Optimal Design Of DCM Flyback Converter

With the growing emphasize on the worldwide energy-saving and environmental protection, the annual energy consumption of the External Power Supply is now being one the most significant environmental aspect, improvements in the electricity consumption of external power supplies should be achieved. This dissertation mainly focused on the optimal design of the DCM Flyback converter with respect to some critical losses. Based on the detailed loss evaluation, the efficiency optimization based on the secondary synchronous rectification, control method and transformer optimization are presented.Based on the research to the control method and the synchronous rectification, a novel soft switching Flyback converter with synchronous rectification is proposed to achieve a higher efficiency without an additional MOSFET. Detailed steady state analysis and design consideration are presented. And both the analysis and experimental results show that the proposed control scheme could effectively realize ZVS at both low and high input as well as any load line.This dissertation also focuses on the winding loss calculation model, and the reason why the traditional winding loss analytical model is not suitable to the Flyback transformer is presented. An improved winding loss analytical model for the Flyback transformer is proposed by considering the phase shift angle of the two currents and building a new magnetic field in the region between each layer. The proposed winding analytical model is verified with FEA simulation as well as experimental results. It proves that interleaving structure does obviously have less ac winding loss in the Flyback transformer. Meanwhile, a modified core loss model of DCM Flyback is also presented in this dissertation to get a more accurate result.Based on the proposed winding loss analytical model and the core loss model, the transformer optimal design is described to show that a lower loss could be reached by less copper through proper design. All the calculated efficiency improvement has been validated with experimental results, and the results turn out to be satisfying.Other parameters which are critical to the optimal design are shown with experimental results. These parameters have much to do with the efficiency of the whole converter once it is fixed. And some methods to reduce the loss at no load are pointed out and analyzed experimentally to get a lower stand-by loss.