>Peter,
> I don't disagree with you, but I have a question.  Don't FET's generate
>most of their internal heating during the transition phase (turning off
>or turning on, just not quite all the way on or off yet).  If so,
>wouldn't this make a case for a lower PWM frequency?

Yes, but usually there are coils and/or capacitors downstream and they are
more important to limit the switching frequency than the transistors.
Coils and transformers cost much more than the active elements in a
commercial design (because they are custom made) and they are more
important for size and efficiency gains. So you push the frequency up as
far as you can while checking for coil core material efficiency curves and
capacitor ESR and self resonant specs all the time. Going to another core
and capacitors may allow you to double the switching frequency and reduce
physical volume 2 times. You will also need better switches for this, and
better RFI suppression, but that is just by the way.

Peter

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