Basic performance of varistor

A varistor is a kind of resistance device with nonlinear volt-ampere characteristics. It is mainly used for voltage clamping when the circuit is subjected to overvoltage, and absorbs excess current to protect sensitive devices. The resistor material of the varistor is a semiconductor. It is a voltage-limiting protection device. Using the nonlinear characteristics of the varistor, when an overvoltage occurs between the two poles of the varistor, the varistor can clamp the voltage to a relatively fixed voltage value, thereby achieving backward Protection of the circuit. The main parameters of the varistor are: varistor voltage, current capacity, junction capacitance, response time, etc. The performance of the varistor has the following aspects:

1. Protection characteristics, when the impact strength of the impact source does not exceed the specified value, the limiting voltage of the varistor is not allowed to exceed the impact withstand voltage that the protected object can withstand;

2. Impact resistance, that is, the varistor itself should be able to withstand the specified inrush current, impact energy, and the average power of multiple impacts in succession;

3. There are two characteristics of life: one is the continuous working voltage life, that is, the varistor should be able to work reliably for a specified period of time (hours) under the specified ambient temperature and system voltage conditions; the second is the impact life, which can reliably withstand The number of specified shocks;

4. After the varistor is involved in the system, in addition to the protection function of the safety valve, it will bring some additional effects. This is called the “secondary effect”, which should not reduce the normal working performance of the system. There are three main factors to consider, one is the capacitance of the varistor itself (tens to tens of thousands of PF), the second is the leakage current at the system voltage, and the third is the coupling of the nonlinear current of the varistor through the source impedance. The influence of other circuits.