Low voltage cut off

386

09:35:31

Stops current flowing through the load (green resistor) when the supply voltage falls below a set value.

Can be used to stop batteries discharging past a set voltage, or to turn of a circuit when the supply voltage is too low for it to function properly.

Cut off limit can be adjusted using the potentiometer.

The mosfet can be replaced with a relay if required, but will draw more power (reduced battery life) and likely result in a bulkier circuit.

Works by using an op amp as a comparator comparing a fraction of the supply voltage (defined by the pot) to a reference voltage (defined by the zener diode). The amp will then only turn on the mosfet if the fraction of the supply voltage is greater than the reference voltage.

published 5 years ago

sesquialtera

5 years ago

A bit alien to me, but if the pot wiper should accidentally be at the positive end of the pot, you are actually applying full psu voltage and more importantly full potential current from the psu to the non inverting input. Perhaps your pot should have a series resistor to limit damage. Which by the way is shown in your calculation. What do you think.

mlira

5 years ago

I don't think an extra resistor is needed in this case, as it only feeds the amp input and the input impedance of op amps is extremely high, so there shouldn't be any current. It would only be an issue if the voltage was more than the amp could handle, but asuming the amp is powered off the same supply you would either need an amp that could handle the voltage or an additional voltage regulator to power it (and the resistor you suggested). I'll add a breif explanation of how it works to the description, but if you turn the pot all the way then all it's doing is telling the amp to turn off the mosfet when the supply is lower than roughly the value of the zener diode.

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