Non Inverting Op-Amp Circuit Analysis

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Discussion Overview

The discussion revolves around the analysis of a non-inverting operational amplifier (op-amp) circuit, specifically focusing on calculating the output voltage (Vout) and the voltage at a specific point (V1) given a sinusoidal input voltage (Vin). The scope includes homework-related problem-solving and technical explanations of op-amp behavior.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a homework problem involving a 1V peak sinusoidal input and seeks to calculate V1 and Vout.
  • Another participant asserts that VB must equal VA for the op-amp to function correctly as an amplifier, indicating a misunderstanding in the initial attempt.
  • There is a repeated inquiry about the designation of terminals, with some participants expressing confusion over the labeling of the non-inverting input as negative.
  • A participant clarifies that the (-) terminal refers to the inverting input, which is used for negative feedback, while the input is applied to the (+) non-inverting terminal.
  • Concerns are raised about incorrect mathematical reasoning regarding the relationship between V1 and Vb, questioning the need to invert Vb.
  • Another participant suggests focusing on nodal analysis for solving the circuit, stating that in an ideal op-amp, V1, A, and B are equal and proposing a method to find Vout using a voltage divider and nodal analysis.

Areas of Agreement / Disagreement

Participants express differing views on the correct interpretation of terminal designations and the mathematical relationships in the circuit. There is no consensus on the initial calculations or the approach to solving the problem.

Contextual Notes

Some participants highlight potential misunderstandings regarding the roles of the op-amp terminals and the assumptions made about ideal op-amp behavior. There are also unresolved mathematical steps in the initial attempt at a solution.

cavalieregi
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Homework Statement


For an input potential (Vin ) which is a 1V (peak) sinusoidal source. Calculate V1 and Vout
upload_2014-11-6_14-49-48.png

Homework Equations


- The laws for an op-amp
- NVM

The Attempt at a Solution


Here is my attempt not sure if correct.
upload_2014-11-6_15-2-34.png
 

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VB = VA otherwise the OP-AMP is not operating as an amplifier. Fix this and you should be right.

This is a non-inverting amplifier, the input being applied to the (+) input.
 
NascentOxygen said:
VB = VA otherwise the OP-AMP is not operating as an amplifier. Fix this and you should be right.

This is a non-inverting amplifier, the input being applied to the (+) input.
Cool, just wondering why it is a negative terminal ?
 
cavalieregi said:
Cool, just wondering why it is a negative terminal ?
Why what is a negative terminal?
 
NascentOxygen said:
Why what is a negative terminal?
On diagram it has (-) for non inverting input.
 
cavalieregi said:
On diagram it has (-) for non inverting input.
(-) is the inverting input of the OP-AMP, used here for negative feedback of some output to reduce the gain from its high open-loop value. The circuit's voltage input is applied to the (+) non-inverting input of the OP-AMP.
 
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in addition to Nascent's points, you did some math solving for Vb incorrectly.
you say V1-Vb=0

so that means V1=Vb
why invert Vb?
 
Dont worry so much about what terminal is negative and so forth assuming this is an ideal amp.
To master op amps just stick to nodal analysis.
In this case, V1=A=B. They are all the same voltage.
We know that no current enters the op amp thru the + and - terminals.
Therefore we can easily find the voltage at A or V1 by using a simple voltage divdier. Vin X (10K/57K) = A
Now you know the voltage at B since the + and - terminals are equal in ideal amps.
Now use nodal analysis, (B / 1k) + (B - Vout)/ 10K = 0.
Solve and you are done.
 
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