What is the use of a varistor? The great feature of a varistor is that when the voltage applied to it is lower than its threshold "UN", the current flowing through it is extremely small, which is equivalent to a closed valve. When the voltage exceeds UN, its resistance value becomes smaller, so that the current flowing through it increases sharply and the impact on other circuits does not change much, thereby reducing the impact of overvoltage on subsequent sensitive circuits. Using this function, the abnormal overvoltage that often occurs in the circuit can be suppressed, and the circuit can be protected from overvoltage damage.