Electronic – Is Multisim simulating right

multisimoperational-amplifier

I am new to Operational Amplifiers and I am trying to simulate a differential amplifier with a gain of 1.2, here it is:

enter image description here

As you can see I am using input voltages higher than VCC and according to datasheet the Common Mode Voltage Range is VCC-1.5V so the Operational Amplifier should work "ok" only with input voltages less than 28.5V am I right?

But on this simulation I am getting a correct output: (40-32)*1.2 = 9.6V. So I can put higher voltages than Vcc or simulation is wrong?

Best Answer

I have tried this with higher voltages and I think, that multisim seems to work correctly when you are not exceeding devices maximum ratings. If you put 100V at the input of op-amp powered from 30V - do not expect any correct results.

In real life op-amp with input voltage above maximum from datasheet would blow up - I dont remember internal structure of LM324, but there are probably ESD protection diodes. They blow up first in that scenario.

My conclusion is - check voltages at input and output pins and make sure they not exceed maximum ratings :)

Also, notice that in your circuit you have voltage dividers at the op-amp inputs and they divide your input voltage by 120ohm/(100ohm+120ohm) = ~0.54.

V2 voltage is divided by R2 and R2, so you have ~21,818V at noninverting input

V1 voltage is divided by R1 and R4, so yoy have ~17,454V at inverting input