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To obtain a high step-up gain with high efficiency in nonisolated applications, a high step-up technique based on isolated-type converters is introduced in this paper. By stacking the secondary side of an isolated converter in addition to its primary side, a high step-up conversion ratio and a distributed voltage stress can be achieved. Moreover, a careful choice of an isolated converter can provide zero-voltage switching, continuous input current, and reduced reverse recovery on diodes. Based on a conventional voltage-doubler-rectifier boost-integrated half-bridge converter, the derived converter satisfies all these features, which make it suitable for high step-up applications. The operational principle and characteristics of the proposed converter are presented, and verified experimentally with a 135-W, 24-V input, 250-V output prototype converter for a LED driver.Index Terms-Boost converter, boost-integrated half bridge (BHB) converter, high step-up converter, isolated converter, zerovoltage switching (ZVS).

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To narrow down the switching-frequency-variation range of an LLC resonant converter, asymmetric pulsewidth modulation (APWM) of the hold-up time is proposed. During the hold-up time, the modulation method of an LLC resonant converter is changed from frequency modulation (FM) to APWM. Since the LLC resonant converter achieves a higher gain with APWM than it does with FM at the same switching frequency, the switching-frequency-variation range is reduced. Therefore, an optimal design of the magnetic components is possible, resulting in a high efficiency under normal operation and a high power density. The proposed control scheme is applied to an 85-W LLC resonant converter.