LED照明技术研发壁垒探讨

近20多年来,LED已在发光效率、寿命、稳定性等方面取得了巨大的突破,孕育着21世纪照明的革命.但目前LED光源在芯片质量、光电性能、封装工艺和材料、散热技术、驱动电路、非成像光学设计、相关标准和性价比等方面还存在问题,使LED在照明的推广应用中呈现说易行难的局面.因此试图通过对研发LED光源的壁垒进行探讨,结合LED...     

LED路灯自由曲面二次光学透镜的设计

半导体发光二极管（LED）的发光效率高、寿命长等优点,使其成为目前道路照明中的应用趋势。针对LED在道路照明上的应用,为获得路面上均匀的矩形配光效果对选定的LED进行自由曲面二次光学透镜的设计,设计出符合城市道路照明标准的LED路灯配光方案,使LED模组直接实现矩形配光。考虑封装后LED的实际配光曲线应用网格对应法利用计算软件标定自由曲面二次光学透镜的离散数据点坐标,对透镜结构进行建模。     

大功率LED灯的散热性能分析

以大功率LED灯具热管理为入手点,从芯片级、封装级、系统集成散热级3个方面,对大功率LED灯散热结构进行了简单的分析。并依据大功率LED灯运行热性能影响因素,对大功率LED灯散热性能优化进行了进一步探究。     

太阳能LED灯

以LED灯为光源,在结合当前研究水平、驱动要求和驱动原理的基础上设计供电电路,设计了一款太阳能LED灯。该太阳能LED灯可最大限度地发光,电路简洁、实用。     

绿色照明和现代灯具

1879年，爱迪生发明了白炽灯，利用电流通过电阻丝发热形成的热辐射发光，实现了实用化的电能向光能的转换，首次将电能用于人造光源，开辟了电气照明的时代，改变了人类照明依靠阳光、烛火的历史。但是，电生热再发光的转换，只有10％的电能转换为光能，效率极低，大部分电能都变成了无法利用的热能。从这个意义上讲，19世纪问世的白炽灯是高耗能产品。在20世纪，人类充分认识了电流通过稀薄气体时放电发光的规律，因而气体放电发光成为人造光源的主体。人造光源已发展为各种荧光灯、高压气体放电灯等种类繁多的产品。20世纪末，人们开始探索电光转换的新技术，专门的固体发光器件(半导体发光二极管LED)从理论和实践上显示了更优异的性能和节能特点，预计在21世纪将成为电光源的主流。     

科技

日前，美国的科学家们设计出了一种防震耐用的塑料发光技术，新灯管不仅能够无噪声地发出轻柔的白光，并且还具有防震，在低温下运行，可弯曲成任何形状以及能效高等优点。20世纪60年代开发的LED技术是目前最高效的发光技术之一。但LED也存在如灯管很容易过热，发出的偏蓝光让人常感不适等缺陷。未来，塑料发光技术有可能克服这些局限性。目前已经有企业表示愿意生产诱导聚合物致电发光灯管，并有望在2013年首次实现量产化。     

光电耦合器及其在可控硅零电压开关中的应用

光电耦合器是近十多年内发展起来的一种新型光电器件。它是由半导体发光器件和半导体光敏器件组合而成,将它们组装在同一个密封的管壳内,其结构如图1所示。连接发光二 极管的管脚作为输入端,连接光敏管的管脚作为输出端。目前多用砷化镓发光二极管做光电耦合器输入端的发光器件,实现电-光转换;用硅光敏二极管或硅光敏三极管作为光敏器     

热循环载荷下BGA封装体热应力特性

构建了热循环条件下球栅阵列(ball grid array,BGA)封装体传热和应力耦合的非稳态理论模型,通过器件自身发热功率随时间变化来实现循环热载荷,研究工作过程中流场、温度场、应力场的动态变化,并采用有限元方法进行数值求解,分析了热循环载荷对器件所处物理场的影响。研究结果表明:热循环过程中,器件整体温度与方腔内自然对流强度在高温保温时间开始时刻出现峰值,在低温保温时间结束时刻出现谷值;BGA封装体最高温点均位于作为热源的芯片上,承受应力最大点位于阵列最外拐点与上下侧材料的连接部位;随着循环次数的增加,每个热循环周期中关键焊点上端点处的最大等效应力不断增加。     

ZnS:Ag薄膜发光显示器件的研究

结构为ITO/SiO2/Ta2O5／ZnS：Ag／Ta2O5／SiO2／AL的薄膜电致发光器件，获得了蓝色电致发光。并发现Ag的浓度对该器件的光学性质有显著的影响，Ag的浓度较高时，器件的发光亮度低，抗击穿性差。浓度在0．05mol％左右时，器件的发光亮度最高。     

LED——colour your life

<正>人类在经历了漫长的火把、蜡烛、煤油灯照明的岁月之后,终于创造性地步入了以电力为照明光源的时代,按发光原理,我们先后共走过白炽灯、荧光灯、半导体灯(LED)三个发展阶段。LED作为在能源极度紧张中应运而生的"绿色照明"新宠儿,由于它的终于     

Thermal effects in packaging high power light emitting diode arrays

The package and system level temperature distributions of a high power (>1 W) light emitting diode (LED) array have been investigated using numerical heat flow models. For this analysis, a thermal resistor network model was combined with a 3D finite element submodel of an LED structure to predict system and die level temperatures. The impact of LED array density, LED power density, and active versus passive cooling methods on device operation were calculated. In order to help understand the role of various thermal resistances in cooling such compact arrays, the thermal resistance network was analyzed in order to estimate the contributions from materials as well as active and passive cooling schemes. Finally, an analysis of a ceramic packaging architecture is performed in order to give insight into methods to reduce the packaging resistance for high power LEDs.     

Experimental and Numerical Investigation of a Microjet-Based Cooling System for High Power LEDs

The optical extraction efficiency and reliability of light emitting diodes (LEDs) relies heavily on successful thermal management due to their inherit dependence on the low junction temperature of LED chips. In this paper, a microjet-based cooling system is proposed for the thermal management of high power LEDs. Experimental and numerical investigations on such an active cooling system were conducted. Thermocouples were packaged with LED chips to conduct an online measurement of the temperature and evaluate the cooling performance of the proposed system. The experimental results demonstrate that the microjet-based cooling system has good cooling performance. For a 2 × 2 LED chip array, when the input power is 5.6 W and the environmental temperature is 28°C, the temperature of the 2 × 2 LED chip array reaches 72°C within 2 minutes and continues to increase sharply if no active cooling technique is applied. By using the proposed cooling system to cool the LEDs, however, the maximum LED temperature measured by thermocouples will remain stable at about 36.7°C, when the flow rate of the micropump is 9.7 mL/s. With consideration of the experimental difficulty, a numerical investigation was conducted on flow and temperature distribution in the microjet device. The feasibility of the numerical model was proven by comparison with experimental results. The numerical results showed that at a flow rate of 3.2 mL/s, the heat transfer coefficient of the impinging jets in the proposed system was about 5523 W/m²·K, and the pressure drop in the microjet device was about 1368 Pa.     

Economic feasibility of solar-powered led roadway lighting

The optical efficacy of light emitting diode (LED) has exceeded 72 lm/W in 2006. This implies that energy can be saved about 75%, as compared to mercury lamps widely used in roadway lighting. In some remote areas where the grid power cannot reach, independent solar-powered lighting using high-power LED provides a promising solution. However, the cost of solar photovoltaic device may cause the application of solar-powered LED roadway lighting to be not economically feasible.The present study investigates the design of the solar-powered LED roadway lighting using high-power LED luminaire (100 W) and estimates the installation cost for a 10 km highway with 2 lanes. LED luminaries are installed on both side of the road with staggered arrangement. The pole distance is 30 m. The cost comparison of LED lighting using grid and solar power with the conventional mercury lamps was carried out. It shows that the installation cost is 22 million USD for LED powered by grid power and 26 million USD for solar-powered. The total installation cost of conventional mercury lighting is 18 million USD. The excess cost of LED mainly comes from the cost of LED lamp and solar PV. But, the cost of power generation and electrical transmission line can be greatly reduced since about 75% energy was saved for LED. This permits the use of smaller copper wire and shorter line length for solar-powered system which in turn saves installation cost. The payback time for the excess investment of LED is 2.2 years for LED using grid power and 3.3 years for LED using solar power.     

A study of an LED backlight thermal module

The present study uses a heat sink plate to conduct natural convection in order to examine different areas of the heat sink and the effects of mounting different quantities of LEDs on the same surface on the thermal mechanism performance. Based on the experimental results, when a heat sink plate is arranged vertically, the channel flow between the fins is parallel to gravity. The LED substrate plate temperature is different from that at the end of the fin, and rises with the increase of total power. The thermal resistance rises slowly and then declines with the increase of LED electric power. As for temperature change of the LED substrate and at the end of the fin, when the temperature difference is increased, it also increases the natural convection thrust. For thermal resistance, the environmental thermal resistance at the bottom of the heat sink plate is lower than at the middle and top sections. These LED power emissions will be changed synchronously. Regarding the LED quantity control, the rate of increase is the highest for the heat sink plate with 30 pcs LED, and the temperature is very high for the heat sink plate with 45 and 60 pcs LEDs when the power approaches 1 W. Moreover, the rising rate is the lowest for the heat sink plate with 60 pcs LEDs. Depending on the brightness requirement, the illuminant is provided by 60 pcs LEDs to obtain a lower temperature so that the system can reduce the thermal protective design. Evidence shows that a high conductivity heat pipe embedded in the channel can provide a more uniform temperature distribution. The present study provides a further understanding on the influence of different illuminant densities on the heat sink structure and the temperature difference in an LED heat transfer device, in order to provide a reference for heat sink design of a backlight module and LED illuminant module evaluation. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20321     

Thermoelectric transformation and illuminative performance analysis of a novel LED-MGVC device

Energy-efficient, small and lightweight high-power light-emitting diodes (Hi-LEDs) are combined with a thermo-generation module (TGM) to transform the heat power generated by the LED into electric energy in the present paper. Variation in the dielectric copper and solder layer thickness in the printed circuit board (PCB) composite was found to affect the thermal performance of the Hi-LEDs lighting system, and a vapor chamber (VC) was shown to provide excellent heat dissipation performance when used with Hi-LEDs. Therefore, VC and PCB (VCPCB) were combined for integration with the Hi-LEDs package system (micro-generator with LED vapor chamber-based plate, LED-MGVC) for performance and illumination comparison. This study analyzes the performance of a novel LED-MGVC device using experimental and illumination-analysis methods with VCTM V1.0. Results depict that the LED-MGVC system provides significant improvement for thermal performance and illumination and thermoelectric properties.     

基于自适应PI控制的太阳能LED照明系统PWM恒流控制器

以PIC单片机为控制核心,提出了一种基于自校正PI控制器的太阳能LED照明系统的PWM恒流控制的设计方案。该方案较好地实现了输出电压的自适应控制,即蓄电池电压足够时实现恒流控制,而当蓄电池电压较低时实现非恒流控制。同时样机实验也验证了方案的正确性。     

Core-shell structured ZIF-7@ZIF-67 with high electrochemical performance for all-solid-state asymmetric supercapacitor

Zeolitic imidazolate frameworks (ZIFs) are considered as a promising material for energy storage in recent years. Here, core-shell structured ZIF-7@ZIF-67 is synthesized in this work. The core-shell structured material can promote electron transfer of inner-outer metals ions of ZIF-7@ZIF-67, quicken diffusion of electrolyte ions and improve the capacitance performance compared to the ZIF-7 and ZIF-67. ZIF-7@ZIF-67 delivers good energy storage ability with a specific capacitance of 518.9 F g⁻¹ at a current density of 1 A g⁻¹ and remarkable stability with a retention of 99.6% after 4000 cycles in the three-electrode system. Furthermore, an all-solid-state asymmetric supercapacitor (ASC) device is assembled based on core-shell structured ZIF-7@ZIF-67 as positive electrode. Impressively, the ASC device displays an energy density of 31 Wh kg⁻¹ at a power density of 400 W kg⁻¹ and an excellent cyclic stability with 99.5% retention after 10,000 cycles at a current density of 10 A g⁻¹. Finally, two all-solid-state ASCs are contacted to power various lighting-emitting diodes (LED). The red LED can be kept glowing for over 10 min. These electrochemical characteristics suggest that core-shell structured ZIF-7@ZIF-67 is a potential material for energy storage device with long-life cyclic stability.     

综合医院电气节能技术措施探讨

以降低A综合医院电能损耗为目的,通过测算空调系统、照明系统、医疗器械等用电负荷,分析医院电耗现状,探讨综合医院电气节能技术措施,有针对性采取更换LED照明、新增电梯电能回馈装置、更换新型节能变压器等措施。通过节电前后的数据对比分析,取得了较好的节电效果,为其他医院电气系统安全可靠、节能经济地运行提供参考。     

热处理渗碳炉控制系统硬件设计

对渗碳炉的主回路和控制回路进行了设计，详细分析了渗碳炉单片机控制的硬件系统，它包括温度控制和碳势控制。该系统由8031单片机，2764／6264存储器，8279键盘／显示，晶闸管触发控制装置，掉电保护电路，报警电路及打印电路等组成，具有可靠性高，测控精度高，自动化程度高，功能丰富等优点。     

An overview of energy efficient solid state LED driver topologies

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.