A dimmable light-emitting diode (LED) driver with mag-amp postregulators for multistring applications

Current imbalance should be avoided when multiple LED strings are connected in parallel. In this paper, a dimmable LED driver with magnetic-amplifier postregulators for multistring applications is presented. Powered by a common master source, parallel LED strings are individually regulated by their corresponding adaptive slave sources for current balancing in this proposal. Without linear current regulators, the proposed driver offers relatively high efficiency. Its structure is simpler than multiconverter structures for red, blue, and green LED applications, and is particularly suitable for LEDs with wide parameter variations. The performance of the proposed driver is experimentally verified by a 16.5-W prototype with a load of three 5.5-W LED strings. © 2006 IEEE.published_or_final_versio

Dimmable High Power LED Driver Using Fuzzy Logic Controller

The use of lighting loads is one of the crucial matters which increases every year. The increasing use then leads to the development of brighter and longer-lasting sources. In addition, the conventional use of lighting loads today, which only emit light at its maximum intensity, does not allow the consumers to adjust the brightness level as needed. Consequently, this condition may cause energy wastage. The LED lighting system is gaining popularity as it is widely used in a wide range of applications. The advantages of LEDs, such as its compact size and varied lamp colors, replace conventional lighting sources. The linear setting of the driver topology using the flyback converter was aimed to control the LEDs with a constant current in order to adjust the variation of the LED light intensity. The closed-loop driver circuit with flyback converter topology was designed as an LED driver with a given load specification from the LED string. A dimmable feature was included for adjusting the intensity of the light produced by the LEDs. Eventually, the fuzzy logic controller (FLC) method was applied to the integrated change setting to obtain a dynamic response

Energy Efficiency and Sustainable Lighting

The lighting of both exteriors and interiors is a field within electrical and lighting engineering, where important technological changes have been taking place oriented towards environmental sustainability and energy efficiency. LED technology has been gradually gaining ground in the world of lighting over other technologies due to its high lighting and energy efficiency and savings. However, some problems related to overheating or associated regulation are emerging. This has prompted the search for new, more efficient, and sustainable forms of lighting. This book presents successful cases related to energy efficiency and lighting that may be of great interest to those trying to enter the world of scientific research

Development of Vehicle Lighting System Using LED Application

A Light Emitting Diode (LED) is a semiconductor device which converts electricity into light. LEDs are preferred over incandescent lamps because of their long life and their availability in various colors and brightness levels. The aim of this paper is to present the development of vehicle lighting system using LED application. In this system, high power LEDs type is chosen as automobile headlight model and controller circuit using microcontroller is considered. The LEDs are driven using buck converter circuit with appropriate Pulse Width Modulation (PWM) signal whereby the PWM signals are generated by microcontroller. The system is divided into 2 modes of operation, manual and automatic. The automatic mode of operation will be operating when the LDR senses the level of light brightness whereby the level of brightness is proportion to duty cycle of PWM. Meanwhile, for the manual mode of operation, 3 switches which are SW2 with 20% duty cycle, SW3 with 40% duty cycle and SW3 with 80% duty cycle are developed. The result shows that the maximum brightness of LED is about 127.6 Lumen at 80% of duty cycle for manual operation mode. Besides, by varying theduty cycle of PWM signal for both modes of operation, manual and automatic, LED brightness can be controlled

LED Roadway Luminaires Evaluation - Final Report

This research explores whether LEDroadway luminaire technologies are a viable future solution to providing roadway lighting. Roadway lighting enhances highway safety and traffic flow during limited lighting conditions. The purpose of this evaluation study is to determine the feasibility of transitioning from standard high pressure sodium (HPS) roadway luminaire to LED roadway luminaire on the MoDOT maintained highway system. This study includes performance evaluations, a feasibility analysis and a potential transition replacement program

Characterizing Light Output Variations from Solid State Lighting Due to High Frequency Electromagnetic Interference

Consumer electronic devices employing active power electronic switching have been increasingly used in the last decade. With the rise in number of these devices, the emission of harmonic currents by these devices has changed both in magnitude and character. The effects of harmonic frequencies up to 2000 Hz on various electrical and electronic devices has been the subject of considerable scrutiny over the past decade. However, newer consumer devices employ switched mode power electronic circuits that switch in the multiple kilohertz range. The emission from these devices, along with power line communication, are sources of high frequency currents in the range of 2 to 150 kHz. As a result, there has been an appreciable rise in the amount of conducted emission in the frequency range 2 to 150 kHz. One of the important outcomes of rising emission in this frequency range is that there have been reported cases of interference with various consumer electronic devices. Among the devices in which interference has been reported are the new generation of solid state LED lamps which have become popular in the last 3-5 years. Considerable research has been done in the past about the effects of light flicker and the modulation of light output from incandescent lamps, on human beings. However, the utilization of power electronic converters changes this paradigm considerably. Unlike incandescent bulbs, where low frequency modulation of input voltage resulted in visible flicker, observations and reports have shown that LED lamps may be susceptible to flicker from frequencies above the 2 kHz mark. As a result, old methods of predicting flicker and studying it may no longer be applicable. This thesis attempts to shorten this gap in knowledge by exploring the topic of LED flicker due to high frequency distortion, and the factors that affect it. This was achieved by exposing LED lamps of various sizes and from various manufacturers, to realistic voltage distortion signals, recorded in the power system. Signals with high-frequency distortion superimposed on to the fundamental, were used. The test set-up used, allowed for the testing of light equipment with various types and levels of distortion at different points on wave. For the first time, experimental results showed that not only does high frequency voltage distortion cause changes in average value of light output and the modulation of light output, but that this change depends upon the point-on-wave at which the high frequency distortion appears. The mathematical tool of cross-correlation was proposed to quantify the effect of point-on-wave of high frequency distortion on light output. The utilization of this tool showed that LED lamps are susceptible to distortion appearing near the peak or near the zero crossing of the input voltage. In order to understand the dependence of LED flicker on the topology of the LED driver, five LED driver development boards available commercially were also subjected to the above mentioned high frequency voltage distortion. The results showed that light flicker from LED lamps is not necessarily a by-product of LED driver topology. The utilization of discontinuous conduction mode of operation and an isolation transformer in the LED driver is not sufficient to disconnect the LED load from input voltage variations. LED drivers of the same topology can behave completely different, likely due to the control methodology employed by each manufacturer. Finally, a simulation model of a popular LED driver solution: a flyback DC-DC converter with primary side regulation was developed to verify the experimental results and perform root cause analysis for the observed phenomena. Changes in control methodology and circuit design were suggested to overcome this flicker problem and evidence of the degradation of circuit components due to excess heat generated by high frequency distortion was shown

A Buck boost-Buck PFC rectifier as an LED driver

The objective of this thesis is to design a buck boost-buck power factor corrector (PFC) to drive a string of High Brightness Light Emitting Diodes (HB-LEDs). Conventional buck-boost converter is used for power factor correction, but it suffers from issues like the inverted polarity of the output voltage, floating drive requirement for its active switch. These issues have been addressed in the proposed PFC converter by an integration of buck-boost and buck topologies. The PFC converter is able to drive load, with nearly unity power factor, significantly low input current total harmonic distortion (THD) with higher efficiency of power conversion. The theoretical analysis and operation of the proposed converter with a 20W LED load have been verified by simulation in MATLAB/Simulink. Finally, the experimental results of a laboratory prototype with an output power of 20W supplied from 110v/50Hz are provided to validate the simulation results

Dimming DC–DC LED Drivers: Power Losses, Luminous Efficiency & Best-in-Class

The aim of this research is to analyze, model, and compare dimming techniques for switched-inductor (SL) light-emitting-diode (LED) drivers. LEDs have become pervasive in modern lighting and automotive applications. LED drivers regulate the LED current that sets their luminous output, where dimming is an important attribute. Dimming techniques fall in one of two categories: "analog" or "duty-cycled" (pulse-width-modulated), and duty-cycled (PWM) dimming decompose into two further classes: series- or shut-switched. A comprehensive analysis of dimming techniques, corresponding power losses, and their dimming capabilities for dc-dc applications is lacking in the literature. This research aims to explain and quantify these important parameters, like luminous flux, dimming range, and luminous efficiency. This research reveals and verifies that analog dimming is the most efficient with the widest dimming range.M.S

Digital implementation of the feedforward loop of the asymmetrical half-bridge converter for LED lighting applications

The Asymmetrical Half Bridge converter (AHBC) has proven to be a promising candidate for LED lighting applications. It provides high efficiency, galvanic isolation and, at the same time, its output filter can be very small and, therefore, easily implemented without electrolytic capacitor. On the other hand, its main drawback is its poor attainable bandwidth. In any ac-dc LED lighting application, the input voltage of the AHBC is provided by a Power Factor Corrector (PFC) converter which has to be also implemented without electrolytic capacitor in order to assure the long lifetime of the whole LED driver. As a consequence, its output voltage (input voltage of the AHBC) is affected by a low-frequency ripple. Due to the poor bandwidth of the AHBC, this voltage ripple will be transferred to the converter output voltage, leading to flickering. A possible solution is using a feedforward loop for cancelling the effect of this low-frequency ripple without affecting stability. Due to the complex and non-linear transfer function of the AHBC, any analog feedforward loop has to be tuned for a given operating point, leading to a poor performance (i.e., high flickering, high ripple) when the AHBC moves away from that point. Dimming, which is a very frequent requirement in many LED drivers, implies large variations of the output voltage and, consequently, moving away from the aforementioned operating point. In this paper, a digital feedforward loop is proposed in order to solve this problem. The digital implementation allows the feedforward loop to perfectly cancel the ripple under any condition (e.g., output voltage variation due to dimming). Besides, despite its complex transfer function, this digital feedforward loop has been designed and optimized for its implementation in small-size microcontrollers. Experimental results with a 40-W prototype prove the usefulness of the proposed feedforward loop and the validity of the equations used in the optimized desig