HB LED driver technology into a hot competition power suppliers

Driven by strong mobile applications, high brightness (HB) LED market in 2001 to 2004 has maintained a staggering growth rate of 46%. Just as people worried about the mobile phone equipment caused when LED saturated market forces are gradually weakening, lighting, car headlights and LCD TV backlight driver LED and other emerging applications market in large numbers, set off LED wave application frenzy. U.S. market research firm Strategies Unlimited predicts that by 2010, HB LED market will reach $8 billion 300 million, more than the total number of more than two times in 2005. So attractive market attracted many manufacturers of food, technology, ADI, Fairchild, NXP and other manufacturers in the LED drive technology, have a good performance. In the field of power management, LED driver technology has become a competitive stage of the technical strength of each vendor competition.

Dimming technology to make a fuss, backlight also need hd"

For display technology, not only the need for high-definition video signal processing, the quality of the backlight adjustment, but also a direct impact on the video display. In order to high-definition technology in the end, the manufacturers in the LED backlight drive technology is really a lot of effort.

Traditionally, the dimming of LED is accomplished by using a DC signal or a filter PWM to regulate the forward current in the LED. Reducing the LED current will play a role in regulating the output intensity of the LED light, however, the change in the forward current will change the color of the LED, because the chroma of the LED will change with the change of the current. Many applications (such as cars and LCD TV backlight lighting) can not allow any color drift of LED. In these applications, because of the presence of different light changes in the surrounding environment, and the human eye is sensitive to small changes in light intensity, the wide dimming range is required. By applying a PWM signal to control the brightness of the LED allows you to change the color of the LED without changing the color.

It is often said that the true Color (True) PWM dimming is the use of a PWM signal to adjust the brightness of the LED. It actually needs to complete the LED on and off operation under the condition of full current and PWM frequency. The resolution limit of the human eye is 60 frames per second, by increasing the frequency of the PWM (e.g., up to 80~100Hz), it is possible for the human eye to see that the light source is continuous. In addition, by adjusting the duty cycle (the total amount of time), but also control the brightness of LED. At present, many LCD TV designers need up to 3000:1 dimming ratio, in order to adjust the brightness of many environmental conditions.

System engineer in the selection of backlight, what is the choice of RGB or white LED? Linear Technology Corporation power product marketing manager Tony Armstrong pointed out that the backlight (RGB or white LED) could be selected according to the specific requirements of the final products to. However, using RGB to replace the LED white LED is justified, because the former has a more broad chromatogram which will significantly improve, the quality of the image, select LCD TV as an example, the consumer of color fidelity is the highest degree of concern. However, the use of RGB LED requires a larger, more complex and more expensive solution.

An LT3476? Channel LED driver is an example of RGB LED driver. Each channel of the LT3476 can drive up to 8 series of 1A LED (red, green, blue or white), so that the LT3476 is capable of driving up to 32 1A LED and providing up to a efficiency of up to. The 4 channels are available through True Color PWM signal to its own independent operation, so as to realize the independent dimming, dimming ratio can be as high as 1000:1. Fixed frequency, current mode architecture enables stable operation over a wide range of supply and output voltages. A frequency regulation pin allows the user to set the switching frequency in the range of 200kHz~2MHz in order to optimize the efficiency and minimize the size of external components. Its thermally enhanced 5 x 7mm QFN package provides a very compact solution for board area, which is well suited for large LCD TV common 100W LED applications.

In addition to similar to the linear PWM signal as a control signal to adjust the brightness, whether there are other techniques can achieve the dimming effect very good? Law, a field application engineer at Brian, has his own opinion, and he argues that one of the key requirements to distinguish between LED drives and standard boost converters is that the LED driver can control the brightness level of the LED. There are three common ways to adjust the brightness: using SET resistance; using PWM technology; and linear adjustment. The easiest way is to use an external SET resistor in the IC. Although this is an effective method, but the lack of flexibility, users can not change the intensity of light. Using PWM technology and linear adjustment can be carried out on the dynamic control of light intensity. But these two methods have their drawbacks. Using PWM dimming LED will cause EMI noise, and cause the white LED color shift toward the blue spectrum. May be slightly offset, but can be detected in sensitive applications. Linear adjustment will reduce the efficiency, and cause the white LED color shift toward yellow spectrum. As for which method is superior, the industry has not yet reached a consensus. As a result, Fairchild developed the latest LED driver, which can be used to adjust the brightness of one or two methods. The FAN5617 uses a charge pump architecture to drive three parallel LED, and a single wire bus is integrated to allow the user to set the light intensity by applying a linear or PWM signal.

However, in terms of this integrated dimming technology is not the first case of flying. According to Beijing Wang Wang Electronics Technology Co., Ltd.