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Current souce vs Voltage source

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voltage source vs current source

Hi there,

I have a very basic question would like to seek a good illustration explanation.

I would like to represent the output resistance of a analog model by using voltage source in series to a resistor, however i have been told that modeling the output resistance by using a current source in parallel with a resistor is a better way. This has lead me to think about the foundamental theory of current and voltage source that i learned during my freshman time.

I hope anyone can explain for the following:
1. What are the differences between current source and voltage source?
2. What are the benefits of each of the source type?
3. Should we model our output impedance by a current/voltage source? WHY?

Thank you for your kind assistance.
 

current source vs voltage source

current source Vs voltage source
current source always provide a constant current irrespective of the load connected across it. So if i increase resistance voltage across it will increase and vice versa.
by ohm's law
While for a voltage source the voltage across the load connected across it will remain constant and the current through it will change as u change the resistance.

modeling
if u r measuring voltage across a resister (parallel) u model the output impedance as a voltage source
while in case of an Opamp current is modulated in the feedback resistor until voltage at -ve terminal is equal to the +ve terminal. Here output is measured along the branched path of the current source

In active device the current in it is modulated hence most devices work on voltage source[/u]
 
current versus voltage

however i have been told that modeling the output resistance by using a current source in parallel with a resistor is a better way.
Click to expand...
Why? On a abstract model level, both circuits are simply equivalent. Modelling a real device, I would choose the model, that is nearest to it's real behaviour. A common drain output stage can be better described as a voltage source with series impedance, while a common source output is nearer to a current source.
 

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