Varistor

Varistors, also known as surge absorbers, are widely used in electronic protection circuits because of their resistance value that changes with external voltage. When the voltage surge strikes, the varistor impedance decreases, causing the line to short-circuit to avoid damage to the electronic components caused by the surge.

The most common is Metal Oxide Varistor (MOV) is composed of metal oxides, such as zinc oxide (ZnO), titanium oxide (TiO2), composed of zinc oxide particles with a small amount of other metal oxides or polymers. The junction between the particles and the adjacent oxide will form a diode effect. At low voltage, there is only a small reverse leakage current. When encountering high voltage, the diode will be due to hot electrons and tunneling effection. The reverse collapse occurs and a large current flows.