What Is the Failure Mode of a Varistor?

Varistors short circuit when an overage in potential is applied to it. These components are made of a material that’s insulating until a predetermined voltage appears across the part. When this voltage occurs, avalanche breakdown causes the varistor to act as a current shunt (Fig. 1); this prevents damage to the load that may result if failure of the protection circuit is undetected. When using varistors, ensure to select one with good durability against repeated surges.

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Fig. 1: Typical Normalised Voltage Versus Current Characteristics Curve for Standard Varistors

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Content and images provided courtesy of TDK’s FAQ..

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