Thanks Brent,

        Yes I assume the power supply is limited. It does shut off when
        shorted but I guess not fast enough. It's a MeanWell
        HLG-600H-24A power supply . I have been wondering if adding a
        second small power supply to keep the driver alive would help
        keep ithe FET out of the linear region.=20


    Well no need to assume.... just looked up the spec sheet for the MeanWe=
ll
    HLG-600H-24A and it is current limited (and is intended to be used in c=
onstant
    current mode for driving LED's etc without destroying
    them)(it really does "mean
    well") adjustable (internally) 12.5 - 25A.

    Knowing this it seems most unlikely the supply would be delivering a cu=
rrent pulse
    capable of destroying your 100A/400A MOSFET. Yes indeed it will be well=
 worth
    trying a second small power supply to keep up the driver. Would not be =
surprised if
    it then happily supplies 25A into a short circuit all day long with no =
ill effect.



I am wondering however about the fact that the voltage is directly=20
across the drain when the load is shorted, so VDS would be 24 volts .=20
Would this kill the device even if the driver was powered by a small=20
supply. If I look at the SOA for the FET STP100N8F6 the 1 ms curve shows=20
25 Amps at about 24 volts . Does this mean I have no choice but remove=20
the power from the FET? I can't find a spec for the time it takes the=20
supply to shut down?
Thanks again,
Jim

--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.