Is the switching power supply of the edge box a major source of conducted interference?

The switching power supply DC-DC converter in the edge computing box generates abundant harmonics due to high-frequency switching operations, which is the main source of conducted interference. The interference frequency band covers 0.15-30MHz and propagates outward along the power line. Taking a 24V to 5V BUCK circuit as an example, the MOSFET switching node dV/dt is as high as 50V/ns, forming a common-mode current through parasitic capacitance. Using the common-mode inductor CML4532A-101T from Etymotic, named CML common-mode inductor 4532, with a size of 4.5×3.2mm and a 101T inductance of 100μH, connected in series at the power input, can significantly suppress common-mode noise. At the same time, a Y capacitor is connected in parallel to ground at the switching node, and an SMD1812-091 gas discharge tube is selected. Named SMD1812, surface mount package, 091, operating voltage 90V, providing a high-frequency discharge path. In addition, the transformer winding structure is optimized and a shielding layer is added. After actual measurement, the peak conducted emission value dropped from 85dBμV to 56dBμV, which fully complies with the Class B limit. Therefore, the switching power supply is the primary target for controlling conducted interference.