my other two sources as well, but I hope you'll trust that I'm not lying to you and accept these as well as the google results. -- mattb @ 2006-10-01T01:30Z

Matt, good job. I just wanted to know what the references really did say exactly. The photos were one way to show me. Be sure to ref those, or at least one, in the article. One thing still unclear to me is how you get the pulldown transistor to have a reverse-biased B-E junction in a TTL logic gate. The paragraph that spans the Jaeger pages says the cut-off region is most commonly used in logic switching as TTL, but I don't see how it can be with that definition. Same goes for RTL and DTL circuits; all use the grounded-emitter configuration, where the B-E junction can never be reverse biased. So this story retains a nagging inconsistency. Pierett is not so explicity self-contradictory, but close. Dicklyon 05:53, 1 October 2006 (UTC)

Here's a twist: this book says that VBE < 0.6 V is "reverse biased". Is that the way you're thinking of it? I always assumed that reverse biased meant a negative relative potential, but this is one way to make the definition as used in your references not contradict the idea that the cutoff region is used in logic switching. Dicklyon 06:05, 1 October 2006 (UTC)

Hmm... Well that's a rather interesting way of looking at it. I guess they are going from the perspective that the junction's built-in potential works against applied bias and are calling "zero bias" what I've usually heard termed "flatband voltage". However, I've never heard anyone call bias anything but applied voltage; all of the equations I've ever used explicitly separate biasing voltage and built-in voltage. I think that book is providing a very non-conventional explanation.

Anyway, I'm not entirely sure how to answer your logic question. Digital logic frankly isn't my thing. I thought that under TTL the BJTs are in saturation and reverse active mode. I know ECL uses BJTs in cutoff, but I don't really have an off-the-cuff answer for you there... I guess I could thumb through the relevant pages to see if I can find an explanation. -- mattb @ 2006-10-01T06:18Z

So is it okay for me to copy my proposed text into the article, or is there anything else that we should talk about first? -- mattb @ 2006-10-02T19:53Z

I would still feel better if you added text to indicate that the definition of cutoff is sometimes extended to include the region of essentially zero current even if the junction biases are zero or slightly forward. This makes it compatible with statements of cutoff as the "off" state in logic circuits. Or, you can go ahead and add your text, and I might "improve" it in that direction. Dicklyon 20:40, 2 October 2006 (UTC)

Well, that's what the text about region overlap was intended to address, but feel free to modify the text once I add it to the article. I'd say that zero bias isn't a situation worth talking about much since it is only theoretically attainable (that is, there will always be some tiny potential difference in a circuit). We talk about it when describing device state in equilibrium, but the entire "operation/bias region" notion implies a non-equilibrium condition. -- mattb @ 2006-10-02T21:11Z

Some questions about convention

In my recent edits to this article I've noticed that convention is sometimes switched around. I think we should introduce and adopt convention for common terms in this article, if only to save us the trouble of typing very common phrases out over and over.

My suggestions:

Use NPN transistors for most of the examples. We'd need only have a few lines explaining what the primary differences between the two types are. The operation region section should also note that "forward" and "reverse" biasing is always with respect to the p side of the junction.
NPN convention means that we'd probably use $V_{BE}$ and $V_{BC}$ to denote junction voltage (unless explicitly talking about PNP), since these are positive for NPN forward biasing.
Similarly, $I_{CE}$ for collector-emitter current since this is the direction of the majority conventional current flow in an NPN device in active mode.
The emitter-base/base-emitter junction will be referred to as the "BE junction"
Collector-base/base-collector: "BC junction"

Since these conventions are pretty arbitrary, I'd be happy with pretty much anything so long as its consistant, so let me know. I think maintaining consistancy with these terms will help the article's readability a good bit. -- mattb @ 2006-10-01T00:41Z

Collector base junction is normally refered to as the CB junct here. 8-)--Light current 00:46, 1 October 2006 (UTC)

Again, it's arbitrary, though I think it makes more sense to reference them with respect to the p sides. -- mattb @ 2006-10-01T00:48Z

Yeah but its nrmally refeered to as the Collector- Base junction in all the literature Ive read!--Light current 00:56, 1 October 2006 (UTC)

Well, in general: $V_{XY}=V_{X}-V_{Y}$ , $I_{X}$ is the current going into terminal X. - mako 08:02, 3 October 2006 (UTC)

Yes, but I'm asking to agree upon a uniform convention for what to call the junctions. That's a little more arbitrary, though I think it makes the most sense to reference them P-N order. -- mattb @ 2006-10-03T16:48Z

P-N order? You mean like B-E for NPN and E-B for PNP? Seems nutty. Dicklyon 19:31, 3 October 2006 (UTC)

My previous comment was addressed to your bullet points 2 and 3. Regarding the junctions, my textbooks seem to be inconsistent in convention, but one simply calls them the emitter and collector junctions. - mako 19:46, 3 October 2006 (UTC)

Well if it seems nutty to you, can you suggest an alternative? As I said earlier I don't care very much about exactly WHAT convention we use as long as the article is consistant, which it currently is not. -- mattb @ 2006-10-03T20:44Z

Pick one. Cite what book you're picking it from. I haven't seen the one I called "nutty"; have you? Dicklyon 21:40, 3 October 2006 (UTC)

Hybrid PI Model

Would someone be willing to write about the Hybrid PI small signal model for the BJT (to go with the other models described here). The small signal approach is a very common way of modeling many nonlinear electronic devices, and the BJT should make a prime example of this. Any comments? --Dirkbike 04:09, 3 October 2006 (UTC)

The h-parameter model described IS basically the hybrid pi small signal model. The section could definitely stand for some cleanup, though. -- mattb @ 2006-10-03T04:42Z

Just wanted to check why my edit adding a note on biasing techniques was removed? Is there some other article where this should be linked? Any other reason? Xcentaur 06:34, 16 October 2006 (UTC)

Well, the collector current article pretty much has no business existing, and I've since changed it to a redirect to this page. Furthermore, it's bad writing style to announce what you're about to enumerate. Especially if it's already been explained in the preceding text. What's more, the wikilink to the biasing article was malformed and the article it links to is of rather poor quality as far as scope and tone go. -- mattb @ 2006-10-19T00:17Z

Regarding inverted mode biasing...

Some recent additions by an anon editor point to some apparant advantages of inverted mode biasing. Frankly I'm a little skeptical of the claims, but I didn't want to revert on sight partially because I don't really understand what the text is trying to convey... Here's the contentious part:

"However the transistor in this mode can be closed more "tightly", the remaining weak collector current being up till one order of magnitude smaller than during the normal wiring. Because of this the inverted wiring is sometimes used in transistor detectors"

The given reference is a rather oldish book (which may explain the germanium transistor example) which I do not have access to. Comments on this? I really can't wrap my mind around how purposely designing with a transistor in a configuration it isn't designed for could be of benefit. I've only ever seen inverted mode used for adding fail safes to circuits, and even then it's rare. -- mattb @ 2006-10-19T00:13Z

Anybody? I'll delete the text if nobody has any explanation of why it should stay. -- mattb @ 2006-11-02T01:45Z

The text you quote is gobbledegook. It needs deleting. Be my guest! 8-)--Light current 01:48, 2 November 2006 (UTC)

I agree. If there's a good source for this idea, let's see it and see what it's trying to say. Dicklyon 02:00, 2 November 2006 (UTC)

Well OK we could make something up to make this make sense. But its not worth it. Its talking about the low leakage phenomenon in inverted mode transistors to enable them to operate as more efficient detectors I think. But .do we care...??--Light current 02:51, 2 November 2006 (UTC)

While we're at it, I've never seen impact ionization effects described as a region of operation. Along with zener breakdown, avalanching is almost always classified as a non-ideality of the device, not a biasing region. Can you show some sources that classify breakdown as a region of operation? -- mattb @ 2006-11-02T02:56Z

Certainly! High speed switching transistor handbook, Motorola 1973 (8th printing). Chapter 9: Avalanche mode switching.--Light current 03:14, 2 November 2006 (UTC)

Forgive me for remaining skeptical, but none of my literature uses this sort of terminology, and google is a little light on it as well. I'll wait for a few other opinions, though. -- mattb @ 2006-11-02T03:40Z

Let me briefly express my concern a little better. If we were to call avalanching (or how about "breakdown" since the Zener process often is not insignificant) a mode of operation, why not also call high frequency gain cutoff a mode of operation? How about the catastrophic high-current-magic-blue-smoke-releasing mode of operation? You'll forgive my sarcasm, but the point is that modes of operation are arbitrarily defined by some standard, and the standard I've always seen used doesn't really take into account non-idealities of the transistor and mostly concentrates on biasing conditions. -- mattb @ 2006-11-02T03:44Z

Subscript T on alpha

Where does the T come from? I understood the F for forward, like on beta. Why the change to T? Dicklyon 17:36, 10 December 2006 (UTC)

I've seen common base gain written with several subscripts, but upon reading the section I've realized that there is some confusion of terms here. The article as it currently stands is incorrect in a couple of places.

\alpha _{T}

is usually the symbol (I've seen) used for the base transport factor, and is almost correctly defined. It is actually the proportion of the majority carrier current component in the collector to the majority carrier current component in the emitter. So for a PNP transistor,

\alpha _{T}={I_{Cp} \over I_{Ep}}

. The bigger problem with the article is how it defines

\beta _{F}

in terms of

\alpha _{T}

. This is incorrect since

\alpha _{T}

is NOT the same thing as common-base DC current gain. If we use

\alpha _{dc}

for the common base current gain (or whatever subscript you fancy),

\alpha _{dc}=\gamma \alpha _{T}

.

\gamma

is the emitter injection efficiency; the ratio of the majority carrier current in the emitter to the total emitter current, or

\gamma ={I_{Ep} \over {I_{Ep}+I_{En}}}

for the PNP. Obviously this is very close to 1 in a typical highly doped emitter. Now, defining

\alpha _{dc}

in this manner, the relationship between "alpha" and beta as given in the article is correct:

\beta _{F}={\alpha _{dc} \over {1-\alpha _{dc}}}

. Going back to the earlier alpha definitions, you can see that

\alpha _{dc}={I_{Cp} \over I_{E}}

(again for the PNP). So there's obviously a mix-up of terms in this section, especially as regards the base transport factor and the common base DC current gain (which are not the same thing). I'll try to fix things. -- mattb @ 2006-12-10T19:49Z

P.S. - You'll notice I threw the word "approximately" into the article text a few times. This is because these simplified relationships do not take into account unwanted current flow between the collector and base due to thermal generation at that reverse-biased junction. Normally you can ignore this current component since it is very small, but for very tiny base current, RG currents dominate and you can observe their effects. -- mattb @ 2006-12-10T20:10Z

Matt, do you have a reference for your definition of alpha? I always thought it was just the C/E current ratio. Dicklyon 21:01, 10 December 2006 (UTC)

Remember, there are two "alphas" here; the one you're defining is the DC common-base current gain (neglecting very low-current effects). The gist of all that I wrote is that

\alpha _{T}

, the base transport factor, is not the same thing as

\alpha _{dc}

or

\alpha _{F}

, the common-base DC current gain. As for sources... I'll go with the three textbooks I have; Semiconductor Device Fundamentals (Pierret 1996), Microelectronic Circuit Design (Jaeger, 2004), Semiconductor Physics and Devices 2nd Ed (Neamen, some year I don't remember). You can likely google the terms "base transport factor" and "emitter injection efficiency" to verify what I've said, as well. -- mattb @ 2006-12-10T22:41Z

Sounds good, if we make it clear that there are several, and put back the usual one that's 1:1 with beta. Dicklyon 23:33, 10 December 2006 (UTC)

Reading difficulty

Holy crap guys, even the discussion page is largely unreadable. I'm not an electrical engineer. Can someone please translate some of the pertinant parts of this page into english.216.57.70.226 22:52, 15 March 2007 (UTC)

Can you be more specific? This isn't the Simple English Wikipedia, so the article cannot be expected to omit technical terminology where appropriate. I don't think that this article is excessively jargony, but it isn't written for the lay man. Some understanding of basic electromagnetics, semiconductor physics, and circuit theory is probably required to totally understand the contents, and frankly one can't hope to gain a good understanding of what a BJT is and how it works without some prerequisite knowledge. I would stick to the transistor article if you're looking for a less technical overview; I think that article does a slightly better job explaining the broad picture. -- mattb @ 2007-03-16T02:32Z

more specifically in the intro paragraph I'd like a sentence or two written for a layman describing the objects function. a layman shouldn't have to know to go to the other description of this object on the transistor page to get a simple answer.

from that paragraph I currently understand:

it has three-terminals(legs)
what its constructed of
some applications where it is used
why it is called what it is called
why Charge flow changes in it
that it is unlike a unipolar transistor
how it is classified

why would a layman want to use it in a circuit? you apply current and then what do you get? how is it useful? —Preceding unsigned comment added by 173.59.6.62 (talk) 11:41, 7 June 2010 (UTC)

Theory and modelling section

I think this section is getting a bit too long. I suggest moving it to a new article on BJT models and just leaving a more condensed version. I'm planning on writing an article on the hybrid pi model (to avoid the redudant parameter explanations on the common emitter, common base, etc. pages) and logically it should be grouped with the h-parameter model currently in this article. Problem is its gonna make the article even more overwhelming, furthering the need for a new one. Any ideas? Roger 20:18, 11 May 2007 (UTC)

Don't be afraid to split stuff into new articles. — Omegatron 02:18, 12 May 2007 (UTC)

I tend to agree with splitting off transistor models into a separate article in order to keep this one a high-level overview. Perhaps just leave behind a short section summarizing the major models and their uses. You don't want to bog down the primary point of an encyclopedia (overview) article with a lot of details. -- mattb 02:51, 12 May 2007 (UTC)

Just split off the Ebers–Moll model to a main article, as is done with the Gummel–Poon model. Maybe also with the h-parameter model if it gets too big. Dicklyon 04:09, 12 May 2007 (UTC)

Small signal amplifiers

Hi. I just removed the following from the biasing article. Perhaps it should be added somewhere in this article (maybe under a section on applications of BJTs).

Configurational Bias

There are three configurations of a transistor. Configuration is the method of connecting any one terminal of transistor common to both input and output circuits. The three types are listed below.
1. Common base (Grounded base) (CB)

Here base is common to both input and output. Emitter-base jn is fwd-biased and collector-base jn is rev-biased.
See full article: Common base

2. Common emitter (CE)

Here emitter terminal is common to both input and output. Emitter-base jn is fwd-biased and collector-base jn is reverse biased.
See full article: Common emitter

3. Common collector (Emitter follower) (CC)

Here collector terminal is common to both input and output. Load is connected to emitter.
See full article: Common collector

Comparison

Parameter	CB	CE	CC
Phase shift between input and output	zero	180	zero
Current gain	less than 1	high	high
Voltage gain	high	high	less than 1
Power gain	moderate	high	low to moderate
Input resistance	low	moderate	high
Output resistance	high	moderate	low

Category: Transistor types

Category:Transistor types has listed NPN and PNP - both of which are disambiguation pages.

Should this be fixed by creating NPN Transistor and PNP Transistor as redirects, and adding them both to Category:Transistor types? --RobBrisbane 12:59, 16 June 2007 (UTC)

I think that is a great idea. NPN transistor and PNP transistor might be better names though. -- RTC 07:34, 17 June 2007 (UTC) Especially as one of them already exists as a redirect. -- RTC 07:37, 17 June 2007 (UTC)

Done. -- RTC 16:00, 19 June 2007 (UTC)

Voltage or current redux

I have again reedited back in a correct account of BJT operation. As per wikipedia citation guidelines, I have referenced a professor at a noted university stating that the BJT is voltage controlled. If a user desires to include text that states that the BJT is current controlled, please cite a respected source that supports that claim, and the details of the phyiscs that supports that claim. Kevin aylward 15:02, 8 September 2007 (UTC)

I have reinserted my removed edits on voltage control as, quite frankly, what I say is the way it is. Further explanation can be found at http://www.kevinaylward.co.uk/ee/voltagecontrolledbipolar/voltagecontrolledbipolar.html. I note Bill Beaty has previously tried to rectify this misunderstanding on how the BJT actually works, many would be wise to take note. Kevin aylward 09:51, 8 September 2007 (UTC)

I have now also added an email respose from Bart Van Zeghbroeck, professor of EE, which should be the final nail in the coffin of those current controlled adherents. Kevin aylward 12:29, 8 September 2007 (UTC)

This was already touched on in #Voltage_or_current.3F. We should definitely rectify any and all misunderstandings of true physics principles (as Beaty is usually very good at), but the way you're writing about it in the article is unacceptable. See WP:SOAP, WP:COI, and so on. If you're intent on "burying" your "opponents", Wikipedia is not the place for you.

If you're willing to cover this in a neutral, authoritative manner, let's discuss how best to proceed.

(Beaty's explanation) — Omegatron 16:46, 8 September 2007 (UTC)

Violations of WP:NPOV, WP:SOAP, and WP:COI by editor Kevin alward

I have reverted [9] the recent edits by Kevin alward for violation of WP:NPOV, WP:SOAP, and WP:COI (linking to his own webpage to support his edits). —Preceding unsigned comment added by Alfred Centauri (talk • contribs) 13:46, 8 September 2007 (UTC)

I have reverted back to my edits. As per wikipedia citation guidelines, a professor at a noted university has been cited stating that the BJT is voltage controlled. If a user desires to include text that states that the BJT is current controlled, please cite a respected source that supports that claim.

The link to my page is in the external links section, it was not in direct support of my claims, therefore does not violate the link to own page. The support for my view is

It is a NPOV as it is the view held in any and all academic physics texts book. To the contrary, there are no authority citations showing that the BJT is current controlled. Look, its

F=q(E + vxB)

Its that simple. The electric field makes charges move. A flow of base charge can not cause the collector current.

The non NPOV is the current controlled view, since there is no academic support for such a view. Kevin aylward 15:09, 8 September 2007 (UTC)

Kevin: your edits were reverted for numerous reasons. Please see your talk page for details. Now, to address your argument.

Look, its
F=q(E + vxB)

You seem to have forgotton that the flow of majority charge carriers from the emitter to the base is due to diffusion, not the Lorentz force from any applied voltage. This is fundamental, Kevin. Let's review: injection of carriers from the emitter to the base is due to diffusion, not acceleration from an applied field (in fact, the electric field within the BE junction 'pushes' the majority carriers away from the CB junction).

The acceleration of the injected charges towards the collector is in fact due to the field associated with the Collector-Base voltage, not the field Base-Emitter voltage. Alfred Centauri 16:07, 8 September 2007 (UTC)

(Kevin, I've moved your quoted comments below mine. Please do not insert your comments in-line with mine again.) Alfred Centauri 20:24, 8 September 2007 (UTC)

Yes, there is a diffusion current and an opposite electric current that balances it due to the in built potential (barrier). The applied Vbe modifies this potential barrier height, and hence the emitter/collector current.

Can you produce a physics derivation showing that the intrinsic cause of collector current is due to the actual magnitude of the base current?

Yes, Vce accelerates the charge from the base to the collector, as already pointed out on the main page. This is well known and illustrates the need for an electric field to move charges.

I tided up the reference to the proff to sound more kosher.

Kevin aylward 16:43, 8 September 2007 (UTC)

Voltage - Current Control Controversy

This section does not report a controversy; instead it promotes one PoV. 1Z 16:43, 8 September 2007 (UTC)

Why?

It is a matter of fact that the BJT is considered a voltage controlled device in standard semiconductor physics. It is truly astounding that there is such a common misconception that the BJT is current controlled, simply because base current exists.

For me the history of this goes back 30 years, to when I was an EE student. I still remember our physics professor going, look, ignor what you may have heard, the BJT is a voltage-controlled device, not current controlled, and this is why.... My latter reference here to Bart Van Zeghbroeck, University of Colorado, is just one of an infinite number of people that support this view. I just cant imagine any university academic saying you know, the BJT is base current controlled. Its just nonsensical. But I suppose...

It is also a matter of fact, not a POV, that the majority of professional analogue designers, i.e. that done by i.c manufactures (billions and billions of chips), use the i=gm.vi, voltage controlled model. It the one that works. —Preceding unsigned comment added by Kevin aylward (talk • contribs) 17:08, 8 September 2007 (UTC)

It is easy to imagine university academics propounding any position on this. But the ones that are serious about the physics teach that the collector current depends on the excess charge in the base diffusing over to the depletion region near the collector, where the field can grab them and accelerate them into the collector. The Early effect is easily explained by that edge of the depletion region moving, so that more charges can diffuse to it easily. As to what designers use, you may be perfectly correct, and we shoud include that fact if it is verifiable. Dicklyon 20:53, 8 September 2007 (UTC)

I dont have a problem with this, but see below on what charge controll actually means.

They also teach that one can use exactly the same underlying principle of calculation for the mosfet, to wit, calculate the charge in the channel due to gate voltage, and then use this charge to calculate drain current, to wit, KW/L.(Vg-Vt)^2.. No one seems to have a problem with then stating that the mosfet is a voltage controlled device.

From a big picture view, the mosfet and bipolar are, essentially, the same (draw them). The both have the same npn junctions, the p-well forming the gate length, is the “base”. The charge in the channel/base region is “induced” by gate/base voltage. Indeed, a mosfet will behave as a parasitic bipolar if one uses the well connection as the base. Kevin aylward 10:28, 9 September 2007 (UTC)

How to proceed: Kevin, to make progress, it would be useful if you would clearly point out the parts of the present text that you disagree with; you can mention them here, or add {{citation needed}} or {{dubious}} tags to passages that you think are not verifiable. You can add new parts, and they will stay if supported by verifiable reliable sources, but may be challenged or removed if not. But if you say in the text that something is incorrect, or that there's a controversy, that very definitely needs a reliable source. It's better to treat multiple viewpoints without making a controversy of it, unless there's a genuine controversy ongoing in the field that has already been reported and analyzed in secondary sources; it's not OK to make up a controversy, or to call one approach incorrect, from the fact that you find multiple viewpoints out there. Dicklyon 17:36, 8 September 2007 (UTC)

Furthermore, to say that the collector current is directly or physically a function of what's happening at the the base–emitter junction is absurd on the face of it.

I disagree. To say that it doesn’t is absurd. The applied voltages directly modulate the junction potentials Kevin aylward 10:28, 9 September 2007 (UTC)

The only influence is via the excess minority carriers in the base; that's why in all accurate models the collector current is charge-controlled and there's at least one state variable for stored based charge in addition to the terminal voltages and currents. Dicklyon 17:41, 8 September 2007 (UTC)

What causes the excess minority carriers? See below on what "charge-controlled" actually means Kevin aylward 10:28, 9 September 2007 (UTC)

I suspect your main point is really not in the physics but in the design field, which is your experise. The statement "In linear circuit design, the current-control view is often preferred, since it is approximately linear" may need to be modified, though "often" may be true, to indicate that the transconductance (voltage control) view is even more often what's used in traditional circuit design. Dicklyon 17:49, 8 September 2007 (UTC)

My point is both. The basic physics and how transister circuits are designed by professionals.

"In linear circuit design, the current-control view is often preferred, since it is approximately linear" may need to be modified. I would certainly agree with that to the extent that in small-signal analysis models, the BJT is a linear transconductor. On the other hand, designers, whether we realize it or not, are effectively linearizing the BJT by using it as a current-controlled device when they have significant series resistance in the base and/or emitter circuit. All one has to do to see this is to convert the circuits looking out of the base and emitter leads of the BJT to their Norton equivalents. Alfred Centauri 21:18, 8 September 2007 (UTC)

Here's another data point [10] and here's the payoff quote:

"This results in a collector current, controlled by a (smaller) base current. ... You can think of bipolar transistor as a current amplifier... or as a transconductance device"

Now one might argue that The Art of Electronics is not an 'academic' reference. On the other hand, it is highly regarded by professional designers while the authors, Paul_Horowitz and Winfield_Hill are indeed academics. It is my opinion that this reference combined with Dicklyon's recently added reference (in the main article) precludes any edit to this article that claims that the BJT is definitively voltage-controlled. Alfred Centauri 00:27, 9 September 2007 (UTC)

Unfortunately for this view is that, Winfield Hill and I have been in correspondence on several occasions in the past, he often posts to the electronics NGs. I am quite confident that his view is that the BJT is fundamentally a voltage controlled device. Even Steven Hawking writes things loosely that are not strictly true, just to convey a basic point. I will attempt to contact Winfield, and get a definitive statement from him to include in this discussion.

Secondly, Bill below explains quite clearly why the BJT can not possible be base current controlled. The only reason I can see why this explanation is not conclusive on eliminating any alleged base current control is a basic lack of understanding of physics. It pointless trying to prove a point to those that do not have the background to understand what is being proved.

The BJT *is* definitively voltage-controlled becuse that is how standard physics describes BJT, for those that have actually taken BJT semiconducter course, to wit:

The phrase "charge-control model" means that, YES, the collector current is taken to be a dependant variable from knowing charge in the base region. HOWEVER, this model calculates by fiat, those charges from the known terminal *voltages. The charges are taken to be dependant variables on the independent terminal voltages. The charges are calculated from voltages. This is the way it is. The reference I have to mind and have actually read, is Modeling the Bipolar Transistor by Ian E. Getreu but I have to will try and confirm this in case my memory on the details of this text is unclear. My guess is that 100% of those making charge-control model claims on the BJT page, have never actually looked at the formal derivation of that model. They use the words, but simply don't know what the words mean. Kevin aylward 10:28, 9 September 2007 (UTC)

You can think of bipolar transistor as a current amplifier Of course you can!

But think for a second. Why didn't Horowitz/Hill simply flat-out state that "The bipolar transistor *is* a current amplifier?" Why do we have to "think" of the transistor as being a current amp? Because it's not one, although it saves lots of trouble if we pretend that it is. Ic=hfe*Ib is a simplified model which works great as long as you don't look inside the transistor. But... is it real, or is it a Lie to children? Here's an analogy: we can also think of electrons as orbiting an atom's nucleus like little planets, and it's a great aid to simplified explanations ...but it's wrong. Ic=hfe*Ib works great for basic circuit design, but it forms a large stumbling block for anyone who tries to understand the internal operation of a transistor.

Here's another way to say it: please explain how the base current can have an effect upon the collector current. This is very important issue. Anyone who claims that Ib really does control Ic must tell us how this control actually works. I know of no reason why the motion of the carriers of Ib could have an effect upon the value of Ic, but I do know a straightforward explanation for the origin of Beta:

As with any simple silicon diode, the thickness of the BE depletion layer is proportional to the voltage applied across B and E. Change Vbe, and you change the depletion layer thickness. And because Ic and Ib are both determined by diffusion across this single depletion layer, Ib and Ic values are "locked together." Ib does not DIRECTLY control Ic. There is no DIRECT path by which the Ib current can be amplified to alter Ic. Instead Vbe determines both Ic and Ib, with Ib being smaller because Ib is caused by relatively rare majority/minority carrier recombination in a very small Base volume. If we connect a current source to the base terminal, Vbe will change, and the width of the BE depletion layer will change, and this alters the value for Ic. Ib did indirectly determine Ic, but it did so by altering Vbe and simultaneously changing the width of the BE depletion layer.

If there was some weird way way alter Ib yet hold Vbe constant (and prevent the depletion layer thickness from changing,) then we'd find that we could set Ib to any value we want, yet it's purported effect upon Ic would be gone. If Vbe can't change, then Ic can't change, and the equation Ic=hfe*Ib no longer works. This illustrates the idea that Vbe controls Ic, and Ib does not.

So, if we want to build a simple amplifier, it helps if we think of transistors as being current amps, even though they don't internally work that way. (And if we want to explain atoms to little kids, it helps if we think of electrons as orbiting the nucleus, even though atoms really aren't like that.) But if we want to become advanced students, and we want to develop a firm grasp on the overall picture of transistor internal operation, then we must first remove a large mental stumbling block from our minds: the false idea that Ib somehow can alter the value of Ic.

PS Imagine if school kids with no physics knowledge insisted that electrons really do orbit around atomic nuclei, and they started a huge fight on the pages of WP to fight with physics teachers who want to explain quantum numbers and the 3D shapes of atomic orbitals. It would be silly and embarrassing. That's how I see this fight between "current control" versus "voltage control." It's the kiddies versus the professionals, and only on WP can the kids win, since emotional opinions rule the day on WP, and knowledge and expertise is basically irrelevant here. The WP rules empower ignorance, guarantee flamewars, and cause thoughtful people to leave in disgust. Sad, and it didn't have to be that way. --Wjbeaty 03:41, 9 September 2007 (UTC)

Why are you knocking down this straw man? Has anyone said that the BJT is a current-controlled device? For the base–emitter junction, it makes just as much sense to treat its I–V curve with either variable being independent and other dependent, depending on how you drive it. In either case, the DC collector current is going to be a substantial fraction of the DC emitter current, but getting the details and AC right will require looking at the physics of excess minority carriers in the base region. Is there something in the article that you would change to explain this better? Dicklyon 03:53, 9 September 2007 (UTC)

By the way, the "kiddies" interpretation you've proposed is really quite offensive, bordering on incivility. Some of the editors may not have the same education you do, but they are not dummies and not just playing around, as far as I can tell. I trust you didn't mean to include me in that. In any case, please review WP:NPA and return to discussing how we can improve the article, instead of talking about other editors and their motives. Dicklyon 04:00, 9 September 2007 (UTC)

Yes, I can see how the kiddies reference can sound offensive, yet, for me it does catch the essence of the truth. By far the majority of professional analogue ic designers, and I mean the ones that design the billions and billions of analogue ics for a living, just don’t design BJTs from the point of view of base current controlled collector current. How do you suppose Barrie Gilbert could have come up with his Gilbert cell multiplier without the voltage controlled model? In my experience, it is truly only the novice designers that have learned bad habits that use this base current controlled idea. Its usually knocked out of them by a mentor engineer in the first few years, if their lucky. We use formulas like, max gain is Va/Vt, Av=gmRL. We correct for base current by subtraction of rbb’.ib from the vbe applied to get vbe’ at the junction etc. etc. I know this may sound pretentious, but this is just how it is. I don’t know how to make these type of facts sound less insulting. The truth often hurts. Kevin aylward 10:55, 9 September 2007 (UTC)

By the way, the "kiddies" interpretation you've proposed is really quite offensive. Dick, the only people that can offend you are those that you grant that power to. Wjbeaty diminishes only himself with such rants. That's too bad because up until now, I have found Wjbeaty to be quite civil and rational. What I don't understand is why Kevin and Wjbeaty, who otherwise seem quite intelligent, can't come to grips with these basic facts: Wikipedia is not about the truth and Wikipedia is not a forum to reveal the truth (from WP:V: "The threshold for inclusion in Wikipedia is verifiability, not truth"). However, it does not follow that grade school physics texts are of equal authority to graduate physics texts despite Wjbeaty's inference to the contrary.

There is no 'fight' here between voltage-control and current-control as Wjbeaty claims. That would be like arguing if the voltage across a resistor causes the current through the resistor or the other way around.

However, let's ask this question: What causes the measured voltage across a conducting PN junction? Is it due to a voltage that has been applied to the junction and that causes diode current? I suggest anyone thinking about answering that question think clearly and carefully before doing so. Hint: How does one actually apply a voltage to a diode etc. and does that process involve the movement of charge (otherwise known as a current)? Alfred Centauri 04:46, 9 September 2007 (UTC)

I have though about it. As noted above, charge generates the power supply voltage, but this is way far removed down the chain. At the operational level, we have a supply voltage that modulates the charge in the BJT, causing transistor action.

Indeed, it's all kind of silly. Why don't they read what the article says, and let us know if something about it needs improving, instead of all this arguing about what nobody has claimed? I think what it says is balanced, correct, verifiable, and not in conflict with all this stuff he's saying, so what's the beef? Dicklyon 04:52, 9 September 2007 (UTC)

It isn’t. It claims that the BJT is base current controlled. It isn’t. The most authoritative university reference on the nature of the BJT that I see, is the one I referenced, which states categorically that the transistor is voltage controlled. I will let you know when I get a response from Winfield. Kevin aylward 10:55, 9 September 2007 (UTC)

Kevins Edits

For those that desire to revert my inclusion of:

It should be noted here that the standard physics model expressed by the term “Charge Controlled Model” is open to misinterpretation as in that in this approach, the base charge is considered the dependent variable as a function of the independent terminal voltages. These currents are then calculated from the voltage dependant charges. This is in contrast, to calculating the currents without the intermediate charge calculation.

Please explain why you disagree with the above claim. The above is a matter of fact,and is clearly requied to avoid misunderstandings. Please explain what physically causes the charge in base. How is this charge casually related to whatever is claimed to be driving the transistor such that it can actually function as an amplifier to an external signal.

Kevin aylward 11:38, 9 September 2007 (UTC)

It is completely irrelevant whether I disagree with this claim or not, Kevin. Why is it that this is so hard for you to grasp? Can you answer that? All that matters is that what you've written above can be verified by an authoritative source. You said: "It should be noted here that the standard physics model expressed by the term So, “Charge Controlled Model” is open to misinterpretation". Please provide an authoritative citation for this statement.

But, there is another thing I want to discuss. You've continued to edit the BJT article while claiming a consensus for your views on this talk page when there isn't. This article is not a battle ground for the truth about BJT operation. And, as I said earlier, there are well known, authoritative references that clearly state that the BJT can be thought of as voltage controlled, current controlled, and charge controlled. Why? Because, these variables are not independent of each other. To claim that one variable is the one while the others are not is just plain silly.

Finally, the tone of your statements on this talk page (and the main article) is often inappropriate. The fact is, the other editors involved in this dicussion are well educated and have the credentials to back that up if that's what you're looking for. Do stop to consider, before hitting that 'Save page' button, that well educated people often disagree. Alfred Centauri 13:19, 9 September 2007 (UTC)

Kevin, I have reverted your edits to my comments as they are considered vandalism. Once again please do not insert your comments in-line with mine. Alfred Centauri 15:00, 9 September 2007 (UTC)

Well, this is a new one to me. Do you post much on the news groups? Its de-facto that the correct NG etiquette is to interleave the originator and replied text. Otherwise it’s a complete nightmare to follow the flow of the debate.

I'll just dump all the prose down here then, and let people try and figure out what goes with what.

Of course its relevant. If you can't explain what “charge controlled model” means, then you can't make any claims about it. Why is this so hard for you to grasp?

It is de-facto misunderstood by the actual comments on this page. Apparently, no one else here can offer an explanation as to what “Charge Controlled Model” actually means, despite quoting it at length, therefore it is trivially obvious that it is being misinterpreted. It does not need an authoritative citation on that basis. How can anyone use a principle if they don’t know what the principle even refers to. Its like stating that conservation of energy means that that I like blue colours.

Additionally, I have stated that I am trying to track down a reference. Or do you consider me a liar?

Oh? You specifically stated:

"Nobody has claimed that base current physically controls collector current."

It is that fact that there appears to be a consensus on, and which I have edited.

Apparently it is. Wikipedia is an encyclopaedia, so as far as reasonable, one does indeed to expect it to represent the truth as far as current knowledge holds.

enjoy. Kevin aylward 17:49, 9 September 2007 (UTC)

Do you post much on the news groups? I have in the past but remember that on usenet, each post is a separate entity and, with the proper reader, one can see the hiearchy including the original post in it's unaltered form. Here however, the talkpage is presented at once and, if your interleave your comments with mine, the question of who said what when becomes almost impossible to determine as it is hard enough to do this already. For example, in the comments I reverted, you wrote:

"Oh? You specifically stated: "Nobody has claimed that base current physically controls collector current.""

But, in reality, I didn't write anything like that. The closest thing I have found is this: "Has anyone said that the BJT is a current-controlled device?" but that was written by another editor. So, once again, please leave my comments intact and simply quote them in your comments if you wish to reply to individual parts. Alfred Centauri 18:08, 9 September 2007 (UTC)

Kevin has taken what I wrote completely away from its meaning in context. "Nobody has claimed that base current physically controls collector current" is in no way contradictory to the statements in the article that he is changing. I have also explained these things to him carefully in email. He seems to want to provoke an edit war. Better that he should learn a bit more about wikipedia editing, such as by reading WP:V and WP:RS and try to find a way to interact more productively. Dicklyon 18:26, 9 September 2007 (UTC)

Winfield Hills Response

I have now recieved an email response from Winfield -- Kevin aylward 17:43, 9 September 2007 (UTC)

The email is reproduced here, unedited:

Start of Winfield quote:

Here's my statement, in response to your request.

Although one can use a small current to bias and use a bipolar transistor, this is generally not a very successful way to use BJTs to make an amplifier, because the current gain, or beta, is very unpredictable from one part to another. Instead we use voltage biasing, and take advantage of a BJTs highly-predictable base voltage, as expressed in the famous Ebers-Moll equation. Usually we employ an emitter resistor, a current source, or another matched transistor, in the bias circuit. After setting up the transistor's operating condition, we finish our analysis and design by carefully considering the impact of the range of base currents we might encounter, e.g., by using the h_FE or beta spread as expressed or estimated from the BJT's datasheet specifications. Yes, beta plays a role, but a secondary role.

Sometimes the use of a high-value emitter resistor or a current source, etc., mentioned above, may dominate the circuit analysis, and we can simplify our description of the transistor to a fixed Vbe drop, like 0.65 volts, etc., and ignore Ebers-Moll, but this does not take away from its importance and significance. After all, in this situation, its Ebers-Moll that lets us determine if the Vbe change is small enough to ignore.

To understand the gain of a BJT amplifier circuit we calculate the BJTs transconductance, which does not vary from part to part, and which is accurately predicted from the Ebers-Moll equation. Once we know the transistor's operating bias current, from the steps above, we know its transconductance: g_m = 40 Ic (at room temp). To be clear, transconductance expresses a (small) change in collector current resulting from a (small) change in a BJT's base-emitter voltage. So it's a voltage-driven amplifier we're analyzing (not a current-driven amplifier). it is Ebers-Moll that lets us to not only determine the amplifier gain, but also its distortion. We can add the small influence of the Early effect to improve the accuracy of the analysis.

Sometimes we place our BJT in a multi-stage feedback circuit, which may dominate in the amplifier gain analysis, and we can simplify the transistor description and ignore transconductance, but this does not take away from its importance and significance. After all, it's what we use to calculate the open-loop gain.

In summary, the amplifier design process is most accurately described by considering the BJT to be a voltage-controlled device, rather than a current-controlled device.

End of Winfield Quote:

I agree with virtually everything Winfield says here particularly this: "the amplifier design process is most accurately described by considering the BJT to be a voltage-controlled device" (emphasis mine). But please note that is a far cry from the claim that "the BJT is a voltage-controlled device". The amplifier [circuit] design process is fundamentally based on models that may or may not have a physical basis. Thus, this info from Winfield doesn't rise to the level of confirming one physical description of transistor operation or the other. Alfred Centauri 18:22, 9 September 2007 (UTC)

I too support and agree with Winfield's statement, and I'm sure there are sources we could cite if someone wants to put something about that into the article. But it says nothing about the physics of the device, and does not address the issues around Kevin's edits, as far as I can tell. He certainly isn't calling the charge-control model a misinterpretation, or denying that the device can be modeled in terms of beta. Dicklyon 18:30, 9 September 2007 (UTC)

I am not saying that the charge controlled model is a misinterpretation. I am saying that people are misinterpreting what the charge control model actually means. I have no bone to pick on that model itself. It is correct. People just don't seem to understand what it is saying. As for the not denying that one can’t use beta in general, this is left to Winfield’s followup email.

Kevin aylward 19:31, 9 September 2007 (UTC)

OK, but let's get away from worrying about "people misinterpreting" and get back to improving the article. What in the article is incorrect? Please provide sources to back up your assertions. Dicklyon 22:29, 9 September 2007 (UTC)

Winfield Second Response

After writing my response, I wandered over to Wikipedia to see what all the fuss was about. I found the little segment wherein H&H AoE is quited to support a current-control model. I think one badly misreads our book in so doing, because we quickly introduce Ebers-Moll to the reader and use it thereafter in our analysis.

You may copy my paragraphs into the Wikipedia discussion if you wish. Ditto for this letter.

As for the Wikipedia article, my preference would be to see both approaches mentioned, but with the serious disadvantage of relying on a given beta stressed, and the advantages of using Ebers-Moll (and its daughter equations) for accurate calculations also stressed.

The so-called "exponential function" aspect is BJT reality, but it's absolutely not a problem, being easily dealt with by using the small-signal transconductance g_m at a given operating current.

In fact, what Ebers-Moll lets us do is observe exactly how g_m changes with collector current, as the output signal traverses from the minimum to maximum voltages, and thereby determine the amplifier's distortion. To my knowledge this cannot be analyzed using the current-control approach.

Kevin aylward 19:25, 9 September 2007 (UTC)

Actually, if you assume constant beta and a diode at the B-E junction, the current-control model trivially leads to the same transconductance versus collector current relationship. But I agree with Winfield that we should represent both methods and that their relative usefulness can be pointed out with reference to a reliable source such as his book. I see no reference to H&H in the article, so I'm not sure what he's referring to about using it as a source for the current-control idea; perhaps an old talk comment. Anyway, let's focus on what the article needs, old talk aside. Dicklyon 22:28, 9 September 2007 (UTC)

I think one badly misreads our book in so doing. Mr. Hill is mistaken. The quote from AoE was not introduced to support a current-control model over any other model. Even a casual read of my comments on this issue reveals that my position is that the voltage-control / current-control model dichotomy is a false one. That is, it is my position is that the views are duals. The fact that AoE mentions both (actually, charge control is also mentioned on the same page, so in fact three views are mentioned) is exactly the reason I put the link and quote up. It has been my understanding that Kevin is convinced that there is only one correct view - the voltage-controlled view and that is why I have been pushing back.

But now, what I'm concerned about here is a subtle confusion regarding context. Mr. Hill appears to be speaking from a design perspective which is a different context than the physics perspective. So, just to make sure that I'm on the same page as everyone else, here is my question: In what context is this discussion of how a BJT is controlled - a design context or a physics context (or both)? Alfred Centauri 23:05, 9 September 2007 (UTC)

One can say that there are two basic approaches to modelling, one based the “real” physics of the situation, the other based on a functional curve fit, which ignores the reason for the relation

The base current controlled view is an approximation, functional curve fit. It is a black box, non physics based model, that whilst producing a basic overview of one main characteristic of BJT operation, is not a sufficiently accurate approximation, or general enough to perform useful design of the majority of production viable BJT circuits. An accurate model that does allow such production of satisfactory BJT circuit designs, is the voltage controlled, physics based model.

The main page needs to address that fact that the base control view is a poor approximation.

It needs to address the fact that a valid authority reference, Bart Van Zeghbroeck Professor University of Colorado Department of Electrical and Computer Engineering, specifically denied that the transistor is a base current controlled device. There is no basis to keep removing this reference, as it is a rebuttal, valid under wikipeda guidelines, to the allegation that the BJT may be considered as a base current controlled device. Yes, all alleged views should be represented, including authoritative references that claim only one view is the correct one.

Kevin aylward 11:04, 10 September 2007 (UTC)

It is, and should be, both. But you are right that Kevin seems to be mixing them up, using statements about design to push ideas about the physics; or so it seems to me. Dicklyon 23:07, 9 September 2007 (UTC)

I am indeed quite clear on both the physics aspect and the design aspect. Winfield, is only addressing the design aspect with his comments here. I am addressing both. From a physics point of view, the transistor is a voltage controlled device. That is, the terminal voltages directly determines the charge in the base, and such charge, directly determines the collector current. From a design point of view, the base current control approach is severely limited in its ability to predict transistor behaviour, for example, multipliers, current mirrors, and distortions. For example see, http://www.kevinaylward.co.uk/ee/bipolardesign2/bipolardesign2.html

And whilst I really do not want to step on any toes, here, I have great respect for Winfield’s views. It is most likely that that my experience of the design of 50,000 transistor analogue integrated circuits, including production designs at major semiconductor companies, e.g. Texas Instruments, gives me an alternative insight. Of course, I could be a twat, but there you go.

Kevin aylward 11:04, 10 September 2007 (UTC)

The Art of Electronics

I've beefed up the section in question with more specific info from, and citations of, Horowitz and Hill. Please comment or further improve it if it's not quite right. I've tried to take Kevin's concerns into account, especially in the final paragraph about what models are used by designers and why. Dicklyon 02:43, 10 September 2007 (UTC)

Bart Van Zeghbroeck on Voltage Control

Result of newsgroup sci.electronics.design discussion 04 December 2004 19:57 - Re: FETs Vesus Bipolars, Why More Efficient?

Ratch, I hate to be the one telling you this but the BJT is indeed a voltage controlled device. The voltage applied to the base emitter junction controls the collector current and the base current is a result of the additional hole injection (for an npn BJT) into the emitter as well as the recombination in the base-emitter depletion region and the quasi-neutral base region. It is tempting to claim that the BJT is controlled by the base current, since that is how a BJT is typically biased; the exponential variation of the current with the base-emitter voltage makes a voltage bias impractical. Any circuit designer will also tell you that any voltage bias can be replaced by its Thevenin equivalent current source. Hopefully this provides you some ammunition to claim that either one can be claimed when treating the device as a black box. Finally, you'll find that a MOSFET biased in the subthreshold region has characteristics that are very similar to that of a BJT.

Bart Van Zeghbroeck Professor University of Colorado Department of Electrical and Computer Engineering Campus Box 425 Boulder, CO 80309-0425 Office ECEE1B41

Kevin aylward 11:55, 10 September 2007 (UTC)

βF

The article, in the Bipolar junction transisitor#Voltage, current, and charge control section, contains the sentence "In analogue circuit design, the current-control view is sometimes used since it is approximately linear. That is, the collector current is approximately βF times the base current" (emphasis added). As far as I can tell, F is not defined in the article, and I don't know what it could be. (Or maybe this was supposed to be β_F, for forward β? --Gerry Ashton 16:05, 10 September 2007 (UTC)

I fixed it back to subscript F for forward. Dicklyon 17:36, 10 September 2007 (UTC)

Ok, however, you reedited back in "with critical gain and speed parameters". This is inaccurate. Critical is not a requirement. As I have noted, and indeed as Winfield noted, it is standard practise for professionals to design with the voltage control model. It is not reserved just for "criticle" parameters. Kevin aylward 08:27, 11 September 2007 (UTC)

Polarity of germanium transistors

Were most germanium transistors, PNP transistors? Were NPN germanium transistors uncommon? 24.26.128.185 (talk) 22:07, 25 April 2008 (UTC)

Answer: generally speaking, Yes, and Yes.

external reference bjt_models.pdf gone

The link www.brookdale.cc.nj.us/fac/engtech/aandersen/engi242/bjt_models.pdf should be updated to a new location or removed. —Preceding unsigned comment added by 130.225.243.80 (talk) 20:31, 10 August 2008 (UTC)

The correct (new) URL appears to be http://ux.brookdalecc.edu/fac/engtech/andy/engi242/bjt_models.pdf. --TedPavlic | (talk) 20:46, 11 September 2008 (UTC)

Ambiguity and repetition

The sentence "This gain is usually 100 or more, but most robust designs only depend on it being very large" is ambiguous. It just doesn't make much sense and should be reorganized.

Section 5.1.1 Ebers–Moll model is redundant with Section 1.2 Transistor 'alpha' and 'beta'. The same concepts and the same equations are presented. One of the two sections should be merged into the other one. I would myself merge 1.2 into 5.1.1.

ICE77 (talk) 05:49, 19 April 2009 (UTC)

Yeah, not great. I worked on it some. I notice the Ebers–Moll section had this emitter efficiency thing disconnected from anything else since this edit back in 2006; I took it out; but there remains an undefined symbol in the base current density formula that might be related; find a source and work on it? Dicklyon (talk) 06:34, 19 April 2009 (UTC)

The sentence "This gain is usually 100 ..." is repeated twice. You fixed the first occurrence but not the second.

I don't know what you are referring to with "emitter efficiency thing disconnected" and "undefined symbol in the base current density formula". Be more explicit so I can see what you are talking about.

ICE77 (talk) 00:36, 4 May 2009 (UTC)

I had removed this bit: "Emitter Efficiency,

\eta ={\frac {J_{n}({\text{base}})}{J_{\text{E}}}}

, is the ratio of current injected into the base to the current in the emitter; the two differ due to backward injection from the base into the emitter and to recombination. See carrier generation and recombination." as it didn't connect to anything, as far as I could tell.

There's still a

n_{bo}

in the formula, and I don't know what it is; the section doesn't say; I haven't tried consulting sources yet. Maybe this n was supposed to be the eta thing that I had removed? Dicklyon (talk) 05:39, 4 May 2009 (UTC)

$\eta$ is just a ratio of currents. $n_{bo}$ most likely refers to the concentration of electrons (n) in the base (b) of an NPN transistor at equililbrium (o) since electrons are minority carriers in the base of an NPN transistor and they are responsible for current in the device.

ICE77 (talk) 23:46, 5 May 2009 (UTC)

Plausible guesses, but neither was connected to anything else in the section, so what we really need is a source; so far I don't see these symbols or anything like them in sources. nbo does look like a carrier density, since it multiplies q. Dicklyon (talk) 04:19, 6 May 2009 (UTC)

Concentration of electrons or holes and electron charge can coexist within a current equation. I have taken notes from a semiconductor book where $q$ and $n$ or $q$ and $p$ are multiplied to obtain a current. $q$ is just a constant. An example of an equation where this is true is the equation for resistivity.

ICE77 (talk) 23:45, 6 May 2009 (UTC)

A simple model of the transistor consisting of an LED and a photodiode

the following section was deleted on may 20, only one day after it went up: "A simple model with many of the properties of a transistor, especially a phototransistor, is a forward biased LED (emitter–base junction) and a reverse biased photodiode (base–collector junction) sharing an anode (base) in a single package so that 99% (1-1/β_F) of the photons emitted by the LED are absorbed by the photodiode. Each electron-hole recombination in the LED produces one photon and each photon absorbed by the photodiode produces one electron-hole pair therefore each electron injected into the base would result in 100 (β_F) electrons at the collector". I will leave this copy here so others can discuss whether it should or should not be included in the article. just-emery (talk) 16:25, 20 May 2009 (UTC)

This is a complicated passage, and it would take me a lot of time to figure out if this is a useful model or not. Things that require serious thoughts by people experienced in the field to figure out should not be made up by Wikipedia editors; they should come from reliable published sources. --Jc3s5h (talk) 16:35, 20 May 2009 (UTC)

It is trivial. If you think its complicated then you are in no position to be judging it. I do not claim that it has all of the properties of a transistor but it obviously does amplify the current. Any high school freshman can see that. just-emery (talk) 16:40, 20 May 2009 (UTC)

Go read Wikipedia:Verifiability. Since you have no source for this, I will resist the inclusion of this passage. Remember, you may think you are an expert, you may even be an expert, but Wikipedia readers have no way to know who you are. --Jc3s5h (talk) 17:12, 20 May 2009 (UTC)

You are trying to confuse the issue. The issue is why on earth this trivial model, which obviously works and makes it easy for beginners to understand (which is what wikipedia is supposed to be about) the operation of the transistor, should be excluded from the article. just-emery (talk) 06:22, 22 May 2009 (UTC)

10,000 electrons injected into the base results in 10,000 electrons appearing at the collector and 10,000 photons created by the led. 9900 of the photons are absorbed by the photodiode which creates 9900 more electrons which travel to the LED and create 9900 more photons and then the electrons move on to the colloctor. 9801 photons are then absorbed by the photodiode. and so on. in the end 100*10,000 electrons reach the collector. 100 times more than was initially injected. 100 fold amplification. just-emery (talk) 06:22, 22 May 2009 (UTC)

It's unclear to me how this example aids in the understanding of a bipolar transistor. That is, would a novice who could grok this example easily be able to transition to the more accurate descriptions of diffusion and drift currents? After all, this sort of feedback process cannot be described so explicitly in a BJT (try giving such a feedback explanation WITHOUT using photons). In a BJT, a field is used to turn off the natural dipole that is created by bipolar diffusion; without the dipole, the diffusion can continue and the BJT acts like a current source (where the voltage it displaces is ohmic loss across the base–collector depletion region that narrows and widens as necessary). That's not only the conventional way of understanding bipolar operation, but it is not that technical. We should stick to conventional explanations that can be found in trusted sources (e.g., textbooks). If you think your photon model is a compelling way of explaining BJTs, you should try to find it in an existing textbook and reference it. If you can't find it, you should submit your novel example to a textbook writer. When your example comes out in print, then some other Wikipedia editor will be able to use it and reference it. —TedPavlic (talk) 13:00, 22 May 2009 (UTC)

The purpose of a model is simplicity, not accuracy. just-emery (talk) 15:15, 26 May 2009 (UTC)

Your model lacks both simplicity and accuracy, and that's what makes it misleading. You are building fictitious behaviors on top of existing sophisticated devices, namely photodiodes and p–n junctions. You cannot be so cavalier as an encyclopedia editor because readers of the encyclopedia count on you to reflect information that can be verified by a large consensus of experts in the field. There is a great risk that someone may misread your highly inaccurate description as a statement of fact. In the end, the essence of your description is that a transistor provides amplification. There is no reason to posit some mechanism for that amplification if it is not the actual mechanism being used. —TedPavlic (talk) 17:15, 26 May 2009 (UTC)

Active-mode PNP transistors in circuits figure incorrect

There is a miror error on the figure associated with the section entitled, "Active-mode PNP transistors in circuits". The arrow indicating the directional flow of the base current "Ib" should point away from the transistor, not toward it. —Preceding unsigned comment added by 199.181.136.59 (talk) 15:49, 1 July 2009 (UTC)

The $6 Man

As one who can barely understand the technobabble on the page, ;D can somebo clarify: is the point-contact design mentioned the same as (or equivalent to) what I've seen described as a "cuprous-contact rectifier"? If not, how do they differ? ("In English, McGee.") TREKphiler ^{hit me ♠} 09:37, 20 November 2009 (UTC)

Ebers-Moll model for a PNP transistor

In the equivalent circuit diagram for the Ebers-Moll model of a PNP transistor, aren't the two diodes shown facing the wrong direction? Shouldn't the cathode of the diode (with the bar) be on the base (n-region) of the transistor? 76.120.125.115 (talk) 04:35, 18 August 2010 (UTC)

Yes, I used an old version of the PNG. Sorry about that, fixed Inductiveload (talk) 12:39, 22 August 2010 (UTC)

Hybrid-pi and h-parameter models

I believe this article should not point to the "hybrid-pi model" article but include it into itself. It's the most important small-signal model. I don't see why the "h-parameter model" should be shown and the "hybrid-pi model" shouldn't. I rather prefer to see the opposite situation which is much more practical.

ICE77 (talk) 18:59, 21 April 2011 (UTC)

Graph

In the graph of the operating characteristics, shouldn't the CE voltage be labeled with a "V" instead of a "U"? This seems confusing.67.141.18.62 (talk) 02:26, 2 June 2012 (UTC)

Schematic is wrong

Please take a look at this page: http://www.markallen.com/teaching/ucsd/147a/lectures/lecture3/10.php

PNP arrow points to wrong direction! — Preceding unsigned comment added by 65.44.170.169 (talk) 14:00, 28 June 2012 (UTC)

In the page linked to by 65.44.170.169 and in the Wikipedia article the arrow for a PNP points toward the base, which is correct. A person drawing a schematic is free to position the arrow toward the top of the page, the bottom of the page, or either side, depending on how the circuit is connected. Jc3s5h (talk) 19:33, 28 June 2012 (UTC)

Doesn't entirely aid clarity to draw one upside down though, does it. Spinning Spark 22:55, 28 June 2012 (UTC)

Theory vs application

As someone else stated, there is an extreme amount of "technobabble" and yet very little information on common uses. As I recall from EE, there are at least two ways BJTs are commonly put to use... Let's see some simple circuits, maybe some biasing... emitter-follower vs. amplification... without going into all the molecular details. — Preceding unsigned comment added by 71.197.246.206 (talk) 04:55, 6 July 2012 (UTC)

Minority carrier device

The BJT is a minority carrier device because most of the charge cariers passing through the control region, the base, are minority carriers with respect to the base. However, it is wrong to say it is a minority carrier device on account of the base current, becase "base current" is taken to mean the current in or out of the base terminal. The base terminal current is not what gets the job done (in the active region); the job gets done by the collector and/or emitter current. Therefore the classification of the device is based on the collector or emitter current. --Jc3s5h (talk) 00:15, 29 June 2009 (UTC)

I see. So "base current" to you refers to the current coming out of the base rather than the large concentration of minority carrier current going up from the base into the collector. Well, you're the boss. Revised. —TedPavlic (talk) 15:58, 29 June 2009 (UTC)

That's true; base current is defined as the current into the base terminal. The collector current can perhaps be called the base–collector current, which is what you probably meant to refer to. Dicklyon (talk) 07:06, 30 June 2009 (UTC)

I probably learned that "minority carrier device" factoid decades ago in my devices class, but has it proved to be useful since then in any of my work with BJTs? I would say definitely not. Acmefixer (talk) 15:07, 25 July 2012 (UTC)

Outtakes

This inline comment (used twice) are better dealt with here (cut/paste):

Where two of the three "Citation needed" tags are, was this comment: "I believe that Horowitz and Hill have a statement nearly identical to this; someone should verify that and replace this Fact with a ref to HH." Widefox (talk) 12:45, 28 July 2012 (UTC)

Widefox's request makes no sense out of context. Please provide text we can search on to find the spot in the article. Jc3s5h (talk) 12:49, 28 July 2012 (UTC)

Clarified above. Here's a diff as well [11] Widefox (talk) 13:47, 28 July 2012 (UTC)

I fixed the passage. Jc3s5h (talk) 21:53, 28 July 2012 (UTC)

Diodes

An NPN[clarification needed] transistor can be considered as two diodes with a shared anode. Our proverbial bright 12-year-old reader is going to say "Hey, I can make a transistor with these two diodes I found" and when she wires it up and tries it, she's going to be disappointed. This needs to be explained better - two back to back junctions, yes, but not just "diodes". --Wtshymanski (talk) 18:15, 1 August 2012 (UTC)

I did some edits to make it more sensible. Please comment or fix it better. That mess was from an unnoticed IP addition of May 4, 2012. Dicklyon (talk) 22:47, 1 August 2012 (UTC)

"..when a positive voltage is applied to the base–emitter junction.."

If the positive voltage is less than 0.6V for a silicon BJT, the junction does not have enough voltage to forward bias it, and no current will flow. The sentence should read "when a current flows between the base and emitter.." or "..if enough positive voltage is applied to the base-emitter junction to cause a current to flow..". One has to remember that the BJT is a current operated device. July 25, 2012 by Watson - my yahoo email account is acmefixer. Acmefixer (talk) 14:59, 25 July 2012 (UTC)

No, it's a voltage controlled device, it's only incidental that the leakage current is proportional to the Emitter-Collector current. 24.121.250.13 (talk) 15:35, 30 September 2012 (UTC)

Point contact transistors

To clarify some confusion arising in recent edits, the operation of point-contact transistors requires minority carrier injection. Spinning Spark 21:11, 22 October 2012 (UTC)

Voltage Controlled Bipolar Transistor

I have added text as the fundamental operation of the bipolar transistor.

Before my edits are considered to be reverted, please refer to the original Gummel–Poon_model paper cited at

http://en.wikipedia.org/wiki/Gummel%E2%80%93Poon_model

A direct quote from this Gummel-Pool paper is (P.828):

“…The new charge control relation arises from the treatment of the transport equation for the carriers that pass between emitter and collector. Use is made of the fact that recombination has only a very small effect on the junction-voltage dependence of the current passing from emitter to collector (later called the dominant current component). Hence for this dependence, but of course not for the base current, recombination is neglected. A direct closed-form solution of the transport equation from inside the emitter to inside the collector is possible…”

It is noted that recombination *is* the base current. Since this base current is neglected (initially) in the Gummel–Poon method of calculating the collector current from the base emitter voltage and collector voltage it is simply not reasonable to then claim that “the collector current is *controlled* by the base current”.

The “charge control” model, by design, as shown above, calculates the base charge resulting from the applied *voltages* at the base and collector. It is noted that the base charge is not the charge flowing out of the base, but the charge in the base region, which has no direct relation to the charge flowing out of the base.

So, fundamentally the bipolar transistor is a voltage controlled device. Any base current that flows is simply a nuisance, and not any way key to transistor operation. This is clearly the opinion of some of the most noted experts (Gummel-Pool) on transistor theory.

If any editor has a more academic *reliable* source that contradicts the Gummel-Pool voltage controlled view above, and can present the basics of an actual theory as to why the bipolar transistor would be base current controlled, present it here, or please leave my latest edits alone. Kevin aylward (talk) 13:29, 27 December 2012 (UTC)

Gummel-Pool is just a model, not a physical explanation.

I agree, but it is a model based on actual device physics. A detailed model based on base current controlling the collector current that is accurate does not exist.

If you know of one, please provide a physics based model that calculates collecter current from knowing base current.

The statement that was added, "It should be stressed that there is essentially, no direct physically casual relation between collector/emitter current and base current", is just wrong.

No it is not. My statment is correct, and validated by gummel-poon. Did you actually read the Gummel-Pool paper?

“…recombination has only a very small effect on the on the junction-voltage dependence of the current passing from emitter to collector…”

Please explain why you do not accept that this reference states two positions. One, that the collector current is dependant on the junction voltages, two, that the base current has a negligible effect, hence its not the base current that controls the collector current!!!

In what way do you suggest that the charge sent into the base from the base terminal actually incites charge to flow from the emitter to collector?

The charge-control point of view depends, obviously, on charge, which is the integral of net current. If the base lead is cut so no current flows, the transistor doesn't work. Reverted. Jc3s5h (talk) 14:17, 27 December 2012 (UTC)

Sure, cut the base lead and no voltage is applied to the base-emmiter junction.

You misunderstand what “charge control model” actual means. You need to go and read and UNDERSTAND the GP paper.

“Charge control model” means to calculate the charge in the base region due to the terminal voltages. The charge in the base region is not the charge comming/going from the base lead. The charge in the base is much, much larger in the base region than that supplied by the base terminal. There is also no direct relation between the charge supplied by the base terminal and the charge supplied by the emitter. Go and read the paper! — Preceding unsigned comment added by Kevin aylward (talk • contribs) 16:42, 28 December 2012 (UTC)

Before the edit war heats up, there can be more than one description. I hesitate to say explanation; there are no explanations in science. There are only theories and models and predictions. What suffices as an explanation is just a retelling of the story in terms of some other theory. In my reading from where I don't remember the best model for the specialist is the charge controlled model.

I agree, for example there are two contradictory theories that have identical equations as that of Special Relativity. The second is the Lorenz Ether theory. It is impossible to distinguish them apart experimentally. However, both models agree with experiment. In the case here, there are no base controls the collector current theories that agrees accurately with experiment.

I am an analog design specialist.

Kevin aylward (talk) 16:34, 28 December 2012 (UTC)

That charge can be held on the base by a voltage source or by squirting the current into base until it charges up to the necessary voltage. It comes down to which model is most appropriate for a situation. The voltage controlled model is non-linear but accurate. The charge controlled model is sort of linear (beta changes with collector current) but can easily be in error by more than a factor of three. In an RF design where the driving stage is low impedance, it makes more sense to think of the bipolar transistor as a voltage controlled source. For small signal work, gm vs. collector current is so repeatable across multiple devices that the manufacturers don't even bother to specify it. If the driving circuit is high impedance and low frequency the current controlled model can be useful, as long as one remembers to consider the full range of beta variation.

You appear to misunderstand what Gummel-Poon "charge controlled model" actually is. Read the paper I cite. The GP model, by design, is a model that, yes, calculates collector current from base charge, but calculates the base charge from terminal voltages. It is not a “apply a charge entered from the base terminal and calculate collector current” model. This is immediately clear from the 1st page text., and the paragraph I cite. The paper makes it quite clear that recombination, i.e. base current, has only a secondary effect. Kevin aylward (talk) 11:52, 30 December 2012 (UTC)

Yes, it may be true that we have only models of reality in the grand big scheme of things. I agree with the general principle of what you are trying to say here. However, this is not appropriate here. This is about the general, accepted descriptions as to how bipolar transistors actually work from accepted device physics. That is, a transistor works by modifying the potential barriers of the base-emitter junction and collector base junctions. Base current is only incidental to transistor operation. This is truly the way it is. I urge you to read any good book on semi-conductor physics to gain this knowledge.

Both points of view belong in the article. But the first model presented should be for the non-specialist. Right now, in my opinion, neither point of view has been presented in satisfactorily to claim the right of first description.

What is the basis for your opinion? Have you taken a first course in semi-conductor physics? Do you have any formal graduate qualifications that indicate that your opinion is valid? Are you a professional bipolar IC designer?

This is an encyclopaedia. The best model should be the one that is accepted as correct by those qualified to know.

I suggest that the paragraph in question start off with " Collector current is approximately β (common-emitter current gain) times the base current" and then explain how the current controlled current source model arises and its limitations on accuracy and then explain the more accurate but non-linear voltage controlled model.Constant314 (talk) 00:59, 28 December 2012 (UTC)

This perpetuates the myth that the bipolar transistor is controlled by its base current. It isn’t. Its controlled by its base emitter voltage.

Please do not revert my edits on the correct description of the operation of the bipolar transistor unless you can provide a true physics based explanation as to why the collector current is actually *controlled* by the base current.

Please do not revert my edits unless you can explain why the description I gave as to the current being controlled by the base emitter voltage, as clearly given by the Gummel Poon paper I cited, is false.

The reality is that, the base current controlled description of the transistor is simply an “old wives tale”. It is impossible, in general, to competently design transistor circuits with such a false understanding of transistor operation. The number of carries entering the base terminal does not control the collector/emitter current. It’s that simple.

It is not an “exaggeration” to clearly explain the true voltage controlled nature of the bipolar transistor. It is necessary in order to correct the very common misunderstanding that leads to much effort being wasted in remedial instruction to new junior analog designers that are unable to design correctly due to such misunderstandings. The

If you wish to discuss this further you can email at kevin_removethis@kevinaylward.co.uk, remove the _removethis — Preceding unsigned comment added by Kevin aylward (talk • contribs) 11:22, 28 December 2012 (UTC)

Kevin, I indented some or your responses and one of my own to make it more obvious to which statement the responds regards. This is the convention for talk pages. It is preferred that you put your new comments at the bottom, although I appreciate the convenience of putting the response within the comments to which you are replying, but it is hard to find them all. If you are going to reply this way, please put your new comments between paragraphs instead of inside them where it may change the meaning. I have partially restored my paragraph and moved your inline comments to the end of the next sentence. I have no intention of changing the meaning of your comments. Constant314 (talk) 17:10, 28 December 2012 (UTC)

Kevin, posting within other peoples comments often destroys the indentations. Please put new comments at the end. I know it will require some extra words to make clear just which statement to which you are replying, but it is worth it. If you persist in doing this, please sign each comment so that we can readily see who is making the comment.Constant314 (talk) 17:26, 28 December 2012 (UTC)

Kevin aylward :" I am an analog design specialist."

Kevin, I believe that you are an expert, but Wikipedia does not accord any deference to experts. Anyone can claim to be an expert, but Wikipedia has no process to vet experts, hence, the comments of an expert such as yourself do not carry any extra weight.

Kevin aylward :"Base current is only incidental to transistor operation."

Base current is important, especially when beta is low, because it has to come from somewhere.

Yes it can often be very, very important, but this does not mean that the base current controls the emitter current. I noted that the 1st order effect of base current can be calculated from knowing the ib.rbb. voltage drop. Certainly the source has to be able to supply whatever base current is required. Base current can also be the dominant source of noise. Kevin aylward (talk) 11:52, 30 December 2012 (UTC)

Kevin aylward :"I urge you to read any good book on semi-conductor physics"

I already agree with you that a voltage controlled charge that control the transistor is the best model.

Kevin aylward :"What is the basis for your opinion? Have you taken ...semi-conductor physics?"

The basis of my opinion is that I am a user of bipolar transistors and I use both models with satisfactory results. Manufacturer's data sheet specify beta. Numerous college text books on electronics use the current controlled current source model.

Kevin aylward : "This is an encyclopedia. The best model should be the one that is accepted as correct by those qualified to know."

We have no way of knowing who is qualified to know.

I agree. The assumption here is that I have given what I consider a very good explanation, partly based on citing THE noted source for transistor modelling, as to why base current does not control emitter current. I gave an explanation as to how the base voltage determined the collector current in the same manner as it determines the diode current in a diode. I assume that those competent to debate would understand the relevance of this and go “wow, the same current flows irrespective of whatever base current flows” and have a light bulb come on as to what that actually means. Kevin aylward (talk) 11:52, 30 December 2012 (UTC)

Kevin aylward : "provide a true physics based explanation"

A physics based explanation is not required. The requirement is usefulness.Constant314 (talk) 18:06, 28 December 2012 (UTC)

I disagree. If it is being claimed that base current physically determines collector current, then there should be a real physics based theory argument that supports such a view. I have referenced papers, by noted physicists, that refute such a view, and gave a simplified description as to why the voltage controlled model is the appropriate one.

Kevin aylward (talk) 11:52, 30 December 2012 (UTC)

My two cents worth

I think you all have good points. We had tried to cover the different viewpoints already, respecting positions argued in a previous round, in the section Bipolar junction transistor#Voltage, current, and charge control. I don't see how changing "controlled" to "operated" in this section is likely to improve anyone's understanding. From the point of view of controlling collector current, using base current as the control makes perfect sense, and this is the conventional way to discuss beta, even if the physical relationship is not "direct", but only via a small difference from the base–emitter current.

It does not make sense to many professional transistor level designers, because it is not correct. Kevin aylward (talk) 11:48, 29 December 2012 (UTC)

As to where "It should be stressed that there is essentially, no direct physically casual relation between collector/emitter current and base current", I can see that not everyone is likely to agree.

I agree that it is very difficult to get people to see the light that what they believed to be true, is false. As yet, I see no evidence of any actual alleged *physics* that would attempt to explain *why* or *how* the base current induces emitter current. Don’t you see this as a clue? Kevin aylward (talk) 11:48, 29 December 2012 (UTC)

If this needs to be stressed, show us some sources that say it needs to be stressed, or at least some sources that stress it, and we can decide how much weight to give that POV. The current inferences from what Gummel and Poon say are not enough to support this kind of statement.

I did, and it does. It was in the GP paper. It was certainly stressed to me in 1980, when I did my university semiconductor physics course. On day one, the professor said (almost) quote “you may believe that the bipolar transistor is base current controlled. This is wrong. It is a voltage controlled device, and this is why…"

This was stated with much vigor by the professor.

The lecture then proceeded with all the goodies of semiconductor doping, Fermi levels, potential barriers etc. and derived the basic equations.

I don’t believe that anyone that has actually done a formal, proper course in semiconductor physics, as related to the operation of a bipolar transistor would make a claim other than that the transistor, is a voltage controlled device. There is no practical theoretical way to deduce the emitter current from knowledge of base current. Transistor operation is based on modifying potential barrier heights. This is all pretty basic stuff. It is easy to verify in any proper university text book. The issue here, is that there are too many unqualified laymen editing Wikki.

I am not posting this in ignorance. I know exactly what I am saying and why. I understand that maybe all laymen, and maybe 95% of practising designers may be deluded as to how transistor work. I am trying to correct that delusion. Kevin aylward (talk) 11:48, 29 December 2012 (UTC)

The rest of the new basic operation paragraph seems less controversial, though somewhat redundant and needs styling work (heading case, formulas, sentence starting with "2nd", etc.). Dicklyon (talk) 17:57, 28 December 2012 (UTC)

There is nothing controversial about the inherent voltage controlled nature to qualified physicists. I don’t see that section as redundant as it shows how the known diode equation results in the same emitter current for the transistor, and hence, how it is the base emitter voltage, not base current, that determines the emitter current. Kevin aylward (talk) 11:48, 29 December 2012 (UTC)

Kevin, your "Basic Operation" section also appears to be a copyvio from your web article. If you wrote that first, you'll need to state an appropriate license on it to be able to copy from it into WP; or if you wrote it in WP first, you should credit WP for that part.

You are welcome to your opinion. I wrote some of the material for WP first and some for my web site first. There is no reason to credit WP or write a licence, as I wrote all of it, apart from any quotes, and give permission here for its use. Kevin aylward (talk) 11:48, 29 December 2012 (UTC)

But your web page is claiming licensing terms incompatible with WP's ("This paper may be reproduced so long as no charge is made and that the paper is reproduced in full with full credit given to it's author).

What I personally post to wikki has nothing to do with any licence on my independent web site. If I post anything to wikki, its free to all. Kevin aylward (talk) 11:23, 30 December 2012 (UTC)

We are not reproducing it in full in WP, and could not if we wanted to, since we only allow things without derivative-works restrictions. You need to make it clear what the actual license is, or we have to remove it from WP. Not a big deal, though, as we're probably removing it anyway. Dicklyon (talk) 18:59, 29 December 2012 (UTC)

…err…ahmm… what do you mean by “We”. You are not wikki, and have no authority over as what gets posted. You are welcome to your opinions though. Kevin aylward (talk) 11:23, 30 December 2012 (UTC)

In either case, linking it in WP as if it's an authoritative source is not a good idea, as it's really just an unpublished opinion piece. In general, such analyses attempting to say that a common viewpoint is a "myth" are not welcome in WP unless from a WP:Reliable source, and even then must not be given undue weight. Dicklyon (talk) 18:49, 28 December 2012 (UTC)

I did not refer to my wep page as an authority. I simply added a link to the external links page. I do not refer to it in any of my wikki edit texts at all. Kevin aylward (talk) 11:23, 30 December 2012 (UTC)

It is not my opinion, I am simply reformatting in layman’s language, the trivially obvious conclusions from the Gummel-Poon paper, as one example qualified source. It is just very, very, unfortunate that they are so few here that are qualified to actually understand that that is what that paper is stating. GP are THE noted experts on this. They state that the “…recombination has only a very small effect on the junction-voltage dependence of the current passing from emitter to collector…” Anyone that does not actually understand the implications of this statement, and the rest of their paper, should not be attempting to mediate my edits. Kevin aylward (talk) 11:48, 29 December 2012 (UTC)

Kevin, you and your professor are free to hold and espouse that opinion, but it's not really well founded.

Says who? My professor had a PhD in physics, you don’t I understand, so it is your opinion that is suspect.

What I state, the professor states, and all relevant physics theory text books states, is very well founded indeed, unfortunately it appears you have missed the basic point I have been making, and missed reading those text books, and missed understanding standard semiconductor theory. Kevin aylward (talk) 11:23, 30 December 2012 (UTC)

The notion of causality there is pretty weak. What causes the increased voltage between emitter and base? The only way to get that increased voltage is to push more current through the junction. That is, the device physics constrains the relationships between the voltages and the currents, via some dynamics involving the minority-carrier charge stored in the base. It really makes no sense to call one variable the cause and another the effect. Consider the lowly resistor and Ohm's law: of voltage and current, which is the cause, and which the effect? Neither. Dicklyon (talk) 18:59, 29 December 2012 (UTC)

Listen up to what I am *actually* saying. I have no fundamental issue with what you write above. In principal, I *agree*. However, it does not address the basic point that I have been making. Sure, it could be (poorly) argued that the current forced into a diode controls the voltage across it, therefore the diode voltage may be argued (poorly) that it is “caused” by the *emitter* *current*. I am not denying this possible (poor) interpretation. What I am denying is that it is the *base* current that *controls* either the diode voltage or diode current. The base current is *not* the emitter current. The base current does not *control* the diode current or the diode voltage. It just flaps in the wind.

Do you deny that, to first order, the emitter current is given by:

IE=Io.exp(q.Vbe/KT)

And that, for reasonable values of hfe, IC=IE.

If you don’t, this discussion is over.

Now, where is the base current term in this 1st order model?

Conclusion?

This is so trivially simple, it’s unreal that, once its been pointed out, that there can be any confusion. Listen up again.

Consider a transistor with its collector open circuit. Apply a voltage to its base emitter. A current will flow in accord with IE=Io.exp(q.Vbe/KT), with all of the diode current now going through the *base* terminal. Now connect a voltage to the collector. Essentially, for the same voltage on the base, the *same* current will flow in the emitter, however, with the collector now sucking up the bulk of the emitter current, the base current now becomes much reduced. So, the emitter current is, essentially, *independent* of whatever base current flows, therefore to claim that the value of base current controls the emitter current is simply absurd. This is how the transistor works. Carriers are injected into the base region from the emitter by applying a voltage at the base emitter junction, and get sucked up by the collector voltage. It’s that simple.

Seriously, what part of “…recombination has only a very small effect…” in the GP paper have you still not understood?

If it were true that base current was important in *fundamental* transistor operation, the GP model would be false, because it is based on that assumption, hence all Spice programs would fail to agree with reality. They don’t. I make my living on knowning that the 50k analog transistor ICs I design, work first time, correctly. It would be very expensive if they didn’t. Money is the final arbitrator in this real universe.

Instead of just making denials to what I post, produce an argument that refutes the logic that I have presented here. Present an argument that actually shows how or why that the emitter current is *controlled* by the base current.

Kevin aylward (talk) 11:23, 30 December 2012 (UTC)

This article already has a brief section on the Gummel–Poon model and even acknowledges the GP is more detailed and predicts non-linearity that EB misses and it has a link to the Gummel–Poon article, which needs a lot of work; it's barely more than a stub. I suggest that Kevin work on the Gummel–Poon article where there is very little be changed, deleted and fought over. Of course the rules still apply about reliable sources, etc. I think the GP section of this article is sufficient for this article. However, I don't there would be any objection if the GP section of this article were expanded with statements such as the GP model is based on solid state physics, does a much better job with large signal behavior, uses Vbe as the control signal and is the model of choice for SPICE, but avoids saying everything else is wrong.Constant314 (talk) 01:51, 30 December 2012 (UTC)

Kevin aylward (talk) 11:23, 30 December 2012 (UTC) In principal, I agree with most of what you say here, except for not highlighting that anything is wrong. As noted above, if it were true that base current physically controls emitter/collector current, then it would appear in the first order equations.

Kevin, please stop interleaving your comments inside the existing discussion, you are making it very difficulty to follow. Or where it is really essential to do so, at least learn how to INDENT properly. Spinning Spark 12:05, 30 December 2012 (UTC)

Kevin, I've just looked again at the G-P paper in the Bell System Technical Journal at http://www.alcatel-lucent.com/bstj/vol49-1970/articles/bstj49-5-827.pdf I did not see any mention of the Schrödinger equation. I did not see any QED. In short, I did not see any fundamental physics. The closest statement about physics was just before equation 10 where article states "The new charge control relation, derived from basic physical considerations ...". Based on the BSTJ article, G-P is just another model.

Also, I did not see anywhere within the article a statement that "stressed that there is essentially, no direct physically casual relation between collector/emitter current and base current". Maybe I missed it. Perhaps you can tell us which page and paragraph and maybe even the sentence or two that stresses no direct physically casual relation between collector/emitter current and base current.

Kevin said: "What I personally post to wikki has nothing to do with any licence on my independent web site"

Wikipedia's policies for using copyrighted or restricted material are designed to protect Wikipedia from copyright infringement. You have to do it their way, or it will be deleted. If you care about getting your message out, then get the required licensing statement on your web site.

Wikipedia policy takes an inclusive stance with regard to differing points of view. No matter how right the G-P model is, no matter how much better it is, as long as there is a sufficient group of editors who believe that the current controlled current source (CCCS) model should be expounded in the article, then you won't be allowed to delete it and you won't be allowed to say that it is wrong. But you can extol the virtues of the G-P model, as long as you don't disparage the other opinions while doing so.

It is not enough that you "referenced papers, by noted physicists, that refute such a view". You are trying to change the majority opinion. The onus is on you to pull out the relevant sentence or two and tell us exactly where to find it in the reliable source.

You "gave an explanation as to how the base voltage determined the collector current".

That's great and deserves to be assessable to this article, preferably on the G-P page. But you haven't given any reliable source that states the that the CCCS model or the E-M model are so egregiously wrong that the very mention of them should be suppressed.

I know this is anathema to you, but, if there are "trivially obvious conclusions from the Gummel-Poon paper" you still cannot put them in the article unless you have a reliable source that states those conclusions.

You "did not refer to my wep page as an authority". The operating rule here is that if the material would not be acceptable written directly into the article then it is also not acceptable if you write it on a web page and post a link to it.

What you say your professor said is hear-say and is not a reliable source.

"We" is the collective group of Wikipedia editors and admins. It even includes you. There are standards and policies that are enforced by the editors and if necessary by the admins. Wikipedia is not usenet. Constant314 (talk) 15:44, 30 December 2012 (UTC)

I have to take issue with your statement "as long as there is a sufficient group of editors who believe that the...model should be expounded in the article, then you won't be allowed to delete it and you won't be allowed to say that it is wrong". While a group of Wikipedia editors might present an obstacle, that is not what should be driving us here. Kevin certainly should be allowed to delete material or claim it to be wrong if that is the mainstream opinion of reliable sources. We would do best to concentrate here on what the opinion of RS are rather than the opinion of Wikipedia editors. Spinning Spark 17:43, 30 December 2012 (UTC)

I understand that a preponderance of credible, authoritative, reliable sources takes precedence over the opinion of the majority.Constant314 (talk) 19:06, 5 January 2013 (UTC)

Kevin, in response to your comments above, at and around "for reasonable values of hfe, IC=IE", let me clarify that I am not trying to say that base current is the cause of emitter current or collector current. I have argued that the notion of causality here is pretty weak; silly even. You are saying it's an error to say the base current "controls" the collector current; I disagree, as this is a common and useful model, whether or not it's directly physical. As for the approximation IC=IE, I'd call that zero-order. The first-order model includes the alpha (or beta/(1+beta)) factor, and explains how base current can control collector current. The fact that many books teach this approach is not an error to be fixed in wikipedia; it's just how it is. Dicklyon (talk) 17:56, 30 December 2012 (UTC)

Unreadable derivation

I have removed the following from the article;

Current–voltage characteristics

The expressions are derived for a PNP transistor. For an NPN transitors n has to be replaced by p, and p has to be replaced by n in all expressions below. The following assumptions are involved when deriving ideal current-voltage characteristics of the BJT^[1]

Low level injection

Uniform doping in each region with abrupt junctions

One-dimensional current

Negligible recombination-generation in space charge regions

Negligible electric fields outside of space charge regions.

It is important to characterize the minority diffusion currents induced by injection of carriers.
With regard to pn-junction diode, a key relation is the diffusion equation.

${\frac {d^{2}\Delta p_{\text{B}}(x)}{dx^{2}}}={\frac {\Delta p_{\text{B}}(x)}{L_{\text{B}}^{2}}}$

A solution of this equation is below, and two boundary conditions are used to solve and find $C_{1}$ and $C_{2}$ .

$\Delta p_{\text{B}}(x)=C_{1}e^{x/L_{\text{B}}}+C_{2}e^{-x/L_{\text{B}}}$

The following equations apply to the emitter and collector region, respectively, and the origins $0$ , $0'$ , and $0''$ apply to the base, collector, and emitter.

$\Delta n_{\text{B}}(x'')=A_{1}e^{x''/L_{\text{B}}}+A_{2}e^{-x''/L_{\text{B}}}$

$\Delta n_{\text{c}}(x')=B_{1}e^{x'/L_{\text{B}}}+B_{2}e^{-x'/L_{\text{B}}}$

A boundary condition of the emitter is below:

$\Delta n_{\text{E}}(0'')=n_{{\text{E}}O}(\exp(qV_{\text{EB}}/kT)-1)\;$

The values of the constants $A_{1}$ and $B_{1}$ are zero due to the following conditions of the emitter and collector regions as $x''\rightarrow 0$ and $x'\rightarrow 0$ .

$\Delta n_{\text{E}}(x'')\rightarrow 0$

$\Delta n_{\text{c}}(x')\rightarrow 0$

Because $A_{1}=B_{1}=0$ , the values of $\Delta n_{\text{E}}(0'')$ and $\Delta n_{\text{c}}(0')$ are $A_{2}$ and $B_{2}$ , respectively.

$\Delta n_{\text{E}}(x'')=n_{{\text{E}}0}(\exp(qV_{\text{EB}}/kT)-1)\exp(-x''/L_{\text{E}})\;$

$\Delta n_{\text{C}}(x')=n_{{\text{C}}0}(\exp(qV_{\text{CB}}/kT)-1)\exp(-x'/L_{\text{C}})\;$

Expressions of $I_{{\text{E}}n}$ and $I_{{\text{C}}n}$ can be evaluated.

$I_{{\text{E}}n}=-qAD_{\text{E}}{\frac {d\Delta _{\text{E}}(x'')}{dx}}|_{x''=0''}$

$I_{{\text{C}}n}=-qA{\frac {D_{\text{C}}}{L_{\text{C}}}}n_{{\text{C}}0}(\exp(qV_{\text{CB}}/kT)-1)$

Because insignificant recombination occurs, the second derivative of $\Delta p_{\text{B}}(x)$ is zero. There is therefore a linear relationship between excess hole density and $x$ .

$\Delta p_{\text{B}}(x)=D_{1}x+D_{2}\;$

The following are boundary conditions of $\Delta p_{\text{B}}$ .

$\Delta p_{\text{B}}(0)=D_{2}\;$

$\Delta p_{\text{B}}(W)=D_{1}W+\Delta p_{\text{B}}(0)\;$

with W the base width. Substitute into the above linear relation.

$\Delta p_{\text{B}}(x)=-\left({\frac {\Delta p_{\text{B}}(0)-\Delta p_{\text{B}}(W)}{W}}\right)x+\Delta p_{\text{B}}(0)$ .

With this result, derive value of $I_{{\text{E}}p}$ .

$I_{{\text{E}}p}(0)=-qAD_{\text{B}}{\frac {d\Delta p_{\text{B}}}{dx}}|_{x=0}$

$I_{{\text{E}}p}(0)={\frac {qAD_{\text{B}}}{W}}\left(\Delta p_{\text{B}}(0)-\Delta p_{\text{B}}(W)\right)$

Use the expressions of $I_{{\text{E}}p}$ , $I_{{\text{E}}n}$ , $\Delta p_{\text{B}}(0)$ , and $\Delta p_{\text{B}}(W)$ to develop an expression of the emitter current.

$\Delta p_{\text{B}}(W)=p_{{\text{B}}0}\exp(qV_{\text{CB}}/kT)\;$

$\Delta p_{\text{B}}(0)=p_{{\text{B}}0}\exp(qV_{\text{EB}}/kT))\;$

$I_{\text{E}}=qA\left(\left({\frac {D_{\text{E}}n_{{\text{E}}0}}{L_{\text{E}}}}+{\frac {D_{\text{B}}p_{{\text{B}}0}}{W}}\right)\left(\exp \left({\frac {qV_{\text{EB}}}{kT}}\right)-1\right)-\left({\frac {D_{\text{B}}}{W}}p_{{\text{B}}0}\right)\left(\exp \left({\frac {qV_{\text{CB}}}{kT}}\right)-1\right)\right)$

Similarly, an expression of the collector current is derived.

$I_{{\text{C}}p}(W)=I_{{\text{E}}p}(0)\;$

$I_{\text{C}}=I_{{\text{C}}p}(W)+I_{{\text{C}}n}(0')\;$

$I_{\text{C}}=qA\left(\left({\frac {D_{\text{B}}}{W}}p_{{\text{B}}0}\right)(\exp(qV_{\text{EB}}/kT)-1)-\left({\frac {D_{\text{C}}n_{{\text{C}}0}}{L_{\text{C}}}}+{\frac {D_{\text{B}}p_{{\text{B}}0}}{W}}\right)(\exp(qV_{\text{CB}}/kT)-1)\right)$

An expression of the base current is found with the previous results.

$I_{\text{B}}=I_{\text{E}}-I_{\text{C}}\;$

$I_{\text{B}}=qA\left({\frac {D_{\text{E}}}{L_{\text{E}}}}n_{{\text{E}}0}(\exp(qV_{\text{EB}}/kT)-1)+{\frac {D_{\text{C}}}{L_{\text{C}}}}n_{{\text{C}}0}(\exp(qV_{\text{CB}}/kT)-1)\right)$

^ R S Muller, Kamins TI & Chan M (2003). Device electronics for integrated circuits (Third ed.). New York: Wiley. p. 280 ff. ISBN 0-471-59398-2.

My original intention was to move it the Early effect article since, without looking at it too carefully it seemed to belong there because it was inserted in the base-width modulation section. However, on a second look it seems to be a derivation of Ebers-Moll. However, without explanation (of at least the symbols used) it is perfectly useless in the article and is likely to discourage a large number of readers. Spinning Spark 09:03, 8 April 2013 (UTC)

Voltage controlled model redux

I just removed the following from the article:

The above discussion described BJTs as current-controlled devices (constant β), however in theoretical discussions it would be more accurate to say that they are voltage-controlled. For an NPN transistor, the voltage applied to the base draws electrons out from the emitter, however these electrons end up being pulled into the collector instead.
The fact that a small base current is needed is simply a consequence of practical factors like recombination and base holes entering the emitter. Ideally a bipolar transistor could be made without these effects, so that no base current would be required for operation (infinite β).
The fact that the parameter β is constant over a wide range of operating parameters (only true in some transistors) is a consequence of the exponential growth of both base and collector currents.

It was inserted at the start of the Ebers-Moll section, but does not seem to be relevant to Ebers-Moll (unless it was intended as a criticism of it). This seems to be a resurrection of the voltage-controlled argument discussed ad nauseum above. By all means lets have a voltage-controlled model in the article, but it needs to be properly explained in a section of its own, and it needs to be properly cited to a reliable source. Spinning Spark 10:50, 22 June 2013 (UTC)

h_fe

I've just created h_fe as a redirect to Bipolar_junction_transistor#h-parameter_model. It's the best link target I could see to hand, but we have a pretty obvious need for an entry-level article on h_fe. Anyone fancy writing a decent explanation? Andy Dingley (talk) 11:18, 24 November 2013 (UTC)

Missleading language in the previous phrasing [12]

I thought I'd leave a few lines in the talk page since my edit in the previous version 'introduced misleading language, and if misleading bits were clarified, the lead would become as long as the whole article'.

"By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where there are minority carriers that diffuse toward the collector..."

Injected charges are (i.e. become) the minority charge carriers in the base. It is not like "well, charges are injected from emitter to base, and then there are also minority charge carriers in the base region and they diffuse toward collector". There are indeed thermally generated electron-hole pairs in the depletion region (which are majorly recombined after generation, and the small remaining portion leads to a reverse current) but this sentence is (should be) talking about injected charge carriers. Also, as a digression, misleading language is much better than misleading information I think; it's statistics (probably not Boltzmann though).

"By design..."

What's special about BJT design is not that collector current is due to flow of charges from emitter to collector. What's special about BJT design is that;

Three layers are properly doped (i.e. N_emitter > N_base ~ N_collector) so that diffusion from emitter will be an optimally effective mechanism in the conduction.
Base layer is kept relatively narrow so that the heavily doped emitter region causes the emitter-base junction to span over almost all of the base region leaving very little neutral (doped) region for annihilation of charge carriers as a result of electron-hole recombination. So, by design, a relatively small current compared to that of emitter's and collector's goes through base (like walking on water).

Here is what happens in active mode (in which BJT is used for amplification purposes rather than switching) step by step:

Forward biased emitter-base junction contracts (compared to equilibrium width). Since emitter is heavily doped compared to base, most of the width of emitter-base junction still lies on the base side.
Majority charge carriers of emitter region are injected into base region where they are minority charge carriers (rather than majority charge carriers).
Since base region is relatively narrow (and therefore, width of the neutral region outside the depletion zone is relatively narrow as well), and since majority charge carrier concentration in base is relatively small, diffusion rate is much larger than recombination (~annihilation) rate. Therefore, most of the emitter current is swept through base-collector junction.
Reverse biased base-collector junction expands (compared to equilibrium width). This means the electric field within the depletion region remains, and indeed gets stronger, in the direction of flow, not against it. Therefore, charge carriers in the base-emitter region drift through neutral region in collector. And finally, from the neutral region of collector, they continue toward the attractive terminal of the voltage source.

Apart from the particular design details given above, the law of the junction explains how the above design is used for amplification purposes:

c_{biased}=c_{equilibrium}~{\text{exp}}\left({\frac {eV}{kT}}\right)

,where c_biased and c_equilibrium are biased and equilibrium concentrations of minority charge carriers at the end of depletion zone in the region to which carriers are injected, e is elementary charge, V is applied voltage, k is Boltzmann constant, and T is absolute temperature. Note that a higher c_biased implies a higher BJT collector current.

Since any change in emitter-base voltage changes the diffusion through base region (and thus in collector current) exponentially, a BJT can be used for amplification purposes.

'Since the central fundamental concept in BJTs' working is minority carrier injection, these devices are classified as minority-carrier devices.'

I think it is important to mention the widely referred working principle (minority carrier injection) of any semiconductor device whose operation relies on carrier motion through junctions.

A note about the terms anode and cathode

Electrical engineers (and Wikipedia) define the anode, for all circuit elements (including batteries), as the terminal to which positive (conventional) flow enters, or equivalently, the terminal from which the negative (electron) flow departs. This definition is intuitive for batteries: Anode of a battery is where the oxidation reaction occurs, which produces electrons and therefore makes the terminal negatively charged, and thus a battery’s anode is where the positive (conventional) flow enters. However, when the term anode is used for other polarized circuit elements such as diodes, the connection of these elements to a battery circuit becomes non-intuitive: anode of the diode is connected to cathode of the battery, and cathode of the diode is connected to anode of the battery (just like connecting two batteries in series; anode to cathode, and cathode to anode). Also note that, in order for a diode to conduct electricity, the p-type semiconductor end must be connected to the positive terminal of the battery, and the n-type end must be connected to the negative terminal of the battery, so that holes and electrons are repelled by the terminals and can overcome the electric field in the depletion region. Therefore, according to definition of the term anode, p-type end of a diode is called anode. However, majority charge carriers in the p-type end of a diode are positive charged (i.e. hole), and calling it anode is non-intuitive.

Due to these inconsistencies, it is better to avoid using terms “anode” and “cathode” unless the discussion is confined to electrochemistry (e.g. batteries), and in general it is always better to refer to terminals of a diode as p-type and n-type terminals, and terminals of a battery as positive and negative terminals.

Apparently there has been a demand for simplification since 2012: "This section may be too technical for most readers to understand. Please help improve this section to make it understandable to non-experts, without removing the technical details. The talk page may contain suggestions. (July 2012)".

Anybody who possess the power of non-misleading language and think that it would improve the article is welcome to incorporate any part of this message, as-is or modified, to the article.

"...if misleading bits were clarified, the lead would become as long as the whole article."

This is interesting.

85.110.21.35 (talk) 19:29, 9 April 2014 (UTC)

The language as of 22:34, 5 April 2014 UTC:

By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where there are minority carriers that diffuse toward the collector, and so BJTs are classified as minority-carrier devices.

The language after a series of edits by 85...

By design, collector current is due to flow of charges injected from high-concentration emitter into base as minority carriers which diffuse toward the collector from there; only a small fraction of the current goes through base. Note that there is also a small leakage current in the reverse direction due to thermal generation of electron-hole pairs within the emitter-base depletion layer. Since the central fundamental concept in BJTs working is minority carrier injection, these devices are classified as minority-carrier devices.

"[2]" at the end of the section name is a link created with Template:Diff2. Not everybody who use wikipedia knows how to use it, but everybody who use wikipedia knows how to follow links. 85.110.21.35 (talk) 20:46, 9 April 2014 (UTC)

The statement "collector current is due to flow of charges injected from high-concentration emitter into base" is implicitly referring to active mode. Modes exist where this is not true.

The statement you've just quoted above was there before I edited, after I edited, and after my edit was 'restored'. It is still there. It's hard to make sense out of your language (I am not saying it is misleading). 85.110.21.35 (talk) 20:46, 9 April 2014 (UTC)

The statement "only a small fraction of the current goes through base" implicitly refers to active mode, and should say that that only a small fraction of the emitter current enters or leaves the transistor through the base contact.

The problem is that it is confusing to make statements in the lead about the active mode when the readers, not having yet read the article, don't know what active mode is. Jc3s5h (talk) 19:48, 9 April 2014 (UTC)

Rather than wasting our and probably others' time, I'd trust your wisdom (in wikipedia). good day/night. 85.110.21.35 (talk) 20:46, 9 April 2014 (UTC)

Anchor duplicates Ebers–Moll heading

When you link to Bipolar junction transistor#Ebers–Moll model, the article actually has two places with the same identifier to jump to. It means the generated HTML page is technically invalid; see the second point under Template:Anchor#Limitations, or tools:~dispenser/cgi-bin/rdcheck.py/Bipolar junction transistor for instance. There is no difference in the dash used (an en dash) between the heading itself and the second Anchor argument. Perhaps my original edit summary wasn’t clear enough, but I hope this clarifies things and you are able to remove the problem anchor again. Vadmium (talk, contribs) 01:46, 29 July 2014 (UTC).

I always thought that anchors could be used to protect against heading name changes, but apparently not. SpinningSpark 07:59, 29 July 2014 (UTC)

Awful

This is one of the worst wiki pages I've ever seen if you measure by content per word. There are reams and reams of unexplained technical babble that, from this talk page, is not even particularly clear to experts, and leans very heavily on the personal experience (eg, original research) of the authors. And in the end there is not really any discussion at all in laymans terms of what this device does. Technicians will probably be getting these formulas out of a technical reference, so it seems very weird to have that emphasis here when it is not accessible to a layman. The whole point of having any technical information is so an educated layperson from another field can have some deeper insight. There is no utility in formulas and discussions that would have meaning or value only to people who are experts in this field. So the point I'm getting at is, if you were to delete this page and replace it with a 50 word explanation of what a bipolar junction transistor is, with NO technical information at all, it would be a higher quality article. And yes, I do value the technical information in most wiki pages. But this one is a total disaster. 76.105.216.34 (talk) 20:36, 5 July 2014 (UTC)

No doubt this article can be greatly improved, but your comment about formulas does not really seem to be justified. There are no really difficult mathematics anywhere in the article and the description of the mathematical modelling of a transistor does not really get underway until well over half-way through the article. Perhaps you could give an example of what you mean in that respect? The workings of a BPJT is difficult to understand, even for those with some electrical science skills. It cannot properly be explained without introducing concepts such as doping, p-n junction and minority carriers, the latter of which has no analogy to help explain it.

One of the problems of an encyclopaedia format is that these grounding concepts are explained in separate articles but there is no guarantee that the user will read them first. In fact, they probably won't. Unlike with a textbook or college course, the reader will dive straight in to the topic they want to know about without first reading, or even knowing about, the basic grounding they need to understand it. Would you like to help improve this article for a general reader? If you do, I would be willing to work with you for technical advice. SpinningSpark 07:41, 6 July 2014 (UTC)

>>"minority carriers, the latter of which has no analogy to help explain it."

I have a feeling that you do not understand what a minority carrier is. A minority carrier can be an electron or a hole according to which type of material, p or n, one is talking about. If you meant to say that there is no analogy for positive charge carriers i.e. holes, you would be wrong.

--H.E. Hall (talk) 22:38, 19 August 2014 (UTC)

Your feeling would be wrong, I know perfectly well what minority carriers are. What I meant was that one cannot add something to, say, the hydraulic analogy that would represent the action of minority carriers to make it more familiar and easier to understand for a general reader. SpinningSpark 00:02, 20 August 2014 (UTC)

I agree with you, this article is awful, abbreviations and technical terms used without explanation, not enough citations, and I think I know why. I decided I would help and replaced the first paragraph (which was un-cited) with the following two paragraphs (cited), as the first several edits I planned to make. Within a few hours my edits were reverted. I am not going to fight a revert war, too bad for wikipedia. Here is what I wanted to add, you decide if they are not a better introductory paragraph than the current first paragraph:

Transistors are three-terminal, semiconductor devices that can control electric current in a manner similar to the way that a faucet controls the flow of water. A control knob controls the flow of water in a faucet. In a bipolar transistor, a small current applied to a control lead (a wire) on the transistor, controls the flow of current through the other two leads on the transistor.

Transistors are used in many different kinds of circuits. You can find them in switching circuits, amplifier circuits, power supply circuits, digital logic integrated circuits, and many other kinds of circuits. There are two families of transistors: Bipolar and Field Effect. This article will deal exclusively with bipolar transistors.^[1] There are two configurations for bipolar transistors: NPN and PNP.

I was getting ready to add an explanation of NPN, PNP, and how silicon is doped to make P and N type materials. --H.E. Hall (talk) 22:38, 19 August 2014 (UTC)

References

^ Practical Electronics for Inventors, Third Edition, McGraw-Hill Co., 2013, p. 429.

Is the "drainpipe analogy" really helpful in explaining this? I'm not sure there's a large contingent of readers who are going to benefit from the hydraulic analogy who are not going to have to quickly abandon it once they have any further interest in the subject. Why introduce a tangential concept in the introduction which has not place in the body of the article? There's a century of physics to explore here! We don't want to waste the reader's time on a mode of explanation that good textbooks on the subject seem not to require. --Wtshymanski (talk) 13:44, 20 August 2014 (UTC)

I agree with Wytshymanski that this kind of talking down to the reader is not useful. Anyone who looks up bipolar junction transistor is likely to at least understand what a junction is. In the most general articles we should not make assumptions about readers' knowledge, but for increasingly more specialised articles it becomes necessary to assume some background knowledge.

However, that's not the reason I reverted you. You have not added an introduction to bipolar junction transistor as you claim. You have added an introduction to transistor. It does not belong in this article. It also does not belong in the lede. The lede is mean to be a summary of the article. Adding material that is not in the body of the article is not appropriate. The lede is also meant to define the topic in the first sentence and bold the title term. Your addition pushed this sentence down to the third paragraph. By the way, it is not usually considered necessary to provide citations in the lede for precisely the reason that it is a summary of the (hopefully already cited) body of the article.

If you had done this in a one-line stub I would have welcomed you and encouraged you to do more. In a well-developed article (and generally on Wikipedia) you need to take a bit more care and be prepared to work together with others. Taking the attitude that we can take your contribution as it is or "too bad for wikipedia" is childish and will get you precisely nowhere. No one will care if you walk off in a huff. SpinningSpark 18:26, 20 August 2014 (UTC)

Voltage Control, Current Control

I've reconsidered the best way to bring this into the article. I think it would be natural to first give the equations for collector current and base current as a function of voltage and then divide the former by the latter. Both currents will have an exponential which will sort of divide out, leaving an equation that collector current is sort of proportional to base current with the proportionality is a function of collector current.Constant314 (talk) 16:14, 2 February 2013 (UTC)

Seems like the hard way to show that the dependence is on base current. Do some people have an easier time considering voltages than currents? In most cases, a base resistor is used, such that you don't need to consider the base voltage. Gah4 (talk) 06:47, 26 April 2015 (UTC)

Images used here are Inconsistent

I have issues with these images.

This image of the PNP BJT schematic symbol:

is not wrong but inconsistent with canonical practice when introducing schematic symbols, which is to show transistor symbols rotated to have the emitter or source terminal at the bottom. The NPN symbol is shown properly in this way. The article on "Electronic Symbols" uses this same inverted PNP symbol. Showing an rotated forms of symbols should be done in that article, if it deemed relevant at all.
This image of the "NPN BJT with forward-biased E–B junction and reverse-biased B–C junction":

is very confusing, and I think, wrong. It shows both conventional (black arrows) and physical (internal) current flows. See "Electric Current: Conventions""[[13]]". Normally only one flow model is applied in explanations. If we are explaining how to design electronic circuits, we use "conventional current flow" (current flows from positive to minus potentials). But explaining the actual physics, as the Diode article does, we should use actual physics and "physical current flow". Since the purpose of this image is to reveal the internal operations of the transistor, we should use only physical current flow throughout.
Other images ("Structure and use of NPN transistor", "Structure and use of PNP transistor", Ebers-Moll models, and subsequent images) show Conventional current flow (black arrows). As explained above, this only applies to design of electronic circuits. So if the purpose of these parts of the article is to how to use the transistors (i.e. design and model circuits) then conventional current flow is correct, but the switch from one to another within the article should be very clearly explained. Or, perhaps a better choice, move these parts to a new article on "designing with transistors" (The topic of current flow direction is a well-known source of confusion in electronics.).

Rich S 10001 (talk) 15:27, 7 September 2014 (UTC)

As for the symbol, it is usually drawn as most convenient for the circuit in question. For one, consider a push-pull amplifier circuit. As to the diagram, the description is of the physics inside the transistor. Outside, one normally considers conventional current. If you really want to know, you need the band structure of the metals used for wires. Many metals have significant hole bands, with aluminum almost as much hole conduction as electrons. But note that the hole vs. electrons in the metal doesn't affect which carriers go into the semiconductor. Then you need a good explanation of what makes an ohmic contact. Gah4 (talk) 07:04, 26 April 2015 (UTC)

Beta vs Hfe

The value of this gain for DC signals is referred to as h_{\text{FE}}, and the value of this gain for AC signals is referred to as h_{\text{fe}}. However, when there is no particular frequency range of interest, the symbol \beta is used[citation needed].

There are different versions between the PNP and NPN active mode descriptions, with one [citation needed] and the other with a citation. It seems to me that β is used in a less formal context, and Hfe when one needs to more exact. One might indicate, in general, the gain of an amplifier without a frequency response graph might be β, but with a graph Hfe, or β without a specific bias, but Hfe once the bias is specified. But is there a reference that explains this detail? Gah4 (talk) 07:16, 26 April 2015 (UTC)

hfe arises from the h-parameters and thus has implied test conditions (short-circuit output) from the definition of h-parameters. The test conditions for beta, on the other hand, must be explicitly stated. Thus, beta can be specified for more realistic operational conditions. The hfe can be thought of as a specific instance of beta under the given test condition. The difference has nothing to do with frequency range. Beta can be specified for DC and small-signal just as well as it can be for hFE/hfe although there is no generally recognised separate symbols for beta for these two cases as far as I know. Most text books simply treat hfe and beta as synonyms. SpinningSpark 12:55, 26 April 2015 (UTC)

Collector current equations

I see this equation under the DC section for the collector current:

i_{\text{C}}=I_{\text{S}}\,e^{\frac {v_{\text{BE}}}{V_{\text{T}}}}\left(1+{\frac {V_{\text{CE}}}{V_{\text{A}}}}\right)

Should the equation be like this instead since it's under the DC section?

I_{\text{C}}=I_{\text{S}}\,e^{\frac {V_{\text{BE}}}{V_{\text{T}}}}\left(1+{\frac {V_{\text{CE}}}{V_{\text{A}}}}\right)

If it should not be then it contradicts these two equations under the Ebers-Moll model:

I_{\text{E}}=I_{\text{ES}}\left(e^{\frac {V_{\text{BE}}}{V_{\text{T}}}}-1\right)

I_{\text{C}}=\alpha _{F}I_{\text{E}}

ICE77 (talk) 19:54, 14 October 2015 (UTC)

Introduction

Although this Wikipedia article has some good explanations and illustrations some parts are very technical and way beyond the comprehension of the non expert. That aside though, I suggest that the introduction could be rationalised and better structured to give a more general, simpler, more readable, and more easily understood introduction to the BJT. CPES (talk) 05:49, 19 October 2015 (UTC)

on/in/of the order of

This article had 'on the order of' which I changed to 'in the order of', thinking the original was just a simple error. Here in the UK, I had never come across the 'on' version. Subsequently Glrx reverted it back to 'on' so it was no error. Intrigued, I did a bit of investigating and it turns out there are three versions: 'on the order of', 'in the order of', 'of the order of'. 'on' is used more in the US, while 'in' is common in the UK, but the strictly correct wording as far as I can tell is 'of the order of'. http://english.stackexchange.com/questions/94451/something-is-of-in-the-order-of

That's the great thing about Wikipedia, you always learn something new. CPES (talk) 10:44, 26 October 2015 (UTC)

Prepositions are screwy. If you want some fun, choose a random verb and then follow it with a prepostion: pull off, pull out, pull through, pull at, pull behind, ...; tie up, tie down, tie on, .... Glrx (talk) 16:31, 26 October 2015 (UTC)

This is less preposition than idiom IMO. Local usage can & does vary a lot, like this case. It can, in some cases, completely change the meaning: in the U.S. & Canada, you'd root for a sport team; in Oz, "root" is slang for sex... TREKphiler ^{any time you're ready, Uhura} 21:10, 26 October 2015 (UTC)

complexity

The article is accurate however it is impossible to understand unless you already understand how a transistor works. It would be benificial to refer out to the transistor wiki page which gives the required backgroud knowlage to fully understand this page—Preceding unsigned comment added by 195.33.114.129 (talk) 13:52, 10 February 2011 (UTC)

There is a Wikipedia page in "Simple English" which is no more than a stub. Would this be an appropriate place to explain things? — Preceding unsigned comment added by 76.254.24.27 (talk) 01:20, 26 June 2016 (UTC)

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Active vs. saturation region

User:Gah4 justifies this edit with the edit summary

In saturation, not so unusual in switching circuits Vbe is about 0.7V, Vce about 0.3V. Go to talk page if you disagree.

The passage in question, before it was changed by an IP editor, stated

That is, when there is a positive potential difference measured from the emitter of an NPN transistor to its base (i.e., when the base is high relative to the emitter) as well as positive potential difference measured from the base to the collector, the transistor becomes active. [emphasis added]

User:Gah4 wants to retain the version by the IP editor, which changes the last occurence of "base" to "emitter". But the sentence says the transistor is active. This is ordinarily taken to mean the active region, which is different from the saturation region, which User:Gah4 mentions in the edit summary. Jc3s5h (talk) 04:06, 6 December 2016 (UTC)

I can't see how it would be correct either way. Why not get a better definition from a source? As for saturation, it is unfortunately defined in roughly opposite ways in bipolar and MOS devices. In bipolar NPN, base > collector would be saturation region (roughly); while emitter > collector would mean that emitter and collector have been interchanged; not a region. Dicklyon (talk) 04:26, 6 December 2016 (UTC)

This book says base < collector in active region; opposite of what our article has been saying, and I agree (though it can go slightly the other way and still be active). Dicklyon (talk) 04:33, 6 December 2016 (UTC)

I think the problem was just that voltage differences were being described in an unconventional direction, and that with that fixed, Gah4's change makes a lot more sense. See if you agree. Dicklyon (talk) 04:49, 6 December 2016 (UTC)

Generally, I'm pretty sure "potential difference measured from A to B" usually is taken to mean V_A - V_B. But is was the other way around here. If there are sources that do it that way, show me. Dicklyon (talk) 05:03, 6 December 2016 (UTC)

OK, first we are talking common emitter configuration. Next, the voltages will all be the other way for PNP vs. NPN, but Vbe and Vce are normally the same sign for active region. There are many definitions here: https://www.quora.com/What-is-saturation-active-region-in-a-transistor but it looks to like any collector current less than saturation is active. At almost, but not quite saturation, such as Schottky TTL, Vce should still be less than Vbe, but not quite as much. But otherwise, the usual descriptions of common emitter mode are in terms of Vbe and Vce. Gah4 (talk) 06:29, 6 December 2016 (UTC)

Complementary Pairs

Why does this article NOT have a "complementary pair" section? It needs to be added. • Sbmeirow • Talk • 04:53, 26 March 2017 (UTC)

Complementary Part Numbers
NPN	PNP	Vceo	Power
2N2222	2N2907	30 V	Low
2N3904	2N3906	40 V	Low
2N4401	2N4403	40 V	Low
2N5551	2N5401	150 V	Low
BC337	BC327	45 V	Low
BC807	BC817	45 V	Low
MPSA42	MPSA92	300 V	Low
S8050	S8550	25 V	Low

Complementary Part Numbers
NPN	PNP	Vceo	Power
TIP31	TIP32	100 V	High
TIP35	TIP36	100 V	High
TIP41	TIP42	100 V	High
TIP3055	TIP2955	60 V	High

Good idea, go for it. Andy Dingley (talk) 08:59, 27 March 2017 (UTC)

Yes. Maybe add a little prose saying what makes them complimentary. Constant314 (talk) 11:08, 27 March 2017 (UTC)

Comment. There's a slippery slope. The article is about the device rather than how it is used. Should there be a section on devices used in push-pull circuits? How about totem-pole circuits? I think it is reasonable to cover circuits that exploit fundamental properties of a BJT: the applications section includes temperature sensors and logarithm converters — but those topics are short. The application section on amplifiers is also short, but it doesn't even mention differential pair (it should; very good matches can be made). The complementary transistor topic is more relevant in an amplifier article and a list of complementary devices is too detailed here. Glrx (talk) 16:11, 5 April 2017 (UTC)

Comment. Yes, but the fact that reasonably complementary devices can be made is worth indicating. That is, even with different mobilities and such, that they can be close enough to allow for appropriate circuits. A link to (I presume it exists) the push-pull amplifier would seem reasonable, without describing it here. A few representative pairs might be nice, but yes, don't list them all. Gah4 (talk) 21:14, 5 April 2017 (UTC)

Comment. The "complementary transistor pair" topic isn't explained anywhere on Wikipedia (but I could be wrong). I've noticed text in articles using the term "complementary pair", but I couldn't find any wikilinks pointing at an article or section that explains what it means. This is a reasonable missing topic, thus solve the problem by adding a section to some article or create a new article, I don't care. Thanks in advance. • Sbmeirow • Talk • 05:08, 6 April 2017 (UTC)
More specifically, does "complementary pair" have any defined or accepted meaning? It always looked to me like more of a marketing concept, to help you choose a pair of roughly comparable transistors, whether any particular parameters were well matched or not. And 20th-century books seem to treat it as a generic concept of pairing a PNP with an NPN, not there are there are particular important pairs of part numbers. Dicklyon (talk) 05:43, 6 April 2017 (UTC)
Comment. Complementary transistor pairs occur beyond bipolar junction transistors. Most notably there is CMOS, but see also Discrete complementary JFETS. I think there is a case for an overview article complementary transistor pair and a case for complementary bipolar junction transistor pair as a separate article. The latter could include links to the pairs we already have articles on and Sziklai pair as well as specific application circuits. SpinningSpark 19:01, 13 February 2018 (UTC)

Ebers-Moll model for NPN transistor

In the Ebers–Moll Model for an NPN transistor I think that α_R I_ED should be α_R I_CD. Further α_F I_CD should be α_F I_ED. —Preceding unsigned comment added by 78.33.14.67 (talk) 08:53, 29 October 2010 (UTC)

Based on my recollection and page 328 of Ben Streetman's Solid State Electronic Devices (1972) I agree with 78.33.14.67. Jc3s5h (talk) 12:40, 29 October 2010 (UTC)

"The unapproximated Ebers–Moll equations used to describe the three currents in any operating region are given below. These equations are based on the transport model for a bipolar junction transistor"

I am checking this model according this lecture, which appears to be ok for me: https://inderjitsingh87.weebly.com/uploads/2/1/1/4/21144104/the__ebers-moll_bjt_model.pdf

But i fail to reach the same result in the unapproximated case. In fact i think the included equations should explicitly include both ISC and ISE reverse saturation currents, instead a generic IS term.

Can somebody verify i am wrong or right, in order to introduce the proper change in the equations?

Hyprwfrcp (talk) 02:39, 23 April 2018 (UTC)

I haven't worked with these equations for a long time, but I find the following definition for I_S in Ian Getreu's "Modeling the Bipolar Transisitor" (Beaverton OR: Textronix, 1976) page 14:

...The number of parameters is reduced by one when the reciprocity principle is applied. The principle is defined by:

\alpha _{F}I_{ES}=\alpha _{r}I_{CS}\equiv I_{S}

Does that resolve your issue? Jc3s5h (talk) 12:44, 23 April 2018 (UTC)

Injection from the base

File:NPN BJT Basic Operation (Active).svg gives a misleading impression of what is going on. It suggests the minority carrier injection from the base into the emitter is comparable to the injection from the emitter into the base. The base's carrier concentration should be much, much, smaller than the emitter's. Consequently, the injection should be very small (fewer available carriers to get jostled across the junction). Judging by the widths of the arrows, $β= i C /(i B1 + i B2)=1.25$ , which is way too low. My guess is $i B1 << i B2$ . Glrx (talk) 00:42, 24 April 2018 (UTC)

OK, but there is a limit to the resolution of the picture. It is usual to build them with higher beta, though power transistors are not so high. I remember in an undergraduate lab where we made our own transistors, that mine was greater than one, maybe 1.25. Someone else was less than one, but it still followed the appropriate relation, and so got credit for it.^[1] (I suspect that the lab has changed over 40 years.) You might get the picture up to 2 or 3, but not much more. Gah4 (talk) 02:03, 24 April 2018 (UTC)

The 2N3055^[2] has a minimum h_FE of 5.0 at 10 amps. Gah4 (talk) 02:15, 24 April 2018 (UTC)

Yes, but the 2N3055's

h FE

at 4 A has the more mundane minimum of 20 (and could go as high as 70). At 10 A, the

V CE(sat)

is 3 V, so the collector probably isn't doing a good job of collecting with a 4 V

V CE

. And none of those numbers suggests the b-to-e minority injection current will dominate the base recombination current as shown in the pix.

I love the

f T

of 2.5 MHz. The cooling hose came off the laser power supply and sprayed water all over the neighboring optics bench, and then the no-longer-cooled power supply blew up. I'd never seen a hole in a TO-3 case and haven't since. Glrx (talk) 08:12, 24 April 2018 (UTC)

References

^ "APh/EE 9 Lab Manual" (PDF). nanofab.caltech.edu. Caltech. Retrieved 24 April 2018.
^ "2N3055 data sheet" (PDF). www.onsemi.com. ON semiconductor. Retrieved 24 April 2018.

Should this sentence end with voltage-control, or current-control?

I'm trying to follow this sentence (and I DO have an understanding of BJTs). It seems to me it should end with " ... so the current-control view is often preferred." (BUT PLEASE READ MY WHOLE COMMENT)

"The voltage-control model requires an exponential function to be taken into account, but when it is linearized such that the transistor can be modeled as a transconductance, as in the Ebers–Moll model, design for circuits such as differential amplifiers again becomes a mostly linear problem, so the voltage-control view is often preferred."

Even just syntactically/semantically, the sentence starts with discussing the voltage-control model, then has a "but," so it would make sense that the remainder talks about the alternative, the current-controlled model. I suspect whoever wrote this knew what they were trying to say, but accidentally wrote voltage instead of current near the end of the sentence.

But then again, if there's a resistor in series with the base, and this resistor is dropping (say) several volts, then the voltage between the (non-base side of the) resistor and the emitter IS approximately linear to the collector current, and this is a "mostly linear" transconductance. Maybe THAT is what the writer meant, but either way, it's not clear.

On the third hand (and I'm starting to think this is the "real" explanation), the reference to differential amplifiers implies (but does not state!) very low signal levels across Vbe (a few millivolts or less), and such signals ride on a small and "mostly linear" portion of the exponential curve (where, for larger signals, the collector current doubles with approximately every 20mV increase in Vbe), and THIS could be what is meant. Even here it should say a linearized voltage-control view, rather than just voltage-controlled view.

I find the sentence confusing, apparently because it is missing some qualifying information, but rather than just adding such info I hope it would be rewritten for clarity. I've never had to think through a sentence so hard even though it might be technically correct.Benbradley (talk) 05:37, 12 December 2018 (UTC)

The sentence should end with voltage control. The control voltage is applied directly to the base in a common emitter configuration. The output is the collector current. The "it" that is linearized is the exponential input voltage to collector current curve.Constant314 (talk) 06:10, 12 December 2018 (UTC)

I think that in a common-emitter configuration the current-control view would be preferred, since it's linear instead of exponential. But in the differential transconductance amplifier, the voltage-control view is preferred, since the behavior is close enough to linear for small voltage differences (and for larger differences you can a tanh compression, approximately at least). Dicklyon (talk) 06:26, 12 December 2018 (UTC)

Current control is linear-ish, with an unpredictable departure from linearity that varies noticeably from device to device. Voltage control is strongly non-linear with a very predictable curve that is strongly matched from device to device. In the diff amp, device matching is far more important than linearity. With regard to the common emitter stage, in my own work, it depends on the nature of the source that is driving the stage. If the driver is high impedance , then I use current control. If it is low impedance, I use voltage control. At high frequency, due to the Miller capacitance, common emitter stages have a low output impedance and hence look like voltage sources. So, a first CE stage is ready to drive a second CE stage with voltage control of the second stage.Constant314 (talk) 19:20, 12 December 2018 (UTC)

I think the sentence is referring to a small-signal analysis, where all nonlinearities are appproximated as linear. In a small-signal analysis a voltage control model would not have the difficulties it would have in a large signal analysis. Jc3s5h (talk) 12:36, 12 December 2018 (UTC)

Germanium Transistor Section

Hi, I would ask that the Germanium Transistor section be changed from:

The germanium transistor was more common in the 1950s and 1960s, and while it exhibits a lower "cut off" voltage, typically around 0.2 V, making it more suitable for some applications, it also has a greater tendency to exhibit thermal runaway.

to:

The germanium transistor was more common in the 1950s and 1960s, and while it exhibits a lower "turn on" voltage (Vbe), typically around 0.2 V, making it more sensitive, it also has a greater tendency to exhibit thermal runaway. —Preceding unsigned comment added by 64.16.215.100 (talk) 21:26, 28 May 2010 (UTC)

A forward biased germanium PN junction is about 0.4V, compared to 0.7V for silicon. I think that Vce is also lower for a saturated transistor, but haven't though about this recently. Both can sometimes be an advantage. Gah4 (talk) 03:30, 17 June 2019 (UTC)

[Muller-1] R S Muller, Kamins TI & Chan M (2003). Device electronics for integrated circuits (Third ed.). New York: Wiley. p. 280 ff. ISBN 0-471-59398-2.

[Practical-2] Practical Electronics for Inventors, Third Edition, McGraw-Hill Co., 2013, p. 429.

[APh/EE9-3] "APh/EE 9 Lab Manual" (PDF). nanofab.caltech.edu. Caltech. Retrieved 24 April 2018.

[2N3055-4] "2N3055 data sheet" (PDF). www.onsemi.com. ON semiconductor. Retrieved 24 April 2018.

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