ESD(electrostatic discharge protection diode) is a component designed and applied to circuit electrostatic protection. When the circuit works normally, it is in the high resistance cut-off state, and the junction capacitance is very small, which will not affect the signal or circuit. When the circuit has abnormal overvoltage and reaches its breakdown voltage, it quickly changes from high resistance state to low resistance state, provides a low impedance conduction path for the instantaneous current, and clamps the abnormal high voltage within a safe level, so as to protect the protected IC or circuit system; When the abnormal over voltage disappears, it returns to the high resistance state and the circuit works normally.