The major feature of a varistor is that when the voltage applied to it is lower than its threshold value'UN', the current flowing through it is extremely small, which is equivalent to a closed valve. When the voltage exceeds UN, its The 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.

         For example: zinc oxide varistor is used in the power circuit of our home color TV. The varistor varistor voltage used here is 470V. When the transient surge voltage exceeds 470V, the large value (non-effective value) The varistor is to reflect its clamping characteristics, pull the excessively high voltage down, and let the subsequent circuit work in a safe range.