Re: electronic PWM variac

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Brady Hauth <bhauth@xxxxxxxxx>

> The small inductance
> of the pole pig should limit current at a high enough frequency.

I take it back, I don't know what the leakage inductance of your pole
pig is. Maybe capacitative effects of your pole pig dominate, and
you'll use that in your current limiting. Maybe you'll want to put
something like one of these
http://www.coilws.com/Powder%20Core%20Inductor/HWT.php between the
IGBT and the pole pig.

> Putting in a small capacitor across the pole pig will prevent heat
> buildup in the IGBT.

That would be true, but then you get heat in the cap instead, which is
probably worse. Stupid me. If you were using enough power to have a
problem with hot IGBTs, you'd need to put a inductive element in with
a resistor of something that would give you a voltage differential
less than the IGBT's rating with your current draw when pulsing on
running through it across it that can handle dissipating that much
energy.