Archive for July, 2010

Design Solutions for Solid-state Lighting Applications

29 Jul

Andreas Pohl of Avago Technologies describes some of the difficulties that designers may experience when designing LEDs into their lighting applications, focusing on thermal, optical and driver issues. This article deals with the difficulties that designers may experience when designing LEDs into their lighting applications. It focuses on the application of discrete 1-watt LEDs in a thermal design that can efficiently dissipate heat from the high power LED (MCPCB, thermal vias), and on lenses that are currently available on the market to address customer-specific design demands. The article also discusses solutions on how to use LEDs in an efficient and space-saving way with small-scale drivers, and parallel or serial circuits.

High-power LEDs for solid-state lighting

Figure 3

Avago Technologies has developed a high-power LED solution that is ideal for designers of architectural and solid-state lighting applications. This high-power LED package targets those applications where efficient heat dissipation, long lifetime and low package height are required.

Due to the industry-standard TO-220 package, designers can use the pad-layout of a power transistor to include this high-power LED into their design. The advantage of this package is its low profile design (3.3mm height) and wide 110-degree viewing angle.

This LED package, which is very thin and provides good light distribution, is extremely useful in lighting application designs such as channel lettering or backlighting. As a result, this LED package from Avago will enable designers to save a lot of design time as they will not need to design a LED-specific soldering pad layout that has to be set it up in their design software.

The advanced heat dissipation capabilities of Avago’s high-power Moonstone™ LED package incorporates a metal slug design that helps to dissipate heat more efficiently through the package (Rth J-P = 10-12K/W depending on the chip technology) which supports reliability and long lifetime performance.

Another factor that plays a key role in extending the life of this LED package is the use of a silicone encapsulation and enhanced phosphor process. Based on 6,000 hours actual light output degradation measurement that was conducted by Avago at room temperature (Tambient = 25°C, Tjunction = 43°C), the average light output was reduced by less than 30 percent in projection after 50,000 hours of continuous operation at 350mA.

Avago’s Moonstone LED package is compatible with standard manufacturing processes such as vacuum-nozzle pick-and-place assembly and reflow soldering and can also be assembled in non-ESD-safe conditions (build-in Zener dioder; ESD Level 16kV). It is also possible to easily hand-solder this LED package; this makes it easier to build-up a demo board to illustrate the advantages of using high power LED light sources, or when manual solder is necessary, to mount the LED onto the board. Moreover, Avago offers an advanced tight binning to eliminate color drifts within one bin which are likely to arise when using a wider white binning structure commonly used in the market.

Thermal management of high-power LED packages

Low thermal resistance helps to reduce the internal chip temperature and to achieve a long life performance. However, the metal slug alone is not sufficient to dissipate the electrical power that is converted to heat and light during operation. A good thermal design helps to significantly improve the lifetime of the lighting fixture by maintaining the junction temperature within a specific temperature range. As a result, a thermal design is needed to control the temperature of the high-power LED.

Figure 1

To be able to use Avago’s Moonstone LED with electrical performance above 1W, it makes sense to have a scalable thermal design. There are basically two approaches that can be used to dissipate the heat from the high-power LED to the ambient:

* Printed Circuit Board (PCB) design using thermal vias and a heat sink
* Metal-core PCB and heat sink

Thermal Vias: This design approach includes a double-sided FR4 PCB, a large copper pad design, as well as metalized holes through the PCB. The soldering pad must be the size that is specified in the datasheet (10.7 x 8.4 x 17 mm), to avoid any mis-alignment after soldering. However, the copper pad must be bigger than the solder mask (copper pad: ca. 20 x 14 mm) and be present on the upper and the lower side of the FR4 PCB.

The heat will than be dissipated from the dice to the metal slug while it is being soldered to the copper pad. Due to the fact that copper is a very good heat conductor, the heat is distributed evenly across the copper pad. The thermal vias conducts the heat from the upper to the lower side of the PCB, to enable efficient heat distribution. It is recommended to have more than 50 thermal vias with a diameter of 0.3mm to 0.5mm on the copper pad area connecting the upper and lower copper pad.

Figure 2

The FR4 PCB with the thermal vias should then be mounted to a heat sink using a thermal interface material like thermal grease or glue (or another thermally conductive material) and screw holes. There are different heat sinks available in the market. It is recommended that designers use an extruded aluminium heat sink in the shape of the copper pad, but it is also possible to use different shaped heat sinks as long as the heat sink is able to connect to the whole copper pad area.

Metal-Core PCB: Using a metal-core PCB (MC-PCB) is probably the most convenient way of designing in the thermal management features. However, the MC-PCB approach is quite expensive if it is a customer-specific design, as the PCB consists of a solid 1.5-3 mm thick aluminum layer, depending on the dimensions of the design.

The thermal resistance junction-board for Avago’s Moonstone Star metal-core PCB is 18K/W. The lower side of the metal-core PCB is isolated, so it can be attached to a heat sink using a thermal interface material. The size and shape of the heat sink should match the size of the metal-core PCB and should be able to dissipate the heat efficiently. There are a variety of different heat sinks available in the market that are suitable for this purpose. Sometimes it’s also a good idea to mount the MC-PCB to a sufficiently thick metal plate to help dissipate the heat more efficiently.

Electrical design

LEDs are current-operated devices that must be driven at a specified current to achieve predictable luminosity and chromaticity levels. The luminosity can be controlled using pulse-width modulation (PWM) which will not affect the chromaticity. Avago’s Moonstone LED can be operated at 350mA, and has forward voltage up to 4.0V; these are the key values that are important for the electrical lighting design.

The most convenient way of driving a high-power LED is to use a high-power LED driver IC. There are several ICs available on the market, and most of them require an input voltage that is higher than the output voltage. Others have an integrated boost stage that converts the input voltage to the desired output level.

In the example below, we will focus on National Semiconductor’s constant current buck IC (LM3404HV). The output current can be adjusted by changing the sensing resistor; however, the input DC voltage needs to be higher than the required output voltage.

Figure 4

It is also possible to drive the high power LEDs using a constant voltage supply and a set of resistors to adjust the current. In this case, the resistors should be matched to the typical forward voltage of the Power LED that can be obtained from the datasheet so that the maximum forward current is not exceeded.

However, to achieve the required current, the resistor approach requires a customized resistor set for each forward voltage the Moonstone could have. Another disadvantage of this approach is the relatively high loss of power due to the electrical power that needs to be dissipated by the resistors. This will lead to a reduced efficiency of the luminaire.

Figure 5

Serial or parallel connection? It is recommended that multiple high-power LEDs be connected serially if the power supply supports the required voltage level. However, it is also possible to drive the high-powered LED in parallel if required.

Optical design

High-Power LEDs provide an advantage over conventional light sources because the light emission is already directional. Hence, it is not necessary to design a reflector to bring the light into a specific direction to get more light out of this light source. Avago’s Moonstone LED has a very wide viewing angle of 110-degrees which makes it an ideal light source for uniform illumination of areas close to the LED opening such as backlit letters on a wall.

On the other hand, the wide viewing angle of the package limits the distance between the LED and a surface that can be illuminated by a reasonable amount of light such as a desk light. Therefore, it is better to focus the 110-degree light beam to a narrower angle that provides a suitable amount of light at longer distances.

A narrower beam angle can be achieved by using a secondary reflector or secondary lenses with the high-power LED package. The optical efficiency of both approaches is between 80 and 90 percent — depending on the connection and internal refraction between the reflector of the LED and the lens or reflector. Avago offers lenses for the most common viewing angles in signage and illumination applications, ranging from 6 to 30-degrees.

As the light spot might be considered irregular for some applications, like spot lights or reading lamps, Avago is working with several lens manufacturers in Europe to provide customers with lenses that create a more uniform light spot. These manufacturers have the ability to customize the shape and size of the lens, radiation pattern or include multiple LEDs into one lens to meet specific customer requirements.

For example, Avago worked closely with a lens supplier in the United Kingdom to help them fulfill the lighting project needs of one of their customers. The customer required a non-standard beam angle to achieve a certain radiation pattern. Though the application required lenses of different viewing angles, the project required lenses of the same height across the different angles.

Additionally, the lenses needed to be mounted on the LED using the normal flange design (plastic ring on Avago’s Moonstone package), and a much more mechanically robust interconnection. As a result, the lens supplier provided a feasible and timely customer specific optical solution for the Avago’s Moonstone power LED package.

About the Author
Andreas Pohl is a product application engineer with Avago Technologies.


LED Garden Lighting Decorates Your Garden

28 Jul

Lighting is very important for your garden, different lighting bring different effects, IF you choose proper lighting for your garden, it will feature magical appearence. LED lights are perfect for outdoor and garden lighting because you have more control of where you place them.

You can use many LED lights such as LED wall lights, LED ground lights and LED ribbons etc around your patio or deck which gives you a great option for outdoor entertaining and to help your garden look great. There many kinds of LED garden lighting for you to choose, just think about which kind of lighting effect you desire and choose the corresponding LED lights.

Why shall we choose LED lights for garden lighting?

Energy efficient
Amazing lighting effects
Make your garden look more dynamic
24 hours lighting for your garden
They are safer to operate
Easily lights up a garden path
Can be placed anywhere as you want
Wide variety of styles

Once you choose the right outdoor lighting which meets your requirements, your garden will become a magical world. LED lights are high energy efficient fixtures which are very easy to operate. Now they are becoming more and more affordable than ever before so you don’t have to worry that you can’t make them work for your needs.

They can also be used for guidance lighting and accent lighting for areas around your garden such as a lit path, patio, porch, doorway, birdbath and more. You can choose lamp-style garden fixtures, low to ground LED lighting and more. Whatever you need to suit your garden today can be done quickly and easily- and all without breaking your budget. These are just some of many reasons to choose LED garden lights. Take the worry out of creating the right garden lighting space today and choose LED. You will then have more control over where you place the lights in your garden.

You don not need any lighting experts, you can do it all by yourself. You can make your garden more beautiful and fantastic without any difficulties. The styles and characteristics are up to you, you just need to choose the right LED lights and place them into right places.

Now it’s time to make your decision, once you determined, the only option left is to begin searching for the garden lighting for you and your needs. The size of your garden, the potential placement of lights, what you want the lighting to illuminate as well as safety issues are the key factors you have to think about.

In a word, LED lights are quite ideal for you to decorate your garden. Long lifetime, durability, waterproof treatment enable them to be used for outdoor lighting. High energy efficiency will greatly save your money. Moreover, they can create fantastic lighting effects.


Use LED Lights to Brighten Up Your Home

28 Jul

LED interior lights feature much more advantages than other light sources when it comes to home lighting. They can emit white light which is brighter than other light sources and they are quite ideal for those who want bright lighting. LED lights can also bring you benefit on power saving, they can greatly save your energy bills than other types of lights. Meanwhile they have a much longer lifetime than other light sources, which means you do not have to change them as often and also saves you maintenance costs.

Good lighting is very important for the health of family members. When the children are doing their homeworks, they need bright and comfortable light to concentrate their attention. LED interior lights can be used in a desk lamp to allow for better visibility on the page or computer where the homework is being done. Also for the children who are afraid of dark night when they sleep, LED lights can also be dimmed by dimmers to deliver a soft night light.

LED lights can also bring benefit to kitchen and bathroom in your home. One of the reasons for both rooms is that these rooms need to have the most cleaning done in order to keep bacteria levels down. Another is to spot any occurrences of mold in climates that are damp year round. LED lights which deliver brighter light can help you to clean the dirt of your bathroom and dishes in your kitchen. The brighter lighting can also help you to see simmers clearly when you are cooking and ensure safety.

The LED ceiling lights is very useful for dinning room since they are dimmable. When used with a dimmer switch, the lights can either be bright for family dinners or can be lowered for an intimate and romantic dinner with just mom and dad. When it is time for clean up, the lights can again be brought to full power so that any spills can be seen and taken care of before the wood of the table or the carpeting is damaged. The lighting is also perfect for getting the good china out of the hutch so each piece can be seen as it is needed.

You can benefit a lot from using LED interior lights which offer strong lighting. Not only do the children need bright lighting when they are doing homeworks, but also LED interior lights can be an aid when cleaning the bathroom or kitchen. Finally, they are perfect for the dining room for either bright family meals or soft lighted romantic dinners. The most important reason is that LED lights do not consume as much power as other light sources. Choose LED lights for your home lighting, you will greatly save your money and time, meanwhile get more comfortable lighting.


RGB LED Lights Categories

26 Jul

There are various different styles of RGB LED lights which can be used in many different ways. RGB lights mean that they combine three colors of red, green and blue. Categories of RGB lights are uncountable but different types will feature different characteristics. Some are designed with controllers that create a variety of color schemes and combinations depending on what the device is used for.

RGB LED lights will run the three colors through a sequence where each one of these colors is visible for a specific length of time. The colors will be performed in a continuous loop until you make a change. Some other colors such as turquoise, yellow, pink and even white light can be created When these three colors are combined together in certain ways. Some of the more advanced designs can create the illusion of hundreds of different colors using just red, green and blue.

RGB LED lights categories:

RGB LED wall washers are always used for decorative lighting to highlight homes or accent objects. Not only can they be used for highlighting the whole room, but also they can be used for accent lighting. RGB LED wall washers can be connected with controllers, and they can be set to rotate through a color sequence that was pre-programmed into the system, also you can set the sequence by yourself through the controller.

Flexible strips comes in rolls with different lengthes, they are very slim and flexible. They can be cut down at specified points and be used in small areas, through connectors, you can also connect two or more strips together to be used for large area. RGB strip lights are compatible with many different controllers and some of them are designed to be waterproof.

RGB rope lights have many uses from lining stairs to decorating the home or buildings. The rope light is basically miniature LED lights wrapped in clear PVC tubing. There are different types of rope lights designed to work in different situations. For instance, some are waterproof and can be used to line swimming pools for nighttime fun and others need to be kept dry.

The above-mentioned RGB LED lights are just a few examples of RGB lights, and their applications are not limited. There are many more ways in which these lights can be used. They can also be used for advertisements and signs except lighting.

RGB lights can attract more attentions than normal lights. The vivid and dynamic light they emit is visible in all kinds of conditions making it possible to light up even the darkest areas. RGB LED lights are energy efficient and durable. Therefore, they can continuously work for a long period without consuming much power.


Reasons to Choose MR16 LED Light Bulbs

26 Jul

Do you think your incandescent bulbs consume too much, cost too much to maintain and couldn’t last long? Are you planning to upgrade your old lighting system in your home or office? Why not consider MR16 LED light bulbs which can offer you lots of benefits. LED bulbs are slowly beginning to take the place of the incandescent bulbs that were the first to be invented.

Energy saving has become a more and more important topic as a result of the frequently occurance of energy crisis. The lighting manufacturers along with the help of researchers have been looking for new modern ways to emit light without consuming so much energy as conventional bulbs. The original LED light bulbs are the ideal solution which has already been incorporated into everything from toys to advertisements.

It is a pity that they do not provide the type of lighting that works well in homes because they just project light to one direction, which means they can not cover the whole room like incandescent light bulbs. However, MR 16 LED bulbs have already solved this problem due to latest technology advances that allow them to provide a wider beam angle so that they can meet the customers’ requirements.

Consumers may ask what I can get from upgrading to MR16 LED bulbs. It is very clear that they can offer you thousands of benefits when comparing with incandescent bulbs. After all, why not take advantage of all the latest technology available whenever possible especially, just try and you will get amazing experience.

Some of the benefits you can expect from the MR16 LED light bulb are listed below:

Consumes much less power
Much longer lifetime than incandescent bulbs
Durable even in extreme weathers
Delivers more lumens
Compatible with many existing sockets

Although the upfront cost of these bulbs is higher than incandescent bulbs, it’s also true that the energy bills they save in long term are much higher than the upfront costs. Also they hardly need any maintenance costs and they don’t need to be replaced as often as incandescent bulbs, they definitely pay for themselves in a very short period of time.

For the portable LED lights such as LED flashlights, when these bulbs are used in them, they can greatly extend the life of batteries, which is because these bulbs use less energy and produce less heat so they don’t drain the batteries as quickly.

Now it is the time to make the switch as a result of the fact that manufactures will soon stop making the incandescent bulbs and incandescent bulbs will be gradually phased out. You don’t have to replace every light bulb in your home but first have a try which will convince you, and then you can start large scale replacement.

As the demand increases, the price of the MR 16 and other LED light bulbs will go down. In other words, when more consumers start buying these products it will help drive down the price making them even more economical. Meanwhile, consider all the money that you’ll save just from not having to replace the bulbs so often and by the energy they save.

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