During the normal use of communication equipment, emi transient interference signals such as lightning surge voltage and spark discharge may occur on the AC power grid and communication lines. The characteristic of transient interference is that the action time is extremely short, but the voltage amplitude is high and the transient energy is large. When the transient voltage is superimposed on the input voltage of the control system, so that the voltage of the input communication device system exceeds the limit voltage of the internal device of the system, the power of the communication device is damaged; when the transient voltage is superimposed on the communication line, the instantaneous high voltage This will damage the components that are transmitted and controlled in the signal loop. In addition, due to power line collision and induction, there may be continuous overvoltage and overcurrent on the communication circuit. If it is not protected, it may damage the communication circuit or device, or even cause fire and loss of life and property. Therefore, appropriate protection measures must be taken to protect communication systems and equipment. Commonly used components generally include: varistors, ceramic capacitors, two or three tubes, and so on.
Two types of components, overvoltage protection devices and overcurrent protection devices, are often used in circuit protection. Today Jinmaoyuan will introduce you to the components that contain these two types.
Overvoltage protection device: Overvoltage protection device usually has high impedance characteristics. When the voltage reaches above its overvoltage protection value, it will switch to low impedance. Once the overvoltage fault disappears, the protection device will return to high resistance state. Recoverable device. Commonly used overvoltage protection devices include transient suppression diodes (TVS), metal oxide varistors (MOVs), and ceramic gas discharge tubes (GDTs).
Transient Suppression Diode (TVS): When the surge voltage comes, the transient suppression diode can change the impedance between the two poles from high to low at a speed of 10-12s, absorbing up to several kilowatts of surge power, making the poles The potential clamp is located at a predetermined value to effectively protect components in the electronic device from surge pulses. TVS has the advantages of fast response time, large transient power, low leakage current, small breakdown voltage deviation, easy control of clamping voltage, and small size.
Metal oxide varistor (MOV): A varistor is actually a sensitive component with a non-linear volt-ampere characteristic. Under normal voltage conditions, this is equivalent to a small capacitor, and when an overvoltage occurs in the circuit. Its internal resistance drops sharply and turns on quickly, and its operating current increases by several orders of magnitude, effectively protecting other components in the circuit from overvoltage and damage. Advantages of MOV: Larger flow rate (100A~70kA) The larger the volume, the larger the surge current can withstand, the complete range and wide range of use.
Ceramic Gas Discharge Tube (GDT): The response time of a gas discharge tube can reach hundreds of ns to several ms, which is the slowest in protective devices. When the lightning overvoltage on the cable causes the gas discharge tube in the lightning arrester to break through the short circuit, the initial breakdown voltage is basically the impact breakdown voltage of the gas discharge tube, and the sustain voltage drops between the two poles after the discharge tube is turned on and turned on. To 20 to 50V.
Overcurrent protection devices: The overcurrent protection devices commonly used in communication equipment mainly include self-recovering fuses (PPTC), which are high-efficiency overcurrent protection devices made of high molecular polymer materials. When an abnormally large current occurs in the communication device, the volume of the self-recovering fuse PPTC polymer rapidly increases, and the impedance increases to a high resistance state, effectively suppressing the passage of a large current, thereby protecting the circuit. When the fault is removed, it will automatically return to the low resistance state, which has no effect on the circuit. Advantages of self-recovery fuse PPTC: Reuse reduces replacement and maintenance costs, superior performance can resist surge current for a long time, and enhance product quality to add value to the product.
Shenzhen Jinmaoyuan Weiye Technology Co., Ltd. is a professional capacitor production factory. Its main products are 3000 hours of electrolytic capacitors, ceramic capacitors, varistors, etc. The products are mainly used in communication equipment, and it can also be applied to electronic/electrical equipment. Security equipment, transportation equipment, automotive electronics, computers and peripherals, consumer electronics and power modules. Welcome everyone to come and discuss