RGB and white LED how to choose?

Jun 21st, 2012 | Posted by | Filed under LED Light

When the need for LCD flat panel displays chooses back lighting lighting, designers often face should use with a pure white light or the RGB light source of the dilemma. drive and RGB drive is different, for example, used for portable electronic devices in the display, or general back lighting lighting applications to drive the highly of have no low inductance low noise led drive IC, and standard drive IC have different performance standards, this is because RGB led and toward the voltage is different, so need different IC architecture. Usually will have a coil of ON/OFF interface and 3 separate resistance can be programmed to control LED current source dimmer and brightness, in addition, it will adopt the “white” mode to optimize red and green and blue LED the current ratio, so, in all three RGB LED programming for when to obtain the best ON the spectrum of.

Different lighting source choice of backlighting

To provide for the display back lighting cold cathode fluorescent lighting (CCFL) has a limited chromatography, and colour bright enough. RGB LED actually expanded the scope of visible light. In addition, in the national television systems committee (NTSC) of the definition of the colors, CCFL shows about 80%, and can be a show of RGB NTSC chromatographic up to 110%, so the screen can show the beauty of image more accurate. Three monochromatic light source, such as red, green and blue (RGB) laser, will get the possibility is the most extensive chromatography.

On the other hand, White LED Tube back lighting lighting is suitable for handheld and active display, because white LED appearance of small size, simple easy to drive, to the mechanical stress not so sensitive, and when compared with CCFL, two times longer life expectancy. However, white LED in the chromatographic aspects and CCFL have the same faults, because white LED light source is equal to broadband. White LED is blue light-emitting diode (LED) on the formation of the phosphor cover, it into a yellow light blue part, the combination of the formation of the spectrum is regarded as the white light.

Compared with a monochromatic light source, RGB LED to lower the cost of providing a close to a narrow frequency of chromatography. RGB LED not only improve the chromatography, and has increased efficiency, because RGB LED only to red, according to the green light and blue light emission light energy. Relative to character, broadband source (such as white LED and CCFL) issued more don’t need the color of light, the lower the purity of chromatography, and so reduce the efficiency. Since different colors of RGB LED can drive alone, then RGB LED the white light of the point or color temperature can correction, and CCFL and white LED the white light of the points are fixed.

RGB and white LED the cost comparison

Choose RGB or white flexible led strip lighting source as lighting, may satisfy the specific requirements of the final product. But because the RGB LED a wider chromatography can degrade the image up to the highest, so use with RGB LED up and white LED is justified, because consumers to buy in what type of LCD TV, may be because bright colours and are willing to pay more. However, the use of RGB LED, scheme size bigger, more complex and more expensive. However, if the wider in chromatographic does not allow products raise prices in the application of white LED through solution as back lighting lighting source, which is an acceptable choice.

Dimmer consider

Traditionally, LED the light is a DC signal or filtering PWM signal regulating flows through the downstream to come to a current LED. Reduce LED current adjustable LED light output density. However, toward the change of the current will lead to leading the color change, because the shade of the current and LED with change. Cars and LCD TV back lighting lighting and so on many kinds of application does not allow a LED emitting light colors have any deviation. Due to the changing environment and around different human naked eye can sense light intensity are a small change. So in these applications require wide dimming range. In light of PWM signal control LED strong, cannot change the emitting light colors and the LED light.

“True Color PWMTM dimmer” through the PWM signal regulating LED brightness. It is essentially frequency PWM with full current through and disconnect LED. Please see figure 1. The limits of the naked human eye for a 60 letter box. By improving the PWM frequency (such as increased to 80 Hz ~ 100 Hz), the human eye feel the pulse light source is the continuous through. In addition, through the modulation work cycle (” on time “Long), can control LED light is strong. Using this method. The LED emitting light colors remain the same, because the current value or zero LED, or a constant value. Many LCD TV designers were required to as high as 3000:1 dimmer than, in order to adapt to the environment a wide range of light changes.

The driver of the practical solutions

RGB LED drive, an example is LingLiEr’s LT3476 four groups LED drive. LT3476 of each channel can drive up to eight stars 1 A parallel LED (red, green, and blue or white), LT3476 can realize drive up to 32 of the star 1 A LED, and efficiency can be as high as 96%. 4 channels may reach their True Color PWM signal independent work, realized as high as 1000:1 independent dimmer than. Fixed frequency, current model architecture in broad power supply voltage and the output voltage range realize the stable operation. Users will be able to use frequent adjustment in stitches 200 kHz ~ 2 MHz frequency range set frequencies in order to optimization efficiency, while the maximum size reduces external components. The heat dissipation enhanced 5mm x 7mm QFN packaging can be for 100 W LED application form by three feet very nice little solutions. This kind of application for large LCD TV is common.

In the LT3476 LED the high pressure sensor output current, realize the buck, lift pressure or booster configuration. Users through an external sensor resistance, can set off each channel output current range. 4 independent drive channel each has within 1.5 A, 36 V NPN switch. Other features include LED to open protection and thermal restrictions.

Another example LingLiEr’s LTC3212, this may maybe be considered a no inductance minimal tone LED generate IC, in easily transportable electronic gadgets check and lighting usages may maybe be driven minimal altitude RGB LED. RGB LED toward the whitened LED voltage and different, so need different IC architecture. LTC3212 has 2.7 V-5.5 V input voltage broad variety wide, to $25 every by LED the mA’s latest motorists three star LED, one for lithium ion/polymer battery app and optimization. LTC3212 ON/OFF the coil of interfaces and three impartial resistance programmable LED latest supply manage dimmer and brightness, understand the simplicity and elastic. The whitened brightness mode may maybe be red, eco-friendly and blue brightness will very likely be LED for the most recent than optimization. In all three RGB LED are arranged for ON, provide just one of the selected spectrum. Standby mode inside the static latest only 400 uA, a complete great offer more will achieve the greatest battery range.

LTC3212 multi-mode cost pump with minimal noise, repaired volume operation mode, can will ripple to some minimum, as well as the element automated mode change volume to accomplish a complete great offer more optimization. LTC3212 in one x mode energy supply, in anybody LED sensor for the stress drop, the element of instances stress gauges (2 x) mode cost pump. inner gentle start-up circuit can stay obvious of surge current, as well as shutdown disconnect, short circuit safeguard and warm shutdown, jointly with other functions, for the IC and LED provide additional protection operation. standard usages consist of hive sort cellphone and mass media participant displays, important lighting, RGB LED back again lighting and whitened light, lighting.

LTC3212 with low height for 12 pick feet DFN (2mm x 3mm x 0.75mm) package. This component only three small capacitance and 1 to 3 set resistance, can form a nice little RGB or white LED current controller and power solutions.

Conclusion

Compared with white LED for RGB LED backlit displays provide for lighting, even need more RGB LED (and therefore need more RGB LED drive), but if a wider chromatography and color more accurate image for considering the point, then increase the complexity is still worth the design. Therefore, the designer decided to adopt the RGB, or white LED back lighting lighting meet demand faced when, in fact, is the cost and performance trade-offs problem.