I have a low battery detection circuit here. When the voltage of the battery goes below 10.5, I have an LED flashing (Uses the NPN transistor and the I/O "1"). This part of the circuit works great. But I also have a shutoff circuit in place where if the voltage of the battery continues to fall and reaches a 2nd threshold, the relay that has BATT and BOUT included in it opens. My first prototype worked well but I was using a relay with a coil voltage rating of 5V (The voltage of CPNP could be as high as 11 V when the battery is at good health). That relay was getting hot.
So I replace that relay with one that is rated up to 12V. But now the system isn't quite working the way it should. If the voltage of BATT is good, the relay turns on like it should, but it will not turn off at the threshold I have set. I noticed when the threshold is met, the collector (CPNP) voltage drops, but still above on 1 or 2 volts which is still enough to keep the relay on. I have added a flydiode to the relay coil as well as placed a 47k ohm resistor on the emitter and base of my PNP resistor but I still get the same result.
Should have I Used a FET instead for this? Is it possible before I place the flyback and the 47 kohm resistor, that I damaged the transistor? I notice when I have OUTPUT 2 set to be low (LM358 <1 volt), there is a still a significant voltage on the PNP side of that 4.7 kohm resistor (between 0.6 to 0.7 away less then emitter). So I think the main goal is to fix the issue with CPNP voltage, how can I make that get closer to zero?