Understand source transformation

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Discussion Overview

The discussion revolves around the concept of source transformation in electrical circuits, specifically focusing on the application of Thevenin's theorem and the treatment of voltage and current sources in various configurations. Participants seek clarification on how to determine Thevenin resistance and the conditions under which source transformations can be applied.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that the Thevenin resistance is found by short-circuiting the voltage source, but question whether the same applies when dealing with a current source.
  • There is a suggestion that when both a voltage source and a current source are present, the resistance found by short-circuiting may differ based on the configuration.
  • One participant proposes that a current source can be treated as an open circuit when removed, while others clarify that short-circuiting a current source leads to incorrect resistance calculations.
  • Participants discuss the limitations of source transformation, noting that if a current source and resistor are in series, transformation to a voltage source is not possible.
  • There is a query about the conditions under which a voltage source and resistor can be transformed into a current source, with some participants affirming that series configurations allow for this transformation, while parallel configurations do not.
  • Some participants mention that there are alternative methods to simplify circuits when direct transformation is not applicable.

Areas of Agreement / Disagreement

Participants express differing views on the treatment of current and voltage sources during source transformation, with no consensus reached on the best methods or conditions for transformation. The discussion remains unresolved regarding specific procedures and outcomes.

Contextual Notes

Participants highlight the importance of understanding the configurations of sources and resistors, indicating that assumptions about circuit behavior may vary based on specific arrangements. There are references to potential tricks for simplifying circuits, but these methods are not detailed.

Who May Find This Useful

This discussion may be useful for students and practitioners in electrical engineering or physics who are exploring circuit analysis techniques, particularly those involving Thevenin's theorem and source transformations.

Air
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I'm trying to understand source transformation and with my research, I have had some confusion. I have two question regarding them and would appreciate any help.


  1. I understand that the thevenin resistance is found by short circuiting the voltage source. Is that also the case when you short circuit the current source? What if it has both sources, what resistance do we find when we short circuit them?
  2. By using source transformation, can we only change to voltage source if the current source and the resistors are in parallel?

Thanks in advance.
 
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Air said:
  1. I understand that the thevenin resistance is found by short circuiting the voltage source. Is that also the case when you short circuit the current source? What if it has both sources, what resistance do we find when we short circuit them?
  2. By using source transformation, can we only change to voltage source if the current source and the resistors are in parallel?

1. You simply make a current source an open circuit. If you think of it a current source keeps the current in one branch constant, if you take it out, there would be no current.

2. Yep.
 


Kruum said:
1. You simply make a current source an open circuit. If you think of it a current source keeps the current in one branch constant, if you take it out, there would be no current.

2. Yep.

1. So if you take out the current source, it's not the same as taking out voltage source. By taking voltage source out, you can find thevenin resistance. By taking current source out, you find nothing? Is that what you are saying? :confused:

2. Great. So if the current source and the resistor are in series then we cannot use source transformation to change to voltage source?
 


Air said:
1. So if you take out the current source, it's not the same as taking out voltage source. By taking voltage source out, you can find thevenin resistance. By taking current source out, you find nothing? Is that what you are saying? :confused:

No, you can take the current source out. You just can't short circuit it otherwise your resistance will be wrong.

2. Great. So if the current source and the resistor are in series then we cannot use source transformation to change to voltage source?

Unfortunately, no. But there are usually some other tricks we can use to make the circuit easier.
 


Kruum said:
No, you can take the current source out. You just can't short circuit it otherwise your resistance will be wrong.

So, if I'm to find the thevenin resistance and have been given both voltage source and current source, is the best method to convert the current source to the voltage source then short circuit the current source?

Kruum said:
Unfortunately, no. But there are usually some other tricks we can use to make the circuit easier.

Hmmm... Can you briefly explain what to do if current source and the resistor are in series and we wish to change to voltage source?
 


Air said:
So, if I'm to find the thevenin resistance and have been given both voltage source and current source, is the best method to convert the current source to the voltage source then short circuit the current source?

You could do that. But then again you can take the current source out and replace it with an open connection.

Hmmm... Can you briefly explain what to do if current source and the resistor are in series and we wish to change to voltage source?

If you have a current source in series with a resistor, there is nothing you can do to change the current source into voltage source. I meant that you can make the circuit easier by using some other tricks. Sorry for confusing you, I'm not natively English.
 


Kruum said:
You could do that. But then again you can take the current source out and replace it with an open connection.

Great, Thanks.

Kruum said:
If you have a current source in series with a resistor, there is nothing you can do to change the current source into voltage source.

Cool. I have a final question regarding this. If the voltage source and the resistor is in series, then it can be changed to current source? If the voltage source and the resistor is in parallel then it cannot be changed to current source?

Kruum said:
Sorry for confusing you, I'm not natively English.

It's ok. You have helped me a lot and your language has been very clear.
 


Air said:
If the voltage source and the resistor is in series, then it can be changed to current source? If the voltage source and the resistor is in parallel then it cannot be changed to current source?

That's right.
 


If you have a current source in series with a resistor, you can eliminate the resistor from your circuit.
The same is true for a resistor in parallel with a voltage source.
 
  • #10


CEL said:
If you have a current source in series with a resistor, you can eliminate the resistor from your circuit.
The same is true for a resistor in parallel with a voltage source.

Providing you have the appropriate circuit to do so.
 

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