智能照明设计的构建模块

1万 · 2011-9-1 23:13

中英文都有，随你看哪种语言，呵呵

By Gavin Hesse, Cypress Semiconductor Corp.
作者：赛普拉斯半导体公司Gavin Hesse

The long awaited “hockey-stick” expansion of the LED marketplace is beginning to take shape as more replacement fixtures are entering the consumer and industrial landscape. As such, more lighting designers are attempting to take a crack at their own LED fixture, whether it be a small MR16 or a larger PAR lamp. Yet herein lies the issue, as customers are not defining the LED fixtures by only the standard Lux and wavelength requirements. LEDs are powerful semiconductor devices, and so allow customers to enter a whole new world of differentiation with their designs.
随着替代照明器具逐步进入消费和工业领域，人们期待已久的LED市场正开始快速发展。在此情况下，越来越多的照明设计人员开始尝试自行设计LED照明器具，如小型MR16或较大型的PAR灯泡。不过问题在于，客户对LED照明器具的要求不仅局限于标准照度或波长而已。LED是功能强大的半导体器件，能使客户推出一系列全新的特色化设计。

Unfortunately, most of these designers are still coming up to speed on the language necessary to understand how to build any of this potential intelligence into their system. This puts them at a disadvantage when it comes to discussions with potential vendors and partners. In fact, some engineers barely know enough to write a useful specification for an intelligent light engine, passing that on to a consultant they barely knew a month previous. If LED designs are the future of the industry and the future of the company, they are too important to fully leave to external forces. Even semiconductor vendors are offering design services, but have limited resources.
不幸的是，大多数设计人员都没有掌握如何才能将潜在的智能转化为系统功能。这就使他们在与潜在的厂商和合作伙伴讨论时处于不利之地。事实上，有些工程师知识非常匮乏，甚至难以编写智能照明引擎的有用规格，因此只能让刚刚联系到的顾问协助编写规格。LED设计代表着产业发展的未来和公司的未来，因此不能完全依靠外部设计力量。尽管半导体厂商也在提供设计服务，但毕竟资源有限。

So what these lighting companies and engineers require is an understanding of the basics, the building blocks of intelligent lighting design.
照明公司和工程师需要了解LED基础知识，掌握智能照明设计的构建模块。

These essential questions can help a designer understand not only how to correctly define his project, but also how to choose an appropriate vendor.
了解这些基本问题，不仅有助于设计人员掌握正确的项目定义方法，而且还能选择适当的厂商。

Building Block #1: Do you require dimming?
构建模块之一：是否需要调光？

This is a tougher question that it appears at face value, as a “Yes” answer sets off a daisy chain of follow-up information. There become three major issues. The first is the input voltage. Low voltage fixtures such as an MR16 that have inputs of 12VAC or 24VAC are more difficult to find solutions that can interface with most TRIACs available in the marketplace, as those TRIACs provide too little additional power off the line to read correctly. As such, there are more limited solutions available in the market for such applications, although companies such as Cypress or Zetex are creating those at this time.
这个问题看似简单，但实际却不然。如果确实需要调光，则会带来一系列的后续问题。这涉及到三大问题。第一个是输入电压问题。MR16等输入电压为12VAC或24VAC的低压照明器具，很难找到能与市场上可用的大多数TRIAC相连接的解决方案，因为这些TRIAC线外供电太低，难以正确读取。因此，尽管赛普拉斯和Zetex等公司正在推出相关解决方案，但市场上针对这种应用的可选解决方案还是非常有限。

The second issue is the type of input dimming required. TRIACs were not made to interface with LED systems and as such are poor options. Your new favorite dimmable AC/DC LED driver may only work with half the Lutron dimmers in your arsenal, and at that only the leading edge dimmers. They also may be unable to correctly read the low and high end of the TRIAC and so will only offer about a 20-40% dimming range without introducing flicker, especially on the low voltage design side. If the input dimming comes from a microcontroller, the power from the AC line needs to be appropriately managed. A standard AC/DC driver from a company such as Advanced Transformer was not made to power a microcontroller that has a 5V input rail. The microcontroller will also require an input signal to modify the output dim waveform, which can introduce the complexity of a communication network.
第二个问题是所需的输入调光类型。TRIAC不是专为连接LED系统而设计的，因此本身不是很好的选择。您所喜爱的新型可调光AC/DC LED驱动器可能只能与现有的一半Lutron调光器协同工作，因此只能选用高端调光器，而且也难以准确读取TRIAC的低压和高压侧，从而只能提供20-40%的调光范围，超出这一范围就会出现闪烁问题，这一点在低压设计方面尤其突出。如果用微控制器进行输入调光，那么必须对AC线路电力加以适当管控。Advanced Transformer等公司推出的标准AC/DC驱动器不是旨在用于给5V输入轨的微控制器供电。微控制器还需要输入信号来修改输出调光波形，而这就会增加通信网络的复杂度。

The final issue is the quality of the dimming waveform itself. All dimming is not equal, and any vendor which claims to offer dimming does not mean it is doing so in an effective manner. For example, the below figure shows the noise generated from a PWM waveform:
最后一个是调光波形本身的质量问题。调光技术良莠不齐，不同厂商推出的调光技术效率不一。例如，下图显示了PWM波形生成的噪声：

SHAPE * MERGEFORMAT
Figure 1: PWM Dimming Waveform
图1：PWM调光波形

Notice the significant noise spikes which are created by the signal, which can introduce a significant amount of radiated EMI, which in turn can introduce flicker. However, a secondary type of PWM signal, using a modified method, has this plot shown in Figure 2. It is fairly easy to see how significantly smoother this second curve is and the advantage it offers, in this example almost 75 dB in noise reduction.
请注意，信号会产生严重的噪声，从而导致大量电磁干扰，进而引发闪烁问题。不过，我们采用修改后的方法实现了如图2所示的第二类PWM信号。显而易见，第二种曲线更加平顺，优势也更为突出。在本例中，其噪声降低了近75 dB。

SHAPE * MERGEFORMAT
Figure 2: Alternate Dimming Waveform
图2：另一种调光波形

Dimming also has issues if it comes from a digital output. An 8-bit PWM only has 256 possible “steps” that can dim a string of white LEDs. Especially at the low range, those steps become visible to the user. However, a 16-bit PWM has over 65000 steps, allowing for a much smoother dimming curve to the customer.
在采用数字输出的情况下，也会出现调光问题。8位PWM只有256个可对一串白光LED进行调光的可能“步进”。在较低范围内，这些步进差异明显。不过，16位PWM有65000多个步进，这就能为客户带来较为平滑的调光曲线。

Building Block #2: Do you require feedback?
构建模块之二：是否需要反馈？

The notion of actually being able to adjust light output on the fly seems to be fairly new to many lighting designers. Most have been used to the principle of having a fuse or safety switch that turns the fixture off if the bulb burns out. This is one of the primary advantages to an intelligent LED system, which can not only be more robust from a lifetime standpoint but more robust from an upkeep standpoint. Any LED system should be able to appropriately track overvoltage, undervoltage, short circuit, open circuit, and thermal runaway conditions.
对于许多照明设计人员而言，能够实际即时调节光输出还是一种全新的理念。如果灯泡烧毁，大多数设计人员都习惯于用保险丝或安全开关关闭照明器具。直接调节光输出是智能LED系统的主要优势之一，不仅能确保照明器具整个寿命周期内的安全性，而且还能提高日常维护工作的稳健性。任何LED系统都应当能够适度跟踪过高、欠压、短路、开路和热逃逸等问题。

Any vendor should be able to offer a circuit similar to the below figure for a simple white light application, in this example from Cypress Semiconductor:
所有厂商都应能提供类似于下图所示的面向简单白光照明应用的电路，本例中的电路来自赛普拉斯半导体公司：

Figure 3: Isolated AC/DC LED Drive Circuit
图3：隔离式AC/DC LED驱动电路

Notice that this is an isolated topology, which is easier to pass UL certification. However, the circuit itself is able to sense what is happening at the load through the tertiary winding of the transformer, and as such is able to recreate the waveform internally and adjust how it drives the LEDs. It also has a temperature sensor attached and will shut down if the temperature rises above a set threshold.
请注意，这是一种更易于通过UL认证的隔离式拓扑。不过，电路本身能通过变压器的第三绕组感应负载情况，因此能在内部重建波形，并调节驱动LED的方式。此外它还具有一个温度感应器，如果温度超过预设阀值，则将关闭。

Temperature, however, is the bane of the existence of LED lighting designers, since LEDs radiate all their heat through the base. This puts designers into an uncomfortable position of having to work more on thermal design than electrical design to ensure temperatures do not rise beyond datasheet junction temperatures of the components on the PCB board. As is widely known, temperature also dramatically affects the flux and color output of the LEDs themselves, which can make the visual appearance of a row of fixtures appear to not be in sync.
但是，温度是LED照明设计人员的大敌，因为LED的所有热量都通过基座发散。这给设计人员造成了难题，必须将更多精力花费在散热设计而非电子设计方面，以确保温度不超过PCB板上元件的数据表结温。众所周知，温度还会大幅影响LED自身的通量和色彩输出，而这会导致一系列照明器具的视觉外观看似是不同步的。

A system with more intelligence driven by a microcontroller can implement an improved temperature compensation algorithm using a simple and cheap thermistor set near the LEDs themselves. After reading the board temperature the following equation is used to convert to the junction temperature of the LEDs:
由微控制器驱动的、更智能的系统通过在LED附近设置简单廉价的热敏电阻，可实施增强型温度补偿算法。读取板温度后，我们可用以下方程式来转换LED的结温：

Figure 4: Junction Temperature Approximation Equation
图4：结温近似值方程式

To simply read the equation, the junction temperature of the LEDs (Tj) is equal to the temperature of the board (Tb) plus the combination of the thermal resistance of the PCB board, the constant current of the LEDs, and the forward voltage of the LEDs. These are all easily discoverable values. This number can then be used to derive any adjustments to the drive current or voltage in order to keep the flux output (or the color output of an RGB series of LEDs) inside the visible limit.
为了简化上述方程式的读取，LED的结温（Tj）等于板温度（Tb）加上PCB板热敏电阻、LED恒定电流和LED正向电压的组合。上述这些数值都比较容易获得。我们随后可用这些数值来调节驱动电流或电压，从而确保通量输出（或RGB系列LED的色彩输出）在可见范围之内。

Building Block #3: How do you want to drive the LEDs?
构建模块之三：您希望如何驱动LED？

This is another simple question that becomes more complex the moment you bring a power engineer to the table. When faced with the omnipresent cost question, most designers will quickly turn to a linear implementation, which can cost almost half the alternative. Unfortunately, the trade-off to a linear drive system is about a 50% hit in the overall system efficiency as well, which tends to kill the “green” advantage of LEDs in the first place.
这个简单的问题在功率工程师加入之后即变得更加复杂。在面对无所不在的成本问题时，大多数设计人员都会很快选择可将成本减少几乎一半的线性实施方案。但不幸的是，线性驱动系统会使整体系统效率降低约一半，这将抵消LED最为重要的绿色环保优势。

This leaves a switching implementation, either a step-down buck or step-up boost topology. This is where the current technology available from vendors becomes more helpful, as there is a wide range of suitable solutions on the market. There are a few features, however, in which variance can be more crucial.
因此，我们只能选择开关式实施方案，或者采用步降降压拓扑，或者采用步进升压拓扑。由于市场上有多种不同的适用解决方案，这时厂商提供的电流技术就会发挥作用。不过，一些特性的轻微差异会造成显著不同的结果。

The first is switching frequency. If a driver is able to switch at 1.5 MHz rather than 1 MHZ it will lower the size of the inductor needed for the circuit, which in turn helps solve the inevitable board space crunch in most retrofit applications. The second is RDSon, as some drivers have integrated high voltage MOSFETs. If that RDSon is too high, over 1 ohm, then the power dissipation will suffer, again killing the efficiency of the system. The final is the efficiency spec, mainly contained within the datasheet. A decent switching regulator can get up to 95% efficiency, which can differentiate a company’s solution effectively in this competitive marketplace.
首先就是开关频率。如果驱动器的开关频率为1.5 MHz而不是1 MHZ，那么就能减少电路所需的感应器，进而有助于解决大多数改型应用不可避免的板上空间紧张问题。其次就是RDSon，因为一些驱动器采用了集成高压MOSFET。如果RDSon过高，超过1欧姆，功耗问题就会很严重，从而再次影响系统的效率。最后一个问题就是如何实现数据表规定的效率规格。适当的开关稳压器效率应当高达95%，这才能让公司的解决方案在竞争激烈的市场中脱颖而出。

Building Block #4: What’s going to set your product apart from the competition?
构建模块之四：如何让产品在竞争中脱颖而出？

To be frank, there is little about the previous questions which will fully differentiate one company’s product over another. There is a veritable crush of companies seeking to carve out a space in this burgeoning LED retrofit market. Many will simply decide to create a non-dimmable or TRIAC dimmable LED fixture and win on cost. These companies will rise and fall based on the commodity pricing of basic components, not on the quality of their overall system.
坦率地说，只有以上问题得到有效解决，才能真正让公司产品在竞争中脱颖而出。很多公司都全力以赴在新兴的LED改型市场中占据一席之地。很多公司选择了直接推出不可调光或TRIAC调光LED照明器具，从而抢占成本先机。此类公司的成败取决于基本组件的价格变化，而与其整体系统质量关系不大。

Companies who instead have a desire to push forward with simple differentiating techniques will carve out unique and stand-alone spaces for themselves. Many lighting engineers simply don’t know enough of what’s available in the semiconductor market to take advantage of simple solutions. Here are several examples:
有的公司则会选择推出简单的特色化技术，他们会为自身赢得独有的细分市场。许多照明工程师对半导体市场中现有的技术并不了解，从而不能充分利用简单解决方案的优势。例如：

Figure 5: Retrofit Block Diagram
图5: 改型方框图

The above block diagram shows a potential retrofit bulb. It takes the AC/DC line voltage such as 120VAC, and then drops it down to a microcontroller which handles the TRIAC dimming of the LEDs. This is a similar approach to items discussed earlier. However, it also interfaces with a motion sensor, a cheap external device, which controls the light being turned on if it detects an individual in the room. This could just as easily be an IR sensor. With this addition that can be in the sub $0.10 range of additional Bill-Of-Materials cost, the product is easily different from competitive products.
以上方框图显示了一个潜在的改型灯泡。它采用120VAC等AC/DC线路电压，并用微控制器处理LED的TRIAC调光。这类似于我们前面讨论过的解决方案，不过它还与运动感应器相连接，这个成本低廉的外部器件会检测屋里是否有人，如果有人就会把灯打开。我们仅需采用IR感应器即可满足要求。本解决方案的物料清单成本只增加了不到0.10美元，而产品已经从竞争对手中脱颖而出了。

A second example would be a table lamp. In the simplest fashion it takes an offline signal and drives a set of white LEDs with no dimming. Again, there are multiple vendors in the market designing this lamp. However, the design is pushed in a new direction with the adding of a capacitive slider on the lamp to both turn the light on and off or to adjust the dimming level. Adding a capacitive slider to a design costs as much as a line of copper. In other words, it is not expensive and yet again, provides a unique advantage.
第二个例子是一款台灯。最简单的台灯就是接到离线信号后点亮一组不带调光功能的白色LED。市场上有许多厂商都能设计这种灯。不过，我们可在灯上添加电容滑块，实现开关灯和调光功能，这是设计方面的一个新方向。添加电容滑块对设计成本的影响很小，只不过相当于增加了一条铜线而已。换言之，这一改型方案一点都不昂贵，却能带来独特的优势。

The final example would be an outdoor backlight, such as behind a restaurant sign. To save energy, a company will want to drive the sign at different levels in the day or at night, but the simplest version of said design will not allow this, as it would require the elimination of the sense resistor on the feedback loop of the current regulator. However, there are products which allow this constant current level to be reset in software, from 350 mA to 700 mA. Now the LED backlight can offer even more energy savings to the potential customer, maximizing efficiency during the entire day.
最后一个例子是室外背光，比方说餐厅标志牌的背光。为了节能，我们希望标志牌的背光强度在白天和夜晚有所不同。最简单的设计可能不带电流调节器反馈回路上的感应电阻，因此显然无法实现这一要求。不过，有些产品允许在软件中重设恒定电流，从350 mA调为700 mA。这样，LED背光就能为潜在的客户带来更高的节能效果，确保整天时间里都能实现最高效率。

There are far more examples that could be discussed outside of these three, from additional communication interfaces, control mechanisms or thermal platforms. The semiconductor market is currently at work providing even more value to lighting engineers. Differentiating a product in this market is not an onerous process, does not have to be costly, and can ultimately help a company position itself effectively.
类似的例子还有很多，如附加通信接口、控制机制或散热平台等。半导体市场目前正积极为照明工程师提供更多增值技术。为市场推出特色化产品其实并不难，也并非会增加成本，但却有助于公司有效实现市场定位。

The Building Blocks discussed are obviously not the only questions necessary to create an intelligent lighting fixture, but they are an excellent start to understanding how to fully utilize the technology available, as well as reduce reliance on expensive consultants or outside vendors. If a company does not learn these lessons well, they will be ill-prepared to face a quickly-moving market in terms of product definition and will be left behind by more nimble and flexible competitors.
显然，本文讨论的构建模块不仅是构建智能照明器具所必须解决的问题，同时也是了解如何全面发挥现有技术功能的极好起点，并可以帮助我们减少对价格不菲的咨询公司或外部厂商的依赖。如果我们不能很好地吸取这些经验，就难以满足快速变化的市场对产品定义的要求，从而被更灵活的竞争对手所超越。

Beginning an LED design can seem tricky and treacherous to companies which began with knowledge on how to bend metal and little else on the electronics side. With a small amount of research, the learning curve does not have to be difficult, and the reward large.
传统厂商过去只考虑金属设计问题，对电子领域知之甚少，因此LED设计起初可能会显得非常复杂。不过，只要稍加研究，就能发现学习曲线其实并不那么难，进而从中大幅受益。