Thanks - looking at the datasheet for that MC34064 it does strike me that my suggested circuit has an issue with lack of hysteresis which could result in oscillation. I suspect the zener biased PNP you're suggesting would also suffer from that (because the battery voltage would recover following cutoff). Chris On Sat, Nov 5, 2016 at 9:53 PM, Antonio Benci wrote= : > Simplest I have seen is a zener biased pnp as a low voltage drop out swit= ch > and a dpdt relay. I'll try to find this, no promises though. You could ev= en > use an MC34064 low voltage detect, suitably biased. > > On 6 Nov 2016 08:17, "Chris McSweeny" wrote: > > > 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 awa= y > > without those if necessary). Is there any simpler way to do it, or if n= ot > > 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 > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=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 .