A few people have implied this but I just want to make it explicit to
save pain and grief:

You cannot simply create a voltage which is 12V above your supply rail
and feed that to your high-side fet gates (at least not without a
zener clamp on each one). This is because initially, when the source
of the high side fet is at 0V, applying Vsupply+12 to the gate would
cause Vsupply+12 of gate-source voltage on the high-side fets. This
would only be for perhaps 100 nanoseconds or so, but could be enough
to punch through the ultra-thin gate oxide layer (due to violation of
Vgs_max spec).

Sean


On 4/27/07, Gerhard Fiedler <lists@connectionbrazil.com> wrote:
> Alan B. Pearce wrote:
>
> > Well, hand winding is definitely an option, for the quantities you quote.
> > Taken to the extreme see if there is an intellectually disabled persons
> > workshop near you, and see if they would be interested in piece work.
> > The company I did my apprenticeship with did this for winding toroids
> > for power supplies for valve transmitter equipment that ran of vehicle
> > power supplies. Worked extremely well.
>
> Thanks for the suggestion -- I'll keep it in mind.
>
> > But another option is to look at small transformers from the likes of
> > Coilcraft. For your purpose I suspect something like a gate drive
> > transformer will do the trick. Have a look at the Coilcraft S5499-D and
> > drive it with a transistor with 50% duty cycle at around 10kHz. We use
> > it like this to provide an isolated drive to some FET gates to turn them
> > on for a DC drive. (see attached picture).
>
> Same here... But overall, I think the transformers add a lot of unnecessary
> overhead here.
>
> Thanks,
> Gerhard
>
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