The solution to the electromagnetic compatibility problem of switch mode power supplies
Speaking from the three elements of electromagnetic compatibility, to solve the electromagnetic compatibility of switching power supply, we can start from three aspects.
1) Reduce the interference signal generated by the interference source;
2) Cut off the propagation path of the interference signal;
3) Enhance the anti-interference ability of the disturbed body.
When solving the electromagnetic compatibility within the switching power supply, the above three methods can be applied comprehensively, with the cost-benefit ratio and the difficulty of implementation as the prerequisite. The external interference generated by the switching power supply, such as power line harmonic current, power line conduction interference, electromagnetic field radiation interference, etc., can only be solved by reducing the source of interference. On the one hand, you can enhance the design of the input and output filter circuits, improve the performance of the active power factor correction (apfc) circuit, reduce the rate of change of the voltage and current of the switching tubes and rectifier diodes, and use a variety of soft-switching circuit topologies and control methods. On the other hand, the shielding effect of the chassis is strengthened, the gap leakage of the chassis is improved, and good grounding is carried out. And the external anti-interference capability, such as surge and lightning strike should be optimised for the lightning protection capability of AC input and DC output ports. Usually, for the combination of 1.2/50μs open-circuit voltage and 8/20μs short-circuit current lightning strike waveforms, a combination of zinc oxide varistors and gas discharge tubes, etc. can be used to solve the problem due to the small energy. For electrostatic discharge, usually in the communication port and the control port of the small signal circuit, the use of tvs tube and the corresponding grounding protection, increase the small signal circuit and chassis, such as the electrical distance, or the use of anti-static interference with the device to solve. Fast transient signals contain a wide frequency spectrum, it is easy to common mode way into the control circuit, using the same method of anti-static and reduce the distribution capacitance of the common-mode inductor, strengthen the input circuit of the common-mode signal filtering (such as the addition of a common-mode capacitor or insertion loss type ferrite ring, etc.) to improve the system's anti-interference performance.
