The FET diode is in parallel to the FET S-D, and would help protect
the supply (battery). However, there is always a V= L *dI/dt term when
you switch the FET on or off, which could cause very high voltages
(positive and negative) on the motor side of the FET. I've never
directly used high power FETs before, but you probably want some
sort of 'snubber' diode to protect from voltages much beyond +15V,
and lower than -1V or so. A lot depends on how sensitive the motor
is to excessive + or - voltages, and the 'L' and dI/dt values.
The power dissipation is also probably somewhat over the simple
I^2*R value, due to the frequency in charging/discharging the load
capacitance (FET + motor). IIRC, the value is proportional to f^2 * C,
at least for CMOS digital logic. A small heat sink won't weigh much,
and would be very effective just under the whirling blades of death.
Dan
In a message dated 9/20/02 7:35:13 PM, [EMAIL PROTECTED] writes:
<< Unless diodes with a lower PRV are much less expensive than these,
I say buy them. When you're a diode, you can never have too high a
PRV. Even at 1200V.
But why do you need external snubber diodes when the IRFp054 has
one built in?
Chris >>
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