Power adapter interference and solutions

According to the factors generated by electromagnetic compatibility, power adapter manufacturers believe that solving the electromagnetic compatibility of power adapters can be started 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 victim

External interference to the power adapter, such as power line harmonic currents, power line conduction interference, electromagnetic field radiation interference, etc., can only be resolved by reducing interference. On the one hand, it can enhance the design of the input/output filter circuit, improve the performance of the active power factor compensation (APFC) circuit, reduce the voltage and current rate of change of the switch tube and the rectifier and freewheeling diode, and adopt various soft switching circuit extensions. Make up the structure and control methods; on the other hand, strengthen the shielding effect of the chassis, improve the leakage of the gap of the chassis, and perform good grounding treatment.

For external anti-interference capabilities, such as surges and lightning strikes, the lightning protection capabilities of the AC input and DC output ports should be optimized. The lightning strike can be solved by a combination of zinc oxide varistor and gas discharge tube. For electrostatic discharge, use TVS tubes and corresponding grounding protection, increase the distance between the signal circuit and the chassis, or select a device with anti-static interference to solve. To reduce the internal interference of the power adapter, you should start from the following aspects: pay attention to the single-point grounding of digital circuits and analog circuits, single-point grounding of high-current circuits and small currents, especially current and voltage sampling circuits, to reduce common resistance interference, Reduce the influence of the ground ring; pay attention to the spacing between adjacent lines and signal properties when wiring to avoid crosstalk; reduce the impedance of the ground wire; reduce the high-voltage and high-current lines, especially the primary side of the transformer and the switch tube, power filter capacitor circuit Enclosed area; reduce the area enclosed by the output rectifier circuit, freewheeling diode circuit and DC filter circuit; reduce the leakage inductance of the transformer and the distributed capacitance of the filter capacitor; use a filter capacitor with a high resonance frequency.

In terms of propagation channels, appropriate addition of high anti-interference ability TUS and high-frequency capacitors, ferrite beads and other components to improve the anti-interference ability of small signal circuits; small signal circuits closer to the chassis should be Add appropriate insulation withstand voltage treatment, etc.; the radiator of the power device and the electromagnetic shielding layer of the main transformer should be properly grounded; the large-area grounding between each control unit should be shielded with a ground plate; on the rack of the rectifier, the rectifier should be considered Electromagnetic coupling, grounding of the whole machine, etc., to improve the stability of the internal work of the power adapter.