Thevenin’s Theorem: Any two terminal circuit having number of linear impedance and sources (voltage, current, dependent, independent) can be represented by a simple equivalent circuit consisting of a single voltage source VTh in series with an impedance ZTh, where the source voltage VTh is equal to the open circuit voltage appearing across the two terminals due to internal sources of circuit and the series impedance ZTh is equal to the impedance of the circuit while looking back into the circuit across the two terminals, when the internal independent voltage sources are replaced by short-circuits and independent current sources by open circuits.
Stepwise Procedure for applying Thevenin’s theorem to simple circuits:
Step I: Identify the load branch (RL): It is the branch whose current is to be determined.
Step II: Calculation of VTh: Remove RL and find open circuit voltage across the load terminals A and B, which are now open due to removal of RL.
Step III: Calculation of RTh: It is the resistance between the open circuited load terminals A & B while looking back into the network with all independent voltage sources replaced by short-circuit & all independent current sources replaced by open-circuit.
Step IV: Thevenin’s equivalent circuit:
Step V: Determination of Load current: