Calculate Output Voltage of Op-Amp Circuit

Click For Summary

Discussion Overview

The discussion revolves around calculating the output voltage of an op-amp circuit, with participants exploring various approaches to solve the problem presented in a homework assignment. The conversation includes attempts at using superposition, Kirchhoff's Current Law (KCL), and considerations of ideal op-amp assumptions.

Discussion Character

  • Homework-related
  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about identifying the type of op-amp circuit and attempts to use superposition to find the output voltage.
  • Another participant suggests using ideal op-amp assumptions and writing a KCL equation at the inverting input terminal to solve for the output voltage.
  • Several participants discuss the implications of switching the + and - inputs of the op-amp, questioning whether it would affect the output voltage and expressing concerns about potential errors in the circuit diagram.
  • One participant calculates an output voltage of -31.5V but questions the correctness of their signs in the equation.
  • Another participant mentions that with the inputs switched, the output would peg at one of the power supply rails, indicating instability due to positive feedback.
  • Multiple participants derive an output voltage of -16.5V using a formula from their textbook, but they express uncertainty about the validity of this result in practical terms.
  • One participant reflects on the importance of understanding the underlying principles rather than relying solely on memorized formulas for op-amp circuits.
  • There is a discussion about the practical implications of achieving an output voltage of -16.5V, with one participant guessing it might use too much power.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct output voltage or the implications of switching the op-amp inputs. There are multiple competing views regarding the calculations and the potential errors in the circuit diagram.

Contextual Notes

Participants express uncertainty regarding the signs in their calculations and the stability of the circuit based on the configuration of the op-amp inputs. There are also references to textbook formulas that may not apply universally to all op-amp circuits.

  • #31
berkeman said:
Get the same answer with two different approaches, and you can feel good about your answer, right? And I'll bet you're starting to like the KCL better about now, right?

I felt pretty good about it until my professor said it was wrong...then checked his notes...then told me it was right (this kind of thing happened twice in lab!) it's the same professor who gave an unsolvable op-amp design test problem...I get the feeling I might have to come to this forum for lots of help this semester lol. I hope I'm not wearing out my welcome.

But yeah, I like KCL because it's difficult to screw it up
 

Similar threads

Replies
15
Views
3K
  • · Replies 13 ·
Replies
13
Views
3K
Replies
34
Views
4K
  • · Replies 12 ·
Replies
12
Views
4K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
21
Views
3K
Replies
1
Views
2K
  • · Replies 44 ·
2
Replies
44
Views
5K
  • · Replies 2 ·
Replies
2
Views
3K