DC Network Theorems Unit 7 – Thevenin Circuits
UNIT 7 – THEVENIN CIRCUITS
UNIT OBJECTIVE
At the completion of this unit, you will be able to simplify one- and two-source circuits by using
Thevenin's theorem.
UNIT FUNDAMENTALS
Thevenin's theorem named after the French engineer M.L. Thevenin, allows for the reduction
of a network into an equivalent voltage and resistance. The equivalent voltage is called VTH.
The equivalent resistance is called RTH.
Thevenizing a circuit allows you to see the effects of changing load conditions without the need
for repeating many Ohm's law equations for each load change. On the equivalent circuit, a
simple voltage divider replaces the more complex network circuit.
Thevenin's theorem reduces the circuit network into VTH and RTH. The reduction occurs with
respect to A and B, the network output terminals. The circuit network is composed of a voltage
source and 4 resistors. RL represents the circuit load.
To calculate VTH, remove RL and apply Ohm's law to determine the output voltage of the
network: VTH between A and B. The polarity of VTH is identical to the polarity of the network
source voltage: A positive with respect to B.