Achieving high efficiency and high power density is emerging as a goal in many power electronics applications. LLC resonant converter has been proved as an excellent candidate to achieve this goal. To achieve smaller size of passive components, the resonant inductor in the LLC converter is usually integrated into the transformer by utilizing its leakage inductance. However, the leakage inductance of transformer is usually insufficient and thus the LLC converter has to be operated in a limited frequency range (this limits the input voltage range accordingly), otherwise the power efficiency will drop dramatically. Therefore, a larger resonant inductance in the LLC converter is expected to operate in a wider input voltage range. This paper proposes a new method to create a larger resonant inductance by using a magnetic shunt integrated into planar windings. The accurate leakage inductance modelling, calculation and optimal design guideline for LLC planar transformer, including optimal magnetic shunt selection and winding layout, are presented. A 280-380V input and output 48V-100W half bridge LLC resonant converter with 1MHz resonant frequency is built to verify the design methodology. A comparison is made between two converters with the same parameters, one using magnetic shunt integrated transformer and the others using traditional planar transformer and external inductor. Experimental result shows the proposed converter with magnetic shunt is capable to achieve comparable high efficiency and regulation capability with the other under a wide input voltage, which verify the optimal design methodology. Above all, this magnetics integration methodology reduces the whole converter's volume and thus increases the power density. Index Terms-magnetic shunt, LLC resonant converter, planar transformer, high frequency, wide input voltage.

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The asymmetrical half-bridge (AHB) flyback converter is capable to achieve zero voltage switching (ZVS) and has lower voltage stress compared to the active clamp flyback converter (ACF). This topology gives much margin for components selection and transformer turns ratio design. It is well adapted to voltage step-down applications. However, the optimal design for AHB flyback converter taking current dip effect causing by components parasitic capacitances, and each component effect to power loss into consideration has never been explored. This paper gives detailed operation and mathematical analyses of this effect. The optimal design procedure with the consideration of each circuit parameter is presented in this paper. The transformer benefits low power loss from interleaving winding layout. A 56W/inch 3 1MHz 65W prototype with 100V-250V input is built to verify the feasibility of the converter. Experimental results show the peak efficiency 96.5% is achieved with 127V input and the whole system efficiency under the entire input voltage range is above 93%. Index Term-AHB flyback converter, high efficiency, voltage step down applications

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This letter proposes a self-driven gate driver solely composed of passive components for synchronous rectification (SR). It utilizes the energy of the converter itself, automatically considers component tolerances and temperature variations of critical design parameters, and tunes the SRs on-time. Furthermore, no microcontroller, auxiliary power supply or current-sensing/voltage-sensing components is required. A great amount of cost is therefore saved. The proposed gate driver is preferable to be used to any resonant converters operating as DC transformers. This letter presents its practical implementation in an LLC resonant converter. Experiment results illustrate that the body diodes conduction and reverse recovery are eliminated.