I made this circuit:
I would like the following:
The LM1 opamp wathching the battery voltage and the output high while the battery voltage higher than 3V. When the voltage drops below 3V, the opamp output go low and turn off the N-channel mosfet, so no more current consuption from the battery (except the watching circuit which is only 1-2mA).
How can I modify this circuit to if once the battery voltage dropped below 3V, never turn off, or turn on olny when the voltage higher than 3.5V?
Now my problem is when turning off because the low voltage, immediately turning on again because the voltage higher than 3.00V.
Best Answer
It sounds like you need an under-voltage-lock-out (UVLO) circuit like this: -
You would select R5 to provide the right amount of positive feedback to ensure the switching points are at 3.0 volts and 3.5 volts. So, once the MOSFET is turned off, U1's output raises the target voltage at point B and this means the Li-ion cell has to "recover" a certain amount before the circuit reactivates the MOSFET and applies power to the load. Once power is re-applied, the op-amp output is low thus setting a lower target voltage at point B hence, the Li-ion has to drop to a lower threshold before the load is disconnected.
You might also be interested in the TLV3011/3012 - it has a voltage reference built in and can be "wired" to have hysteresis.