IGBT Chopper

A useful thing to have for testing high voltage transformers is a simple chopper. This one switches a 600 V IGBT with an adjustable frequency between 50 Hz and 29 kHz (lower frequencies are possible with an external timing capacitor) and any duty cycle between 0 and 100%.

A LM393 dual comparator is used as a linear sawtooth oscillator and PWM comparator. The IGBT’s gate is simply driven with an emitter follower pair.
The schematic is simple enough for basic perfboard construction.