Question about Thevenin Equivalent Vth

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Discussion Overview

The discussion revolves around the determination of Thevenin equivalent voltage (Vth) in circuits with independent sources. Participants explore the use of superposition in calculating Vth and address specific circuit configurations, particularly when terminals are positioned in various locations within the circuit.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • One participant questions whether superposition can be used to find Vth in circuits with multiple independent sources, suggesting that it can simplify analysis.
  • Another participant confirms that superposition can indeed be used to find Vth.
  • A participant expresses confusion about determining Vth when the terminals are positioned in the middle of the circuit, seeking clarification on the approach.
  • One participant asserts that the terminals are not actually in the middle and provides a calculation for Vth based on a redrawn circuit.
  • A participant asks why they cannot use a specific current and resistor to determine Vth in a different circuit configuration, referencing Kirchhoff's laws to explain their reasoning.
  • Another participant explains that Vth can be calculated using the voltages across components in a parallel circuit, providing a specific calculation for Vth.

Areas of Agreement / Disagreement

Participants generally agree on the use of superposition for finding Vth, but there is some confusion regarding specific circuit configurations and the application of Kirchhoff's laws. The discussion remains unresolved regarding the best approach for certain terminal placements.

Contextual Notes

Participants reference specific circuit diagrams to illustrate their points, but the discussion does not resolve the assumptions or conditions under which the calculations are made. There is also a lack of consensus on the implications of terminal placement on the determination of Vth.

Dethrocutionx
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Hi guys,

I have a question that is nagging me quite a lot. Let us say that we have a circuit who has two independent sources (any combination of voltage and current sources). In the determination of Vth, can we choose whether or not to use superposition to find this Vth? Because my understanding was that you could use superposition to simplify the analysis or choose to leave both the sources in and find the equivalent voltage. Am I correct?

Thanks guys :).
 
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Yes you can use superposition to find this Vth voltage.
 
Thanks! Appreciate it. I have another question related to the determination of Vth. I have an example I am doing where the A and B terminals are in the middle. What does one do to determine this Vth then? Because when the terminals are on the left or the right, it makes sense how we are taking a look at this circuit's inner workings. But the confusion is there when it is in between.

Here's a picture of the problem:
https://www.dropbox.com/s/e3tfnt05unozupw/20121207_164124(0).jpg
 
Well In your diagram A,B terminals are not in the middle.
Because we always can redraw it to this form

attachment.php?attachmentid=53720&stc=1&d=1354924675.jpg


And Vth = - 1mA*1KΩ = -1V and Rth = 1KΩ
 

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Dethrocutionx said:
https://www.dropbox.com/s/ctix99089gdmzqm/20121207_171919.jpg?m

I somewhat understand how we can get Vth to be 6V using the left side of the circuit. Why can't we use the 2mA and the 2kΩ resistor to determine the same Vth?
The answer is that the second Kirchhoff's law doesn't allow us to do so.
Why? I hope that this diagram explains everything

attachment.php?attachmentid=53722&stc=1&d=1354928896.png


As you can see Vth voltage is equal to

Vht = V2 + V3 and also Vth = V1 (In a parallel circuit, the voltage across each of the components is the same)

therefore

Vth = 2mA * 3KΩ = 6V
 

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That makes perfect sense! Thank you so much :). I truly appreciate it
 

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