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An overview of energy efficient solid state LED driver topologies
摘要： LED lamps are projected as prospective successors of incandescent lamps with high efficiency and a long lifetime. Therefore, there is a need to develop energy efficient LED driver topologies for achieving constant current regulation, despite the effects of temperature on the LED V‐I characteristics. This paper presents the salient features of various LED driver topologies with a focus on power density, multi‐string operation, renewable energy utilization, soft switching, optical wireless communication, reliability and size. The performance of the above topologies is analysed in terms of the number of components, converter switching frequency, galvanic isolation, power rating and efficiency. This paper takes a look at efficiency improvement methods while dwelling on aspects of lifetime and reliability prediction of LED drivers. The paper will anticipate some of the future trends associated with the adaptation of wide bandgap power semiconductor materials, smart LED lighting for the internet of things (IoT) and programmable LED lamp drivers. This detailed technology review is extremely useful for researchers, designers and engineers in choosing the right topology.
关键词： photovoltaic,dimmable LEDs,light emitting diode,organic LEDs,DC‐DC converters
更新于2025-09-12 10:27:22
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Two-dimensional analysis of the nonuniform quantum yields of multiple quantum wells for AlGaN-based deep-ultraviolet LEDs grown on AlN templates with dense macrosteps using cathodoluminescence spectroscopy
摘要： AlGaN-based deep-ultraviolet light-emitting diodes (LEDs) incorporating uneven multiple quantum wells (MQWs) with inclined and terrace zones, which were fabricated on an AlN template with dense macrosteps, have exhibited a high internal quantum efficiency (IQE). To investigate the microscopic structure of uneven MQWs, cathodoluminescence (CL) mapping characterization was carried out, and the maps of the CL intensity at 300 K relative to that at 38 K were obtained for uneven MQWs that targeted 265 and 285 nm LEDs. At an electron beam current of less than 1.0 nA, the signals from inclined and terrace zones of the uneven MQWs were confirmed to satisfy the non-saturated excitation condition at 300 K. Nonradiative recombination (NR) was insufficiently frozen even at 38 K, specifically on the terraces in the 265 nm MQW, suggesting high concentrations of NR centers due to point defects (PDs). In contrast, NR in the 285 nm MQW at 38 K was closer to freeze-out. The concentration of PDs in the 285 nm MQW was likely to be lower than that in the 265 nm MQW. Finally, the ratios of the CL intensity at 300 K to those at 38 K were mapped, demonstrating an approach to creating an approximate map of IQE. The values in the CL intensity ratio maps are discussed by considering the analytical error factors. The results support the model of localized current injection through Ga-rich stripe zones in the n-AlGaN cladding layer.
关键词： AlGaN,cathodoluminescence spectroscopy,internal quantum efficiency,deep-ultraviolet LEDs,multiple quantum wells
更新于2025-09-12 10:27:22
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Variations of Saponarin Content in Young Barley Leaves Illuminated with Different Light-Emitting Diodes (LEDs)
摘要： In this study, the effect of light on the regulation of flavonoid production in young barley leaves (YBLs) was investigated. YBLs following germination were illuminated with different light-emitting diode (LED) lights, i.e. blue, red, far-red light, along with fluorescence and dark conditions as controls, and as the main flavonoid, saponarin content of YBLs was analyzed quantitatively with HPLC. In addition, the antioxidant activities of the crude ethanoic extracts of YBLs were analyzed by several antioxidant assays. The content of saponarin in blue light-illuminated barley leaves is two or three times higher than those in barley leaves with other lighting conditions, i.e. red, far-red, and the content with fluorescence and even dark conditions as controls. However, the levels of saponarin among the leaves illuminated with other lighting systems show no significant difference. And, the antioxidant potentials of the extracts of YBLs demonstrated same tendency shown in saponarin levels. Our results suggested that blue lighting conditions might evoke the photoprotection changes in YBLs, leading elevated level of saponarin, consequently increasing their antioxidant potentials.
关键词： blue light,Young barley leaves,saponarin,LEDs,sprout
更新于2025-09-12 10:27:22
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Transition metal ion Co-Doped MgO–MgF2-GeO2:Mn4+ red phosphors for white LEDs with wider color reproduction gamut
摘要： Mn4+-activated non-rare-earth based red phosphors are excellent down conversion materials for phosphor-converted light-emitting diode (pc-LEDs) based solid-state lighting applications. However, the low quantum efficiency of Mn4+ activated red phosphors under InGaN based blue LED excitation hinders their use in phosphor-converted LEDs. To enhance the absorption at an excitation wavelength of around 420 nm in Mn4+-doped MgO-MgF2-GeO2 (MGF: Mn4+), which is a conventional red-emitting lamp phosphor, we doped MGF: Mn4+ phosphors with transition metal oxides (Sc2O3, Lu2O3, Y2O3, and La2O3) replacing MgO. When excited using 420 nm light, the absorption ratio of the synthesized phosphors with Sc2O3 (Sc-MGF:Mn4+) was 58% with an internal quantum efficiency (IQE) of 55% as compared to the 35% IQE of the pristine MGF-Mn4+ phosphor. White LEDs were fabricated using Sc-MGF-Mn4+ (red), and β-SiAlON:Eu2+ (green) on InGaN chips (λem = 450 nm) and their performance was compared to the optical performance of LEDs fabricated using K2SiF6:Mn4+ as the red phosphor. According to the National Television System Committee (NTSC) standard, the color reproduction coverage with an Sc-MGF:Mn4+ phosphor-loaded white LED was 121% by the International Commission on Illumination (CIE) 1976, and 80% by the BT.2020 standard. The coverages are 9% and 6% higher than the coverages of LEDs fabricated using K2SiF6:Mn4+ as the red phosphor according to the NTSC and BT.2020 standards, respectively. Our simple approach to enhance the IQE of Mn4+ activated phosphors by co-doping transition metal oxides can be extended to other Mn4+ activated phosphor systems for applications that require enhanced absorption, higher luminescent emission intensity, and a wider gamut of color reproduction.
关键词： MgO-MgF2-GeO2,Mn4+ activated red phosphors,Solid-state lighting,White LEDs,BT.2020
更新于2025-09-12 10:27:22
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Bright high-colour-purity deep-blue carbon dot light-emitting diodes via efficient edge amination
摘要： Deep-blue light-emitting diodes (LEDs) (emitting at wavelengths of less than 450 nm) are important for solid-state lighting, vivid displays and high-density information storage. Colloidal quantum dots, typically based on heavy metals such as cadmium and lead, are promising candidates for deep-blue LEDs, but these have so far had external quantum efficiencies lower than 1.7%. Here we present deep-blue light-emitting materials and devices based on carbon dots. The carbon dots produce emission with a narrow full-width at half-maximum (about 35 nm) with high photoluminescence quantum yield (70% ± 10%) and a colour coordinate (0.15, 0.05) closely approaching the standard colour Rec. 2020 (0.131, 0.046) specification. Structural and optical characterization, together with computational studies, reveal that amine-based passivation accounts for the efficient and high-colour-purity emission. Deep-blue LEDs based on these carbon dots display high performance with a maximum luminance of 5,240 cd m?2 and an external quantum efficiency of 4%, notably exceeding that of previously reported quantum-tuned solution-processed deep-blue LEDs.
关键词： carbon dots,deep-blue LEDs,amine-based passivation,external quantum efficiency,high-colour-purity
更新于2025-09-12 10:27:22
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[IEEE 2019 25th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) - Lecco, Italy (2019.9.25-2019.9.27)] 2019 25th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) - Influence of the use of a thermal pad on electric, optical and thermal parameters of selected power LEDs
摘要： In this paper the influence of the use of thermal pads on electric, optical and thermal parameters of LEDs is considered. For a selected type of power LED operating with a thermal pad and without it, such parameters as: thermal resistance, optical efficiency, power of emitted radiation are measured for selected values of diode forward current. The results of measurements obtained for both manners of diode assembly are compared. Some characteristics illustrating electric, thermal and optical properties of these diodes are shown and discussed. It is proved that the use of a thermal pad makes it possible to achieve better values of operating parameters of the considered power LEDs and lower values of the device internal temperature, which guarantees longer life time of the considered devices.
关键词： power of emitted radiation,thermal resistance,optical efficiency,power LEDs,thermal pad
更新于2025-09-12 10:27:22
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[IEEE 2019 25th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) - Lecco, Italy (2019.9.25-2019.9.27)] 2019 25th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) - Comparison of Model Order Reduction and Thermal Network Approaches in the Extraction of Dynamic Compact Thermal Models of LEDs
摘要： The Delphi4LED project is identifying methodologies for the extraction of multi-domain, electro-opto-thermal compact models of LED packages. The temperature dependent opto-electro model provides the thermal model with a thermal power dissipation, the thermal model provides the opto-electro model with a junction temperature. Together they are co-simulated to convergence whereupon both thermal and optical behaviour is predicted. Such models would be used by lighting designers to provide rapid indication of the performance of a proposed luminaire design. The thermal portion of the multi-domain model is required at least to provide temperature prediction of the chip junction and potentially phosphor and solder connection point temperatures. Equivalent thermal networks or reduced order models are both candidate approaches for the thermal model. This study will detail the extraction process for both, compare their performance and accuracy and discuss pros and cons regarding their possible adoption.
关键词： thermal networks,LEDs,Delphi4LED,reduced order models,compact thermal models
更新于2025-09-12 10:27:22
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Transfer-Free Graphene-Like Thin Films on GaN LED Epiwafers Grown by PECVD Using an Ultrathin Pt Catalyst for Transparent Electrode Applications
摘要： In this work, we grew transfer-free graphene-like thin films (GLTFs) directly on gallium nitride (GaN)/sapphire light-emitting diode (LED) substrates. Their electrical, optical and thermal properties were studied for transparent electrode applications. Ultrathin platinum (2 nm) was used as the catalyst in the plasma-enhanced chemical vapor deposition (PECVD). The growth parameters were adjusted such that the high temperature exposure of GaN wafers was reduced to its minimum (deposition temperature as low as 600 °C) to ensure the intactness of GaN epilayers. In a comparison study of the Pt-GLTF GaN LED devices and Pt-only LED devices, the former was found to be superior in most aspects, including surface sheet resistance, power consumption, and temperature distribution, but not in optical transmission. This confirmed that the as-developed GLTF-based transparent electrodes had good current spreading, current injection and thermal spreading functionalities. Most importantly, the technique presented herein does not involve any material transfer, rendering a scalable, controllable, reproducible and semiconductor industry-compatible solution for transparent electrodes in GaN-based optoelectronic devices.
关键词： transparent electrodes,transfer-free,PECVD,LEDs,heat spreading,gallium nitride,graphene
更新于2025-09-12 10:27:22
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Color Development and Phytochemical Changes in Mature Green Chili (Capsicum annuum L.) Exposed to Red and Blue Light-Emitting Diodes
摘要： Exposure of mature green ‘Takanotsume’ chili fruit to blue and red light-emitting diodes (LEDs) was investigated. The red LED accelerated the red color development of chili as indicated by higher a* and chroma values, as well as lower hue angle and total chlorophyll compared to the blue LED and darkness (control). These were linked to increases in β-carotene, free-capsanthin and total carotenoids. The carotenoid biosynthesis-related genes: lycopene-β-cyclase (Lcyb), β-carotene hydroxylase (CrtZ), and capsanthin/capsolubin synthase (Ccs) were up-regulated by the red LED after 2 days of the experiment. The blue LED was more effective in increasing the expression of the phytoene synthase (Psy) gene at day 1 of experiment. The total phenolic, vitamin C content, and antioxidant capacity were also higher in the blue LED-treated chili. Results suggest that the responses of each carotenoid-related gene to the light wavelengths and the accumulation of phytochemicals are specific characteristics of this chili cultivar.
关键词： phytochemicals,carotenoids,LEDs,carotenoid biosynthesis,mature green chili,Antioxidant
更新于2025-09-12 10:27:22
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Energy transfer and tunable photoluminescence of Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ phosphors for near-UV white LEDs
摘要： A series of apatite-type Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ phosphors have been successfully synthesized by the high-temperature solid-state reaction method. Phase structures were examined based on X-ray diffraction, the results indicated that the obtained Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ samples were well crystallized without impurity phase. The photoluminescence emission and excitation spectra and the decay curves were investigated in detail. The main energy transfer from Tb3+ to Eu3+ was verified to compliance with the dipole-quadrupole mechanism. The luminescence colors of the Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ phosphors can be easily tuned from green light (0.2570, 0.3766) to white light (0.3674, 0.2813) by adjusting the proportion of Tb3+ and Eu3+ ions. The investigations indicated that the Sr6Gd2Na2(PO4)6F2:Tb3+, Eu3+ phosphors can be used as a qualified candidate for application in white light-emitting diodes.
关键词： Near-UV white LEDs,Phosphors,Sr6Gd2Na2(PO4)6F2:Tb3+,Energy transfer,Photoluminescence,Eu3+
更新于2025-09-12 10:27:22