Yu-Kang Lo

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.

Active-Clamping ZVS Flyback Converter Employing Two Transformers

This paper presents a two-transformer active-clamping zero-voltage-switching (ZVS) flyback converter, which is mainly composed of two active-clamping flyback converters. By utilizing two separate transformers, the proposed converter allows a low-profile design to be readily implemented while retaining the merits of a conventional single-transformer topology. The presented two-transformer active-clamping ZVS flyback converter can approximately share the total load current between two secondaries. Therefore, the transformer copper loss and the rectifier diode conduction loss can be decreased. Detailed analysis and design of this new two-transformer active-clamping ZVS flyback converter are described. Experimental results are recorded for a prototype converter with an ac input voltage ranging from 85 to 135 V, an output voltage of 24 V and an output current of 8 A, operating at a switching frequency of 180 kHz.

Design and Implementation of RGB LED Drivers for LCD Backlight Modules

In this paper, a backlight module driver driving high-power red, green, and blue light-emitting diodes (RGB LEDs) for a 19-in liquid crystal display is proposed. The DC-DC series resonant converters (SRCs) with zero-voltage switching and constant-output-current control are implemented to drive the RGB LED arrays. Phase-shifted pulsewidth modulation dimming control is adopted to effectively narrow the load variations and improve the output voltage regulations of the SRCs. A DSP-based hysteresis control algorithm is performed to track the white-color point and the specified backlight luminance. Analysis and design considerations of the proposed drivers are presented in detail. Experimental results agree well with the theoretical predictions and confirm the validity of the proposed approach.

A High-Efficiency AC-to-DC Adaptor With a Low Standby Power Consumption

A two-stage burst mode control scheme for an AC-to-DC adaptor is proposed in this paper. An upper limit for the output voltage is set to turn off both AC/DC and DC/DC controllers at no load. The burst-mode operations of the DC/DC and the AC/DC converters are in turn enabled when reaching the lower limit of the output voltage. Load analysis at standby mode is performed. A 50-mW no-load power loss is observed on an 80 W/12 V prototype adaptor.

Grid-Connected Photovoltaic System With Power Factor Correction

A combined grid-connection/power-factor-correction technique for a photovoltaic (PV) system is proposed in this letter. A maximum power point tracking dc/dc converter served as a charger for the battery bank. A bidirectional inverter is applied as a generator/discharger during daytime, supplying power to the load. The inverter can also be used as a charger to maintain the minimum required voltage level of the batteries when the PV power is insufficient. Experiments on a 1-kW PV system show satisfactory results of the power management and the unity power factor at the utility side.

Phase-Shifted Full-Bridge Series-Resonant DC-DC Converters for Wide Load Variations

This paper presents the design of a phase-shifted full-bridge series resonant converter (PS-FB SRC). The proposed FB SRC features a novel two-mode operation. It is operated in series resonant mode at normal loads. The switching frequency is varied to regulate the output voltage. The fixed-frequency phase-shifted pulse width modulation, on the other hand, is used to adjust the effective duty cycle and regulate the output voltage at light loads. The proposed converter exhibits high conversion efficiency for wide-range load conditions. The relationships among the voltage gain, the switching frequency, and the effective duty cycle are discussed and analyzed. Finally, a 48-V/42-A prototype is implemented. Experiments are conducted to verify the theoretical analysis.

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.

Analysis and Design of an Interleaved Active-Clamping Forward Converter

This paper presents a new interleaved active- clamping zero-voltage-switching (ZVS) forward converter, which is mainly composed of two active-clamping forward converters. Only two switches are required, and each one is the auxiliary switch for the other. The circuit complexity and cost are thus reduced. The leakage inductance of the transformer or an additional resonant inductance is employed to achieve ZVS during the dead times. The duty cycles are not limited to be equal and within 50%. The complementary switchings and the resulted interleaved output inductor currents diminish the current ripple in output capacitors. Accordingly, the smaller output chokes and capacitors lower the converter volume and increase the power density. Detailed analysis and design of this new interleaved active-clamping forward converter are described. Experimental results are recorded for a prototype converter with an ac input voltage of 85-135 Vrms, an output voltage of 12 V, and an output current of 16 A, which operates at a switching frequency of 150 kHz.

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.

Analysis and elimination of voltage imbalance between the split capacitors in half-bridge boost rectifiers

The voltage imbalance between the split capacitors in a halfbridge boost rectifier is reviewed in this letter. It can be proven that the optimal compensation strategy is to add only a DC component in the source current. The adverse effects of the imbalance elimination control loop to the input power factor are studied. The analytical results are verified through experiments.