How to rectify EPS conducted emission defects?

When EPS conducted emission (CE) tests fail, the following system steps can be followed for rectification:

1. Data Analysis: Analyze the test spectrum to determine whether the excessive frequency points are concentrated in 150kHz-1MHz (switching frequency and its harmonics) or 1MHz-30MHz (high-frequency ringing, etc.).

2. Differentiate Noise Modes: Determine the dominant differential mode frequency band by temporarily paralleling/removing the X capacitor; determine the dominant common mode frequency band by temporarily adding or removing the Y capacitor or common mode inductor.

3. Targeted Filtering Enhancement: If the common mode exceeds the limit, check and strengthen the common mode inductor, for example: replace it with a higher impedance CM series inductor, or add a Y capacitor (pay attention to safety leakage current). If the differential mode exceeds the limit, check and increase the size of the X capacitor, or add a differential mode inductor.

4. Check Filter Grounding: Ensure that the grounding path of the filter, especially the Y capacitor, is extremely short and connected to a low-noise reference point (chassis).

5. Source Inspection: Check if there is severe ringing in the switching waveform, optimize the drive, or add buffer absorption.

6. Layout Inspection: Check whether the installation position of the input and output filters is close to the port and whether the wiring before and after them is isolated.