According to the factors of EMC, the EMC of power adapter can be solved from three aspects:

(1) Propagation path of interference signal

(2) Enhance the anti-interference ability of the interfered body

(3) Reduce the interference signal generated by the interference source

To the external anti-jamming ability, such as surge, lightning strikes, should optimize the AC input and DC output port lightning protection ability. The combination of zinc oxide varistor and gas discharge tube can be used to solve the lightning strike. For electrostatic discharge, TVS tube and the corresponding grounding protection, increase the distance between the small signal circuit and the housing, or use anti-static interference devices to solve the problem. To reduce the internal interference of the power adapter, we should start from the following aspects: pay attention to the single point grounding of digital circuit and analog circuit, the single point grounding of large current circuit and small current, especially current and voltage sampling circuit, in order to reduce the common resistance interference and reduce the influence of the ground loop; When wiring, pay attention to the spacing between adjacent lines and the nature of the signal to avoid crosstalk; Reduce ground impedance; Reduce the area surrounded by the high voltage and large current lines, especially the original side of the transformer and the switching tube, the power filter capacitor circuit; Reduce the area surrounded by the output rectifier circuit, the continuing diode circuit and the DC filter circuit; Reduce the leakage inductance and filter capacitance of the transformer; Filter capacitors with high resonant frequency are used.

External interference caused by the power adapter, such as harmonic current of the power line, power line conduction interference, and electromagnetic radiation interference, can only be solved by reducing the interference. On the one hand, strengthen the shielding effect of the casing, improve the gap leakage of the casing, and conduct good grounding treatment. On the other hand, it can enhance the design of input/output filter circuit, improve the performance of active power factor compensation (APFC) circuit, reduce the voltage and current change rate of switching tube and rectifier diode, and adopt various soft switching circuit extension structure and control mode.

In terms of transmission path, TUS with high anti-interference ability, high frequency capacitor, ferrite magnetic beads and other components should be appropriately added to improve the anti-interference ability of small signal circuit; Small signal circuit close to the housing, should add appropriate insulation and pressure treatment; The radiator of the power device, the electromagnetic shielding layer of the main transformer should be properly grounded; Large area grounding between each control unit shall be shielded by ground floor. In the frame of the rectifier, the electromagnetic coupling between the rectifiers and the whole machine ground layout should be considered to improve the stability of the internal work of the power adapter.

I hope you can solve the above problems smoothly!