The varistor's resistance is infinite and the service life

1. The resistance of the varistor is infinite

A varistor is a resistive device with nonlinear volt-ampere characteristics. It is mainly used to clamp the voltage when the circuit is under overvoltage, and to absorb excess current to protect sensitive devices. When the voltage applied to the varistor is below its threshold, the current flowing through it is extremely small, which is equivalent to a resistor with an infinite value. When the voltage applied to it is below its threshold, it is equivalent to an open state switch. When the voltage applied to the varistor exceeds its threshold, the current flowing through it surges, which is equivalent to an infinitely small resistance. When the voltage applied to it is above its threshold, it is equivalent to a closed state switch. Therefore, its resistance is infinite when measured because the voltage applied to the varistor is below its threshold.

2. The age of the varistor

The characteristic of the 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 The value becomes smaller, so that the current flowing through it surges and the influence on other circuits does not change much, thereby reducing the influence of the overvoltage on the subsequent sensitive circuit. With this function, it is possible to suppress abnormal overvoltages that often occur in circuits and protect circuits from overvoltages.

The varistor can be used for 8-10 years under normal conditions. If the varistor is overloaded and exposed to high temperatures, it will reduce its useful life. Because of the aging of the varistor itself or the multiple shocks of temporary overvoltage, the leakage current of the varistor is rapidly increased, resulting in overheating damage. The varistor has a short service life and performance will decrease after multiple impacts. It needs to be replaced after long-term use.