Planar Wireless Charging Technology for Portable Electronic Products and Qi

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Past, Present and Future Trends of Non-Radiative Wireless Power Transfer

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Dynamic photoelectrothermal theory for light-emitting diode systems

This paper presents a dynamic photoelectrothermal theory for light-emitting diode (LED) systems. In addition to photometric, electrical, and thermal aspects, this theory incorporates the time domain into the generalized equations. A dynamic model for a general LED system is developed for system analysis. This theory highlights the fact that the luminous output of an LED system will decrease with time from the initial operation to the steady state due to the rising temperature of the heat sink and the LED devices. The essential thermal time constants involved in the LED systems are explained. The time factor is critical in understanding how much the luminous output will decrease with time and is essential to the optimal designs of the LED systems that are operated continuously (e.g., general lighting) or momentarily (e.g., traffic lights). Experiments on several LED systems at different time frames have been conducted, and the practical measurements confirm the validity of this theory. © 2011 IEEE.published_or_final_versio

Morphing Switched-Capacitor Converters with Variable Conversion Ratio

High-voltage-gain and wide-input-range dc-dc converters are widely used in various electronics and industrial products such as portable devices, telecommunication, automotive, and aerospace systems. The two-stage converter is a widely adopted architecture for such applications, and it is proven to have a higher efficiency as compared with that of the single-stage converter. This paper presents a modular-cell-based morphing switched-capacitor (SC) converter for application as a front-end converter of the two-stage converter. The conversion ratio of this converter is flexible and variable and can be freely extended by increasing more SC modules. The varying conversion ratio is achieved through the morphing of the converter's structure corresponding to the amplitude of the input voltage. This converter is light and compact, and is highly efficient over a very wide range of input voltage and load conditions. Experimental work on a 25-W, 6-30-V input, 3.5-8.5-V output prototype, is performed. For a single SC module, the efficiency over the entire input voltage range is higher than 98%. Applied into the two-stage converter, the overall efficiency achievable over the entire operating range is 80% including the driver's loss

Reduction of Energy Storage Requirements in Future Smart Grid using Electric Springs

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Dynamic Prediction of Correlated Color Temperature and Color Rendering Index of Phosphor-Coated White Light-Emitting Diodes

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Integration of an Active Filter and a Single-Phase AC/DC Converter with Reduced Capacitance Requirement and Component Count

Existing methods of incorporating an active filter into an AC/DC converter for eliminating electrolytic capacitors usually require extra power switches. This inevitably leads to an increased system cost and degraded energy efficiency. In this paper, a concept of active-filter integration for single-phase AC/DC converters is reported. The resultant converters can provide simultaneous functions of power factor correction, DC voltage regulation, and active power decoupling for mitigating the low-frequency DC voltage ripple, without an electrolytic capacitor and extra power switch. To complement the operation, two closed-loop voltage-ripple-based reference generation methods are developed for controlling the energy storage components to achieve active power decoupling. Both simulation and experiment have confirmed the eligibility of the proposed concept and control methods in a 210-W rectification system comprising an H-bridge converter with a half-bridge active filter. Interestingly, the end converters (Type I and Type II) can be readily available using a conventional H-bridge converter with minor hardware modification. A stable DC output with merely 1.1% ripple is realized with two 50-μF film capacitors. For the same ripple performance, a 900-μF capacitor is required in conventional converters without an active filter. Moreover, it is found out that the active-filter integration concept might even improve the efficiency performance of the end converters as compared with the original AC/DC converter without integration

Elimination of an Electrolytic Capacitor in AC/DC Light-Emitting Diode (LED) Driver With High Input Power Factor and Constant Output Current

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Self-Configurable Current-Mirror Circuit With Short-Circuit and Open-Circuit Fault Tolerance for Balancing Parallel Light-Emitting Diode (LED) String Currents

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Maximum Energy Efficiency Operation of Series-Series Resonant Wireless Power Transfer Systems Using On-Off Keying Modulation

Maximum energy efficiency in wireless power transfer (WPT) systems can be achieved through the use of magnetic resonance technique at a certain load resistance value. However, practical load resistance is not constant. Previously, a switched mode dc-dc converter was used in the receiver circuit to emulate an equivalent load resistance for maximum energy efficiency. In this paper, a new approach based on the On-Off Keying is proposed to achieve the high energy efficiency operation over a wide range of load power without using an impedance-matching dc-dc power converter. This simple and effective method has reduced average switching frequency and switching losses. It can be applied to any series-series resonant WPT system designed to operate at a constant output voltage. Practical measurements have confirmed the validity of the proposal