2n3055 transistor flyback driver

2n3055 flyback driver


This driver is among the simplest, with just six components it will be able of delivering high voltage with a strong enough current for various experiments.

There is also a push-pull version of this driver, more on that can be found following this link: http://wiki.4hv.org/index.php/Flyback_transformer


WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

Read this document about safety! http://www.pupman.com/safety.htm


The transistor used in this circuit should not have a voltage rating higher than 250V, due to the higher base current needed of higher voltage rated transistors, this might in some cases cause problems where the self-resonating circuit can no longer drive the transistor.

At voltages higher than 12 VDC input, the components will dissipate a lot of heat and the 2n3055 transistor is most likely to burn as it is not rated for more than 15 A and it has to be derated even further for case temperatures above 25 oC.

MOSFETs are not suitable in this driver.

The frequency of operation in this circuit is determined by the capacitor across the transistors emitter and collector, experiment with the value of this capacitor to find the best performance, this capacitor have to be a good film or foil type (MKP/MKT)



The driver is supplied with 12 to 17 VDC from a computer ATX PSU.





3rd may 2008

The driver is built on a piece of vero board with multiply resistors to obtain the needed wattage rating, this is far from optimal as the load sharing between them is horrible, to ensure better sharing.

The 2n3055 transistor is mounted on a 30 x 10 cm aluminium profile, this is just about enough to keep it alive doing long runs.

4th may 2008

I experimented with voltages between 12 to 17 VDC, there is no incredible performance with higher voltage compared to the amount of heating the higher voltage generates.

Different capacitors were tried, ranging from 10 nF to 300 nF, 220 nF was found to work the best for my flyback transformer.

8 primary windings and 4 feedback windings gave the best results.



7th may 2008

18 to 20 mm sparks were achieved

Keeping the electrodes just far enough apart for no spark to jump, a beautiful corona breakout is visible.

With the output coupled through a home made salt water capacitor it was possible to have loud and very bright sparks.



This is a very simple and cheap circuit to achieve around 20 kV high voltage, but where it excels in simplicity it lacks a lot in stability and efficiency.

A rough estimate is that 25-50% of the input energy is wasted as heat in the transistor.

It is cheap and simple, but inefficient and unstable.



39 thoughts on “2n3055 flyback driver”

  1. As strange as it sounds this design is more flexible that it appears superficially. I worked with several transistors and found that a MJE13009 and similar along with much higher filter cap (50v 4000uf) ; higher wattage resistors will bring this to a workable level. not as efficient as the ZVS but not too poor either. The small TO-220 transistor must be efficiently heat-sinked – yet is does not appear to warm up at
    5 amps and 18v. I pushed it higher for short periods and it survived and gave surprising performance.
    The real problem with this design (aside from it basically being less efficient than the Mazzelli) is that the transistor should really never be a 3055 & the resistors should always be higher wattage than 2 and 5 watts.
    (IMO) The Mazelli drivers that occasionally fail are generally due to people not using heat sinks or poorly made one as well.

  2. What purpose does the small capacitor across the protection diode serve? I have mine set up with the diode but without the capacitor and it works fine.


  3. Hi Alex

    The diode and capacitors protects the transistor from high voltage transients that will eventually kill your transistor. The circuits works fine without, but it might die faster than if it had protection.

    Kind regards

  4. Thanks, I meant I have the diode in place and know it is to protect the transistor but what is the small capacitor for? isn’t the diode enough on its own to protect the transistor.

    I have the diode but not the capacitor.



  5. Hello, I have made a similar driver to the one shown above but with MJ15003 transistor and a P600M diode, schematic from (By Dr Kilovolt) http://4hv.org/e107_plugins/forum/forum_viewtopic.php?37658
    the 25V capacitor doesn’t seem to charge and therefore I get not HV OUT. i then tested the transistor with a different circuit, it worked fine….any help?
    thanks v. much

    PS. you can checkout the video of the circuit in action in first chat by Dr Kilvolt

  6. I have built your driver as closely as I could with parts from RadioShack but I cant get any spark. I had to “make” my own resistors to get the values you have listed. For the 27R 5W I used 2 10ohm 10W resistors and an 8ohm ‘Non-inductive’ 20W resistor in series. Then for the 500R 2W I used 2 1Kohm 1 watt resistors in parallel. For the main cap I used a 4700uF Cap. For the .27uF cap I used 3 .1uF Caps in parallel. Then for the diode I used a BYV29FX-600. As for the wire windings I used 20AWG hookup wire. The only things that I can think would make this not work would be the rubber wire coating is too thick or that the direction of winding matters.

    Thanks for any help!

  7. Thank you for you quick response! I swapped the feedback coil connections and I don’t get anything. I think that my 2n3055 may be dead. When I do a diode check every possible way I get 0V except for neg to collector and pos to base I get .5V.

  8. Hey Austin

    As you say yourself, the direction of the winding, or as its called the phasing of the feedback coil could be opposit of the primary coil and thus be driving it 180 degrees out of phase, try to switch the feedback connections around.

    Kind regards

  9. Hello, I believe your schematic is wrong: shouldn’t the words locations Emitter and collector be reversed? ha? Waiting for your reply- Regards Karl

  10. Sarthak Singh

    what if we use more turns for primary and secondary coil like 29 for primary and 11 for secondary

  11. Hi Sarthak Singh

    More primary turns would give a smaller Volt/turn ratio and the output from the secondary side would be smaller, more turns are however needed if you want to run at a higher input voltage.

    More feedback turns would increase the drive voltage to the transistor, be careful not to damage your transistor by adding too many turns.

    Kind regards

  12. Hey Mads

    I built this driver using an MJE13009 and a 0.22µF capacitor across it. I’m using this flyback transformer http://www.hrdiemen.com/reparation/flyback/model/8891 from a TV, and I’m powering the circuit from an ATX power supply. I’m only using a 1000µF filter cap.

    I’ve tried various winding combinations, but the arcs strike at around 5mm and stretch to around 10mm at most. It pulls between 1A and 2A from the power supply.

    Is there anything I could tune in this circuit or should I instead just go ahead to the next level and build a Mazzilli driver? 🙂

  13. Hey NT

    I also tried with a MJE13009 transistor, many years ago, but if I remember correct I had the same issues, I think it has to do with the internal construction of the MJE13009 that have a much higher voltage rating than the 2N3055 and it has been seen they are harder to drive in self resonant circuits without a designated driver.

    What input voltage have you used? Is the transistor heating up?

    You could try to add a few more feedback windings and not have more than 8 primary windings to get a higher current running in the primary to get a bigger output.

    Have you read the other comments on this page, others have also tried their luck with similar transistors.

    Kind regards

  14. Okay, I tried more winding combinations, 4–8 primary turns and all the way up to 14 feedback turns. The sweet spot is around 5 primary turns and 8 feedback turns, where the arc is a couple of millimeters longer than previously (but nowhere near the 20mm you got with the 2N3055). The circuit now pulls around 3A at 12V.

    I’ve mounted the transistor on a 5x5cm heatsink from an ancient power supply, and it gets too hot to touch within minutes. Do you have any idea how to mount TO-220 and TO-3P devices on CPU heatsinks?

  15. I finally bothered to set up a couple of server power supplies in series to try this circuit at 24V. The new sweet spot seems to be 10 primary turns and 4 feedback turns. Arcs strike at 6mm and stretch up to 20mm, and they look slightly “flamey” (like the arcs from the Mazzilli driver, but these are not nearly that fat). The transistor heats up to scorching temperatures within minutes despite the fan.

    I’m going to try the Mazzilli driver next. Actually I have four of those server power supplies for some 48V madness…

  16. Hey ntoskrnl

    This circuit is only meant for low power continues run, as you have experienced, taking this up in power will also dissipate a lot of power in switching losses due to the very inefficient self-resonant driving of the MOSFET.

    The ZVS driver will love you for a stable 48VDC supply, but remember to use 200V rated MOSFETs, their internal gate structure works the best with that driver scheme and 200V gives you enough headroom to use 48VDC supply. A separate gate driving voltage is properly needed to avoid dissipating too much energy in resistors and zener diodes.

    Kind regards

  17. I just built the ZVS driver (pretty much identical to yours). It works great and no parts get hot.

    Unfortunately it turns out that some sort of protection in the power supplies is kicking in as they occasionally shut down, typically when the arc breaks. I wonder what protection this could be and how to work around it. Perhaps a huge capacitor? Or an MOV in case it’s the over-voltage protection?

    Also, I think my flyback is done for… The high voltage negative pin started arcing to the one next to it.

  18. Hey ntoskrnl

    Good that you have it working 🙂

    It sounds like a over voltage protection, when you suddenly remove the heavy load the voltage rises faster than the supply can regulate and it shuts itself down. Perhaps some added capacitance on the output of the power supply could even the spikes out.

    You flyback transformer is properly fine, arcing between the bottom pins is normal as we tend to over drive these small transformers by a lot. What you can do is provide some isolation between the pins with pieces of plastic and super glue. You could also varnish it or if possible, mold it all shut in epoxy.

    Kind regards

  19. I cut off the problematic pin and put a blob of hot-melt glue on it, but it still arcs. Seems like the glue didn’t form an airtight seal with the epoxy or something. I wonder what material would be more suitable for isolation?

    I’m concerned that the flyback is fried because previously it only sparked single sparks very occasionally. Now the arc between the pins is continuous, thick and white, which renders the thing unusable. Why would it change all of a sudden unless it had somehow failed internally?

    I tried measuring but I didn’t find any continuity between the problematic pin and either end of the high voltage circuit.

  20. You best bet for isolation is to use super glue, it makes strong and deep joints in the existing plastic or epoxy.

    Maybe it is time to find another flyback transformer if the arcing is so severe 🙂

    If you have any additional questions about the ZVS driver, please ask them in that article and not this for the 2n3055 driver.

  21. I’m having a problem with ATX PSU. I attached 10w 10ohm resistor in 5v line, and DC devices are working fine. However the PSU turns off as soon as I attach the flyback driver. Please send me some reference on your PSU.

  22. Hey Sunny

    It sounds like your PSU is shutting down due to overcurrent. I did nothing special to keep my PSU running, not even a load on the 5V line. I only used a jumper to turn it on in the ATX plug.

    Kind regards

  23. I have a question: will the capacitors prevent the 2n3055 to burn? Because I built a driver (I think that it is like your schematic but without capacitors) that works perfect at 12V, even for long periods of time like 15 minutes, but I need more voltage so when I try with more than 12V, for example 15 or 19, the transistor burns instantly, I don’t know exactly why.

    My transistor is mounted on a big and expensive heat sink.

  24. Hi Ram

    This is a low current high voltage power supply, what kind of lamp do you want to supply from such a high voltage? Gas filled tubes like neon could be a possibility, but if you are thinking of something like high pressure metal gas lamps, this power supply could maybe be used as the arc starter, but a high current supply at lower voltage is needed to run the lamp.

    Kind regards

  25. You could use regular transformer ratio calculations to estimate the output voltage, but this does not account for resonant rise or resistances.

    The best way is to use a defined set of spheres, knowing the air pressure and humidity and measure the spark length between them, this way it properly the easiest and most accurate way for amateurs to measure high voltage with out expensive equipment.

  26. Hi, I have some issues with this circuit (or any other circuit) not working with my transformer.
    I have 2 TIP35C transistors and some 2N3055s, both of which seem to be working with maybe only minor damages. My power sources include a dying 9v battery, a Li ion, and a high current laptop charger (18v, 4.7A). All of which i test out on every circuit variation.
    I’ve wound many new primary coils with different amounts of turns, same and opposite polarities, and the most i was able to get was an extremely small amount of oscillation with maybe 500 volts output (with metal-melting heat on the transistor). I’m using a homemade transformer, but I’ve multimetered it to where im positive the coil and coupling are both good. Is it the transistors or what? Nothing’s working! 🙁

  27. Hi William

    What kind of transformer are you trying to drive? Is it a flyback? Is it a iron core? Attach a picture of it if you are not sure.

    Kind regards

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