Switching losses have been confused with the switching power supply designers, since the power semiconductor devices in the switching process, there is a current, the voltage on the device at the same time, thus inevitably switching losses, if the switching power supply switch and output rectifier diodes can achieve zero-voltage switching or zero-current switching, its efficiency can be improved significantly.
　　Loss switching power supply mainly: loss of passive components and active components loss. Switching losses caused by the switching process will total approximately 5% to 10% of the input power, significantly reduce or eliminate the loss can be increased by 5% to 10% of the most effective way is to soft-switching technology or zero-voltage switching power supply efficiency switching or zero current switching technology. Among the many soft-switching scheme, more practical high-power full-bridge converter, usually zero phase shift control voltage switching, this control method requires the primary side for additional inductance to ensure a continued flow switch tube Under the zero-voltage state conduction, due to the large RMS current flowing through this additional inductance fever (although much smaller than the RC snubber circuit), which in low-voltage power conversion is not adopted. Passive lossless snubber circuit is characterized not destroy conventional PWM control mode, the design / debugging simpler. Nevertheless, passive lossless snubber circuit and quasi-resonant / zero-voltage switching mode, there are some disadvantages, such as can only achieve soft switching off as well as in a flyback converter is not suitable for large load range. Soft switch active clamp is to improve the single tube forward / flyback converter efficiency and effective method, the initial patent restrictions now expired, universally applied.