2. A device that maintains the terminal voltage of a generator or other voltage source within required limits despite variations in input voltage or load.
3. A circuit that includes a sensor capable of monitoring the load and restoring the output voltage to close tolerance limits despite changes in both the load and the input voltage.
4. Any electrical or electronic device that maintains the voltage of a power source within acceptable limits.
The voltage regulator is needed to keep voltages within the prescribed range that can be tolerated by the electrical equipment using that voltage.
Voltage regulators also are used in electronic equipment in which excessive variations in voltage would be detrimental.