Varistor is a voltage limiting protection device. By utilizing the nonlinear characteristics of sensitive resistors, when overvoltage occurs between the two poles of the sensitive resistor, the sensitive resistor can clamp the voltage at a relatively fixed voltage value, achieving protection for the subsequent circuit. The main parameters of varistor include voltage, current capacity, junction capacity, response time, etc. Varistor is a voltage sensitive component made of nonlinear volt ampere characteristics of semiconductor materials, referred to as MOV, which is a nonlinear over-voltage protection semiconductor component sensitive to voltage, and is represented by the character symbol MOV in the circuit.

Varistor is a voltage limiting protection device. By utilizing the nonlinear characteristics of sensitive resistors, when overvoltage occurs between the two poles of the sensitive resistor, the sensitive resistor can clamp the voltage at a relatively fixed voltage value, achieving protection for the subsequent circuit. The main parameters of varistor include voltage, current capacity, junction capacity, response time, etc. Varistor is a voltage sensitive component made by using the nonlinear volt ampere characteristics of semiconductor materials, referred to as MOV, which is a nonlinear over-voltage protection semiconductor component sensitive to voltage. The circuit is represented by the character symbol MOV, and the varistor symbol is shown in the following figure

The characteristics of varistor and the function of circuit board are analyzed.

Equivalent to a variable resistor, connected in parallel with the circuit. When the circuit is in normal use, the varistor has high impedance and small leakage current, which can be regarded as an open circuit and has little impact on the circuit. However, when the high surge voltage comes, the resistance value of the varistor drops instantaneously (its resistance value is from m ω (Megaohm) level becomes m ω (m Ω) level, while flowing a large current, place the overvoltage clamp at a certain value. The surge withstand capacity of varistor depends on the physical size, so different surge current values may be obtained.

The biggest characteristic of the varistor is that when the voltage applied to it is lower than its threshold UN, the current flowing through it is very 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 surges while the impact on other circuits changes little, thus reducing the impact of overvoltage on subsequent sensitive circuits. By utilizing this function, abnormal overvoltage that often occurs in the circuit can be suppressed and the circuit can be protected from overvoltage damage.