A circuit or device that produces an output voltage that is substantially constant and independent of variations either in the input voltage or in the load current, i.e. it acts as a constant-voltage source. Such a device is most often used as a voltage regulator.

An early form of voltage stabilizer was based on the gas-discharge tube. Such circuits have now largely been superseded by circuits based on solid-state devices, such as the Zener diode (Fig. a) or the bipolar junction transistor (Fig. b). In the series stabilization circuit shown in Fig. b the load impedance is in series with the circuit.

(a) Zener diode stabilizer circuit (b) Series stabilizer circuit