This paper describes a complete digital PWM controller IC for high-frequency switching converters. Novel architecture and configurations of the key building blocks are A/D converter, compensator, and digital pulse-width modulator, are introduced to meet the requirements of tight output voltage regulation, high-speed dynamic response, and programmability without external passive components. The implementation techniques are experimentally verified on a prototype chip that takes less than 1 mm/sup 2/ of silicon area in a standard 0.5 /spl mu/ digital complementary metal oxide semiconductor (CMOS) process and operates at the switching frequency of 1 MHz.

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High-frequency digital PWM controller IC for DC-DC converters

This paper proposes a concept of electrolytic capacitor-less light-emitting diode (LED) driver, which converts the commercial ac voltage to a pulsating current with twice the line frequency driving high-brightness LEDs. As no electrolytic capacitor is used, this driver possesses the unique advantage of long lifetime to match with that of LEDs. A method of injecting the third and fifth harmonics into the input current to reduce the peak-to-average ratio of the output current is also proposed. While ensuring that the input power factor is higher than 0.9 to meet regulation standards such as ENERGY STAR, the proposed method allows the peak-to-average ratio of the output current to be reduced to 1.34 theoretically, which is beneficial for the safe operation of the LEDs. As an example, a flyback-based electrolytic capacitor-less LED driver is proposed, and its operation is analyzed. In order to inject the third and fifth harmonics into the input current, the function of the duty cycle in a half-line cycle is derived. It is then simplified to a fitting function, which can be easily implemented with the input voltage sensing. A 25 V, 0.35 A output prototype is built and tested in the laboratory, and the experimental results are presented to verify the effectiveness of the electrolytic capacitor-less LED driver and its control method.

A Method of Reducing the Peak-to-Average Ratio of LED Current for Electrolytic Capacitor-Less AC–DC Drivers

The nonresonant single-phase dual-active-bridge (NSDAB) dc–dc converter has been increasingly adopted for isolated dc–dc power conversion systems. Over the past few years, significant research has been carried out to address the technical challenges associated with modulations and controls of the NSDAB dc–dc converter. The aim of this paper is to review and compare these recent state-of-the-art modulation and control strategies. First, the modulation strategies for the NSDAB dc–dc converter are analyzed. All possible phase-shift patterns are demonstrated, and the correlation analysis of the typical phases-shift modulation methods for the NSDAB dc–dc converter is presented. Then, an overview of steady-state efficiency-optimization strategies is discussed for the NSDAB dc–dc converter. Moreover, a review of optimized techniques for dynamic responses is also provided. For both the efficiency and dynamic optimizations, thorough comparisons and recommendations are provided in this paper. Finally, to improve both steady-state and transient performances, a combination approach to optimize both the efficiency and dynamics for an NSDAB dc–dc converter based on the reviewed methods is presented in this paper.

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Overview and Comparison of Modulation and Control Strategies for a Nonresonant Single-Phase Dual-Active-Bridge DC–DC Converter

The photometric, electrical, and thermal features of LED systems are highly dependent on one another. By considering all these factors together, it is possible to optimize the design of LED systems. This paper presents a general theory that links the photometric, electrical, and thermal behaviors of an LED system together. The theory shows that the thermal design is an indispensable part of the electrical circuit design and will strongly influence the peak luminous output of LED systems. It can be used to explain why the optimal operating power, at which maximum luminous flux is generated, may not occur at the rated power of the LEDs. This theory can be used to determine the optimal operating point for an LED system so that the maximum luminous flux can be achieved for a given thermal design. The general theory has been verified favorably by experiments using high-brightness LEDs.

A General Photo-Electro-Thermal Theory for Light Emitting Diode (LED) Systems

DC microgrids have attracted significant attention over the last decade in both academia and industry. DC microgrids have demonstrated superiority over AC microgrids with respect to reliability, efficiency, control simplicity, integration of renewable energy sources, and connection of dc loads. Despite these numerous advantages, designing and implementing an appropriate protection system for dc microgrids remains a significant challenge. The challenge stems from the rapid rise of dc fault current which must be extinguished in the absence of naturally occurring zero crossings, potentially leading to sustained arcs. In this paper, the challenges of DC microgrid protection are investigated from various aspects including, dc fault current characteristics, ground systems, fault detection methods, protective devices, and fault location methods. In each part, a comprehensive review has been carried out. Finally, future trends in the protection of DC microgrids are briefly discussed.

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DC Microgrid Protection: A Comprehensive Review

A Single LED is very small, and their luminance is related to the amount of driving current. Sufficient luminance for an illuminator requires many LEDs to be connected together and a constant current supplied to each LED. Therefore, the LED drive circuit must have constant-output-current control and/or constant-luminance control. We propose an LED drive circuit that consists of a boost-type DC-DC converter with constant-output-current control and constant-luminance control. This circuit is a switching regulator-type circuit controlled by pulse width modulation (PWM). Both the power and the constant-current control can be provided by a single system, without any ballast resistor or auxiliary current control circuit.

/pdf/an-led-drive-circuit-with-constant-output-current-control-238xl67dkm.pdf

An LED Drive Circuit with Constant-Output-Current Control and Constant-Luminance Control

Bidirectional dc-dc converters, which make possible the bidirectional transmission of power, have become indispensable in recent years due to the diversification of the power supply network, including the use of batteries. Of these, the dual active bridge (DAB) dc-dc converter features a simple mechanism and symmetric circuit architecture, making possible the equal transmission of power in both directions. Because of these advantageous characteristics, DAB dc-dc converters are in wide use. However, this circuit has the intrinsic problems that, during light-load conditions, switching surges occur and power efficiency decreases. This paper proposes digitally controlled operation as a new method to resolve these problems and reports on an experiment that was carried out using a 1-kW system. In addition, for both buck and boost modes, output power characteristic equations were derived through application of the extended state-space averaging method, and a loss-included circuit analysis was carried out for the circuit used in the experiment. It was thereby demonstrated that circuit loss was smaller for the proposed operation than that for conventional operation. In the loss-included circuit analysis, for both proposed and conventional operations, equivalent circuits that approximated circuit loss as a single resistance were used. As a result, it was confirmed that, with the operation proposed in this paper, without the use of a snubber circuit, switching surges could be reduced significantly and also that, during light load, there was a power efficiency improvement of up to 16%. In addition, a loss-included circuit analysis with a single equivalent resistance has been done. The resistance value is assigned with the averaged circuit total resistance. By the analysis, a relation between phase difference and output power is obtained. The results were confirmed with the experiment.

A Power Efficiency Improvement Technique for a Bidirectional Dual Active Bridge DC–DC Converter at Light Load

This paper presents circuit design techniques for reducing the effects of magnetic flux, occurred from the planar transformer, on gallium nitride high-electron-mobility transistors (GaN-HEMTs) in 5-MHz 100-W high power-density LLC resonant dc–dc converters. For investigating the effects of magnetic flux on a GaN-HEMT, power device model for finite element method (FEM) simulation is proposed. In order to confirm the validity of the model, the quantitative evaluation is conducted with FEM simulation, and experiment using evaluation boards. Moreover, the optimization of printed circuit board layout is considered using the verified model with FEM simulation, for reducing the effects of magnetic flux on GaN-HEMTs while reducing the area of converter. In the experiments, 5-MHz 48 V/12 V 100 W unregulated LLC resonant dc–dc converter with efficient power conversion GaN-HEMTs is built as the prototype to verify the optimized layout. The maximum power efficiency can be achieved 91.28%, and the power density can be achieved 32 W/cm3.

Circuit Design Techniques for Reducing the Effects of Magnetic Flux on GaN-HEMTs in 5-MHz 100-W High Power-Density LLC Resonant DC–DC Converters

This paper presents implementation report for slope monitoring on Wireless Sensor Network (WSN) system by use of IEEE802.15.4 (ZigBee). The purpose of this research is the construction of WSN system which can be sensing and monitoring the deformation of the ground caused by heavy rain in mountain areas with radio communication devices and sensor devices. For the stable data acquisition, some electrical and environmental problems should be solved. In this paper, the techniques for dynamical transition of the communication mode depending on battery capacity, a method of protecting wireless nodes from the lighting, and a optimized design of antenna for WSN are proposed. The experimental results which the proposed system installed at actual test field show that the dynamic wireless network configuration. Moreover, the status of field can be predicted by the obtained data from the improved system.

Design of stable wireless sensor network for slope monitoring

The Dual Active Bridge (DAB) DC-DC converter is one of the most popular circuits for bi-directional applications because of simple structure. However, DAB DC-DC converter has few problems such as the surge voltage and hard switching in specific conditions. These problems are caused by the relationship between the output power and phase difference, which causes device breakdown and deterioration of power efficiency. For the design of Input-Series and Output-Parallel (ISOP) converter system with DAB DC-DC converter, the problem is also occurred and more severe because of its high voltage. In this paper, the design technique of ISOP with DAB for suppressing the surge voltage and realizing the high power efficiency in wide load range is proposed. As the result, this method reduces the switching surge, and the power efficiency is increased by 22.5% at light load.

Yoichi Ishizuka

Papers

An LED Drive Circuit with Constant-Output-Current Control and Constant-Luminance Control

A Power Efficiency Improvement Technique for a Bidirectional Dual Active Bridge DC–DC Converter at Light Load

Circuit Design Techniques for Reducing the Effects of Magnetic Flux on GaN-HEMTs in 5-MHz 100-W High Power-Density LLC Resonant DC–DC Converters

Design of stable wireless sensor network for slope monitoring

High efficiency design for ISOP converter system with dual active bridge DC-DC converter