Light-emitting diodes (LEDs) are coming strongly into the lighting market due to their advantages over conventional lighting solutions: energy efficient, controllable in both light and color, long lifetime, lack of a warm-up period, and high power density. Some of these advantages will make LED light sources to be more than just a light bulb, being able to transmit data, control light color, hue, and intensity or even detect people in indoor environments. Nevertheless, these advantages attributed to LED capabilities are, in reality, achieved thanks to the LED driver. This paper reviews the current state-of-the-art strategies to drive LEDs from ac power grids with special emphasis into removing the most limiting component from the point of view of the lifetime, which is the electrolytic capacitor, while achieving a flicker-free performance of the light output of the LED driver. Moreover, it focuses on analyzing the required regulations, challenges, and applicability of LED drivers in both single-phase and three-phase ac power grids.

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A Review on Flicker-Free AC–DC LED Drivers for Single-Phase and Three-Phase AC Power Grids

A novel single-stage light-emitting diode (LED) driver with high voltage gain for LED automobile headlight is proposed in the paper. The converter is made up of two parts, which are the boost cell and double LLC cell, and the two parts are integrated by sharing the switch. Since the number of the system components is reduced by integrating the switches, the cost decreases. The boost circuit works in the continuous conduction mode with double voltage gain, and the double LLC cell connected in series can decrease the peak current and increase the efficiency of the system. A 30-W prototype is proposed in the lab, with 30 high-brightness LEDs connected in series. The experimental results well confirm the theoretical prediction, and the efficiency of the system for the full load is higher than 92%.

A Single-Stage LED Driver Based on Double LLC Resonant Tanks for Automobile Headlight With Digital Control

In this paper, a self-oscillating boost converter with a blocking diode is proposed to meet the desire for simple, cost-effective, high performance, and highly efficient LED drivers. As compared with traditional self-oscillating converters, the proposed converter demonstrates several appealing advantages including design simplicity, robustness, soft-switching characteristics (zero-voltage switching and zero-current switching), tight current regulation, and high efficiency over a wide line/load range. The control stage is implemented with a compact and low-cost industry standard controller, which assumes multiple roles in switching and LED current regulation. A type III compensator with anti-windup is designed to limit the maximum LED current at startup and to achieve tight LED current regulation at steady state. The efficiency and desired transient/steady-state performances are verified with SPICE simulation and a prototype circuit, which demonstrate a maximum efficiency of 95.9% and 2.3% ripple factor for the LED current. The robustness of the proposed driver is verified under a range of power supply voltage and different numbers of LEDs at the load side. In addition, the circuit is modified to implement high efficiency pulsewidth modulation dimming between 5% and 95%.

Low Cost High Performance LED Driver Based on a Self-Oscillating Boost Converter

This paper introduces a megahertz-frequency resonant dc–dc converter that inherently achieves a load-independent output current while maintaining high efficiency across a wide output voltage range. These properties make the proposed converter well-suited for automotive light-emitting diode (LED) driver applications, where a varying number of LEDs need to be driven with a constant current. The proposed converter achieves load-independent output current by utilizing an LCL -T resonant network, and achieves high efficiency using a comprehensive design optimization methodology. This LCL -T resonant converter is also capable of regulating its output current at any desired value by utilizing phase-shift control. The performance of the LCL -T resonant converter is theoretically and experimentally compared with an LC 3 L and an LCLC resonant converter. For the experimental comparison, prototypes LCL -T, LC 3 L , and LCLC resonant converters are designed to operate at 2 MHz and across an output voltage range of 3.3–49.5 V while supplying a constant 0.5 A output current to the LEDs. The LCL -T resonant converter prototype achieves a peak efficiency of 91.1%, which is 0.6% and 1.8% higher than the peak efficiency of the LC 3 L and the LCLC converter prototypes, respectively. Furthermore, the LCL -T converter prototype maintains 0.8% and 1.6% higher average efficiency over its 15:1 output voltage range relative to the LC 3 L and the LCLC converter prototypes, respectively.

High-Performance Megahertz-Frequency Resonant DC–DC Converter for Automotive LED Driver Applications

This paper presents an improved current mode control for a DC-DC buck converter which works as an electronic drive to feed the lighting system based on power LEDs. The automotive industry requires LED based lighting system with fast lighting changes, besides a constant voltage and a forward current are needed to maintain the required luminous flux despite the load changes. Based on a controller previously reported, here a model based controller is proposed which is aimed to reduce the number of the sensors maintaining the performance of the drive. Numerical results are performed in order to validate the controller.

A buck converter controller design in an electronic drive for LED lighting applications

This paper presents an electronic ballast based high power LEDs for headlights automobile. The ballast is based on a buck converter to feed a load of high power LED. The load is divided into five high power LED (10W), in automobile lighting systems rapid changes of lighting is required (power changes), therefore the buck converter must deliver constant voltage levels to changes in power and further the current necessary to maintain a flow of light required. To solve this problem this paper proposes a control law for buck converter control, which maintains a fixed voltage level for the different power (10.9W, 21.8W, 32.7W, 43.6W, 54.5W) dynamic response to these changes is fast and constant levels of current and luminous flux at each change of load is maintained.

Analysis of buck converter control for automobile LED headlights application

This paper presents a self-oscillating electronic ballast for a 36 W LED string. The design consists of a simple control that reduces the component number and cost of the ballast. Self-oscillating converters are popular in compact fluorescent lamps; therefore, it is proposed the use of this self-oscillating control technique for the LED lamp. The self-oscillating LED driver represents a very suitable solution in compact LED products. This paper describes the design of a self-oscillating electronic ballast at high frequency. The output of the sine wave of the resonant inverter is rectified and, then its high frequency yields a reduction in the value of output capacitor.

Design of self-oscillating electronic ballast for power LEDs

In this paper presents the study and implementation of a model for an ultraviolet light-emitting diode (UV LED). This model is used to characterize series and parallel UV LED arrangements. The proposed model can be used for different power LED. An exponential expression of a term that describes the electrical characteristics of the V-I curve of a UV LED is used. The principle of implementation of UV LED is described, and in this way they can be used in simulation software. The proposed model this designed for any number of LED in series or parallel. To perform the proposed model radiation is analyzed in terms of temperature and power.

A model for electrical characteristics of high power UV LED

This paper presents a self-oscillating electronic driver for a 36 W LED string. The design consists of a simple control that reduces the component number and cost of the driver. Self-oscillating converters are popular in compact fluorescent lamps; therefore, it is proposed the use of this self-oscillating control technique for the LED lamp. The self-oscillating LED driver represents a very suitable solution in compact LED products. This paper describes the design of a self-oscillating electronic driver at high frequency. The output of the sine wave of the resonant inverter is rectified. This LED driver not require of electrolytic capacitors, because LED is operated with pulsating output current.

Analysis and design for self-oscillating LED driver with high frequency pulsating output current

This paper presented a comparative study in function reliability between dc-dc converters used in power LED. Between dc-dc converters more used to power LED are the Buck and Flyback converter, because the Buck provides a lower output voltage than the input, and in the case of flyback has galvanic isolation. The study has objetive to determine the reliability obtaining the failure rate of the system and the average time when failures occurs, because the LED driver must have an average life similar to the LED lamp. The reliability analysis is based in the standard MIL-HDBK-217, for this study performed was used a LED load of 54.6 W in both converters. The results have shown that the buck converter has a lower failure rate and a higher mean time between failures, therefore has a longer useful life.

http://ieeexplore.ieee.org/iel7/7389728/7395064/07395107.pdf

G. Vazquez

Papers

Analysis of buck converter control for automobile LED headlights application

Design of self-oscillating electronic ballast for power LEDs

A model for electrical characteristics of high power UV LED

Analysis and design for self-oscillating LED driver with high frequency pulsating output current

Comparative analysis of the reliability of drivers for power LED