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Registered Member #54263
Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35
Well, its not truly single-FET due to interrupter, but the oscillating part is really simple and has one FET. In Russia we call such topology "kacher".
Primary L1 is tuned via contour C5 to get the SSTC working as close to E-class as possible.
C5 (and VT4 D-S) voltage in this case is as high as tripled supply voltage. Using irfp460 with its limitation of 500V D-S we can set supply to approximately 180V, however, 150 (110 thru full-bridge rectifier) is used for reliable operation. Interrupter frequency is set to approx. 20 Hz, duty cycle 7-8%. At 180V this coil produces 23cm (9") streamers, at 150V streamers are a bit shorter. PSU for this coil contains 2 separate transformers: 220VAC->9VAC and 220VAC->110VAC, each with its own rectifier. Coil needs grounding and cannot be grounded to mains.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
I've built coils like this, where the secondary ground connects to main switch gate for gate drive. My interrupter worked by placing a small FET from main transistor's gate to source to short out the gate drive current from the secondary. Any reason you did not choose this method?
Registered Member #54263
Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35
Steve Ward wrote ...
I've built coils like this, where the secondary ground connects to main switch gate for gate drive. My interrupter worked by placing a small FET from main transistor's gate to source to short out the gate drive current from the secondary. Any reason you did not choose this method?
Perhaps it will give the same result, but I cant choose both methods at the same time. Power-side interrupter also allows A-class audiomodulation. And I dont see any cons.
Registered Member #54655
Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82
I built this same circuit with an irfp460 but with no interrupter, running on half wave rectified 110V and I got 6 inch sparks :). This has to be the simplest solid state tesla coil ever! I used a 12 volt TVS though. I see that you used a 15 volt TVS why is that?
Registered Member #54263
Joined: Thu Jan 15 2015, 09:54AM
Location: Perth
Posts: 35
During several hours of this coils' life no mosfet was blown up. Due to very low duty cycle of interrupter FETs are almost cold, so with 150V its pretty stable. However, streamer of this coil may in some cases (when you dont use mains transformer) be connected directly to the mains. Thus, it's unsafe to touch the streamer. Also, if you try to catch the streamer while running at 180V, you probably can blow up VT4.
Registered Member #54655
Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82
How do the values of the voltage divider resistors r5 and r6 effect things? As it is, with 150 volts in, it puts 37.5 volts across the TVS. It would seem to make sense to set those values so that the gate bias is less than 15 volts.
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Direct feedback Single-FET E-klasse SSTC: 9" sparks
