| The trend of reducing size, weight of portable equipments and more requirements on system efficiency, harmonic current, EMC put new challenge to the design of power supply.Flyback converters are widely adopted for low power applications due to its simplicity and low cost. Aiming at improving full load and light load effciency of low power Flyback converter, this thesis focuses on the application of assymmetrical active-clamp circuit.Previous design guidelines and advantages, disadvantages for active-clamp circuit in Flyback converter are reviewed. Based on the obtained results, a novel assymmetrical controlled active clamp circuit for Flyback converter is developed. With the proposed control method, the energy in the leakage inductance can be fully recycled and the soft switching for is achieved for the main switch. Further more, this method can be adopted in variable-frequency control to greatly improve efficiency at light load condition. The detailed operation principle and design considerations of key parameters are presented. The simulation and experimental results valadate the advantages mentioned above.This thesis also investigates the feasibility of high frequency Flyback converter. Generally, the switching frequency is limited by switching loss and leakage energy caused by Flyback transformer. The proposed control method solve the problems, therefore, it allows a reliable high swtching frequency operation without a significant increase of system losses. Experimental results based on a 64W/400kHz prototype are provided to demonstrate the converter performance.
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