Output impedance

In electrical engineering, the output impedance of an electrical network is the measure of the opposition to current flow (impedance), both static (resistance) and dynamic (reactance), into the load network being connected that is internal to the electrical source. The output impedance is a measure of the source's propensity to drop in voltage when the load draws current, the source network being the portion of the network that transmits and the load network being the portion of the network that consumes.

Because of this the output impedance is sometimes referred to as the source impedance or internal impedance.

Circuit to the left of central set of open circles models the source circuit, while circuit to the right models the connected circuit. ZS is output impedance as seen by the load, and ZL is input impedance as seen by the source.