How to filter out differential mode interference in a concentrator?

Differential-mode interference in the concentrator exists between the L and N power lines, mainly caused by rectifier bridge commutation and fast switching of the switching transistors, with the frequency band concentrated in the 150kHz-1MHz range. The core of filtering differential-mode interference is designing an effective differential-mode filter network. At the power input, an LC low-pass filter is constructed using a differential-mode inductor PBZ3216E120Z0T (12μH) and an X2 capacitor (0.22μF/275VAC). The saturation current of the differential-mode inductor must be greater than 1.5 times the maximum input current. The X capacitor should be a low-loss CBB film capacitor.

During PCB layout, the differential-mode filter circuit should be compact, with inductor and capacitor leads as short as possible to reduce parasitic parameters. For the DC/DC secondary side, a ferrite bead PBZ1608E600Z0T can be added at the output to suppress high-frequency differential-mode ripple. This filter network can reduce the peak value of differential-mode conducted emissions by 20dBμV, ensuring the concentrator still meets the EN 55032 Class A limit requirements under full load.