TVS, called transient voltage suppressor, is divided into unidirectional and bidirectional. Unidirectional TVS is mainly used in DC circuits, and bidirectional TVS is used in AC circuits. The TVS application is anti-parallel in the circuit. When the circuit works normally, it is in the cut-off state (high impedance state), which does not affect the normal operation of the circuit. When an abnormal overvoltage occurs in the circuit and reaches its breakdown voltage VB, it quickly changes from a high resistance state to a low resistance state, absorbs and discharges the overcurrent generated by the abnormal overvoltage to the ground, and clamps the abnormal overvoltage at the same time. Within the safe range that the first-stage circuit can withstand, so as to protect the subsequent-stage circuit from being damaged by abnormal overvoltage. When the abnormal overvoltage disappears, the resistance of the TVS returns to the original high resistance state.