In a wide variety of lighting applications, the adoption of LEDs continues to be strong. This consistently strong momentum means that analog IC suppliers that offer LED driver ICs will have a good business momentum. In the past year, high-brightness (HB) LEDs have met some key performance standards, which has led to a significant increase in demand for LED driver ICs that are required to power LEDs in all end-market applications.
The demand for LED driver ICs is currently in its infancy, and by examining several factors that will drive this demand into an accelerated growth phase, we have found that LEDs will clearly become mainstream lighting sources. Some of the main drivers are: automotive lighting, large flat-panel high-definition (HD) LCD TVs, handheld devices, LED light output, cost factors for LEDs, and the potential use of LEDs to replace incandescent lamps.
Audi is the first car manufacturer to use LED headlights in a variety of models, and it has been in use since 2008. Audi's automotive lighting system consists of two main low-beam headlights. The system consists of two LED arrays, each with four active components. The other three LED arrays (each containing two LED ICs) are located behind the optical lens and their task is to control the light/dark boundary and headlight illumination range. For high beam headlights, the four LED arrays are located adjacent to the low beam array. Near the lower edge of the lighting system, a row of 24 LEDs form the daytime running lights (DRL). However, it is these daytime running lights that make the Audi car look new and exciting, and the appearance of the Audi car is very popular with car buyers. Soon after, many other manufacturers followed suit, Mercedes, Jaguar, Lexus and Porsche, all offering similar daytime running lights.
The LED headlight system is lagging behind in adoption, which is mainly due to cost. However, some early signs of 2011 seem to indicate that this situation will start to change, because in fact, LEDs allow for more flexible design choices, while LED efficiency increases the cost/performance balance. Therefore, we now see that LED headlamps are available as an optional accessory for all models of Cadillac, Toyota and Lexus. For example, the Cadillac Escalade, the Lexus LS600H (Lexus LS600H) and the Toyota Prius can all be equipped with LED headlights.
LED driver ICs have many advantages when used to drive LEDs that provide backlighting for HD flat panel TVs. These ICs enable LED driver circuit solutions to be slim, compact and flat. These ICs also operate at high switching frequencies to reduce the capacitance value, size and cost of the output capacitor in a charge pump based topology. In an inductor-based DC/DC switching topology, this high switching frequency reduces the value, size, and cost of the inductor and output capacitor. In addition, in some cases, the LED driver IC may include a built-in Schottky diode and a boost diode, thus reducing the number of external components. This in turn reduces design complexity, solution size and cost.
From moving image blurring to color reproduction, LCD high definition televisions (HDTVs) have various drawbacks. That is to say, in the current generation of LCD HDTVs, true black cannot be achieved, and the dynamic range of all colors is low. Traditional HDTVs are backlit with CCFL tubes and offer contrast ratios of only 450 to 650 cd/m2. The main problem with these HDTVs is that CCFL backlighting cannot be completely turned off or partially dimmed.
Conversely, if high-brightness LED backlighting is used, the LED array in the backlight “group†(up to 1,600 LEDs for a 46-inch display) can be locally dimmed or turned off, making it almost more than a CCFL design. A high level of contrast ("4,000 cd/m2). In addition, by adjusting the brightness of the backlighting LED group, more midtone colors can be reproduced, making the picture more vivid. Another benefit is the ability to completely turn off the LEDs partially, thereby reducing motion image blurring. By completely turning off the LEDs between frames, image blurring associated with fast moving objects is virtually eliminated. In addition, the very high response speed of LEDs is critical when solving CCFL backlighting LCD TVs that often encounter fast moving image blurring problems.
Many mobile phones today have built-in digital camera capabilities for high-resolution still images and video. The increased performance of the camera also results in the need for a high power white light source to use the camera indoors or in dim ambient light conditions. Among the cell phones equipped with cameras, white LEDs have become the main source of light, because white LEDs have all the features that modern cell phone designers want: small size, large light output, "flash" and continuous "video" Object illumination. Large output power LEDs have been developed specifically for use as integrated camera sources.
Similarly, almost any battery-powered consumer handheld device uses a color active matrix LCD to display the different types of information and data that users need. However, the challenge for manufacturers is to ensure that users can read information from these displays in any type of environment. To achieve this, manufacturers must provide a color LCD with the right amount of backlighting. This kind of backlighting is usually provided by white LEDs, which vary in size depending on the size of the display. White LEDs come in a variety of combinations. This, in turn, has led to a need for compact, high efficiency, and low noise LED driver ICs that require such driver ICs to power white LEDs.
Important factors driving the growth of the LED marketThe light output of high-power or high-brightness LEDs has exceeded this critical milestone per Watt 100 lumens, and some manufacturers claim to have reached 200 lumens per Watt in the lab. This means that in terms of efficiency, LEDs now exceed CFL (80 lumens per Watt). However, further projections indicate that by 2012, LEDs will achieve a light output of 150 lumens per Watt. Another advantage is the long life of the LED. Depending on the calculation method, white LEDs have a lifetime of at least 10,000 hours, and some even claim to have reached 50,000 hours. In addition, LEDs are “green†products because they do not contain any hazardous materials.
These advances are important because the US Department of Energy has announced that lighting consumption accounts for 22% of the electricity generated in the United States. Extensive use of LED lighting may halve lighting power consumption. From another perspective, by 2027, LED lighting has the potential to reduce annual energy use by as much as 500 million barrels of oil, accompanied by a reduction in carbon dioxide emissions.
The cost of LED lighting has dropped very rapidly. The price of a single white LED (a few white LEDs that make up an LED, which accounts for most of the cost of LEDs) was about $5 a few years ago, and has fallen to less than $1 in the past year. Many analysts in the LED industry predict that in the coming year, the price of LED lights will reach acceptable levels for consumers, and LED lights will replace incandescent lamps. Some LED manufacturers have announced that they have designed a light-emitting chip that can power LEDs, enabling LEDs to produce light output comparable to the 75W incandescent lamps that are extremely popular in the home. This type of LED chip typically requires 12W to 15W in order to provide such light output.
What are the challenges that high-brightness LEDs bring to driver ICs?Today, one of the key performance features that LED driver ICs must have is the ability to fully dim the LEDs. Since the LED is driven with a constant current, where the DC current value is proportional to the brightness of the LED, there are two ways to dim the LED current by changing the LED brightness. The first method is analog dimming, in which the DC current value of the LED is proportionally reduced by reducing the constant LED current value. Reducing the LED current can result in a change in LED color or inaccurate LED current control. The second method is digital or pulse width modulation (PWM) dimming. PWM dimming turns the LED on and off at a frequency equal to or higher than 100 Hz, and the human eye is not aware of the switching of this frequency. The duty cycle of the PWM dimming is proportional to the brightness of the LED. At the same time, the LED current remains the same value when turned on (as set by the LED driver IC), thus keeping the LED color at high dimming ratio. change. In some applications, this PWM dimming method provides a dimming ratio of up to 3000:1.
Linear Technology's LED driver ICs use a conversion topology that meets the input voltage range requirements while meeting the required output voltage and current requirements, especially in the case of high-brightness LEDs. Current and voltage. Therefore, Linear Technology's high-brightness LED driver ICs generally have the following features:
(A) Wide input voltage range
(B) Wide output voltage range
(C) High efficiency conversion
(D) Strictly regulated LED current matching
(E) Low noise, constant frequency operation
(F) Independent current and dimming control
(G) wide dimming ratio range
(H) Small and compact footprint, with minimal external components required
Linear Technology has a wide range of products to meet LED driver design needs, two of which are the LT3754 and LT3956.When white LEDs are used for backlighting large flat panel displays, Linear Technology's new LT3754 solves design problems associated with driving white LEDs. The LT3754 is an innovative LED driver IC for HDTVs with flat panel displays up to 26 inches or larger. This boost mode LED driver has 16 separate channels, each with a Vf of approximately 3.2V, capable of driving up to one LED string consisting of 15 50mA LEDs. Therefore, each LT3754 can drive up to 240 50mA white LEDs. As a result, a 26-inch LCD HDTV may require only one LT3754 to provide the necessary backlighting. All 16 channels are controlled by a single PWM input and can provide PWM dimming ratios of up to 3,000:1.
The LT3754 uses a small inductor and even a more compact ceramic output capacitor. The only other components required are a single input capacitor, a MOSFET, and a current setting resistor, as shown in Figure 1. Each channel follows a programmable main current to allow 10mA to 50mA of LED current per string of LEDs. These channels can also be connected in parallel to provide greater LED current. The output voltage adapts to changes in LED Vf for optimum efficiency, and open LED faults do not affect the operation of other connected LED strings. The LT3754 is available in a compact 32-pin, 5mm x 5mm QFN package.
Figure 1: 38W LED driver drives 16 strings of LED strings with 15 50mA LEDs per string
16 STRINGS 50mA UP TO 45V: 16 strings, 50mA, up to 45V
Now, with an array of 18 LEDs in series, a 25W white LED headlamp can be configured, and the 350mA current flowing through the LED produces the desired light output. However, one major obstacle is how to drive such a configuration efficiently and simply. One possible solution is to use Linear Technology's recently introduced LT3956 monolithic LED driver. The LT3956 is a DC/DC converter designed to operate as a constant current and constant voltage regulator. It is ideal for driving high current, high brightness LEDs (see Figure 2).
Figure 2: 94% efficiency white light LED headlight driver with 94% efficiency
TRANSIENT: Transient
LED STRING: LED string
The LT3956 includes an internal low-side N-channel power MOSFET rated at 84V/3.3A, driven by an internally regulated 7.15V supply. Its fixed frequency, current mode architecture provides stable operation over a wide range of supply and output voltages. A ground-referenced voltage feedback (FB) pin is used as an input to several LED protection functions and also allows the converter to operate as a constant voltage source. The frequency adjustment pin allows the user to set the frequency from 100kHz to 1MHz to optimize efficiency, performance or external component size.
The LT3956 senses the output current on the high side of the LED string. High-side detection is the most flexible method for driving LEDs, allowing boost, buck, or buck-boost mode configurations. The PWM input provides up to 3,000:1 LED dimming ratio, while the CTRL input provides additional analog dimming.
in conclusionAny LED driven with an LED driver must be able to provide the necessary light output at the lowest power so as not to cause significant thermal design limitations in the final system. Fortunately, in terms of lighting designers, there are both high-efficiency LEDs and high-performance LED drivers that provide the features they need most: a large amount of light output at moderate power and at a reasonable cost.
Whether the game can be played smoothly depends on the low latency of the projector, whether it can be optimized to within 30ms, or within 50ms, which is difficult for non-professionals to perceive. However, the cable and network speed and the configuration of the computer (game console) have an impact on the game delay, so you can't completely throw the pot to the display device.
The first is the problem of memory. Be sure to choose a larger one, the bigger the better, otherwise the screen will freeze. The second is that the resolution must be above 1080p, otherwise the details of the projected game screen will not be clear, which will greatly affect the game experience and viewing experience. The other is about motion compensation. The game screen is generally faster for animation playback. It must be equipped with motion compensation, otherwise the screen will be stuck.
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