2906279

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TVS – Varistors, MOVs

Varistors and MOVs are both components used in circuit protection and are also known as, respectively, voltage-dependent resistance and metal-oxide varistors. TVS stands for transient-voltage-suppressor, and they are used to provide surge protection in applications where power sources with unprotected outputs, such as solar cells, home appliances, or other power-related applications, are used. Varistors are widely seen in consumer electronics as they limit voltage transients.

Varistors

Varistor (VDR), or voltage-dependent resistor, is a non-linear resistor which has a voltage-dependent resistance. It is composed of a sintered mixture of semi-conductive materials, such as zinc oxide, and is sometimes referred to as a VDR (also, Varistor Disc Resistor). Its resistance decreases with an increase of applied voltage, and VDRs have a breakdown voltage at which the resistance drops significantly. Varistors demonstrate predictable current-limiting behavior during transient overloads, so they are widely used as a consumer protective device for overvoltage protection.

The working principle of a Varistor is that when the device is subjected to a transient voltage, the resistance of the device decreases. It is this decrease in resistance that causes a decrease in voltage across the device, and thus it can act as a voltage-limiter, or a surge protector.

MOVs

MOVs, or metal-oxide varistors, are electrical components used for overvoltage protection, and have a distinct working principle compared to that of varistors. MOVs are also referred to as Surge Protective Devices (SPDs). They consist of a metal oxide compound (zinc oxide) and are designed to ‘clamp’ incoming voltage transients to safe levels.

MOVs have a higher voltage rating than varistors, and this is due to the fact that MOVs have a \'positive temperature coefficient\', which means that their resistance increases with temperature. In the event of a high voltage transient, the MOV will act to “clamp’, or limit, the voltage, preventing it from exceeding a safe level.

MOVs are typically used in applications where long-term overvoltage protection is required, as they have a longer lifespan than varistor-based surge protectors. Moreover, MOVs are generally used in combination with other types of protection devices, such as fuses or positive temperature coefficient resistors.

2906279 Application Field and Working Principle

Varistors and MOVs are both used in applications where circuit protection is required, such as home appliances, consumer electronics, power outlets, and solar cells. Varistors provide surge protection by decreasing the resistance when a voltage transient occurs, whereas MOVs act to “clamp” incoming voltage transients. Due to their higher voltage rating, MOVs are more suitable for applications where long-term overvoltage protection is required.

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