At 01:55 AM 7/24/99 -0400, you wrote:
>I am a bit confused here: why would the FETs require more precautions? The
>only thing I can think of would be that the power dissipation for a FET
>goes as the second power of current,and for a darlington/BJT, as the first
>power of current. Granted,this makes a big difference as current goes to
>infinity, but in certain cases, you might burn up the BJTs way before the
>FETs if the RDSon of the FETs is really low.

It's actually even worse than that. The R of the MOSFET increases with
temperature and current, so unless you go overkill or have protection you
have a big problem. With comparable devices, the bipolar will usually take
a lot more abuse(assuming it has enough drive current). Generally in a
small application it's easy enough to use a larger MOSFET, but I've
designed 1200 amp motor controllers and it makes sense to put in good
protection so you can use fewer MOSFETs.

Cheers,
Bob