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[DPRG] Overvoltage protection

Subject: [DPRG] Overvoltage protection
From: Paul Bouchier bouchier at classicnet.net
Date: Sat Sep 11 22:58:59 CDT 2010

Ignore this request - I realized shortly after sending it that all I need is
a 5.5V Zener on the output rail. It will limit transient overvoltages;
persistent current-limited overvoltage will fry the zener (then anything
else downstream, but at least I'll know what happened; and outright
regulator failure (not current limited) will cause the zener to blow the
input fuse. Sorry for the spam. One component, and it was obvious.


> -----Original Message-----
> From: dprglist-bounces at dprg.org 
> [mailto:dprglist-bounces at dprg.org] On Behalf Of Paul Bouchier
> Sent: Saturday, September 11, 2010 9:19 AM
> To: 'dprglist'
> Subject: [DPRG] Overvoltage protection
> Does anyone know a good overvoltage protection device 
> suitable for protecting a 5V regulated rail? I've now blown 
> up 2 routers when they were being driven off a 78ST105 3-pin 
> 5V switching regulator and am beginning to think that that 
> device may go over voltage when battery input conditions get weird.
> Low component count is valuable to me - I've seen the crowbar 
> circuits with the 6.2V zener, but a 1-chip or 1-chip + 1 SCR 
> or FET circuit would be nicer. Either crowbar or FET pass 
> transistor or other techniques would be fine. It would need 
> to protect the output of the 78ST105 (1A capacity).
> Thanks for any advice
> Paul
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