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Since 2006 buyLED.cn has helped hundreds of home and business owners become greener and cut their lighting costs through the use of LED lighting.

Our expertise goes beyond simply selling LED products and also includes comprehensive energy evaluations, project specification and lighting design advice.

Our many years of experience buying, testing and working with LED lighting means we know what we’re talking about when it comes to LED technology and we sell only the best of the best LED products at competitive prices.

When it comes to LED lighting you can expect the best at buyLED.cn including:
Expert Guidance

Many people are unsure of what and how to buy, when they decide to switch to LED lighting.
Since LED technology is so new, we understand that it’s critical to teach people about the technology. Our website has the most comprehensive LED buying information on the web if you’re just looking for information including buying guides, articles and more.

If you contact us for advice, our LED specialists will tell you how it is, instead of saying “Our LED bulbs are the best”, we will honestly tell you what works and what won’t be suitable for LED lighting.

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Full-color LED video display screen has become popular in recent years for various applications such as indoor/outdoor commercial advertisement, stadium billboards, traffic message signs…etc. Thanks to the evolution of LED technology which enables lower cost, higher luminance, uniform wave-length and better efficacy LEDs available, the LED display screen makers are able to build high quality display screen with cheaper cost. With the advent of Full-HD video, the need for building higher resolution LED display screen supporting higher grayscale-level and higher refresh rate is continuously driving the LED display makers to upgrade their system specification. The improvement of LED display refresh rate and grayscale-level is associated with several electrical factors, including (1) the channel current output response rate (OE[note1] response rate) of the LED driver, (2) the speed of system clock (DCLK) used to transmit pixel data from control board to the LED driver in a cascaded daisy chain, (3) the scanning methodology of the LED module board which usually is a trade-off between BOM cost and luminance degradation, (4) the transmission throughput to transmit display pixel data from the video control system to the LED display panels.

Conventional LED drivers with moderate OE response rate and DCLK can usually provides LED display makers just-enough performance to build a medium-class screen, by trading off display quality to gain system stability at reduced BOM cost and cheaper PCB design. Such LED drivers, however, fall short to meet the ever-growing pursuit for higher resolution, refresh rate and grayscale-level. As such, EnE Technology is rolling out a series of LED drivers with SnapDriveTM [note2] technology to address this demand. The SnapDriveTM technology expedites the LED driver’s OE response rate and DCLK without having suffered the distortion of output current, while at the same time it also alleviates the heat dissipation of LED and hence prolongs the life-time of LED. By taking advantage of the SnapDriveTM drivers, system makers are now able to push the frontier of their design specification to embrace high quality video such like Full-HD.
[Note 1] OEis an input pin of the LED driver IC used to enable/disable the output current driving of LEDs
[Note 2] SnapDriveTMis a series of LED drivers developed by EnE with footprint compatible with conventional (TB62746) drivers

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Encapsulation is generally adopted in packaging of lamp-LEDs. The encapsulation procedure is to pour liquid epoxy into the LED moulding chamber first, and then insert the LED bracket that has undergone the press welding, then put the mould into the oven, and the LED gets shaped when the epoxy solidifies.

The procedure of encapsulation sounds rather simple, while the following points should be paid attention to:
1. To fit the die bars onto the aluminum ship in a certain direction, drift the dust, and then put the mould into the 125℃ oven for 40 minutes for warm-up.
2. Prepare the required quantity of epoxy, put the epoxy into the 45℃oven for 15min for defoaming.
3. pour the epoxy into the mould, pre-bake the mould (3φ to 5φ products at 125℃ for 60 minutes; 8φ to 10φ products at 110℃ for 30 minutes and then at 125℃ for 30 minutes)
4. Release the product from the mould, bake at 125℃ for 6 to 8 hours.

If the encapsulation process is not properly conducted, the following are possible results:
1.Bracket inclined to one side, inserted too deep or too shallow, upside down, stained with epoxy, yellowed(oxidation, high baking temperature or long baking time)
2.Air bubbles in bowl shape, pearl shape, thread shape, or pinhole bubbles on the surface
3.Impurity, excess epoxy, insufficient epoxy, nebulization
4.Water mark on the epoxy surface, damage or crack of epoxy (aging glue or wrong ratio), yellowed epoxy (excessive ratio of A glue )

QFN Packaging Solves The Heat Dissipation Problem of LED Display

Currently, almost all LED display manufacturers face the problem of heat dissipation during PCB design, with the thermal effect of drivers disturbing the normal light emitting property of LED and further influencing the color uniformity of the overall display. This article will illustrate how headaches can be prevented by changing the packaging of driving chips.

Quad Flat No Leads Packaging- the technology is named by Japan Electric Device & Equipment Community

QFN is a new surface mounting technology (SMT) encapsulated in plastic and features its small size and dimension, with a welding plate on the bottom. Unlike conventional SOIC packaging, there is no L-shape wire in QFN, thus the conductive channel is shorter and the coefficient of self-induction and resistance of the wire inside the package is lower, so it provides excellent electrical performance. Also, as the elimination of the L-shape wire reduces the antenna effect, the EMC/EMI is reduced in QFN package. Additionally, it provides good heat dissipation via the exposed lead die-pad. The pad has direct heat dissipation passage to release the heat of the chip inside the package. Usually the pad is directly welded to the circuit board and the heat emission holes in the PCB can help dismiss the extra power consumption to the brass-connected floor to absorb the redundant heat as well as reach better common ground effect. The QFN package has already been widely used in handsets and Notebooks, while is on the point of booming in LED display field.

Comparison of QFN and SOP in Heat Dissipation and Size
Generally, the size of SOP is 104 mm2(8X13×1.9mm) while the size of QFN is merely 16mm2 (4X4X0.9mm), which is only 1/6 to 1/7 of the former. As a result, QFN provides more flexibility in design of displays with small intervals.

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LED digital display is a semi-conductive lighting component, with light emitting diode (LED) as its elementary unit. By the number of segments the digital display is made of, there are 7-segment digital displays and 8-segment ones, with the latter with one more LED unit (also displays one more decimal point) than the former. By the number of the figure “8″ displayed, there are 1-digit, 2-digit, 4-digit LED digital displays and so on. And by the way in which the LED units are connected, there are common anode digital displays and common cathode digital displays.

There are mainly two kinds of LED components: digital displays and dot matrix. As a kind of LED components, 8-segment digital display is also called 8-digit display. It is divided into 8 segments: A, B, C, D, E, F, G, and P, with P representing the decimal point. The digital displays usually use 10 pins, 1 pin for each segment and the other 2 interconnected pins at the common end of the digital display. The digital display can display time, date, temperature and other information that can be represented by digitals.

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The thermal resistance of a material is its resistance against thermal conduction. The unit of thermal resistance is degree per watt, representing the temperature difference across a structure when a unit of heat energy flows through it in a unit time. After the LED is lighted and the thermal conduction stabled, as every watt of power on the chip surface being consumed, the temperature difference between the PN junction and the linking bracket or heating panel is the thermal resistance value of the LED. The thermal resistance value is most often represented as θ or R; the temperatures of the joint face and of the point to which the heat has been conducted as Tj and Tx respectively, and the heating output as P. The higher the thermal resistance value is, the more difficult the heat is being conducted, and thus higher component temperatur. From the thermal resistance value, the heating condition of the component can be decided or estimated. The lower the thermal resistance value is, the faster the chip dissipates heat. Therefore, to lower the temperature of the PN junction in the chip is helpful to lengthen the lifespan of LED.

What are the main factors influencing the thermal resistance value of LED components? And how can its influence be decreased?

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Silicon carbide is also called “emery powder” or “refractory sand.” The usual manufacturing process of SiC is to combine silica sand, tar (or coke), woodchip (and salt when manufacturing green SiC) and other materials in an electric resistance furnace at a high temperature. Silicon carbide is usually divided into two categories, the black SiC and the green SiC, both having a hexagonal crystal structure, a density of 3.2 -3.25g/cm³ and microhardness of 2840-3320kg/mm2. The black SiC is manufactured with silica sand, tar and high quality silica as main materials in an electric resistance furnace at a high temperature. It is of hardness between corundum and diamond, mechanical robustness higher than corundum, crisp and sharp. The green SiC is manufactured with tar and high quality silica as main material, salt as additive, and in an electric resistance furnace at a high temperature. The hardness of green SiC is also between corundum and diamond, and mechanical robustness is higher than corundum.

Silicon carbide is of high hardness, good thermal and electrical conductivity, and is oxidation resistant under high temperature. It can be used as abrasive material or be made into abrasive tools such as abrasive wheel, sharpening stone, grinding unit, abrasive segment and so on. It can also be used as high temperature material and deoxidant in metallurgy. There are four major fields where silicon carbide is in general application: functional ceramics, high grade refractory, abrasive and metallurgy materials. And high-purity silicon carbide can further be used in semi-conductor and silicon carbide fibre production. Due to its unique physical and electrical properties, silicon carbide has become the best semi-conductor in some applications such as short wavelength photoelectric cell, high temperature, radiation resistant element and high frequency, high power component. Its major advantages are as following:

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1.Introduction

In recent years, LED lighting efficiency has largely increased from 35lm/W (2006) to 100lm/W (Q1′2009). Judging from the increasing LED efficiency, LED products are expected to replace traditional lighting, especially in high power consumption products. Due to the extensive lighting market, there are various new market entrants in the recent years. However, the quality of the LED products became a huge concern, especially among the new companieshad not been the expert in the lighting field before. On the other hand, LED’s characteristic is obviously different from that of the traditional lamp. For example, increase of halogen lamp efficiency is depended on increasing the heat, but overheating is a problem for LEDs. Directivity of LEDs are very different from that of traditional lamps. Differences between LEDs and traditional lamps are showed in Table I. Due to the existing differences, the thermal, optical, power, mechanism, and control of LEDs becomes crucial in their design as lighting products.

In the recent two years, the topic LED streetlights have been widely discussed due to the scale of its market and its power-saving performance, especially for replacing the 250W or 400W mercury lamp. To build LED streetlights, the key issue is to reach and meet a specific specification. For example, it needs to guarantee a lifespan of 5 years (though LED lifespan is approximately 50,000hours); meet the specific light pattern requirement to comply with roadway regulations, reach dust and water-resistance at IP65, provide enough mechanism strength, etc. Based on these requirements, the design of LED streetlights need to take into consideration the thermal, optical, power, and mechanism. LED lifespan depends on the LED junction temperature, (see Figure 1). Cree has published data to show the relationship of lifespan versus light maintenance for different junction temperature. Therefore, to guarantee a 50,000 hours life, the LED junction temperature has to be controlled under 75C. As for the illumination uniformity of roadway, the batwing light pattern is inevitable. The cut-off light pattern for glare limitation is also required. The other important subject is the driver (power) design and LED light module design. As there is minor difference in drive voltage of each LED, uniform drive voltage of LEDs built into the streetlights cannot be guaranteed. Therefore, an imperfect circuit design will induce a non-uniform current to drive LED which will impact its lifespan. AOP understands that issues related to its designwill directly affect the quality of LED streetlights, hence, AOP has combined thermal, optical, power, mechanism in its LED design to ensure the quality of the streetlights.

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Foreword
AC responses of LED drivers are critical but usually ignored in LED display applications. AC responses affect the major performance of LED display panels, such as grayscales, linearity, EMI, and reliability. Although there is trade-off within these requirements, LED drivers can provide balance. This article will further explain the importance of the AC responses of LED drivers and PCB design techniques to help engineers to design LED panels with good grayscale images.

Minimum OE pulse width vs. Linearity
LED panel manufacturers are asking more on the grayscale improvement to enrich color of image on LED panels which satisfy audiences more. More than 1024 grayscales of each color is now a common requirement for full color LED panels. At the same clock frequency, short OE pulse width and response time (tr / tf) may help achieve more grayscales. Yet, the design of short OE pulse width sacrifices the linearity, which means the proportion between the input data and output brightness. For example, the output voltage waveform of in Fig.1 is shorter than the OE pulse width, and the linearity result is shown in Fig.2. Obviously, the linearity of LED luminance is no longer proportional to the setting of OE pulse width especially when OE pulse width is less than 0.1us. As a result, the linearity is not good for this condition.

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The structure of modern automobile lamps is becoming more and more complicated, at the same time the function is being improved gradually. The development of automobile lamps has experienced four stages.

The first generation of automotive light source is fuels (candles, coal oil or acetylene). These fuels burn to emit lights. Fuels can only satisfy the requirement of early stage automobile lamps due to its low luminous efficiency, weak light intensity, unstable performance, complex operation and etc. shortcomings.

The second generation of automotive light source is incandescent lamp. Incandescent lamp was invented by Edison in 1879. In the year 1913, Americans for the first time apply incandescent lamp in Cadillac cars to act as headlamps. From then on, automobile lamps have undergone a series of revolutionary reformations and the automotive illumination has entered the electric age. Following that, new technologies like reflector, starter, generator and storage battery were invented successively. It was not until the year 1925 that the automobiles adopted incandescent lamps widely. In 1950s, halogen tungsten lamp was invented and quickly become the dominating light bulb for automotive strong light source.

The third generation of automotive light source is HID (high intensity discharge). Be provided with advantages of high luminous efficiency, high brightness and high reliability, HID has replaced incandescent lamp and halogen tungsten lamp to become a new choice for automotive light source.

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