The functions of each pin of VIPER12A are as follows: pin 5678 is connected to the leakage set of the internal FET, pin 12 is the source pole of the internal FET, pin 3 is the feedback input, and pin 4 is the VDD. Generally, 5678 pin external AC220 voltage after bridge pile rectification (about 300V),12 pin ground,4 pin output 18V, and 5V also has 18V by 7805,3 pin voltage feedback and external 18V regulator to form a voltage regulator circuit,