What is SPD varistor?

SPD varistoris a resistance device with nonlinear volt-ampere characteristics, which is mainly used to clamp the voltage when the circuit is under overpressure, absorb excess current, and protect sensitive elements. The English name is abbreviated to“ Voltage Dependent Resistor”， Short name is“ VDR” Or“ Varistor”。 The resistance body material of pressure resistor is semiconductor, so it is a variety of semiconductor resistor. Currently,“ is widely used; Zinc oxide” (ZnO) pressure reducer, its main material is composed of divalent element zinc (Zn) and hexavalent element oxygen (O). So from the perspective of material, zinc oxide varistor is a kind of&ldquo- Group oxide semiconductor”. In Taiwan, China, the pressure resistor is called“ Surge Absorber”, Sometimes called“ Electric shock (surge) suppressor (absorber)&rdquo

SPD varistor is a limiting protection device. Using the nonlinear characteristics of the varistor, the past voltage appears between the anodes of the varistor. The varistor can clamp the voltage to a relatively fixed voltage value, thus protecting the subsequent circuit. The main parameters of the varistor include voltage reduction, flow capacity, bonding capacity, response time, etc

SPD varistorhas a response time of ns, which is faster than gas discharge tube and slightly slower than TVS tube. The response speed of overvoltage protection commonly used in electronic circuits can meet the requirements. The junction capacitance of the varistor is generally in the range of hundreds to thousands of Pf. In many cases, it cannot be directly applied to the protection of high-frequency signal lines, nor can it be applied to the protection of AC circuits. Because the junction capacitance is more, it should be fully considered when designing the protection circuit. The flow capacity of the reducing resistor is relatively large, but smaller than that of the gas discharge tube. Voltage induction resistor (VDR) is a nonlinear over-voltage protection semiconductor element sensitive to voltage

What is the basic performance of SPD varistor? Let's make a brief analysis

(1) When the protection characteristics and the impact strength of the impact source (or the impact current Isp=Usp/Zs) do not exceed the specified value, the limiting voltage of the reducing resistance cannot exceed the impact resistance voltage (Urp) that the protection object can withstand

(2) Impact resistance, that is, the pressure reduction resistance itself, must be able to withstand the specified impact current, impact energy and the average power when multiple impacts occur successively

(3) There are two life characteristics. One is continuous working voltage life. That is, the time (in hours) that the pressure resistor must operate stably under the specified ambient temperature and system voltage. The second is impact life, that is, the number of times that can withstand the specified impact

(4) Decompression resistance intervention system, except for“ Safety valve” In addition to the protection effect of, there will also be additional impacts, which is the so-called“ Secondary effect”, The normal operation performance of the system cannot be reduced. There are three main factors to consider at this time. The first is the capacitance of the varistor itself (tens to tens of thousands of PF), the second is the leakage current under the system voltage, and the third is the influence of the nonlinear current of the varistor on other circuits through the combination of source impedance