varisztors

Varistors, short for voltage-dependent resistors, are electronic components designed to protect circuits from overvoltage transients. Their key characteristic is their non-linear resistance; they exhibit very high resistance at normal operating voltages but their resistance drops sharply when the voltage exceeds a certain threshold. This behavior allows them to effectively shunt away excess current during voltage spikes, preventing damage to sensitive downstream components.

Varistors are typically constructed from semiconductor materials, most commonly zinc oxide (ZnO). The material's electrical properties are engineered to create the desired voltage-dependent resistance. When an overvoltage occurs, the zinc oxide grains become conductive, creating a low-resistance path that diverts the surge current away from the protected circuit and dissipates it as heat. Once the overvoltage subsides, the varistor's resistance returns to its high state, and the circuit resumes normal operation.

The main parameters for specifying a varistor include its working voltage, which is the maximum continuous AC or DC voltage it can withstand without significant current flow, and its clamping voltage, which is the maximum voltage that appears across the varistor when it is subjected to a specific surge current. Varistors are widely used in power supplies, surge protectors, and various electronic devices to safeguard against lightning strikes, power line surges, and electrostatic discharge.