Kaizer SSTC I


This is my first solid state Tesla coil, so I went with a sturdy and proven schematic made by Steve Ward. A lot of other coilers have replicated this circuit with great success and therefore it is easy to find information how it works and how to troubleshoot it.



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



One of the differences from the original circuit is that I use 230VAC input instead of 115VAC. So capacitors and MOSFETs have a higher voltage rating.

The interrupter will be changed to go down to a very low break rate.



Bridge 2x IRFP460s MOSFETs in a half bridge configuration
Bridge supply 0 – 230VAC from a variac, 8A rectifier bridge and 330uF smoothing capacitor0 – 325VDC on the bridge.
Primary coil 115 mm diameter, 1.78 mm diameter isolated copper wire, 10 windings.
Secondary coil 110 mm diameter, 275 mm long, 1000 windings, 0.25 mm enamelled copper wire.
Resonant frequency Self tuning at around 250 kHz.
Topload 100 mm small diameter, 240 mm large diameter, toroid.
Input power Continues Wave mode: 1000 W at 230VAC input voltage.
Spark length up to 250 mm long sparks running interrupted.





22nd January 2009

I began the construction of the half bridge circuit in a small plastic box, the heat sinks are a Pentium II heat sink cut in half. The bridge is made from copper wire size 2.5mm² / AWG14.

The bridge is made from a 8A bridge rectifier with 330uF 450V smoothing capacitor, two IRFP460 MOSFETs with MUR1560 diodes, two 0.68 uF 400VAC film capacitors for the voltage splitter and 10R gate resistors.

The driver circuit is made on vero board with a external 12VDC power supply.



23rd January 2009

When I first tried to run the driver circuit separately to test the driver before connecting it to the MOSFETs, it only resulted in the MOSFET driver chips (UCC37321/UCC37322) catching fire and burning up like a small volcano. This did of course upset me when it happened once more when I had changed the chips. This led me to seek help and I learned that running the driver chips unloaded, without a MOSFET or GDT connected to the outputs, the chips will oscillate into oblivion and burn them self down.

With the complete circuit put together it all worked except the primary coil was phased wrong, but it was no problem since I used banana plugs for the primary connections.

I ran the coil as CW (Continues Wave, non interrupted so its switching at its resonant frequency) to stress it to its maximum, which also did result in failures at 230VAC in, drawing around 4 to 5A.

The secondary coil was grounded to the mains ground in my house, but by accident I were using a plug without a earth connection in, so the secondary earth was arcing to the phase and neutral in my power bar. Pushing around 1 kW into this rather small circuit with passive cooling became enough combined with HF noise on the phase and neutral and one of the MOSFETs exploded violently and the other died silently. Here I discovered my design did not make it easy to change the MOSFETs, a important thing to consider in future constructions.

For the next couple of days I could not get the coil to work again. Everything in the driver circuit was changed and measured with a oscilloscope without finding anything out of order. It was first when I by accident measured short circuit connections with a DMM that I discovered one of the secondary windings on the GDT was not connected to the MOSFET, it was because the gate resistor was destroyed from the short circuit of the MOSFETs. Changing the 10R resistor made the whole thing work like a charm again.



Here are some pictures from the first light, input power is from 30VAC to 230VAC at up to 5A.


Audio modulation

I use a audio modulator made by the user Reaching (Martin Ebbefeld) from 4hv.org.

For sound input I use a cheap children’s keyboard from a toy store, its far from perfect for the job, especially because its waveform is highly distorted and its not clean tones but seems to involve a lot of modulation inside it to simulate different instruments. But its cheap and expendable.

Watch the film and look at the schematics for more about the audio modulation.



Building this clone of Steve Wards SSTC5 was a great introduction to solid state Tesla coils, I now have a understanding of how it works from interrupter to driver to bridge.

Further projects with this circuit will be a complete rebuild with audio modulator and a full bridge of MOSFETs, this will be a separate project.



In thew following videos, the SSTC I is playing music from the interrupter shown in schematic for the SSTC II.

31 Responses to Kaizer SSTC I

  1. Daniel R says:

    I wanted to ask you what you think of Steves DRSSTC schematic with the flip flop circuit, so that the interrupter never shuts off the UCC’s. I came up with a way to use another 555 with the feed back as part of its timing instead of the 74HC109.

    does it actually need a “flip-flop” device? because some times the output wont line up and will send out a very short on time


  2. Mads Barnkob says:

    Hey Daniel

    I am only working with his universal driver as Steve called his own older designs for obsolete compared to the new driver.

  3. marshal says:

    I am wondering, what is c4 for in the schematic, is it a dc blocking cap or it it used for something else?

  4. Mads Barnkob says:

    Hey Marshal

    Its a DC blocking capacitor that should stop the heavy DC currents from flowing at the rather low DC voltages that the GDT sees. If you have problems with lower values, try using a larger, up to some uF and with a 100nF in parallel, this should take care of resonance in the GDT primary drive circuit.

  5. Alex says:

    Hi Mads, I am looking to start experimenting with SSTC’s and was wondering if I could use a 36v supply for the half-bridge if I lowered the primary coil turns and perhaps made the secondary coil a bit smaller. I understand that I will get a much lower spark output from the secondary coil but I don’t mind too much as this would be my first time making a SSTC.

    This 36v supply is 3 12v 7ah lead acid battery’s and I don’t need long runs from the SSTC whilst experimenting so I can afford to allow for a higher current draw in return for using a lower voltage.

    Just wondering if that would work? And would I need to adjust anything else such as C8 and C9 in order to allow for more current to be drawn?


  6. Mads Barnkob says:

    Hey Alex

    I have limited experience with low voltage SSTCs as I have no problem using mains supply, as an electrician I am comfortable with it.

    You could omit the capacitors and make the half bridge as this http://webpages.charter.net/dawill/tmoranwms/Elec_IndBridge.gif

    You should properly look for some 100V higher current rating MOSFETs

    Kind regards

  7. Alex says:

    Thanks for that Mads.

    About using mains power, I am waiting until I can find/source a variac before I start using mains power with my projects. I am fine using mains for small low voltage step down transformers or items that have been commercially designed and tested for mains use, I am just slightly wary of connecting homemade circuits to it without a variac.

    Plus I have my parents who don’t like the idea of me doing any electronics, seriously if a light-bulb blows or something happens they always blame me and my electronics! Talk about ignorance right.

    Anyway enough ranting and on to finding a decent piece of tubing to wind my secondary coil onto.


  8. Benjamin says:

    Hello, I want to ask if it is possible to run this design without a variac?
    The question is if it is possible to run this SSTC directly of the mains 230 VAC with a bulb as current limiting for charging the capacitor in the start, and after the capasitor is charged, just bypas the bulb and run the tesla coil directly from mains suply, without using a variac?

  9. Mads Barnkob says:

    Hi Benjamin

    It is possible to run it as you say, but be aware that you have to design it carefully to run at full voltage from day one, doing first light and testing and tweaking a variac will save you some headaches.

    If you don’t have a variac, maybe use a 230v to 48v transformer or something in that manner, for testing, else you just risk a BOOM at full voltage and will have to rebuild and fault find on burned tracks.

    Kind regards

  10. Alex says:

    Would the gate drive UCC chip stage work at lower frequency’s of around 50khz (for driving a flyback transformer)? Or would I need to alter the value of the DC blocking capacitor to something larger, as most schematics I have seen that don’t use the UCC chips always use 1uF for this cap.

    Since the chip I am using has out-of-phase outputs (sg3525) I plan on using two of the same chips, would that still work?

    I am basically trying to solve the problem of heating mosfets on my half-bridge since the heatsink for mine gets too hot to touch after a few minutes.


  11. Mads Barnkob says:

    Hey Alex

    The DC blocking capacitor I use here is on the edge of being too small, but its okay for 300kHz. At 50kHz you should properly use around 2uF. We want the capacitor to act as almost a short at our frequency, so if you can keep Xc under 2 Ohm, it should be good enough. (math: Xc = 1/(2*pi*f*C) )

    If you want to go further into detail, look at the series RLC resonant frequency of the capacitor, your working frequency must be lower than the capacitors self resonance, else it will start acting like an inductor.

    When using inverted outputs from your PWM ic, there is no problem with using two of the same UCC drivers.

    Which size gate resistors do you use for your MOSFETs?
    How large is your heat sink?
    How are you driving them in this setup?

    Kind regards

  12. Alex says:

    Hi Mads, I gave the chips a try using a 1uF cap and the result was the chips got warm and the MOSFET’s still got hot. a strange thing to note is that as I increased the frequency past around 50khz the primary coil voltage of the GDT would drop, all the way down to 7vac at 85khz.

    I am driving them in a half-bridge configuration, 36v on the bridge and 15v for the logic/gate drive. I am using 22 ohm gate resistors (is that too large for 50khz?) and IRFP260’s, the heatsink is out of an old ATX supply and it has two smaller heatsinks screwed onto it via the spare mounting holes.

    My gate drive transformer materiel is type 77 from eastern voltage research and I have wound the primary and secondary’s using tri-filer windings to reduce leakage inductance. With the MOSFET’s connected the GDT only seems to draw around 40-60mA max (depends on frequency).

    I am trying to get it working with a flyback transformer first before I go ahead and attempt to make a SSTC, but can’t seem to make it work without the heating problems.

    Did any of your half-bridge heatsinks get hot at all after just minutes?



  13. Mads Barnkob says:

    Hi Alex

    A lot of my stuff heats up quickly if I run it on the edge of what I designed it for, your heat sink does however should relatively small as nothing good usually comes out of a ATX PSU.

    Try with 10 or 5 Ohm gate resistors and see if it helps on the MOSFET heating, UCCs do get warm, its a big job done from a little package, true to fix a small heat sink on them if you like, or parallel two of them, put on top of each other.

    Kind regards

  14. Alex says:

    Thanks Mads, I will look around for a larger sink. The one I have doesn’t have big fins and the PSU had a fan to help with cooling (it was only a 250w PSU too) if I recall.

    I will give some 10 ohm resistors a try too. One thing I noticed is that one of the chip outputs gives out .2v less than the other one (between output and ground). Not sure why or what affect that could have on the operation of the circuit, I did try a spare chip I have and that was the same. The only thing I can think of is the 0.1uF caps between pins 1, 9 and ground and 2, 16 and ground, one cap is slightly larger by 1nF. Could that be enough to upset the “balance”? They are film caps too.

    Can’t wait until I get my scope so I can actually see what is going on ( : , Just need to decide between Rigol DS1052E or Owon Sds7102.



  15. Mads Barnkob says:

    Hey Alex

    Those are some terrible heat sinks, cost minimized.

    Do you have capacitors across the supply for UCCs? Right next to the IC. 1nF difference should not matter.

    I just quickly looked at the specifications, I have a Rigol DS1052E and I must say that the Owon looks like a better choice.

    Kind regards

  16. Alex says:

    Well I tried using 10 ohm gate resistors and it made no difference, still heating up within minutes (this is with-out audio modulation too). I also tried a larger heatsink but it still got hot.

    Yes the UCC’s have decoupling capacitors, .1uF right next to the pins. I’m stumped as to what is causing this. I put my multimeter set to measure AC volts across the drain and source pins of the lower MOSFET and it read 0.876vac as the voltage drop when the bridge had 12v on it drawing around 1.2 amps. Forgot to measure it with 36v though but the current draw is usually 3-5 amps @ 36v. I know my meter is not an accurate way to measure this but I think it gives some sort of indication.

    I guess the only thing to do now is scope the circuit and see what that shows : / . I might have to pay import duty tax on the thing if customs get their hands on it, which is annoying.


  17. 田仲 says:

    Of circuit diagram, 1μF What is 0,1 μF?

  18. タナカショウ says:

    How long can this sstc move?

  19. タナカ says:

    How much time can this sstc move?

  20. Alex says:

    Hi Mads, just dropping by your site again to let you know that I went for the Rigol scope in the end and so far it has been an excellent choice. I nearly went for the Owon but it was about £150 more expensive, so I decided since I am only using it for hobby use the Rigol would be more than I will ever need.

    I am just wondering what you use when scoping primary/high drain-source waveforms. Do you use a 100x probe or will a few turns of wire around a high current conductor connected to a probe? Most of my circuits right now are powered by my bank of lead acid battery’s so the scope is the only thing referenced to mains earth.

    Any pointers here would be appreciated, Don’t want to blow this scope up just yet!


  21. Mads Barnkob says:

    Hey Alex

    Excellent choice for a hobby scope 🙂

    I use current monitors from Pearson, they are expensive, but worth it all, you can some times find them cheap on ebay. I got a 101 and 110 model.

    I also got a tektronix 1000 Volt differential probe, then there is no worries about grounding the circuit through your scope. If you can not afford this, you need to have your circuit galvanic isolated from mains and earth the negative rail of the circuit. So there is a prefered grounding compared to currents wanting to flow through your scope probes.

    Kind regards

  22. Photonned86 says:

    Very nice coil! Im curious, did you notice heavier kickback to the fets while pulling an arc to ground? Mine run completely cool at 110 mains until I start drawing arcs, and then this start blowing up 🙁

  23. Mads Barnkob says:

    Hey Photonned86

    I have not had any problems like that. It could be that it is just a heavier load on the MOSFETs when you have a direct strike to ground and they simply blow up from excessive current.

    Kind regards

  24. Photonned86 says:

    Thank you very much Mads! Is it possible then to saturate a core on the primary to prevent such things? Before I go doing random things I would much rather talk to a professional ;D


  25. Theo says:

    I built this design but I made the secondary 15 inches tall instead of the recommended height on the schematic. Could this extra height be decreasing the spark length?

  26. Mads Barnkob says:

    Hey Theo

    The higher Q factor of a bigger secondary coil could result in a worse power transfer, but since this is a half-bridge driven coil it is not a perfect choice for long sparks. How long sparks did you get?

    Kind regards

  27. Jose Luis Rubalcava says:

    Hi Mads!
    You are made an excellent work to share it, thank you. We are builting SSTC I and do not know, where is antena or where does it plug in?

    could it connect with the stick that touches the spark?

    thanks for read this message and regardS


  28. Mads Barnkob says:

    Hi Jose Luis Rubalcava

    Look at the schematic, the antenna is shown just after the input rectifier and capacitor. The antenna is capacitively coupled to the input of the hex schmitt invter IC, protected by two 1N60 diodes.

    Do not make sparks to the antenna!

    Do not place the antenna so close to the secondary coil that there begins to form corona/sparks from the antenna.

    Place antenna about half way up of secondary coil, and only as close as to make the coil run stable, this will change depending on power level and spark length. Long sparks can make it become unstable as the load from the spark pulls the resonant frequency down a lot.

    Kind regards

  29. Asdfire says:

    Hello, I have some questions about the circuit , my gate drivers when connected to only the gdt get really hot after just a few seconds, I checked with and oscilloscope and they give a wave but if I leave them running for more than a few seconds they get damaged. I’m supplying them with 12V.

  30. Mads Barnkob says:

    Hi Asdfire

    The UCC drivers can not be run open loop, without a load connected. So you need to either have some load resistors on the secondary side of the GDT or connect it to the gates of the MOSFETs.

    When the UCC drivers run unloaded they can start oscillating and will heat up very fast, as you also described, this will eventually damage them.

    Please join our forum at http://www.highvoltageforum.net and make a thread about your Tesla coil build 🙂

    Kind regards

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