Re: Nyquist and Fuses

marc@... wrote:

> Different subject members--I used to work for a fuse
> manufacturer. Never use a fuse to protect a sensitive
> FET. Circuit breakers and fuses are remarkably slow
> devices and will keep delivering the juice long after
> the semiconductor has been oxidized to a lump of sand.

Of course. There are quite expensive fuses that can protect
large power semi's from overloads, but the fuses often cost
hundreds of dollars. A fast, electronic circuit should be there
to detect overloads and shut the semiconductor off. That
is the primary mechanism of defense. The fuse is there to
prevent the motor, power supply, power traces on the
circuit board, etc. from all going up in flames. (Literally.)
In such gear as large servo drives and multi-horsepower
motor drives the energy stored in the capacitor bank
is enough to completely destroy not only the power
semi's, but all the wiring, circuit boards and other components,
too. THAT is what the fuse is designed to protect.
So that the equipment can be repaired, rather than
replaced.

Jon