nowbotmike

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• Multisim Op Amp Change To Nano Voltage Light
• Multisim Opamp Change To Nano Voltage System
• Measure Voltage Gain In Multisim

When i change LM324 with 'virtual opamp' it works as expected - there is no negative voltage at output. I know that LM324 is far from ideal but i think it doeesn't have ability to produce negative voltages, especially when there is no capacitor or inductor in this circuit. My question is - what am i doing wrong? What should i set in Multisim to.

• Dec 01, 2010  Current to voltage converter based on op-amp Reply to Thread. Discussion in 'The Projects Forum. Why not use a single op amp, and change the value of the feedback resistor using a window comparator that selects the next higher value feedback resistor when the Vout high threshold is exceeded, or the next lower value feedback resistor when the.
• Sep 07, 2013  Professor Kleitz presents the theory for the design of a gain-of 10 Inverting OpAmp circuit. The design is then demonstrated using MultiSim.

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

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?

AndresAndres

Multisim Op Amp Change To Nano Voltage Light

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2 Answers

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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 :)

Multisim Opamp Change To Nano Voltage System

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

KamilKamil$endgroup$$begingroup$

On the one hand, you are only applying 21.8 V to the input pins of the op-amp, so you are not violating the common mode input specs.

On the other hand, simulators are not necessarily good at detecting unusual conditions. Overvoltages, overcurrents, or thermal runaway conditions are often not modeled accurately (or at all) by SPICE-like simulators.

Whether your circuit works in real life might depend, for example, on how the three voltages (V1, V2, Vcc) are ramped up when you turn the circuit on, or how they ramp down when you turn the circuit off.

Measure Voltage Gain In Multisim

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