Flyback driver #2: NE555 quasi-resonant

This single transistor flyback driver topology was created in response to achieve higher efficiency and higher output voltages from ordinary CRT television flybacks (diode split flybacks), for experiments such as x-rays or ionic lifters, without having to make any external HV multipliers. Since these flybacks are normally sealed in epoxy and can withstand an output voltage of 50 to 75 kilovolts, why not use them in drivers such as this one… :)  Moreover, the simplicity of this circuit also adds a possibility of some simple audio modulation of the arc. So, let’s begin!

Quasi-resonant flyback driver schematicThe quasi-resonant topology

But to say the least, the first driver I have built with this topology had an AC flyback and an input power supply rated just 60 watts. The result was a compact, short-circuit proof, high voltage “lab” supply with frequency control, some active cooling, audio modulation (singing arc, or a plasma speaker), two 5-15 kV high voltage outputs (AC and DC) to play with things such as plasma globes, small Jacob ladders, multipliers, and so on. The machine, due to its intended purpose, did not provide big fat arcs – however I think it’s still impressive and worth mentioning. Behold!

 High voltage enthusiasts, who are familiar with the classic NE555 flyback driver, will notice the foil capacitor across the primary winding, which really makes wonders. (More on this here.) The output voltage depends on the oscillator frequency (set it to variable 15-30kHz for output voltage fine-tuning), number of primary turns and on the resonant capacity. Fewer turns, lower frequency and lower cap values such as 100-330 nF are going to produce over 60 kV out of a DST flyback with ease; more turns, higher frequency and higher capacity (up to 1 uF) will yield smaller output voltage with more current. Tune these factors to get the best output which suits for you. Do not forget to include the gate protection circuit (diode+resistor) on the MOSFET, but if the resonant mode is not used, omit this. Lastly, use the fifth pin for PWM audio modulation – you are going to need a 0.5-1.5W amplifier for best results. If you are not going to use this, ground the 100n cap.

And now, the moment you have been waiting for:

The Monster Flyback Driver !

More than 50 kilovolts out of a single flyback at 20 volts input

Tired of measly sparks? This flyback driver is for you then! To allow higher voltage inputs and bigger power outputs, get a separate 12-16V DC supply (a few watt transformer, e.g.) for the NE555 oscillator part. I do not suggest using a stabiliser like 7812, LM3xx’s since they are prone to the strong EMI this machine generates, and you do not want to fry the 555 chip with excessive voltage spikes… Then, substitute the “IRF5x0″ transistor for a better type with at least 200V Udss and low Rds(on), i.e. IRFP250, IRFP460 or similar. Change the heatsink and the resonant capacitor if needed (a 330n-680n 250V AC MKT/MKP is enough), disconnect the primary winding which went to the positive pole of the previous supply and you are good to go!

I have given the nickname “Monster” to my second flyback driver based on this topology, because when you switch it on, all hell breaks loose. High-pitched whine, strong hiss and vast amounts of ozone are produced, high voltage wires are moving on their own, nasty static charges build up on everything conductive, strong ionic wind and corona discharge are felt even 0.5m far from the anode wire, some serious EMI is sent back to the mains: speakers buzz and hiss violently, ADSL router loses connection at times….These are just a few signs that the machine is alive and kicking.

When properly tuned, this topology draws between 4 to 8 amps at load, in a supply voltage range of 18 up to 30 volts, excluding the first example of my driver, which drew 3 amps and had been constructed for low power emphasis in mind.

The thing you see here has an IRFP250N and the oscillator frequency is freely tunable between 16-30 kHz, giving an output voltage circa 20 to 55 kilovolts DC unloaded (at full blast, the arc ignition distance was 7.5 cm which might be roughly 55-60kV). That corona discharge between the high-voltage anode and a concrete wall is also spectacular..

A note to add: this circuit should never be powered on with no load, if the output voltage is designed to be over 40 kilovolts. Make a “safety spark gap” or something – if you let the anode to hiss free-to-air and the primary winding polarity is in incorrect phasing, the internal diodes of the DST flyback might not survive this (check if there’s no corona/arcing/hissing between the primary and high voltage secondary). Do not use a computer monitor flyback, they have an internal high voltage capacitor whose bottom pins will arc over at 30kV and up.

Audio modulated “Singing arc”

Old prototype version

67 Responses for Flyback driver #2: NE555 quasi-resonant

  1. Steffen D. says:

    Do you work with tube Radios?
    These resistor values ALWAYS lead me to Tube Radio Sites…..also the diode.
    But verry cool!

  2. rabz says:

    your said for results we should use 150VA and 18-24V right???
    can you tell me this 18-24V is peak value of voltage, if i use driver with 2n3055 then voltage which is going to fed into the fly back is of peak value 24V or i’ve to consider RMS value???

  3. Dan says:

    For the “smallGen” schematic, is it necessary to have a diode on the high voltage side of the secondary winding of the flyback? I am not sure what an EHT diode is and what the ratings listed are for??

    • Jozef says:

      Nope, it’s not mandatory. I’ve used an AC flyback with an additional rectifier to get both outputs.
      The diode itself is rated 30kV 30mA.

  4. SomeOne says:

    Nice !, thanks very much !

  5. Santiago Gutiérrez says:

    I need help. (Sorry for my poor English, in fact my mother tonge is Spanish)
    I build that circuit in my protoboard but I can’t get the same results like you, my spark is half centimeter long. I tried using two 3055 instead only one conecting base to base, colector to colector, etc, but I have not the spark I expected. Can you tell me how many turns of wire did you put in the flyback?
    Saludos from Argentina.

    • Jozef says:

      Use a 12V supply for the NE555 and a separate, filtered 20-30Vdc 8A supply for primary. Start with a good heatsink, 330n MKP resonant cap and, 12 primary windings.
      To increase power and output kilovoltage, decrease primary windings.
      P.S.: My mother tongue is also not English.

    • rabz says:

      can you send me your circuit information bcz mw too using two 2n3055 in my circuit

  6. Love this circuit. Built it some time ago. Very stable

  7. Adas says:

    To je skvelý driver, ale je to zvláštne, nebolo by lepšie náboj z GATE odoberať bipolárnym tranzistorom? Vieš čo myslím. Určite by to urýchlilo nabíjanie a vybíjanie a tým pádom by to malo znížiť ohrev MOSFETu.

    • Jozef says:

      Vitaj, nakresli schému jak konkrétne si to myslel. S tým zapojením sa dá dosť špekulovať a zrovna sa nejedná o nejaké dvakrát účinné, na to sú už iné topologie.. a nebudí ich prachsprostý časovač, ale poriadny gate driver :)

    • Adas says:

      Tak jasné, gate drivery sú najlepšie, ale ja rád čo najjednoduchšie (napr. ZVS :D). Myslel som niečo takéto, že proste bipolár vybíja GATE.

      Inak fakt sa mi lúbia niektoré tvoje experimenty, si pánko :D Môžeš čeknúť aj môj Youtube kanál, nie je síce zďaleka tak “profesionálny”, ale mám tam niektoré na fest zaujímavé veci (gogo311)

  8. Lukas says:

    Great work! I made this one too, nice circuit, works good, but I want louder sparks.

  9. bill says:

    have built similar circuit to this, but high voltage leaking back to 555 blows it up, I measured 190 volts on chip supply, tried all ways to stop it, no success, any ideas, thanks

    • Jozef says:

      Ground the driving IC, MOSFET’s source and the flyback transformer return pin ( + if it does not help, the ferrite core too). Hope you are not alliowing the output to hiss freely anywhere near the IC…

  10. bill says:

    your scematic does not show pin 3 of 555 connected, can you clarify, thanks

    • Jozef says:

      I’m pretty sure it shows :)

    • bill says:

      sorry you are right it is connected, I did,nt enlarge image, I can see it now, I have used my circuit to drive a tesla I,m getting 4 inch sparks with 12v input,have also used it to drive two flybacks in series! very impressive,

  11. Debjit Roy says:

    In the schematic its written if RC1 not used short it, it will be open not short

  12. Anonymous says:

    Very impressive. Please give model number of flyback and what model TV it came out of.

  13. Andrew T. says:

    Built the circuit. Didn’t work. I must have screwed something up. Hooked up my scope to pin 3, didn’t even get any kind of oscillations going on.

    • Jozef says:

      Replace the chip..

    • Andrew T. says:

      The chip was brand new. I did switch it out. I did find some errors I made though. I corrected them. Now I’m getting pulses that are just spikes on a line. They are very small though. The amplitude of the spikes is in the millivolt range.

    • Jozef says:

      You might have fried it once more, check all connections, probable cold joints and try again.

      Seriously now: if, constructing such a simple circuit like this, makes you problems, you should back away from the high voltage hobby… And far.

      I do have a disclaimer up above, but I think I would not want to hear you have been killed by one of my creations..

    • Andrew T. says:

      I’ve actually been doing high voltage stuff for several years now. I’ve also successfully made several 555 astable driver circuits. I know the dangers as well. I appreciate your concern though. Anyways, thanks for your help. I’ll probably figure it out eventually.

  14. Zack says:

    I made a 120v version of this circuit, with the exception that I copied the TV’s RLC filter on the transistor. So far I have only used the original primary @ 120v. To get best power out I need to mod my driver to have Duty Cycle adjustment. I’m also getting no audio modulation, LM386 Audio Amp?

    Other than that this is a Super Simple circuit & makes a sick HV Driver!

  15. Ion says:

    k2749 is good for this application? I do not have another power transistor for this moment. thanks…

  16. asdsdfs says:

    show the surcit diagram
    and i have a flyback of a monitor (i know abowt the high voltage capacitor)
    plugted the transformer in a 555 surcit over a mosfed and a put a cuple of AA batteries and ive got like 3 milimeter arc

  17. Fandango says:

    Nice generator.
    I build a prototype according your schematic and it works fine. It produces a lot of Ozone!
    In fact it have a little differences, because I used an old Samsung FSA-14A003 flyback. With 10 turns on the primary side, I noted poor performance, so I decided to use the winding between pins 2 and 3 of the flyback, and the results were very cool. For the RC1 I used a 2.2nF/400V cap and a 1N4937 fast recovery diode for the protection of the 555 IC (pin 3). For the MOSFET I used an IRF630B.
    I have noted that the 555 IC, after 20 seconds, begins hot, Thus, I put a 10K resistor between the gate and the GND of the MOSFET, with the aim of guarantee it turn off. However I noted that was spend of time, because it takes no effect.
    Why do you think the 555 IC is been hot?

    • Jozef says:

      That’s strange.. Does it get hot even when you disconnect the gate?
      I’d probe the output with an oscilloscope to see whether you’re getting a nice square wave, both stand-alone and with gate connected.
      IRF630s work here fine but their internal resistance is quite high so they tend to heat up.

    • Fandango says:

      Thank you Jozef.
      I did measure the output with the oscilloscope and noted that the square wave does fade-out slowly. Thus, I did replace the 555 IC and now everything is ok.
      I did tune the frequency for the flyback (39kHz) and the performance is really nice.
      By the way, the IRF630B MOSFET is not heating so much. I did put a little heatsink and is working fine (at least for 2 minutes of continuous operation generating Ozone). The current seams to be small. I will measure some day.
      Anyway, thank you for share your circuit and your experience.

  18. jasshopper says:

    what is the input voltage and current of the power supply you used?and also what is the output voltage and current from the flyback?would a computer psu work for this?

    • Jozef says:

      The first low powered version used a small 12v~ 60VA transformer (rectified, ofc). The second was built with a 20 volt, 120VA SMPS – for best results, use a supply 18 to 24 volts rated at least 150VA.

    • jasshopper says:

      by first did you mean the prototype? and could you please tell the output voltage and the output current coz i’m thinking of building a tesla coil with this and to find the value and the voltage of the capacitor bank i need to know them.
      Also, thank you for making this post.

    • Jozef says:

      Yes, the first was meant the “white cage”, low powered dual output version.
      To do a spark gap Tesla coil I’d recommend building a halfbridge or a ZVS but this ought do the trick for micro SGTCs just fine.

  19. Pedro pin says:

    Hello Jozet

    the best for my project is a multiplier and if possible with variable voltage
      very difficult?
    another application for these circuits DC is electrostatic painting


  20. Pedro pin says:

    Good day to all
    This monster generates DC?
    The Amp is lethal?
      thank you very much

    Pedro pin

    • Jozef says:

      Well, it depends on how it is built.

    • Pedro pin says:

      Thanks for answering Josef
      I need to build a circuit to use as delivered 50KV electrostatic flock for a machine must be DC.
      If you can give me a help I appreciate it


    • Jozef says:

      This thing has no problems delivering 50 kilovolts unloaded when tuned right.
      I am not quite sure what did you mean with “electrostatic flock” but I’d go with a diode split flyback out of CRT TVs. Or if you want to be absolutely sure you could make a multiplier, e.g.


  21. Denis says:

    Tell me, what another DST can I use? Because, I have no that. Thanks :)

    • Jozef says:

      It works with any kind of television flyback. Diode split rectified transformers from CRT TV’s, with a properly set air gap, worked best for me.

    • Denis says:

      Thanks :) Your driver is very cool. I’ll plan to make the device with NE555, I have one television flyback TVS-110L4 (made in USSR) for this :) But 1st, I want to build a device with lamps (tubes) 6P45S, I have all elements for this, but no have more time :)

  22. geordi says:

    when i used a other mosfet it blow out. so i changed back to the irf 450 but now nothing happens. can it be that my 555 is broke? cuz i dit not use the diode and resistor at pin 3 to gate of mosfet.

  23. geordi says:

    can i use the IRFP450 instead of the IRFP250?

  24. Mathías says:

    Anyway, I will make both drivers, the ZVS and this one. It will be funny! :D

  25. Mathías says:

    I have just one question: Is this circuit better than the zvs driver? Because I have all the components to make the resonant zvs driver but not this one.
    Greetings from Uruguay.

    • Jozef says:

      This circuit is nice if an intention is to get maximum voltages out of a flyback, by tuning the resonant capacitor you alter the efficiency, too.
      A ZVS is more efficient since it pumps more current into the flyback, but it is difficult to get higher kilovoltages without stressing the flyback much.

    • Mathías says:

      At 12V input: How much voltage can you obtain?… with a zvs of course.

    • Jozef says:

      “With a ZVS of course”, and my article above is about something else.. :P

      How many kilovolts on output you get depends on your setup; i.e. your flyback, number of primary turns, resonant cap, input supply power (and voltage drop), etc.

      Frankly, at twelve volts you’re going to be bashed with low efficiency as the MOSFETs are not going to get open to fully conductive states. I’d recommend at least 18 to 24 volts as a starting value.

    • Mathías says:

      I just need no more than 12 KV to operate a homemade Marx generator. 8|

    • Jozef says:

      Well that would suffice. In case any driver of yours would have put a higher voltage than you need, even if it’s not a regulated supply, it is possible to make a spark gap which is going to limit it (approx. 1kv per 1mm ignition distance, depends on electrodes, humidity etc, this rule stops working above 30 kV).

      Damn nested comments.. have to get rid of them..

    • Mathías says:

      Ok, thank you! :)
      Ok, ¡Gracias! ;)

  26. Wallas says:

    Parabens, gostei muito, sou do brasil!

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