What is SPD varistor?

SPD varistoris a resistance device with nonlinear volt-ampere characteristics, which is mainly used to embed voltage when the circuit is over-voltage, absorb excessive current, and protect sensitive devices. The resistance material of rheostat is semiconductor, so it is a kind of semiconductor resistance. In Taiwan, China Province of China, SPD varistors are called "surge absorbers" or "surge suppressors (absorbers)". Varistors can be divided into protection varistors and circuit function varistors according to different purposes

The varistor is a kind of voltage limiting protection device. Using the nonlinear characteristics of the SPD varistor, an overvoltage occurs between the two poles of the varistor, which can clamp the voltage at a relatively fixed voltage value, thus realizing the protection of the later stage circuit. The main parameters of the SPD varistor are: voltage sensitive voltage, current capacity, junction capacitance, response time, etc. The response time of the varistor is ns, faster than the air discharge tube and TVS The tube is slightly slow. In general, its response speed to overvoltage protection of electronic circuit can meet the requirements. Generally speaking, the junction capacitance of the varistor is in the order of several hundred Pf to several thousand Pf. In many cases, it should not be directly applied to the protection of high-frequency signal lines. When applied to the protection of AC circuit, the junction capacitance will increase the leakage current, so it should be fully considered when designing the protection circuit. The current capacity of the varistor is large, but less than that of the gas discharge tube

What is the use of SPD varistor? The characteristic of the varistor is that when the voltage applied to it is lower than its threshold value 'UN', it is equivalent to a closed valve, and the current flowing through it is very small. When the voltage exceeds UN, its resistance value decreases, making the current flowing through it surge, thus reducing the impact of overvoltage on subsequent sensitive circuits, and having little impact on other circuits. Through this function, the circuit can be protected from overvoltage damage and the abnormal overvoltage that often occurs in the circuit can be controlled

SPD varistorApplication type: The voltage/current acting on the varistor should be different in different applications, so the requirements for the varistor are also different. Distinguishing this difference is very important for correct use

SPD varistorBasic performance: (1) When the impact strength of the impact source does not exceed the specified value, the limit voltage of the varistor is not allowed to exceed the impact withstand voltage that the protected object can withstand. (2) Impact resistance, that is, the varistor itself should be able to withstand the specified impact energy, impact current, and the average power when multiple impacts occur successively. (3) After the varistor is inserted into the system, in addition to the protection function of "safety valve", it will also bring some additional effects, called "secondary effect", which should not reduce the normal working performance of the system. At this time, three factors are mainly considered, one is the leakage current under the system voltage, the other is the capacitance of the varistor itself, and the third is the influence of the nonlinear current of the varistor on other circuits through the coupling of the source impedance