How should surge protection for power FTU feeders be designed in a tiered manner?

The feeder surge protection is designed with a tiered approach, discharging surges in stages based on energy levels.

The first stage (inlet): uses a 2R600L-8×6 gas discharge tube (600V/5kA) to dissipate high energy.

The second stage (equipment inlet): uses a 14D511K varistor (510V/4kA) paired with a CMZ7060A-701T common-mode inductor.

The third stage (board level): uses an SMBJ24CA TVS diode (24V/600W).

The fourth stage (chip level): uses an ESD5V0D8B.

Inter-stage coordination: decoupling is achieved through inductors or resistors to ensure the preceding stage activates first.

Through this tiered design, the system can withstand an 8kA lightning strike with a 10/350μs waveform, meeting the IEC 61000-4-5 Level 4 test requirements.