On Thu, 26 Sep 2002, Morgan Olsson wrote:

*>Can=B4t normally make hundreds of amps, if it did, then just arrange th=
e
*>tracks intelligently and it pulls down correctly anyway.

That is exactly what I meant and wrote in my original posting. And the
lowly 1000uF low ESR smpsu output cap will cause current in excess of 100=
A
for microseconds when shorted by a crowbar.

*>For using fets, the turn on is not well enough defined, and also too
*>soft/high resistance.

Huh ?! 9 milliohms too high for you ? Turn on slope is very well defined
for a characterised FET. For an uncharacterised one use a comparator to
drive it, as you would for a thyristor.  Plus the FET circuit is self
restoring so the crowbar will not take out the whole circuit if a single
event transient is present. Thyristors in precise crowbar role are often
steered by a TL431 or equivalent anyway. The thyristor firing voltage is
also not well defined over temperature and spread between components, whe=
n
driven with a simple voltage divider. Or with a +/- 15% zener.

Peter

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