# A problem about two-port network.

#### Feng Yu

Joined Jun 20, 2015
5 Circuit as the picture shows,with the independent current source generate current 2V1.
Need to find the admittance matrix Y.
{I1=Y11*V1+Y12*V2
I2=Y21*V1+Y22*V2

#### The Electrician

Joined Oct 9, 2007
2,887 Circuit as the picture shows,with the independent current source generate current 2V1.
Need to find the admittance matrix Y.
{I1=Y11*V1+Y12*V2
I2=Y21*V1+Y22*V2

MOD NOTE: Link to forum sticky corrected.

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#### Feng Yu

Joined Jun 20, 2015
5 In a) case,set V1=0,
I2=-I1,V2=5*I2 ====>Y12=-1/5 and Y22=1/5
But in case b) V2=0,
I dont know if the indepen current generator still effect to the circuit,or it just be opened.

#### WBahn

Joined Mar 31, 2012
26,398
Circuit as the picture shows,with the independent current source generate current 2V1.
How do you figure that it is an independent current source? It seems like the current is dependent of V1, does it not?

#### WBahn

Joined Mar 31, 2012
26,398
In a) case,set V1=0,
I2=-I1,V2=5*I2 ====>Y12=-1/5 and Y22=1/5
But in case b) V2=0,
I dont know if the indepen current generator still effect to the circuit,or it just be opened.
It is NOT an independent current generator. You should have been through analyzing circuits that have dependent sources LONG before you got to two-port networks.

You simply have a circuit that has a voltage-controlled dependent current source. So set up the mesh and/or node equations that govern it.

#### Feng Yu

Joined Jun 20, 2015
5
It is NOT an independent current generator. You should have been through analyzing circuits that have dependent sources LONG before you got to two-port networks.

You simply have a circuit that has a voltage-controlled dependent current source. So set up the mesh and/or node equations that govern it.
My fault,its a voltage-controlled dependent current source.
But what I meas is I don't know if the 2V1 source provides the current to the node or it's opened. Let me clear my question:

I1+I2=0
or
I1+I2+2V1=0
?

#### WBahn

Joined Mar 31, 2012
26,398
You have three currents coming into the top node.

Your first equation requires that the current coming out of the dependent current source be zero.

If that is the case, what does that require that V1 be?

If V1 is not zero, then (2 A/V)·V1 is not zero, right? If that's the case, then how can your first equation be valid?

#### Feng Yu

Joined Jun 20, 2015
5
You have three currents coming into the top node.

Your first equation requires that the current coming out of the dependent current source be zero.

If that is the case, what does that require that V1 be?

If V1 is not zero, then (2 A/V)·V1 is not zero, right? If that's the case, then how can your first equation be valid?
Thanks,I got it.
I confused with the wire rightside.