Different Types of Varistors and Why Are They Important

Formed by the combination of “variable” and “resistor,” the word “varistor” refers to a type of electrical device that has an electrical resistance which changes based on the applied voltage. As a result of this functionality, varistors play a crucial role in protecting electronic circuits from voltage surges and transients, making them useful in a wide variety of electrical systems. For more information on these protective devices, read on as we delve into the common types of varistors and how they work.

What Are Varistors?

A varistor is a type of electrical component whose resistance is nonlinear, meaning it does not stay at one specific value and can change between different resistance values. For this to work, varistors rely on semiconductor materials like zinc oxide (ZnO) which has an electrical conductivity that can change to become more or less conductive due to its environment. More specifically, varistors will usually have a high resistance at normal operating voltages, but rapidly change to a low resistance when subjected to excessive voltage conditions. This unique characteristic makes them an ideal choice for surge protection applications.

Why Are Varistors Important?

Without any protective instruments in place, electrical circuits are vulnerable to voltage spikes and other sudden changes caused by events, such as lightning strikes and electrostatic discharge (ESD). These sudden surges can exceed the designed voltage limits of sensitive components, causing them to fail. In such cases, varistors are able to protect sensitive components by diverting excess voltage away, dissipating it harmlessly in other areas.

Common Types of Varistors

One of the most common types of varistors is the metal oxide varistor (MOV), a resistor made up of a ceramic disc with two metal plates on either side and a layer of zinc oxide grains in between. As a result of this design, when the voltage across the varistor is below its threshold value, the zinc oxide acts as an insulator, allowing only a small amount of current to flow through the device. However, when the voltage exceeds the threshold, the zinc oxide grains break down, creating a conductive path that allows a large current to pass through the varistor. This effectively keeps the voltage at a safe level and protects connected equipment.

Another popular type of varistor is the silicon carbide varistor (SICV). SICVs are made of silicon carbide (SiC) and offer better performance compared to MOVs in terms of energy absorption and response time. More specifically, they can handle higher surge currents and have lower clamping voltages. These characteristics make SICVs suitable for applications that require fast response times and high energy absorption capabilities, such as in power distribution systems. In addition to MOVs and SICVs, there are other types of varistors available, including selenium oxide varistors and avalanche diodes. Like their counterparts, each type has its own unique characteristics and is suited for specific applications based on factors such as voltage ratings, response times, and energy absorption capabilities.

Applications for Varistors

Varistors find extensive use in various electrical and electronic systems. They are commonly employed in power strips, surge protectors, and voltage regulators to safeguard sensitive equipment like computers, televisions, and other electronic devices. When a voltage surge occurs in these types of equipment, the varistor activates and redirects excess energy to protect the connected devices. This ensures that the voltage reaching the devices remains within safe limits, preventing damage and extending their lifespan.

Varistors are also used in industries where electrical noise suppression is crucial. This is because they can suppress voltage spikes caused by motor startups, transformer switching, and other high-power operations. By effectively clamping the voltage, varistors help maintain a stable electrical environment, preventing disturbances and ensuring the smooth operation of machinery.


Altogether, varistors are vital electrical devices that protect electronic circuits and associated equipment from voltage surges and transients. By incorporating them into electrical systems, we can enhance their resilience and safeguard sensitive devices from the damaging effects of voltage fluctuations. Here at Internet of NSN, we offer an array of superior-caliber electrical components, including a wide range of high-quality varistors. If you are currently on the search for such devices to support your assembly, we invite you to browse our online catalog of available products and make use of our RFQ service to receive competitive quotes for your comparisons. Our team of experts are available 24/7x365 to answer customer inquiries and requests, so do not hesitate to reach out directly!


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