The Solution to Electromagnetic Compatibility of Stabilized Power Supply
From the perspective of the three elements of electromagnetic compatibility, to solve the problem of electromagnetic compatibility of switching power supplies, we can start from three aspects: first, reduce the disturbance signal generated by the disturbance source; second, cut off the propagation path of the disturbance signal; third, Enhance the anti-harassment ability of the harassed body. When solving the internal compatibility of the switching power supply, the above three methods can be used comprehensively, based on the cost-benefit ratio and the ease of implementation. Therefore, external disturbances generated by switching power supplies, such as power line harmonic currents, power line conduction disturbances, and electromagnetic field radiation disturbances, can only be solved by reducing the source of disturbance. On the one hand, it can enhance the design of the input/output filter circuit, improve the performance of the APFC circuit, reduce the voltage and current change rate of the switch tube, rectifier and freewheeling diode, and adopt various soft switching circuit topologies and control methods, etc.; the other On the one hand, strengthen the shielding effect of the casing, improve the gap leakage of the casing, and perform good grounding treatment. For external anti-disturbance capabilities (such as surges and lightning strikes), the lightning protection capabilities of the AC input and DC output ports should be optimized. Usually, for the combined lightning strike waveform of 1.2/50μs open-circuit voltage and 8/20μs short-circuit current, due to the small energy, it is usually solved by combining zinc oxide varistors and gas square electric tubes. For electrostatic discharge, usually in the small signal circuit of the communication port and the control port, use TVS tube and corresponding grounding protection, increase the electrical distance between the small signal circuit and the chassis, etc. to solve or select devices with anti-static disturbance. The fast transient signal contains a wide frequency spectrum, and it is easy to pass into the control circuit in the form of common mode. The same method as anti-static is used to reduce the distributed capacitance of the common-mode inductance and strengthen the common-mode signal filtering of the input circuit (plus Common mode capacitors or insertion loss ferrite cores, etc.) to improve the immunity of the system.
To reduce the internal disturbance of the switching power supply, realize its own electromagnetic compatibility, and improve the stability and reliability of the switching power supply, we should start from the following aspects: ①Pay attention to the correct partition of the digital circuit and the PCB wiring of the module circuit; ②Digital circuit and Decoupling of the analog circuit power supply; ③Single-point grounding of digital circuits and analog circuits, single-point grounding of high-current circuits and low-current circuits, especially current and voltage sampling circuits, to reduce common resistance disturbance, reduce the impact of ground rings, and pay attention when wiring The spacing between adjacent lines and the nature of the signal can avoid crosstalk, reduce the area surrounded by the output rectifier circuit, the freewheeling diode circuit and the branch filter circuit, reduce the leakage of the transformer and the distributed capacitance of the filter inductor, and use high resonance frequency filter capacitors, etc.
