Generally, the ESD diode is connected in parallel with the protected IC. The voltage and current is a special non-linear curve. When the loaded voltage across both ends is lower than standard rated voltage, the resistance of component is approaching infinity and almost there is no current flowing through interior. When an abnormal overvoltage occurs and reaches the breakdown voltage, the resistance changes from high to low rapidly and gives the transient current a path. At the same time, it suppresses the overvoltage under the safe level so that it can protect IC or circuit. While the abnormal overvoltage disappears, the components can be returned a high impedance state. Therefore, the operating mode is off-on-off.