Switching power supply lightning protection circuit design scheme
Instantaneous high voltage lightning surge as well as signal system surge is an important cause of poor instrument stability, the main sources of signal system surge voltage are induced lightning, electromagnetic interference (EMI), radio interference and electrostatic interference. Metal objects (such as telephone lines) are affected by these interfering signals, will make the data in transmission to produce error codes, affecting the accuracy of transmission and transmission rate. How to design lightning protection circuits has become a key issue in instrument development.
Lightning surge analysis
The most common hazards of electronic equipment is not caused by direct lightning strikes, but due to lightning strikes occur in the power supply and communication lines induced by current surges. On the one hand, due to the high degree of integration of the internal structure of electronic equipment (VLSI chip), which results in a reduction in the level of voltage and overcurrent resistance of the equipment, and a reduction in the ability to withstand lightning (including induced lightning and operational overvoltage surge), on the other hand, due to the increased number of paths of the source of the signals, the system is more susceptible than before to the intrusion of lightning waves. Surge voltage can run from the power line or signal line and other ways into the computer equipment, we discuss these two aspects separately:
1) Power surge
Power surge and not only from lightning strikes, when the power system has a short-circuit failure, cut large loads will produce power surge, the power grid stretches for thousands of miles, whether it is a lightning strike or line surge the chances of occurrence are very high. When you are hundreds of kilometres away from the distant occurrence of a lightning strike, lightning surge transmission through the grid at light speed, after the substation and other attenuation, to your computer may still have thousands of volts, this high pressure is very short, only a few dozen to hundreds of microseconds, or not enough to burn the computer, but for the computer's internal semiconductor components but there is a great deal of damage, as the old stereo noise than the new to be larger because of the damage to the internal components of the same! With the deepening of these damages, the computer will gradually become more and more unstable, or may cause the loss of your important data.
U.S. GE determined that the general family, hotels, flats and other low-voltage distribution lines (110V) in 10,000 hours (about one year and two months) occurred between the line more than double the original operating voltage surge voltage reached more than 800 times, of which more than 1,000V there are more than 300 times. Such a surge voltage is entirely possible one-time damage to electronic equipment.
2) Signal system surge
Signal system surge voltage is the main source of induced lightning, electromagnetic interference, radio interference and electrostatic interference. Metal objects (such as telephone lines) affected by these interfering signals, will make the transmission of data in the error code, affecting the accuracy of transmission and transmission rate. Eliminating these interferences will improve the transmission condition of the network.
Based on the above technical defects and conditions, this paper designs a single-phase parallel lightning surge-resistant switching power supply circuit based on varistors and ceramic gas discharge tubes according to practical use.
