Confused with Nodal Analysis and Voltage Sources! HELP!

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Discussion Overview

The discussion revolves around the challenges of applying Nodal Analysis in circuit analysis, particularly when voltage sources are involved. Participants seek to clarify the method for determining node voltages in circuits with voltage sources, contrasting it with scenarios involving current sources.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about applying Nodal Analysis with voltage sources, having learned the method primarily with current sources.
  • Another participant suggests posting the specific circuit to receive more tailored assistance.
  • A participant introduces the concept of 'supernodes', explaining that nodes connected by a voltage source can be treated as a single node, with a voltage difference equation established between them.
  • It is mentioned that when there is only one voltage source, one can typically choose the negative terminal as the reference node, but multiple voltage sources may necessitate the use of supernodes.
  • Another suggestion involves performing a source transformation, converting a voltage source in series with a resistor into a current source in parallel with a resistor, depending on the circuit configuration.
  • A participant asserts that if one can analyze circuits with current sources, they can also analyze those with voltage sources by applying Ohm's law to convert voltage to current.

Areas of Agreement / Disagreement

Participants present various methods and approaches for handling voltage sources in Nodal Analysis, indicating that there is no single agreed-upon method, and multiple perspectives remain on how to effectively address the problem.

Contextual Notes

The discussion does not resolve the specific challenges faced by the original poster, and the applicability of the suggested methods may depend on the specific circuit configuration and assumptions made.

Ali Inam
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The question might be simple for you guys but the problem is that it is not for ME !


I have a circuit and I have to determine the node voltages by Nodal Analysis method.

And the one which I learned was in cases when we had a current source, I could simply write the equations using KCL.


But I am totally confused in such cases when I have a voltage source, and I have been asked to do the same (i.e calculate the nodal voltages).

Please HELP OUT !
:cry:
 
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If you post the circuit you're having trouble with, you will be more likely to get help.
 
Look up 'supernodes'. Basically, the nodes on either end of the voltage source combine into a single node. If the nodes are, for example, A and B, and the voltage souce between them 12v, then:

A - B = 12v (where A - B just means "the voltage difference between A and B")

Since A and B are treated as a single node, your KCL equation for the 'supernode' will have to include current going in and out of both nodes.
 
If there is just one voltage source, it is easy to choose one of its nodes (usualy the negative terminal) as the reference node. For an example, check out this:
http://circuits.solved-problems.com/resistive-circuits/problem-1-11-solving-circuit-nodes-nodal-analysis/
If there are more than one voltage source, you may have to use supernode. You can find an example http://circuits.solved-problems.com/resistive-circuits/nodal-analysis-6-node-circuit/"
 
Last edited by a moderator:
Depending on what your circuit looks like, you may also be able to do a source transformation of a voltage source in series with a resistor to a current source in parallel with a resistor.
 
If you can do it with current source, then you can definitely do it with voltage source. Just simply use the ohm law to convert the voltage to the current. For example, I=V/R, if You have the KCL equation,then just replace I variable with V/R by using ohm law.
 

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