ShenZhen LED

How to choose LED Driver IC?

2010-09-16T19:31:00.000-07:00

LED has established its unshakable position in the backlighting of portable devices. Even in the backlighting for the large-sized LCD panel, it has started to challenge the mainstream CCFL. In lighting, LED is especially popular in the market due to its highlighted features like energy-efficiency, environmental friendliness, long lifetime, and low maintenance. The driver circuit is a crucial and integral part of the LED. Whether in lighting, backlighting or the display panel, the choice of the technical architecture of the driver circuit must correspond to specific applications.

The LED lighting mechanism goes as follows: when the forward voltage is applied to both ends, the minority carrier and majority carrier in the semiconductor recombine to release surplus energy, giving off photons. The main functions of the LED drive circuit are to transfer the AC voltage into a constant power supply and match the voltage and current according to the requirements of LED devices. Apart from safety need, the LED driver circuit must also include two other basic features:

First, a constant current should be kept as long as it is possible, thus the output current variation is able to be maintained between the range of ±10％ especially when the power supply change goes beyond ±15％range. Here are the reasons for having a constant current driver when using LED as the monitor, other lighting devices or backlighting:

1.To prevent the drive current from exceeding the maximum rate and further affecting its reliability.

2.To meet expected brilliance requirements and ensure the color and brilliance homogeneity of each LED.

Second, the driver circuit should keep low power consumption so that the LED system efficiency can remain at a high level.

PWM (Pulse Width Modification) is a traditional light adjusting technology, which uses simple digital pulses to switch on and off LED driver from time to time. The system only needs to supply wide and narrow digital pulses in order to easily change the output for adjusting LED brilliance. The advantage is that the technology is able to provide high quality white light with high efficiency through easy application. But there is a fatal disadvantage: it is susceptible to EMI (electromagnetic interference), sometimes even produces audible noises.

Voltage boost is an important task of the LED driver circuit, divided into two different topological modes, namely, voltage boost via the inductor and charge bump. As the LED is current-driven, and the inductor is most efficient at the moment of current transfer, so the greatest strength of voltage boost via inductor lies in the high efficiency, which can reach 90% if properly designed. However, its weakness is as much remarkable, i.e., strong EMI, which imposes high requirements on systems of telecommunication products such as mobile phones. With the appearance of charge pumps, most mobiles don’t boost voltage via the inductor. Of course, the efficiency of voltage boost via the charge pump is lower than that in the other way.

No matter in lighting or backlighting applications, the product designer has to face the problem of raising the driver transfer efficiency. To improve the transfer efficiency is not only beneficial for portable products to extend standby time but is also an important means to solve the LED thermal dissipation problem. In lighting, the use of the high power LED also underlines the problem of enhancing the transfer efficiency.

LED needs current and voltage stabilizing components at work, which should be featured with high divided voltage and low power consumption, otherwise, the highly efficient LED will lower the overall system efficiency because of high working consumption, contradicting the principle of energy-saving and high efficiency. Therefore, the main current limiting circuit should use highly efficient circuits like the capacitance, inductor or switching circuit with power supply as it is possible to ensure the high efficiency of the LED system instead of the resistor or the series voltage stabilizing circuit. The series constant power output circuit can keep the LED light output constant in a wide range of power supply, but normal IC circuits will lose some efficiency. The adoption of switching circuit with power supply is able to guarantee constant power output with high transfer efficiency under dramatic voltage variation of the power supply.

At present, LED with its luminous efficacy is far from replacing the three band fluorescent lamps, yet LED lights can efficiently work under safety extra low voltage (SELV), for instances, underwater lights in swimming pools or paddling pools, mining lamps. Besides, LED has unique advantages in the direct use of green energy like solar energy, wind energy, or emergency lights. Particularly in light adjusting, LED cannot only realize zero to one hundred percent adjusting, but also maintain high efficacy during the whole adjusting process without hurting the durability, which is a difficult task for gas discharge lights.

How to improve the brightness of LED display

2010-09-12T20:58:00.000-07:00

Wed, 07/09/2008 - 17:12 — daisy.chen from www.ledinside.com
LED brightness can be improved through the following two methods:

1. To increase the light output of the chip itself: light output can be increased through improving the luminescence efficiency of the chip’s active layer or improving the external light extraction efficiency by optimizing chips’ shape or making larger scale chips that run high density current.

2. To use the light effectively. In other words, to increase the amount of light that irradiate towards the needed direction. In this method, light wave control technology is used. Through a better design of the optical structure shaped by the packaged epoxy resin, the light can be controlled to shine towards expected direction, thereby improving the brightness of LED.

The above are the methods to improve LED brightness, if the brightness of LED display runs under expectation, methods listed below can be adopted:

1. To alter the current magnitude that runs through the LED. Generally, LEDs allow a 20 milliampere operating current continuously. Only red LED has saturation phenomenon, other LEDs’ brightness are in direct ratio with the current amount that runs through them.

2．To realize grey scale control through adopting PWM (Pulse-Width Modulation) method. That is to change the width of the light pulse (duty cycle) periodically. If the time for the relighting cycle is short enough (in other words, the refresh rate is high enough), the dithering of the luminescence pixel can not be felt by eyes thanks to the visual persistence trait. As it is more adaptive to adopt digital control to realize PWM, meanwhile, as microcomputer is widely used to provide the content to display in LED screens, nearly all of the LED control systems are composed by main controller, scanning board and display control device. Main controller firstly captures data of all colors’ brightness in one particular screen image from the display adapter, then to distribute the data to the scanning boards. Each scanning board takes charge of certain rows of the LED display and the LED display control signal in each row can be transmitted in serial mode. Currently, there are two serial modes to transmit display control signal. One way is to make centralized control of each pixel’s grey scale in the scanning board. More detailed steps: the scanning board analyzes the data of each row of pixel received from the controller (PWM process), then the board will transmit the open signal of each row to corresponding LED light, controlling each LED to be lit on or to keep off state. The signal is transmitted in serial mode and in the form of pulse (the pulse signal will be 1 if it indicates LED to turn on, contrary, the signal will be 0). The device used in this method is less, but the data amount being transmitted is comparatively larger. In every relighting cycle, the grey scale level is in direct ratio with its pulse amount for each pixel, that is to say, 16 grey scale levels need 16 pulses and 256 grey scale levels need 256 pulses. As in LED display, the working frequency for the devices is limited, only 16 grey scale levels is achieved generally.

3. The serial transmitting content for the scanning board is not the on or off signals of each LED, but an eight-bit binary brightness value. If every LED has its distinct PWM to control its lighting time, a pixel under 16 grey scale levels need only 4 pulses and 256 grey scale levels need only 8 pulses in one relighting cycle, reducing serial transmission frequency greatly. Through this grey scale decentralized control method, 256 grey scale levels control can be achieved easily.

LED Panel Purchasing Guidance-part 2

2010-08-30T19:11:00.000-07:00

Why it takes longer time to produce outdoor display?

1) procurement of raw materials: purchasing the led takes long time, specially when you have to import , it takes even longer time.

2) the complexity of production process: subject to PCB design, production casing, irrigation plastic, tune white balance, etc.;

3) the structure of demanding: the general design for the box, need to consider wind, rain, lightning and so on.

How to help customers choosing the right display?

1) what need to be shown?

2) viewing distance and viewing angle

3) resolution requirement

4) requirement of environment

5) cost control

What is the genaral ratio of width and hight for the display?

Picture and text: subject to what you want to show.

Video display: normmaly it is 4:3 or near this proportion. Ideal proportion is 16:9

How many pixels can one control system control?

Communications screen Card A: single color, dual color 1024 x 64

Communications screen Card B: single color: 896x512, two color;896x 256

DVI dual color display:12801x768. DVI full color led display: 1024x512

what are the factors to consider when design the size of the screen?

when design the size of the display, there are 3 factors very important.

1) the needs of displaying content

2) space limitation

3) according to the module size and resolution

More than 10 kilowatts buck should start screen equipment.

Communication requirements: communication distance is long for the definition of communication.

To be installed to display the type of communication lines used by the length of the standard to install communications lines.

The prohibition of communication lines and power lines in the same pipe line alignment.

Installation requirements: about the level of the installation screen does not allow backward - to the installation of lifting up and down adjustment rod - wall to be installed before installing forward off hook - landing position to increase support for the installation of bolts.

Indicators display power consumption and power requirements of what?

Screen is divided into the average power consumption of the power consumption and maximum power consumption. Also known as the work of the average power consumption is usually the actual power consumption. Power consumption is the largest start-or full-bright at the time of extreme circumstances, such as power consumption, maximum power is AC power supply (wire, switches, etc.) must take into account the elements. Average power consumption is generally the largest power of 1/3. Display is a large-scale

precision electronic equipment, safe use and reliable to work, its power supply input AC220V or AC220V power supply connected to the computer ¡s input must be grounded. Note: The computer ¡s power supply input AC220V grounding terminal connected with the computer chassis.

Display of the installation requirements?

Power requirements: power supply wiring should be in the body size of the screen 220V electricity power supply, FireWire grounding line 0 line; 380V electricity supply, the three 10-line ground line of fire line; the front lines with the 0-line the same wire cross-sectional area; more than 10 kilowatts buck should start screen equipment. Communication requirements: communication distance is long for the definition of communication. Installed to display the type of communication lines used by the length of the standard to install communications lines. Prohibition of communication lines and power lines in the same pipe line alignment.

Installation requirements: about the level of the installation screen, do not allow the dumping after the lifting rod to regulate the installation of up and down before the installation of wall mounted hook falling forward landing position to increase support for the installation of bolts.

What issues should be considered for outdoor screen design and installation ?

The main issues of outdoor screens are as follows:

1) Screen installed in the outdoor sun and rain often, the wind dust cover, the work environment. Electronic equipment to be wet or damp can cause serious short-circuit or even fire, and even lead to failure of fire, resulting in losses;

2) Screen may be caused by strong electric lightning attack Magnetic;

3) Significant changes in ambient temperature. Display the work itself should have a certain amount of heat, if the ambient temperature and the heat is too high and non-performing, integrated circuits may not work correctly, and even burned down, so that shows that the system does not work;

4) Wide audience, require line-of-sight distance requirements of wide field of vision; ambient light changes, in particular, may be subject to direct sunlight.

The special requirements of the above, outdoor display must be:

1) Screen body and the screen body and architecture must be strictly waterproof junction leakage; screen body in order to provide good drainage measures, in the event of a smooth water emissions; (2) and building on the screen to install lightning protection devices. The main screen and the casing to maintain a good grounding, grounding resistance is less than 3 ohms, so that high current caused by lightning discharge in time;

3) The installation of ventilation to cool the screen so that the internal body temperature of -10 ℃ ~ 40 ℃ between. Screen behind the body above the axial fan is installed, from the heat;

4) Choice of working temperature -40 ℃ ~ 80 ℃ industrial level integrated circuit chip, the temperature is too low to prevent the winter so that the screen could not be activated. ;

5) In order to ensure a strong ambient light in the case of remote visualization, we must choose ultra-high brightness light-emitting diodes;

6) Shows that the new optional wide angle medium tube, wide angle, color pure, consistent coordination, more than 100,000 hours life. Show that the outer packaging for the media the most popular along with over a square cylinder, silicone sealed, non-metal assembly; its refined aesthetic appearance, sturdiness and durability, with the anti-direct sunlight, dust-proof, waterproof, anti-high temperature, anti-short-circuit the "Five Anti" feature.

LED Panel Purchasing Guidance-part 1

2010-08-22T19:36:00.000-07:00

What need to be considered when deciding the size of the display?
1) What is the minimum watching distance and then decide the size of the display according to the actual space.

2) Pixel pitch and resolution

3) The space for installation and maintainence

4) The angle from the display to the ground

What content do you want to show?

1) TEXT. Based on the size of the text and the resolution need.

2) Normal video.320 x 240 dot matrix

3) Number standard DVD display: ≥640 x 480 dot matrix

4) Complete computer video: ≥800 x 600 dot matrix

What are the requirements for the led display brightness according to the Environmental brightness?

General requirement for the brightness are as follows:

1) Indoor:>800CD/M2

2) Semi indoor: >2000CD/M2

3) Outdoor( facing North):>4000 CD/M2

4) Outdoor( facing south):>8000CD/M2

Requirement for the brightness of RED, GREEN and BLUE when show white:RED, GREEN, BULE plays different role when showing white. The fundamental reason is due to the human eye retina has different feeling for different wavelengths of light. After a large number of experiments and rest, we come to the following ratio for the reference: Simple red-green-blue light ratio: RGB 3:6:1 accurate brightness ratio: 3.0:5.9:1.1

Why the high quality led display requires pure green led?

In the production of the led display, we should use the trichromatic LED lamp with high lunimous efficiency and rich color. So that in the chromaticity diagram of color in the triangle area and near the tongue as far as possible in the color spectrum curve, to meet the needs of rich color and the issue of sufficient brightness and the tongue-shaped curve for the 515nm wavelength of light best, so high-end LED display selected wavelength close to 515nm pure green LED light pipes, such as the choice of 520nm, 525nm or 530nm wavelength LED light tube.

Why choose DVI graphics card standard interface?

1）international standards for the computer interface

2) No need to open the chassis, can be easily installed;

3) High-memory and strong dynamic screen display capability

4) Good compatibility of hardware and software

5) Supports all operating systems and application software

6) High-volume production, low cost, easy maintenance.

Can the display be controlled with Laptop?

no, Laptop ¡s graphics card is built-in, there is no DVI port, can not be achieved in connection with the control system.

What are the differences of NICHIA chip and othe domestic led chip except price?

1) Chip: Nichia company produce their chip independedtly while the domestic company always use the chips from America or Taiwan.

2) Packaging: Nichia company packaging independently, no branch factory in China.But for the domestic chip, there are many factories do the packaging.

3) Consistency: for the Nichia led in one lot, the wavelength has little difference, But for the domestic led, consistency is relatively poor

4) Life span: Nichia led has relarively longer life span, Domestic led attenuate faster.

Indoor full-color module and SMD full-color display, What is the difference?

1) light-emitting parts: the module full color screen display is generally green, the price of pure green module is higher; SMD generally use pure green chip;

2) image quality: full-color pixel module looks rough, low brightness and there always mosaic;SMD full color led display has better consistency and higher brightness;

3) maintenance: full-color module is not easy to maintain. The cost of replacing the entire module is high; the SMD full-color module is easy to maintain, maintenance can be carried out by replacing a single lamp;

Can the SMD3528 used for outdoor display? Why?

No. Outdoor screen has high demand of installation and structure, SMD3528 LED unable to adapt to the harsh outdoor environment; at present SMD display can not to meet brightness requirements of outdoor display

MORE INFORMATION: http://www.era-led.com/

Shenzhen ERALED Optoelectronics Co., Ltd

2010-08-01T18:44:00.000-07:00

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More Information: http://www.era-led.com/