Application of varistor

The purpose of applying the varistor is different depending on the application, the voltage or current stress acting on the varistor is different, and the requirements for the varistor are also different.

Depending on the purpose of use, varistor can be divided into two categories: varistor for protection; varistor for circuit function.

Protective varistor:

1. Differentiate between power protection, signal lines, and varistor for data line protection. They must meet the requirements of different technical standards.

2. Depending on the continuous operating voltage applied to the varistor, the varistor across the power line can be divided into two types, AC or DC. The aging characteristics of the varistor under these two voltage stresses different.

3. According to the abnormal overvoltage characteristics of the varistor, the varistor can be classified into three types: surge suppression type, high power type and high energy type.

(1) Surge suppression type: refers to a varistor used to suppress transient overvoltages such as lightning overvoltage and operating overvoltage. The occurrence of such transient overvoltage is random, non-periodic, and the peak value of current and voltage may be Very big. Most varistors fall into this category.

(2) High-power type: refers to the varistor used to absorb the continuous pulse group appearing in the cycle, for example, the varistor connected to the switching power converter, where the impulse voltage cycle occurs, and the cycle knows that the energy value can generally Calculated, the peak value of the voltage is not large, but because of the high frequency, the average power is quite large.

(3) High-energy type: refers to a varistor for absorbing electromagnetic energy in a large induction coil such as a generator excitation coil and a lifting electromagnet coil. For such applications, the main technical indicator is energy absorption capability. The protection function of the varistor can be repeated many times in most applications, but it is sometimes made into a "disposable" protection device like a current fuse. For example, a short-circuited varistor connected in parallel to some current transformer load.

Varistor for circuit function:

Varistors are mainly used for transient over-voltage protection, but similar to the volt-ampere characteristics of semiconductor regulators, they also have a variety of circuit component functions, such as:

1. DC high voltage and small current regulator components, the stable voltage can be up to several thousand volts, which is not possible with silicon regulator

2. Voltage fluctuation detecting element

3. DC battery shifting element

4. Voltage equalizing element

5. Fluorescent starter