Pulse Width Modulation Dimming Research Articles

Reverse polarity optical Orthogonal frequency Division Multiplexing for High-Speed visible light communications system

The radio frequency spectrum, which has been steadily getting smaller, is under pressure from growing cellular data traffic. A more dependable communication channel is required. To setup the communication medium, VLC uses LED illumination. In order to increase network throughput, the goal of this study is to analyze and model signal conditioning techniques in the visible spectrum. VLC technology offers synchronized illumination of LED lamps as well as wireless broadband connectivity. Using the real-valued O-OFDM baseband signal, optical orthogonal frequency division multiplexing (O-OFDM) offers a viable modulation option for very-low-bit-rate (VLC) systems to modulate the optical carrier's instantaneous power to attain gigabit data rates. However, one important design difficulty preventing VLC from being commercialized is how to combine industry-favored pulse width modulation (PWM) dimming technology while retaining a dependable, broadband connection. In this paper, Reverse Polarity optical orthogonal frequency division multiplexing (RPO-OFDM) is proposed as a new signal format for combining the fast O-OFDM contact signal with the comparatively slow PWM dimming signal, as both signals contribute to the illuminative brightness of the LED. The average SNR, additional testing demonstrates that the suggested method outperforms the Asymmetrically clipped optical OFDM (ACO), Optimized Flipped Optical (OFO) and DC biased optical OFDM (DCO), and algorithms in similar operating conditions.

An Approach to Improve Energy Efficiency during Antimicrobial Blue Light Inactivation: Application of Pulse-Width Modulation Dimming to Balance Irradiance and Irradiation Time.

Antimicrobial blue light (aBL) is an effective non-destructive inactivation technique and has received increasing attention. Despite its significance, the existing research has not thoroughly delved into the impacts of irradiance and irradiation time on enhancing energy efficiency during aBL inactivation and the explanation of the enhancement effect of pulse exposure. In this paper, a series of Escherichia coli inactivation experiments with different duty cycles, pulse frequencies, and irradiation times were conducted, and the relative concentrations of reactive oxygen species (ROS) were measured under corresponding conditions. A two-dimensional (2-D) Hom model was proposed to evaluate the effect of irradiance and irradiation time. The results show that, compared to continuous exposure, pulsed aBL (duty cycle = 25%) can save ~37% of the energy to achieve the same inactivation effect and generate a 1.95 times higher ROS concentration. The 2-D Hom model obtains the optimal combination of average irradiance and time according to the desired reduction and shows that the irradiation time has a higher weight than the irradiance (1.677 and 1.083, respectively). Therefore, using pulse exposure with a lower average irradiance for a longer period of time can achieve a better inactivation effect when consuming equivalent energy. The proposed pulse-width modulation dimming approach helps promote the application of the aBL technique.

Design of smart light source based on bi-color LED with single duty cycle for correlated color temperature adjustment

Color-adjustable light sources facilitate both mood lighting and daylight harvesting. A single duty cycle can be used by a bi-color LED to adjust the correlated color temperature (CCT) by associating it with the duty cycle of the pulse width modulation dimming signal of the cool and warm white LEDs. The one-to-one mapping relationship between the single duty cycle and the CCT is based on the color mixing theory of bi-color LEDs. A method to correlate the dimming signals for bi-color LEDs is presented. The influence of the time characteristics of the two basic signals on dimming and CCT adjustment is analyzed. The dimming system of bi-color LEDs is designed, and the method used to adjust the CCT with a single duty cycle is verified. The experiment showed that the CCT can be accurately adjusted by the proposed method.

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%.

A High-Power LED Driver Based on Single Inductor-Multiple Output DC–DC Converter With High Dimming Frequency and Wide Dimming Range

This article proposes an LED driver circuit which is wide-range continuous dimmable for high power lighting application. The proposed LED driver is based on single-inductor–multiple-output (SIMO) dc–dc converter. A pulsewidth modulation (PWM) control strategy is applied on the LED driver to control the brightness of LEDs flexibly and precisely, with which the dimming frequency can be increased significantly, and the dimming ratio for all branches can be adjusted separately. PWM dimming would cause the inductor current overshooting when dimming switch alters from off to on , which makes the LED current varying. To suppress the inductor current overshooting, a sampling–holding circuit is adopted in the feedback loop of the proposed LED driver. A prototype of the proposed LED driver is fabricated and tested. The measurement results show that the dimming frequency can be increased to 10 kHz, the dimming ratio can be set from 5% to 100% with a minimum pulsewidth of 5 $\mu$ s, and the inductor current overshooting is suppressed from 150% to approximately 0%. The proposed LED driver can output more than 80 W and achieve a conversion efficiency of 97%.

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

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%.

Analysis, design, and experimentation of the active hybrid‐series‐parallel PWM dimming scheme for high‐efficient off‐line LED drivers

This study presents a high power factor (PF) light-emitting diode (LED) driver featuring a pulse width modulation (PWM) dimming technique. The integrated buck-flyback-buck converter (IBFBC) is built by connecting a buck converter to the integrated buck-flyback converter's output. The IBFBC ensures a constant output current regulation as well as high PF at all dimming ratios. The purpose of the output buck converter is to clear up the discontinuous power operation created by the PWM dimming. This occurs when the buck converter absorbs the output power, at LED switched-off, and sends it back to the input. Thus, the IBFBC maintains the operational enhancement shown by the hybrid-series-parallel (HSP)-PWM technique, ensuring greater efficiency. This study explains the operating principles of the IBFBC using circuit diagrams as well as an average model for the entire converter. Moreover, the study presents a mathematical analysis of the IBFBC power flow. It provides guidance on how to select the optimum value for the output buck inductance. A 230V, 50Hz input, 160V output, 100W AC-DC converter operating at 100 kHz has been implemented. The prototype is fully tested to demonstrate the active HSP-PWM technique. An efficiency ranging 50-86% corresponding to the dimming ratio of 5-100% is reached, where 5% dimming refers to an output power of 4W.

Peak Current Control of Multichannel LED Driver With Selective Dimming

A novel selective dimming method of the output channels of a multichannel LED driver is proposed in this paper. This LED driver comprises a front-end ac-dc boost power factor correction converter followed by symmetric half-bridge isolated nonresonant dc-dc converter and symmetric voltage-multiplier rectifier with purely capacitive output filters. By controlling the duty ratios of the secondary side switches, which are strategically placed at the output voltage-multiplier-based rectifiers, the average LED current and hence the brightness of individual channels are controlled. Moreover, a unique primary side peak current control is implemented to control the peak currents of LEDs during pulsewidth modulation dimming, which prevents electromigration-related fast aging of the LEDs. This driver also has the advantages of high power (>120 W) operation capabilities, and high efficiency (>94%) with primary side switches zero voltage switching turning on and secondary side rectifier diodes zero current switching turning off. A detailed analysis and design procedure of the proposed converter is presented. To validate the analysis, an industry-standard 150 W prototype is developed, which is digitally controlled by a cost-effective non-DSP microcontroller. The experimental results are in perfect agreement with the claims. A comparison for universal ac input and isolated LED drivers with selective dimming is displayed.

Voltage-Controlled GaN HEMT-LED Devices as Fast-Switching and Dimmable Light Emitters

This letter reports a novel voltage-controlled light emitter with fast switching speed and dimming capability using a monolithically integrated GaN HEMT-LED device. The integrated HEMT-LED device, with a transconductance of 113 mS/mm and large light emitting area ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$450\times 470\,\,\mu \text{m}^{2}$ </tex-math></inline-formula> ), exhibits a fast switching speed of 15 MHz. When functioning as an optical transmitter, a data rate of 16.7 Mbit/s was demonstrated. By reducing the duty cycle of the pulsed gate voltage from 100% to 0.1%, the light intensity decreased accordingly, and a linear pulse-width modulation dimming performance with a wide dimming range (0.1%–100%) and high dimming ratio (51 282:1) was achieved.

Analysis and Experiments on a Single-Inductor Half-Bridge LED Driver With Magnetic Control

This paper presents the analysis and experiments of a variable inductor (VI) based LED driver for dc grid lighting applications. The proposed driver requires only a series inductor and a transformer as major components to drive the LED lamp from a half-bridge inverter. By introducing a VI as the series inductor, the LED current can be controlled independently from any other parameter, which makes it possible to drive and regulate several LED branches from the same half-bridge output. Other advantages of the proposed converter include inherent open-circuit and short-circuit protections, zero-voltage switching for the bridge transistor and zero-current switching for the output rectifier diodes, simple dynamics, possibility of analog and pulse width modulation dimming, constant switching frequency operation, and high efficiency. The converter is thoroughly analyzed and modeled for both steady-state and dynamic operation. As another novelty of this paper, the dynamic response of the VI has been studied and taken into account to obtain the complete transfer function of the VI-controlled system. In addition, some housekeeping issues that usually arise when dealing with VI, e.g., how to drive the VI bias winding, are solved in this work. Experimental results provided from a 50 W laboratory prototype demonstrate the correctness of the performed analysis and the good possibilities of the proposed converter.

Power quality improvement using bridgeless‐Landsman converter for LED driver

This study presents a bridgeless-Landsman converter for power factor correction (PFC) of light-emitting diode (LED) driver. It is targeted for high brightness LED driver with pulse-width modulation dimming for brightness control. This PFC converter is used to feed dual output flyback DC–DC converter which supplies power to the LED module and forced cooling unit with galvanic isolation. The brightness control of LED is performed by three independent synchronous buck converters. The PFC converter is designed to operate in discontinuous input inductor current mode for inherent PFC at universal AC mains. A prototype of the proposed PFC LED driver is developed to validate experimentally the design and model. The power quality indices of the proposed LED driver are evaluated at rated and light load conditions for universal AC mains (90–265 V) with brightness control. The power quality indices are found within acceptable range of international harmonic standard IEC 61000-3-2 for universal AC mains.

Design of an energy-saving controller for an intelligent LED lighting system

In this paper, we present an energy-saving controller that is capable of shaping the light output of an LED lighting system autonomously based on data received from sensors. We implement an optimized smart algorithm on a controller to process the sensor feedback and employ pulse width modulation dimming to vary the brightness of the luminaire. A wireless sensor module was designed to provide accurate sensor feedback to the controller. A purpose-built smart luminaire complete with an LED driver was designed and constructed to study the performance of the control system. We validate the energy saving potential of the designed controller under different real world situations. It is shown experimentally that the controller achieved 55% energy savings in a continuous usage pattern environment and 62% energy savings in a discrete usage pattern environment under our test conditions. A cost analysis showed that the proposed energy-saving system is 32% more cost-effective than a near-equivalent commercial system while promising greater energy savings through the use of additional energy-saving techniques.

Reducing the stroboscopic effects of LED luminaires with pulse width modulation control

Pulse width modulation for dimming the light output of LEDs has become common. When pulse width modulation is used at low frequencies unwanted visual artefacts including flicker perception and stroboscopic effects may occur. These artefacts need to be avoided or at least reduced to a minimum in order to obtain high user acceptance. In this paper, an optimized phase-shifted pulse width modulation method is described, implemented and validated in a visual experiment. The method is intended to minimize the stroboscopic effect on a reference surface by first optimizing the LED units of a single LED luminaire and then co-optimizing several of these luminaires. The optimized pulse width modulation waveforms are then compared to standard pulse width modulation dimming methods. In the visual experiment, 13 subjects rated the extent of the stroboscopic effect of standard and optimized waveforms in a white painted experimental room. The results indicate that the optimized waveforms are indistinguishable from constant light.

Fixed‐frequency adaptive off‐time controlled buck current regulator with excellent pulse‐width modulation and analogue dimming for light‐emitting diode driving applications

This study presents an ideal synchronous buck current regulator for variety of light-emitting diode (LED) loads from wide input voltage range. By using high-side power switch matched sense, the regulator maintains high current accuracy and high system efficiency. The adjustable current sense threshold provides a full-range analogue dimming and the fast output enable/disable function allows for high-frequency pulse-width modulation (PWM) dimming. In addition, the two dimming methods are easy to implement and have highly linear range. An adaptive off-time control is adopted to regulate an accurate constant current for its fast response and no need for control loop compensation, while its disadvantage of variation of switching frequency is overcome. The proposed circuit has been fabricated with 0.35 μm 40 V bipolar-CMOS-DMOS (BCD) process successfully. The experimental results confirm that the LED driver can operate within 6–40 V input voltage, and can drive a 1–10 output series connected LEDs. The switching frequency is fixed at 500 kHz with a variation of ±2%. The measured system peak efficiency is up to 95% at 1 A LED current and 10 V output voltage. The settling time at the PWM rising edge is <3.5 μs which is well beneficial for fast PWM dimming.

A Dimmable LED Driver With Resistive DAC Feedback Control for Adaptive Voltage Regulation

This paper proposes a dimmable energy-efficient light-emitting diode (LED) driver for applications in interior lighting. High efficiency is achieved by an adaptive voltage regulation, which minimizes power losses in the linear current regulator. A digital control mechanism employing a resistive digital-to-analog converter for feeding the analog feedback input of a dc–dc converter is introduced. It is shown that the digital control methodology gives maximum design flexibility and enhances control over regulation speed and stability. In an experimental setup, the proposed concept is verified and evaluated. Operating at an input voltage of 24 V, the LED driver provides a relatively wide output voltage range of 3.5–38 V. Output current is regulated to 700 mA with a steady-state precision of more than 98.8%, whereas pulsewidth modulation dimming with a frequency of 1 kHz and shortest on-time of 4 $\mu\hbox{s} $ is employed. A peak efficiency of the complete system of 93.9% is achieved.

Dual-Purpose Offline LED Driver for Illumination and Visible Light Communication

This paper presents a dual-purpose offline LED driver with illumination control and visible light communications (VLC). LEDs, due to their nonlinear I-V characteristics, are driven by constant current sources. The proposed dual-purpose offline LED driver realizes a constant current source by a buck converter without a capacitor using average current mode control. VLC is implemented through variable pulse position modulation scheme using a shunt switch in parallel to LED string. Conventional LED drivers are typically designed to perform illumination control with pulsewidth modulation (PWM) dimming at low frequencies (<; 20 kHz), which results in audible noise due to the mechanical vibrations of inductors and piezoelectric properties of ceramic capacitors. The proposed converter presents an illumination control with PWM dimming frequencies above the audible range. The detailed control and modeling of the proposed dual-purpose LED driver using high-frequency model of LED string is discussed. The effects of the phosphor on phosphor-based white LEDs for VLC are reported. The proposed driver is experimentally evaluated on 110/120 ac mains with 450-lm output. The linear characteristics of PWM dimming for data transfer of 2 Mb/s are demonstrated. Detailed simulation and experimental results to validate the operation of the proposed converter are presented.

효율적인 고출력 LED 디밍 제어를 위한 회로 설계 및 구현

The conventional dimming control methods of LED (Light-emitting dioades) include Analog, PWM (Pulse Width Modulation), and FM (Frequency Modulation) Control. Analog dimming is controlled by adjusting forward current of Power LED. Although Analog dimming is possible to control linearly the brightness levels on a whole range (0%~100%), it comes into existence a variation of wavelength by changing the Power LED's forward current. PWM dimming has achieved by varying in duty of full current flowing to the Power LED. Generally, PWM dimming doesn't make variation of wavelength but have difficulty with adjusting the linear brightness level between 0% and 10%. FM dimming method is on the same wavelength as PWM dimming, however, it has problem of flickering at low level of dimming. This paper propose a efficient dimming control method of Power LED in order to overcome the disadvantages of the above mentioned methods. We apply to Analog method in low level of dimming control and use PWM method in dimming range from 10% to 100%. For the experiment, we design and implement a circuit and test the proposed method. Consequently, we can control the linear brightness of Power LED across the whole range and get the constant wave at different dimming level. The experimental results show the benefits of the proposed method.

OLED Electrical Equivalent Device for Driver Topology Design

In this paper, a hardware equivalent of an organic light-emitting diode (OLED) was designed and investigated. This substitution OLED device is based on a circuit-equivalent OLED model and can be used to design and test OLED dedicated drivers. Indeed, OLEDs are available on the market, but they are still very expensive and hard to obtain. Compared to a real OLED, the substitution device is cheap and robust and can be easily duplicated. Moreover, a photodetector is not required to measure the light output waveform. This can be simply done by measuring a voltage across a resistance. This model can be used, for instance, to simulate a large OLED panel made of several associated single OLEDs for various series/parallel connection strategies. It can also be used to simulate aging phenomena by changing the values of some of its components. This might be useful for the definition of strategies to compensate aging effects like luminous flux depreciation. Another advantage of such a device is its use for power supply tests as it could serve as a substitution load, at maximum deviation from standard OLED electrical characteristics. We discuss the theoretical model that was used as a basis for developing the device. The accuracy of the model was then evaluated, particularly in pulsewidth-modulation dimming conditions. Then, the hardware equivalent device was compared to a real OLED. Finally, an example of the potential use of this substitution device is given: It was successfully used to investigate the “overdrive” technique in order to increase OLED light output rise time. This technique improves the light output rise time by a factor of over 4.

Bridgeless electrolytic capacitor‐less valley‐fill AC/DC converter for offline Twin‐Bus light‐emitting diode lighting application

To match the key features of light-emitting diode (LED) lighting source and further save power, LED lighting driver also requires long life, while maintaining high efficiency, high power factor, pulse-width modulation dimming and low cost. However, a typical LED lighting driver has the following drawbacks: (i) utilise bulky electrolytic capacitor as storage capacitor with short lifetime; (ii) employ a low-frequency diode bridge as the rectifier cell; and (iii) engage multiple stages cascade structure for multiple LED strings. To overcome the aforementioned shortages, this study proposed a bridgeless electrolytic capacitor-less AC/DC converter for offline LED lighting application. In the proposed converter, the conventional diode rectified bridge is replaced by Totem-pole bridgeless configuration for reducing the number of semiconductors in the line-current path. Meanwhile, the valley-fill circuit is introduced to further reduce the capacitor size. As comparison to its counterpart, the proposed circuit requires only one quarter of the capacitor energy when considering the energy amount (CV 2 ) as the capacitor sizing criterion. Furthermore, the isolation type of the studied circuit is compatible with Twin-Bus configuration for achieving higher overall system efficiency. Finally, the experimental results, taken from a laboratory prototype rated at 50 W, are presented to verify the effectiveness of the proposed converter.

A Dual-Output Integrated LLC Resonant Controller and LED Driver IC with PLL-Based Automatic Duty Control

This paper presents a secondary-side, dual-mode feedback LLC resonant controller IC with dynamic PWM dimming for LED backlight units. In order to reduce the cost, master and slave outputs can be generated simultaneously with a single LLC resonant core based on dual-mode feedback topologies. Pulse Frequency Modulation (PFM) and Pulse Width Modulation (PWM) schemes are used for the master stage and slave stage, respectively. In order to guarantee the correct dual feedback operation, Phased-Locked Loop (PLL)-based automatic duty control circuit is proposed in this paper. The chip is fabricated using <TEX>$0.35{\mu}m$</TEX> Bipolar-CMOS-DMOS (BCD) technology, and the die size is <TEX>$2.5mm{\times}2.5mm$</TEX>. The frequency of the gate driver (GDA/GDB) in the clock generator ranges from 50 to 425 kHz. The current consumption of the LLC resonant controller IC is 40 mA for a 100 kHz operation frequency using a 15 V supply. The duty ratio of the slave stage can be controlled from 40% to 60% independent of the frequency of the master stage.