I would like to protect the batteries from over discharge, so I want to make a protection ciruit.
I made this:
I want the following: 2x 9V battery in series, so total voltage is 18V. The regulator is 8V, the mosfet is N-channel. If the first battery voltage is greater than 8V, the op-amp output will high, so the N-channel mosfet gate voltage will be high and the mosfet will open.
If the first battery voltage drop below 8V, the op-amp lower the output, so the mosfet is off, and no more power consuption from the battery.
The problem is the following:
The mosfet doesn't turn off when the battery voltage drops below 5V. (in this example only, I didn't find 8V regulator in LTSpice)
The opamp output not 0V else its ~2v output so the mosfet doens't turn off.