LED Strings Research Articles

Optimization for Spectral and Power Characteristics of Bicolour LED Driver

LED-powered luminaires have the ability to offer cutting-edge features like temperature adjustment and color management. Color shift creates discomfort in human eyes. So it is essential to design a LED driver which will precisely control the color parameters of the LED driver. Precise control of color parameters like CRI, CCT, color intensity is very complex and challenging. This paper describes the nonlinear optimization methodology for the design of blended LED light sources. This paper presents the methodology that enables LED strings regarding various parameters, e.g. high color rendering index (CRI) and high luminous efficacy of a blended bi-color (namely red CCT-2500K and blue CCT-9000K) LED driving system. Due to the applied optimization, the obtained CRI is maintained 98.03%. The overall luminous intensity depends upon the combined luminous flux which depends upon the current control of both LED sources. These optimized LED currents ensure the desired CCT. The achieved luminous efficacy is 90% at two optimal peak wavelengths 601 nm and 426 nm respectively. Power loss is minimized by frequency optimization. At the same time power parameters i.e. low THD and high P. F. is also maintained. The nonlinear optimization is verified in Ltspice simulations and experimentally for two different luminaire strings.

Considerations on Practical Implementation of Current Source Mode Single-Inductor Multiple-Output LED Driver

There are many possible LED lighting applications where separate regulation of the LED current (luminous flux) of individual LED strings would be desirable—specialized variable correlated color temperature lights for ambient lighting, decorative lighting, surgical lights, horticultural lights, etc. Separate regulation of the current or light flux of individual LED strings is associated with a known problem: the necessity of using a controllable LED driver for each string, which increases the total component count, overall system complexity and costs. One of the possible solutions—a current source mode single-inductor multiple-output LED driver—was discussed in previous different papers. However, the practical implementation of this solution was not discussed in detail. This article aims to correct this omission.

RED FOX-BASED FRACTIONAL ORDER FUZZY PID CONTROLLER FOR SMART LED DRIVER CIRCUIT

Recently, traditional lighting has been replaced by high-power LED (HPLED) due to its significant developments, prolonged lifetime, high brightness, high reliability, and high energy efficiency. Even though conventional converters can precisely match each LED's current, they have some limitations when driving a long string of LEDs. To solve this issue, this paper presents a novel red fox optimized fractional order fuzzy PID Controller (RF-FOFPID) based high gain improved transformerless dc-dc (ITDC) boost converter for a smart LED driver circuit with optimal voltage regulation capability. The error bias is increased to zero by applying FOPID to the fuzzy logic-based compensation steps. The Red Fox optimization algorithm is used to adjust the control parameters of the fractional-level fuzzy PID controller with higher precision to solve limited problems with diverse search spaces. The Simulink model of the proposed converter was created using the MATLAB software tool Simulink and compared with controllers using fractional order PID, fuzzy PID, and conventional proportional integral derivative (PID). The results demonstrated that in terms of minimum overshoot, settling time, rise time, and steady-state error, the proposed converter based on RF-FOFPID outperforms current converters in voltage regulation.

Single‐stage triple‐output Cuk power factor correction converter

SummaryTraditional multiple‐output AC‐DC power supply with power factor correction (PFC) function usually employs a two‐stage cascaded topology that is composed of prestage PFC converter and N independent poststage DC‐DC converters to achieve PFC and voltage or current regulation of N outputs. Hence, the conventional two‐stage cascaded multiple‐output AC‐DC power supply needs N + 1 magnetic components as power inductors or transformers and N + 1 controllers, which increases the cost and size of the multioutput converters. The conventional multiple‐string AC‐DC LED driving circuits usually employ a two‐stage topology to realize PFC and independent current regulation of each LED string. To address the issue of complexity, high cost, and large size of the two‐stage multistring LED driving circuit, a single‐stage triple‐output Cuk PFC converter is proposed by cascading boost converter and single‐inductor triple‐output buck converter with sharing main power switch in this paper. The topology operation principle, control strategy, design consideration, and operation characteristics of the proposed circuit are investigated in detail. With the switch sharing and inductor multiplexing technologies at the same time, the proposed converter utilizes only single‐stage converter to achieve PFC function, independent regulation of triple‐channel output current, and flicker‐free with low twice line frequency LED current ripple. The proposed converter is verified by a 50‐W experimental prototype of LED driver for triple string LEDs. The proposed converter only uses two power inductors and a set of controller to achieve greater than 0.945 PF, up to 90.5% efficiency, low LED current ripple, and independent current regulation for triple LED strings with different forward voltage, which may significantly reduce the cost and size of the traditional AC‐DC multistring LED driving circuit.

A High Power Factor LED Driver with Intrinsic Current Balancing Capability

The research proposed a novel LED driver with the functions of power-factor correction (PFC) and current balancing. A flyback converter and a Class-D series resonant converter were integrated by sharing an active switch to form a single-stage circuit topology. The flyback converter played the role of a PFC circuit. The component parameters were designed to make the flyback converter to operate at discontinuous-conduction mode (DCM). In this way, the input line current can be sinusoidal, resulting in near unity power factor and low total harmonic distortion in current (THDi). The resonant converter was connected in series with a differential-mode transformer with a turns ratio of 1 to drive four LED strings. The current of the four LED strings will be automatically and evenly balanced by using the 1:1 transformer. This article analyzed the different modes of operation in detail, derived the mathematical equations and designed the parameters of the circuit components. Finally, a 72-W prototype LED driver was implemented and tested. A satisfactory performance has verified the feasibility of the proposed LED driver.

Long Life Power Factor Corrected LED Driver with Capacitive Energy Mechanism for Street Light Applications

Conventional switch-mode LED drivers have problems such as poor performance in harmonic distortion, flickering, power factor correction, stresses on the switches, high switching losses, large size, and high cost. To resolve these problems, we propose a long-life LED driver with the ability of power factor correction. The proposed system is based on the integration of a half-bridge LLC resonant converter and two boundary-conducted boost converters. Both boost converters share a common inductor designed in such a way that both boost converters work in boundary conduction mode to attain the natural power factor correction. Half-bridge LLC resonant converter has soft switching characteristics, which assure the zero-voltage switching (ZVS) of primary-side switches and zero-current switching (ZCS) of diodes on the secondary side. This significantly reduces switching losses and improves the overall efficiency of the system. Voltage divider capacitors are used on the input side, which minimizes the bus voltages. The proposed system has two identical secondary windings with a coupled inductor to eliminate the mismatch between them, which powers two independent LED strings. The simulation of a 100-watt 240 V AC converter yields the approximate sinusoidal shape of the input current. It shows that the switches on the primary side are operated in ZVS and the diodes in ZCS. At 240-volt AC input, the efficiency is 87.4%, the total harmonics distortion (THD) is 10.98%, and the power factor (PF) is 0.98.

Single‐immittance‐network‐based inductive‐power‐transfer systems for driving multistring lighting‐emmiting diodes with current balance

Multistring arrays of LED in parallel connection are widely applied in lighting fields. Active control and passive methods are utilized to guarantee equal current sharing between different strings with a common voltage source. Compared with active control, the passive methods that adopt purely passive components without real power dissipation are good candidates. Currently, an inductive power transfer (IPT) converter providing a constant voltage (CV) line, followed by some immittance networks that convert the CV line to constant current (CC) outputs, is commonly used to drive multiple LED strings. However, in such a two-conversion-stage scheme, the component count is as many as 3 × N $$ 3\times N $$ , where N $$ N $$ is the number of LED strings, which deviates from compact, low-cost, and simple design ideas. To address it, this paper aims to develop a single-immittance-network-based IPT system to drive multistring LEDs with the current balance. The proposed IPT system can directly provide a CV to CC conversion to drive multistring LEDs with the benefits of simplifying the circuit design, size, and cost. The proposed IPT system also features programmable luminous power, zero-phase-angle (ZPA) input, IPT technology, and load-independent-current (LIC) output. Detailed analysis, implementation, and experiment are presented in this paper.

Fully Decoupled Current Control and Current Balancing of the Modular Structure for LED Color-Mixing System

For LED color-mixing, the different color LEDs need to be controlled independently, so a fully decoupled current control and current balancing of the modular structure is proposed for LED color-mixing system. The capacitive current-balancing structure is combined with the quasi-boost converter to realize the decoupled current control and current balancing in each module. The capacitive current-balancing structure is based on the relative reactance of the capacitor with respect to the equivalent resistance of the associated LED string. The inductor in quasi-boost converter is used to further stable the output current flowing through each LED string, and the switch in quasi-boost converter for controlling the current of each LED string adopts the parallel connection to protect LEDs from the current-spike caused by the switch. The structure is modularity and scalability so that the different color LEDs can be added and removed easily. Compared with SIMO (Single-Inductor-Multiple-Output) structure, the proposed structure has no cross-coupling issues. The LED string currents working with PWM mode have a good current-balancing performance since the equivalent resistance of LED string is much smaller than the reactance of capacitors. In addition, the resonant capacitors separate the grounds of the power source and LED strings, so all the switches in parallel with LED strings do not need the isolated gate drivers. A prototype with RGB modules has been built and evaluated, and the experimental results have a good agreement with the theoretical analysis.

Design Optimization of an Efficient Bicolor LED Driving System

There are some challenges involved in the design of a multicolor LED driver, such as the precise control of color consistency, i.e., maintaining the correlated color temperature (CCT) and luminous intensity. CCT deviation causes a color shift of composite light. This paper approaches the method of nonlinear optimization of the LED currents of two LED sources to achieve the desired CCT. A bicolor blended-shade white LED system is formed by using a warm color LED source of 1000 K CCT and a cool color LED source of 6500 K CCT. By using a nonlinear optimization methodology, the reduced deviation of the blended CCT and optimum LED currents are obtained. The optimized currents in the two LED strings are maintained by the control circuit of the single-ended primary inductor converter (SEPIC). The obtained reduced deviation of the CCT is 43 K, and the precision is 99.15%. Again, harmonics in the input current hamper power quality, i.e., reduce the power factor and increase power loss. This paper proposes the harmonic reduction technique to achieve the lowest value of total harmonic distortion (THD) through the nonlinear parametric optimization of the SEPIC. Measured THD = 4.37%; PF = 0.96; and efficiency = 92.8%. The system stability was determined and found to be satisfactory.

Load-Independent Hybrid Resonant Converter for Automotive LED Driver Applications

In this article, a hybrid resonant LED driver for automotive illumination applications is proposed. The employed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> resonant network provides load-independent output current characteristic and accomplishes full soft-switching operation of the semiconductor devices within the desired input voltage range. To provide constant frequency operation and nonpulsating input current, a continuous conduction mode boost structure is merged into the resonant network. Also, the analog dimming capability range of 50%–100% is attained for the LED string by adjusting the main switches operating duty cycle. Detailed theoretical analysis of the proposed LED driver is presented. To verify the analysis and effectiveness of the proposed topology, a 40-W laboratory prototype is designed and implemented for the input voltage range between 8–18 V.

Four-Channel Buck-Type LED Driver with Automatic Current Sharing and Soft Switching

A buck-type LED driver together with automatic current sharing and high step-down voltage conversion ratio but without complex control is proposed. The proposed LED driver can not only achieve zero voltage switching (ZVS) turn-on by adding only one resonant coupled inductor, which resonates with parasitic capacitors of active switches, but also can obtain lower voltage gain and better conversion efficiency. In this paper, the operating principles and design considerations of the proposed converter are discussed in detail. In addition, the number of LED strings can be extended to more than four channels. Finally, the theoretical analysis and performance of the proposed LED driver are verified by simulations and experiments using a field-programmable logic gate array (FPGA) named EP3C5E144C8N as a circuit control kernel.

GÜÇ FAKTÖRÜ VE FLICKERI DİKKATE ALAN BİR TEPE AKIM MODU KONTROLLÜ SEPİC LED SÜRÜCÜ TASARIMI

In this paper, a peak current mode controlled single ended primary inductor converter (SEPIC) LED driver is proposed to control the brightness of the LED. One string of 37 series connected LEDs is adopted as output of the circuit. The proposed control strategy is based on measuring MOSFET peak current value using a shunt resistor. When this voltage reaches peak threshold value, controller turns off MOSFET. The output current is adjusted to desired levels by changing this peak threshold value. The power factor in the AC power supply side is low because of the full wave bridge rectifier with capacitor filter at the input of the converter. The proposed control strategy is applied with power factor correction (PFC) circuit where input voltage is multiplied by control voltage to achieve high power factor. In PFC circuit, although the line current waveform is slightly distorted due to voltage limitations in integrated circuit (IC) chip used for the proposed control strategy, power factor is kept above 0.9 for operation region between 100mA-300mA. In addition, flicker on LED string is measured for operating current region and flicker limits are revealed. Adjustable output current levels, low flicker on LED string, MOSFET peak current control at each cycle, fast output dynamics, and high power factor are acquired by the proposed control strategy.

Precise Luminous Flux and Color Control of Dimmable Red-Green-Blue Light-Emitting Diode Systems

A generic red, green, and blue (RGB) LED system encompasses complex interactions of power, heat, light, and color, which pose a major challenge for achieving precise control over luminance and color-mixing in high-quality lighting applications. In this article, new nonlinear empirical models of a practical RGB LED system with closed-loop control are formulated. They enable precise prediction of luminous flux and color coordinates by using the three distinct reference voltages as the control variables for independent current regulation across the RGB LED strings. The proposed empirical models are experimentally verified by using a hardware prototype of a dc–dc single-inductor three-output LED driver with proportional–integral compensators and time-interleaving control scheme. The measured values of luminous flux and color coordinates agree closely with the predicted values from the models.

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.

Bridgeless Isolated AC LED Driver

A novel bridgeless isolated AC LED driver is developed, which improves LED utilization and application flexibility due to a coupled inductor inserted between the bidirectional switch and the LED module without any output electrolytic capacitor. By reducing the turns ratio of the coupled inductor, the voltage across the secondary side will be decreased so as to lessen the voltage across the LED strings and hence reduce the number of LEDs, thereby making the load design of the AC LED driver more flexible. It is noted that the coupled inductor plays a role of not only galvanic isolation but also inductor behavior as well as transformer behavior. Therefore, during the turn-on period of the bidirectional switch, the coupled inductor can transfer the energy to one LED string and store the energy simultaneously, whereas during the turn-off period of the bidirectional switch, the coupled inductor can release the stored energy to the other LED string. That is, two LED strings are conducted over a pulse-width-modulated (PWM) period for any half-cycle, implying that LED utilization is upgraded. As for LED dimming, it is realized by directly tuning the control signal for the bidirectional switch without any dimming circuit. Eventually, the basic operating principles and theoretical deductions are given along with some experimental results provided to verify the effectiveness of the proposed AC LED driver topology.

A high-power PCCM LED driver based on GaN eHEMT with hybrid dimming modes

PurposeThe purpose of this study is to design a more flexible and larger range of the dimming circuit that achieves the independence of multiple LED strings drive and can time-multiplex the power circuit.Design/methodology/approachThe state-space method is used to model the BUCK circuit working in Pseudo continuous conduction mode, analyze the frequency characteristics of the system transfer function and design the compensation network. Build a simulation platform on the Orcad PSPICE platform and verify the function of the designed circuit through the simulation results. Use Altium Designer 16 to draw the printed circuit board, complete the welding of various components and use the oscilloscope, direct current (DC) power supply and a signal generator to verify the circuit function.FindingsA prototype of the proposed LED driver is fabricated and tested. The measurement results show that the switching frequency can be increased to 1 MHz, Power inductance is 2.2 µH, which is smaller than current research. The dimming ratio can be set from 10% to 100%. The proposed LED driver can output more than 48 W and achieve a peak conversion efficiency of 91%.Originality/valueThe proposed LED driver adopts pulse width modulation (PWM) dimming at a lower dimming ratio and adopts DC dimming at a larger dimming ratio to realize switching PWM dimming to analog dimming. The control strategy can be more precise and have a wide range of dimming.

A Novel Single-Switch Single-Stage LED Driver with Power Factor Correction and Current Balancing Capability

A novel single-switch single-stage high power factor LED driver is proposed by integrating a flyback converter, a buck–boost converter and a current balance circuit. Only an active switch and a corresponding control circuit are used. The LED power can be adjusted by the control scheme of pulse–width modulation (PWM). The flyback converter performs the function of power factor correction (PFC), which is operated at discontinuous-current mode (DCM) to achieve unity power factor and low total current harmonic distortion (THDi). The buck–boost converter regulates the dc-link voltage to obtain smooth dc voltage for the LED. The current–balance circuit applies the principle of ampere-second balance of capacitors to obtain equal current in each LED string. The steady-state analyses for different operation modes is provided, and the mathematical equations for designing component parameters are conducted. Finally, a 90-W prototype circuit with three LED strings was built and tested. Experimental results show that the current in each LED string is indeed consistent. High power factor and low THDi can be achieved. LED power is regulated from 100% to 25% rated power. Satisfactory performance has proved the feasibility of this circuit.

Voltage Regulation and Power Consumption Analysis of LED Driver using Switched String Method

This paper discusses an AC/DC buck converter-based LED driver to reduce the voltage from 230VAC to 12VDC with a few strings of LEDs. This led driver is designed with a cost-effective circuit because using a single inductor, single inductor multiple-output (SIMO) can reduce the number of components, control the current independently and precisely on each LED string simultaneously, compared to using an inductor on each LED string. To control current and voltage, PWM (Pulse Width Modulation) control is used as a MOSFET signal switch. This MOSFET calculates the duty cycle so that the desired DC output according to the LED specifications can be realized. The circuit was analyzed using PSpice software. The test based on the duty cycle shows that the highest output voltage is obtained with a work cycle of 10% resulting in a voltage of 5.9V and a current of 32.4mA. Meanwhile, achieving the output value based on the led specification with a voltage of 12V and a maximum current of 31mA has been achieved at a duty cycle of 4.7%. This AC/DC buck converter circuit not only lowers the voltage but can overcome dimming and provide a uniform light output on each LED with an output voltage of 12VDC. The experimental results show that this AC/DC buck converter circuit has been tested and can be applied to the Led driver system.

A Two-Stage Automotive LED Driver With Multiple Outputs

This article presents a two-stage automotive LED driver architecture delivering independently regulated output currents to multiple LED strings. The system consists of a multiphase noninverting buck-boost front-end stage, which allows for a wide battery voltage range, followed by high-frequency immittance-network-based LCL-T resonant converters, which operate as current sources over wide output voltage ranges. The two-stage buck-boost + resonant (BB+resonant) architecture takes advantage of the buck and boost capability of both stages, and the flexibility in setting the intermediate bus voltage to minimize losses. Advantages of the BB+resonant architecture include the use of lower voltage rated devices and soft switching in the resonant stage, leading to reduced losses and size. Experimental results are provided for a prototype consisting of a 250-kHz two-phase front-end stage and 2-MHz LCL-T resonant stages delivering independently regulated 1 A currents to four LED strings with N = 1$-$ 18 LEDs. The measured system efficiency is greater than 88% over wide input (8$-$18 V) and output (3-50 V) voltage ranges, with a peak efficiency of 93%.

An Efficient Color LED Driver based on Self-Configuration Current Mirror Circuit

The string channel of Color LED driver with precise current balancing is proposed. It is noted that to drive a multiple LEDs string is by using a proper current source, due to the level of the brightness LED depends on the quantity of the current flows. In the production of LEDs, the variation in the forward voltage for each LED has been found significantly high. This variation causes different levels of brightness in LEDs. Then, controlling load current of LED by using a resistor to limit the LED current flowing is considered by associated with the forward voltage, instantly. Current sources have been designed to become immune to the above problem since it regulates the current, and not the voltage which flows through the LEDs. Hence, constant current source is the essential requirement to drive the LEDs. Besides, it is complex for color LEDs, dependent on the number of control nodes and dimming configuration. To arrange an accurate load current for the different sets of string color LEDs, the efficient LED driver is required, in which the current sharing is complement to each LED strings. Therefore, this paper suggests a color LED driver with self-configuration of enhanced current mirrors in multiple LED strings. The load currents have been efficiently balanced among the identical loads and unequal loads. The comparable efficiency of the string color LEDs losses has been shown thoroughly.