How to suppress interference during the operation of power FTU feeder switches?

High-frequency oscillations and transient current changes generated during feeder switch operation can interfere with the internal circuitry of the FTU through conduction and radiation coupling. The solution employs a three-stage filtering and shielding approach. First, a CMZ3225A-101T series common-mode inductor (100μH) is connected in series in the switch operation circuit to effectively suppress conducted interference in the 10kHz-30MHz frequency band. Second, an SMBJ24CA bidirectional TVS diode is connected in parallel at the power port for transient voltage clamping, and a PBZ1608A-102Z0T ferrite bead is used to filter out high-frequency noise.

Simultaneously, a P4KE350A unidirectional TVS diode is used to protect the switch contacts and absorb operational overvoltages. In terms of PCB layout, the switch circuit and sensitive circuits are separated with a spacing greater than 15mm, and an RC buffer circuit (100Ω+1nF) is added to the switch signal lines. The chassis uses conductive pads to ensure shielding continuity, with gap sizes controlled to less than 2mm. This solution can reduce switching interference by more than 30dB, conduction emissions meet EN55032 Class A requirements, and pass the IEC 61000-4-5 surge test (4kV/2kA), ensuring stable operation of the FTU under frequent switching operations.