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In designing a LLC resonant converter, the ratio of magnetizing inductance (L M ) to resonant inductance (L R ), the inductor ratio (K) is usually considered. In high power density adapter, both adapter size and efficiency are important factors. Considering the size of adapter, high K design can be more attractive. But, wide frequency variation of high K design results in design difficulty of magnetic elements and decrease in efficiency. To solve these drawbacks, an adaptive link voltage variation (ALVV) control is proposed. With the proposed control method, the LLC resonant converter can be operated at the resonant frequency despite the output voltage variation. The control strategy and schematics are presented, and verified experimentally.I.

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This paper proposes a two-stage configuration of AC/DC converter employing load-adaptive link-voltageadjusting technique with load power estimator. The proposed technique helps to maintain high efficiency over all the load condition despite the output voltage varies according to the load power. In addition, since the proposed circuit uses low-loss load power estimator to adjust the output voltage, it can achieve high power density more than 14W/in 3 . Experimental results with 80W notebook computer adaptor are provided to verify the validity of the proposed converter.Index Terms-AC/DC converter, two-stage configuration, output voltage variation.