A voltage regulator is a device that stabilizes the output voltage. The voltage regulator consists of a voltage regulating circuit, a control circuit, and a servo motor. When the input voltage or load changes, the control circuit samples, compares, and amplifies, and then drives the servo motor to rotate, causing the position of the voltage regulator carbon brush to change. By automatically adjusting the coil turn ratio, the output voltage is maintained stable.

The voltage regulator has an input voltage adaptation range. The IEC standard states that if the input voltage changes within the range of ± 20 of the rated value, it will automatically sound and light an alarm and cannot stabilize the output voltage within the required range. The output voltage adjustment rate is the effect of the change in output quantity caused by the change in input voltage. When the load is at the rated value, the input voltage is raised from the rated value to the upper and lower limits of the source voltage range, and the maximum change in output voltage is measured (±). The smaller the value, the better, which is an important indicator for measuring the performance of AC voltage regulators.