CLD/CRD requirements of 24 ma or greater.

How about using a current source chip like this

or an adjustable voltage regulator wires as current limiter? It also depends on your voltage compliance range and the max expected dissipation. And mind stability issues.

Another option could be paralleling CLDs but those things are rare beasts, not many sources.

Polyfuse?

John

You know, I never thought about pairing them. I think I actually have enough room on the edge of the board to drop a couple of smt packages there..

One of the other guys has a temporary fix that actually seems to be comical in some ways. He places a 40 ma 24 volt panel mount incandescent lamp in there. It acts as a short indicator and protection all at once..

But I don't want any more units to be distributed to our other locations of operation before I fix this. I already had a bunch of boards done so it's not like a simple fix with a couple of drag and drops on the screen. But I can patch in a couple of smt CLDs until those boards are used up.

We'll look into that.

Thanks

THat was my first idea how ever, I think the response time maybe a little to slow.

I have a 2.49 ohm load R so that I can a 10..50 mv translation and that R isn't vary large. 1/8 W

The supply used for the sensor is a 15 watt unit and must remain that size for other things so I need to come up with a basic limiting source for the sensor input.

I was thinking about doing a JFET current limit that I could pot into a discrete looking thing how ever, it looks a little rough when looking around for JFETS that I can get my hands on that has Idss well above 20ma

This does not have to be a precision current limit but it does need to have a small foot print to squeeze it in there.

Jamie

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hat

since you have 24V and only need 50mV for the sense you could easily add a series resistor, polyfuse or a PTC

clamp the sense resistor with a diode, that should keep its dissipation at around 1/8W until the ptc or poly fuse reacts

-Lasse

These are cool:

These are depletion-mode (normally on) mosfets. Pick one with Idss higher than you need, and add a source resistor to bring it down.

A 3t voltage regulator (LM317, LM1117) and one resistor makes a nice little current limiter, too.

John

Take a look at the J310 available from Mouser.

John S

Kinda weak...maybe the MMBFJ108, available from Mouser for about 0.40/ ea, IDSS MIN of 80mA, but the BVDS like most of these small signal types is about 25V.

The DN2535 looks to be the winner!

It looks like I can use that one "Idss of 150 ma" directly as is with out an R. :)

And Thanks to Fred Bloggs on boosting the CLD ratings PDF.

Jamie