HelloSupport
Electrical
- May 25, 2011
- 4
I am building a couple of simple detector circuits to determine if our board has seen an overvoltage or ESD event. The limiting reagent is that it must be real cheap because it will go onto several thousand boards. And when I say cheap, my boss doesn't want to dole out $1.10 for 15mA fuses. He wants to use cheap 5cent components that would fail rather quickly, and our technician can simply measure with a voltmeter.
To detect an electro static field, I'm using a circuit like this:
Ridiculously Sensitive Charge Detector
but with a zero ohm resistor or a 2milliamp inductor or a 2.5V Tantalum capacitor instead of the LED. But the problem is that these devices take far more abuse than they are rated for. I can run 1AMP through the 2milliamp inductor and it still shows no measurable in-circuit difference. On larger voltage Tantalum capacitors I can kill one with reverse voltage ~equal to its full voltage rating, but the 2.5V tantalum caps can take more than 5V of punishment. I'm thinking of using a simple signal diode with minimal Power Dissipation capability, Ifsm=Current Forward Surge Maximum less than 30mAmps but haven't gotten those diodes yet. A cheap voltmeter looking at Hfe sees the difference on the diodes that I do have, but they are 4.3V Zeners. Are Zeners more susceptible to failure than signal diodes?
My question would be, in this circuit, is there a cheap device that anyone has seen fail far too easily that would be usable? Perhaps a cheap Op-Amp? I’ve tried to blow the gates on our JFET but they are remarkably robust.
Hopefully, the circuit fails in the open circuit mode, but that is not all that necessary. I tried Aluminum Electrolytic caps that are advertised to fail in the open mode but they fail in short circuit, (and they fail far above their rating) so that didn't work.
Also, to monitor a 5V power rail, a 5.5V Zener would pull any extra power above 5v, and hopefully that current would kill the next item in series. What would be the best item?
And the last circuit is simply a long wire to pick up ESD and funnel it to Ground rather than through our chips on board, with an indicator device between the wire and Ground. I'm pretty sure the best candidate for this is the Tantalum Capacitor but I'm hoping to hear of some cheap current-sensitive device that drives engineers crazy because they fail so often. What would be the best candidate?
To detect an electro static field, I'm using a circuit like this:
Ridiculously Sensitive Charge Detector
but with a zero ohm resistor or a 2milliamp inductor or a 2.5V Tantalum capacitor instead of the LED. But the problem is that these devices take far more abuse than they are rated for. I can run 1AMP through the 2milliamp inductor and it still shows no measurable in-circuit difference. On larger voltage Tantalum capacitors I can kill one with reverse voltage ~equal to its full voltage rating, but the 2.5V tantalum caps can take more than 5V of punishment. I'm thinking of using a simple signal diode with minimal Power Dissipation capability, Ifsm=Current Forward Surge Maximum less than 30mAmps but haven't gotten those diodes yet. A cheap voltmeter looking at Hfe sees the difference on the diodes that I do have, but they are 4.3V Zeners. Are Zeners more susceptible to failure than signal diodes?
My question would be, in this circuit, is there a cheap device that anyone has seen fail far too easily that would be usable? Perhaps a cheap Op-Amp? I’ve tried to blow the gates on our JFET but they are remarkably robust.
Hopefully, the circuit fails in the open circuit mode, but that is not all that necessary. I tried Aluminum Electrolytic caps that are advertised to fail in the open mode but they fail in short circuit, (and they fail far above their rating) so that didn't work.
Also, to monitor a 5V power rail, a 5.5V Zener would pull any extra power above 5v, and hopefully that current would kill the next item in series. What would be the best item?
And the last circuit is simply a long wire to pick up ESD and funnel it to Ground rather than through our chips on board, with an indicator device between the wire and Ground. I'm pretty sure the best candidate for this is the Tantalum Capacitor but I'm hoping to hear of some cheap current-sensitive device that drives engineers crazy because they fail so often. What would be the best candidate?