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Dependent and Independent Sources

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khushboo652

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Independent Sources

I read that Independent sources such as ideal voltage source and ideal current source are those which does not depend on any other element in the network.But i do not understand how super position theorem is used only with independent sources,i see that registers are connected in that network then how it is independent sources?Please clear my doubt.
 

Re: Independent Sources

I would interprete an ideal voltage/current source as one without internal resistance, not temperature or load dependency etc. So independent from external or other parameter. A 100% stable voltage or current.

Enjoy your design work!
 

Re: Independent Sources

khushboo652 said:
I read that Independent sources such as ideal voltage source and ideal current source are those which does not depend on any other element in the network.But i do not understand how super position theorem is used only with independent sources,i see that registers are connected in that network then how it is independent sources?Please clear my doubt.
Click to expand...

In case the input-output transfer (gain of the dependent source) of the voltage or current source depends on some control voltage or current within the network the voltage-current relations are not linear anymore. That means the precondition for the superposition theorem (linearity) is not fulfilled.
 

Re: Independent Sources

khushboo652,

I read that Independent sources such as ideal voltage source and ideal current source are those which does not depend on any other element in the network.But i do not understand how super position theorem is used only with independent sources,i see that registers are connected in that network then how it is independent sources?Please clear my doubt. .
Click to expand...

You wrote "registers". Do you really mean resistors? What do they have to do with your questions? Circuits containing dependent sources are still linear circuits. The reason why the superposition method does not work too well for dependent sources is that when you set the other sources to zero, the dependent sources do not activate. Now the General Immittance Theorem (GIT) works even when dependent sources are present.

Ratch
 

Re: Independent Sources

Ratch said:
khushboo652,
Circuits containing dependent sources are still linear circuits........

Ratch
Click to expand...

Hi Ratch, are you really sure? Perhaps you reconsider your claim?
 

LvW,

Hi Ratch, are you really sure? Perhaps you reconsider your claim?
Click to expand...

Yes, I am sure. As long as a dependent source adds to the output proportionately, the circuit is linear.

Ratch
 

Ratch said:
LvW,
Yes, I am sure. As long as a dependent source adds to the output proportionately, the circuit is linear.
Ratch
Click to expand...

Hi Ratch, that means: If the source is linear the circuit remains linear, right?
I think, everybody will agree. (Isn't this trivial?).
But what about dependent sources with properties as mentioned in my reply #3 ?
Regards
 

LvW,

Hi Ratch, that means: If the source is linear the circuit remains linear, right?
I think, everybody will agree. (Isn't this trivial?).
But what about dependent sources with properties as mentioned in my reply #3 ?
Regards
Click to expand...

If a circuit consists of several dependent voltages such V = K*I, where K and I are linear functions, then the circuit will be linear provided the circuit elements (RLC) are linear.

Ratch
 

Ratch said:
LvW,
If a circuit consists of several dependent voltages such V = K*I, where K and I are linear functions, then the circuit will be linear provided the circuit elements (RLC) are linear.
Ratch
Click to expand...

Hi Ratch, I am sure that nobody will argue against it. If all circuit elements are linear - the whole circuit will be linear as well.
However, I am afraid, that you did overlook my advice to read again my posting#3.
In this reply I have mentioned dependent sources with input-output transfer functions (gain of the dependent source) that are controlled by a voltage or current within the network. I repeat: The transfer function is not a constant but depends on a network parameter.
I hope you can agree that in this case there are non-linearities within the network prohibiting the application of the super-position theorem (see the original question).
Regards
LvW
 
Last edited:

LvW,

I did look over your post and I thought I answered it. Apparently I just don't "get it". Perhaps your could illustrate with a simple example.

Ratch
 

Ratch said:
LvW,
I did look over your post and I thought I answered it. Apparently I just don't "get it". Perhaps your could illustrate with a simple example.
Ratch
Click to expand...

Ratch, do you really need an example? Each realistic opamp macromodel contains controlled non-linear sources.
 

LvW,

Ratch, do you really need an example? Each realistic opamp macromodel contains controlled non-linear sources.
Click to expand...

I don't recall seeing any. Show me just one example.

Ratch
 

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