> does have a built in DS diode

AFAIK all FET internal diodes are intrinsic and "accidental", in
that they are part of the manufacturing process

> I'm guessing adding an external as well wouldn't be a bad idea

AFAIK (again) the internal diodes are never as good as a Schottky
which conducts at a lower voltage. It's the same with PICs. Although
there's an internal diode from eg pin to ground, an external Schottky
is much much better protection

For motors, I put a proper ultrafast diode at the motor terminals.
Most recent was a BYV42E-200, and I've used ones from the
MUR range too. Together with a couple of ceramic caps this very
effectively suppresses hash and EMI

An acquaintance, Russell knows who, is forever stuffing FETs as
he doesn't believe in a few extra components, and he suffers for
it. He's apparently happiest when bitching about replacing drive
semis and I've given up trying to convince him he'd be just as happy
by doing a competent job in the first place. He simply can't see
beyond the amperage rating and accept that FETs can be easily
prone to damage

> Do you think a GS diode is needed as well?

Generally a 12V ZD is adequate for a standard FET which needs
> 10V Vgs to turn on hard. If Vgs is lower than 10V then a zener
of Vgs + a volt pr two should do

Joe


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