Re: Strange Mosfet Results

From: Peter (pmolsen_at_one.net.au)
Date: 08/04/04 

Date: 3 Aug 2004 23:31:12 -0700

This is getting even stranger! I remembered reading about gate ringing
in mosfets and found a ST data*** that recommended inserting a 4k7
resistor on the gate to stop it. I therefore got another new mosfet
and hooked it up that way. At least then it did not die, but it acted
even stranger. As soon as any of the OTHER mosfets came on, the one I
was testing turned on spontaneously without any input from the chip. I
put a multimeter between the diode (coming from the 595 output) and
the 4.7k resistor and it read 2v. The 595 output was still at 0v.

Oops, I spoke too soon. I was using a 0.27 400V cap a minute ago as a
trial. I just changed it back to a little 0.01 "metalised ceramic
disc" and the mosfet just died as soon as I switched on. Could it be
that the 40v is too much for those little caps?

Anyway this whole idea of a cap between gate and source doesn't seem
to be helping.