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

  • Thread starter Thread starter hemant03
  • Start date Start date
  • Tags Tags
    Amplifier
Click For Summary

Discussion Overview

The discussion revolves around a participant's simulation of an inverting amplifier in LTSpice, where the output does not match the expected theoretical result. The focus is on troubleshooting the simulation setup and understanding the circuit behavior under different conditions.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that the output voltage (Vout) is approximately 0V instead of the expected -Vin, suggesting a potential issue with the negative power supply connection.
  • Another participant proposes that the non-inverting input should be connected to a reference voltage (2.5V) to achieve the expected output behavior, challenging a common misconception about the output voltage formula.
  • A different participant emphasizes that the simulation is providing correct results based on the given conditions and suggests clarifying the choice of power rails and reference voltage.

Areas of Agreement / Disagreement

Participants express differing views on the correct setup for the inverting amplifier simulation, particularly regarding the power supply connections and reference voltages. No consensus is reached on the best approach to resolve the output discrepancy.

Contextual Notes

Participants mention assumptions about power supply configurations and reference voltages, which may affect the output results. The discussion does not resolve these assumptions or their implications for the simulation outcomes.

hemant03
Messages
15
Reaction score
0
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
 

Attachments

Engineering news on Phys.org
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
 

Similar threads

  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 26 ·
Replies
26
Views
4K
  • · Replies 39 ·
2
Replies
39
Views
5K
Replies
5
Views
3K
Replies
9
Views
8K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 15 ·
Replies
15
Views
3K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 2 ·
Replies
2
Views
4K