The varistor is one of the most important components in the design of the power supply safety. Its function is to absorb the excess current when the circuit is over voltage. Because of its mass production, and a wide range of applications, has been widely used in various fields of electronic products.
The composition of the pressure sensitive resistance
The varistor is a semiconductor material, so it is a variety of semiconductor resistor. Now a large number of "Zinc Oxide" (ZnO) varistors, its main material has two valence elements (Zn) and (O) constitute. So from the material point of view, Zinc Oxide varistor is a kind of "II-VI semiconductor oxide".
The working process of the varistor circuit
I believe we all know the varistor effect, but it is the overvoltage protection circuit by using the method of what? When it in the above its threshold voltage is lower than the "UN", the minimum current flowing through it, the equivalent of a closed valve, when the voltage exceeds UN. The current flowing through it in the equivalent of the valve open. By using this function, we can suppress the abnormal overvoltage in the circuit and protect the circuit from over-voltage damage.

Different application categories
Depending on the application, the voltage and current stress on the varistor are not the same. Therefore, the requirements of the varistor are not the same, it is very important to distinguish the difference. According to the purpose of the use of different, can be divided into two categories, one is the protection of pressure-sensitive resistors, and the other is the circuit function of the varistor. The following, to the introduction of the two varistor.
Protection with pressure sensitive resistance
This type of varistor is mainly used to distinguish between the power supply protection, and the protection of the varistor is often used for signal lines and data lines to protect them to meet the requirements of different technical standards. The varistor, according to the continuous working voltage is different, can be used to distinguish cross power line varistors for AC or DC, with two types of varistor in the two voltage aging characteristics under different stress.
According to the characteristics of the abnormal overvoltage, the varistor can be divided into three types: surge suppression, high power and high energy.
Surge suppression varistors, is used to inhibit the varistor lightning overvoltage and switching overvoltage and transient overvoltage, the transient overvoltage appeared to be random, non periodic, peak current and voltage can be very large. The vast majority of varistors fall into this category.
High power type thermistors, varistors is used for continuous pulse group absorption cycle, for example, and then varistor in switching power converters, this impulse voltage cycle, and the cycle shows that the energy values can be calculated, the peak voltage is not large, but because of the high frequency, the average considerable power.
High energy varistors, refers to the absorption of excitation coil, magnetic energy from the varistor voltage lifting electromagnet coil for large inductance coils, for this type of application, the main technical indicators is the energy absorption capacity.
The protection function of the varistor, under the vast majority of applications, can be repeated many times, but sometimes it is made into a current fuse, such as a "one-time" protection device. For example, a short circuit contact voltage sensitive resistor connected to a certain current transformer load.
Voltage sensitive resistor for circuit function
In the circuit, transient overvoltage protection mainly depends on the pressure sensitive resistance can be achieved because of the body there are close to the semiconductor Zener volt ampere characteristics, so that it can play a role in the diversification of circuit. The varistor in the circuit as it can for many purposes: high voltage DC small current voltage stabilizing element, the stable voltage can be up to thousands of volts or more, which is beyond the reach of the silicon zener voltage fluctuation detection; DC shift components; components; pressure components; fluorescent promoter element.
In this paper, we introduce the varistor in the circuit safety regulation, from the concept of the varistor to the principle of operation, and then to the different application classification, are explained in more detail. For beginners, is to consolidate the basic knowledge of an article. We hope that after reading this article, you can have a further understanding of the safety of the varistor.