Statement: Any network containing active and/or passive elements and one or more dependent and/or independent voltage/or current sources can be replaced by an equivalent network containing a voltage source (Thevenin‟s equivalent voltage VTH or VOC) and a series resistance (called Thevenin‟s equivalent resistance RTH)
Figure below represents a linear network containing resistances and voltage sources.
To measure Vth, the load resistances is disconnected and voltage is measured across open terminals A and B.
To find Rth the source is replaced by its internal resistance and the resistance is measured across A and B .
The internal resistance of an ideal voltage source is zero and that of an ideal current is source is infinite. The equivalent circuit is obtained by connecting Voc or Vth and Rth in series.
RL is connected between A and B of eq. circuit.
Load current is given by IL =VTH/ (RTH+RL) figures above illustrate the concept of Thevenin‟s theorem