Source transformations doesn't always produce same result?

  • Thread starter eng_stud
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  • #1
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I was under the impression that a source transformation doesn't change a circuit at all, which I guess is an oversimplification.

If you have a series RC circuit, with a DC voltage source, after the transients have died out, all voltage will be across the capacitor, and none across the resistor, as there is no current flowing anymore (when cap is fully "charged"), right?

If you now do a source transformation, changing the DC voltage source to a DC current source, with the resistor in parallel, you now have a parallel RC circuit with a DC current source. Now, surely, current will never cease as it has another path through the resistor. So after the capacitor is charged, all current goes through the resistor. So in this case there's voltage across both the resistor and capacitor?

This might all be incredibly obvious. I just want to make sure there is nothing here that I have misunderstood!:)
 

Answers and Replies

  • #2
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Follow-up question: If you have a circuit with a 10 A dc current source, with a 3 Ohm resistor and a 0.02 F capacitor in parallel, what determines the resulting voltage across the parallel setup? When the capacitor is fully charged? Or the voltage that would have been the source had we done a source transformation? (i.e. v=ir=10*3=30 V across both components).

I'm assuming the latter?
 
  • #3
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Your understanding in both posts is correct. With a current source, a resistor and capacitor in parallel the final source voltage will be equal to the current times the resistance.
 
  • #4
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Thanks, skeptic2!
 

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