I'm powering a project with a 2-cell 7.4V LiPo battery. What circuit do I add to make the unit stop drawing power when the voltage from the battery drops below 6.4V? The goal is to protect the LiPo battery from discharging below 3V/cell.
In all the following a TLV431 1.25V reference is specified.
When on the TLV431 on voltage is about equal to the reference voltage - NOT 0V.
TLV431 current is a battery load even when output is off. At about 100 uA this drains about 2.5 mAh/day.
Voltage sensing divider is also a battery load. This can be small.
Hysteresis is not used in any of the following circuits - except the one copied from internet. A whiff of hysteresis could be used to stop battery on/off cycling when load is removed. Ask if unclear how to do this.
(1) Opamp based
(2) N Channel FET, low side switch.
(3) P Channel FET, high side switch.
(4) From web - similar to my N Channel low side circuit.
Here R6 adds hysteresis.
You could use a reset IC like the MAX809. This will output a low level when the input voltage is below the device's threshold. If the input voltage is higher than the threshold the output follows the input.
You can use this voltage to switch an N-channel MOSFET, like the FDC653N.
I am not at all familliar with LiPo batteries.
But To detect the Voltage level going below certain limit, You can always use OP-AMPS...
I have this age old book... Hope it helps you--