A Two-Stage Buck-Boost Integrated LLC Converter With Extended ZVS Range and Reduced Conduction Loss for High-Frequency and High-Efficiency Applications

Two-stage cascade architecture is widely used in the modular power supply applications. In order to reduce the additional component number caused by the cascading structure, the power switch integration technique is proposed in numerous literature studies. However, the power switch integration leads to both the efficiency degradation and the abnormal gain of the stage employed. In this article, the four-switch noninverting buck-boost converter is merged with the LLC resonant converter. The proposed integration method has no awful influence on the efficiency and the gain of the LLC stage. Meanwhile, the soft switch capability of the integrated bridge can be enhanced due to the accumulation of the two currents of the buck-boost stage and the LLC stage during dead time. Moreover, the current of the two-stage will commutate to cancel out with each other during the conduction period, reducing the conduction loss and improving the overall efficiency. The benefits of the integrated bridge make the proposed converter appropriate for the high-frequency and high-efficiency application. Finally, a 720-W 1-MHz prototype is built to prove the performance of the proposed converter. The prototype achieves a peak efficiency of 96.4% and the input voltage range of 250-420 V.