> >I would run this thing at 80 to 100KHz.  Anything higher would turn
into a NASA
> project.
>
> Be prepared to use litzwire at this level of power.  Break out the
checkbook!


How about using a sandwiched secondary winding between two half
primary
windings. Just stacking the two windings on top of each other will
definately fry a small snubber circuit away due to the large leakage
inductance spikes.

I've designed several 3kW offline switchers using a two-switch forward
converter, running in series production for five years now without any
problems.
However if you have little or no experience in higher power switch
mode power supply design I wouldn't try to design/build a reliable
500W switching power supply. It's not only the transformer that's
tricky to build, also PCB layout, control loop design, snubber design,
active and passive component selection etc. all are very important
issues in this case.


Daniel...