Research On High Efficiency Synchronous Rectifier Flyback Converter

With the continuous improvement of science & technology and people’s living standards,the demand for resources is increasing,and the energy consumption is also growing.Therefore,how to improve the utilization of energy has become a major problem in contemporary society.As a typical topology in switching power supplies,flyback converters are widely used in low-voltage,high-current,low-power applications,especially in power adapters and mobile charging fields due to their simple structure,low cost and small size.However,the traditional flyback converter has low efficiency about 85%,which can’t satisfy high efficiency requirement.Therefore,studying the new control modes for the flyback converter to improve its efficiency is of great value.Firstly,the synchronous rectification(SR)flyback converters with the traditional CCM/DCM,DCM and BCM modes are analyzed in detail,and the operation principles of each mode are presented.After that,optimized parameters of the converter based on each mode have been designed out.Three 12V/2.5A output experimental prototypes with different control mode are developed,and the experimental waveforms and test data of the prototypes are analyzed.Secondly,to resolve the cross conduction problem between the primary switch and secondary SR in the CCM SR flyback converter,a new type of flyback circuit structure with transformer winding short circuit and a new double pulse PWM control strategy are proposed.These two solutions can effectively eliminate the shoot-throgh current in CCM SR flyback converter so that the efficiency of the converter can be improved obviously.Moreover,the overall efficiency can be optimized in the whole input voltage range.Detailed operation principle analysis and optimization design of the proposed two schemes are presented.After that,two CCM/DCM experimental prototypes are developed.The feasibility of the two schemes are verified by the experimental results.Finally,a CCM/BCM hybrid mode control strategy based on the proposed dual-pulse PWM control has been applied to the SR flyback converter.This control mode allows the converter to operate in CCM mode under low voltage and BCM mode under high voltage.The operation principle and circuit parameters design are introduced in detail,and an experimental prototype is developed.The prototype waveforms and data are analyzed.At the end of the paper,the experimental results of six experimental prototypes are compared,and the advantages and disadvantages of each model are analyzed.The comparison results show that the CCM/BCM hybrid mode control has the best average full load efficiency.