SSTC: ClassE Tuning 1
The Class E autoresonator Solid State Tesla Coil with a new IRFP450 mosfet. Here I have it running on 33 volts DC input, and it’s doing its RF thing at about 650 kHz or so. The secondary’s radiated field is shown on the scope, using a bit of metallized plastic foil for a pickup. The output is pretty sinusoidal when I’ve got the driver right at that Class E input waveform to the primary. It depends sensitively on the setting of the gate bias pot and also the environment around the resonator. When I get the DC supply built onto the board I should be able to get up to 150 volts input and make plenty corona, I hope. If the mosfet can stand the strain, that is. The original design called for a 17N80 mosfet, which I can’t find locally. As I get the primary and the pickup coils properly positioned, and the breakout terminal trimmed to the right length and the gate drive bias set just right… I can go higher and higher in input voltage without overheating the mosfet. The point of the Class E waveform is to get the mosfet to switch right at the zero voltage level of the primary’s inductive collapse. This reduces losses in the mosfet and makes up for the slower rise-fall times of the pulses to the primary. The little “knees” in the sinusoidal output indicate where the mosfet isn’t quite hitting the zero crossing exactly yet. The Class E performance isn’t quite there yet. I might need to play with the circuit’s inductances some or use a different design for the pickup loop. The …
