I have a circuit that has constant current but the load drops in resistance over time. I need to be able to shut off the circuit once a voltage level drop is reached. The voltage starts at -95vdc and reaches -10vdc when I would like the circuit to shut off. Any ideas would be great appreciated.
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Greg d'Eon
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pascal88
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A comparator of some sort is needed. A simple solution is to use a TL431 shunt regulator which detects the voltage across R8 and remains "on"as long as |V_R8| > 10V . When it turns off there are a range of things it could do. Easiest is to have it operating a PNP with grounded emitter which then intereacts with the two existing transistors. – Russell McMahon Mar 21 '15 at 13:50
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Thank you Russell. I ended up using an op-amp and a reference resistor divider. Works great! The TL431 seems simple so I will give that a try as well. Cheers – pascal88 Mar 22 '15 at 19:16