I have a circuit that's supposed to cut off at <4V. It instead caps the voltage at 3.3-ish and reduces the voltage linearly below that.
Zener – 3.3v
Source – 5V +-5V
Low voltage cutoff circuit with Zener and BJT
low-voltageundervoltage
Related Solutions
Based on the information you've provided so far, the schematic posted below will allow you to build something that works and that you can play around with using the active stuff you have on hand.
Since the LM393 is a dual comparator, you should spare out the unused one by connecting its + and - inputs, and its output, to ground.
If you want to, you can also connect your LED in series with R5 to watch it blink, but make sure you don't connect it backwards or you'll destroy it.
Also, watch out for that 80 volts; it can give you a nasty little sting.
The Linear Tech circuit is nothing more than a simple comparator circuit. If you really can't find the parts, just replace the LT1495 with another low power comparator. The LT1389 still seems to be widely available, but yet again, any old low current 1.25V reference will do.
Best Answer
A zener diode is not a perfect stop for current, there is still some leakage. Further because you are using a darlington pair type setup there is a very high beta allowing just even a little bit of current is still enough to tun them on.
Also this is just my best guess, your question is not very clear.