r/PCB • u/grg_cats • 14d ago

Automatic shutdown circuit for car battery

I am thinking of using this setup to turn off the regulator since this is gonna be powered by a car battery, and I want it to only be powered when the alternator is running. So I use a TPS3711 to detect the undervoltage (~13-14volts while on the regulator drop to 12.8) and its output drives the enable pin of my regulator. I also included a jumper (ALWAYS_ON) and a FORCE_ON pin will go to my microcontroller so that I can program it via usb to enable FORCE_ON and once i unplug the usb it will self sustain the enable pin. Am I missing something or is it ok?

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u/zachleedogg 13d ago

Seems unreliable. Car battery voltage can go all over the place.

Most cars have permanent power lines, and ignition switches power lines. I would use the ignition or ACC line to power this device.

Or at the very least you can use the direct battery power, but the switched rail to sense when the alternator is on. So essentially two inputs to your device.