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Okay so I tested the half-bridge today...I connected a pair of UCC's up and ran a 50kHz tone through the input, and had the output connected to the GDT for the half-bridge. Connected to the half-bridge was a flyback with a 12 turn primary and 12V input.
When I turned it on all I got was a slight hissing noise coming from the half-bridge's direction. Nothing got warm, well the driver chips might of hard to tell. My guess is, is that my GDT core is no good? Any ideas?
EDIT: I tweaked it a little (gave the bridge 24VDC) and i got little sparks, here's a video...
This is just my initial impression, but you don't have enough turns on your GDT. I'd shoot for around 12-18 turns, as that seems to be the standard range everyone successfully uses. I use 15 turns on my half bridge GDT, and it is wound on an EMI supression core from Mouser. Works just fine.
Remember MOSFET gates need 10V to fully turn on so make sure you're feeding your UCC chips at least 10.5V .
I have found that when switching at higher frequencies the number of turns should be decreased, and actually I did get this working with mains voltage using another GDT...and I just realized I forgot to retest the original GDT. Also yes, I have 12 volts going into the UCC's, and the gates are clamped with 15V zeners. :)
I have seen a few coils that use capacitors inside the secondary to add capacitance, and reduce the resonant frequency. I was thinking I could do something similar with this coil to bring the frequency down to say 500kHz.
It would take 5.6pF to bring it down to 500Khz. Using 12 of these in series would give me just about 5.6pF at 37.8kV. According to this equation - Vsec = Vpri * sqrt( Lsec/Lpri) - my secondary voltage would only be about 8.5kV.
So my question is, do you think those capacitors can handle it?
It would take 5.6pF to bring it down to 500Khz. Using 12 of these in series would give me just about 5.6pF at 37.8kV. According to this equation - Vsec = Vpri * sqrt( Lsec/Lpri) - my secondary voltage would only be about 8.5kV.
The equation you quote only applies to SGTCs. It is based on the complete energy transfer from the primary cap to the secondary tank.
In a SSTC there is a continuous input of energy to the primary. The secondary voltage can ring up indefinitely due to resonance effects and is only limited by losses in the secondary tank. The major source of energy losses in the secondary are the sparks.
If you e.g. use a toroid without a breakout point, you'll likely exceed your caps voltage ratings. With a breakout point it depends much on the power your driver is able to supply. The only safe way is to measure the secondary base current to get an estimate of the secondary voltage.
Okay, I don't have the tools to do that right now...I don't even have a voltmeter right now...So I will just get some surface mount high voltage caps, and solder them in a spiral to be able to get like 60 or so inside the secondary. I'll get some epoxy to case them in too. If it doesn't work, then uh oh I guess x.x
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Mini Audio Modulated Tesla Coil
