>	I'm using a 100nF capacitor in parallel with the Mosfet.
>	It seems to eliminate the spike.
>
>	Mark Jordan
>
>On 28 Dec 2007 at 17:13, Bob Axtell wrote:
>
>>  Enki wrote:
>>  > I'm doing some tests with the FDN337N Fairchild Mosfet.
>>  >	It is working switching a 24V @ 500mA relay in series with a 1 ohm
>>  > resistor. The relay has the usual 1N4007 diode.
>>  >	If I don't use the diode, the back EMF when the Mosfet switches off
>>  > goes up to ~40V, the Mosfet breakdown voltage, for 10mS.
>>  >	Just out of curiosity, I let the Mosfet switch the relay each second
>>  > without the diode, some 100.000 times, 50% duty cycle.
>>  >	The Mosfet seems not care about the energy absorved during the
>>  > breakdown period. It warms up to some 40C.
>>  >
>>  >	My question is:
>>  >
>>  >	Is there any expected long term problem running the circuit without
>>  > the diode?
>>  >
>>  >	The design WILL use the diode, my question is just to satisfy my
>>  > curiosity.

You'll want to use a faster diode than a 1N4007.  Also, Google "snubber".

-- 

---
Chris Smolinski
Black Cat Systems
http://www.blackcatsystems.com
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