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Ideal voltage/current sources

  1. Mar 6, 2007 #1
    Can someone please explain why ideal voltage/current sources are short circuit for voltage source and open circuit for open circuit in small signal analysis??? Any mathematical proof to this?
  2. jcsd
  3. Mar 6, 2007 #2


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    Staff: Mentor

    I would think of it in terms of [tex]Z = \frac{dv}{di}[/tex] (although there may be other ways).

    For a good voltage source, the output voltage is very stiff (doesn't change much) as the output current changes, so

    [tex]Z = \frac{dv}{di} = \frac{0}{di} = 0[/tex]

    But for a good current source, you get very little change in the output current over a wide range of output voltages, so

    [tex]Z = \frac{dv}{di} = \frac{dv}{0} = infinity[/tex]

    EDIT -- okay, I give up. How do you make the little infinity symbol in LaTex? "\inf" didn't work.
  4. Mar 6, 2007 #3
    Berkman is correct.

    Voltage source can provide infinite amount of current. And a current source can provide an infinite amount of voltage.

    Z = V/I

    [tex] \infty [/tex]
    Last edited: Mar 6, 2007
  5. Mar 7, 2007 #4


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    Staff: Mentor

    Thanks waht! :biggrin:
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