Theveninækvivalent

Theveninækvivalent is a method in circuit theory that allows a linear electrical network to be replaced by a single voltage source in series with a resistance, viewed from two terminals. The equivalent circuit produces the same voltage-current behavior at the terminals for any external load as the original network. Thevenin's theorem applies to linear, bilateral networks containing independent sources and passive elements; dependent sources may be present as long as the network remains linear.

Thevenin voltage, Vth, is defined as the open-circuit voltage across the two terminals. Thevenin resistance, Rth, is the resistance seen from the terminals with all independent sources deactivated; if dependent sources exist, a test source is used to determine the effective resistance. An alternative method for circuits with only independent sources is Rth = Vth / Isc, where Isc is the short-circuit current across the terminals.

To determine the Thevenin equivalent, first calculate Vth with the output open. Then find Rth by deactivating independent sources and computing the impedance seen at the terminals (or by using the Vth and Isc relationship). Once obtained, the Thevenin circuit, a voltage source in series with Rth, can simplify analysis of how different loads affect voltage and current, support quick power calculations, and aid in design and teaching of circuit behavior.

Limitations include nonlinearity and time-variant behavior. Thevenin equivalents are exact only for linear, time-invariant networks at a specified operating point; they do not generally apply to nonlinear components or circuits whose behavior changes with load in a non-linear way.