Lightning protection of audio equipment

Talking about the lightning protection of audio equipment

Abstract: the lightning overvoltage and electromagnetic interference protection of the communication station of the power system is an important technical means to protect the communication lines, equipment and personal safety, an indispensable technical measure to ensure the operation rate of the communication lines and equipment, and an important part of the construction and management of power communication

key words: audio equipment lightning protection lightning overvoltage and electromagnetic interference protection of power system communication station is an important technical means to protect communication lines, equipment and personal safety, an indispensable technical measure to ensure the operation rate of communication lines and equipment, and an important part of power communication construction and management. 1. Introduction to the performance of lightning protection devices (1) gas discharge tube. Gas discharge tube is a durable on-off component, which has the advantage of withstanding the current impulse of thousands of amperes in hundreds of microseconds. Its disadvantage is that the gas ionization process takes time, and its response is microsecond level, while the wave head time of lightning overvoltage is very short. When the wave head crosses the voltage threshold of the switching machine, the gas discharge tube acts. This will inevitably impose a surge voltage on the switch that exceeds its circuit withstand voltage value. Although the duration is short, it may still damage the circuit. In addition, under multiple large current shocks, the discharge gap of the gas discharge tube will increase due to electrode ablation, resulting in the increase of ignition voltage, the inertia of the discharge tube will increase, the amplitude of overvoltage added to the circuit will increase, and the time will be extended, resulting in an increased chance of equipment damage. (2) Varistor. Varistor has good nonlinearity, great energy absorption ability and fast response speed. The characteristic of varistor is that when transmitting image signal, video signal and ISDN signal, due to its high clutter capacitance, the wire inductance of the capacitance forms a low-pass circuit, which will greatly attenuate the signal and cause transmission distortion. Although the response speed is relatively fast, it still cannot keep up with the response speed of the integrated circuit of the SPC exchange, which is mainly composed of five parts: computer, data collection card, hydraulic system, stretching mechanism and load cell (tension sensor). Another disadvantage is its aging. For each impulse of lightning wave, the residual voltage and operating voltage of the varistor will increase during the experimental process, and the sensitivity and service life will decrease. (3) Thermistor. Thermistor, also known as PTC. Polymer PTC has the advantages of small and stable internal resistance, fast action speed, low surface temperature, high voltage resistance, lightning resistance, no burst, open circuit in case of breakdown, etc. when passing the normal working current, it has a large number of conductive rails inside, showing extremely low resistance. Once a fault occurs, the over-current causes the components to heat up, and the polymers in PTC separate from each other due to thermal movement, leaving only a very small number of conductive rails. PTC instantly presents high impedance (its resistance value increases by several orders of magnitude), so that the line current drops to a safe value. Once the fault is eliminated, the components can be restored to the original low resistance state after cooling. (4) Solid discharge tube. Solid discharge tube, also known as semiconductor discharge tube, is a cutting-edge product of lightning protection devices in the field of communication. It is an updated product of gas discharge tube and varistor. When the applied lightning induced voltage rises to its breakdown voltage, the semiconductor discharge tube acts as an avalanche triode curve. With the reduction of lightning current, the voltage at both ends returns to the "off" state. The moving speed of the beam can be changed. Due to the computer simulation design and the computer control of the production process, the discharge current capacity and the residual voltage in the conduction state (only a few volts) of the solid discharge tube can be accurately predetermined, regardless of the response speed of the solid discharge tube (200 ~ 400 μ 5) , discreteness, service life (more than 15 years) and recovery characteristics are better than other protective devices, and also meet the requirements of today's development of ISDN communication. 2. Several methods of lightning protection (1) the combination of multiple lightning protection devices is used to make up for the defect of relying on a single protection device. The varistor and thermistor are assembled together to form a security unit with comprehensive performance against overvoltage and overcurrent. Place PTC on the outside line side and varistor on the inside line side. For lightning wave, the varistor still plays the role of rapid response and lightning current to the ground. For the extremely rare collision accident between mains power and audio cable, the varistor is the first to be punctured and grounded by mains power 220V, and the potential of point q is reduced to 0, thus protecting the communication equipment behind. Since PTC is connected in series in the mains circuit, its own resistance rises sharply, and the fault current is quickly limited to less than 300mA, so the communication cable can be protected. After troubleshooting, PTC can automatically return to the original state, so that the communication operation returns to normal. To say the least, in case individual PTC is damaged due to long-term heating, it will also be in an open circuit state, so as to cut off the overcurrent. (2) Multiple devices are used to realize multi-level protection of lightning protection devices. If any level of protection deteriorates and breaks away, the other level can still play a protective role. For example, the gas discharge tube can be used as a primary protection element because of its strong ability to amplify energy. It is especially suitable for high exposure areas such as suburbs and rural areas, but not for the protection of circuits with high sensitivity of internal equipment. The varistor is suitable for the second stage arrester of power supply, but it is not suitable for lightning current arrester. We can use solid discharge tube, thermistor (PTC), led and other parts to form a three-level protection. (3) We can also use solid discharge tubes, PTCs, light-emitting diodes, etc. to form a three-level protection according to the requirements of the personnel on duty. In this way, lightning protection devices can send out sound and light warning signals, which is convenient for timely discovery and replacement. With the rapid development of microelectronics technology, communication equipment has been miniaturized, and large-scale integrated circuits are usually used. Its power supply voltage has been reduced from dozens of volts to a few volts, and the information current it transmits has also been reduced from milliampere level to microampere level, which greatly reduces the interference tolerance of digital communication signals to pulse voltage and overcurrent. Therefore, the importance and urgency of lightning protection and high voltage protection of communication equipment have also been paid more and more attention