Re: electronic PWM variac

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Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>

That was me.
http://tesladownunder.com/Solid%20State.htm#Solid%20state%20variac.
It really wasn't developed much as I got distracted into other things 
and I didn't finalise the schematic.  You do lose a relatively large 
amount of mains power in the snubber to keep the spikes down so some 
things get hot but I haven't spent a lot of time on it to optimise 
it.  The bridge rectifier worked fine though but I suspect that big 
switching spikes would be hard to suppress in a high current system.
As for the IGBT, I used a microwave oven (inverter type) one which 
are about 20 - 30A 600V.

Peter

> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
>
> A few months back, someone mentioned that they had built an 
> "electronic variac" using a bridge rectifier and a single PWM FET. 
> (I've done this for non-tesla coiling loads, like motors.)
> I was curious about the ratings of that FET?
> If I wanted to build something along these lines rated at, say, 50A, 
> what sorts of inexpensive switching devices are there out there?  It 
> would be driven by something like an 555, and the chopping rate can 
> be pretty low (few kHz to maybe 20 kHz or so), so it's not quite 
> like running an SSTC at 300 kHz.  I'd use a isolated power supply to 
> power the 555 and FET drive circuitry.  The 60A, 600V bridge 
> rectifier's not a problem.....
> Jim...