Talk:Flyback transformer

How pedantic do we want to be?

Strictly, the flyback transformer converts the deflection power supply voltage, not the "mains" ( input AC) voltage, to high voltage. Is this worth distinguishing in the text, without turning this into an article on TV repair? --Wtshymanski 05:24, 20 Apr 2005 (UTC)

I thought it was desirable for all transformers to have high inductance windings (not just flybacks) in order to extend LF response and cut down the magnetising current. Am I wrong? Does the author intend to say good coupling or low leakage inductance? Light current 16:48, 31 August 2005 (UTC)[reply]

I am not sure if the difference is best described in terms of the inductance. A "normal" (non-flyback) transformer is designed with a large magnetizing inductance---larger than a typical flyback transformer, in fact--but that inductance can only store a very small amount of energy. If you try to "charge up" the magnetic circuit in an ungapped ferrite transformer then it will saturate with only a very small amount of energy stored. In normal operation, the secondary sucks energy out nearly as fast as the primary puts it in, so this is not a problem.

A flyback transformer is distinctive not for its inductance, but for its ability to store energy (on the order of P_out/f_switching). The gap decreases the inductance, but it increases the ability of the transformer to store energy.

Au contraire. The inductance is crucial. Without it, the primary current wouldn't ramp up and the output wouldn't be a saw tooth current. 86.178.14.98 (talk) 13:14, 12 April 2011 (UTC)[reply]

This article need improvement

Wtshymanski & Light current have good points. The deflection power supply is typically on the order of 70vdc and it is not correct to claim line voltage (AC) as the input to the LOPT. Additionally the inductance of mains (50/60Hz) transformers must be made high in order to reduce the magnetising current to acceptable levels and also to prevent saturation (applies to audio as well). On leakage inductance, it would be highly undesirable to have high leakage inductance in a LOPT as leakage inductance represents stored energy that has to be adsorbed by snubber circuits. In the case of mains transformers, if the output is driving a capacitive load (eg the voltage multiplier in a microwave oven) a high leakage inductance would be desirable in order to zero the power factor. I am not an audio expert, but I would imagine that the leakage inductance of an audio transformer would be quite low to insure minimal parasitic inductance in the circuit. It should also be made clear that the LOPT and associated circuitry is operated as a switched mode power supply and outputs a square voltage waveform given that the circuit switches between positive, constant di/dt and negative, constant di/dt. Additionally the voltage multiplier is not distinct from the "rectifier" as a CW multiplier intrinsically has a DC output. The author of the claims that the LOPT is responsible for the wine of monitors - this cannot be correct as all monitors operate with horizontal scans in excess of 40kHz - well above the range of human hearing. A much more likely source of audible sound is the mains stepdown transformer which may operate within the range of human hearing.

Many units with CRT's use a degausing coil, which makes a loud HUM sound when they start up.cmacd 19:30, 16 February 2007 (UTC)[reply]

That is true - and completely irrelevant in the current context. And: only cheap crappy ones (such as in many domestic TVs) make a loud hum. 86.163.86.161 (talk) 17:15, 24 February 2011 (UTC)[reply]

The deflection power supply depends on the design of the circuit and the technology used. In valve days (vaccuum tube if you don't speak English), the deflection supply could be as high as 600 volts (with the deflection circuit itself producing around 400-500 of them depending on which side of the pond you live). 86.163.86.161 (talk) 17:01, 24 February 2011 (UTC)[reply]

This article seems to be about a particular application of flyback transformers (CRTs). The discussion of the electrical componant gets lost in the discussion about a particular application. There are other uses of flyback transformers, and I think that the detailed CRT discussion should have its own page. —Preceding unsigned comment added by 206.197.156.11 (talk) 12:57, 27 March 2009 (UTC)[reply]

Especially these days when the primary use is in flyback type switch mode power supplies, given that CRT televisions are obsolete. 86.163.86.161 (talk) 17:01, 24 February 2011 (UTC)[reply]

"The primary winding of the LOPT is driven by a relatively low voltage sawtooth wave ..."

No it isn't. The input current to the primary winding is a switch (usually a transistor these days) which is either on (short circuit) or off (open circuit). The input to the transistor is not saw tooth in any shape or form, it is a switching pulse. The output from the transistor would not ba sawtooth either were it not for the inductance of the primary of the transformer. When the switch switches on, current starts to build up in the primary increasing from zero to its maximum courtesy of the inductance. When the switch switches off, the current has to collapse to zero very quickly. Thus the current in the primary, and hence the secondary is sawtooth (however, the voltage certainly isn't). As the current collapses, there is considerable energy stored in the magnetic core. It is this energy that is exploited, and is coupled out using suitable secondary windings and a simple half wave recifier to provide the basis of a power supply.

The article requires a complete rewrite, to correct the many errors and to make it application non specific. I would do it, but I don't presently have the time. 86.163.86.161 (talk) 17:12, 24 February 2011 (UTC)[reply]

Just found the time. My years spent servicing and repairing television and (more lately) exotic video display systems wasn't wasted after all! 86.183.175.209 (talk) 16:56, 7 April 2011 (UTC)[reply]

Not to merge

A user placed the floowing in the article, at has been remouved "A better description is on flyback converter. This whole article is merely about the application in the TV, the only place where it is synchronized with the flyback of an electron beam, even computer monitors do not do it this way." Since the Flyback system si specific to televson and related techniques, I don't think the comment is valid, but wanted to perserve it just so it is not acted on. cmacd 19:30, 16 February 2007 (UTC)[reply]

wonder if Historical alternative should be mentioned

Before the flyback (1940s) - Tv sets sometimes used an RF power supply for the High voltage, which could be lethal. The flyback system will be loaded so much that it does not normaly kill.cmacd 19:32, 16 February 2007 (UTC)[reply]

Question

"Flyback transformers are a frequent source of TV tube failure."

I can't imagine how this could occur. CRTs are pretty robust things, like most thermionic devices, and I cant imagine any real world LOPT failure putting damagingly high V or i onto the tube. Tabby (talk) 23:26, 25 November 2007 (UTC)[reply]

This article does not correctly define the term.

A "flyback transformer" by definition is not, in fact, a high-voltage transformer, nor is it even a step-up transformer. This article, while thorough, useful, and generally well-written, is a very limited definition. It belongs more as a discussion topic in a broader article than as the entire definition.

A flyback transformer is actually a coupled inductor used in a DC/DC converter. All energy transferred to the secondary is stored in the transformer core by the primary winding during one part of the cycle and released through the secondary winding during the other part. This differs from a traditional transformer, where flux generated the by the voltage-seconds on the primary is opposed simultaneously by the flux generated by the volt-seconds on the secondary. The core in a traditional transformer merely facilitates coupling between the windings but does not store the energy being transferred.

A flyback converter as used in a television is a special case of this topology. It generates high voltage and does all of the things described in this article.

The following article more accurately explains the meaning of the term "flyback transformer": http://en.wikipedia.org/wiki/Flyback_converter —Preceding unsigned comment added by Molain (talk • contribs) 02:01, 26 January 2010 (UTC)[reply]

It doesn't even correctly define its function. For television deflection use, the opening paragraph claims that it steps a relatively low voltage into a higher voltage to deflect the electron beam in a cathode ray tube. This is completely incorrect. The transformer provides a large current to the deflection coils. It provides practically no voltage at all, because the windings of the deflection coil are (for this purpose) a short circuit (typically 200 milliohms). The windings do have a small inductance which does provide a small voltage drop due to reactance, but ultimately, it is the high current that does the job. 86.163.86.161 (talk) 16:54, 24 February 2011 (UTC)[reply]

How to change a flyback transformer

how do i change a flyback transformer —Preceding unsigned comment added by Rcaman (talk • contribs) 01:24, 15 March 2010 (UTC)[reply]

If you are not trained or experienced in performing this type of service, it would be best to submit the job to someone who has the proper qualifications. There can be dangerous voltages present around a flyback transformer, making it hazardous if you don't know what you are doing. Wikipedia is not a "how to" guide, so information and guidance on how to perform this type of service would need to be found elsewhere. At the very least, if you insist on attempting it, it is essential to disconnect the CRT and ensure that all voltages around the flyback are discharged. Wearing thick rubber gloves while working on high voltage circuitry is an advisable precaution. Wildbear (talk) 02:30, 15 March 2010 (UTC)[reply]

The canonical answer is "Very very carefully". --Wtshymanski (talk) 17:01, 7 April 2011 (UTC)[reply]

Purpose of flyback transformer.

The sole original purpose of the device was to produce the high deflection currents required for the CRT. In original (like 1930's) TV sets, the high voltage for the CRT was not derived from the line output transformer (aka flyback transformer). It was derived from a winding on the mains transformer that these early sets were equipped with. Apart from being downright lethal, this method was a considerable fire risk due the poor insulating materials then available.

The task of generating the high voltage was moved to the line output transformer, when mains transformers were no longer used when the AC/DC design was adopted. Although modern usage of these transformers no longer generates the high voltage required for CRTs, there are several designs that produce high voltages for other purposes (e.g. particle accelrators). It is therefore not correct to say that these devices no longer produce high voltages, but it is correct to state that they no longer produce large currents (for deflection purposes where they were produced at practically zero voltage). 86.163.87.193 (talk) 16:49, 30 July 2011 (UTC)[reply]