I am looking for a device which cuts off the connection between batteries and the system just like a circuit breaker when my 12V battery goes below 9V(for example) for preventing it from dying completely. I can use a comparator circuit and a power relay however wondering if something off the shelf can do the job.

  • \$\begingroup\$ One analog way is a self driven relay with excitation voltage at 9V . Additionally a power pfet with gate tied to ground can be configured or chosen such that it will shut off if supply VDS drops below a certain threshold \$\endgroup\$ – crasic Mar 6 '19 at 19:57
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    \$\begingroup\$ Watch that relay solution. If its excitation voltage is 9V, its dropout voltage is likely to be about 4V, which won't be very good for the battery. \$\endgroup\$ – Brian Drummond Mar 6 '19 at 20:15
  • \$\begingroup\$ This concept is about half of a battery protection circuit for a Lithium-Ion cell (the other half is to prevent overvoltage on charging). You could try Googling "battery protection circuit". If what you're powering doesn't pull extreme currents (i.e., if it's not a car starter battery) then a mosfet driven with a reference and a comparator, instead of a relay, may work well. \$\endgroup\$ – TimWescott Mar 6 '19 at 22:17

You did not indicate the current load, so here are a couple of alternatives.

The first possibility is an actual battery-protection IC, or you can coax a high-side driver or power sequencing switch to do the job. But you would still need to add some circuitry around any of them to make them work.

A second possibility is just a circuit with an adequate PMOS. There is quite a bit threshold variability and you would want something steeper than a gradual current reduction. Just adding a Zener might be enough. Here are a couple of ideas that should be refined somewhat before being put in practice.


simulate this circuit – Schematic created using CircuitLab

But you might want to add some hysteresis, so that the removal of consumption from your circuit does not turn the pass switch back on and you end up with a power oscillation.


simulate this circuit

And of course, you could put together a similar circuit with a relay instead.

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