Junction capacitance varistors typically hundreds to thousands of magnitude range Pf

Mov varistor grade ns response time, faster than the gas discharge tube, slightly slower than the TVS tube, under normal circumstances electronic circuit for overvoltage protection to meet the requirements of its response speed. High voltage varistor junction capacitance range is generally on the order of hundreds to thousands of Pf, in many cases should not be applied directly the protection of high-frequency signal lines, and the application of the AC circuit protection, since it will increase the junction capacitance greater leakage current protection circuits designed to take full account. Metal oxide varistors  through-flow capacity is larger, but smaller than the gas discharge tube. Varistors referred VDR, it is a non-linear voltage-sensitive semiconductor element overvoltage protection.

When applied to the varistor voltage is below its threshold, the current flowing through it is extremely small, it is equivalent to a resistance infinite resistance. That is, when a voltage is applied on top of it is below its threshold, which is equivalent to an OFF state of the switch.
When applied to the varistor voltage exceeds its threshold, the surge current flowing through it, which is equivalent to the resistance infinitely small resistance. That is, when added on top of it higher than its threshold voltage, which is equivalent to a closed switch.

Varistor resistive material is a semiconductor

"Mov varistor" is a kind of non-linear voltage characteristics of resistance devices, mainly used for in-circuit withstand overvoltage voltage clamp, absorb excess current to protect sensitive devices. English name called "Voltage Dependent Resistor" abbreviated as "VDR", or called "Varistor". Varistor resistive material is a semiconductor, so high voltage varistor is a variety of semiconductor resistor. "Zinc oxide" Now a lot of use of (ZnO) varistor, its main material divalent element zinc (Zn) and hexavalent elemental oxygen (O) of the composition. So from the point of view of materials, the zinc oxide varistor is a "Ⅱ-Ⅵ family-oxide semiconductor." In China Taiwan, metal oxide varistors  called "surge absorber", sometimes also referred to as "electric shocks (surge) suppressor (absorber) . "

Varistor is a voltage limiting protection devices. The use of nonlinear characteristics of the varistor, when an overvoltage occurs in between the two poles of the varistor, the varistor voltage can be clamped to a relatively fixed voltage value, in order to achieve protection of the post-stage circuit. The main parameters of varistors are: varistor voltage, current capacity, junction capacitance and response time.