Shih-Jen Cheng

A High-Efficiency Dimmable LED Driver for Low-Power Lighting Applications

This paper presents a dimmable light-emitting diode (LED) driver with adaptive feedback control for low-power lighting applications. An improved pulsewidth modulation dimming technique is studied for regulating the LED current and brightness. Under universal input voltage operation, high efficiency and high power factor can be achieved by a coupled inductor single-ended primary inductance converter power factor correction (PFC) converter with a simple commercial transition-mode PFC controller. The operation principles and design considerations of the studied LED driver are analyzed and discussed. A laboratory prototype is also designed and tested to verify the feasibility.

LED Backlight Driving System for Large-Scale LCD Panels

This paper presents an LED backlight driving system for large-scale liquid crystal display panels. High efficiency, high power factor, circuit simplicity, and low cost can be achieved by using a single-stage charge-pump asymmetrical half-bridge converter. To regulate the LED current and brightness for the LED backlight system, some current sharing methods are presented and compared. The requirements for the current sharing and luminance balance among paralleled LED arrays can be satisfied while current ripple is eliminated significantly. Because of the addition of bypass diodes, an alternative current path can be offered when a single LED fails. The LED array will not be extinguished. Reliability of the LED backlight system can thus be improved effectively. A laboratory prototype has been built and tested. The simulation and experimental results are shown to verify the feasibility of the proposed method.

A Single-Stage Soft-Switching Flyback Converter for Power-Factor-Correction Applications

This letter presents a single-stage soft-switching Flyback converter for power-factor-correction (PFC) applications. High power factor and high conversion efficiency can be achieved by a simple single-stage circuit with soft-switching features. The operation principles and design criteria for the studied PFC converter are analyzed and discussed. A laboratory prototype is also built and tested. Finally, the experimental waveforms for this prototype circuit are shown to verify the feasibility of the proposed scheme.

A module-integrated isolated solar microinverter

This paper presents a module-integrated isolated solar microinverter with pseudo-dc link. The studied grid-tied microinverters can individually extract the maximum solar power from each photovoltaic panel and transfer to the ac utility system. High conversion efficiency and high maximum power point tracking accuracy can be achieved with the studied pseudo-dc link topology. The operation principles and design considerations of the studied solar inverter are analyzed and discussed. A laboratory prototype is implemented and tested to verify its feasibility.

High-Efficiency Digital-Controlled Interleaved Power Converter for High-Power PEM Fuel-Cell Applications

A high-efficiency digital-controlled interleaved dc-dc converter is designed and implemented to provide a regulated high voltage output for high-power proton-exchange-membrane fuel-cell applications. Ripple cancellation on input current and output voltage can be achieved by the studied interleaved dc-dc power conversion technique to reduce hysteresis energy losses inside the fuel-cell stacks and meet battery charging considerations on the high-voltage dc bus. An active-clamped circuit is also used to reduce the voltage spike on the power switches for raising the system reliability. The operation principles and the design considerations of the studied power converter are analyzed and discussed in detail. Finally, a 10-kW laboratory prototype is built and tested. The experimental results are shown to verify the feasibility of the proposed scheme.

Design and Implementation of a Single-Stage High-Frequency HID Lamp Electronic Ballast

We present a single-stage electronic ballast with a high power factor feature for driving high-intensity discharge (HID) lamps. A new frequency-modulation technique is proposed to eliminate the acoustic resonance problem in HID lamps under high-frequency operation. The proposed method has the merits of simple circuit and low cost; thus, it is suitable for use in commercial applications. The conducted emission caused by the high-frequency electronic ballast can be also effectively reduced. The operating principles and design considerations of the proposed electronic ballast are analyzed and discussed in detail. A 35-W laboratory prototype is designed and implemented. Simulation and experimental waveforms are given to verify the feasibility of the proposed method. The results are satisfactory.

Single-Stage Voltage Source Charge-Pump Electronic Ballast With Switched-Capacitor Dimmer for Multiple Fluorescent Lamps

This paper presents a single-stage electronic ballast for driving multiple fluorescent lamps in which a dimming control scheme is proposed to regulate the lamp current. A laboratory prototype is built and tested, and it is found that the unity power factor can remain under individual lamp brightness control. The experimental results are therefore shown to verify the feasibility of the proposed method.

Design and Implementation of a Photovoltaic High-Intensity-Discharge Street Lighting System

This paper presents a photovoltaic (PV) high-intensity-discharge (HID) street lighting system. A single-ended primary inductance converter (SEPIC) is studied for maximum power point tracking (MPPT) and battery charging. High conversion efficiency and high MPPT accuracy can be achieved under different atmospheric conditions. A pulse-current-charging scheme with an adaptive rest-period is also applied to avoid battery overcharging. An electronic ballast circuit is also designed to release the solar energy stored in battery for powering HID lamps. The studied PV HID street lighting system is connected to the ac-line utility with a SEPIC power factor correction converter. High input power factor can be achieved when energy is drawn from the ac-line utility to drive the HID lamp and to prevent the battery from over-discharging. The proposed PV HID street lighting system has the advantages of high power density, simple circuit, and long lifetime. The operating principle and design considerations were analyzed and discussed in detail. A laboratory prototype was implemented and tested. The experimental results were shown to verify the feasibility of the proposed scheme.

A Single-Stage SEPIC PFC Converter for Multiple Lighting LED Lamps

This paper presents a SEPIC PFC converter for driving multiple lighting LED lamps. With the aid of this converter, high power factor and high efficiency can be achieved by a simple single-stage circuit with low device stress features. A burst-mode dimming method is used to regulate the current and brightness of multiple LED lamps. A laboratory prototype is also built and tested. With the prototype, high power factor can remain under universal input voltage operation and individual lamp brightness control.

Analysis and Design of a Push–Pull Quasi-Resonant Boost Power Factor Corrector

This paper proposes a novel power-factor corrector (PFC), which is mainly composed of two-phase transition-mode (TM) boost-type power-factor correctors (PFCs) and a coupled inductor. By integrating two boost inductors into one magnetic core, not only the circuit volume is reduced, but also the operating frequency of the core is double of the switching frequency. Comparing with single-phase TM boost PFC, both the input and output current ripples of the proposed PFC can be reduced if the equivalent inductance of the coupled inductor equals the inductance of single-phase TM boost PFC. Therefore, both the power-factor value and the power density are increased. The proposed topology is capable of sharing the input current and output current equally. A cut-in-half duty cycle can reduce the conduction losses of the switches and both the turns and diameters of the inductor windings. The advantages of a TM boost PFC, such as quasi-resonant (QR) valley switching on the switch and zero-current switching (ZCS) of the output diode, are maintained to improve the overall conversion efficiency. Detailed analysis and design procedures of the proposed topology are given. Simulations and experiments are conducted on a prototype with a universal line voltage, a 380-V output dc voltage and a 200-W output power to verify its feasibility.