The plug-in varistor is a metal oxide semiconductor nonlinear resistance element with zinc oxide as the main component; the resistance is more sensitive to the voltage, and when the voltage reaches a certain value, the resistance is quickly turned on. Because the plug-in varistor has good non-linear characteristics, large flow rate, low residual voltage level, fast action and no continuous current. It is widely used in lightning protection of electronic equipment.

Main parameters of plug-in varistor:

    1. Residual voltage: the highest peak voltage of the plug-in varistor at both ends when it passes a large current with a regular waveform.

    2. Flow capacity: After a regular waveform current is applied to the varistor at regular time intervals and times, the maximum current amplitude that the varistor can refer to when the voltage change rate is still within the regular scale.

    3. Leakage current: the current flowing through the varistor under the effect of referring to the voltage.

    4. Extra working voltage: The effective value of the power frequency voltage applied across the varistor for a long time is allowed. The varistor's temperature rises after absorbing the transient overvoltage energy, and it can be cooled normally at this voltage without heat damage.

    The shortcomings of the plug-in varistor: (1) Large parasitic capacitance The varistor has a large parasitic capacitance, generally on the scale of hundreds to thousands of picofarads. In the high-frequency signal system, it will cause high-frequency signal transmission distortion, and then cause the system to operate normally. (2) The existence of leakage current The leakage current index of the varistor is not only related to the normal operation of the protected electronic system, but also related to the aging and service life of the varistor itself.

    The damage form of the plug-in varistor: (1) When the energy of the varistor exceeds its extra capacity when suppressing the transient overvoltage, the varistor will be damaged due to overheating, mainly manifested as short circuit and open circuit.