# I need some specifics about supernodes

#### barrett50

Joined Feb 1, 2016
14
Hey everyone! So I'm not looking for the answer to the question in the attached file. Rather, my class recently went over supernodes, and I'm just wondering if I need to create one for the dependent voltage source shown in the file. The main reason it's confusing me is the fact that it is connected between a node and a reference node. Any info would be great. Thanks!

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#### WBahn

Joined Mar 31, 2012
26,398
You can create one, but it won't do anything for you. You know the voltage at the top of the dependent source (it's KvVx), so just push on.

#### MrAl

Joined Jun 17, 2014
7,895
Hey everyone! So I'm not looking for the answer to the question in the attached file. Rather, my class recently went over supernodes, and I'm just wondering if I need to create one for the dependent voltage source shown in the file. The main reason it's confusing me is the fact that it is connected between a node and a reference node. Any info would be great. Thanks!
Hi there,

I agree with Wbahn, you dont need one.

A super node would normally be necessary when you have a floating voltage source. That's because you dont really know the voltage at either terminal of a floating voltage source until after the analysis is done. So you need to solve for two voltages say v1 and v2, which involves two nodes say n1 and n2.

In this circuit however, you already know that the bottom voltage is zero volts (0v), so you have nothing to solve for at the bottom node. At the top node you still have to solve for that voltage however, but it's only one node so there's nothing that needs to be shorted out.

The reason for creating a super node in the first place is so that you can write the equations as if the source was a short circuit for current but an open circuit for voltage, and this helps because you can call the currents entering or leaving both nodes the same but still call the voltage something other than zero, and that helps so that you can write the equations easier because of that temporary pseudo change of topology.

This is if i understand your question correctly. If you intended to form a super node somewhere else or in some other way you can state that now. If fact, if you did have something else in mind it would be best if you mentioned it now.

#### barrett50

Joined Feb 1, 2016
14
Hi there,

I agree with Wbahn, you dont need one.

A super node would normally be necessary when you have a floating voltage source. That's because you dont really know the voltage at either terminal of a floating voltage source until after the analysis is done. So you need to solve for two voltages say v1 and v2, which involves two nodes say n1 and n2.

In this circuit however, you already know that the bottom voltage is zero volts (0v), so you have nothing to solve for at the bottom node. At the top node you still have to solve for that voltage however, but it's only one node so there's nothing that needs to be shorted out.

The reason for creating a super node in the first place is so that you can write the equations as if the source was a short circuit for current but an open circuit for voltage, and this helps because you can call the currents entering or leaving both nodes the same but still call the voltage something other than zero, and that helps so that you can write the equations easier because of that temporary pseudo change of topology.

This is if i understand your question correctly. If you intended to form a super node somewhere else or in some other way you can state that now. If fact, if you did have something else in mind it would be best if you mentioned it now.
Thank you for taking your time to write all of that up! Yes, you understood my question perfectly.

#### MrAl

Joined Jun 17, 2014
7,895
Hi,

You are welcome

After you do a few super nodes you soon start to realize that the impedances at the first node combine with the impedances at the second node, almost as if they were just one node in that respect. The difference is that we still have to recognize that there are still two voltages (not just one) which is the same as there is with two nodes separated by non zero impedances.