25 Sep
2002
25 Sep
'02
2:33 p.m.
At 10:54 PM 9/25/02 +0100, you wrote:
A better solution is to use a crowbar circuit. It's
only 3 components!
+5V o--------------+-----------------------+
| |
| |
--- |
^ | 5v6 Zener |
| |
+-------------------\ |
| \ V Thryistor/SCR
/ ------ to carry full PSU current
\ 100R |
/ |
\ |
| |
| |
0V o---------------+-----------------------+
Excellent advice. However, repeated "accidents" can stress the
SCR enough that it will eventually fail. The trick is to
insure that the peak safe current for the SCR is not exceeded
before the fuse blows. So you either
include somewhat higher resistance wiring between the regulator
output decoupling caps and the SCR or a very small inductor in series
before the SCR.
carlos.
--------------------------------------------------------------
Carlos E. Murillo-Sanchez carlos_murillo(a)nospammers.ieee.org
ground? Seems like you'd want inline fuses
between the unregulated supply
and the backplace as well for this kind of test...
You want something that will fail safely if the crowbar trips, sure.... A
fuse is a pretty good choice.
-tony