Understanding KCL and the In=0 Principle in OMP Amplifiers

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Discussion Overview

The discussion revolves around the application of Kirchhoff's Current Law (KCL) and the principle that the input current (In) is zero in operational amplifiers (op-amps). Participants are examining a specific example from a textbook that involves analyzing current directions and relationships in an op-amp circuit.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that according to KCL and the In = 0 principle, the relationship I_25 = -I_100 should hold true, but the textbook states I_25 = I_100.
  • Another participant asserts that no current flows into or out of the inputs of an ideal op-amp, suggesting this is a key point in understanding the problem.
  • A different participant proposes that the correct interpretation should be I_25 = -I_100, emphasizing the importance of current direction in the analysis.
  • One participant expresses agreement with the viewpoint that the direction of current must be considered, indicating that the final answer should reflect the assumed direction with a negative sign if it is opposite.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between I_25 and I_100, with some supporting the textbook's claim and others challenging it based on their interpretations of current direction and KCL. The discussion remains unresolved regarding the correct relationship between these currents.

Contextual Notes

There are unresolved assumptions regarding the direction of current flow and how it affects the application of KCL in this context. The discussion does not clarify the specific definitions or conventions used in the textbook example.

Saeed.z
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i came across an example in my textbook as shown :

http://img593.imageshack.us/img593/8444/img1314i.jpg

if we used KCL and In = 0 :

In = I_100 + I_25

=> I_25 = -I_100

but as being written in the answer , I_25 = I_100 !

could anyone explain it for me ? thanks
 
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No current flows into or out of the + or - inputs of an ideal op amp.
Hope this helps
 
Wouldn't the technical answer be [itex]i_{25}=-i_{100}[/itex] since the direction in the diagram is opposite to the actual direction? My textbooks take into account the assumed direction, and if the final answer is supposed to be opposite to the assumed direction, you merely place a minus sign in front of it to indicate that it is in the opposite direction to the supposed direction.
 
Completely agree with Sandy Bridge
 

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