Surge protectors are essential components for safeguarding electronic devices from surge damage caused by induced lightning. As electronic products become increasingly integrated into daily life, surge protectors are becoming more familiar to the public. In reality, lightning protection for electronic systems is still a relatively new field, with many争议存在 regarding the selection and application of surge protectors. This article explains issues such as the response time of surge protectors and the operation sequence of multi-stage surge protectors.

Section 2: Operation Sequence of Multi-stage Surge Protectors

When a single-stage surge protector fails to suppress the侵入overvoltage to below the specified protection level, a surge protector with secondary, tertiary, or more stages of nonlinear suppression elements should be used.

The non-linear components Rv2 and Rv2 are both voltage-sensitive resistors. In practical applications, RV1 can also act as a gas discharge tube, and Rv2 can be a voltage regulator or a surge suppression diode (TVS). The isolation element between the two poles, Zs, can be an inductor Ls or a resistor Rs. If the conductive voltages of RV1 and RV2 are Un1 and Un2 respectively, the selected components are always Un2 > Un1.

Someone believes that when the invasion surge wave is applied to the X-E terminal, it's always the lead copper of stage RV1 that is affected first, followed by the stage. In reality, it's possible for either stage or the lead to be affected first, depending on the following factors:

(1) The waveform of an invasion shock wave, primarily the speed of sound in the current front (di/dt).

(2) The relative magnitude of the conduction voltages Un1 and Un2 for the non-linear components Rv1 and RV2.

(3) The nature of the isolation impedance Zs is whether it is resistive or inductive, as well as its magnitude.

When Zs is the resistance Rs, it is usually the stage that conducts first. After the stage conducts, it only conducts when the surge current I reaches iRs + Un2 ≥ Un1. After the stage conducts, since the equivalent impedance of the stage at high currents is much smaller than the sum of Rs and the equivalent impedance of the stage. Therefore, most of the surge current is dissipated through the stage, and the current dissipated through the stage is much smaller. If the stage is a gas discharge tube, the residual voltage after conduction is usually lower than the conduction voltage Un2 of the stage, so the stage is cut off, and all the remaining surge current is dissipated through the stage gas discharge tube.

If Zs is the inductance Ls and the initial rate of rise of the侵入 current is quite fast, and the condition Ls(di/dt) + Un2 > Un1 is met, the stage will conduct first. If the limiting voltage during stage conduction is Uc1(1), then as the rate of rise of the侵入 current (di/dt) decreases, the stage will conduct only when the condition UC1(1) ≥ Ls(di/dt) + Un2 is satisfied. After the stage conducts, the voltage at the output terminal Y will be suppressed to a lower level.