How should surge protection for industrial servos be designed in a tiered manner?

Surge protection for servo systems must be designed according to the IEC 61000-4-5 standard. Industrial equipment typically requires line-to-line ±2kV and line-to-ground ±4kV. Etymotic's Coordinated Protection Concept:

Level 1 (Coarse Protection): A gas discharge tube (GDT, such as 2R600L-8X6) or varistor (MOV, such as 14D511K) is used at the equipment inlet to absorb most of the energy, clamping the voltage to a lower level (e.g., 1000V).

Level 2 (Fine Protection): A TVS diode (such as SMCJ75CA) or a decoupled varistor is used before the internal circuitry to further clamp the voltage to a safe range (e.g., 75V). The two levels are isolated by decoupling components (inductors, resistors, or fuses) to ensure that the first level activates first.

Design Considerations: Calculate the current-carrying capacity (Iimp, Imax) and energy tolerance of each stage of the device to ensure coordination. Simultaneously, the grounding path of the protection circuit must be low impedance and short. Through hierarchical design, surge voltages of several kilovolts can be limited to the range that the board-level circuit can withstand, thus protecting core components.