* Question

What are the key specifications to consider when selecting a varistor?

* Answer

When selecting a varistor, the following specifications are critical:

Varistor Voltage (V₁mA): The voltage at which the varistor begins conducting significantly, typically defined at a test current of 1 mA.

Clamping Voltage: The maximum voltage that appears across the varistor when it is conducting peak surge current—this determines how well it can protect downstream components.

Peak Pulse Current (Ipp): The highest surge current the varistor can handle without damage, often specified for an 8/20 µs waveform.

Energy Rating (J): The maximum energy, in joules, that the varistor can absorb in a single surge event.

Response Time: Typically less than 25 ns, indicating how quickly the varistor reacts to an overvoltage event.

Capacitance: Important for high-speed or signal line applications, as excessive capacitance can degrade signal integrity.

Operating Temperature Range: Ensures the varistor functions reliably in the intended environmental conditions.

These parameters help ensure the varistor offers effective and reliable protection tailored to the voltage level, energy threat, and application environment.