Re: A Variable Question.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

> > I was musing over the cost of a descent variac.
> >
> > Anything worth while on E-Bay costs a small fortune to ship, and my
> > local surplus store wants gold for even a tiny trashed unit.
> >
> > While I was crying in my milk, I cleaned out some boxes and found my
> > stash of 150A Power HexFET's. I have several of these monsters that I
> > used as R/C switches in my Battlebots endeavors.
> >
> > My question is does anyone have plans for or know of them for a FET
> > based variable AC power supply? Basically an electronic variac!
> >
> > With 2 or 3 of these things in parallel you could conceivably create a
> > 200A "variac".
> >
> > Any info on something like this hiding out there??

Haven't seen anyone do it AC-wise, but myself and an another engineer have
the patent for this same type of regulation
for a solid state high voltage DC regulator which is used in radar
applications.  In our typical application we can regulate a high voltage
supply (say 60kV) with less than 10mV ripple which is quite impressive.  The
inherent problem though is that the FETs will get extremely hot and need to
be liquid cooled as you would be operating in the FET's linear region.  We
have an enormous amount of heat output with only about 2A current.  I think
if you tried doing this for high power AC, you'll run into all kinds of
problems.

Dan