How to rectify the conduction emission failure of the PMS (Power Measurement System) switch?

PMS conducted emissions (CE) test failures typically manifest as exceeding limits at certain frequency points between 150kHz and 30MHz. Rectification requires systematic analysis:

First, identify the nature of the exceeding frequency points: If the exceedance is in the low-frequency range (<1MHz), it is usually related to differential-mode interference and grounding impedance; increasing the capacitance of the X capacitor or the inductance of the differential-mode inductor (such as PBZ3216E120Z0T) can help. If the exceedance is in the high-frequency range (>1MHz), it is often related to common-mode interference; strengthening common-mode filtering is necessary, such as increasing the inductance of the common-mode inductor CMZ1211-501T or optimizing the grounding of the Y capacitor.

Second, check the filter circuit layout: whether the filter's input and output lines are separated, whether they are close to the power supply input, and whether the grounding is good (using short and wide grounding wires).

Then, check the internal noise sources: whether the switching frequency of the power supply and its harmonics fall into the exceeding frequency range; fine-tuning the switching frequency can help avoid this.

Additionally, check if the PCB ground plane is intact to provide a low-impedance return path for noise. Finally, consider adding an additional ferrite core to the power lines. Through targeted rectification, the value of the frequency point exceeding the standard can usually be reduced by 10-20dB, meeting the limit requirements.