How to filter out the noise during the opening and closing operation of a power FTU?

The opening and closing operation noise has a wide frequency spectrum and high energy, requiring multi-band filtering. A three-stage filtering method is adopted:

The first stage uses a PBZ2012E600Z0T ferrite bead (600Ω@100MHz) in series in the operating circuit to filter out high-frequency noise.

The second stage uses an SMBJ24CA TVS diode in parallel at the power supply port to absorb transient overvoltage.

The third stage uses RC filtering (1kΩ+100nF) on the signal line with a time constant of 0.1ms. Simultaneously, a 1mm thick metal shield is added to the operating mechanism.

On the PCB, the distance between the operating signal line and the sensitive line is greater than 20mm. With this filtering scheme, the operating noise is attenuated by more than 40dB in the 10kHz-100MHz frequency band, and the false alarm rate is less than 0.001%, meeting the IEC 61000-4-5 surge test requirements.