Roy Lewallen wrote:
Most supplies I've seen with both crowbar and current limiting use
fold-back current limiting. When the current exceeds the set limit (due
to too heavy a load or to the crowbar firing), the current drops back to
a level considerably lower than the limit current, and one which the
crowbar can tolerate indefinitely.

Yeah, and not only the crowbar, but the supply itself can likely
tolerate it better! :-) Especially if it's a linear supply. Paul:
imagine a linear supply designed to deliver 24V at a couple amps. The
input to the regulator part might well be nominally 30 volts or more,
to accomodate low line input and drop in the regulator pass element.
At high line, it might be 33V. In normal operation, the regulator
might drop 9 volts at a couple amps, dissipating 18 watts. An SCR
crowbar might drop 1.5V. At 2 amps, that only 3 watts, but the
regulator would be dissipating over 60 watts. But with foldback
limiting, the dissipation would drop in both the SCR and the regulator,
staying in pretty much a constant ratio. With a switching regulator,
things probably wouldn't be nearly as bad, but the dissipation may
still go up in the switching parts if you short the output.

The other thing I've seen is a crowbar for fast response, and a
latching shutdown fed back to the supply that holds it off until
something is reset.

Cheers,
Tom