The electromagnetic compatibility problem caused by communication switching power supply is quite complicated because it works in the switching state of high voltage and high current. In terms of electromagnetic compatibility of the whole machine, there are mainly common impedance coupling, line-to-line coupling, electric field coupling, magnetic field coupling and electromagnetic wave coupling. The three elements of electromagnetic compatibility are: interference source, propagation path and interfered object. Co-impedance coupling mainly refers to the electrical common impedance between the interference source and the interfered object, through which the interference signal enters the interfered object. Line-to-line coupling is mainly the mutual coupling caused by parallel wiring of wires or pcb lines that generate interference voltages and interference currents. Electric field coupling is mainly due to the existence of potential difference, the induced electric field generated by the coupling to the disturbed body. The magnetic field coupling is mainly the coupling of the low-frequency magnetic field generated near the high-current pulse power line to the interference object. The electromagnetic wave coupling is mainly due to the high-frequency electromagnetic wave generated by the pulsating voltage or current, which radiates outward through space and couples to the corresponding disturbed body. In fact, each coupling method cannot be strictly distinguished, but the emphasis is different.
In a switching power supply, the main power switching tube works in a high-frequency switching mode at a very high voltage. The switching voltage and switching current are both square waves, and the frequency spectrum of the high-order harmonics contained in the square wave can reach the square wave frequency. more than 1000 times. At the same time, due to the leakage inductance and distributed capacitance of the power transformer, and the working state of the main power switching device is not ideal, when the high frequency is turned on or off, a high frequency and high voltage peak harmonic oscillation is often generated, and the high order Harmonics are transmitted to the internal circuit through the distributed capacitance between the switch tube and the radiator or radiated to the space through the radiator and transformer. Switching diodes used for rectification and freewheeling are also an important cause of high-frequency interference. Because the rectification and freewheeling diodes work in a high-frequency switching state, due to the influence of the parasitic inductance of the lead wires of the diodes, the existence of junction capacitance, and the reverse recovery current, they work under very high voltage and current change rates, resulting in high-frequency oscillation. Because the rectifier and freewheeling diodes are generally close to the output line of the power supply, the high-frequency interference generated by them is most likely to be transmitted through the DC output line.
In order to improve the power factor, the communication switching power supply adopts an active power factor correction circuit. At the same time, in order to improve the efficiency and reliability of the circuit and reduce the electrical stress of the power device, a large number of soft switching technologies are used. Among them, zero voltage, zero current or zero voltage zero current switching technology is the most widely used. This technology greatly reduces the electromagnetic interference generated by switching devices. However, the soft-switching non-destructive absorption circuit mostly uses l and c for energy transfer, and uses the unidirectional conductivity of the diode to realize the unidirectional conversion of energy. Therefore, the diode in the resonant circuit becomes a major interference source of electromagnetic interference.
In комуникация превключване мощност доставки% 2c енергия съхранение индуктори и кондензатори са общо използва да форма l и c филтър вериги към филтър диференциал режим и общ режим смущения сигнали и конвертиране AC квадрат вълна сигнали в гладка DC сигнали. Поради на разпределени капацитет на на индуктивност бобина % 2c на самостоятелно резонансна честота на на индуктивност намотка е намалена % 2c така че а голям брой на висока честота смущения сигнали преминават през индуктивност намотка и разпространява навън заедно AC мощност линия или DC изход линия. За филтър кондензатори% 2c като на честота на на смущения сигнал се издига% 2c поради на ефект на олово индуктивност% 2c на капацитет и филтриране ефект ще продължи да намаляване докато го достига резонанс честота и по-горе% 2c го ще напълно губят на роля на на кондензатор и да стане индуктивен. Неправилна употреба на филтър кондензатори и твърде дълго олово проводници са също а причина на електромагнитни смущения.
Communication switching power supply has high power density, high degree of intelligence, and MCU microprocessor, so there are voltage signals ranging from high to nearly a thousand volts to as low as s several volts, from high-frequency digital signals to low-frequency analog signals, power supply The internal field distribution is quite complex. Неразумно pcb окабеляване, неразумно структурно дизайн% 2c неразумно мощност линия вход филтър% 2c неразумно вход и изход мощност линия окабеляване% 2c неразумно дизайн на процесор и откриване верига% 2c всички от което ще доведе до нестабилна система операция или намаляване риска на електростатичен разряд и мощност отказ. имунитет към преходни изблици% 2c мълния удари , пренапрежения и проведени смущения% 2c излъчени смущения и излъчени електромагнитни полета.
The research of electromagnetic compatibility generally uses the electromagnetic field detection instruments stipulated in cispr16 and IEC61000 and various interference signal simulators and auxiliary equipment, in the standard test site or inside the laboratory, through detailed test analysis and combined with the understanding of circuit performance. Conduct analytical research.
