Franclim F. Ferreira, Pedro Guedes de Oliveira, Vítor G. Tavares

Thévenin's and Norton's theorems

The Thévenin’s and Norton’s theorems are dual and applicable to linear circuits.

The Thévenin’s theorem establishes that any linear circuit seen from one port may be represented by a voltage source (with a value equal to the open circuit voltage) in series with an impedance (with a value equal to the impedance seen from that port, after short-circuiting all independent voltage sources and opening the independent current sources).

To this circuit we call the Thévenin configuration.

The Norton’s theorem establishes, dually, that any linear circuit seen from one port may be represented by a current source (with a value equal to the short-circuit current) in parallel with an impedance (with the same value as in the Thévenin's theorem).

To this circuit we call the Norton configuration.

It is evident form these two theorems that a Thévenin configuration can be transformed to a Norton one and vice-versa, if V_o = Z I_s.