# PSpice question: CCCS and the use of a "shunt resistor".

#### kostoglotov

Joined Jan 27, 2016
5
I read that to avoid inductor loop errors when using the CCCS (E) in PSpice, the controlling current should be taken through a low Ohmage shunt resistor.

I was just figuring out the Thevenin voltage for a circuit that contains a CCCS, and decided to use one of the 3 ohm branch resistors, thinking that that would do the same thing as a shunt resistor, since the current through the branch is modeled as being the same before and after the resistor, so it should act the same way as a lower ohmage shunt resistor. This was not the case, and has a drastic effect on the Thevenin equivalent that is determined by a probing current at the outside terminals.

Clearly, the CCCS (E) in PSpice is not directly seeing the current between two parts of a branch, so how do these CCCS's work? How are they actually being controlled?

#### crutschow

Joined Mar 14, 2008
33,318
I would think it would be a high resistance shunt resistor, not low.

#### ronv

Joined Nov 12, 2008
3,770
I read that to avoid inductor loop errors when using the CCCS (E) in PSpice, the controlling current should be taken through a low Ohmage shunt resistor.

I was just figuring out the Thevenin voltage for a circuit that contains a CCCS, and decided to use one of the 3 ohm branch resistors, thinking that that would do the same thing as a shunt resistor, since the current through the branch is modeled as being the same before and after the resistor, so it should act the same way as a lower ohmage shunt resistor. This was not the case, and has a drastic effect on the Thevenin equivalent that is determined by a probing current at the outside terminals.

Clearly, the CCCS (E) in PSpice is not directly seeing the current between two parts of a branch, so how do these CCCS's work? How are they actually being controlled?
Maybe a picture and a definition of CCCS???

#### eetech00

Joined Jun 8, 2013
3,628
I read that to avoid inductor loop errors when using the CCCS (E) in PSpice, the controlling current should be taken through a low Ohmage shunt resistor.

I was just figuring out the Thevenin voltage for a circuit that contains a CCCS, and decided to use one of the 3 ohm branch resistors, thinking that that would do the same thing as a shunt resistor, since the current through the branch is modeled as being the same before and after the resistor, so it should act the same way as a lower ohmage shunt resistor. This was not the case, and has a drastic effect on the Thevenin equivalent that is determined by a probing current at the outside terminals.

Clearly, the CCCS (E) in PSpice is not directly seeing the current between two parts of a branch, so how do these CCCS's work? How are they actually being controlled?
CCCS = Current Controlled Current Source

A CCCS is an "F" device, not an "E" device.

In Spice, a CCCS is used to copy current from one branch to another branch.

Usually, a Voltage source configured as a current monitor (V=0) is placed in the branch to be copied. The Voltage source provides the source current for the CCCS. The voltage source is then specified as the current source in the CCCS. Thus, the current in the CCCS is controlled by the current in the branch the voltage source is monitoring.

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