> >        Now I am wondering if any of you have experience with sourcing
> >PWM current from an un-regulated supply.  I am thinking that maybe I can
> >simply step down the ac line, full wave rectify it, and synch my PIC PWM
> >timing to the zero crossing.  I use IRF520 MOSFETs to switch the current.
> >This would insure that my driving waveform would be uniform for each cycle.
> >I do not believe that having a non-DC source current is any problem.  After
> >all, I am only heating wire.

I'm wondering - why not just use a triac and NOT convert to DC?  Yes, you need
to sense the zero crossing.  It's EASY!  Just add one resistor.  The app.
notes show you how.

--

            -- Paul Greenwood --  (pablo@austin.ibm.com)

Newton's Fourth Law:  Every action has an equal and opposite satisfaction.