Varistor
The most important feature of varistor is that when the voltage applied to it is lower than its threshold value "UN", the current flowing through it is very small, equivalent to a closed valve, when the voltage exceeds UN, its resistance value becomes smaller, so that the current flowing through it surges and the impact on other circuits is little changed, thus reducing the impact of overvoltage on subsequent sensitive circuits. By using this function, the abnormal overvoltage which often appears in the circuit can be suppressed and the circuit can be protected from overvoltage damage.