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Conventional boost power factor correction (PFC) converter is only suitable for two-stage power conversion system due to its high output voltage. Inherent step-up characteristic limits its applications in single-stage low voltage output. In this article, a boost-type single-stage step-down resonant PFC converter, which combines a boost PFC converter and a resonant switched capacitor network by using one active switch, is proposed and analyzed. Similar to conventional boost PFC converter, the proposed converter can achieve unity power factor and low input current ripple in universal-input applications. Moreover, the proposed converter can achieve step-down voltage conversion. Furthermore, high-efficiency is realized due to single-stage power conversion. The proposed converter is studied in terms of operation principle, voltage gain, power factor analysis, and key circuit parameters design. Finally, a 70-W prototype with 96.05% peak efficiency is built to verify the theoretical analysis results. [ABSTRACT FROM AUTHOR]

An integrated buck–boost–buck-type single-switch multistring resonant light-emitting diode (LED) driver is proposed and analyzed. It combines buck–boost and buck converters to achieve passive current balancing and power factor correction. With this circuit configuration, the proposed LED driver employs only one low-side connection active switch, resulting in a very simple control requirement involving one closed-loop controller for regulating one output current. Other output currents can be balanced automatically by resonant capacitor and storage capacitors, making the control strategy economical. In addition, high efficiency is achieved due to single-stage power conversion. Taking three-string LED driver as an example, the proposed buck–boost–buck-type single-switch LED driver is studied in terms of operating principle, current balancing principle, power factor (PF) analysis, voltage gain, and key circuit parameter design. Finally, an 84-W high-PF three-string LED driver prototype with 94.3% peak efficiency is built to verify the analytical results. [ABSTRACT FROM AUTHOR]