英文
The LED lighting power supply design
Problems of design：
1. Electrolytic capacitors and LED life issues do not match
2. Common cause of LED lights flashing and approach
3. PWM dimming the impact on the life of LED dimming control
4. Using RIAC LED brightness of the potential problems
In the LED lighting power supply design, there are several design challenges: life electrolytic capacitors do not match with the LED, LED lights flashing common causes and solutions, PWM dimming of the LED's life impact of the use of TRIAC LED dimming control brightness of the potential problems. ON Semiconductor Senior Application Engineering Manager Cheng were in the text before the occurrence of these problems causes and solution to start on.
1.Electrolytic capacitors and LED life issues do not match
LED lighting is an important consideration is the LED drive circuit and the LED itself should be able to compare the work of life. Although the reliability of the factors affecting driver circuit a lot, but the overall reliability of electrolytic capacitors have a critical influence. In order to extend the service life of the system, which requires focused analytical applications in capacitors, and select the appropriate electrolytic capacitors.
In fact, the effective working life of electrolytic capacitors in large part by environmental temperature and the role of the internal impedance of the ripple current caused by impact of the internal temperature rise. Electrolytic capacitor electrolytic capacitor manufacturer's rated life is based on the maximum rated temperature, exposure to the environment and to exert maximum rated ripple current conditions obtained. At 105 ° C rated life of typical capacitance may be 5,000 hours, capacitance compared to the actual working stress suffered by the lower rating level, the more effective long working life. Therefore, on the one hand, choose rated long life and can withstand high operating temperatures of electrolytic capacitors rated to extend the working life of course. On the other hand, according to the actual stress and temperature, you can still choose a lower temperature rating and rating life of the capacitor, thereby providing a more cost-effective solutions; another point of view, a proper consideration in the design of the stress and temperature, can effectively extend the service life of electrolytic capacitors, to better match with the LED lifetime.
For example, ON Semiconductor meet "Energy Star" standards for off-line-based solid state lighting LED driver GreenPoint ? reference design chosen Panasonic ECA-1EM102 aluminum electrolytic capacitor, its rating of 1000 μF, 25 V, 850 mA, 2,000 hours and 85 °C. Assuming 50 °C ambient temperature conditions, the capacitance of the useful life over 120,000 hours. Therefore, strive to make LED driver circuit in the appropriate temperature conditions and properly handle the heat dissipation, LED driver circuit can be achieved with LED working life of the matching problem.
In general, if the LED drive circuit must use the electrolytic capacitor, it must strive to control the application of power capacitors and suffered operating temperature, thus extending the maximum capacitance of working life in order to match with LED life; the other hand, designers should also be possible to avoid the use of electrolytic capacitors.
https://www.doczj.com/doc/818650697.html,mon cause of LED lights flashing and approach
Usually the human eye can perceive frequencies up to 70 Hz flicker of light, above this frequency will not be perceived.Therefore, in LED lighting applications, if the pulse signals frequency below 70 Hz low-frequency components, the human eye will feel the flicker. Of course, in specific applications, there are several factors that may cause LED light flashes. For example, in offline LED lighting low-power applications, a common power supply topology is isolated flyback topology. ON Semiconductor to meet the "Energy Star" 8 W solid-state
lighting standards-based off-line LED driver GreenPoint ? reference design, for example, because the flyback voltage regulator sine square wave power conversion bias is not to provide a constant primary energy, Dynamic Self-Supply (DSS) circuit may be activated and trigger a flashing light. To avoid this problem, must be made to the initial bias in each half cycle part of the discharge, the corresponding need to properly select the bias circuit constitute the capacitance and resistance value.
In addition, even in the use of power factor correction to provide excellent support of TRIAC dimming LED driver applications, also called electromagnetic interference (EMI) filter. By the TRIAC step (step) induced transient current EMI filter will stimulate the natural resonant inductor and capacitor. If this resonance characteristics lead to reduced input current below the holding current TRIAC, TRIAC will be closed. After a short delay, TRIAC will turn often to stimulate the same resonance. In a semi-input power waveform cycle, this series of events may be repeated several times to form the visible LED blinks. To address this problem, TRIAC dimmer is a key requirement is very low input capacitance EMI filter and the capacitor to be able to through the TRIAC and the winding impedance decoupling. According to the formula, dimming module capacitance decreases, then it can increase the resonant circuit of resistance, on the principle of vibration suppression, restoration of the desired circuit.
3.PWM dimming of the LED's life impact
Its very long life LED, PWM dimming LED will not hurt the life expectancy; even as PWM dimming LED to help reduce the heat, in fact, also help to extend the LED life expectancy. Of course, in the system design, the need for effective detection and control of LED temperature, to ensure reliable operation LED，reflecting its long life and low maintenance cost advantages.
4.LED dimming control using TRIAC brightness of the potential problems
Current TRIAC dimming is fairly popular with the market welcomed the dimming mode. TRIAC dimmer originally designed for incandescent lamps, but such as ON Semiconductor has introduced a leading provider of support TRIAC dimming of the LED driver is ideal for LED lighting is provided in the TRIAC dimmer. However, this approach has its limitations lie, such as increased circuit complexity, affect the power factor; dimming level is relatively limited and so on. ON Semiconductor, as applied to the first green high-performance electronic products, energy efficient silicon solutions provider recently introduced for residential and commercial LED lighting applications. This device is using the critical conduction mode (CrM) anti-shock structure of a single-stage topology to provide power factor higher than 0.95,so they save DC - DC (DC-DC) conversion section, simplifying the circuit. This is low even when the device also offers high energy efficiency; comply with all regulatory requirements and overall system optical efficiency requirements. In addition, this device is compatible with the front end of TRIAC dimmer and dimmer along the transistor, depending on the use of dimmers, LED light output can be adjusted to less than 2%, providing excellent dimming performance.
5. ON Semiconductor's LED driver pushing the recent hot program
Semiconductor recently introduced several important energy-efficient GreenPoint ? LED driver reference design is:
1) 3W to 5 W LED driver reference design. This reference design for MR16 LED replacement with the size and characteristics of configuration, have been carefully constructed and tested for driving high-brightness LED. This reference design is based on buck - boost topology, using ON Semiconductor's non-isolated constant current configuration, the work of about 150 kHz (kHz) frequency NCP3065 switching regulator. This reference design circuit for track lighting, automotive lighting and landscape lighting, 12 Vac or 12 Vdc applications, regardless of input and output LED line voltage to change, provide a smooth steady flow of current. This reference design also provides a unique auto-detection circuit, supporting 12 Vdc or 12 Vac power input，while maintaining the target output current.
2)Isolated Constant Current LED Driver 8 W GreenPoint ? reference design. This reference design is expected to meet the United States, "Energy Star" (ENERGY STAR ?) residential lighting applications, version 1.1 Solid State Lighting (SSL) requests the designers designed the same have been carefully constructed and tested, used to drive portablelamps,cabinets corridors within the lamps and other lighting and outdoor applications in 1-8 high-power LED. This reference design uses a novel circuit configuration，without additional passive power factor correction (PFC) network, you can under the conditions provided in the 115 Vac power factor above 0.85，reducing component count, and easily meet the residential LED Applications power factor requirements.This is designed to support 90 V to265 Vac universal input voltage, using ON Semiconductor integrated fixed-frequency current-mode controller and 700 V MOSFET in the NCP1014 switching regulator integrated circuit (IC).
3) High power factor for offline TRIAC dimmer LED driver GreenPoint ? reference design. This reference design uses NCL30000 this critical devices，intended for the United States, "Energy Star" commercial and residential lighting applications. NCL30000 operating temperature range of -40 °C to +125 °C, to ensure that for most solid-state lighting (SSL) applications, the scope of work under different circumstances. NCL30000 has a typical value of 24 microamps (μA),low startup current and low typical operating current of 2 mA, with energy-efficient design. NCL30000 other key features include programmable on-time limiter, zero current detection (ZCD) sensor module, gate drivers, and application CrM switching power supply required by the other PWM circuit and protection.
6.Semiconductor LED driver design advantages
ON Semiconductor offers a wide range of different LED-driven programs for a wide range of applications: automotive, mobile / portable (mobile phones and digital cameras, LCD backlight and camera flash), the large size of the LCD screen (laptop, netbook, LCD TV ) in LCD backlighting, signs, buildings, and general illumination.
ON Semiconductor's offerings span three kinds of LED driving method: linear program (very simple procedure with few external components), DC - DC (DC-DC) inductive switching converter (used to provide energy efficiency and high current) and the charge pump switching converter (used to provide energy efficiency and compact size).
Overall, no matter what kind of LED lighting applications, no matter what kind driver program, no matter what kind dimming method, regardless of what common power supply voltage, ON Semiconductor may provide a suitable LED driver program to meet of customers the different needs.
7. Current LED lamp features:
High-power LED street lamp with conventional high pressure sodium lamps is different is that high-power LED street lamp light source with low voltage DC power supply, power from the GaN-based blue LED and yellow phosphor-based synthesis of highly efficient white LED, LED (Light Emitting Diode, abbreviated as LED) is based on the formation of semiconductor PN junction with the faint light of the high power solid-state light source can, in certain positive bias voltage and injection current into the P region into the hole and electron diffusion region N After the active region to be issued by the radiative photon light energy directly into electrical energy.
LED lamp as light source, which compared the traditional lamp light source has many advantages：
1. LED Street light, point of itself, does not diffuse light, to ensure optical effect;
2. LED lamp has a unique secondary optical design, LED street lamp light shines on the area required for lighting, that is the road to further improve the light efficiency and save energy;
3. LED light source efficiency of the current has reached 100lm / W, but there is still
much room for development, the theoretical value can reach 250lm / W. The luminous efficiency of high pressure sodium lamp with the power to increase only increase, and therefore, the overall optical efficiency stronger than the high pressure sodium lamp LED lamps;
4.LED street light color rendering than the high-pressure sodium lamp high pressure sodium lamp color rendering index of only 23, while the LED lamp color rendering index can reach 75 or more, from the visual psychological perspective, to achieve the same brightness, LED street lamp illumination average of lower than 20% above the high-pressure sodium lamp (lighting the light of British standard); and, in the middle of the visual level, the human eye in high color temperature environments with low color temperature than the environment can identify more easily things, to avoid the occurrence of some danger;
5. LED street light decline of small, one-year decline of less than 3% of light, using 10 years of road use is still to achieve illumination requirements, therefore, LED street lamp design, the use of power can be lower than the high-pressure sodium lamp;
6. LED lights that automatically adjust light, to achieve different times to meet the lighting requirements, the maximum possible reduction in power, saving energy;
However, recently heard the views of many experts and scholars, that the LED lights to replace high pressure sodium lamp as technically immature. The main reasons are the following:
1. LED luminous efficiency and high-pressure sodium lamp can not be compared
2. LED’s light is too concentrated, the poor uniformity of illumination
3. LED street light failure severe, life is not long
4. LED lamp itself, the excessive weight, not easy installation, wind
5. LED lamps and high cost, can not be widely
We view one by one according to the above analysis:
1. Luminous efficiency
At present, LED light-emitting efficiency of Looking at the figures do not as high pressure sodium. LED light efficiency is generally 65 ~ 75lm / w, but with the technology, LED light effects increased each year, while the high-pressure sodium lamp can reach 125lm / w. However, the high-pressure sodium lamp of the spectrum are relatively concentrated in yellow, it The color temperature is relatively low, only 2000 ~ 2500K, and LED color temperature higher than can reach 3500 ~ 4500K. Another high pressure sodium light is launched to 4, with much of the light can not reach the road. Also, high pressure sodium lamp color index is poor, only 23 or so, feeling faint; the LED's high CRI, can reach 75 to 80. Road bright, comfortable. So from a practical perspective glow, LED but much higher than the high-pressure sodium lamp. The LED can replace 250W 135W high pressure sodium lamp, or 300W for mercury. 135W of LED, the output of only about 7020 lumens luminous flux (after the second optical design, will be lost), to reach the road when the number is still 6500 lumens lumens, while the average road surface illuminance can reach 16Lux (12m high pole). 250W high pressure sodium lamp luminous flux output of 20,000 lumens. But the road to reach the number of only 7000 lumens lumens. Illumination of the road about 30 ~ 40Lux, because the color difference coefficient, LED illumination correction factor is 2.35 times, high pressure sodium lamp of the correction factor of 0.94 times. So 135W of LED illumination of the ground later amended to 37.6Lux, while the high-pressure sodium lamp illumination revised 28.2 ~ 37.6. Both very. Therefore, 135W of LED can replace 250W high pressure sodium lamp, LED can be 1.85 times the energy, energy efficiency is about 50%.
2. Irradiation Uniformity
Indeed, if not a secondary optical design, LED's light is more concentrated, they must be secondary optical design, to light intensity distribution was bat-shaped.
3. LED light failure problems
Now, some businesses, in order to cut costs, with hundreds of φ5 small power LED. But this low-power LED light is a very serious decline, and its decline to 80% of the light life of only 1,000 hours. Therefore, the need for long-term use of the street as it is absolutely not allow use of such low power LED's. As a high-power LED, the light failure would be much better.
4. LED lights of the weight problem
LED street lamps, and high pressure sodium replacement in the process, in order to prevent excessive LED street lamp cap, a number of LED lamp manufacturers as much as possible to reduce the weight LED lamp. From the original single lamp about 30 kg, down to the present more than 10 kg. Also further reduce the weight of a downward trend.
5. LED lamps and high cost, can not be widely
LED street light is composed of many parts, of which the most efficient light-emitting device is chip, the price is also the most expensive part of the chip. Now the chip light effect in 65 ~ 75lm / w, but the major chip makers have greater photosynthetic efficiency in the development of the chip. Just imagine, with the advancement of technology, once developed to a very high luminous efficiency level, then use the number of chips less than now, but will also decrease the price of chips. By that time, LED lights overall price will fall.
8. LED lamp features the future:
Think, LED street lamp replacement high pressure sodium lamp, energy saving and emission reduction is a trend in the future. LED lamps to develop, I think that needs attention in the following areas:
1. increased luminous
2. things right for the second optical
3. solution heat
4. modular
A.Optic need to increase the extension from the high-power LED technology, chip technology and other infrastructure level to further improve. At present, domestic and foreign production of white LED's LED chips is first placed in the package substrate, with gold for bonding, and YAG phosphor coating around the chip, and then epoxy resin coating. Resin not only protect the chip from the role it has played the role of the condenser. From the LED chip emits blue light shines around the phosphor layer after numerous scattered reflection, absorption, and finally sent to the outside.LED (blue) of the spectral lines of the peak at 465nm Department issued a half-value width 30nm.LED some blue excitation yellow YAG phosphor layer, so that yellow light (peak 555nm), part of the blue light, directly or reflection After the outgoing and finally outside the blue and yellow light for the dichroism, that is white. Flip Chip Technology (FlipChip) can be compared with the conventional LED chip packaging technology for more efficient light extraction. However, if the chip is not below the increase in light-emitting layer electrode reflection layer reflecting light energy waste, will result in the loss of about 8% of the light. So bottom reflective layer material must be increased. Chips on the side of light must use the mirror to be reflected heat sink to increase the light extraction device. And the sapphire substrate in flip-chip (Sapphire) and epoxy resin optical surfaces should be combined with a layer of silica gel to improve the chip out of the refractive index of light. After the improvement of optical packaging technology, can increase the high-power LED light extraction device (flux).
B.LED lighting equipment to optimize the design to improve the quality of LED's used. Therefore, high-power LED light source of secondary optics optical design, to meet the large cast light and flood lighting with light demand is particularly urgent. Through the second optical design technology, plus a reflector design with multiple optical lens and a light non-spherical surface, can improve the light extraction efficiency of the device.Traditional light source direction 360 °, lamp reflectors will depend on the majority of light reflected to a
specific location, only 40% of the road just to reach directly through the glass, the other just by re-projected lamp reflector lamps , the efficiency of the lamp reflector generally only 50% to 60%, so 60% of the light output within the lamp is in a loss of 30% to 40% of the then projected onto the road on. A significant portion of the light source output is limited to the internal heat lamps consumed. LED lights are pre-shoot most of the light ray, can achieve> 95% of the light effect, which is different from other LED light source of one of the important features, if not a very good use of this feature will make the advantages of large LED discount. Most high-power LED lamp assembly as is the number of LED chips, light shines to so many different directions, we give full play to the overall chip package characteristics, the lens to be resolved, through optical design, according to different needs, with different convex curve , relying on the lens to the light assigned to different directions to ensure that the light angle large can reach 120 ° ~ 160 °, a small can of light gathered in 30 °, lens, once finalized, the production process to ensure the premise, the same kinds of lamps Optical characteristics of distribution also reached consensus. Completely by repeated trial, constantly sum up experience, to make LED lamps to lighting requirements of the standard bat wing type of light. At present the tunnel lights, street lamps and general lighting applications has reached their respective places of lighting requirements.360毕业设计网https://www.doczj.com/doc/818650697.html,
9.Conclusion
Recommendation: uniform LED standards,improve quality and stability, the establishment of market competition, co-ordinating body, to avoid vicious competition, and vigorously promote the concept of quality LED, avoid adverse impact instance, to get people to accept the LED is ideologically can achieve its long life The advantages and improve the level of choice and use of LED. In summary, LED lights replace the high-pressure sodium lamp, road lighting is the inevitable trend of the future.
中文
有关LED照明电源设计难题的探讨
设计问题：
1.电解电容寿命与LED不相匹配的问题
2.LED灯闪烁的常见原因与处理办法
3.PWM 调光对LED的寿命有何影响
4.利用TRIAC调光调控LED亮度的潜在问题
在LED照明电源设计中，存在以下几个设计难题：电解电容寿命与LED不相匹配、LED灯闪烁的常见原因与处理办法、PWM 调光对LED的寿命有何影响、利用TRIAC 调光调控LED亮度的潜在问题。
1.电解电容寿命与LED不相匹配的问题
LED照明的一个重要的考虑因素，就是LED驱动电路与LED本身的工作寿命应该能够相提并论。虽然影响驱动电路可靠性的因素有很多，但其中电解电容对总体可靠性有至关重要的影响。为了延长系统工作寿命，需要有针对性地分析应用中的电容，并选择恰当的电解电容。
实际上，电解电容的有效工作寿命在很大程度上受环境温度及由作用在内部阻抗上的纹波电流导致的内部温升影响。电解电容制造商提供的电解电容额定寿命是根据暴露在最高额定温度环境及施加最大额定纹波电流条件下得出的。在105°C时典型电容额定寿命可能是5,000小时，电容所实际遭受的工作应力相比额定电平越低，有效工作寿命也就越长。因此，一方面，选择额定工作寿命长及能够承受高额定工作温度的电解电容当然能够延长工作寿命。另一方面，根据实际的应力和工作温度，仍然可以选择较低额定工作温度和额定寿命的电容，从而提供更低成本的解决方案；换个角度说，在设计中考
虑保持适当的应力和工作温度，可以有效地延长电解电容的工作寿命，使其更能与LED 寿命相匹配。
举例来说，安森美半导体符合“能源之星”固态照明标准的离线型LED驱动器GreenPoint?参考设计选择了松下的ECA-1EM102铝电解电容，其额定值为1000 μF、25 V、850 mA、2,000小时及85°C。在假定50°C环境温度条件下，这电容的可用寿命超过12万小时。因此，尽力使LED驱动电路工作在适宜的温度条件并妥善处理散热问题，就能
总的来看，如果LED驱动电路中必须使用电解电容，那就必须努力控制电容所受的应用力及工作温度，从而最大程度延长电容工作寿命，以期与LED寿命配；另一方面，设计人员也应该尽可能地避免使用电解电容。
2.LED灯闪烁的常见原因与处理办法
通常人眼能够感知到频率达70 Hz的光闪烁，高于这个频率则不会感知。故在LED 照明应用中，如果脉冲信号出现频率低于70 Hz的低频分量，人眼就会感受到闪烁。当然，在具体应用中，有多种因素可能导致LED灯闪烁。例如，在离线式低功率LED照明应用中，一种常见的电源拓扑结构是隔离型反激拓扑结构。以安森美半导体符合“能源之星”固态照明标准的8 W离线型LED驱动器GreenPoint?参考设计为例，由于反激稳压器的正弦方波功率转换并未给初级偏置提供恒定能量，动态自供电(DSS)电路可能会激活并引发光闪烁。为了避免这个问题，必须使初级偏置能够在每个半周期部分放电，相应地，需要恰当选择构成这偏置电路的电容和电阻的量值。
另外，即使是在使用提供极佳功率因数校正、支持TRIAC调光的LED驱动应用中，也要求电磁干扰(EMI)滤波器。由TRIAC阶跃(step)引起的瞬态电流会激发EMI滤波器中电感和电容的自然谐振。如果这谐振特性导致输入电流降至TRIAC维持电流之下，TRIAC 将会关闭。短暂延时后，TRIAC通常又会导通，激发同样的谐振。在输入电源波形的一个半周期内，这系列事件可能会重复多次，从而形成可见的LED闪烁。为了应对这个问题，TRIAC调光的一项关键要求就是EMI滤波器的输入电容极低，且这电容要能够通过TRIAC及绕线阻抗解耦。根据公式，调光模块中电容减小的话，就能够增大谐振电路的电阻，原理上就抑制振荡，恢复想要的电路工作。
3.PWM 调光对LED的寿命有何影响
LED本身的寿命很长，PWM调光并不会损及LED的预期寿命；甚至由于PWM调光帮助减小LED发热量，实际上还能帮助延长LED预期寿命。当然，在系统设计中，需要有效地检测及控制LED温度，保证LED可靠工作，体现其长寿命和低维护成本的优势。
4.利用TRIAC调光调控LED亮度的潜在问题
当前TRIAC调光是一种颇受市场欢迎的调光方式。TRIAC调光器最初是为白炽灯设计的，但诸如安森美半导体这样的领先供应商也推出了支持TRIAC调光的LED驱动器，非常适合在LED照明中提供TRIAC调光。但这种方式也有其局限所在，如增加电路复杂性、影响功率因数、调光级别相对有限等问题。安森美半导体身为应用于绿色电子产品的首要高性能、高能效硅方案供应商，最新推出了用于住宅及商业LED照明应用的LED驱动器NCL30000。这器件使用临界导电模式(CrM)反激架构，以单段式拓扑结构提供高于0.95的功率因数，故又省却直流-直流(DC-DC)转换段，简化了电路。这器件即使在低电平时也提供极高能效，符合各种规范要求及整体系统光效要求。另外，这器件兼容于前沿TRIAC调光器及尾沿晶体管调光器，视乎所用的调光器，LED光输出可调至低于2%，提供优异的调光性能。
5.安森美半导体近期热推的LED驱动方案
安森美半导体近期推出了几款重要的高能效GreenPoint? LED驱动器参考设计，分别是：
1) 3W至5 W LED驱动器参考设计方案。这参考设计采用适合MR16 LED替代的尺寸及特性配置，经过了精心构建及测试，用于驱动高亮度LED。这参考设计基于降压-升压型拓扑结构，使用安森美半导体的非隔离型恒流配置、工作在约150千赫兹(kHz)频率的NCP3065开关稳压器。这参考设计电路适合轨道照明、汽车照明及景观照明等12 Vac 或12 Vdc应用，不论输入线路及输出LED电压如何变化，均提供平坦的电流稳流。这参考设计还提供独特的自动检测电路，支持12 Vdc或12 Vac电源输入，同时维持目标输出电流。
2) 隔离型8 W恒流LED驱动器GreenPoint?参考设计方案。这参考设计是为期望符合美国“能源之星”(ENERGY STAR?)住宅照明应用1.1版固态照明(SSL)要求的设计人员而设，同样经过了精心构建及测试，用于驱动便携台灯、橱柜内照明及户外走廊灯等应用中的1到8颗大功率LED。这参考设计采用新颖的电路配置，无须增加额外的无源功率因数校正(PFC)网络，即可在115 Vac条件下提供高于0.85的功率因数，减少了元器件数量，并轻松满足住宅LED应用功率因数要求。这设计支持90 Vac至265 Vac的通用输入电压工作，采用安森美半导体集成了固定频率电流模式控制器和700 V MOSFET的NCP1014开关稳压器集成电路(IC)。
6.安森美半导体LED驱动设计优势
安森美半导体提供众多不同的LED驱动方案，用于宽广范围的应用：汽车、移动/便携(手机和数码相机的LCD背光及相机闪光)、中大尺寸的LCD屏幕(笔记本、上网本、液晶电视)的LCD背光、标志、建筑物，以及通用照明。
安森美半导体提供的产品涵盖3种LED驱动方法：线性方案(极简单且极少外部元件)直流-直流(DC-DC)电感型开关转换器(用于提供高能效及较大电流)，以及电荷泵开关转换器(用于提供高能效及紧凑的尺寸)。
总的来看，无论是何种LED照明应用，无论需要何种驱动方案，无论需要何种调光方法，无论采用何种常见电源电压供电，安森美半导体均可提供适合的LED驱动器方案，满足客户的不同需求。
7.当今LED路灯特点：
大功率LED路灯与常规高压钠灯路灯不同的是，大功率LED路灯的光源采用低压直流供电、由GaN基功率型蓝光LED与黄色荧光粉合成的高效白光二极管，发光二极管（Light Emitting Diode,简写为LED）是基于半导体PN结形成的用微弱的电能就能发光的高效固态光源，在一定的正向偏置电压和注入电流下，注入P区的空穴和注入N区的电子在扩散至有源区后经辐射复合而发出光子，将电能直接转化为光能。
LED作为路灯的光源，它和传统路灯光源比较有许多优点。
1、LED路灯本身具有光的指向性，没有光的漫射，保证光效；
2、LED路灯有独特的二次光学设计，将LED路灯的光照射到所需照明的区域，即路面，进一步提高了光照效率，达到节能目的；
3、LED的光源效率目前已达100lm/W,而且还有很大的发展空间，理论值能达到250lm/W.而高压钠灯的发光效率是随功率增加才有所增加，因此，总体光效LED路灯比高压钠灯强；
4、LED路灯的光显色性比高压钠灯高，高压钠灯显色指数只有23左右，而LED路灯显色指数可达到75以上，从视觉心理角度考虑，达到同等亮度，LED路灯的光照度平均可以比高压钠灯降低20%以上（参照英国道路照明标准）；而且，在中间视觉水平下，人眼在高色温环境里比低色温环境更容易辨别事物，避免了某些危险状态的发生；
5、LED路灯的光衰小，一年的光衰不到3%,使用10年仍达到道路使用照度要求，因此，LED路灯在使用功率的设计上可以比高压钠灯低；
6、LED路灯可以自动调光，能实现在满足不同时段照明要求，最大可能的降低功率，节省电能；
但是，最近听到不少专家学者的意见，认为LED作为路灯来取代高压钠灯在技术上还不成熟。主要的理由有以下几点：
1、LED的发光效率无法和高压钠灯相比
2、LED的照射过于集中，其照射的均匀度差
3、LED路灯的光衰严重，寿命不长
我们根据以上的观点逐一进行分析：
1、发光效率问题
目前来说，LED的发光效率从数字上来看的确不如高压钠灯。LED现在的光效一般在65~75lm/w,而且随着技术的发展，LED的光效每年都在提高，而高压钠灯可以达到125lm/w.但是，高压钠灯的光谱比较集中于黄色，它的色温比较低，只有2000~2500K,而LED的色温较高，可以达到3500~4500K以上。另外高压钠灯的光线是向四处发射的，有很大一部分光无法到达路面。还有，高压钠灯的显色指数差，只有23左右，感觉昏暗；而LED的显色指数高，可以达到75~80.路面明亮，感觉舒适。所以从实际的发光效果来看，LED反而可以比高压钠灯高出很多。135W的LED可以取代250W的高压钠灯，或300W的水银灯。135W的LED,其输出光通量大约只有7020流明（经过二次光学设计，会有所损失），到达路面时的流明数仍为6500流明，而路面的平均照度可以达到16Lux （12m高杆）。250W高压钠灯的输出光通量为20,000流明。但到达路面的流明数就只有7000流明。路面的照度大约为30~40Lux,由于显色系数的差别，LED的照度修正系数为2.35倍，高压钠灯的修正系数为0.94倍。所以135W的LED经过修正以后地面的照度为37.6Lux,而高压钠灯的修正后的照度为28.2~37.6.二者相当。所以，135W的LED可以取代250W的高压钠灯，LED可以节能1.85倍，节能效率约为50%.
2、照射均匀度问题
的确，如果不进行二次光学设计，LED的照射是比较集中，所以一定要进行二次光学设计，使其光强分布图呈蝙蝠形。
3、LED的光衰问题
现在有的商家，为了降低成本，就采用几百只φ5的小功率LED.然而这种小功率的LED的光衰是非常严重的，其光衰至80%的寿命只有1000小时。所以，作为需要长期使用的路灯是绝对不能允许采用这种小功率LED的。作为大功率LED,其光衰就要好很多。
8.未来LED路灯特点：
个人认为，LED路灯替换高压钠灯，是今后节能减排的一个趋势。LED路灯要发展，我认为在以下几个方面需要注意：
1、提高光通
2、弄好二次光学
3、解决散热
4、模块化
A.光通的提高还需要从大功率的LED的外延技术、芯片工艺等基础层次进一步提升。目前，国内外制作白光LED的方法是先将LED芯片放置在封装的基片上，用金丝进行键合，然后在芯片周围涂敷YAG荧光粉，再用环氧树脂包封。树脂既起保护芯片的作用又起到聚光镜的作用。从LED芯片发射出的蓝色光射到周围的荧光粉层内经多次散乱的
反射、吸收，最后向外部发出。LED（蓝）的光谱线的峰值在465nm处，半值宽为30nm.LED 发出的部分蓝色光激发黄色的YAG荧光粉层，使其发出黄色光（峰值为555nm），一部分蓝色光直接或反射后向外发出，最终达到外部的光为蓝黄二色光，即白光。芯片倒装技术（FlipChip）可以得到比传统的LED芯片封装技术更多的有效出光。但是如果不在芯片的发光层的电极下方增加反射层来反射出浪费的光能，则会造成约8%的光损失。所以底板材料上必须增加反射层。芯片侧面的光也必须利用热沉的镜面加以反射，增加器件的出光率。而且在倒装芯片的蓝宝石衬底（Sapphire）与环氧树脂导光结合面间应加上一层硅胶材料以改善芯片出光的折射率。经过光学封装技术的改善，可以大幅度的提高大功率LED器件的出光率（光通量）。
B.LED照明器具进行优化设计，提高LED的使用质量。因此研究大功率LED光源二次光学配光设计，满足大面积投光和泛光照明配光需求尤为迫切。通过二次光学设计技术，设计外加的反射杯与多重光学透镜及非球面出光表面，可以提高器件的取光效率。传统光源照射方向为360°，灯具依靠反射器将大部分光线反射到特定方位，只有40%左右的光是直接透过玻璃罩到达路面的，其他的光是通过灯具反射器再投射出灯具的，灯具的反射器的效率一般仅为50%~60%,所以有60%左右的光输出在灯具内，是在损失了30%~40%后再投射到路面上的。光源光输出的很大一部分被限制在灯具内部发热消耗掉。LED灯的绝大部分光线都是前射光，可以实现>95%的光效，这是LED区别于其他光源的重要特性之一，如果不能将这一特性很好利用，会使LED的优势大打折扣。大多数大功率LED灯由于是多个LED芯片拼装，要将这么多光源照到不同方向，我们充分发挥芯片整体封装的特点，采用透镜加以解决，通过光学设计，根据不同需要，配备不同凸面曲线，依靠透镜来将光线分配到不同方向，保证出光角度大的可以达到120°~160°，小的可以将光线聚集在30°以内，透镜一旦定型，在生产工艺保证的前提下，同种灯具的配光特性也就达到了一致。完全可以通过经过多次试制，不断地总结经验，能够使LED路灯达到道路照明标准要求的蝙蝠翼光型。目前隧道灯、路灯和一般照明灯已达到各自应用场所的照明要求。
9.结论
建议：统一LED标准，提升品质稳定性，成立市场竞争协调组织，避免恶性竞争，大力宣传LED的品质观念，避免受不良实例的影响，要让人们从思想上接受LED其实是可以实现其寿命长的优点的，提高选择和使用LED的水平。综上所述，LED路灯替换高压钠灯，是今后道路照明的必然趋势。