What are the application types of varistor?

1、 Varistor

"Varistor" is a kind of resistor with nonlinear volt ampere characteristics, which is mainly used to clamp the voltage when the circuit is under overvoltage, absorb excess current, and ensure the sensitive device. The English name is "English name" Voltage Dependent Resistor, abbreviated as "VDR", Or called "Varistor". The resistance body material of varistor is semiconductor, so it is a semiconductor resistance. The widely used "zinc oxide" (ZnO) varistor is the main material of zinc, which is composed of divalent element (Zn) and hexavalent element oxygen (O). Therefore, from the perspective of materials, zinc oxide varistor is a "Ⅱ - Ⅵ oxide semiconductor". varistor is called "Ⅱ - Ⅵ oxide semiconductor" in Taiwan, China, China A "surge absorber", sometimes also known as an "electric shock (surge) suppressor (absorber)".

Varistor is a voltage limiting protection device. Using the nonlinear characteristics of the varistor, when the overvoltage occurs between the two poles of the varistor, the varistor can place the voltage clamp to a relatively fixed voltage value to achieve subsequent power maintenance. The basic parameters of varistor include: varistor voltage, current capacity, junction capacity, response speed, etc.

The response speed of varistor is ns level, faster than that of gas discharge tube and slower than that of TVS tube. Generally speaking, the response speed used for overvoltage protection of electronic circuits can meet the requirements. The junction capacitance of varistor is generally in the range of hundreds to thousands of PF. In many cases, it should not be directly used for maintenance of high-frequency signal lines. When used for protection of AC circuits, due to the increased leakage current caused by its junction capacitance, it is necessary to fully consider when planning the protection circuit. The varistor has a large flow capacity, but it is smaller than the gas discharge tube. VDR is a nonlinear overvoltage protection semiconductor component that is sensitive to voltage.

2、 Application type of varistor

The application types of varistor in the circuit include: varistor can be used in parallel or in series in the circuit. Parallel use can improve the value of anti surge current, but it is required that the nominal voltage of parallel equipment should be consistent. Series use can increase the nominal voltage value in practical applications. Generally speaking, the nominal voltage value after series connection is the sum of two nominal voltage values.

Varistors can protect circuits of IC and other equipment from damage caused by electrostatic discharge, surge and other temporary currents (such as lightning strike). The application of varistor can be divided into four types:

The first type is the power cord or the connection between the power cord and the ground. As a varistor, when the power line and remote transmission power line encounter lightning strike, representative application sites should buffer electronic equipment. In general, the online indirect varistor is effective for the induction pulse between lines, while the online indirect varistor is effective for the induction pulse between the transmission line and the ground. If the connection between lines and the connection between lines are further combined, it can better absorb surge pulses.

The second type is the connection in the load, mainly used to absorb the induction pulse caused by the sudden opening and closing of the induction load to avoid damaging the components. Generally speaking, it only needs to be connected in parallel with the inductive load, but depending on different current types and kinetic energy levels, it can be selected to be shared with the R-C series absorption circuit.

The third type is the connection between contacts. The key to this connection is to prevent the induced charge switch connector from being burned by the electric arc. In general, varistors can be connected to contacts.

The fourth type is mainly used for the protective connection of semiconductor equipment, mainly used for semiconductor equipment such as thyristors and high-power transistors. It is generally connected in parallel with the protective equipment, limiting the voltage to be less than the withstand voltage level of the protective equipment, and is an effective protection for semiconductor equipment.

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