[Moved] problems regarding initial value in opamp 741

Hello there,
I am using opamp 741 to compare two voltage levels.
Here I have supplies 3.5V as Vin,and a Vref of 2V to the inverting terminal through a potentiometer,but I get a constant initial value of 1.17V,when I connect the non-inverting terminal to ground and a value of 3.12V when connected to Vcc.
I have tried all the possible ways I knew,but am unable to initialize it properly.
Please help me out.

741 works on dual supply i.e. +V and -V. Also, the op-amp is not rail to rail.
can u share the schematic? this will help in solving the problem.

yes but it is not necessary to have a negative supply instead I connected -Vcc to ground.

A lousy old 741 opamp was designed 46 years ago to use ONLY a +15V and a -15V power supply.
But some of them might work with a +5V and -5V power supply.

Its datasheet shows that its inputs might not work if they are within 3V from the positive or negative supply voltage and the output cannot go within 5V from the positive or negative supply voltage when it has a 2k ohms load.

Like ANY opamp, if its inputs are biased at half the supply voltage and coupling capacitors are used then a single positive power supply +10V or more can be used. Then its negative supply pin is connected to 0V. But the inputs must never go below +3V and its output will never go near 0V nor near the positive supply voltage.

So your positive power supply voltage is much too low, your reference inverting input voltage is too low and your non-inverting input must never go less than +3V.

It sounds like you are using it as a comparator, but it is an old opamp, not a comparator. It can compare voltages near half the supply voltage and its output can be near half the supply voltage.

OK thanks for your information,I missed that part of it.
So could you suggest me any other alternatives.

U can use LF356/LM324 but there are better specifically designed rail to rail single supply op-amp like OPA 324. U can go to ti, microchip, analog devices etc. websites and use parametrized selection table to select best op-amp for your application.

An LF356 or LM324 are basic op amps similar to a 741 but will operate down to 0V input and output with a single supply. Unlike a rail-rail type their inputs and outputs can only go to within a volt or so the the positive rail but that should be sufficient for you requirements with is Vcc is 5V or greater.

For doing comparisons a comparator may work better, such as the LM339. It has faster operation and the output (but not the input) can go the the positive rail. But note that the output needs a pull-up resistor to the positive rail for proper operation.