From: Spehro Pefhany
Subject: Re: Using the body diode of a MOSFET to protect against relay back EMF
References: <firstname.lastname@example.org> <3E2E0300.57EC698F@earthlink.net>
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Date: Wed, 22 Jan 2003 03:10:06 GMT
NNTP-Posting-Date: Tue, 21 Jan 2003 22:10:06 EST
On Wed, 22 Jan 2003 02:33:17 GMT, the renowned Robert Baer
> Yes, but the inductance will ersonate with its capacitance and that of
>the FET, so the voltage will tend to swing negative almost as much as it
>did in the positive direction.
> It is *that* swing that is being asked about.
> I have found it very difficult to use a diode in parallel with the
>FET, in a manner that will shunt that current away from the FET.
The diode should drop about 700mV at 50mA.
> One might think of a schottkey diode, since the forward drop is a lot
>lower; but the reverse voltage rating stinks (making it useless for this
Why do you want to do this? I've had to do it with big MOSFETs because
of the slow recovery of the body diode, but I don't see why you'd be
having any problems.
What exactly are the symptoms? This is a fairly wimpy MOSFET to be
switching an inductive load at those voltages and currents, are you
getting SOA problems?
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