Light-emitting Diode Driver Research Articles

A Modified Forward PFC Converter for LED Lighting Applications

A modified forward power factor correction (PFC) converter for light-emitting-diode (LED) lighting applications is proposed in this paper. The proposed circuit topology is an integration of a forward converter and a flyback converter with a multi-windings transformer. The flyback converter is operated as an auxiliary voltage source (AVS) connected in series with the rectified ac grid voltage to achieve low harmonic current distortion and high power factor. The magnetizing inductance energy is recycled to charge the capacitor in the AVS. The commonly used constant on-time control and primary side regulation can be easily adopted to control the proposed LED driver. The operation principle of the proposed converter is presented followed by the mathematical derivation of the parameter design. An 80 W prototype converter was built and tested to verify the performance of the proposed PFC converter. Experimental results show that the proposed PFC converter can comply with the IEC 61000-3-2 standard with high efficiency, low current harmonics, and a nearly unity power factor under universal input voltage range.

Estimate the Meaning-Time-To-Failure of LED driver using Numerical simulation

The Meaning-Time-To-Failure (MTTP), also known as Electromigration Analysis is an estimation of product life. Light-Emitting Diodes (LEDs) are usually driven by constant current switched-mode power supplies, which are invented early than LEDs for lighting applications. While LEDs themselves are extremely reliable and have a long lifetime, the electronic LED drivers in experiment usually fail due to overheating causing Printed Circuit Boards (PCBs) explosion, inability provide current/voltage input to the LEDs over their whole lifetime. This paper proposes a numerical simulation method to predict fault location on PCB of LED driver based on 2-way coupling electro-thermal multiphysic analysis, then applies the analytic models to calculate the time to failure of the points on PCB of LED drivers. The procedures can be applied to assist managers in assessing risk and making LED-based lighting system reliability decisions.

Electrothermal Model for Power LEDs Based on the Equivalent Resistance Concept for LED Driver Design

An electrothermal LED model for the design and simulation of light-emitting diode (LED) drivers based on the concept of the equivalent resistance is proposed in this article. The main contribution of this work is the integration of the temperature variables as the encapsulation temperature, heatsink temperature, and the ambient temperature in an electrical model based on the equivalent resistance of power LEDs. Therefore, an improved model is achieved by including these temperatures. This is because the LED temperatures are critical variables in the LED performance that could reduce the useful life of the LEDs or may even destroy them. Therefore, these temperatures must be considered in the design of LED drivers. The “equivalent resistance” concept has been previously used in the electrical modeling of power LEDs without considering the temperature variables, and this model was used to achieve fast simulations in LED-driver systems. The proposed model is oriented to the area of electronic engineering and it is recommended for the design and simulation of LED-converter systems. Experimental and simulation results are obtained that demonstrate the performance of the proposed model.

LED Current Balancing Scheme Using Current-Fed Quasi-Z-Source Converter

This article presents a novel two-channel light emitting diode (LED) current balancing method using current-fed (CF) quasi-Z-source (qZS) dc-dc converter. The proposed LED driver is simple in structure and requires minimal number of component counts. Currents flowing through the two LED strings are automatically balanced owing to charge (amp-sec) balance condition on capacitors in the CF-qZS network. Since current balancing is achieved automatically by passive components, current control of the proposed converter is very simple. In addition, the proposed circuit uses only one active switch and one diode. The operating principle and characteristics of the proposed two-channel LED driver are analyzed in detail. To verify validity of the proposed converter, 80 W prototype is built and tested.

A Variable Inductor Controlled Single-Stage AC/DC Converter for Modular Multi-Channel LED Driver

Light-emitting diodes (LEDs) are widely used in street lighting, landscape lighting, liquid crystal display (LCD) backlighting, healthcare, etc. As an important part of LED lighting products, LED driver plays a vital role in maintenance costs reduction, energy saving and lifetime prolongation. In this paper, a single-stage LED driver is proposed, which is integrated by a totem-pole bridgeless power factor correction (PFC) unit and several modular LCL-T resonant rectifiers. The totem-pole bridgeless PFC unit and the LCL-T resonant rectifiers are integrated by sharing switches, which can simplify the circuit and reduce the system cost. The output current can be regulated by applying the variable inductor control. Constant duty cycle and fixed switching frequency operation can be achieved as well. The operating principle and the performance of the proposed converter are analyzed in this paper. In addition, a precise parameter design method is proposed by considering the high-order harmonics. At last, an experimental prototype is established to validate the proposed parameter design and variable inductor control method.

Development of Four-Channel Buck-Type LED Driver with Automatic Current Sharing

A buck-type light-emitting diode (LED) driver is proposed herein. The proposed LED driver automatically possesses current sharing and high step-down voltage gain. Without complex control, the proposed LED driver, with a single input and multiple outputs, can achieve automatic current sharing of four-channel LED strings, even under the different number of LEDs of each LED string. Furthermore, as compared with the traditional four-phase interleaved buck converter with a single input and a single output having current sharing required, the proposed circuit has the duty cycle up to 0.5, not 0.25, meaning that under the same input voltage the latter has a wider output voltage range than that of the former. Above all, if the proposed circuit with N outputs, then it still has the duty cycle up to 0.5, not one over N as shown traditionally. Moreover, as compared with the current sharing based on the differential-mode transformer, the proposed circuit has no magnetic resetting loop required. In this paper, the operating principles and design considerations of the proposed converter are discussed. Finally, the theoretical analyses and performances of the proposed LED driver are verified by simulation and experiment.

A 91.15% Efficient 2.3–5-V Input 10–35-V Output Hybrid Boost Converter for LED-Driver Applications

This article presents a hybrid boost converter architecture for improving the efficiency of light-emitting diode (LED) drivers used in mobile applications. By cascading a low-switching frequency time-interleaved series–parallel switched-capacitor (SC)-stage with an inductive-boost converter, we facilitate lower voltage-rated switches, thus significantly reducing the switching losses. Charge-sharing losses of the SC stage are minimized by soft-charging flying capacitors with the inductor of the boost (BST) stage. Fabricated in 180-nm bipolar CMOS DMOS (BCD) process, the prototype converter generates 30-V output voltage from a Li-ion battery source. It can provide a load current in the range of 0–100 mA with an excellent peak power efficiency of 91.15% at 30 mA, which represents a 3% improvement over the state of the art.

A single‐stage bridgeless LLC resonant converter with constant frequency control based LED driver

In this article, a single-stage bridgeless LLC resonant converter with a constant frequency control method is proposed for a high-brightness light-emitting diode (LED) driver. LED strings require drivers with high power density and high efficiency. This article presents a novel LED driver circuit topology based on switch integration and the switching controlled capacitor (SCC) technique. By combining the merits of a totem-pole bridgeless boost PFC unit and a high frequency SCC-LLC half-bridge resonant converter, the proposed topology can achieve high efficiency. Due to the SCC-LLC circuit topology structure, constant frequency control of the LLC resonant converter is achieved by the regulation of the equivalent resonant capacitance. The proposed novel LED driver topology can automatically achieve soft-switching characteristics and a high power factor. The operating principle of different operation modes and the characteristics of the proposed LED driver are analysed in detail. Finally, to demonstrate the feature of the proposed topology, a 100 W/70 V laboratory prototype is built. The satisfactory experimental results correspond with the theoretical analysis and parameter design.

Thermally conducting yet electrically insulating epoxy nanocomposites containing aluminum@electrochemically exfoliated graphene hybrid

The development of miniaturized and highly integrated microelectronic products has motivated the current importance of synthesizing heat-dissipation materials with high thermal conductivity and excellent electrical insulation. Although graphene is attractive for improving the thermal conductivity of polymers owing to its high aspect ratio and outstanding thermal conductivity, it significantly deteriorates electrical insulation capability, limiting its practical application in polymer composites for thermal management of electronics and systems. In this work, we used planetary ball milling to synthesize a hybrid powder Al@EEG consisting of electrochemically exfoliated graphene (EEG) and surface-passivated aluminum particles. This ball milling prevents contact between graphene sheets by uniformly dispersing EEG in Al matrices without the conventional surface modification or chemical treatment process of graphene, thereby imparting thermal conductivity and electrical insulation to the hybrid powder. The resulting epoxy composite, containing 35- wt% Al@EEG hybrid, retains an electrical resistance of 1014 Ω·cm or higher and a thermal conductivity of 1.43 W m−1 K−1, which is 499% higher than that of neat epoxy. The as-designed material points the way to polymer-based, thermally conductive, electrically insulating composites for various electronic components such as printed circuit boards and light-emitting diode driver cases.

A flicker-free decoupled ripple cancellation technique for LED driver circuits

Light-emitting diode (LEDs) even though are the major lighting source, they suffer from flickering which has adverse effects on human health. With this wide increase in usage, more focus has been on minimizing the ripples, which is the root cause of flickers in LED driver circuits. Initial solution of electrolytic capacitor suffers from shorter lifetime, bulky weight, and high risk of fault. In this regard, a series current ripple cancellation (RC) technique has been proposed in this paper for flicker free operation. The key features of the proposed RC method include unity power factor (UPF) at source end, simple control, and reduced smoothing capacitance value. The proposed system has been validated in both MATLAB/Simulink environment and experimental investigations. Further, detailed analysis and comparative evaluation with the state-of-the-art work reported in the literature has been presented.

Research of the Negative Influence of Dimmed LED Luminaires in Context of Smart Installations

This article deals with the investigation of the negative impacts of dimmed public, industrial and office LED (light emitting diode) light installations. This approach is required due to the uncertain design of LED ballasts, while manufacturers do not implement the required PFC (power factor correction) function. Therefore, the focus is on a brief description of the principles of negative influences such as: low power factor, high inrush current and high total harmonic distortion based on direct confrontation with actual standards (IESC EN, NEMA, ENERGY STAR). Further, the behavior of LED drivers is explained under nominal load and dimmed up to critical level. Presented findings confirm issues reported by users from larger installations where LED fittings are dimmed over a certain level. The article includes recommendations for consumers and producers of LED fittings about main issues from the scientific and user points of view. Presented facts conclude on the necessity of studying the marginal operating state of LED fittings aiming at THD (total harmonic distortion), PF (real power factor) and inrush currents.

An Extendable Half-Bridge Dimmable Multi-Channel LED Driver for DC/DC Grid lighting Applications

In this paper, a light emitting diode (LED) driver with multiple outputs, suitable to use with DC grid supply, is proposed. The proposed LED driver provides the ability to individually control the brightness of each output channel. In order to control the output power of each channel, a burst control mode is employed resulting in reduction of conduction losses. Moreover, the half bridge switches are turned on and off at zero voltage (ZV) with a fixed switching frequency; therefore, the switching losses is reduced and efficiency is further increased. Design and implementation have been simplified by choosing the same structure of the resonant series for outputs. A two-channel DC/DC converter is simulated and tested to verify the theoretical analyses.The presented converter operates above resonant frequency to decrease total harmonic distortion and reduce the size and weight of the components. Therefore, it is suitable for high power application of multi-channel drivers.

Design of New Over-Temperature Protection Light-Emitting Diode Driver Circuit and Improvement Method of Visual Design

The overall design of light-emitting diode (LED) display control system was completed at first. For the problems of LED driver chip such as low accuracy of constant current output, high power consumption, poor stability, and single over-temperature protection function, the double temperature hysteresis and over-temperature buffer protection function of circuit were designed. The low-power constant-current module of LED driver module included an operational amplifier, a MOS tube with negative feedback control, and the driving current required to achieve high-precision reference current conversion. The temperature control points were set in hysteretic and overtemperature buffer modules for the working temperature, and power MOS tube was turned off in time to reduce the driving current to a constant driving current, thus reducing the power consumption of circuit. In addition, to improve the image quality of LED display, a visual refresh logic circuit was designed. The display cycle was divided into 32 segments by logic circuit, with 128 gray clock cycles in each segment, and duty ratio was controlled by 12 bits of gray data. In test, the multi-value output bandgap reference voltage was simulated at first. In range of –30 °C–130 °C, the fluctuation of voltage in this temperature range met the requirements of circuit. During simulation of buffer circuit of the LED driver module, it was found that output terminal can perform good voltage following, so as to meet the needs of circuit. The design of visual refresh logic circuit can greatly improve the refresh rate of pulse width modulation (PWM).

Design of a high performance AC-DC LED driver based on SEPIC topology

Light emitting diodes (LEDs) are current driven devices. So, it is essential to maintain the stability of LED voltage and current. Variation of temperature may cause of instabilities and bifurcations in the LED driver. Driving LEDs from an offline power source faces design challenges like it have to maintain low harmonics in input current, to achieve high power factor, high efficiency and to maintain constant LED current and to ensure long lifetime. This paper proposes the technique of harmonics reduction by using parametric optimization of Single ended primary inductor converter (SEPIC) based LED driver. Without optimization of SEPIC parameters input energy will not be properly transferred to the load and this un-transferred energy will be transmitted to the source. Consequently, the quality of input current will be hampered i.e. harmonics will contaminate the input current. Focussing this, the paper has presented the design of a non-isolated integrated-stage single-switch constant current LED driver operating in discontinuous conduction mode (DCM) in SEPIC incorporating the design of control circuit with soft start mechanism. This LED driver has achieved a good efficiency (90.6%) and high-power factor (0.98) with reduced harmonics (3.35%). System stability has been determined and simulation studies are performed to confirm the validity of the LED driver circuit. A laboratory prototype is built.

Comprehensive survey and critical evaluation of the performance of state-of-the-art LED drivers for lighting systems

The adoption of light-emitting diodes (LEDs) for lighting applications is becoming increasingly relevant as this recent technology is advancing. Given the recent uptake of LED lighting technologies for distinctive end-uses, the research community has also committed to the development of an ever-increasing range of power electronic converters that are suitable for yielding maximum quality lighting, high efficiency, and long lifetimes. As one of the most recent and promising technologies of the moment, it is vital to fully understand the performance and merits of each state-of-the-art LED lighting technology. Accordingly, this paper compiles essential information about a broad range of state-of-the-art LED lighting systems, aiming to compare their performances in terms of efficiency. Based on the comparative analysis, the main merits and drawbacks of each LED lighting system architecture are obtained. Then, a detailed evaluation of the performance of a particular LED lighting system and the corresponding control strategy is developed, thereby enabling a clear view of the evolution of the performance of the system as a function of parameters like supply voltage and number of driver channels.

A Novel High-Power-Factor Electrolytic-Capacitorless LED Driver Based on Ripple Port

In this article, a novel high-power-factor electrolytic-capacitorless light-emitting diode (LED) driver based on the use of a ripple port is presented. The ripple port consists of adding an extra power processing circuit at the output of the converter that injects energy to compensate for the output current and voltage ripples. In this work, the main converter is built by using a flyback converter operating in the discontinuous conduction mode (DCM). The ripple port is implemented by adding an extra winding to the flyback coupled inductors, together with an extra switch, a capacitor, and an inductor. The additional switch is used to inject energy to the output in the time intervals, in which the flyback output current is low, thus reducing the output current ripple. The proposed converter is analyzed in detail, and a design methodology is proposed. A design example for a 27-V/1-A LED lamp is presented. Simulation and laboratory experiments have also been carried out. It is demonstrated that the proposed solution can achieve a reduction on the output current ripple of around 65% compared to the solution without ripple port for the same total capacitance and maintain a high power factor of 0.994.

Digital Fuzzy Current Controlled Light-Emitting Diode Driver with Power Factor Correction

This paper presents the design and development of a fuzzy peak current controlled (FPCC) single-stage single-phase nonisolated AC/DC high-power factor LED drive. The proposed controller includes a fuzzy logic controller (FLC) in the loop voltage and a peak current controller in the loop current for an integrated nonisolated LED driver to attain a high-power factor (PF). The proposed control avoids complexities related to nonlinearities of the converter. The control action is initially derived from a group of rules written in accordance with experience and intuitive reasoning. The proposed technique is realized using a DSP processor (TI-TMS320F2812), which is capable of executing a high number of instructions in one cycle. A 70 W, 350 mA LED driver operating with an input of 90 V-230 V, 50 Hz was designed and implemented using MATLAB/Simulink. The results of the driver are in accordance with international regulations. The steady-state and transient responses are validated experimentally.

Fuzzy self-tuning PID control of MC3 LLC resonant LED drivers

An MC3 LLC resonant light-emitting diode (LED) driver is a multi-channel constant current (MC3) output solution based on LLC resonance. Through an effective combination of multiple transformers and a DC block capacitor, this driver allows constant current outputs in multiple channels when the LED channels are unbalanced. This study considers a fuzzy self-tuning proportional integral derivative (PID) control strategy that allows for the self-tuning of PID parameters according to fuzzy inference rules designed using the relationship between the current gain and the switching frequency. Thus, when LED channels are unbalanced, the system allows a constant current output for each of the channels and controls the input voltage disturbances well. Simulation and experimental verifications are carried out, and a 20 W 4-channel constant current power supply design based on LLC resonance is obtained for the LED driver. This realizes soft-switching of the switching device, which reduces system loss and improves system efficiency. Moreover, the adjustment time of the proposed method is half that of fixed-parameter control methods, and the overshoot of the proposed method is smaller than that of fixed-parameter control methods. When compared with PID controllers with fixed parameters, the proposed method is more robust. When a system is disturbed, it recovers faster and has a smaller range of current fluctuation with the proposed method.

Electrical model formulation for multicolor light‐emitting diode modules and its application to design dimmable driver

SummaryA multicolor light‐emitting diode (LED) module comprises LED chips of more than one type or color and is frequently used for spectrally tunable lighting applications. In this paper, electrical models of such multicolor LED modules are formulated taking two basic circuit configurations into account, namely, (i) conventional, where a parallel string is made of one particular LED type, and (ii) nonconventional, where a parallel string is composed of different LED types. For deriving the model equations, the basic exponential model of a single LED chip has been applied, which is experimentally found to be the suitable option out of the four existing models, namely, linear, parabolic, exponential, and modified Shockley models. The formulated models are experimentally validated, results of which show maximum deviations of 4.71% and 4.19% from the measured data in the nonlinear and the linear operating regions, respectively. The formulated models are utilized to design dimmable, isolated LED drivers for red‐green‐blue (R‐G‐B) LED module. Performance evaluation of the drivers is conducted in Matlab‐Simulink. The results reveal the satisfactory operation of the LED modules in terms of current and power regulation, branch current matching, and fast response and thus establish the effectiveness of the proposed algorithm.

Quasi‐constant bus voltage CrCM boost PFC fed LLC resonant converter in high power LED lighting systems

SummaryThis paper deals with a two‐stage LED (light emitting diode) driver on the basis of front‐end boost converter operating in critical conduction mode (CrCM) and second stage LLC resonant converter for driving an LED lighting load. The boost converter operates in the valley switching mode to reduce switching power loss with less component stress. The ZVS (zero voltage switching) operation of both the half‐bridge semiconductor switching devices reduces the switching losses, which improves the system efficiency. Moreover, to ensure the stability of the DC‐bus voltage, state‐space analysis is also carried out for the CrCM boost converter. The first stage provides the power factor correction (PFC) over the universal AC mains and maintains a constant DC‐bus for the next stage. The second‐stage converter maintains a ripple‐free output voltage to an LED load. This circuit has reasonably minimized the design complexity as compared with single‐stage variable DC‐bus PFC integrated resonant converters and also gives improved efficiency in an isolated configuration. In order to validate the system, a 150‐W prototype is investigated, and experimental findings are analyzed in‐line with theoretical results at universal AC mains.