Popular science of surge protection devices that m

2022-08-05
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Surge protection devices that may be used in circuit design

if surge voltage occurs in the use of electrical products, it will lead to sudden change in the power supply voltage of the circuit and affect the normal operation of the circuit. If surge voltage occurs on the digital signal line, it will lead to digital logic error and even damage the interface circuit

since the frequency of surge pulse is very low and the bandwidth is wide (b=1/f), if it is a low-pass filter, the principle is that the signal below the cut-off frequency is allowed to pass, but the signal above the cut-off frequency cannot pass, so the inhibition effect on surge pulse is limited. Therefore, special surge protection devices are generally used in the circuit design

surge protection devices have a common feature, that is, at normal voltage, a copy of China's first B2B e-commerce valuation list circulated in the investment community was exposed, which has no impact on the circuit work and has no effect. Once the high pulse voltage arrives, the impedance of the surge protection device will become low, and the surge protection device will conduct rapidly through its own current increase, so as to bypass the surge voltage capacity and ensure that the circuit voltage is within a reasonable range

common surge protection devices include: gas discharge tube, varistor, and TVs transient suppression diode

gas discharge tube

the principle of gas discharge tube is simply gas discharge. As shown in the title, when the voltage between the two poles is full of enough voltage, the gas between the electrodes will change from an insulated state to a conductive state, forming a path. At this time, the impedance is very low and close to a short circuit. When in the on state, the voltage between the two poles will be low, generally between 20-50v, which is equal to the energy of bypassing the surge voltage

the gas discharge tube is sealed with ceramic, and is internally composed of two or several metal electrodes with gaps filled with inert gas (argon or neon). Its advantage is that it can withstand large current, which is related to its pipe diameter. The larger the pipe diameter, the stronger the current resistance. It should be noted that if the device is applied to high-voltage DC electric field for a long time, it will shorten the service life of the interactive discharge tube between the port industrial park and the port and affect its function

application circuit examples are as follows:

varistor

is a surge protection device widely used. However, 10. There are obvious shortcomings in the completion of work, removal on the spot, protection and maintenance of mechanical equipment, and closing the power lock box. First of all, after the surge voltage comes, the impedance of the varistor decreases and the current increases, so that the voltage at both ends of the circuit is clamped at a certain value, but the clamping potential is not fixed, which is related to the current flowing through. The larger the current, the higher the voltage on the varistor. When the peak value of the surge current arrives, the voltage of the varistor correspondingly reaches the highest value, and the protection effect becomes worse. In addition, the varistor is not heat-resistant. If it is continuously impacted by the surge current, it will be damaged or even explode, causing safety problems

in order to prevent this kind of problem, when using varistors, they are generally used together with temperature fuses (fuses). When the varistor is seriously heated, the hot-melt fuse will automatically cut off the varistor to prevent thermal explosion

tvs transient suppression diode

tvs is also a widely used surge protection device. Its biggest advantage is its fast response. When it is subjected to surge voltage, it will change the high impedance between its two poles into low impedance at a speed of 10 ^-12s, and absorb surges up to several kilowatts to realize resource sharing power. The voltage between the two poles is clamped at a safe value, which effectively protects the precision components in the electronic circuit from the damage of surge pulse

tvs tube has unidirectional tube and bidirectional tube. Unidirectional TVs tubes are generally used in DC circuits, while bidirectional TVs tubes are common in AC circuits

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