On 20 Jul 2011 at 22:31, Tony Duell wrote:
Actually, in my experience, a crowbar circuit is
often used on a PSU
with electronic overcurrent protection, and said protectiuon should
operate if the crowbar fires due to an overvotlage. However, there's a
second line of overcurrent protection (e.g. a fuse) that will operate
if the electronic protection doesn;t (e.g. becasue the PSU control
circuitry is totally malfunctioning).
I've got a couple of linear supplies that use just that design--an
SCR crowbar driven by a comparator following a LM723 regulator stage--
the 723 has overcurrent protection, so it all hangs together.
(and there is a fuse on the primary of the transformer as well)
The HP9800 machines that I lkeep on going on about, and some of their
periphearlas are like that. They use 723s either as linear or switching
regulator controllers and have crowbars on the outputs. They do use the
current limiting circuitry of the 723, and if that doesn't help there's a
mains fuse.
-tony