Analyzing this operational amplifier circuit with DC

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Discussion Overview

The discussion revolves around analyzing an operational amplifier circuit presented in a qualifying exam sample. Participants are exploring the implications of the circuit's design, particularly the relationship between the input voltages and the physical feasibility of the circuit as drawn.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant shares their attempt at solving the circuit problem, referencing a textbook but noting a lack of examples that connect the power supply to the amplifier.
  • Another participant asserts that the circuit has a fundamental problem and is non-physical, questioning its origin from a textbook.
  • A participant mentions that the circuit is from qualifying exam samples and expresses frustration over the absence of solutions.
  • Concerns are raised about the validity of the circuit, with one participant suggesting that the task may be to identify the circuit's flaws to receive credit.
  • There is a discussion about the necessity of DC bias connections for op-amp inputs to supply bias currents and set the operating point, indicating a potential issue in the circuit design.
  • One participant seeks clarification on the placement of connections in relation to the circuit's configuration.

Areas of Agreement / Disagreement

Participants generally disagree on the validity of the circuit, with some asserting it is fundamentally flawed while others are attempting to understand the implications of the design. The discussion remains unresolved regarding the specifics of the circuit's issues.

Contextual Notes

There are missing assumptions regarding the circuit's design and its physical feasibility, as well as unresolved questions about the implications of the op-amp's input conditions.

ZoeDale
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Homework Statement
a) Treat the operational amplifier in the circuit below as ideal and solve for Vo.
b) Treat the op amp as a non-ideal device that is powered by VCC and VEE; describe several ways in which your answer in part a) will change.
Relevant Equations
KVL; KCL;
Hi all, I attached my attempt at a solution in the attached picture. I am using the textbook titiled as ”electronic circuit analysis“ by David E. Johnson, and op amp is in chap 3;
while I did not find any example that attach the Vee and Vcc with amplifier . It seems that v+ = v- doesn’t hold in this scenario; can anybody give me some hints?

thanks!
 

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Um, that circuit has a fundamental problem, and is non-physical. SPICE, for example, would throw an error if you tried to analyze it. Are you sure this came from a textbook?
 
this is a problem from our qualify exam samples for practice. No solutions provided. :cry:
 
ZoeDale said:
this is a problem from our qualify exam samples TAT for practice. No solutions provided.
Well, that circuit is complete nonsense as drawn, so there is no solution to the problem. Maybe that is the test of the problem -- you are supposed to reply that the circuit is nonsense in order to get credit.

Can you say what is totally wrong about that circuit?

1701990267207.png
 
berkeman said:
Um, that circuit has a fundamental problem, and is non-physical. SPICE, for example, would throw an error if you tried to analyze it. Are you sure this came from a textbook?
Seems that v+ can not be equal to v- in the ideal condition; or the non-ideal condition. But I can not figure out what will happen in the circuit; Can you give more hints on that? Thank you!
 
ZoeDale said:
Can you give more hints on that?
Opamp inputs must have some DC bias connection to somewhere to supply their input bias currents and to set the DC operating point. Do you see the issue now? :smile:
 
berkeman said:
Opamp inputs must have some DC bias connection to somewhere to supply their input bias currents and to set the DC operating point. Do you see the issue now? :smile:
oh, you mean they should be on each side of the lying triangle's waist, separately?
 
ZoeDale said:
oh, you mean they should be on each side of the lying triangle's waist, separately?
Sorry, I don't understand your response.
 

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