Talk:Flyback transformer

Does air gap increase ability to store energy?

"The air gap increases the reluctance of the magnetic circuit and therefore its ability to store energy."

Air gap increases reluctance, so less B-field occurs per applied H-field. And since the stored energy is measured by volume integral of product of H and B-fields, stored energy will tend to decrease as the air gap increases.

An expert of this topic should revise this statement and remove it if necessary.

AhmedHan (talk) 06:03, 2 May 2014 (UTC)

You can apply more H-field, as the core will require more H to saturate. So more air gap leads to more energy storage capability (although you should resize windings to the new higher current)

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)

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)

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)

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)

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)

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)

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)

"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)

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)

The major error here is that everyone (and the article) is incorrectly assuming that the both the primary and secondary currents are sawtooth to the extent of incorrectly assuming that the deflection coils were energised from the secondary. The primary current is indeed a sawtooth (or at least it would be but for the presence of other components designed to make it more 'S' shaped). The secondary current is not a sawtooth in any shape or form. The EHT rectifier sees to that only allowing the large flyback pulses to pass. The deflection coils are connected in series with the primary of the transformer. Indeed: for deflection purposes, the secondary might just as well not be there as indeed it wasn't in early television designs. DieSwartzPunkt (talk) 15:53, 10 November 2012 (UTC)

Not to merge

A user placed the floowing in the article, at has been removed "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 is specific to television and related techniques, I don't think the comment is valid, but wanted to preserve it just so it is not acted on. cmacd 19:30, 16 February 2007 (UTC)

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)

No they didn't. Prior to 1940, the only available circuit was to derive the EHT from the mains transformer (which was lethal). Due to the poor insulating materials available, breakdowns and even fires were not unknown. After 1940, before the EHT shifted to the output transformer (and virtually all rear projection TVs did this) the EHT was produced by a self contained oscillator driving a ringing choke converter (actually a transformer). These usually operated at about 1kHz (not RF), though the frequency was not critical. Rear projection TVs usually used a tripler circuit to produce the 25,000 volts required but regular TVs just rectified the pulse train from the transformer. 185.69.145.2 (talk) 17:56, 3 March 2021 (UTC)

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)

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)

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)

Even worse: when the device is used purely for line deflection purposes (i.e. no secondary functions), it isn't even a transformer, but just a simple inductor (but still with an air gap in its magnetic circuit). The modus operandi given in the article is thus completely wrong in that there is no secondary side current. Even the 'primary side current' is wrong as two important points have been completely overlooked.

First: the sawtooth wave generated does not rise steadily from zero to its final value and then fly back to zero. Such a circuit would be useless (unless you really do want to display a picture on only one quarter of the tube face). Since it is desired to deflect the electron beam from one side to the other, the scan circuit must generate a scan wave that starts at some negative current and then more or less (see second point) varies steadily to the same current but positive before flying back.

Second: the last thing that is wanted is a saw tooth current wave shape. What is required is a wave that varies more slowly at first, reaching the greatest rate of change as the beam passes through the centre point and then slows off again as it approaches the other side of the screen. This is because the deflection sensitivity of any cathode ray tube is not constant across the face. It increases as the beam is deflected away from centre. This is purely down to geometry in that that the screen is not a sphere around the apparent deflection centre. The flatter the screen and the greater the deflection angle, the greater the effect. 109.153.242.10 (talk) 16:22, 10 January 2012 (UTC)

A long time later but... For television deflection purposes, the line output transformer was probably the most misnamed part of a television. For deflection purposes it was just am inductor in series with the deflection coils which produced a sawtooth current when suitably switched (even the 'line output valve/transistor' was nothing of the kind but just simply a switch). Any transformer action came solely from its convenient secondary function of generating the CRT accelerating voltage from the energy stored in it (along with its own boosted supply voltage). It is certainly not an impedance matching device as its name would suggest.

However having said all that: the name 'line output transformer' is, in fact, a historical hangover from the very early days of television (from 1936 up to about 1950). The first television deflection circuits consisted of an oscillator that produced a sawtooth voltage (usually based on a thyratron), that fed the signal to a linear power output valve (the 'line [or frame] output pentode' - which really was an amplifying output valve). A transformer was required to match the relatively high anode impedance of the pentode valve to the lower impedance of the deflection coils. Thus, at this time, the parts were correctly named.

Television manufacturers were always looking for ways to eliminate as many parts as possible, and the more recent line deflection systems were a way of eliminating a relatively expensive thyratron and it associated components. Even though the line output valve and the line output transformer no longer fitted those descriptions, the names nevertheless (as they often do) stuck. 86.164.109.106 (talk) 13:16, 3 March 2021 (UTC)

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)

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)

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

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)

And all I've read about television electronics says the opposite. The flyback transformer uses the large *currents* needed to run the deflection yoke to produce large *voltage*. Maybe some old-timey sets had a HV winding on the power transformer that rectified line frequency to produce a couple of kilovolts, but I can't imagine a set larger than 5 or 6 inches would have used that method. References here would be the key. --Wtshymanski (talk) 17:07, 30 July 2011 (UTC)

All TVs prior to the AC/DC design, and for a while afterwards, used mains derived EHT, primarily because the idea of deriving it from the LOPT hadn't been thought of. Even after it had, projection TVs continued to derive the 25kV required from a source other than the LOPT - initially the mains transformer and later when AC/DC designs appeared, from a self contained EHT generator (an early example of a flyback transformer that dispensed with the need to produce high deflection currents). It was largely for insulation reasons that it was separated from the LOPT and it was always oil immersed. 86.163.87.193 (talk) 08:03, 31 July 2011 (UTC)

This is interesting. About 3 years ago, we discovered a hitherto unknown door hidden behind a rack in our stockroom. Inside we found much very old stock including 2 very old television sets. They were actually brand new in their original cartons. From the labelling, we knew they were delivered in 1937. Manufactured by (IIRC) someone like White-Hibutson (or something like that). They were the same model and used a 12 inch CRT that was long enough that it had to be mounted vertically (and viewed via a mirror mounted in the top door of the cabinet). For the purposes of this discussion, the TV model had a mains transformer, and the EHT was most definitely derived from the mains transformer using a nice thick cable leading from it to the valve (or tube) rectifier (which in turn fed a (physically) large black reservoir capacitor in parallel with the tube - later sets omitted this capacitor and just used the capacitance between the internal and external 'dag' coatings instead). The manufacturer's data for the tube showed that it operated with a final anode voltage of 14 kilovolts (consistent with the 15 kV rating of the reservoir capacitor). This means that the line output transformer had no function other than to produce the high currents required for horizontal deflection. This current is produced at almost no voltage as TV line deflection coils have near zero resistance and very little inductance.

In case anyone is wondering, we did not power up the TV, partly because the 405 line broadcasts with which it worked had long since ceased transmission, but mainly because powering up anything with electrolytic capacitors which have not been used for 70 years is not to be taken lightly. 212.183.128.104 (talk) 14:58, 1 August 2011 (UTC)

My recollection is that the manufacturer was White-Hibertson, but my memory is such that either of us could be right. White-Hibertson was a UK manufacturer of television sets for the very top end of the market. Twelve inch would have been a very large TV for the 1930's and a very expensive and substantial piece of furniture, but entirely consistent with their target market. The EHT reservoir capacitor made a comeback in the early 1950's with the introduction of the metal cone CRT which allowed larger screen sizes than were previously available - albeit still with a circular screen. This was a CRT with a metal cone with a glass screen bonded to one end and a glass neck with the electron gun bonded to the other. They were not popular with TV engineers, as the metal cone was connected to the final anode and was thus live with the full EHT. They were, however, still unable to compete with the screen sizes available with projection type TVs for many years. It was around the mid 1950's that saw a considerable improvement in CRT manufacturing techniques which allowed the introduction of all glass rectangular (almost) tubes in larger sizes that made the projection system obsolete - at least for a few decades. 86.166.69.59 (talk) 12:09, 3 August 2011 (UTC)

Incidentally: some info on a 1939 receiver with mains transformers (and mains derived EHT) can be found here. Since this is only a 7 inch set the EHT is fairly low at around 3500 volts (according to tube data sheet). 86.166.69.59 (talk) 13:06, 3 August 2011 (UTC)

This aticle is about the flyback transformer, and this discussion should be confined to discussing the article and its content. It is not a suitable place to discuss television design through the centuries. DieSwartzPunkt (talk) 15:16, 3 August 2011 (UTC)

Actually, most of the discussion is relevant. There are those who have the idea that the LOPT's primary purpose is to generate the high voltage for the CRT and that line deflection is convenient secondary function. In reality it is the other way around as betrayed by the first television designs using the LOPT solely to generate the large deflection currents required with no power supplying function at all. The early mains transformered sets did not even have a requirement for an efficiency rectifier to recover the energy in the magnetic circuit as the transformered power supply was able to produce the required voltage to run the line output stage. As ever in Wikipedia, finding good citations for technology this old can be very difficult. The one above cites that such sets existed but little else. 86.166.69.59 (talk) 11:00, 4 August 2011 (UTC)

Some minimal research would indicate that your recollection is faulty. The company you refer to is 'White-Ibbotson'. White-Ibbotson was founded in 1950 and continued to trade until 1954 until it either merged with or became G.D.Developments (which is unclear). White-Ibbotson only ever manufactured projection televisions based on the Mullard 2.5 inch MW6/2 CRT. Also, no pre war direct view television used an EHT as high as 14kV - in fact not until rectangular tubes appeared. As Wtshymanski correctly surmised, pre war sets used an EHT voltage of just a few thousand volts, and indeed this was often derived directly from the mains transformer (I have not found one exceeding 4kV - though that doesn't mean there isn't one) which is why early sets had such a dim picture. The only known exception was the Dutch firm Philips who produced a projection set in 1937 with (for that time) a whopping 25 inch (diagonal) screen based on a 4 inch projection tube using a mains derived 25kV EHT. The EHT was from a votage doubler energised from a ~10kV winding on the mains transformer. The EHT unit was constructed such that opening the unit cut off the input supply and shorted the reservior and smoothing capacitors. This did not prevent a serviceman disconnecting the EHT lead from the CRT and leaving it exposed. The set was a failure, as Philips found it more economical to buy the sets back rather than keep providing replacement CRTs under warranty. The tube was driven so hard that it typically only lasted a few weeks - bearing in mind that television broadcasting in 1937 was only for a couple of hours each day (the set shown at the Radiolympia exhibition was allegedly withdrawn from the show after just 2 days as its CRT had failed). Philips produced a smaller screened version (but still 23 inch diagonal) the next year using an improved version of the same tube (which, I believe is the set refered to below). DieSwartzPunkt (talk) 13:11, 9 August 2011 (UTC)

And for Wtshymanski, here is a link to a very early 1938 projection TV that used 25,000 volts EHT - derived entirely from the mains! 86.184.24.172 (talk) 16:28, 4 August 2011 (UTC)

Factual accuracy

This article is still very much based on guesswork and supposition. It is far from accurate as shown by the above discussion. Areas of concern include (but are not limited to):

• The article is mostly centred around a discussion of television deflection systems. Although this is an application of a flyback transformer, it is by no means the sole application. Most other applications are power supply related rather than TV deflection related.

• That the article insists that the TV deflection circuit has to use a transformer. This is not correct. The device acts solely as an inductor for deflection purposes. The transformer part is purely for the secondary function of power supply. Indeed early TV sets that derived the tube's high voltage directly from the mains transformer did not have a transformer in the deflection circuit, only an inductor.

• The article describes a circuit producing a saw tooth current varying from zero to some maximum value. Such a circuit would be useless for a television deflection system unless the viewer is content to watch a picture displayed on one quarter of the tube face only. The article does not describe how a deflection current varying from a minus maxima to a positive maxima is achieved.

• The article describes a system that is designed to produce a linear ramp to the saw tooth current. This is the last thing that is required as the deflection sensitivity of a CRT increases as the beam departs from the screen centre. The deflection circuit has to produce an 'S' shaped ramp to the waveform. The article does not describe how this is achieved.

Most (but not all) of these points not necessarily relevant to a purely flyback type power supply DieSwartzPunkt (talk) 15:41, 10 November 2012 (UTC)

Article needs work

Most of the electrical components pages could use a bit of tidying up, but...

Out of all the different articles of this sort, the expected quality of this page is much lower than the actual quality.

It's obviously lower rank than resistors and capacitors and the like, but it's still far from an obscure component. Considering the noteworthiness of the topic of this article, it really ought to get a bit of dedicated attention one of these days (imho)

50.46.228.138 (talk) 23:02, 10 January 2014 (UTC)

Where is the information?

This article is empty. I can see there is discussion about this though. There are no schematics or diagrams, no numbers or units, and seemingly no facts. Half the article goes off into television repair, which does not even apply to the main article. — Preceding unsigned comment added by 99.229.12.128 (talk) 23:31, 17 March 2016 (UTC)

Horrible article

It doesn't even explain why the transformer is called a "flyback". You keep reading and reading and it's still a mystery.

I found this Stack Exchange post somewhat useful: http://electronics.stackexchange.com/questions/235991/what-is-a-flyback

• Was it really "invented as a means of controlling the horizontal movement of the electron beam in a cathode ray tube"? Or was it invented as a way of getting rid of excess energy during the "flyback" phase of this horizontal movement, and using this energy to solve another problem (generation of high voltages)?

• What distinguishes a flyback transformer from "normal" transformers? Do all flyback transformers have a series diode at the secondary? Is it really series or is it parallel?

• How is a flyback transformer used to produce low voltages (claimed under History)? What is special about a flyback transformer that makes it useful for this?

• When was it invented, and who invented it?

A5 (talk) 02:51, 31 May 2016 (UTC)

• It's called a flyback transformer because "flyback" in TVs needed a sawtooth wave - a slow scan across the tube, then the most rapid return possible. This required a transformer (look at Fourier analysis) which was capable of high frequency operation in order to cope with the slew rate of the fast voltage drop during the flyback phase. Even though the signal was a fairly low frequency overall, it's the steepness of that part of the curve.

This required a transformer with a high quality ferrite core, rather than iron laminations.

The availability of cheap high requency capable transformers made them suitable for all sorts of things. When used as a HT inverter, they could be run at high frequencies. These were easy to make from transistor inverters, and the higher frequencies allowed more efficient voltage multipliers to be used in their HT stages (lower value capacitors with lower losses).

Sadly, WP has little content on the old techniques of analogue TV and CRT circuitry, especially not for the black & white era. Andy Dingley (talk) 17:36, 22 December 2019 (UTC)

Almost complete nonsense. For the purpose of producing the deflection signal in a post 1950's TV set, the part required a single winding only, wired in series with the deflection coils. Any additional windings are solely for the purpose of supplying high voltage for the CRT plus a boosted supply for the deflection circuit itself.

The term 'line output transformer' is a historical artefact from before 1950 when the part really was an output transformer matching the high impedance of a real amplifying output pentode to the low resistance of the deflection coils. The pentode was fed with a (more or less) sawtooth wave generated from a thyratron oscillator. The expensive thyratrons (one for frame and one for line) were deleted once it was figured out how to make a much simpler circuit that would generate the required sawtooth current using a simple switch and an inductor (though it is not quite that simple). Both types of circuit require a ferrite cored component, but the later requires an air gap in the magnetic core to increase its reluctance and hence the available stored energy without the risk of saturation.

As many have noted above, the circuit described in this article is all but useless for television deflection purposes. I cannot argue with your basic premise that this is a horrible article. 185.69.145.2 (talk) 18:16, 3 March 2021 (UTC)