OP-Amp Comparator malfunctioning


Joined Aug 1, 2013
The transistor is just for refernece the actual transistor model is C945.
That is not just a different part - it is a completely different *type* of part. Please fix the schematic so we can see what we are dealing with.

To be clear - In Electrical Engineering, a correct schematic is not an option - it is ***everything***. This is a help forum; the help is free. But our time has value and we do require a little respect.


Thread Starter

Hamza Mustafa

Joined Mar 1, 2018
If I may suggest the problem, the relay continuously changing states maybe due to the fact as the battery supplies load its voltage decreases slightly and at time of lower cut off as the load gets disconnected the voltage rises slightly causing a disturbance on the pins of op-amp. Hysteresis will solve the problem but I don't require a band wide enough so that the load supply does not start when charging is available. Otherwise the suggestions from the members have been quite beneficial in understanding the design errors.


Joined Jan 29, 2010
hi Hamza,
The decrease in the power supply sensing network voltage, when another switched component draws more power from the supply is a common problem in comparator circuits,
This is why it is important to have the sensing network powered from its own stabilised voltage reference.

Hysteresis around the comparator is also important, usually a positive feedback resistor is sufficient to give the required hysteresis.
It is possible to use a second comparator to give a very wide hysteresis range.