On Wed, 31 May 2006, Wouter van Ooijen wrote:

>>> So a 15V/400mA diode would do. But I would pick an 1N4004,
>> becase that
>>> is my 'mid-current' yellybean diode.
>>
>> As long as the relay is not going to get turned on again
>> before the current
>> from the last on phase decays and the diode turns off.  The
>> reverse recovery
>> time of 1N4004 is rather slow, so otherwise you get some
>> nasty effects if
>> you turn the switch on while the diode is still conducting.
>
> What would be a sure-reliable suggestion? something like an 1N5819?

Either that or 1N4004 and series RC snubber in parallel to slow the 
pulse down a little so the 1N4004 can cope with it. The 1N4004 is not 
just slow, it has a relatively large Rs which causes the reverse voltage 
to be much higher than you think it is, at least initially. This will 
result in an impressive narrow peak that can raise as much as 1/2 Vcc 
(in the conduction direction of the diode of course). The series RC 
snubber will deal with that.

Peter
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