What do your waveforms at 13.56 MHz look like? Wonder what FETs you are using up there. My next missions is to move up to 20, 15 and 10 meters with CMCD. Any pointers would be appreciated.
Jay,
I am away on a business trip, but I will get some pictures in a week or two of the gate drive.
These AE amplifiers use RF drive, and two power FET's in parallel to make 3KW out of 200 VDC. They have three power conversions in the box, 3 phase 208VAC to unregulated DC (with small energy storage cap - PFC correction), then DC to DC regulated 0-200VDC, and then DC to RF. Overall they are 55-65% efficient depending on the power level and the individual unit.
I am new to these technologies and my time with them has been limited. It appears to me though that RF drive has a problem over digital drive. With RF drive in order to get the FET gates over ~ 8 volts peak, the pulse width gets too wide. I definitely see the unit efficiency drop several % as the RF drive amplitude increases. Conversely as the drive amplitude decreases, I see the % efficiency increase. I tune the RF drive (a coil to bend) while monitoring the fet drain saturation voltage and reducing the gate peak level until I see the the fet 'ON' drain voltage start to rise a tiny bit, and then go back until I am 'just' saturated. There is nothing to tune on the Drain side.
Jim
WD5JKO