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From: Jim Thompson
Subject: Re: Short Circuit Detector
References: <firstname.lastname@example.org> <email@example.com>
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Date: Fri, 11 Oct 2002 16:19:45 GMT
NNTP-Posting-Date: Fri, 11 Oct 2002 12:19:45 EDT
Organization: Cox Communications
On Fri, 11 Oct 2002 18:17:07 +0200,
"fred bartoli" ,
In Newsgroup: sci.electronics.design,
Entitled: "Re: Short Circuit Detector",
Wrote the following:
|For copper planes, sheet resistance is about 0.5mohm/square for 35um and
|1mohm/square for 17um thickness.
|So you'd better have a sensitive meter, (maybe add a gain stage).
|Then set to say 100/500mA the current, and protect your circuit with a
|schottky between vcc-gnd : it's easy to have the psu voltage button
|accidentally turned in case it happens the short opens... by himself. (I had
|that and once corrected for the short I just had to drop the fried board :-(
|> "Nico Coesel" wrote in message
|> > "red rover" wrote:
|> > >Does anyone have link to a design for
|> > >short circuit detector? I recall that Bob
|> > >Pease had a design for one in his Analog
|> > >Troubleshooting book. I believe it was
|> > >basically a micro ohmeter with an audio
|> > >output and you worked your way around
|> > >the pcb homing in on the fault.
|> > >
|> > >Anybody here made one? Any good success?
|> > I've found that most short circuits on a PCB are in power
|> > distribution. In case of such a short circuit I simply connect a PSU
|> > set at a -safe- low voltage (current limit set to 1A; depending on
|> > minimum trace width) to the board. By measuring the voltage accross
|> > the decoupling capacitors (to start with) I can determine the area
|> > where the short should be. The closer you get to the short circuit,
|> > the less voltage you measure.
|> > --
|> > Reply to nico@nctdevpuntnl (punt=.)
I once cured some shorted thick-film substrates by applying a 5V/200A
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
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