Hi Chris, The TL431 is really a useful part and dirt cheap. Here is a stackexchange l= ink with a schematic: http://electronics.stackexchange.com/questions/213304/tl431-low-battery-cut= -off It will likely oscillate as shown, so I'd suggest one more resistor(and/or = maybe a capacitor), from output to the TL431 sense terminal. Simulation in LTSpice should get you across the finish line pretty quickly. Friendly regards, Bob ________________________________________ From: piclist-bounces@mit.edu on behalf of Chris = McSweeny Sent: Saturday, November 5, 2016 2:16 PM To: Microcontroller discussion list - Public. Subject: [EE] Really simple cutoff circuit A request from a friend - he's after a really simple cutoff circuit to disconnect an external battery when it drops below a certain voltage. The best I can come up with is an op-amp with the negative input biased with a zener diode and resistor (and a voltage divider on the positive input) to create a schmitt trigger, with the output driving a FET, a total of 6 components (excluding any caps, but my feeling is we could get away without those if necessary). Is there any simpler way to do it, or if not is my circuit likely to be reliable? About 100 of these circuits needed, so we're into proper small batch fabrication rather than hobbyist scale, and it is for a commercial operation my friend runs (I'm hoping there is some budget for this, and it might even lead to other opportunities). Thanks, Chris --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .