Why is my simulated inverting amplifier output not matching the expected result?

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The user is experiencing unexpected output from a simulated inverting amplifier in LTSpice, expecting Vout to equal -Vin but measuring approximately 0V instead. Key suggestions include ensuring the negative power supply is correctly set to -5V and connecting the non-inverting input to 2.5V for proper reference. The discussion clarifies a common misconception about the output voltage formula, emphasizing that Vo = V(+) + Av * (V(+) - V(-)), which aligns with the simulation results. Proper configuration of power rails and reference points is crucial for achieving the expected output. Adjusting these parameters should resolve the discrepancy in the simulation results.
hemant03
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Hi,
I was trying to simulate a simple inverting amplifier in LTSpice. However, the results that I get don't agree with what I am supposed to get.
Please look at the PDF attached.
Based on the current law, it is easy to tell that Vout = -Vin. But I am seeing Vout = app. 0V.
Am I missing something. Please help
 

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Have you connected your negative power supply to 0V or -5V?
You won't get lower volts out than your negative rail.
 
The non-inverting input should be connected to V3/2 or 2.5 V. That way when V1 is at +5 V the output will be at 0 V and when V1 is at 0 V, the output will be at 5 V. And of course when V1 is at 2.5 V, the output will be at 2.5 V.

There seems to be a common misconception that the Vo = Av * (i(+) - i(-)). If that were true when V1 is equal to 2.5 V you would see 0 V at the output instead of 2.5 V. The correct formula is Vo = V(+) + Av * (V(+) - V(-)).
 
The simulation is giving you the correct answer for the conditions you've given it. You just need to decide whether you want +&- power rails and to use 0V as your reference or to use +5 and 0, in which case, your reference (non-inverting input) should be connected to 2.5V
 
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