Universal AC Input High-Density Power Adapter Design With a Clamped Series-Resonant Converter

Power density and size are important features in compact ac-dc power adapters today. The push for power density, however, requires high conversion efficiency to reduce thermal stresses and smaller magnetics to fit into the required volume. Flyback converters have traditionally been adopted in compact power adapters due to their simplicity, acceptable performance, and low cost. In this paper, we present the design and fabrication of a high-density laptop adapter with a single-stage clamped series-resonant converter as a possible alternative for power adapters in portable electronics. The target is to achieve power densities and scalability in power from 45 to 100 W. The converter is frequency controlled and all switches exhibit zero-current switching. In this paper, we show that by utilizing the magnetizing inductance, the converter can be tuned for zero-voltage switching, and by adding a switched capacitor circuit to extend the input voltage range, we can realize a very compact design that is suitable for power adapters with or without power factor correction. Low transformer stresses compared with Flyback-type designs enable high densities, even with a resonant magnetic. Prototype test results with a 45-W laptop adapter are presented. Results are presented from a prototype design demonstrating high efficiency with a power converter density of 8.5 W/in
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and means to further increasing the conversion efficiency with synchronous rectification are discussed.