# Thevenin's equivalent circuit

When I have to calculate a Thevenin's equivalent circuit which has a current controlled voltage generator, what should I do to calculate the open circuit equivalent voltage to the terminals in question? Is there any difference between a circuit that hasn't any controlled generators? Can you guys give me some examples? Thank you in advance,I know that this could be a stupid question for those who had studied circuits for a long time!

Anyway, here is the circuit i was trying to solve, if you guys want the data just ask • What do you know about Source Transformation? It seems to me that you would need to transform the current source into its equivalent voltage source. – R. Johnson Dec 18 '15 at 22:28
• As i said i already tried to solve that and obviously i transformed the current source into its Thevenin equivalent. I obtained the series connection between E and I*R1, but at the end i found out a negative voltage between A and B terminals. Is that possible or I just miscalculated? – presgiovanni Dec 18 '15 at 22:34
• Apologies, I didn't see anywhere in your description that you already attempted to solve the problem. It helps us give you an answer if you tell us what you have already attempted. . . – R. Johnson Dec 18 '15 at 22:42
• I just applied KVL to the loops i obtained after the semplification you suggested to find the current that flows in the first resistance (and then the voltage of the controlled generator, as Rm is known). After that i obtained that the tension between the terminals in question was equal to the tension of the controlled generator, as apparently in the fourth resistance didn't flow any current. But that tension i found out was negative and this gave me some problems :) – presgiovanni Dec 18 '15 at 22:57

## 1 Answer

In general, find the open circuit voltage (Voc) using whatever methods works: node, mesh, superposition or source transformation (the latter not usually applicable with dependent sources).

Then to find the Thevenin resistance, either calculate Voc/Isc, or short the independent voltage sources and open the independent current sources, but leave the dependent sources in circuit and calculate the resistance that way. A trick that can help in that case is to excite the circuit either with a 1A current source at the circuit terminals and use node analysis, or a 1V voltage source at the circuit terminals and use mesh analysis.

There's a good description of this process and some worked examples here: http://www.allaboutcircuits.com/technical-articles/thevenin-theorem-dependent-source-circuits/

By the way, where you use "controlled generator", I've used "dependent source". They're interchangeable.

If you're stuck at a particular point in this process, try a more specific question.

• That's clear! That website goes immediately in my bookmarks, thank you :) – presgiovanni Dec 18 '15 at 23:13