High-brightness Light-emitting Diodes Driver Research Articles

Dimming Techniques Focusing on the Improvement in Luminous Efficiency for High-Brightness LEDs

The pulse width modulation (PWM) dimming mode features good dimming linearity and has been widely used for driving high-brightness light-emitting diodes (HBLEDs), in which the brightness change is reached by modulating the duty cycle of the dimming signal to regulate the average current flowing through LEDs. However, the current-illuminance characteristic curve of most LEDs is nonlinear in nature. Namely, under the same lighting power fed, the conventional PWM dimming cannot make the LED exert its best luminous efficiency (LE) specified in datasheets. This paper focuses on the study of further improving LED luminous efficacy via dimming manipulation. Thereby, two multilevel current dimming techniques with varied dimming signal voltage and varied current sensing resistance are presented. With limited dimming capability, the proposed dimming strategies can efficiently raise the luminous flux ratio without increasing the power consumption. A prototype constructed for a 115 W HBLED driver is developed and the devised dimming schemes are realized by a digital signal controller (DSC). Experimental results exhibited with illuminance-power curves and CIE1931 and CIE1976 chromaticity diagrams are given to validate the theoretical derivation and effectiveness. Compared with conventional PWM dimming, under the same illuminance, the driver average output power is respectively reduced by 17.08% and 13.17%; the improvement in average illuminance under the same output power is 13.66% and 11.17%, respectively. In addition, the entire average LE boost has respectively increased by 21.36% and 16.37%.

An AC–DC PFC Single-Stage Dual Inductor Current-Fed Push–Pull for HB-LED Lighting Applications

An ac–dc single-stage driver for high-brightness light-emitting diodes (HB-LEDs) with galvanic isolation is presented in this paper. The driver is based on a dual inductor current-fed push–pull converter with each inductor operating in boundary conduction mode (BCM). The interleaving between the two inductors enables the converter to reduce the high input current ripple inherent to a BCM. Moreover, it is fully compliant with IEC 1000-3-2 Class C and it is able to achieve a high power factor (PF). Its low component count, simplicity, and overall outstanding characteristics make this current-fed topology suitable for medium power range HB-LED drivers in low-cost applications. The proposed topology has been tested on a 100-W prototype for the full range of the US single-phase line voltage, feeding several HB-LED strings, with an output voltage equivalent to 48 V at full load. The prototype achieves a maximum efficiency of 92% with a 0.99 PF, 8% total harmonic distorsion at full load while guaranteeing a good quality light.

Multicell Three-Phase AC–DC Driver for HB-LED Lighting Applications

High-brightness light-emitting diodes (HB-LEDs) are becoming omnipresent across all aspects of illumination products, due to their incredible characteristics such as efficiency, reliability, long lifetime, controllability, etc. This paper proposes power conversion topologies to drive medium to high power HB-LEDs in three-phase power grids when these connections are available. For that reason, an evaluation of several drivers for medium to high power HB-LEDs in three-phase power grids is done. Moreover, a new topology is proposed, which complies with IEC 1000-3-2 Class C requirements, achieves high power factor, low total harmonic distortion, and the capability to have a flicker free behavior while disposing of the bulk capacitor and having galvanic isolation. The HB-LED driver is based on a modular approach with several cells working together with their inputs connected to the three-phase network and their outputs connected in parallel generating a dc output. Each one of these cells is a dc–dc converter operating as a loss free resistor. In order to validate the concept, a prototype has been built by the use of flyback converters operating in discontinuous conduction mode. Furthermore, it operates in the full range of the European three-phase line voltage, which varies between 380 and 420 V, and it supplies an output voltage of 48 V with maximum power of 90 W.

Improving the Dimming Performance of Low-Power Single-Stage AC–DC HBLED Drivers

The design of efficient single-stage high-brightness light-emitting diodes (HBLEDs) ac–dc drivers with power factor correction (PFC) in low-power applications is addressed in this paper. The PFC is achieved by using a switching converter with both step-up and step-down voltage capability. It is well known that a good tracking of the input reference current close to the zero crossing is challenging, in particular when the LED output current is low, hence jeopardizing the power quality at low power levels. A solution is proposed to improve the power quality in ac–dc LED drivers under inner current loop based on a variable hysteresis modulation scheme. An adaptive hysteresis window modulated by the input voltage and the output LED current reference is used. The double modulation strategy helps to avoid the distortion near the zero crossings of the input current and to improve the dimming performance of the HBLEDs. This results in a low value of total harmonic distortion (THD) under low current/power conditions and therefore in a very good dimming performance in single-stage ac–dc HBLEDs drivers with PFC. The operation principle of the proposed technique is presented and numerical simulations are shown to demonstrate its functionality. A laboratory prototype is designed and tested to verify its feasibility obtaining a significant improvement in terms of power quality. Under universal input voltage operation, good efficiency and low THD can be achieved even for low power levels.

Active Input Current Shaper Without an Electrolytic Capacitor for Retrofit Lamps Applications

The evolution of solid-state lighting technology has transformed traditional solutions in lighting. High-brightness light-emitting diodes (HB-LEDs) have become very attractive light sources due to their excellent characteristics, namely high efficiency, a long lifetime, and low maintenance. It is evident that HB-LED drivers must be durable and efficient in order to enjoy these advantages. Moreover, to replace incandescent bulbs, the ac-to-dc HB-LED driver must be simple and have low size and comply with international regulations (i.e., injecting low-frequency harmonics into the mains supply). With the last modifications regarding low-power lighting equipment (i.e., <; 25 W), the authors have traditionally focused their efforts on increasing efficiency by sacrificing sinusoidal input current, yet all their solutions obviate the suppression of the traditional electrolytic capacitor of ac-to-dc converters, highlighting that this is the price to pay for a simple and low-size solution. This paper, however, puts forward the design of a simple and low-size ac-to-dc HB-LED driver for retrofit lamps without an electrolytic capacitor in order to extend its lifetime. The solution proposed here derives from a well-known technique used in the past, the active input current shaper (AICS), but without an electrolytic capacitor in this case. If the electrolytic capacitor of an AICS is removed, then low-frequency ripple arises at its intermediate dc bus, adding some distortion in the line input current over the proper natural one of an AICS. However, this addition is slight in comparison to the proper natural distortion of AICSs. Moreover, the low-frequency ripple at the intermediate bus is not transferred to the output with the help of the rapid output dynamic response of the AICS, which prevents flicker. This paper presents a theoretical analysis that guarantees a compromise between compliance with international regulations and the use of capacitor technologies other than the electrolytic design. Finally, a 24-W experimental prototype has been built and tested to validate the theoretical results presented in this paper.

Bridgeless canonical switching cell based PFC converter for high power LED driver

This paper deals with power factor correction (PFC) in high-brightness (HB) light emitting diode (LED) module using a bridgeless canonical switching cell (BL-CSC) converter. This application is designed for large area LED projection application with full brightness control of HB red-green-blue LED module. A PWM technique is used for brightness control of LED driver. This BL-CSC PFC converter is used to feed dual flyback DC-DC converter which supplies power to the cooling unit and the LED module with galvanic isolation. Synchronous buck converters are used for brightness control using PWM dimming technique of the multiple LED strings. The BL-CSC PFC converter is designed for discontinuous inductor current mode operation to provide natural PFC at AC mains. A working prototype of the proposed LED driver is developed for experimental verifications. The performance parameters of the proposed HB LED driver is evaluated for a full brightness control capability with high power factor at universal input AC (90–265 V). The improved power quality parameters observed at AC mains are found within the acceptable limits of international power quality standard IEC 61000-3-2.

Using the Loss-Free Resistor Concept to Design a Simple AC–DC HB-LED Driver for Retrofit Lamp Applications

Currently acknowledged as a rapidly emerging technology, high-brightness light-emitting diodes (HB-LEDs) are considered the true alternative to many mature technologies (i.e., incandescent bulbs, compact fluorescent lamps, etc.) due to their high efficiency, low maintenance, and durability. It is evident that the HB-LED driver must be durable and efficient to achieve these advantages. Moreover, in the case of replacing incandescent bulbs, the ac-dc HB-LED driver needs to be low cost and to have a high enough power factor (PF) to comply with international regulations. This paper presents a new proposal to design a simple low-cost ac-dc HB-LED driver for retrofit bulb lamps. The proposed solution originates from a very simple concept: the use of a switching-mode power supply (SMPS) acting as a loss-free resistor (LFR) connected in series with the rectified mains to shape the line input current. For the proposed application, it is obvious that the LFR needs to have a very simple topology to be economical. However, efficiency cannot be ignored. This paper proposes the flyback converter working as an LFR connected in series with the rectified mains, operating in boundary conduction mode (BCM) in order to improve its efficiency. First, a static analysis of the proposed concept will be presented. A distortion analysis of the input current of the proposed ac-dc HB-LED driver will then be carried out to test compliance with international regulations. Finally, two 12-W experimental prototypes have been built and tested in order to validate the theoretical results presented in this paper. These results show the proposed ac-dc HB-LED driver to be a low-cost high-efficiency quasi-sinusoidal input current option for designing retrofit lamps.

Hybrid-input power supply with PFC (power factor corrector) and MPPT (maximum power point tracking) features for battery charging and HB-LED driving

In this paper, a MSEBC (modified-SEPIC embedded-boost converter) is proposed, which can deal with either utility power or PV (photovoltaic) power to serve as HB-LED (High-Brightness Light-Emitting-Diode) driver and battery charger. While connected to utility, the proposed converter can perform PFC (power factor corrector) for universal line input. Once power failure occurs, it can draw energy from PV panel with MPPT (maximum power point tracking). Even if there is no utility power and PV energy, the MSEBC still can power on HB-LED from battery bank to achieve uninterruptable lighting feature. The topology of MSEBC is mainly derived from SEPIC-type converter as well as an embedded boost converter to develop a single-stage configuration, instead of multi-stage or two-stage type. Even though it only has single stage, both functions of HB-LED driving and battery charging still can be accomplished. In the MSEBC, a coupled inductor is adopted to replace the second inductor of traditional SEPIC and the chock of boost converter. A microprocessor-based controller is developed to accomplish all converter functions. A prototype, which have the functions of dealing with universal line input 85 ∼ 265 Vrms, performing power factor correction, tracking maximum power for PV panel, lighting HB-LED, and charging/discharging battery, is carried out. Key measurements have verified the feasibility, functionality, and validity.

Design-Oriented Analysis and Performance Evaluation of a Low-Cost High-Brightness LED Driver Based on Flyback Power Factor Corrector

This paper presents a new control strategy for power factor correctors (PFCs) used to drive high-brightness light-emitting diodes (HB-LEDs). This control strategy is extremely simple and is based on the use of standard peak-current-mode integrated controllers (PCMICs), reducing its cost and complexity in comparison to traditional PFC controllers. In fact, this method is an alternative implementation of the one-cycle control to PFCs belonging to the flyback family of converters, without introducing high complexity for reducing the total harmonic distortion. In this case, the use of a simple exponential compensation ramp instead of a linear one is the proposed solution for drawing a sinusoidal input current. Moreover, the line current is cycle-by-cycle controlled, and therefore, the input-current feedback loop is extremely fast, which allows the use of this type of control with high-frequency lines. The proposed idea is to apply this simple control to a one-stage PFC in order to design a low-cost ac-dc HB-LED driver. However, the application of this control strategy to PFC belonging to the flyback family of converters is not obvious. Design-oriented considerations about its implementation in PCMIC will be provided. Finally, an experimental prototype of this driver was developed.

Tapped-Inductor Buck HB-LED AC–DC Driver Operating in Boundary Conduction Mode for Replacing Incandescent Bulb Lamps

High-brightness light-emitting diodes (HB-LEDs) are recognized as being potential successors of incandescent bulb lamps due to their high luminous efficiency and long lifespan. To achieve these advantages, HB-LED ballast must be durable and efficient. Furthermore, for this specific application, ac-dc HB-LED ballast requires a high-step-down ratio, high power factor and low cost. This paper presents a tapped-inductor buck power factor corrector (PFC) operating in boundary conduction mode design for replacing incandescent bulb lamps. This low-cost solution presents a suitable high-step-down ratio without galvanic isolation in order to produce an output voltage of about 20 V from line voltage. In addition, the tapped-inductor buck PFC maintains high efficiency in comparison to other one stage solutions widely used to design low-cost ac-dc HB-LED drivers (e.g., flyback PFCs). Static analysis, input current distortion analysis, and an average small signal model of the tapped-inductor buck PFC have been implemented in this paper both to check the validity of the proposed solution and to provide a suitable design procedure of the ac-dc HB-LED driver. Finally, a 12-W experimental prototype was developed to validate the theoretical results presented.