- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Power Supplies for LED Driving || Linear Power Supplies
摘要： Linear power supplies for driving light-emitting diodes (LEDs) are preferred for a number of reasons. The complete absence of any electromagnetic interference (EMI) radiation is one important technical reason. Low-overall cost is an important commercial reason. However, they also have disadvantages: in some applications they have low efficiency and hence they introduce thermal problems. It may be necessary to add a heat sink, thus increasing cost and size.
关键词： switched linear regulators,voltage regulators,current circuits,LEDs,Linear power supplies
更新于2025-09-19 17:13:59
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585a??nm light-emitting diodes inhibit melanogenesis through upregulating H19/miR-675 axis in LEDs-irradiated keratinocytes by paracrine effect
摘要： 585 nm light-emitting diodes have been proven to suppress melanogenesis in melanocytes. However, whether LEDs will influence normal human epidermal keratinocytes (NHEKs) and paracrine effect of LEDs-irradiated NHEKs in melanogenesis remains unknown. Objective: To elucidate the possible mechanisms in vitro of anti-melanogenic activity of 585 nm LEDs on paracrine effect of NHEKs and its exosomes. Methods: NHEKs irradiated with different fluences of 585 nm LEDs were evaluated the cell viability by CCK8 assay. Irradiated medium of NHEKs was co-cultured with melanocytes. Melanin content, tyrosinase activity and melanogenic enzymes activities were detected. Exosomes from NHEKs medium were isolated and characterized by electron microscopy and nanoparticle tracking analysis. The expression changes of H19 and its encoded exosomal miR-675 were analyzed. Results: Irradiation with 585 nm LEDs from 0 J/cm2 to 20 J/cm2 had no cytotoxic effect on NHEKs. After co-cultured with irradiated medium of NHEKs, melanin content and tyrosinase activity were reduced and the melanogenic activities were downregulated on both mRNA and protein levels of microphthalmia-associated transcription factor (MITF), tyrosinase (TYR) and tyrosinase-related protein 1 (TRP-1). H19 and its derived exosomal miR-675 from NHEKs, which has been proven relevant to melanogenesis, were significantly upregulated after irradiation. Furthermore, H19 knockdown and miR-675 inhibition in NHEKs could attenuate the inhibition effect of 585 nm LEDs on melanogenesis. Conclusions: This study demonstrated that 585 nm LEDs could inhibit melanogenesis via the up-regulation of H19 and its derived exosomal miR-675 from NHEKs, which was considered as a novel paracrine factor in regulating melanogenesis.
关键词： exosomes,H19/miR-675,melanogenesis,Light-emitting diode (LEDs),keratinocyte
更新于2025-09-19 17:13:59
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Correlation between performance and compositional grading in quantum well of deep UV-LED
摘要： A novel AlGaN/AlGaN multiple-quantum-wells light-emitting diode (LED) structure with linearly graded Al-content in the quantum well (QW) is thoroughly investigated in order to observe the effect on the electrical and optical performances of the devices. The results confirm that the polarization-shape across the active region highly depends on the concentration profile of aluminium, which eventually plays a critical role in determining the overall radiative recombination by promoting hole injection, as well as, improving the electron hole wave-function overlap. In order to correlate, two modified structures with variation in the compositional grading in the quantum well both along and opposite to the growth direction have been studied, and compared to a conventional structure. The outcomes reveal that the structure with Al composition grading in the QW which varies from 72 % to 76 % in the growth direction enhances the device performance.
关键词： Quantum Well (QW),Internal quantum efficiency (IQE),Deep ultra-violet (DUV) LEDs,Compositional grading
更新于2025-09-19 17:13:59
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Recorded color rendering index in single Ce,(Pr,Mn):YAG transparent ceramics for high-power white LEDs/LDs
摘要： Transparent ceramic (TC) is an incredibly promising color converter for high-power white LEDs/LDs. However, the preparation process of multiple structured TC with high color rendering index (CRI) is complicated and of technical challenge, and the inability of a single structured TC to achieve a high CRI significantly limits its real application. In this study, high quality single structured Ce,(Pr,Mn):YAG TCs with the 'wide peak' and 'narrow peak' red light emission were designed and fabricated by the solid-state reaction and vacuum sintering method. Compared with the emission spectra of the Ce:YAG TC, synchronous doping Pr3+ and Mn2+ ions into Ce:YAG TCs resulted in an inhomogeneous broaden of the full width at half maximum (FWHM) from 91.7 nm to 102.2 nm. Impressively, the CRI of the single Ce,(Pr,Mn):YAG TC based high-power white LEDs was as high as 84.8, and the correlated-color temperature (CCT) of the white LEDs/LDs were 5450 K and 3550 K, respectively. Furthermore, when the addition amounts of Pr3+ and Mn2+ were 0.2 at.% and 0.8 at.%, respectively, the prepared Ce,(Pr,Mn):YAG TC displayed a high quantum efficiency (IQE=48.14%) and an excellent color stability (only 5% fluctuation). Therefore, this work not only shows how to overcome the spectrum deficiencies of single structured TCs that restrains the intrinsic CRI improvement, but also provides a reference for the pursuit of a high luminescent property. It significantly reinforces the understanding of CRI problems of TC based high-power lighting, which is crucial for the real application of white LEDs/LDs.
关键词： color rendering index,Ce,(Pr,Mn):YAG,synchronous doping,high-power white LEDs/LDs,Transparent ceramic
更新于2025-09-19 17:13:59
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Highly efficient near-UV-excitable Ca2YHf2Al3O12:Ce3+,Tb3+ green-emitting garnet phosphors with potential application in high color rendering warm-white LEDs
摘要： Inorganic phosphors with broadband near-ultraviolet (near-UV) excitation and efficient visible emissions are highly important for fabricating high-performance near-UV-pumped white light-emitting diodes (LEDs). Herein, we reported on novel efficient near-UV-excitable Ce3+/Tb3+ ions co-activated Ca2YHf2Al3O12 (CYHA) green-emitting garnet phosphors, which were successfully prepared through a high-temperature solid-state reaction process. X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, elemental mapping, photoluminescence, CIE color coordinates, internal and external quantum efficiency, and temperature-dependent emission spectra were used to characterize the samples. Interestingly, due to the efficient energy transfer from Ce3+ to Tb3+ ions in CYHA, the CYHA:Ce3+,Tb3+ samples presented a wide excitation band in the 370-470 nm region peaking around 408 nm owing to the 4f-5d transition of Ce3+ ions, and under 408 nm excitation they showed intense characteristic sharp green emissions around 543 nm corresponding to the 5D4→7F0-6 transitions of Tb3+ ions. The energy transfer mechanism from Ce3+ to Tb3+ ions was ascribed to the quadruple-quadruple interaction, and the energy transfer efficiency reached as high as 93.2%. Notably, the composition-optimized CYHA:0.03Ce3+,0.6Tb3+ sample exhibited high internal quantum efficiency (IQE) of 78.5% and external quantum efficiency (EQE) of 56%, which were much higher than those of the Tb3+ singly-activated CYHA:0.6Tb3+ sample (IQE = 8%, EQE = 2.2%). Finally, a prototype white LED device was made by combining a 400 nm near-UV-emitting LED chip with the phosphor blend of the as-prepared CYHA:0.03Ce3+,0.6Tb3+ green phosphors, commercial BaMgAl10O17:Eu2+ blue phosphors and commercial CaAlSiN3:Eu2+ red phosphors, which emitted bright warm-white light with good CIE chromaticity coordinates of (0.391, 0.356), low correlated color temperature of 3528 K and high color rendering index of 92.3 under 120 mA driven current. This work opens up new opportunities for the development of efficient color converters toward near-UV-pumped warm-white LEDs with high color rendering index.
关键词： white LEDs,green-emitting garnet phosphors,Ce3+/Tb3+ co-activated,near-UV-excitable,energy transfer
更新于2025-09-19 17:13:59
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Lumen Degradation Lifetime Prediction for High Power White LEDs based on the Gamma Process Model
摘要： Nowadays, due to the advancement of design and manufacturing technology, there are many consumer products with high reliability. Similarly, the competition in the business sector influences the product development time to become shorter and that makes it difficult for manufacturers to evaluate the reliability of current products before new products are released to the market. This phenomenon is manifested in the lighting industry, especially for the high power white light-emitting diodes (LEDs) as these products have a long lifetime and high reliability. Currently, the standard to predict the lifetime of LEDs is based on a deterministic nonlinear least squares method which has low prediction accuracy. To overcome this, degradation models are being used to study the reliability of such products, considering the uncertainties and the quality characteristics whose degradation over a period of time can be related to the product lifetime. A stochastic approach based on gamma distributed degradation (GDD) is proposed in this study to estimate the long-term lumen degradation lifetime of phosphor-converted white LEDs. An accelerated thermal degradation test was designed to gather luminous flux degradation data which was analyzed based on maximum likelihood estimation (MLE) and the method of moments (MM) to estimate the parameters for the GDD model. The MLE method has shown superiority over MM in terms of the estimation of the model parameters due to its iterative algorithm being likely to find the optimal estimation. The lifetime prediction results show that the accuracy of the proposed method is much better than the TM-21 nonlinear least squares (NLS) approach which makes it promising for future industrial applications.
关键词： Luminous flux degradation,Gamma distributed degradation (GDD),Method of moments,Light-emitting diodes (LEDs),Maximum likelihood estimation
更新于2025-09-16 10:30:52
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Investigating the Efficiency Droop of Nitride-Based Blue LEDs with Different Quantum Barrier Growth Rates
摘要： In this study, GaN-based blue InGaN/GaN light-emitting diodes (LEDs) with di?erent growth rates of the quantum barriers were fabricated and investigated. The LEDs with quantum barriers grown with a higher growth rate exhibit a lower leakage current and less non-radiative recombination centers in the multiple quantum wells (MQWs). Therefore, the LED with a higher barrier growth rate achieves a better light output power by 18.4% at 120 mA, which is attributed to weaker indium ?uctuation e?ect in the QWs. On the other hand, the localized states created by indium ?uctuation lead to a higher local carrier density, and Auger recombination in the QWs. Thus, the e?ciency droop ratio of the LEDs with a higher barrier growth rate was only 28.6%, which was superior to that with a lower barrier growth rate (39.3%).
关键词： and growth rate,nitride-based LEDs,e?ciency droop,quantum barrier
更新于2025-09-16 10:30:52
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Novel Siloxane-Modified Epoxy Resins as Promising Encapsulant for LEDs
摘要： This study investigated a new category of transparent encapsulant materials for light-emitting diodes (LEDs). It comprised a phenyl group that contained siloxane-modified epoxy (SEP-Ph) hybridized with a cyclic tetrafunctional siloxane-modified epoxy (SEP-D4) with methylhexahydrophthalic anhydride (MHHPA) as a curing agent. The SEP-Ph/SEP-D4 = 0.5/0.5 (sample 3) and SEP-D4 (sample 4) could provide notably high optical transmittance (over 90% in the visible region), high-temperature discoloration resistance, low stress, and more crucially, noteworthy sulfurization resistance. The lumen flux retention of the SEP encapsulated surface mounted device LEDs remained between approximately 97% and 99% after a sulfurization test for 240 h. The obtained comprehensive optical, mechanical, and sulfurization resistance proved the validity and uniqueness of the present design concept with complementary physical and chemical characteristics.
关键词： crosslinking density,surface mounted device LEDs,encapsulant,sulfurization resistance,siloxane-modified epoxy
更新于2025-09-16 10:30:52
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Efficient green-emitting Ca2GdZr2Al3O12:Ce3+,Tb3+ phosphors for near-UV-pumped high-CRI warm-white LEDs
摘要： In this work, we reported novel efficient Ce3+/Tb3+ co-doped Ca2GdZr2Al3O12 (CGZA) green-emitting phosphors by traditional solid state method. The phase purity, crystal structure, morphology, photoluminescence properties, internal quantum efficiencies (IQEs), and thermal stability of the samples were systematically investigated. The obtained results revealed that there was an obvious spectral overlap between the emission spectrum of Ce3+ singly doped CGZA phosphors and excitation spectrum of Tb3+ singly doped CGZA phosphors, and efficient energy transfer from Ce3+ to Tb3+ ions existed in Ce3+ and Tb3+ co-doped CGZA phosphors. The Ce3+→Tb3+ energy transfer mechanism was ascribed to the dipole-dipole interaction. The CGZA:Ce3+,Tb3+ phosphors exhibited a broad excitation spectrum in the wavelength range of 370-470 nm with a maximum at 408 nm corresponding to the spin-allowed 4f-5d transition of Ce3+ ions. Upon near-ultraviolet (near-UV) excitation at 408 nm, the composition-optimized CGZA:0.02Ce3+,0.8Tb3+ sample showed intense sharp narrow-line emissions at 485, 543, 591, 629, 643, 663, and 679 nm due to the 5D4→7FJ (J = 6-0) transitions of Tb3+ ions, along with a good IQE of 51%. Lastly, a white LED device was fabricated by using as-prepared CGZA:0.02Ce3+,0.8Tb3+ green phosphors, commercial BaMgAl10O17:Eu2+ blue phosphors, and CaAlSiN3:Eu2+ red phosphors, and under 300 mA driven current it gave bright warm-white light with a low correlated color temperature of 3969 K and a high color rendering index (Ra = 91.2). Our work provides a new perspective for the design and fabrication of efficient color conversion materials toward near-UV LED-based warm-white LEDs.
关键词： Garnet,Ce3+ ions,White LEDs,Phosphors,Tb3+ ions,Photoluminescence
更新于2025-09-16 10:30:52
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3D-printed, home-made, UV-LED photoreactor as a simple and economic tool to perform photochemical reactions in high school laboratories
摘要： In the paper we present the simple manufacturing of an easy and economical UV-A photoreactor using a desktop 3D printer and its application in chemical transformations. PLA (polylactic acid) was used as inexpensive and not toxic polymer for the 3D printing process, while commercially available decorative ultraviolet LEDs (UV-A) have been employed as a light source. With this device, the photoreduction of benzophenone was performed in high yield and short times, compatible with the duration of a typical laboratory experiment in a high school program.
关键词： UV-LEDs,benzophenone,photoreduction,photoreactor,3D printing
更新于2025-09-16 10:30:52