High efficiency asymmetrical half-bridge flyback converter using a new voltage-driven synchronous rectifier

This study presents a high efficiency asymmetrical half-bridge flyback converter using a new voltage-driven synchronous rectifier that operates over a universal input voltage range (75-265-V) with a fixed 5-V DC output voltage. Both power semiconductor switches of the proposed converter primary operate asymmetrically under zero voltage switching to achieve high efficiency and low switch voltage stress. Because the proposed converter uses the transformer leakage inductance as its resonant inductance, its structure is simplified. The proposed synchronous rectifier can cover a universal input voltage range and can maintain control in a narrow switching period, features that are essential in converters with universal input voltage. The synchronous rectifier switch of the proposed converter conducts under zero voltage/zero current switching conditions with a discontinuous conduction mode. The operational principle and steady state analysis of the proposed converter are explained, and a design example for a 100-W prototype is discussed in detail. Experimental results for the designed prototype converter with universal input voltage are shown. The author also shows that the efficiency of the proposed converter can be improved significantly.