Operational Amplifier Homework Question

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Discussion Overview

The discussion revolves around a homework question regarding the calculation of voltage V2 in a non-inverting operational amplifier circuit in terms of the input voltage Vos. Participants explore different methods to arrive at the solution, including the nullator hypothesis and potential divider concepts.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant states that V2 can be expressed as V2 = Vos x (R2/(R1+R2)), referencing the non-inverting amplifier configuration.
  • Another participant questions the dimensional correctness of the initial equation and clarifies that the gain of a non-inverting op amp is always greater than or equal to 1 unless feedback is applied.
  • Several participants discuss the assumption that the voltage across resistor R1 is equal to Vos, which leads to deriving the current i and subsequently solving for V2.
  • One participant confirms that assuming the voltage across R1 is Vos is a valid approach for solving the problem.

Areas of Agreement / Disagreement

There is some agreement on the validity of assuming the voltage across R1 is Vos, but there are differing views on the initial equation for V2 and its dimensional correctness. The discussion remains unresolved regarding the best approach to derive V2.

Contextual Notes

Participants have not reached a consensus on the correct formulation of V2, and there are unresolved questions about the assumptions made regarding the circuit configuration and the implications of feedback.

Ariastity
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Homework Statement


What is the value of V2 in terms of Vos?

Homework Equations

The Attempt at a Solution


In the class, we were told that this is just a non-inverting amplifier, thus V2= Vos x (R2/R1+R2).
However, I want to work out the solution by applying nullator hypothesis (voltage difference between the two op amp inputs is 0) only, without realising that the top part is a potential divider.

Is it correct to assume that the voltage across R1 is Vos? That way, I can get the current i to solve for the voltage across R2.
http://[PLAIN]http://i64.tinypic.com/a0i5hs.jpg
http://i64.tinypic.com/a0i5hs.jpg

upload_2016-12-8_12-34-15.png
 
Last edited by a moderator:
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Ariastity said:
Is it correct to assume that the voltage across R1 is Vos? That way, I can get the current i to solve for the voltage across R2.
Yes, that's a valid assumption here.
 
Ariastity said:
In the class, we were told that this is just a non-inverting amplifier, thus V2= Vos x (R2/R1+R2).
A non-inverting op amp gain is always >=1 unless the feedback is active (another amplifier section). So I hope you were not told that ...
... and I assume you meant Vos x R2/(R1+R2) otherwise your equation is dimensionally wrong.
 
Ariastity said:
Is it correct to assume that the voltage across R1 is Vos? That way, I can get the current i to solve for the voltage across R2.
http://[PLAIN]http://i64.tinypic.com/a0i5hs.jpg
View attachment 110118
Yes - with this assumption you get I=Vos/R1=(V2-Vos)/R2.
This equation can simply be solved for V2.
 
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