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This paper proposes the size reduction methods for two-stage Boost-LLC converter to achieve high power density in 60W AC-DC adapter. The two-stage converter has high component count, and the passive components such as inductor, transformer, and capacitor occupy the most of the area. In order to make the converter have small size, this paper proposes the size reduction methods of passive components: the design of low link voltage, the design of the resonant tank without additional inductor and with high resonant frequency, and the design of C L-C filter replacing output capacitor. A 60W (16.8V 13.65A) prototype adapter is designed and implemented to verify the feasibility of the proposed methods. The converter achieves 14.5W/in 3 power density with the methods.I.

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In general, LLC converters show great promise in applications that require high efficiency, especially under light load conditions. In particular, LLC converters feature wide gain capability with pulse-frequency modulation and zero voltage switching over entire load conditions. However, output voltage increases in light load conditions. In this study, Bode plot and impedance asymptotes analyses were conducted to obtain insights into the regulation characteristics of LLC converters under light load conditions. To improve the regulation characteristic of LLC converters, a new resonant tank with an additional capacitor is proposed. The design guideline for the proposed LLC converter is determined by the Bode plot and impedance asymptotes analyses. Therefore, the proposed LLC converter achieves the light load regulation while maintaining the advantages of typical LLC converters.

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