Metal oxide varistors have nonlinear volt ampere characteristics. At normal operating voltage, MOV exhibits a high resistance state with minimal leakage current. However, when overvoltage occurs at both ends of the solid-state relay and the voltage exceeds a certain threshold, the resistance of the MOV will rapidly decrease.

In this way, most of the overvoltage energy will form a current through the MOV, thereby limiting the voltage rise at both ends of the solid-state relay. MOV can absorb the energy generated by overvoltage, convert it into thermal energy and dissipate it, protecting the components inside the solid-state relay from being broken down or damaged by excessive voltage.

Specifically, when the peak voltage applied to the AC terminals of a solid-state relay exceeds its maximum voltage capacity, it may cause damage to the components inside the relay. Parallel MOVs can quickly conduct and absorb some of the overvoltage energy when overvoltage occurs, reducing the actual voltage applied to the solid-state relay to a certain extent, thereby protecting the solid-state relay.

The area size of MOV determines its ability to absorb power, while the thickness of MOV determines the voltage value of protection. Generally speaking, for solid-state relays of different voltage levels, corresponding specifications of varistors can be selected. For example, solid-state relays in the 220V series can be equipped with varistors ranging from 500V to 600V; The 380V series solid-state relay can select varistors ranging from 800V to 900V; The 480V series solid-state relays can be equipped with varistors ranging from 1000V to 1100V.

It should be noted that in addition to MOV overvoltage protection, solid-state relays usually have other protective measures such as RC absorption circuits inside. But in some places with high reliability requirements, such as power compensation capacitor switching, motor forward and reverse rotation, stricter comprehensive protection measures may need to be taken. At the same time, it is necessary to ensure good heat dissipation of solid-state relays, as their internal chips will experience certain power losses during operation, which will be dissipated in the form of heat. Poor heat dissipation may affect their operational reliability.