Current source in series with resistor

[rajohns08]

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?

Homework Equations

The Attempt at a Solution

My teacher told us this in class but i can't 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?

 

[berkeman]

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?

Homework Equations

The Attempt at a Solution

My teacher told us this in class but i can't 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?

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

.

 

[MRSquared]

My teacher told us this in class but i can't remember if a current source w/ resistor in series is same as 0 current or infinity current.

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.

 

[berkeman]

Neither. However, the statement "a current source with 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.

Why do you say that? The output impedance of a current source is high (infinite for an ideal current source).

 

[MRSquared]

Why do you say that? The output impedance of a current source is high (infinite for an ideal current source).

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:

 

[CEL]

Why do you say that? The output impedance of a current source is high (infinite for an ideal current source).

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.

 

[berkeman]

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:

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.