The Silicon Chip designed coil driver system.

I love the way this is put together mechanically , my only gripe is the 5w base resistor that gets very hot.

To keep it cooler I have connected it thermally to the case and added an external heat sink.

The four diodes you can see on the PCB are 75v zenner diodes connected in series accross the collector and emittor of the switching transistor. This is designed to limit the voltage to 300v. You can see this happening in one of the traces in the oscolloscope section.

The IGB transistor does not need these because they have protection built in. The thing that bugs me here is the maximum collector emitter voltage quoted for this IGB transistor is 380v. If you have a look at my traces it goes well over 400v. It does not seem to effect it as I have ran it on the bench for hours without any problem.