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Thévenin Equivalent

Any linear circuit seen from two terminals can be replaced by a single voltage source $U_{th}$ in series with a single resistor $R_{th}$ . This is a huge simplification when analyzing how the circuit behaves with different loads, since you only need to compute the equivalent once.

U_{th}=U_{\text{open}}

the open-circuit voltage across the terminals

R_{th}=U_{\text{open}}/I_{\text{short}}

resistance from the open- and short-circuit values

Symbols

$U_{th}$	Thévenin voltage	V
$R_{th}$	Thévenin resistance	$\Omega$
$U_{\text{open}}$	open-circuit voltage	V
$I_{\text{short}}$	short-circuit current	A

Example

Open circuit $U_{\text{open}}=10$ V, short circuit $I_{\text{short}}=2$ A:

$R_{th}=10/2=5$ Ω.

Find

R_{th}

with the sources turned off, or from the ratio of the open-circuit voltage to the short-circuit current.

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