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Figure 9 Experimental set

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Table more than one current source set ( left ) and a single current source settings ( Right ) data

From these data it is clear that changes LEDVF operating in parallel will result in uneven current distribution. Even for the classification of the LED, you can see a similar effect , in a parallel array of the current series lamps are unevenly distributed . Improved parallel lamp current distribution between the groups is one way to increase each lamp group ballast resistor . This helps to make the current distribution uniform, but the main problem is due to the power consumption of the ballast resistor and reduces efficiency. LED Strip

Depending on the design of the above problems may be ignored . However , if the system designer there are concerns about the effect , you can use a single series lamps as the preferred topology. In this solution , you can still use the LM3406 and other components, but it will increase the complexity of the system , GU10

because of the need for the transmission of the new front-end components beyond 12V ~ 14V supply voltage for the LED driver power supply. Then , LED drivers reduce this new voltage power supply for a single set of LED lights . This can be done between the DC power supply and an increase LM3406 boost DC / DC power levels easily achieved, as shown in Figure 10 . With this topology, the series of all LED lamps have the same current, regardless of the value of each LED VF is.

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Summary

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This paper discusses a number of application examples of automotive electronic systems and the corresponding switching power supply topologies and compatible with National Semiconductor integrated circuit , in which many LED driver ICs are very suitable for automotive electronic systems designers efficient design .

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The following simple analytic with you about the composition of LED circuit has its performance :

First, the circuit

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The need to use more LED products , if all the LED series , LED driver outputs will require a higher voltage : If all of the LED in parallel , you need a large LED driver output current. All of the LED in series or parallel , not only limits the usage of LED Yan , and parallel LED load current is large ,

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the drive will increase the cost of the solution is the use of hybrid approach . Series , parallel LED quantity evenly distributed , so that the distribution of LED series in a same voltage support on the road with a series branch current on each LED is basically the same , consistent brightness , while the current through each series branch also similar .

Second, the circuit performance analysis

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When a branch road with a series of poor quality LED short circuit, regardless of mode or LED Bulb constant current regulator type drive type drive mode, the current through the series circuit will increase , it is easy to damage the series branch of the LED. This large current through the LED string damaged , due to the current through the larger , more performance for disconnection . Disconnect one LED series branch ,

if the use of the regulator -type drive, the driver output current will decrease , without affecting all the remaining LED work . LED Module

If a constant-current type LED drive mode , since the driver's output current remains unchanged , the remaining distribution of the LED current will increase , easy to damage all of the LED. The solution is as much as possible in parallel LED, this is only when disconnecting a LED , the distribution of the remainder of the LED current is not , and will not affect the rest of the LED work .

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Such parallel lines after the first series has the advantage of simple lines , brightness stability, high reliability , and low consistency requirement of the device , the device does not require special selection , even if the individual LED single tube failure of the entire light emitting element also smaller. Large changes in the work environment factors in the case , use this connection form of the light emitting element more satisfactory results .

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Arsenide ? Epitaxy by different processes can be divided into LPE ( Liquid Phase Epitaxy ), MOCVD LED Lighting china ( metal organic vapor phase epitaxy ) and MBE ( molecular beam epitaxy ) . LPE technique is low, mainly used for general light-emitting diodes , and the higher level of MBE technology , easy to grow epitaxial thin and high purity, smoothness is good, but production capacity is low, the epitaxial growth rate slow. MOCVD addition to high purity, good flatness , the production capacity and MBE epitaxial growth faster than the speed , so now mostly in MOCVD to produce.

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First, the process is expensive GaAs substrate into the chemical vapor deposition furnace ( SR MOCVD, also known as the epitaxial furnace ) , and then pass into the III, II metal element alkyl compound ( methyl or ethyl compound ) Steam and nonmetal (V or VI element ) hydride ( or alkyl matter) gas at a high temperature , the occurrence of thermal decomposition reaction of III-V or II-VI compound deposited on the substrate ,

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growing a layer of thickness of only a few microns (1 mm = 1000 microns ) and the compound semiconductor epitaxial layer . Length GaAs epitaxial layer film which is often known as epitaxial wafers . Epitaxial wafers processed by the chip , the power will be able to send out ? Very pure monochromatic colors such as red, yellow and so on. Different materials, different growth LED Bulb conditions, and the type of the epitaxial layer structure can change the light ? Colors and brightness. In fact, a few microns thick epitaxial layer, the true light which is also only a few hundred nanometers ( 1 micrometer = 1000 nanometers ) thick quantum well structure.

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Abstract : This paper introduces the characteristics and UV communication channel model with LED Downlights LED as light source, a photomultiplier tube to UV light receiver design wireless digital communications system solutions , developed a prototype wireless ultraviolet communications equipment , experiments under different conditions . Experimental results show that at night, sunny , close-up , calibration of the communication is better than during the day , rain, long-distance, under the conditions of uncalibrated communication results verify the feasibility of wireless ultraviolet communications . LED Module

UV wavelength of 10 ~ 400nm, the shortest wavelength of the spectrum part, radiated by the sun , known as ultraviolet , UV transmission performance and transmission quality of the atmosphere within the closely related , such as the concentration of O3 in the atmosphere , the concentration of the scattering particles , size , uniformity, geometry size. Study molecules and particles in the atmosphere scatter the main consideration and Mie scattering Rayleigh scattering . LED Flexi Strip

At the same time , the mode of transmission of ultraviolet light to scatter dominated , although transmission attenuation serious, but can bypass certain obstacles, these two determines the UV communication system can achieve all-weather NLOS communication (Non Line Of Sight, NLOS). With the domestic segment -blind UV LED production line in operation , UV Communication implementation would be more feasible .

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1 Background

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UV been proposed as a means of communication early in the last century , when the U.S. military asked for naval maritime communications . Country nearly two years, research in this field , there are some , including the National Defense University in 2007, studied a helicopter UV communication system , in this study is the first to use solar-blind segment LED dot matrix as a light source , and in the prototype to achieve communication ;

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Chongqing University photoelectric research Laboratory in 2006 and also completed a UV -based voice systems design and implementation, reflecting the sensitivity of the system and all have a good anti-jamming performance . LED Flexi

In the meantime, the industry-leading University of California Center for UbiquitousCommunication by Light Laboratory , achieved in 2007 in the use of optical power 0.5mW 10 24 cell array UV LED as light source , 00K modulation mode UV Communication data transfer rates of up as shown in Table 1 , including the sight communication (Line Of Sight, LOS) and non- line of sight communication in two ways.

From Table 1 , the error rate of UV -sight and non- line of sight communication data transfer rate

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A19, E14/17, E26/27 bulb

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Some lamp types are also referred to as the screw socket (Edison socket) and candle lamps . Most of incandescent bulbs , using CFL or LED replacement products to meet most application requirements .

System Structure

The input voltage directly from the AC power source , lamp type : E14/17 ( Candle ), A19/E26/27 screw type, rated power : 1 ~ 5W for candle lamps , 4 ~ 17W incandescent replacement for . Dimensions shown in Figure 11 . T8 Tube

Design Challenges

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For candle lamps LED driver design challenge is a small PCB space, the space is less than MR lamp space and work on AC input voltage power supply. Using LED driver designed to replace incandescent lamps , PCB space than its candle lamps or MR lamp big , rated power is larger, and therefore LED driver is also large, the actual results are still limited PCB space , similar as candle lamps . For screw bulb design , PF and THD is almost mandatory. There are additional dimming function requirements.

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Requires greater than 75% efficiency . The design of compatible dimmers little short comment including compatibility with a variety of the holding current , the light in a wide range of linear within the range of work , and flicker .

Fairchild Semiconductor Solutions

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Fairchild's primary regulator controller shown in Table 1 . When operating in the current regulation mode, the drain current IPEAK and the peak inductor current discharge time TDIS the output current can be estimated , as in the steady state output current and the diode current as average . TRUECURRENT using Fairchild's innovative technology, constant current output can be precisely controlled .

PAR16, 20,30,38 lighting system structure

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The lamp type is AC voltage input power ratings from 4W ~ 20W, lamp holder for the screw -type E26/27 or two needle GU10, shown in Figure 13 .

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With a larger lamp size , there is a fairly large space to accommodate the LED driver solutions, and PF and low THD is still mandatory.

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Design Challenges

These LED lights will cause a higher wattage higher Vds, peak ( peak ) through MOSFET, which requires a higher rating BVDss MOSFET. For high voltage spikes , since the input current is higher , BVDss rating must be reduced. Figure 14 shows the summary of the voltage spike Vds, peak = Vin + nVo + Vos, which is the reflected output voltage nVo , also known Vro. Ceiling Light

Buffers typically used to limit the peak voltage Vos , the buffer will consume energy, thus reducing the LED driver efficiency :

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Fairchild solution shown in Table 2 , the single stage flyback of the two methods shown in Table 3 .These LED lights will cause a higher wattage higher Vds, peak ( peak ) through MOSFET, which requires a higher rating BVDss MOSFET. For high voltage spikes , since the input current is higher , BVDss rating must be reduced. Figure 14 shows the summary of the voltage spike Vds, peak = Vin + nVo + Vos, which is the reflected output voltage nVo , also known Vro. LED Downlights

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Compared with the traditional lighting , LED lamps do not need to use the filter or filters to LED Bulb produce colored light , not only high efficiency , pure light color , and can dynamically change the color or gradient . Changing the color temperature while maintaining a high color rendering index, to meet different application needs. But it also raised new packaging requirements embodied in:

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( A ) Modular

By a plurality of LED light ( or modules ) connected to each other to achieve good lumen output can be superimposed , high-brightness lighting requirements. Through modular technology allows multiple point light sources or LED modules in accordance with the random shapes are combined to meet the lighting requirements in different fields .

( Two ) to maximize the efficiency of the system LED Flexi Strip

In order to improve the optical efficiency of LED lamps , in addition to the appropriate LED power , it must also adopt efficient cooling structure and process , as well as optimizing internal / external optics designed to improve overall system efficiency.

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Usually tested for LED aging 6000 hours Lumen maintenance LM (Lumen Maintains), in LED Downlight with the exponential law , if 6000 hours after LM> 91.8%, can be claimed 25,000 hours of life , if LM> 94.1% can be claimed 35,000 hours of life , but time does not exceed the projected life test time of 6 times.

DLP projectors after nearly 20 years of development , in recent years gradually been serious impact LCD products , in response to changes in market conditions , the use of LED light source DLP projectors in the last three years has been large-scale promotion and application.

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As we all know , the traditional DLP projectors most criticized is its use of UHP light source, 6000 hours average life expectancy has led to the user's never been able to reduce costs , while the LED light source UHP places 10 times the life of a good solution this problem. But whether it perfect LED light source of it ? In use it and pay attention to what ?

First, the brightness and color gamut selection

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LED light source While traditional outdoor LED display has long reached the K -class lumens DLP applications but is still generally stay in this range 600-800 lumens ( brightness mode ) , so the use of the environment ambient light to do more stringent controls to the customer for the LED light source brightness is insufficient sensitivity to a minimum.

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And because of the wide color gamut LED light source characteristics ( see figure ) , so we have a LED Lighting china chance in a more complex environment applications . If the ambient light is usually cool white or incandescent, it is recommended that the color temperature can be adjusted in the range of 7500-9300K , the human eye perception higher brightness, more vibrant colors .

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Second, the heat

Since spectral characteristics of the LED light source , resulting in the same light conditions , the heat generated by the light source section than UHP ( see figure II ) . So the entire projection display unit for thermal design requirements and temperature control requirements will be higher . The current mainstream cooling methods are mainly two kinds of air-cooled and water-cooled . Should have their advantages and disadvantages. More traditional air-cooled , mature, slightly higher than the water-cooled air-cooled cooling efficiency , but the design more difficult, long-term reliability to be tested .

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Figure II

Third, the maintenance

Because traditional UHP light shorter life , brightness decreases rapidly , resulting in a put into use, requires a higher frequency of periodic testing, to the brightness , color uniformity maintained at a certain level . The LED light source of high life, low attenuation characteristics of a good improvement in this situation , while the absence of the color wheel , also without regard to the long-running drive for the optical output color dust impact ( see Figure III). This will greatly reduce the manpower needed for maintenance expenditures . LED Downlights

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Figure III

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Fourth, the cost

As the life expectancy of the LED light source 60000h, and there is no color wheel , so in theory the normal use of the device within a period of no longer considered consumables expenses ,

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In summary , LED light source projector using effects , maintenance costs compared to the UHP a major step forward , as soon as possible as long as the light source brightness breakthrough can be expected within a certain time it will dominate the high-end large-screen market.

To design a product , we must first determine the structure of the LED package with who ; Next, consider how to adapt these packages ; few opportunities at our option , the optical structure is built on top of these packages ; we play a lot of creativity can not be good . The following describes the process of LED lighting design and analysis of key issues .

First, the semiconductor lighting application problems

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1 , heat

2 , the lack of standards, product varies greatly

3 , there is a price and design quality problem , the final consumers LED lighting, lack of confidence

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2.2LED grain substrate

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LED grain is mainly used as a substrate LED die between the circuit board and the system heat exported media , by wire , eutectic or flip chip manufacturing process combined with the LED die . And based on thermal considerations, currently available LED crystal substrate mainly ceramic substrate mainly to the preparation method of different lines can be roughly divided into :

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thick film ceramic substrate , low temperature co- fired ceramic and thin film ceramic substrate three kinds , in traditional high-power LED components , mostly thick-film or LTCC substrate as grain heat the substrate , then gold wire mode the LED die and the ceramic substrate binding .

As stated in the introduction , this golden thread link limits the heat loss along the electrode contacts the performance . Therefore , in recent years , domestic and foreign manufacturers are all efforts towards solving this problem . Its solutions have two , one is looking for high thermal coefficient of the substrate material to replace the alumina, contains silicon substrate , silicon carbide substrates, anodized aluminum plate or aluminum nitride substrate , wherein the substrate material silicon and silicon carbide semiconductors characteristics,

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so that at this stage encounter more stringent test, and anodized aluminum substrate is anodized oxide layer due to insufficient strength susceptible to fragmentation lead to conduction , so that in practical application is limited, and therefore , at this stage more mature and is common to accept a higher degree of aluminum nitride substrate as heat ; however ,

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currently limited to aluminum nitride substrate NA conventional thick film processes ( silver LED Lighting china plastic printing material shall be subject to 850 ℃ atmosphere after heat treatment, its reliability problems in materials ) , therefore , the aluminum nitride substrate thin film processing lines need to prepare the system .

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Abstract: The traditional single LED display control problems , the development of ARM-based device uses touch screen technology and Zig-Bee wireless transmission technology campus bulletin board LED remote control system.

0 Introduction

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In recent years , LED electronic display as a kind of high-tech products has attracted much attention. It can be displayed in real time or loop play text, graphics and image information , has displayed a rich ,

ornamental and strong, easy to modify the display , high brightness, long life, stable and displayed a variety of advantages , has been widely used in many fields . With the continuous development of LED display industry , people on the LED display to control the increasingly high demand , especially in the LED display of the remote control , the traditional single LED display control has been difficult to meet the multiple LED display applications.

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Currently, the campus bulletin board LED use more and more, for the promotion and dissemination of notices , but its control is still based on a single block LED bulletin board controls the mainstream, manipulate, and update the display information is very inconvenient. In this context , the design of the LED on the current campus bulletin board system for research and improvement, the original LED bulletin board based on adding the ZigBee transceiver module , designed an ARM-based devices , the use of touch screen technology and ZigBee wireless LED transmission technology campus bulletin board system .

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A control system hardware design

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1.1 S3C2440 processor control board module

On this hardware platform embedded Linux real-time operating system for the entire LED campus bulletin board system management and control. S3C2440 chip supports touch -screen interface , which includes a touch -screen controller , four external transistor , there is an external voltage source. Touch screen interface controls , selection control signal (nYPON, YMON, nXPON, XMON) and analog pin with the pin and touch screen panel is connected to the external transistor .

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1.2 PS2 keyboard module

PS2 keyboard transmission protocol based on the following data formats for data transmission : a start bit ( always logic 0 ) , 8 data bits ( LSB first ) , a parity bit ( odd parity ) , a stop bit ( always logic 1 ) , an acknowledge bit ( used only on the host device communication ) . Keyboard transmit timing shown in Figure 2 .

1.3 LCD modules LED Flexi Strip

Using a 7-inch LCD screen , and its Video Color System : PAL / NTSC; high-definition, wide viewing angle, 16:9 and 4:3 can be any conversion ; Best resolution : 800 × 480; Contrast Ratio: 200:1 ; 7-inch LCD screen is mainly used for the main display and input control interface updates the display of text .

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0 Introduction

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In the white LED lighting technology development, the use of LED high modulation frequencies , White LED communication as an emerging communications technology has been of great concern . According to communication theory, reduce the error rate of the judgment in two ways : First, to increase the input optical power ; First, improve the signal to noise ratio . In the communication system, the white LED , white LED light emitted as visible light , and the divergence angle is large, basically harmless to human eyes ,

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no electromagnetic damage , etc., by increasing the transmission power of the white LED light source , to improve system reliability sex . The receiving end determines the SNR performance of the whole communication system [ 2 ] . Our white LED communication system based on the analysis of interference noise , LED Flexi

the noise-limited system, the introduction of the band-pass filter and a new image optical system , the use of noise matching low noise amplifier design and interference limited system using a band-stop filter, subcarrier modulation , an additional filter capacitors and other measures proposed dual- limited noise and interference based on a new type of receiver design solutions.

White LED technology is the use of the communication speed of LED devices emitting the blink response characteristics , the LED emits imperceptible with the naked eye high rate modulation of the optical carrier signal for modulation and transmission of the information ,

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