Analysis and design of a dual-mode flyback converter

This letter presents a dual-mode control scheme to improve the efficiency of a flyback converter in a wide load range. The proposed flyback converter features a novel dual-mode operation. The valley-switching technique is adopted to reduce the switching loss at light load. On the other hand, the fixed off-time (FOT) control with continuous conduction mode (CCM) operations decrease the conduction losses at heavy load. The principles and design procedures of the proposed dual-mode controller are discussed and analyzed. Finally, a 140-W dual-mode flyback converter with an output voltage of 19 V is implemented. Experimental results agree with the theoretical analysis.