Dimming Method Research Articles

A Study on the Multiple Control Techniques for LED Dimming of Single Stage LLC Resonant Converter

This paper proposes the multiple control techniques for light emitting diode (LED) dimming of a single stage LLC resonant converter. In recent years, LEDs have emerged as a new next-generation light source and replaced conventional lighting devices such as incandescent and fluorescent lamps. Further, the use LEDs is increasing in many fields owing to their versatility and other advantages. However, LEDs are not available in commercial power; therefore, a driver circuit is required. Accordingly, the interest in LED driving circuits has increased, and there is an increasing demand for higher efficiency and further maximizing light efficiency and lifetime. A typical LED driver circuit comprises of two stages, i.e., a power-factor correction (PFC) stage and a DC/DC converter stage. This configuration results in unnecessary losses, in addition to the drawback in terms of a large driving-circuit volume. Further, when the conventional PWM dimming method is applied to an LLC resonant converter, there is a limit on the usable frequency range. The frequency cannot be indefinitely increased because the switching frequency is inversely related to the output characteristic. Thus, dimming function over a wide range is impossible. Therefore, to improve the overall efficiency of a LED driver circuit, a single-stage configuration is used to reduce the number of devices that cause unnecessary loss, and an asymmetric converter is used to reduce the voltage stress across the switch. Additionally, this paper proposes a converter circuit with a wider dimming range and PFC function through frequency-control, switching ratio control, and upper switching ON/OFF control.

제로에너지 건물을 위한 첨단 외피의 최적제어 방법에 관한 연구

In this study, an algorithm for control of SPD(Suspended Particles Display) on Smart Skin was proposed. The office with SPD located in Jeonju, Jeollabuk-do was modeled and simulated using TRNSYS18. Through simulation, the energy and lighting consumption of building were analyzed The two kinds of control algorithm(SPD and dimming control method for cool energy and lighting energy saving(CASE 1) and improved control method(CASE 2)) were compared. For this research, Two models(with and without SPD and dimming control) were analyzed by comparing the cooling energy and the light energy consumption was reduced 15.1%, and the lightind energy consumption was reduced by 39.2% more than the model without SPD and dimming control. But, at the improved control method(CASE 2) the cooling energy consumption was reduced of more 2.5% and lighting energy consumptions was reduced of more 18.3% than CASE 1. When using SPD and dimming control, lighting energy consumptions showed more sensitive to solar radiation than cooling energy consumptions. As the improved control method(CASE 2) showed more advantageous saving tate than SPD and dimming control metrhod for cool energy and lighting energy saving(CASE 1), it was found that the improved control method (CASE 2) must be utilized in practice for SPD and dimming control.

Efficiency Improvement of Multichannel LED Driver With Selective Dimming

There is a widespread application of selective dimming of multichannel LED drivers. In this article, two new selective dimming methods to improve the efficiency of multichannel LED drivers are proposed. The proposed methods are based on a two-stage multichannel LED driver that consists of an ac–dc boost power factor correction converter at its front-end and a dc–dc non-resonant converter at its second stage. Primary side digital peak current control method is applied to the dc–dc converter to control the LED peak currents during selective dimming operation. The auxiliary back-to-back switches are connected across each transformer winding either at the primary side or secondary side to perform selective dimming. The duty ratios of these auxiliary back-to-back switches are varied at lower than switching frequency of dc–dc converter to control the brightness of LED loads. The proposed topologies offer high efficiencies in both full load and during selective dimming operations, and meet the IEEE 1789 recommendation with 3 kHz dimming frequency. The design of the proposed dc–dc converters, modes of operation as well as detailed theoretical analysis are presented in this article. A 150-W prototype of the proposed LED driver with a non-DSP microcontroller is implemented to verify the feasibility of such LED drivers. Comparisons between the proposed methods and the converters reported previously are presented in the article.

Performance analysis of a backlight dimming method using weighted mean-square-error based on joint edge-saliency characteristics

In this paper, a new backlight dimming method using weighted mean-square-error (MSE) based on joint edge-saliency characteristics is proposed. In contrast to conventional backlight dimming methods that cannot accurately evaluate the saturation error and determine the optimal clipping point to achieve the best trade-off between image quality and power consumption, the proposed method, with consideration of human visual characteristics, analyzes the joint edge-saliency characteristics based on spatio-temporal saliency map and edge-strength map of the input images, and weights the MSE accordingly. It can therefore evaluate the allowable saturation error and determine the optimal clipping point. Simulation results show that the proposed method outperforms other benchmark methods in the case of overall consideration of image quality and power consumption. Additionally, the proposed method maximizes the power reduction rate while successfully preserving image details in the regions of interest and maintaining high perceived image quality. Our results also show that the average computation time of the proposed algorithm was reduced by up to 30.184%, 19.162% and 8.027%, respectively, compared with I2GEC, SMVA2 and SPBD algorithms.

Visibility of the phantom array effect according to luminance, chromaticity and geometry

Light-emitting diode-based lighting systems are now applied in both general lighting and automotive lighting. Time-modulated control methods such as pulse width modulation are frequently applied as a dimming method. This paper presents the characteristics of the visibility of the phantom array effect according to luminance, chromaticity and angular field of view. The threshold frequency of the visibility of the phantom array increases in proportion to the logarithm of the luminance of the light source. As the angular field of view of the light source increases, the threshold frequency of the visibility of the array decreases exponentially over a range from 0.125° to 4° in our experimental conditions. The threshold frequency at which the array is visible depends on chromaticity at high light source modulation frequencies. When designing time-modulated light sources, our findings can be applied so as to minimize the phantom array effect.

Improved‐efficiency quasi‐two‐stage current‐source‐mode SIMO LED driver

Single-inductor-multiple-output (SIMO) light-emitting-diode (LED) drivers are attractive, practical solutions for lighting applications. An SIMO LED driver is usually constructed with conventional voltage-source-mode dc-dc converters. Current-source-mode (CSM) converters, though being highly suited for current driving, are less studied. Simple control, low cost and independent dimming function are among the advantages of CSM SIMO converters. The limiting factors of CSM SIMO converters, however, include the relatively low efficiency and the restricted number of outputs under low-frequency pulse-width modulation (PWM) dimming control. In this study, an adaptive current bus technique to the CSM SIMO converter is applied. Results show that a significant improvement in efficiency can be achieved. The low-frequency PWM dimming method is also analysed and redesigned. Also, we compare the voltage stress in the CSM SIMO converter with traditional input-series-connected structure. Results show that the CSM SIMO converter achieves a high-voltage step-down ratio without the use of transformers. This study presents detailed analysis and experimental results of the CSM SIMO converter with adaptive current bus.

P‐40: E‐Mirror Automatic Dimming Reflectance Control

For the electronic display based rear view mirror (E‐Mirror) systems, there is a need to demonstrate automatic mirror dimming. This document describes the approach to accomplish the automatic dimming control function for the bi‐modal E‐Mirror including a user preference control method. The user preference control is based on a unique constant dimming ratio method that appears “linear” in nature to the user. This unique user preference control is made possible with a new mathematic concept of a negative fractional power function together with a constant reflectance ratio concept.

28‐2: A Novel Local Dimming algorithm with HDR for VR system based on GPU

As the screen of VR is very close to human eye and the optical lens has amplification effect, VR needs high PPI to meet people's visual requirements. High PPI panel with side‐emitting LED backlight is difficult to realize high contrast ratio(CR). Local Dimming based on direct‐illumination LED can not only save backlight power consumption but also improve the CR of the VR system. The point spread function(PSF) of LED plays an important role in Local Dimming technology. However traditional PSF always adopts approximate calculation method with low accuracy, which causes luminance distortion. In this paper, a method of PSF measurement and data processing was proposed. It can describe the spread strength and range of one single block LED actually. One improved LCD compensation algorithm was demonstrated in this paper. The light leakage characteristic of liquid crystal was considered. It can keep the hue consistent. The proposed Local Dimming method has low distortion and high dynamic contrast range. This paper also presents a method for implementing Local Dimming algorithm by GPU, which can display Local Dimming effect in real time of VR system with high frame rate.

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.

The establishment and analysis of noise model for pulse modulation dimming method and square-wave modulation dimming method

When measuring the oil concentration lower than 10 mg/L in reinjection water based on ultraviolet fluorescence method, high thermal power of the light source will reduce the accuracy of measurement results. To reduce the thermal power of light source, pulse modulation dimming method (duty ratio less than 50%) was proposed to replace square-wave modulation dimming method (duty ratio equal to 50%). Two noise analysis models for pulse modulation and square-wave modulation dimming method were built. Signal-to-noise ratio (SNR) of measurement results for two methods were compared. The relationship between SNR and light source power was derived. The optimum choices of current amplitude and duty ratio for pulse modulation dimming method were proposed under the condition of the same signal-to-noise ratio. Results show that the light source power for pulse modulation dimming method is less than 21% of that for square-wave modulation dimming method under the condition of the same signal-to-noise ratio. Finally, signal demodulation models of two dimming methods were simulated by MATLAB software. The simulated relationship of SNR for two methods is consistent with the theoretical analysis results.

A High Accuracy Weak Voltage LED Analog Dimming Method

A weak voltage analog dimming method for high precision light emitting diode (LED) current control with N-Bits analog static offset calibration (N-Bits ASOC), dynamic offset cancellation (DOC) and K-times dimming duty to voltage (KD2V) conversion is presented. The N-Bits ASOC circuit decreases the analog dimming error to V OSMAX /2 N - 1 by pre-calibrating the error amplifier offset. Moreover, through a smart combination of KD2V circuits and DOC amplifier, the KD2V and DOC operational amplifier magnify the dimming reference and LED current sense voltage K-times, respectively, which reduces the residual dimming error K-times without any modification to the LED current sampling resistor. Based on the 0.18μm 5V/40V Bipolar-CMOS-DMOS (BCD) process, experimental results for a cell phone backlighting driver show that the analog dimming ILED error reduces to 30μA at maximum 200mV LED current feedback voltage. This deviation mostly keeps constant through a dimming duty range of 0.5% to 100% and VIN range of 2.7V to 5.5V. Furthermore, a 200-sample measurement data suggests that this method is effective even when dimming duty is smaller than 0.5% for mass production.

PWM Dimming Method for Capacitor-Clamped Current-Sharing Circuit in LED Backlight System

When multichannel light-emitting diode (LED) strings are applied in display backlight application, it’s necessary to keep the brightness identical and adjustable. This paper deals with the capability of pulsewidth modulation dimming control method for capacitor-clamped current sharing circuit. By detecting the rising-edge of dimming pulse and turn on the switches of current sharing circuit in rotation, this method can achieve current sharing at any dimming frequency and dimming ratio. What is more, to improve the dynamic response of LED current and achieve a high dimming ratio, a control method based on the output voltage feedforward is proposed, which can decrease the rising time of the LED forward current significantly. The operational principle and parameter design are analyzed in detail. Based on this analysis, a three-string current sharing circuit driven by Buck converter is fabricated and tasted in the laboratory. Experimental waveforms demonstrate the validity.

Current-Source-Mode Single-Inductor Multiple-Output LED Driver With Single Closed-Loop Control Achieving Independent Dimming Function

Single-inductor multiple-output (SIMO) light-emitting diode (LED) drivers have the advantages of being compact, efficient, and low cost. However, the voltage-to-current transfer function of each output of the SIMO converter is not independent, with significant cross regulation issues that necessitate the use of complex closed-loop control for achieving independent dimming function. This paper proposes a current-source-mode (CSM) SIMO dc-dc converter from duality principle, which is shown to be more suited for LED driving due to widened control range of the duty cycle and inherently inductor-less LED driving topology. The outputs of the CSM SIMO dc-dc converter are inherently independent, resulting in very simple control requirement involving only one closed-loop controller for providing the constant current feeder, and several simple open-loop controllers for independent dimmable driving of LEDs. Simultaneous voltage step-up and step-down of multiple outputs is an added feature that simplifies the input power source requirement, especially for portable applications. The whole system is simple, reliable, and low cost. Taking the CSM single-inductor dual-output dc-dc converter as an example, we illustrate the circuit operation and establish a small-signal model for facilitating the design of the feedback control. A direct duty-cycle dimming method is described. Experimental tests are presented for verification.

An AC Input Inductor-Less LED Driver for Efficient Lighting and Visible Light Communication

This paper presents an ac-powered inductor-less light-emitting diode (LED) driver, which can simultaneously provide efficient illumination and data transmission capability by modulating light output. The proposed driver does not have passive components’ speed limitation compared to the conventional switching converter-based driving solutions for visible light communication (VLC). Besides this, harmful low-frequency flicker is mitigated with an accurate 1/ ${x}$ circuit and the dimming compensation method. In addition, the digitalized power stage and controller utilized in the proposed driver can achieve smooth transitions among multiple current paths, while the keep-and-restore technique and auxiliary turn-on switch help to further increase the VLC data rate. The integrated circuit of the proposed driver is implemented and fabricated with a 0.35- $\mu \text{m}$ , 120-V high-voltage CMOS process. Measurement results show that under a 110- $V_{\text {AC}}$ , 60-Hz input, the peak efficiency of the proposed design is over 89% and the low-frequency flicker is reduced to below 10%. The driver supports up to 8-Mb/s on–off keying non-return-to-zero data transmission for a 1-m distance between the LED module and the receiver.

Comparison of modelling and measurement results of spectra emitted by a programmable lamp

Nowadays artificial light with optimized spectrum is used in many different applications. For instance, it is widely used in museums and exhibitions to illuminate the art. Moreover, such light stimulates the growth of plants, or can be applied in industry and healthcare. To achieve the best results for each application, adjusting of dedicated spectrum is required, that is a complicated task. The ongoing research is focused on simplifying this process. In this paper we present the developed lamp with programmable spectrum, and its user interface. Predicted and measured output spectra are investigated. Full Text: PDF ReferencesMottier, P., LEDs for Lighting Applications, Willey (2009) CrossRef Pimputkar, S., Speck, J.S., DenBaars, S.P., Nakamura, S., "Prospects for LED lighting", Nature photonics 3 (4), 180 (2009) CrossRef Knulst, A. J., Mooijweer, R., Jansen, F. W., Stassen, L. P., and Dankelman, J., "Indicating shortcomings in surgical lighting systems," Minim. Invasive Ther. Allied Technol. 20 (5), 267–275 (2011) CrossRef Blaszczak, U., Gryko, L., Palkowska, A., Kulesza, E., Zajac, A., "Color mixing in LED illuminating system for endoscopic purposes", Lighting Conference of the Visegrad Countries (Lumen), IEEE (17 November 2016) CrossRef Nanya, K., Ishigami, Y., Hikosaka, S., Goto, E., "Effects of blue and red light on stem elongation and flowering of tomato seedlings", Acta Hortic. 956, pp. 264–266 (2012). CrossRef Cegielski, T. , Bujalski, D. , Kowalczyk, K. , Gajc-Wolska, J. , Hemka, L., "Use of light emission programming in tomato grow light system", Proceedings of Electrotechnical Institute 63 (273), 79-94 (2016) CrossRef Mazikowski, A., Feldzensztajn, M., "Lamp of adjustable spectrum for photographic usage", Proc. SPIE 10445, Photonics Applications in Astronomy, Communications, Industry, and High Energy Physics Experiments, 104450K (2017) CrossRef CREE Inc, Cree® XLamp® XT-E LEDs Product family data sheet (accessed 16 April 2018). DirectLink Dyble, M., Narendran, N., Bierman, A., Klein, T., "Impact of dimming white LEDs: chromaticity shifts due to different dimming methods", Optics and Photonics 2005, San Diego, California, United States DirectLink

A rapid local backlight dimming method for interlaced scanning video

AbstractThis paper presents a rapid local backlight dimming method for interlaced video to improve the efficiency of displaying interlaced video. In the proposed method, we combine the line average deinterlacing algorithm with the local backlight dimming algorithm. In order to reduce the computational complexity and the backlight power consumption, three novel methods are proposed. The first is to add the sparse method to process the deinterlaced image. Second, the improved dynamic threshold method is used to calculate the dimming factor. And third, the odd field and even field of the same frame use the same backlight brightness to do backlight dimming. The simulation results show that the proposed method can reduce the computational complexity and power consumption, and the experiment results verify that the method can provide high display effect.

Weight Threshold Check Coding for Dimmable Indoor Visible Light Communication Systems

To provide energy savings and ecological benefits, dimming control is a crucial factor in indoor visible light communication (VLC) system where desired brightness levels can be achieved. General dimming control methods have an adverse effect on communication, e.g., limiting the achievable data rate or degrading the error performance. In this paper, we propose a code-based method weight threshold check code (WTCC), which can achieve dimming control as well as improve spectral efficiency further. Moreover, the proposed WTCC has a low implementation complexity with a simple encoding/decoding structure. Finally, simulations have been carried out in terms of normalized power requirement, spectral efficiency, and error performance, which prove WTCC can provide a balance between the two basic functions of VLC: illumination and communication.

Joint Error-Dimming Control Using Constant Weight Coding in Visible Light Communication Systems

To enhance commercial implementation, visible light communication (VLC) should facilitate dimming control and reliable data transmission simultaneously, where users can adjust the brightness levels arbitrarily. Constant weight code (CWC) based dimming method can achieve higher spectral efficiency, but the codewords need further selection to exponentially map the massage. In this paper, based on CWC, we proposed a method to achieve dimming control as well as improve error performance via optimizing the average Hamming distance of the codeword set. Simulation results show that the optimal codeword set can achieve better error performance.

An Adaptive Backlight Dimming with the Edge Enhancement Technique

Backlight dimming, which decreases the backlight luminance level and performs pixel compensation, is known as the most effective way to reduce the power consumption of portable electronic devices with LCD. In this paper, we propose an adaptive backlight dimming technique that preserves the quality of details in images even when the backlight luminance of LCD devices is greatly reduced. The proposed backlight dimming method consists of the following two steps: clipped point selection and image compensation. In the first step, to reduce power consumption, the proposed approach selects a suitable clipped point according to the chosen level for a given image based on the maximum and average value. In the second step, several parameters are adaptively chosen according to the characteristic of a given image. These parameters are then used to compensate pixels with an edge enhancement technique. The simulation results show that at the same clipping point the proposed method has higher detailed information than others.

GLOBAL ENERGETICS OF SOLAR FLARES. IV. CORONAL MASS EJECTION ENERGETICS

ABSTRACT This study entails the fourth part of a global flare energetics project, in which the mass m cme, kinetic energy E kin, and the gravitational potential energy E grav of coronal mass ejections (CMEs) is measured in 399 M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission, using a new method based on the EUV dimming effect. EUV dimming is modeled in terms of a radial adiabatic expansion process, which is fitted to the observed evolution of the total emission measure of the CME source region. The model derives the evolution of the mean electron density, the emission measure, the bulk plasma expansion velocity, the mass, and the energy in the CME source region. The EUV dimming method is truly complementary to the Thomson scattering method in white light, which probes the CME evolution in the heliosphere at r ≳ 2 R ⊙, while the EUV dimming method tracks the CME launch in the corona. We compare the CME parameters obtained in white light with the LASCO/C2 coronagraph with those obtained from EUV dimming with the Atmospheric Imaging Assembly onboard the SDO for all identical events in both data sets. We investigate correlations between CME parameters, the relative timing with flare parameters, frequency occurrence distributions, and the energy partition between magnetic, thermal, nonthermal, and CME energies. CME energies are found to be systematically lower than the dissipated magnetic energies, which is consistent with a magnetic origin of CMEs.