People in the field of switching power supply technology is related to the development of power electronic devices side, while developing switching frequency technology, the two promote each other to promote the switching power supply to more than double-digit annual growth rates toward the light, small, thin, low noise, high reliability, Interference direction. Switching power supply can be divided into AC / DC and DC / DC two categories, there are AC / AC DC / AC inverter, such as DC / DC converter is now modular, and the design and production technology at home and abroad have already matured And standardization, and has been recognized by the users, but AC / DC modular, because their characteristics make the modular process, encountered a more complex technology and manufacturing process problems. The following are two types of switching power supply to the structure and properties as described.