A Guide to Flyback Transformers

Unless professionally required, a lot of high voltage enthusiasts do not wind their high voltage transformers at home. This task would be nearly impossible to do without proper coil winding, insulation potting and vacuum-sealing machinery. Thus, high voltage transformers from everyday electronic appliances, such as CRT TVs and computer monitors, microwaves, automobile ignition coils etc., are used. This article will be regarding the so-called “flyback transformers”, a well-known term in the high voltage hobby, and their various types of construction and output.

Firstly, what is a flyback transformer? Well, if you take a peek into every classic “fat” CRT television or monitor, whether vintage or modern, you are going to find one. Basically, it is a ferrite transformer with an air gap and 2 or more coils, sealed in epoxy or interlaced in an insulation paper, whose outputs go to the television screen. These transformers run on ultrasonic frequencies, mostly in the 15-50 kHz range, and are designed to provide 15 to 35 kilovolts for the screen’s electron beam. This output is easily located; it is the thick red wire with a scary looking suction cup connected to the screen… Newer flybacks also have, in addition to numerous other things, a high resistance resistor cascade, dipped in epoxy, to provide information about the high voltage output to the internal driving circuitry of a TV or monitor. These flybacks also have two or three “knobs” (potentiometers), to adjust the focus and brightness of the electron beam. Depending on age of the TV or monitor which you might have disassembled, you are going to meet with these types of flyback transformers:

These are 6 different kinds of flyback transformers which I have met with.

Type 1): These 6-8 kV AC flybacks were used in conjunction with a voltage multiplier, like this one.
Absolute maximum allowable output voltage 10 kV~ at 15 kHz (PAL horizontal frequency). Prevalent in many Czechoslovak, Soviet and other color television sets of the 1980s. Has many layers of insulation foil. Primary windings are located below the secondary.  Use these flybacks for all the lower voltage, higher current needs. Will sustain at least 500 watts of output power, if ran in short periods or with adequate cooling.

Type 2A): A 10 kV AC compact flyback for portable black and white television sets with secondary dipped in epoxy. Maximum output voltage 12-14 kV AC. Used with an external rectifier block. Not suitable neither for higher voltages nor high output currents.

Type 2B): The same as 2A, however with the high voltage rectifier integrated to the secondary, so it is a DC flyback. Has slightly less secondary turns. Used in TESLA “Merkur”.

Type 3): Prevalent in all black and white sets from early 1960s up to circa 1978. This AC flyback has the secondary dipped in epoxy and is similar to a kind colloquially named the “disc-shaped flyback”. It was used along with a vacuum tube rectifier, like the DY86, DY87 or 1Y32. This particular type has been made by the Czechoslovak TESLA in mid-70s and the maximum output voltage was something over 20 kV AC at 15 kHz. Used in my first quasi-resonant driver.

Type 4A): These DC flybacks are found in every CRT computer monitor and are called the DST flybacks (diode-split transformers) because of the several high voltage diodes and secondaries inside. In addition to the high resistance resistor cascade and focus/screen tuning potentiometers described above, these kinds have an integrated high voltage filtering capacitor (few nanofarads at >=30 kV), or – optionally – a HV capacitor for dynamic focus. Because of the capacitor, these flybacks can hold a charge enough to shock you even after a week. The bottom pins will start arcing over, also because of the internal capacitor, if the flyback is overdriven above 30 kilovolts.

Type 4B): Like the 4A, these DC flybacks are also diode-split (DST), however these are found in every modern CRT TV-set from mid-90s and onwards. These have just two screen-tuning potentiometers and no internal capacitors whatsoever, so they can be safely overdriven to circa 50 kilovolts DC; albeit some beefy ones might give you even 70-80 kV with ease. This flyback type has been used in my Monster flyback driver.

A practical problem with DST flybacks – types 4A and 4B in the picture – would be locating the high voltage return (ground) pin on the bottom. If you’re lucky to find yourself a datasheet for your particular flyback (or its HR-marked equivalent name in an online conversion table), then it is a cinch. If that is not an option, you can try the circuit tester published here to find it. As a last resort, you can try constructing a low powered flyback driver, like the “2n3055” single-transistor one, then powering it on and placing the anode wire close to the bottom pins. You know you have found the right pin to which the anode makes a continuous arc.

And that is about it, folks. Hope this article explained some practical facts 🙂

40 Responses for A Guide to Flyback Transformers

  1. Doug says:

    What are some signs that the fly back transformer needs to be replaced/repaired on a 32 inch RCA “fat” tv. Mine snapped and sizzled. Now no pic or sound. Just snowy and hisses. Expensive fix?

  2. Anonymous says:

    can you tell me how can i identify flyback internal capacitor because i want to use flyback in my project without internal cap. it also

  3. Eduardo Brasil says:

    Hi, I am interested in construction of a 150kv or more HV source using the output of one of you circuits as an input to a halfwave cockcroft walton circuit. Is that feasible? Could be done with modern DST flybacks? Old AC flybacks are hard to find or not much reliable.
    Thank you and congratulations for your work!

  4. Anonymous says:

    Is 145dcv input on the primary winding of a flyback for LG TV 15 inches normal?

    • Jozef says:

      Yes, the circuits use the original primary coil that is encapsulated inside the flyback. First two bottom pins.

  5. Michael says:

    Which is better, an ohm or an inductance meter to find the correct taps on a flyback transformer?

  6. Mackie says:

    Where can I locate Type 1 Flybacks? You say Soviet and Czech TVs have them. What brands are those TVs?

  7. shankarlingam says:

    good article.can you please suggest any flyback transformer without rectifier ,for jaccobs ladder,tesla coil.

    • Jozef says:

      You don’t have to use an AC flyback, you’re free to go with a rectified DST. Of course, in both cases, it depends on your coil – spark gap tesla coils are not spectacular when they’re built too small, and a flyback transformer supply for your coil might be not enough.

      Try keeping an eye on potential transformers, or get at least 4-5 microwave oven transformers for a big SGTC and forget about the flybacks.

  8. Sam says:

    I need an AC flyback transformer for my voltage multiplier. I could not find any supplier on the internet!! Can you help me get it?

    • Jozef says:

      Nope – I’ve got mine for free, from sorted scrapyards (where they collected such stuff and sent them for “ecological” disposition later). Back then (about 6 years ago) there were people cleaning up their cellars, stumbling upon a black and white TV set once in a while. Desoldering and disassembling old stuff was the way I started around with electronics, if you buy yourself everything you’re doing it wrong 😉

      Other than that, the vintage flybacks go for crazy prices on auction sites… Needless to say, technically, it is possible to modify a DST transformer to have AC on output, however it’s a matter of time before it chews through the windings insulation.

    • Jozef says:

      Then again, you can wind your own high voltage secondary if God gave you a whole lot of assertivity and patience. If you’re not going over a few kilovolts AC, insulating foils can be used.. afterwards, oil or epoxy + a vacuum pump. It’s more tedious than making a Tesla coil secondary and it’s quite unrewarding – because if you screw up, everything goes to hell, with accompanied arcing in-between the windings inferno. 😉

  9. Samuel says:

    ahoj, z crt televize se mi podařilo vymlátit tenhle flyback http://www.donberg.ie/catalogue/line_output_transformers/hr_7875.html ale ani s tím schématem nemůžu přijít na to co je primár a co feedback coil a taky bych rád věděl jestli to je typ 4A nebo 4B myslím si že 4A ale jistota je jistota předem děkuji za odpověd

    • Jozef says:

      Primár si obvykle navineš sám na odkrytú časť jadra, ten pôvodný by si využil jedine ak by sa jednalo o budič typu polomost a pod.
      Ak to bolo z telky, tipoval bych skôr typ 4B), teda bez vn kondenzátora vnútri.

    • Samuel says:

      jde o to že tam není skoro žádné místo na namotání primáru a i kdyby tak kolik zavitu a jaký průměr?

    • Jozef says:

      No to závisí čo za budič ideš postaviť, s akým vstupným napätím a pod.

  10. Martin Hudoba says:

    Hojky, kúpil som z číny ten 4B aj s ZVS driverom.. napájal som to zdrojom 24V 10A a bežalo to fakt skvelo, skúšal som Jacob’s Ladder a len také obyčajné oblúky (strašne ma to fascinovalo :D) a potom zrazu, po 2 dňoch sa mi odtrhla katóda ktorá vychádza zo spodku trafa, no tak som to normálne prispájkoval naspäť a skúsil som to zapnúť znovu. A tu zrazu pozerám, že to ide nejáko slabo, prišlo mi to divné tak som skúšal prenastavovať tie FOCUS a SCREEN potenciometre ale žiadny rozdiel.. tak som sa vrhol na web, a našiel som túto stránku (fakt dobrá musím uznať :)), no a tu čítam že ten transformátor nemôže bežať naprázdno lebo sa spália tie diódy, no a vtedy mi to cvaklo.. ja som si spálil zopár diód a práve preto mi to teraz ide tak slabo.. teda aspoň myslím. Či myslím správne to už nechám na tvoju odpoveď 😀 No a ešte jedna vec, nepredal by si mi jedno ba i viac 4B tráf? 🙂

    • Jozef says:

      Serus, to trafo si pravdepodobne uvaril tými oblúkmi – ak by odišli diody, na výstupe by sa bola objavila striedavina, zasršalo by to ako malý teslák a vnútorné vinutie by zhorelo v medzizávitových skratoch, pretože vnútorná izolácia týchto traf nie je stavaná na striedavý prúd.
      Tie dva potenciometre slúžili na ostrenie el. lúča obrazovky, laicky povedané ovplyvňujú výstup z tých dvoch tenkých vn káblov popri tej kaskáde.
      O problematiku som sa zaujímal tak 2-3r dozadu, tie trafá už nemám – navštív zberné dvory, poprípade napíš na inzerát že zbavíš ľudí starých TV/monitorov za odvoz, určite sa ti ozvú 🙂

  11. alyasa says:

    Dear sir. I did a course in basic electronics,which really intrigued me.Now I want to further my knowledge in this field,what books would you recommend buying?

    • Jozef says:

      I cannot, I hadn’t any electronics courses nor did I study any paper books about this, its just practical knowledge and the élan that drives you forward.

  12. Juraj Kubiš says:

    Ahoj, našiel som transformátor v jednej vyhodetej televízii. Má iba dva potenciometre, ale je rozmerovo trocha menší ako 4B na obrázku. Nevieš mi povedať, či aj ten môj je schopný vydržať tie napätia ako 4B? Ďakujem 🙂

  13. J says:

    Great site.
    My project requires a power supply with the following specifications:

    Input: something in the range of 3- 50V DC.
    Output: tunable volatge from 30kVpp – 80kVpp with a ramp waveform at tunable frequencies from 1 kHz – 10 kHz.

    Do you have any suggestiong to get me started? What is the best way to go about this? Can you recommend some websites or books to help me with this project?


  14. bill says:

    How hard do you think it would be to use a high heat gun and take 4A or 4B apart?

  15. Ask says:

    Dear sir, how can get an out put of 1.5 or 2 kv from a 12 volt car battery by using fly back transformer.

    • Jozef says:

      For what setup and how much output current? Winding your own transformer might be a better option.

  16. Justin says:

    But how can you identify the higher-voltage transformers? Higher output voltages mean longer spark.

    Also, where can specs be found? I’m told it is possible to charge a flyback with too much voltage and melt it. I want the biggest spark I can get, but I don’t want to break the thing.

    • Jozef says:

      In layman’s terms, output kilovoltage rises with arc starting distance. It’s not linear, but a very coarse term of 1mm ~ 1kV spark ignition distance, applies for spherical electrodes, under “normal pressure and humidity” and direct current, for up to circa 20 kV, then the relation starts to become non-linear.

      When a spark is struck and an arc forms, it depends on the power of your supply on how long you can stretch it.

      If you overvolt a flyback, it will cause arc-over. External arc overs (like to the core, or somewhere between contact points) are easier to manage if the power is cut within a second or two, again depends on the power of your supply. I.e. you can scrape off the conductive shit it burned through, or put it into oil.
      However if it arces over internally between secondary windings, you’re out of luck.

      In case you overvolt a DC flyback, like a diode-split transformer (DST), you’ll destroy the rectifiers inside and AC will eat up its secondary insulation in a while.

      You don’t “melt” a flyback with excessive voltage output. This depends on the power (current) you’re running through it + what the ferrite core can take. Again depends on the flyback, how thick is the ferrite core, secondary wire diameter, driver, etc.

      I’ve successfully pumped 500 watts short term through a “Type 1” flyback (check the pic above) at a voltage of approximately 5 kV.

  17. Wildfire Phoenix says:

    Hello, I am just wondering has a powerful flyback driver been made from a 1995 Sony Trinitron PC monitor parts yet? I am asking because I just tore apart the monitor mentioned above earlier.

    • Jozef says:

      Any kind of television/monitor flyback will work. The best I have met for high current (halfbridge or ZVS driver) was type 1).

      4B) class, especially those from big TVs, are good for 40-50 kV alone, when driven with a resonant driver e.g.

  18. nitheesh chandran says:

    goog article sir,,,, sir i like to do a project with flyback transformers,,it is to show how they are working,,, can you give me circuits related to that??

  19. ivan says:

    Nice article.

    Hi, can you recommend me some sites to buy the 4A or B, I searched a lot but i don’t saw them anywhere…

    • Jozef says:

      Desolder them. Take a visit to your local scrapyard (with a bottle of brandy as bribe, if they won’t let you in) and tear them off circuit boards of CRT TVs.
      On the other hand, German eBay sellers give them away for a few EUR a piece sometimes. It depends.

  20. Anton Yugay says:

    Super article. Could you recomend some literature about operation of fly-back transformer?

    • Jozef says:

      Well there’s one or two high voltage-inspired books in Czech, as for literature in English I cannot provide you an exact title though you might be interested in TV repair manuals or similar.

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