What Is a Metal Oxide Varistor?

A "varistor" is a resistive device with non-linear volt-ampere characteristics. It is mainly used to clamp the voltage when the circuit withstands overvoltage, and absorbs excess current to protect sensitive devices. The English name is "Voltage Dependent Resistor" abbreviated as "VDR", or "Varistor". The material of the resistor body of a varistor is a semiconductor, so it is a variety of semiconductor resistors. The "zinc oxide" (ZnO) varistor, which is now widely used, has a main material composed of the divalent element zinc (Zn) and the hexavalent element oxygen (O). So from the perspective of materials, the zinc oxide varistor is a kind of "II-VI oxide semiconductor". In Taiwan, varistors are called "surge absorbers" and sometimes "electric shock (surge) suppressors (absorbers)."

Varistor

A "varistor" is a resistive device with non-linear volt-ampere characteristics. It is mainly used to clamp the voltage when the circuit withstands overvoltage, and absorbs excess current to protect sensitive devices. The English name is "Voltage Dependent Resistor" abbreviated as "VDR", or "Varistor".

l When the voltage applied to the varistor is lower than its threshold, the current flowing through it is extremely small, which is equivalent to a resistor with infinite resistance. In other words, when the voltage applied to it is lower than its threshold, it is equivalent to an off-state switch.

l When the voltage applied to the varistor exceeds its threshold, the current flowing through it increases sharply, which is equivalent to an infinitely small resistance. In other words, when the voltage applied to it is higher than its threshold, it is equivalent to a closed-state switch.

Before selecting a varistor, you should first understand the following related technical parameters: the nominal voltage refers to the voltage value across the varistor at the specified temperature and DC current ^[1]

Various diameter sizes: SMD, 5mm, 7mm, 10mm, 14mm, 20

Power system

Surge suppressor

security system

Motor protection

Automotive electronics

Household appliances

What is the use of a varistor? The biggest feature of a varistor is when it is added to it

The voltage / current applied to the varistor should not be the same for different applications.

Therefore, the requirements for varistor are also different. It is very important to distinguish this difference for correct use.

According to the purpose of use, varistor can be divided into two categories: varistors for protection, varistor for circuit function.

(1) Protection characteristics, when the impact of the impact source is strong (or

1. Nominal varistor voltage (V): Refers to the varistor when the pulse current through a specified duration (usually 1mA, duration is generally less than 400mS)

Protection principle of surge absorber: When the varistor is in the ready state, it has a very high impedance (several megaohms) compared to the protected electronic component and will not affect the characteristics of the original design circuit. But when the sudden surge

The most common varistor is

Zinc Oxide, ZnO

Silicon Carbide, SiC

Titanium Oxide, TiO2

Application Principle of Zinc Oxide Varistor

The varistor is used in parallel with the protected electrical equipment or components. When lightning overvoltage or transient operating overvoltage Vs occurs in the circuit, the varistor and the protected equipment and components simultaneously bear Vs. Because the varistor responds quickly, it quickly appears in nanoseconds. Excellent non-linear conductive characteristics. At this time, the voltage across the varistor drops rapidly, which is far less than Vs. In this way, the actual voltage on the protected equipment and components is much lower than the overvoltage Vs, which makes the equipment and components Protected against overvoltage.

1. Varistor voltage: refers to the voltage value across the varistor at the specified temperature and DC (usually 1mA or 0.1mA). Record as V1mA or V0.1mAo

2. Maximum continuous voltage: refers to the maximum effective value of the sinusoidal AC voltage or the maximum DC voltage that can be continuously applied across the varistor at a specified ambient temperature for a long time.

3. Limiting voltage: refers to the maximum voltage peak across the varistor when a specified magnitude of inrush current (8,20s) is passed.

4. Rated power: refers to the maximum average impact power that can be applied to a varistor at a specified ambient temperature.

5. Maximum energy: The maximum primary impact energy that can be applied to a varistor when the varistor voltage does not exceed ± 10% and the impulse current waveform is 10,1000 s or 2 ms.

6. Current capacity (maximum inrush current)

Common varistor models: 5D, 7D, 10D, 14D, 20D, 32D and other models, varistor also has anti-riot function