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Forums
4hv.org :: Forums :: Tesla Coils
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SSTC Help

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MRacerxdl
Wed Nov 28 2007, 11:54PM Print
MRacerxdl Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Hi all, I am again trying to make a SSTC (One time I will get it to work :P)
Now I have studied more of Tesla Coil works and Solid State works, also I made some experiencies with MOSFET's.

I am trying (again) to make a Simple Solid State Tesla coil, and I made this circuit for it:
Link2
The oscilator generates frequencies with range 19kHz to a few mHz with perfect square (the Decoupling caps are not show on the schematics), the frequency was measured with a Frequencimeter and the Perfect Square with a Osciloscope of a friend.

Ok, the Oscilator is working, I have teste the TC4429 and its working too. The GDT I tested with the osciloscope to, the output its not the perfect square wave but its goes good for it, the voltage on the GDT exit its arround 12V (1:1:1 GDT). Ok all good with primary circuit and the GDT, my problem goes with the mosfets.

I use the IRF540 because the voltage I use is low, and I want to make a small sstc, I think the IRF540 should be enough to a small sstc.
The problem is, the IRF540 gets too hot in a few secs, and it doesnt goes a good current flow (I tested with a lamp as the primary of the coil, it get 2 times lower bright than if I put direct to the 48V DC Supply).

What is wrong with the circuit? I forgot something? (Not the Fast Diodes, I will use then later)
PS: The current its not enough to make anything on the tesla coil :(, the ressoant frequency of the secundary its arround 450kHz (calculed))
My 48VDC Supply have 2 1000uF caps in parallel.

If someone knows what is going on here, please answer this post :D

Thanks
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ragnar
Thu Nov 29 2007, 12:31AM
ragnar Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425
If you have a 1:1:1 gate-driver transformer and you're driving it with TC4429 drivers running from 12V, you will only ever get 12V of voltage difference on the secondary of your gatedriver:

i.e. you will get (relative to the MOSFET's source) +/- 6V

Since the MOSFET's gate should be driven above +8V to turn it on properly, it sounds like you're not even getting close.

I don't know if your TC4429 chips can take 24V -- if they can't, consider changing to a 1:2:2 gate-driver transformer, or driving it with two TC4429 chips running out of phase.
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MRacerxdl
Thu Nov 29 2007, 02:49PM
MRacerxdl Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Ok, I using now a 1:2:2 GDT, I will test it and post some results later. I think its working now, but I need to test it on a Tesla Coil first.
The TC4429 can support 18V max and 20V for peak (only for peak, they run very hot at 20V).

Thanks for the answer :D
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MRacerxdl
Thu Dec 13 2007, 12:59AM
MRacerxdl Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Ok, I have made that changes here, the GDT is new, and its rated at 1:2:2. I have remaded the High Side Board with the IRF540.

Ok now The config is that:

The GDT Drivers is a TC4429 with a 100uF capacitor in series with GDT Primary.
The HighSide Have the GDT Plugged at Mosfets Gates and Sources with 2 zener diodes to limit the voltagem (the two zener diodes is in series, and in paralel with GDT secondary). Two IRF540 and a 275Vac 0.47uF Capacitor (I think its polyester ones)

The GDT Driver supply was 12V. The HighSide with IRF540 supply was 48V.
First I put 20kHz on the GDT Driver and Put a Speaker instead the Tesla Primary (For See if its going enough current). All things sounds to be working.
After that I put the Tesla Coil (the fres of secondary is about 680kHz without topload, with the topload I think its 600 or 580Khz), and set the oscilator for about 600kHz. Turned on, and nothing happen. Turned off, and I see that IRF540 gets hot (not too much, I think that is normal).

I didnt get any mm sparks (I have tryed to put a fluorescent lamp near the top of tesla, for see if glow, but nothing happened)

Someone have any ideas that could be the problem?
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KresoLiubov
Thu Dec 13 2007, 06:26AM
KresoLiubov Registered Member #1153 Joined: Mon Dec 03 2007, 07:27PM
Location: Croatia
Posts: 213
In first tests its best to connect small lamp directly to output of secondary so even if you are completly out of tune there will be some indication.

Maybe you are out of tune and have to small primary turns. Use 12 V to powers fets it will give you longer time to tune sstc without overheating fets. And can you limit output current of your power supply? Did you phase gdt outputs on mosfets properly? Second one need to be reverse.

Regards
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MRacerxdl
Sun Dec 16 2007, 03:50AM
MRacerxdl Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Yes its fased correct, I solved a problem of my Oscilator (it was oscilanting at max 200kHz, my coil is 500kHz), but now I can oscilate to 800kHz max, from 200kHz.
Now I have a different output. I am using a 14 turn (arround 9cm of diameter) and a 470nF 275Vac Polypropilene Capacitor. 2 IRF540 supplyed with 48V. When I turn on without oscilator nothing happens (thats good), when I put the oscilator On (At a 12V battery for avoid intereferences) my Transformer (and all amplifiers, sound boxes) get a 60 Hertz noise, when I am Approaching the Ressoant Frequency of the secundary, the noise gets louder. Ok, all working, the Fets are not too heat (I have a fan cooling it) but I didnt get any sparks at end of the secondary. Why??
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Mates
Sun Dec 16 2007, 06:52AM
Mates Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Mestre Racerxdl wrote ...

Yes its fased correct, I solved a problem of my Oscilator (it was oscilanting at max 200kHz, my coil is 500kHz), but now I can oscilate to 800kHz max, from 200kHz.
Now I have a different output. I am using a 14 turn (arround 9cm of diameter) and a 470nF 275Vac Polypropilene Capacitor. 2 IRF540 supplyed with 48V. When I turn on without oscilator nothing happens (thats good), when I put the oscilator On (At a 12V battery for avoid intereferences) my Transformer (and all amplifiers, sound boxes) get a 60 Hertz noise, when I am Approaching the Ressoant Frequency of the secundary, the noise gets louder. Ok, all working, the Fets are not too heat (I have a fan cooling it) but I didnt get any sparks at end of the secondary. Why??

How strong is your power supply? Do you have an air gap between your primary and secondary? Can you light a incadescent tube when placed on your top load? Dou you have a sharp break out point?
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MRacerxdl
Sun Dec 16 2007, 05:00PM
MRacerxdl Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
My Power Supply can supply 6A at 48V. I have 2cm between the Primary and Secondary, but the Primary is at a 0,5cm plastic. I didnt try a Incadescent Tube, I only try a Flurorescent tube (because it was easier to see if there is any sparks, the tube gets light, but here, it doesnt get anything. I didnt make a breakpoint on the oscilator, I was think that is only for current Purpose.
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