A varistor is a resistor that changes in resistance with voltage in a certain range of current and voltage, or a resistor that is sensitive to voltage. The corresponding English name is "VoltageDependentResistor", abbreviated as "VDR"".
The biggest characteristic of the varistors with them when the voltage is lower than the threshold it "UN", the minimum current flowing through it, the equivalent of a closed valve, when the voltage exceeds UN, the current flowing through it in the equivalent of the valve open. By using this function, the abnormal overvoltage in the circuit can be suppressed, and the circuit can be protected from over-voltage damage. Varistor is one of the most widely used voltage limiting devices. Widely used in automotive electronics, communication, computer, consumer electronics, military electronic products, especially in the protection of LCD, keyboard, I/O interface, IC, MOSFET, CMOS, mobile phone, DVD, sensor, AV, ABS, MP3, PDA, motor control board, USB interface and high-speed data signal line.
Should pay attention to when choosing the varistor is continuously applied in the power supply voltage of the two ends of the varistor, can not exceed the maximum continuous operating voltage degree "listed in the specification + value?. We should take full account of the fluctuation range of the work voltage of the grid (or circuit), and keep enough allowance when choosing the voltage sensitive value of the varistor.
Generally, the range of fluctuation is 30%, and the maximum surge current through the varistor shall not exceed the maximum impact current in the technical specification. In view of the need to withstand multiple shocks, the surge current value which can withstand more than 10 shocks should be selected. The clamping voltage of the varistor must be less than the maximum voltage (i.e., the safety voltage) that the protected component or device can withstand.