Abstract
In the field of switching power supply, LLC resonant topology has drawn much attention for the advantages of easily realizing zero-voltage-switching (ZVS) and zero-current-switching (ZCS) from no load to full load. However, in the condition of heavy load current, Secondary rectifier power loss accounts for the majority of total power losses, which is an obstacle to efficiency improvement. To solve this problem, a driving scheme for an adaptive synchronous rectifier (SR) with a low-cost digital microcontroller (MCU) is proposed, aiming to reduce the SR body diodes conduction. With the proposed driving scheme, the drain-source voltage of SR is sensed by a SR gate driver integrated circuit (IC). According to the conducting information, the SR on-time can be tuned every nth switching period (n=2, 3, 4…) by MCU to the optimal condition. Moreover, power losses of the main components would be analyzed and associated loss models would be derived in detail. In the end, a 300-kHz 300-W 380V/12V prototype is built to confirm the proposed method, which achieves above 97% peak efficiency.
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