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Current source in series with resistor

  1. Apr 28, 2010 #1
    1. In the case of a current source in series with a resisitor, can this be transformed to just a current source with 0 resistance, or is the resistance infinity in the Norton equivalent?



    2. Relevant equations



    3. The attempt at a solution
    My teacher told us this in class but i cant remember if a current source w/ resistor in series is same as 0 current or infinity current. And is the answer the same for the equivalent norton resistance?
     
  2. jcsd
  3. Apr 29, 2010 #2

    berkeman

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    Staff: Mentor

    A current source in series with a resistance is not a standard representation. The standard representations are a current source (infinite Zout) in parallel with a resistance, or a voltage source (zero Zout) in series with a resistance:

    http://en.wikipedia.org/wiki/Thévenin_equivalent

    http://en.wikipedia.org/wiki/Norton's_theorem

    .
     
  4. Apr 29, 2010 #3
    Neither. However, the statement "a current source with a resistor in series is same as 0 resistance" would most likely be what your teacher said, because the resistor would not affect the output current.
     
  5. Apr 29, 2010 #4

    berkeman

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    Why do you say that? The output impedance of a current source is high (infinite for an ideal current source).
     
  6. Apr 29, 2010 #5
    I agree that an ideal current source has an infinite output impedance in parallel with the source, but I was just replying to the OP's question about resistance in series with the source. :uhh:
     
  7. May 1, 2010 #6

    CEL

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    Because the current through the series resistor is independent of the value of the resistor and is input totally to the load.
    Of course, there is a voltage drop through the series resistor, but the voltage and current in the load are not affected.
     
  8. May 1, 2010 #7

    berkeman

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    You guys are correct that the series resistor does not affect the current from the current source. I think in your statement here, you left out the word "resistor", so the slightly corrected quote would be:

    "an ideal current source has an infinite output impedance in parallel with the source resistance"

    I think we are in agreement. I work with current source network transmitters a lot, so the output impedance and output compliance (how close you can drive your output waveform near the rails) are things I deal with quite a bit.
     
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