Theveninäquivalent

TheveninÄquivalent, also called Thevenin equivalent, is a representation of a linear two-terminal network as a single voltage source in series with a resistor. It embodies Thevenin's theorem, named after Henri Thevenin, and is widely used to simplify circuit analysis.

Determining the Thevenin equivalent: Vth is the open-circuit voltage across the terminals when the load is removed. Rth is found by turning off all independent sources and calculating the resistance seen from the terminals. If the network contains dependent sources, they must remain active; Rth can be found by applying a test source at the terminals and computing Vtest and Itest, with Rth = Vtest / Itest.

Scope and limitations: Thevenin equivalents apply to linear, bilateral, time-invariant networks for a given pair of terminals and for a specified frequency in AC analysis. They hold for DC and AC steady-state. They do not apply to nonlinear elements, switching networks, or networks where the relation between terminal voltage and current depends on the history or operating point beyond the specified condition.

Relation to Norton and usage: The Thevenin and Norton forms are duals; a Thevenin circuit with Vth and Rth is equivalent to a Norton circuit with In = Vth / Rth in parallel with Rth. They are used to analyze how a load behaves, to combine sources, and to optimize power transfer, which occurs when the load equals Rth in purely resistive cases.