Varistors

A varistor, short for "voltage-dependent resistor," is an electronic component designed to protect electrical circuits from voltage surges. It is a type of metal oxide varistor (MOV) that utilizes the non-linear voltage-current characteristic of zinc oxide to limit voltage transients.

Definition:
A varistor is a passive electronic component that exhibits a highly non-linear current-voltage (I-V) relationship. It allows a normal operating voltage to pass through with minimal impedance but offers a very low resistance path when subjected to overvoltage conditions, thereby diverting excessive voltage away from sensitive circuitry.

Function:
The primary function of a varistor is to protect electrical and electronic equipment from voltage spikes or surges that can be caused by lightning, power line switching, or other transient events. It acts as a sacrificial device, clamping the voltage to a safe level and preventing damage to the circuit.

Applications:
Varistors are widely used in various applications, including:
1. Telecommunications - Protecting equipment from lightning strikes and power surges.
2. Power Supplies - Clamping voltage spikes that can damage sensitive electronic components.
3. Automotive Systems - Protecting the electrical systems of vehicles from transient voltages.
4. Industrial Control Systems - Safeguarding against voltage fluctuations that can disrupt operations.
5. Home Appliances - Ensuring the safety and longevity of electronic devices in household settings.

Selection Criteria:
When selecting a varistor, the following criteria should be considered:
1. Voltage Rating - The varistor should have a voltage rating that matches the maximum voltage expected in the circuit.
2. Continuous Operating Voltage (COV) - The varistor should be able to withstand the continuous operating voltage without degradation.
3. Leakage Current - Should be low enough not to affect the performance of the circuit.
4. Response Time - Should be fast enough to respond to voltage transients effectively.
5. Energy Absorption Capacity - Must be sufficient to handle the energy of the transient voltage without failure.
6. Physical Size and Mounting - Should fit the available space and mounting requirements of the application.
7. Temperature Range - Should operate effectively within the temperature range of the application.

In summary, a varistor is a critical component in circuit protection, offering a non-linear resistance that clamps voltage spikes and ensures the safe operation of electrical and electronic systems. Its selection should be based on a thorough understanding of the application's requirements and the varistor's specifications.
Please refer to the product rule book for details.