An Automatic Voltage Regulator (AVR) is an electronic device that regulates the voltage in an electrical system by maintaining a constant voltage output despite fluctuations in the input voltage. It is used to stabilize the voltage of the power supply and protect the connected equipment from damage due to voltage fluctuations. The AVR typically monitors the input voltage and adjusts the output voltage by controlling the excitation of the alternator or transformer. The AVR uses feedback control to regulate the output voltage, ensuring that it stays within a pre-determined range. The range of output voltage that an AVR can regulate varies, depending on the specific application. AVR's are commonly used in various types of electrical equipment such as generators, voltage stabilizers, UPS systems, and other power systems to maintain a stable power supply. The use of an AVR can help prevent damage to equipment caused by overvoltage or undervoltage, which can result in malfunction or failure of electrical devices.