Introduction to LED digital tube

1. What is a "varistor"

"Varistor is a term in Chinese Mainland, which means" resistance varies with voltage within a certain current and voltage range ", or" resistance is sensitive to voltage ". The corresponding English name is" Voltage Dependent Resistor ", which is abbreviated to" VDR ".

The resistance material of varistors is semiconductor, so it is a variety of semiconductor resistors. The widely used "zinc oxide" (ZnO) varistors are composed of divalent element (Zn) and hexavalent element oxygen (O) as their main materials. So from a material perspective, zinc oxide varistors are a type of "II-VI group oxide semiconductor".

In Taiwan, China, China, the varistor is named after its purpose, which is called "surge absorber". Varistors are sometimes referred to as "surge suppressors (absorbers)" depending on their purpose.

2. The "safety valve" function of varistor circuit

What is the use of varistors? The biggest characteristic of a varistor is that when the voltage applied to it is below its threshold "UN", the current flowing through it is extremely small, equivalent to a closed valve. When the voltage exceeds UN, the current flowing through it surges, equivalent to the valve opening. By utilizing this function, it is possible to suppress the frequent occurrence of abnormal overvoltage in the circuit and protect the circuit from damage caused by overvoltage.

3. Application type

The purpose of using varistors varies in different usage scenarios, and the voltage/current stress acting on them is not the same. Therefore, the requirements for varistors are also different. It is important to distinguish these differences for proper use.

According to different usage purposes, varistors can be divided into two categories:

① Protective varistors;

② Varistors are used for circuit functionality.

3.1 Protective Varistors

(1) Distinguish between varistors used for power protection, signal line protection, and data line protection, as they must meet different technical standards.

(2) According to the different continuous operating voltages applied to the varistor, varistors used across power lines can be classified into two types: AC and DC. The aging characteristics of varistors under these two voltage stresses are different.

(3) According to the different abnormal overvoltage characteristics that varistors can withstand, varistors can be classified into three types: surge suppression type, high-power type, and high-energy type.

Surge suppression type: refers to a varistor used to suppress transient overvoltages such as lightning overvoltage and operational overvoltage. The occurrence of such transient overvoltages is random, non periodic, and the peak value of current and voltage may be large. The vast majority of varistors belong to this category.

High power type: refers to a varistor used to absorb continuous pulse groups that occur periodically, such as varistors connected in parallel to a switching power converter. Here, the impulse voltage occurs periodically, and the period is known. The energy value can generally be calculated, and the peak voltage is not large, but due to its high frequency of occurrence, its average power is quite large.