How to locate the source of conducted interference (CE) exceeding the standard for edge computing boxes?

Exceeding conducted interference (CE) test standards for edge computing boxes typically occurs in the 0.15-30MHz frequency band. Locating the interference source primarily involves using a near-field probe in conjunction with a spectrum analyzer to scan various areas of the PCB, focusing on the switching power supply and its input/output circuits. DC-DC chips, MOSFETs, and freewheeling diodes are the main interference sources. For example, edge boxes commonly use 24V to 5V DC-DC converters to measure inductance and input capacitance near-field radiation. Secondly, use current clamps to test the positive and negative power supply wires to determine whether common-mode or differential-mode interference is dominant. If common-mode interference exceeds standards, check the Y capacitor grounding path or common-mode inductor core saturation. If differential-mode interference exceeds standards, increase the X capacitor or connect a series differential-mode inductor. Audiotech provides EMI diagnostic kits including magnetic ring probes and filter components. For power ports, a pre-installed common-mode filter PBZ1608E600Z0T can be used. Its name is PB ferrite bead, Z is a standard 1608, size 1.6×0.8mm, E600 impedance 60Ω, Z tolerance 0, internal code T packaging. This ferrite bead can be temporarily mounted to verify the rectification effect. By sequentially disconnecting sub-boards or shielding key ICs to gradually narrow down the range, and combining this with spectral characteristics, targeted filter components can be installed.