Search

This letter proposes a switched capacitor (SC)-based continuously adjustable modular bidirectional dc–dc converter. The structure of the proposed converter consists of three types of modules, series–parallel SC converter module, regulating module, and resonant SC converters module. A basic configuration of three modules working in buck operating mode is analyzed in detail. The boost mode operation is symmetrical to the buck mode. The regulation module provides all regulation capability, and the other two modules operate at fixed duty cycle and provide the main conversion ratio. A prototype of the basic configuration was built to verify the theory. The peak efficiency of the prototype is 97.15%. [ABSTRACT FROM AUTHOR]

In order to increase the power density and the lifespan of light-emitting diodes (LED) drivers, several studies have proposed active ripple compensation (ARC) techniques for minimizing the converter bulk capacitance. However, a common side effect of the ARC method is the increase in the total harmonic distortion (THD) of the converter input current. In this context, a frequency-based ARC technique is proposed as an alternative to the conventional ARC methodology, in which the duty cycle is modulated. The analyses presented in this article show that the frequency-based ARC approach applied to resonant converters has a better performance than the one used in hard-switching converters, since it allows for a huge capacitance reduction with a small THD increase. Furthermore, this article presents a generalized analysis of ARC techniques applied to integrated offline LED drivers, which reduce the number of components and the overall LED driver cost. The input current harmonic content and the output ripple reduction have been theoretically predicted for several converters. Experimental results gathered from a 96-W laboratory prototype supplied from a 127-V 60-Hz grid attested the superior performance of the frequency-based active ripple compensation, since a capacitance reduction of 66.6% has been obtained with an increase of only 0.9% in the THD. [ABSTRACT FROM AUTHOR]

This article presents an LED driver for lighting and visible light communication (VLC), which utilizes the light of the LEDs to wirelessly transmit data by modulating their instantaneous current. The solution proposed in this article seeks to unite the high efficiency of switched-mode power supplies with the wide bandwidth of linear power amplifiers (LPAs) to achieve high-speed communications. The hybrid converter processes the energy from a 48-V dc bus with an efficiency of 94% while supplying a 20-W LED load, and providing 3.68 MHz of bandwidth for VLC. Details regarding frequency limitations are provided in terms of a Laplace model. The impact of the LPA on the overall efficiency is mitigated by adopting specific design constraints. Finally, experimental results are shown from a prototype working with signals aimed at multicarrier multilevel modulations based on orthogonal frequency division multiplexing. [ABSTRACT FROM AUTHOR]

This article presents a deep analysis of the low-frequency ripple transferred from the bus voltage to the light-emitting diode (LED) current in integrated two-stage power converters, operating as offline LED drivers. This analysis presents a design methodology to select the optimum power control stage converter to the LED load and to reduce the bulk capacitance. The main focus is to analyze the ripple transfer ratio of the three main nonisolated dc–dc converters, namely buck, boost, and buck–boost. Moreover, this article presents a step-by-step case study for an existing converter and the proposed converter supplying a 26.9-W Luxeon 3014 LED load. The experimental results show that the integrated buck and boost converter requires a bus capacitance of 1200 μF, whereas in the integrated buck and buck–boost converter, the capacitance is reduced to 680 μF by applying the method proposed. This represents that the replacement of a boost converter by a buck–boost converter on the second stage allows a 50% reduction of the bus capacitance while keeping the same current ripple. [ABSTRACT FROM AUTHOR]

In this paper, a dual half-bridge LLC resonant converter with magnetic control is proposed for the battery charger application. The primary switches are shared by two LLC resonant networks, and their outputs are connected in series. One of the LLC resonant converters is designed to operate at the series resonant frequency, which is also the highest efficiency operating point, and the constant output voltage characteristic is achieved at this operating point. The second LLC resonant converter adopts magnetic control to regulate the total output current and voltage during both constant current charge mode and constant voltage charge mode. Meanwhile, the function decoupling idea is adopted to further improve the system efficiency. The significant amount of the power is handled by the LLC resonant converter operating at the series resonant frequency, whereas the second LLC resonant converter fulfills the responsibility to achieve closed-loop control. By carefully designing the resonant networks, the zero-voltage switching for primary switches and zero-current switching for secondary diodes can be achieved for whole operation range. A 320-W experimental prototype is built to verify the theoretical analysis, and the maximum efficiency is measured about 95.5%. [ABSTRACT FROM AUTHOR]

Light-emitting diode (LEDs) have a promising prospect because of its outstanding advantages: 1) long lifetime, 2) environmentally friendly, 3) flexibility of color mixing, 4) high illumination efficiency, etc. Based on the electrical characteristics of LEDs, a constant current driver is needed to support the LED working performance. With the wide applications of LEDs, many new technologies are presented. In this paper, advantages and disadvantages of different LED drivers are discussed. A detailed technology review is presented which is good for researchers and engineers to make right choices in design and selection of LED drivers. [ABSTRACT FROM PUBLISHER]

This paper proposes a new 48-V dc-fed dimmable LED driver based on a resonant-switched-capacitor topology (RSCT), where the analog-based dimming feature is accomplished by means of a variable inductor (VI). The proposed topology is based on the classic RSCT step-up double mode converter and it provides a simple and cost-effective solution while guaranteeing a wide dimming range. In order to implement an analog-based dimming, the control of the dc current in the LED lamp is required. This technique proposes to replace the resonant inductor by a VI, which will control the rms value of the resonant current, and, therefore, the mean value of the LED lamp current. In order to evaluate the feasibility and performance of this method, a 22-W LED lamp and driver prototypes were built. The most relevant experimental results are presented and briefly described. [ABSTRACT FROM AUTHOR]

This paper presents a comparative investigation, design and development issues about six different single-stage topologies, applied as electronic ballasts, for electrodeless fluorescent lamps. The ballast is intended to feed a 100 W lamp at 250 kHz, with dimming feature. The proposed topologies use different converters for the power factor correction (PFC) stage: Buck-Boost, SEPIC, Zeta, Cúk, Flyback, and Boost. All of them operate in discontinuous conduction mode. A resonant half-bridge inverter is used as lamp power control (PC) stage. The integration of both stages (PFC and PC) is proposed in this paper. In this way, it is possible to reduce the number of active switches, as well as simplify the required driving and control circuitry. Experimental results demonstrate the feasibility of the proposed dimming technique that achieved around 56% lamp power dimming, from 100 W down to 44 W. The implemented topologies attained high average power factor (>0.98), and low line current average total harmonic distortion (<;15.3%). A comparison among all the proposed topologies in terms of power factor, harmonic distortion, efficiency and number of components is presented. Finally, a comparison between an integrated and a nonintegrated SEPIC half-bridge converter is also performed. [ABSTRACT FROM AUTHOR]

A single-stage offline power supply for LED lighting applications, based on the integration of a buck power factor corrector (PFC) and a tapped buck dc/dc converter, is presented in this paper. In addition to the high step-down capability and the output current regulation, the proposed topology effectively provides PFC to comply with the harmonic injection and energy-saving standards EN 61000-3-2 and Energy Star. The low bus voltage level, resulting from the use of an input step-down PFC stage, actually allows the use of film technology capacitors, instead of short lifetime electrolytic capacitors, to filter the bus voltage and reduce the LED current ripple component at twice the line frequency. Due to the high reliability, the simple structure, the good line-side spectral performance, and the low component count, the proposed topology effectively results to be very suitable for medium-power solid-state lighting applications, as in the case of LED downlighting. The issues related to the operation of the presented solution and to its design optimization will be carefully discussed. A prototype of the proposed ac/dc converter has been built and tested. The main experimental results will be described. [ABSTRACT FROM PUBLISHER]

This paper proposes an offline single-stage light-emitting diode (LED) driver based on a novel approach to reduce low-frequency ripple in LED arrays supplied from mains, while assuring high input power factor (PF). The proposal employs a series resonant dc–dc converter integrated into a bridgeless boost power factor correction (PFC) stage. The resonant stage works to reduce the low-frequency ripple transmitted from the output of the PFC stage to the LEDs with only small power losses. This solution achieves three main goals: 1) reduction of the bulk capacitance used at the dc bus, allowing for the use of long-life film capacitors; 2) increase in the overall efficiency of the LED driver owing to the low switching and conduction losses in the shared switching network; and 3) assuring high input PF. Experimental results of a driver without electrolytic capacitors for a 100-W street lighting LED luminaire are presented, showing overall efficiency in excess of 92%, input PF greater than 0.97, and line current harmonic content in compliance with the IEC 61000-3-2 standard. [ABSTRACT FROM AUTHOR]

This paper presents a new control method and a detailed project methodology for the optimized connection method of two converters, aiming to reduce the redundant power processing, in order to supply high-power light-emitting diodes (LEDs) with reduced capacitance and high efficiency, directly from the ac line. This connection method allows dealing with two major issues related to the LED driver: capacitance reduction and efficiency increasing. The first converter provides power factor correction, whereas the second converter controls the current through the LED. The basic idea consists in making the second converter to process only the low-frequency ripple (LFR) of the first converter, thus smoothing the LED current. In this way, the LFR is managed by the second stage, so that the capacitance of the first stage can be significantly reduced. The proposed control method can achieve better results for the low-frequency compensation. In addition to that, a high power factor and a low harmonic content are obtained, fulfilling the IEC 61000-3-2 Class C requirements. A laboratory prototype with a rated power of 75 W and an input voltage of 220 \Vrms/60 Hz was built in order to show the feasibility of the idea. The measured overall efficiency of the converter was 91%, and electrolytic capacitors were avoided. [ABSTRACT FROM PUBLISHER]

This paper deals with the capability of pulse width modulation (PWM) dimming operation added to the high-power factor-integrated buck-flyback converter (IBFC), which was developed in previous works for LED lighting applications. First, the two main dimming techniques will be introduced, namely, analog dimming and PWM dimming. Then, the three main PWM dimming schemes found in the literature, that is, enable dimming, series dimming, and parallel dimming, will be briefly discussed. Afterwards, the IBFC topology will be tested performing both analog and enable dimming. In addition, a new proposal is introduced: the high-frequency series PWM dimming technique, which overcomes all the challenges faced when developing PWM dimming capabilities in low slew-rate constant-current fixed-frequency-controlled converters and offers all the advantages of PWM dimming over analog dimming while maintaining good efficiency. The proposed dimming-technique control loop, as well as the laboratory tests, will be presented, discussed, and compared to analog dimming and PWM dimming, showing satisfactory results in terms of dimming ratio, input current total harmonic distortion (\THDI), and power factor. [ABSTRACT FROM AUTHOR]

Due to the high rise in luminous efficiency that high-brightness light-emitting diodes (HB-LEDs) have experienced in recent years, many new applications have been researched. This paper covers a streetlight LED application using the offline integrated buck–flyback converter (IBFC) developed in previous works. In this application, the converter is used to provide power-factor correction from a universal ac source. A control loop using the LM3524 IC has been implemented for testing the feasibility of Enabling pulsewidth modulation dimming mode. First, the LED load has been linearized and modeled in order to calculate the IBFC topology properly. Second, the converter has been designed and tested at the laboratory. The converter has also been modeled in order to design a fixed-frequency constant-current control. The dynamics of all the stages involved in the closed loop have been taken into account in order to develop an adequate controller. Finally, the experimental results obtained from the laboratory tests are discussed. [ABSTRACT FROM AUTHOR]

In this paper, a novel topology to supply metal halide (MH) lamps using sinusoidal waveform with superposed third harmonic is proposed. By employing this technique, the lamp is supplied with an approximated square waveform, but it reduces the harmonic content and, therefore, electromagnetic interference and radio-frequency interference. The proposed topology is analyzed and designed for a 35-W MH lamp with ceramic discharge tube. Experimental results prove that lamp operation is stable at operating frequencies where acoustic resonances were previously observed when supplied with purely sinusoidal waveforms. In conclusion, the proposed technique could be a feasible solution for stable operation of MH lamps. [ABSTRACT FROM AUTHOR]

In this paper, a low-cost electronic ballast for high-pressure sodium vapor lamps is presented. The proposed ballast is a two-stage circuit that requires only one switch and one inductor for each stage. The power-factor-correction stage is a buck dc-to-dc converter operating in discontinuous conduction mode to meet the IEC-61000-3-2 Class C requirements. The inverter stage is a low-cost nonresonant topology, based on a buck-boost inverter controlled by means of a specific current-mode control implementation. In addition, a novel and simple circuit, compatible with the presented inverter, is proposed to ignite the lamp. Furthermore, this circuit implementation provides protection against broken lamps. [ABSTRACT FROM AUTHOR]