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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]

Conventional buck power factor correction (PFC) converter has the disadvantage of high harmonic currents, which limits its applications. In this article, a buck type single-switch integrated PFC converter is presented and analyzed. It is composed of buck and flyback PFC converters by using only one active switch, which benefits from simple control. The buck and flyback PFC converters are input-parallel and output-parallel connected. With critical conduction mode constant on time control, the effect of dead zone of buck input current is eliminated by flyback unit. Therefore, the input harmonic currents of the proposed converters can easily meet IEC61000-3-2 Class C limits. With the advantages of buck and flyback PFC converters, the proposed converter can achieve high efficiency and low total harmonic distortion in universal-input applications. Simplified steady-state analysis and design considerations are introduced in this article. Finally, a 96-W prototype with 94.5% peak efficiency is built to verify the 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]

A flicker-free single switch multi-string LED driver with high power factor and current balancing is proposed and analyzed. It combines a pre-stage boost PFC converter and multiple second-stage buck dc–dc converters by a single active switch and multiple dc-link capacitors. With the proposed circuit configuration of multiple dc-link capacitors, the output current of each LED string can be balanced. Therefore, by controlling the output current of one LED string, the output currents of other LED strings can be controlled via current balancing of dc-link capacitors. The effect of the ripple of dc-link voltage on each output can be eliminated by fast voltage mode control loop. Therefore, flicker-free low ripple current for each LED string is achieved. With small voltage ripple across dc-link capacitors, the turn on time of active switch is almost constant in a half line cycle. Therefore, power factor correction can be achieved with inductor current of pre-stage operating in discontinuous conduction mode (DCM). Finally, prototypes of dual-string LED driver with 90–135 Vac input and 175–265 Vac input for 47 W output power are built to verify the studied results. [ABSTRACT FROM AUTHOR]

A novel high-efficiency resonant light emitting diode (LED) backlight driver with passive current balancing and dimming is proposed and analyzed in this paper. The proposed LED driver achieves uniform brightness of each LED string by the charge balance of the resonant capacitor, which benefits from high efficiency. By controlling the output current of one LED string, the output currents of other LED strings can be controlled via current balancing of resonant capacitors, which makes its control simple. The proposed LED driver uses only one active switch, which decreases circuit volume and simplifies the control. Furthermore, a wide load range can be achieved by controlling the turn-on duty ratio of the single power switch of the LED driver with a fixed frequency. Finally, a prototype of a high-dimming-ratio small-size three-string LED driver is provided to verify the studied results. [ABSTRACT FROM PUBLISHER]

A resonant single-stage single-switch four-output LED driver with high power factor and passive current balancing is proposed. By controlling one output current, the other output currents of four-output LED driver can be controlled via passive current balancing, which makes its control simple. When magnetizing inductor current operates in critical conduction mode, unity power factor is achieved. The proposed LED driver uses only one active switch and one magnetic component, thus it benefits from low cost, small volume, and light weight. Moreover, high-efficiency performance is achieved due to single-stage power conversion and soft-switching characteristics. The characteristics of the proposed LED driver are studied in this paper and experimental results of two 110-W four-output isolated LED drivers are provided to verify the studied results. [ABSTRACT FROM AUTHOR]