Electrical – 6v battery low voltage cut-off circuit


I have a circuit that draw 150 ma and i use 6V/4Ah dry cell to supply. Voltage regulator of this circuit needs minimum 8V so I use boost converter to draw the battery voltage to 8 volts.This converter works up to 2 volt.

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I would like to stop this module when battery goes below 4-5 volt. I tried this circuit with converter. enter image description here

It worked but when i connect the converter to system the input voltage of the converter is decrease and converter is not work even battery at 6V. I would like to learn why this circuit not worked and what can i do to work this circuit for cut off the voltage under 4-5 volt.

Best Answer

The usual way of doing this is to use a comparator circuit that compares a reference voltage with the battery supply voltage. If the battery supply voltage falls below the reference voltage, the comparator disconnects the load e.g. with a P-channel FET.

As for the reference, you can use a simple zener diode (which is not a good reference) or better a voltage reference (e.g. TL431). Because the comparator also needs to be powered with the battery (down to 5V), you need to use a much lower reference than 5V. So you could e.g. take a 2.5V reference and compare that with the comparator against a voltage divider with 1:1 resistor ratio from the battery.