Ideal voltage/current sources

  • Thread starter jinyong
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  • #1
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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?
 

Answers and Replies

  • #2
berkeman
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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.
 
  • #3
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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

infty
[tex] \infty [/tex]
 
Last edited:
  • #4
berkeman
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infty
[tex] \infty [/tex]
Thanks waht! :biggrin:
 

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