he high frequency transformer is the most important part of the switch power supply. There are many topologies in switching power supply. For example, half bridge power conversion circuit, when the two switch transistor turns conduction to generate 100kHz high frequency pulse wave, and then through the high frequency transformer transformer, AC output, high frequency transformer turns ratio of each coil is determines how much output voltage. Half bridge transformer circuit typical of the most prominent is the three high frequency transformer: main transformer, drive transformer and auxiliary transformer (standby transformer transformer), each have their own standards in the state.