The idea was to build a very small and compact Tesla coil as a gift for my mother that works in various science classes for the lower grades in public school.

This driver circuit is very similar to the one used in Kaizer SSTC I. This time I have made a PCB containing both driver circuit and bridge.


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


I knew this would get claustrophobic with so little space for a complete interrupter, driver and bridge.

Using the enclosure as the heat sink is the reason why a low break rate is chosen, to avoid excessive heating.


Bridge2x IRFP460 MOSFETs in a half bridge configuration
Bridge supply230VAC directly from the wall, 4A rectifier bridge and 330uF smoothing capacitor
Primary coilRev 1: 55 mm diameter, 1.38 mm diameter isolated copper wire, 10 windings.Rev 2: 80 mm diameter, 1.38 mm diameter isolated copper wire, 10 windings.
Secondary coilRev 1: 50 mm diameter, 200 mm long, 1430 windings, 0.127 mm enamelled copper wire.Rev 2: 75 mm diameter, 165 mm long, 1500 windings, 0.1 mm enamelled copper wire.
Resonant frequencyRev 1: Self tuning at around 470kHz.Rev 2: Self tuning at around 180 kHz.
ToploadRev 1: Made of two bottoms from beer cans, 65mm diameter and 30mm in height.Rev 2: 45 x 152 mm turned aluminium toroid.
Input powerInterrupted mode: ?W at 230VAC input voltage.
Spark lengthRev 1: up to 140 mm long sparks.Rev 2: up to 250 mm long sparks.

 SSTC Schematic and PCB files

PCB file for ExpressPCB


21st July 2009

I designed a compact single sided PCB that contains both driver and bridge section on a mere 65 x 75mm board. Here is newly etched board, traces are a bit shaky as I have drawn them all by hand.

The MOSFETs uses the enclosure as a heat sink, I sanded down the paint for metal contact and use pads to isolate between MOSFETs and enclosure.

BPS is kept low, but can be varied from 4 to 20 BPS, to avoid excessive heating as the enclosure is not an optimal heat sink.

In the bottom of the following picture you can see the bridge rectifier mounted to the enclosure and the input filter for 230VAC in. The red wires lead to the 330uF/400V smoothing capacitor and the 100nF/1600V Rifa capacitor is the DC blocking capacitor in the primary circuit.

The coil is connected directly to 230VAC without any kind of voltage regulation and also requires a external 12VDC supply for the driver.

Antenna and primary coil connections are temporary solutions for the sake of demonstrating the Tesla coil in working order. A fold out antenna from a small radio or such will be added later. Some kind of support with banana jacks with a secondary and primary coil mounted on will be added, to avoid wrong phasing of the primary coil.

Here the complete setup is size compared to a 330ml beer can

 SSTC Sparks

Here is one of the more spectacular spark pictures I have taken, in my eyes it looks like a demon waving its arms over the head which also have a distinct face with glowing eyes and a open mouth, or maybe I am just seeing things from inhaling too much ozone 😀

24th July 2009

I borrowed a expensive macro lens for my Canon 350D camera and took some pictures with great details of the sparks, very sharp pictures!

 Revision 2

1st August 2009

Doing a short demonstration I adjusted the antenna with my hand while the coil was running, this resulted in unstable oscillations and the bridge was short circuited. I am now replacing the destroyed MOSFETs and here I can feel the disadvantage of servicing on a compact design.

A new secondary coil is in the making, it is wider, shorter and have half the resonant frequency of the first. It will be fitted nicely on a piece of acrylic for a complete look.

19th August 2009

The new secondary is finished, it took me about 8 days to do the winding as it is very intensive to wind with such a thin wire. Keeping the wire tight, windings close to each other, not pulling the wire too hard from the spool, watch for jams and overlaps and it all have to be done with a bright light very close to get a good view.

It uses the topload from my VTTC I, a 45 x 152 mm aluminium toroid, with this it have a new resonant frequency around 180 kHz.

Top of secondary was filled with epoxy to insulate the brass bolt from the inside of the secondary and the bottom earth connection is fastened with a nylon bolt.

It is all fitted onto a piece of acrylic with additional protection around the primary connections so it no longer possible to touch any conducting part of the primary circuit.

 SSTC 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.


I am very satisfied with the final result, that I got to fit everything and use the enclosure as a heat sink turned out real good. Heating is not a problem with run times at about 2-3 minutes which is also the durations its been built to be demonstrated for.

Enclosure dimensions are 125W x 80D x 50H mm.

Revision 2 looks even better, performs better but was also a lot of work to wind the new secondary with such a thin wire.


Revision 1

Revision 2

101 thoughts on “Kaizer SSTC III”

  1. Please help. I need a little info. I cant get this coil to fire without touching and holding the antenna first.
    I used your schematic to a tee. I also tried switching the antenna coupling diodes to 5 v zeners, Still no luck.

    Thanks again. CJ

  2. Have you tried moving the antenna closer to the secondary coil?

    My antenna is often within 6 – 8 cm from the coil and will occasionally have a bit of corona at the end

  3. I will try to build 1
    can I add audio modulation circuit to this design? or will it cause a problem?

    thanks in advance

    sorry for my English level

  4. Hello shahar

    If you look at the schematics for the SSTC II, you can see how it was audio modulated. You can use the exactly same design for this smaller Tesla coil.

    Kind regards

  5. Hello,
    I’m very interesting in your project, so I decided to build it. I have a question to you, namely how many turns is on the GDT transformer?

    Thank you very much.

  6. hello again
    I have hard time finding 75m”m tube for the secondary coil
    if i use 70m”m tube instead what are the constants i should keep?(secondary coil frequency, turns ratio, diameters ratio etc)

    Thanks in advance

  7. Hey Shahar

    There are no constants in designing a Tesla coil, but there are some general rules of thumb to stay within. There are many guides about this elsewhere, so I will not get into details.

    You can without any problem use a 70 mm tube instead of 75 mm, if you want to keep the same frequency, wind some more windings on it 🙂

    Kind regards

  8. hello again
    sorry for having too many questions but i have few more:
    -can i plug it to the house grounding or should i try to find another option?
    (i am at 3rd floor and the water pipes are mostly insulated so only the water will be used as conductor if i plug it to them)

    -i done making 1500 laps on the coil and it is shorter than it should have been
    after a good look i saw there was some overlaps once a while. is it good enough or should i start over and work slower so there will be no overlaps at all or only few of them?

    -can i plug the audio trough optocopler to protect the player or will it add more noise or something?

    and last one:
    -i tried to plug the main circuit to power to test it and the second i plug it the transistors burn and short circuited can it be caused by plunging it before i turned on the driver so they was off for too long? and if not do u got another idea that can cause it? (my transistors rated for 16amp and 500V)

    thank you in advance (again….)

  9. i found that i excellently switched the source and drain of the mosfets so that’s probably the reason they blown
    so the last question is irrelevant

  10. Hey Shahar

    For a small Tesla coil you could use the house grounding, just not use any or make a artificial ground plane beneath the coil out of aluminium paper or other metal sheet.

    Over lapping windings are not good because they break the even surface of the coil and you could get problems with corona forming at these points. But in a small Tesla coil you should not worry about this and if you see it as a big problem, add more varnish to insulate the spots even more.

    You could use a opto coupler circuit to protect your audio source, I should also have used one on all my projects as I killed a little iPod shuffle with a flyback driver 🙂

    See if you get hold of a variac or a step down transformer so you can test your circuits at lower than full power, there are often small problems that you can discover at lower voltage and its hard to find faults after it all went BOOM!

    Kind regards

  11. thank you for your help
    variac is much over my budget but i will try to test it with step down transformer
    about what voltage should i test it on?

    thank you again in advance

  12. Hey shahar

    At about 30-50 Volt AC in, you should be able to lit up a flourescent light bulb or tube. At 100 Volt AC in you should begin to see break out and sparks.

    Kind regards

  13. i add a 3.5A fuse to protect the rectifier and it burned quite fast
    should it use mire than 3.5A with the 4A rectifier?
    and i tried to use old step sown i had to test it but it burned aswell. so ill try to get better one.
    and is there any way i can test the control circuit with out the main circuit?(i tried but got no output probably because there was nothing for the antenna to receive)

  14. can i use .47uF 400v capacitor instead of 150nF in the half bridge? if not what changes should i make, also in the driver section i’m using .47uF instead of the .1uF(C4) near the GDT.

  15. Hey Jass (and zak)

    I used 150nF because of the limited space in the small box. If you calculate the reactance of the capacitor at the frequency you run the coil at, you might find that several, maybe 3-5uF gives a much lower resistance to the primary current.

    The AC filtering capacitor C4 in series with the GDT can be sized between 0.1uF to 1uF at the power levels and frequency used for driving a Tesla coil bridge.

    Kind regards

  16. I made all the circuit part exactly as your, the secondary is 3.5inch in diameter and 12inch long, the power supply is using a SMPS line filter connected directly from mains(220v AC) to half bridge.
    The problem is the MOSFETs get hot even after just 3 sec of running.
    Is the input voltage too high? if so is there a more powerful MOSFET i could use? I need
    to run it for atleast 15 min continuous.
    Thanks for help

  17. Hey jass

    Are you saying there is no rectifiers in between the line filter and half bridge? You need to supply it with either half- or full-wave rectified DC.

    Kind regards

  18. Of course there is rectification and the tesla coils works but the MOSFET gets hot pretty fast. I’ve put 10 turns on the primary.

  19. Hi jass

    Could you upload some pictures of your tesla coil, it would make it easier to help you, there could be a million causes to why the MOSFETs heat up. You can now upload attachments directly in your comment here on the site.

    Which value gate resistor are you using? It could be that if it is too large the MOSFETs switches too slow, spend too much time in the linear region where it dissipates a lot of energy.

    Kind regards

  20. Hey jass

    You tried to upload pictures that were bigger than 2MB, then it will fail and not show up.

    I took a look at your pictures and two things come to mind

    1) Do you know what kind of ferrite core you have used for the GDT? Is it a high permability ferrite core or is it some powdered iron core you pulled out of a power supply? A powdered iron core will not work at these high frequencies and thus it will only drive your MOSFETs in the linear region due to saturation of the core, not enough current can pass to the gates.

    2) It looks like your antenna is used as strike rail towards the wire from the topload, you should move the antenna so far away that there is not even corona showing on top of it at full input voltage. You just risk damaging the feedback circuit. You could also make a little distance between the antenna wire and the primary leads.

    Kind regards

  21. 1)The ferrite core was taken from a SMPS(computer power supply) and 22AWG wire was wound on it by me.
    2)The output from the coil is feeble like 2-3cm so i kept the antenna near.

    I’ll look for a better ferrite core.
    also does the gate resistor affect the bridge, because i’ve used a 2W instead of 1/4W?
    Thank you

  22. Also I’ve a ferrite core taken from a flyback(two ‘C’ shaped ones) could i use it as my GDT? if so could you please explain how?

  23. Hey jass

    The flyback core will be much better, despite it is much bigger than needed and not optimal at all, but it will however work. Put the two cores together so it forms a “circle” and wind your GDT as you normally would, if you have 15 turns, spread them out so they cover all the window area all the way around the “circle”.

    The core you found in a SMPS is most likely a iron powder core used as output inductor, they are absolutely no good as GDT.

    4R7 2W is good, when I have used 1/4W it is my experience that the gate resistor also blow up if you blow up the MOSFETs.

    Kind regards

  24. Sorry for the inconvenience, but i’ve got one more question.
    i’ve got a ferrite transformer(i’ve uploaded photos), could i use that as my GDT if so which meathod is workable? or is it better to stick with the flyback core?
    On the transformer these are written “8250 GA6” is its permeability(8250)?
    Thank you

  25. Hi jass

    Just use the transformer core like if it was a normal transformer, do a trifiliar winding on the plastic bobbin around the centre leg. Like on the edited picture I attached.

    I think those numbers and letters on the plastic bobbin is just the model number of the plastic bobbin and has nothing to do with the core materiel.

    Kind regards

  26. hi, any way i can get the pcb circuit trace for this build? the gerber or eagle files?

  27. Hi,
    Thanks for the PCB file. I have one question, on the PCB layout i didn’t find the bridge rectifier. Is it not needed? or is it being run off the board with the atx line filter? I see it in the schematic is why I’m asking.

  28. Hey Kishan Jhaveri

    The bridge rectifier was mounted directly after the mains input socket, if you look close at the pictures you can see it is mounted with a screw into the side of the box, just behind the line filter. It is needed with either half wave or full rectification, you can not feed this circuit AC.

    Kind regards

  29. Hello Mads,

    I was trying to find a hint in your posts and in the comments how the variac should be rated, but I could not find any specifications. You have used a 4A rectifier (or 8A in earlier versions), so this means 1kW (2kW) for the variac? Or could it be much smaller rated?

    You know, the higher wattage a variac has, the more it costs 🙂

    A reply would be much appreciated!

  30. Hello Matthias

    With this little coil you could do fine with a 4A variac, the variac you can see I use in the video is a 10A.

    Do not buy a completely new, there are plenty to be found used from old work shops, radio amateurs etc.

    Kind regards

  31. Hey Teemu

    I have not measured the primary current in a SSTC yet, but you can calculate it using Ohms law. Divide the DC bus voltage with the reactance of the primary coil. The result should be your primary peak current.

    Kind regards

  32. what should the output be after c4? i dont seem to be triggering my mosfet gates. when i power up nothing happens.

    red dots are sites in question

  33. Hi Prabodh

    Adjust your antenna, maybe more it closer.

    Across the primary of the GDT you should see a square wave and on each of the secondary windings it should be the same signal, just inverted for one of the MOSFETs.

    Be sure to have the GDT connected to the MOSFET gates when testing, you need a load on the GDT to see the proper wave forms.

    Kind regards

  34. Hey,

    I built the SSTC exactly like the schematic, but nothing works. If I invert the UCCs, putting the 37322 in the place of 37321 and 37321 in the place of 37322 it works, but only in CW. What can I do to fix it?


  35. Hi Athos

    By changing the MOSFET driver ICs around you are changing the phasing of driving the bridge and thus the secondary coil. Normally you just change the phasing of the primary coil to get it to oscillate in phase with the feedback antenna phasing.

    I am not sure what should not make the interrupter work, as it is only a matter of pulling a signal high on the MOSFET driver ICs.

    Kind regards

  36. Saattvik Thourwal

    It is or was a flyback core. Which I broke in half accidentally and wound the trifler coil around it.

  37. Hi Saattvik

    You can use it if you have the other half, you need to complete the magnetic loop in order for enough flux to be a good and working GDT. You can “repair” it with a thin layer of super glue, but that will act as a air gap in the core and limit the performance. But it will work.

    Kind regards

  38. Hi MaxElectron

    You can use 150 nF, but you might experience that the sparks are more like full wave rectified unsmoothed, with a low enough capacitance you will see larger voltage sag.

    You need the ultra fast diodes to bypass the internal slow diode of the MOSFET, to unnecessary losses.

    Kind regards

  39. Hi again Mads! (i commented on your sstc 2)

    I have all the parts fitted together, and just 1 part left to place on the pcb.
    I noticed that there is no space for the r1 (100k resistor that comes right after the variable resistor) on the pcb, so do you place it outside the pcb?
    And why did you decide to change your 555 circuit?

    Have you tried to run it on full bridge? 🙂
    King regards

  40. Hi magnus

    You found an error in my PCB layout 🙂 I added the 100K resistor later to get a even slower maximum BPS of the 555 timer, you can see on one of the pictures that the 100K resistor is soldered directly onto one leg of the potentiometer in the enclosure side.

    I changed the 555 circuit to get 1-10 sparks per second, so I was sure it would not over-heat when only using the enclosure as heat sink.

    It was only my SSTC2 that was a full-bridge.

    Kind regards

  41. Hi Mads!
    I got it working!
    It worked for a couple of seconds, then the mosfets blew up.
    Maybe a bad ferrite core or some signale interferance from the coil?
    I am currently working on a new brige circute, so hopfully i will get it working again.
    You dont supposedly want to share your musical interupter pcb with me? Would save me the truble of making one 🙂
    Thanks for your help 🙂

    Kind regards

  42. Hi Magnus

    Great that you got first light! How did they blow up? Did they actually explode? where the MOSFET came apart, did it just have a crack?, did it spew a hot flame out through a melted hole? or was it just a silent death?

    Ii is my experience that interference will make a coil run unstable, but not explode. It is more likely that you had inadequate gate drive or that the GDT delivers a distorted signal.

    But for the MOSFETs to really explode, corss conduction is needed so that they short out the DC bus and thus the energy in the DC bus capacitor will be burned across the MOSFETs.

    I made the musical interrupter on a veroboard, so I do not have a design to share 🙂

    Kind regards

  43. Hi again 🙂
    One MOSFET came apart, and the other one looked like nothing had happend (it to was not working). More like a small bang, not that loud. The transistors and rest of componets where unharmed.

    My ferrite core is made of N30 grade material, so i dont think the ferrite core is at fault.

    My only idea is that maybe a shorted out somehow, or a unstable signal from the antenna ;(

    I think i will try to make a full bridge circute when i have time 🙂

    Kind regards

  44. Hi Magnus

    Even a unstable antenna signal should be corrected by the hex Schmidt trigger IC to a nice and clean square signal, the GDT protects against cross conduction, so the only thing left could be failing/too low gate drive voltage so that one MOSFET, the one that exploded, conducts a full short circuit current and the one in the linear region just burns up a lot of energy, while it has a higher RDS(on), and will get very warm, but properly not explode like the other did.

    Chances are that they are both damaged, gate resistors might also be damaged, be sure to solder them out and measure them, or just change them out to be sure.

    Kind regards

  45. Hi there again Mads 🙂
    Just cant seem to get it running. I turn it on, and bom, the fuse goes, and the mosfets are destroid. Probably killed 12+ mosfets. Maybe becouse i turn on 220v ac directly? Do you have the pcb file in Eagle format? would love to get the pcb professionally made.

  46. Hi Magnus

    Something is clearly wrong with your coil, it could just be minor tweaks needed for it to handle full input voltage, I really advice on and use it myself, a variac to slowly ramp up the voltage.

    You have no idea what is going on if it just explodes at turn on 🙂

    I do not have the files for eagle, only for pcbexpress, which is too expensive to use, I just use the program because its quick and easy.

    Kind regards

  47. What happens if I increase the capacity from c12 to 10,000uf?
    What is the advantage or disadvantage?

  48. Hi Max

    I only used 330 uF because this coil has such a low break rate of 1 to 50 sparks a second, so that is not enough to drain the capacitor before its recharged from rectified mains.

    If you are planning to run with higher break rate, higher DC bus capacitance is a good idea to avoid voltage sag and the coil could go into working as if it was running on half wave rectified mains. 10000 uF is however much more than this little coil needs, a couple of thousands uF should be enough.

    Besides that, if you have 10000 uF on the DC bus and the MOSFETs fail, it makes for a much bigger, louder and more destructive explosion, so be sure to capture it on video 🙂

    Kind regards

  49. Hi Mads!

    Very nice coil you got there. I built mine according to your description, but now that I put it into a box it has started to do wierd things. It seems like the circuit is running but I don’t get any sparks. When i grab the end of the antenna tough, the coil makes over 30cm sparks to air. No matter how I place the antenna and what lenght I use it won’t start arcing untill it is touched. Whenever I let go it stops again. (it only runs while touched.) I tried connecting the ground of the secondary and logic level ground to earth ground but that made no difference. Any ideas or suggestions?


  50. Hi Mark

    Your body is basically a capacitor that you discharge into the antenna when you touch it, this gives the driving circuit a pulse that can start up the coil.

    So either your feedback via the antenna is too weak, that the leakage through the gate drive to the bridge is not enough for it to pick up.

    Did you change anything in your gate drive, antenna setup?
    Did you ground all unused input pins on the 74HC14 IC?
    What kind of enclosure did you install the circuit in? Could there be some shielding disrupting the antenna feedback?

    Kind regards

  51. Hi again Mads

    I have not changed anything, everything is just as in your schematic.
    The encloser is one of those general white plastic junction boxes for wires, so I do not think that it would make any difference in the feedback.
    I also discovered that the antenna has a tendency to spark towards the middle of the secondary, while no output is visible. And strangely at mid-height on the secondary I do get nice sparks. I discovered this accidentally by putting a screwdriver near the coil while running and it arced through the inslulation of the secondary to the metal screwdriver. After discovering this when I tried to get sparks on top of the coil, it was the same…No sparks.
    So the secondary coil sparks from it’s middle (but not from the top) even if I do not touch the antenna.
    If my body acts as a capacitor, could putting a cap bitween ground and the antenna solve this wierd problem?

    Thanks for the advice

  52. Hi Mark

    It sounds like you have problems with a proper RF ground to the secondary base, try to lay out some sheets of aluminium foil underneath the coil and connect that to your RF ground bar, this will act as a artificial ground plane.

    Putting a capacitor in will not help, what your body does is discharging, once, into the feedback circuit and it starts the oscillation and it can hereafter run itself from the feedback, a permanently installed capacitor would not have that charge available all the time, unless you add a startup oscillator circuit, but this should not be necessary, it should work from antenna feedback alone.

    You just have to go through your circuit once more and look for errors, when something worked and you took it apart and put it together again and it does not work, that is a pretty clear indicator on something not being right 🙂

    Kind regards

  53. Heloo Mads
    I will try to make SSTC and use your shematics.
    Can you tell me if the C11 next to 555 is electrolytic capacitor or film capacitors?
    On jour PCB photo I soo electrolytic. I am wrong?

  54. Hi Mato
    Yes, C11 is a electrolytic capacitor, it is a part of the timing circuit and does not need to be a film capacitor.

    Kind regards

  55. Daniyal Hussain

    I’m having trouble in making of GDT, i’d tired many experiments but not succeeded. I want to raise a question; is there any possibility that i can used “Schaffner IT 242/243” pulse transformer instead of?

  56. Hi Daniyal Hussain

    No, you can not use a small pulse transformer like that, its only rated for a maximum of 1A peak current.

    A GDT is not hard to make, you need to study more and make sure you do things right.

    Kind regards

  57. is there any possibility of this circuit running in interrupted mode? my UCC gate driver does not work pin 3 ENBL. So I thought about cutting the power to the IC 74hc14.
    That’s just an idea, can this work?

  58. Andrew Villalpando

    Hi, I got a couple of silly question, in the schematic I noticed the lack of the DC blocking capacitor, but, is it totally necessary? I’ve been saw a couple of designs of sstc and I don’t see it in those. So is it an optional cap? And what is the purpose of the two 150nF capacitor on the half bridge, forgive my ignarance. Thanks in advance

  59. Hi Andrew

    The capacitor voltage splitter can be used as a part of the voltage doubler if you want a higher supply voltage. It can also as here just be used for a midpoint and blocking capacitor instead of tying the other end of the primary coil directly to ground.

    If you look up half-bridge with load connected to ground that is the alternative to leave these capacitors out.

    Kind regards

  60. Hi Max

    A control scheme based on turning a 74-series IC on/off is a very bad idea as you completely loose control of which state it is in, you got no idea if its on/off/something inbetween and it will mostly likely damage the IC or MOSFETs/IGBTs due to improper switching.

    Kind regards

  61. Andrew Villalpando

    So, correct me if I’m wrong, both 150nF capacitor, without the RIFA capacitor, are they actually blocking the DC?, or need the extra capacitor in series with the primary coil. I’m telling this based on the schematic of the Steve Wards’ Mini SSTC that only uses two 0.67uF capacitors in series between the + rail and – rail, with the primary coil attached in the middle, or the oposite implementation, like the Loneoceans’ SSTC 2, that only uses one MPP in series with the primary. So, what is the difference between this two configurations. I hope I’ve explained that clearly.

  62. Hi Andrew

    Two are only needed if you are using it as a part of a voltage double and yes they will work as DC blocking capacitors.

    I wanted to initially use voltage double, but it was not needed as I got 230VAC supply and the reason Steve Ward uses it is that USA only has 120VAC mains.

    Kind regards

  63. Andrew Villalpando

    Thank you very much Mads, I’ve learned a lot from your page, keep being that generous.


  64. HI, im working on a similar project and i was wondering if there was a easy way to incorporate ocd, ive had some problems with lowing up the mosfets that iv been using and f there was a easy way to do this that would be awesome

    thanks Baleb

  65. Hi Caleb

    You will have to do the current sensing on the primary DC bus side and it can be hard to catch a over-current situation if the difference from 30A normal operation to 50A explosion.

    You could use a fast microcontroller or a elaborate analogue circuit along with a hall effect current sensor like the https://www.allegromicro.com/en/Products/Current-Sensor-ICs/Zero-To-Fifty-Amp-Integrated-Conductor-Sensor-ICs/ACS723.aspx

    As you can see this quickly gets complicated and it might be easier to just step up to build a DRSSTC which can incorporate the over-current protection in a easier way as the resonant current which is much higher and lower duty cycles makes the use of CT possible.

    Kind regards

  66. hi, looking your setup puzzles me, i had a megatonne of problems with insulation between secondary and primary, it keeps arcing but without actual burns, the circuit goes crazy, it stops working and obviously i can’t push power taking away the ballast, let’s say that at 50% of power it starts with this annoying problem, tried anything, it’s two PVC pipes with 8mm thick wounded sheets of clear plastic soaked with oil, it arcs at 5cm from bottom (end of prim.), the secondary is 36cm of winding… unbelievable!! i think it’s some sort of capacitive coupling problem, i could try a flat prim. but this reduces the coupling coefficient

    any tips?

  67. Hi Alex

    It sounds like you have a problem with grounding of the secondary coil, flash-overs at the bottom is natural if you do not have a good ground connection.

    Kind regards

  68. Hi Mads,
    I plan to use a transformer from a SMPS for a GDT (image below). I’m not quite sure if it’ll work, but it’s logic to think it will since it is designed for high frequency rectangular pulse. What do you think?
    But if SMPS transformers are so easy to obtain (just grab an old PSU), why are they rarely used as a GDT? That leads me to suspect only few of them actually work.
    It’ll be helpful to hear your opinion.
    A first time coiler.

  69. Hi Hiro Kuroshi

    You are absolutely right about these being high frequency transformer and yes the material would be fine for a GDT.

    Now why they are not used. They are often varnish together and will break if you try to get it taken apart. Some have a large air gap in the middle core and that is not desirable in a GDT.

    Suitable GDT ring cores are quite cheap, so its not much money saved on reusing these, its better to look for MOSFETs 🙂

    Some coils have used these PCB transformers for GDTs before and they work if you find some with the right permeability like you would in a ring core.

    You should come to https://highvoltageforum.net and show us your work 🙂

    Kind regards

  70. Andrew Villalpando

    Hi, Mads

    I build the SSTC II from loneoceans, but I get very little sparks from a 80V bus, I think one problem is the ground of the secondaty coil, where should it go?. Mains ground, circuit ground or where. I’m a little bit confusing

    Kind regards

  71. Hi Electron

    A solid state relay is just a MOSFET or IGBT with a large heat sink and maximum specified current, you have to watch out for the switching times, as these are used for mains current it might be a very slow turn on/off.

    Kind regards

  72. Hello Mads,

    -Will a 12Vac, 12VA pcb tranformer be able to power the driver circuit plus 1 cooling fan or i will be needing more power directly from e.g. a smartphone charger?

    -The GDT is 15:15:15 turns?

    -I am thinking to make a pcb for driver + power circuit, will 2oz copper layer with around 3-4mm traces be enought for the power circuit?

    Thanks in advance

  73. Hi John Smith

    12VA will properly do okay, you could run into problems in CW mode, so better run interrupted and check if the voltage is sagging on the gate drive supply when running higher BPS.

    The GDT is 15:15:15.

    That PCB will do just fine, if you feel like it, you could reinforce the power traces with copper wire on top and still keep them thin and your board small.

    Kind regards

  74. Hi Mads,
    thanks for your reply about the gdt, i choose to use external v12 sypply, in order to be able to use variable voltage input for power circuit.
    A couple more questions:
    -will those caps can be used as voltage halfer: https://www.tme.eu/en/details/mkp-x2-150n_305/x2-y2-polypropylene-capacitors/wima/mkx2aw31504c00kssd/

    -will this cap can be used as the dc blocking cap: https://www.tme.eu/en/details/fkp1-100n_1600/standard-polypropylene-capacitors/wima/fkp1t031007e00kssd/

  75. Hello Mads, i tried replicate your circuit and i have some questions.

    Grounding 74hc14 unused pins meaning ground to earth or connecting to negative of the driver power supply?
    The capacitors used for the driver, what type are they?
    And lastly, the 2nd version of your primary coil says its 1,38mm diameter, the full outer diameter with insulation, or 1,38mm is the copper inside? Better question, what AWG you used.

    I replicated the circuit on a breadboard, the secondary coil has no visible output, although it can light a lamp dimly
    Already tried reversing the primary.

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