Development of Active-Clamp Flyback Converter for Improving Light-Load Efficiency

Conventional active-clamp flyback converters suffer increased conduction losses due to the extended conduction time of the auxiliary switch during light loads. To tackle this problem and improve light-load efficiency, this paper proposes a novel control strategy. This strategy is designed to limit the generation of excessive conduction losses by the auxiliary switch during light loads. The proposed control strategy also employs the quasi-resonant valley switching technique within a single switching cycle to activate the auxiliary switch. This enables the main switch to achieve zero-voltage switching characteristics during its operation. Moreover, once the converter reaches medium loads, the auxiliary and main switches operate in a complementary manner with a fixed frequency. This operation allows both switches to achieve zero-voltage switching, leading to a significant reduction in switching losses. The operating principle and control strategy of the 65W active-clamp flyback converter with the novel control approach have been thoroughly analyzed and discussed. Experimental results have confirmed the effectiveness of this strategy, validating its ability to improve the overall efficiency of the converter under various load conditions.