RadioBanter - View Single Post - PSUs: current-limiting and crowbarring

legg

On 20 Oct 2006 13:28:19 -0700,
wrote:

Hi gang,

Is it not feasible to use a crowbar circuit across a PSU's output if
that PSU has a current-limiting feature? I can imagine a situation
arising where an over-voltage causes the crowbar to close, generating a
short-circuit condition which activates the current limiting. The
output will then be stuck at not enough amps to blow the upstream fuse,
but enough current to smoke the crowbar (which is not designed to be
kept conducting for any length of time of course). Is there some way to
have both over-current and over-voltage protection working together in
harmony?

A properly designed crowbar should be able to handle the current and
stored charge of the supply it's monitoring. If a crowbar fails short
in the process, it's still doing it's job, but that is unlikely to
happen if foldback limiting occurs.

OVP and current limiting are both possible using small-signal
techniques, but the OVP's latch may require an independant method of
crossing the isolation barrier for effect.

RL