Voltage regulator issue

Hermie

I'm using the 7805 and 2940 5v reg to power my stamps. I found out the hard way that when a regulator fails, for whatever reason, it puts out almost as much as the voltage in (12v).·Which in turn blows up the stamp and everything else connected to the regulator. So I thought a little protection would be a good idea. I want a simple componant that senses more than 5 volts and shuts off. I first tried a 2n2222 and a pnp. But there's a loss of a half a volt. Which means I would be running everything at 4.5, and that causes some sensors issues. I found a 12v relay that doesn't kick in until 7v, but it also drops the voltage until it hits 7v, and I'm concerned that the coil would be overworked long term.· I could use another stamp with a 0831·to do the job, but that would defeat the purpose.

Anyone have a simple solution? I'm sure I'm not the first to attack this problem!

·

Mike Green

You want what's called a crowbar: en.wikipedia.org/wiki/Crowbar_(circuit)

There's an IC that, with an SCR, forms an accurate crowbar: www.onsemi.com/pub_link/Collateral/MC3423-D.PDF

Post Edited (Mike Green) : 6/30/2009 5:42:30 PM GMT

Hermie

Thanks Mike!· That's exactly what I was looking for....and the price is right....many thanks!



Ron