As large numbers of solid state light source, light-emitting diode (LED lights), incandescent increasingly lonely. In the past few years, LED technology has been tremendous progress, making LED cooling, packaging and process technology advances have higher brightness, higher efficiency, longer life and lower cost.
However, the efficiency of energy conversion, thermal management, and production costs, LED still has further room for improvement. For example, LED efficiency has been greatly improved. Many improvements in the LED from the better chip to produce light, and there are better ways to get light from the chip and its package. Similarly, 20mA white LED prices have significantly reduced this LED has just launched, lots of share offer for $ 1. At present, 20mA white LED may be approved purchase price of less than 30 cents to buy.
LED lighting applications needs analysis
Of course, all these advances not only promoted the LED as the lighting of use in different applications, but also stimulated the demand for LED driver IC. To understand the design and manufacture of LED driver IC to face obstacles, it is necessary to understand the white LED light-emitting What are the conditions. White LED with a constant current source driver, so that the white points of light will not change (that is, the brightness must be consistent). In addition, since the white LED is a diode, then it must overcome its internal forward voltage drop (Vf). Vf with the white LED current value will change with changes in temperature. Under normal circumstances, within the entire operating temperature range, 20mA white LED Vf in the range from 2.5V to 3.9V. Most applications, multiple white LEDs, these LED may also be configured in parallel, in series or series-parallel hybrid forms. This means that the white LED driver IC must be able to provide for the specific configuration of multiple LED current and voltage and the voltage converter topology used in this IC must also meet the input voltage range and output voltage and current requirements.
The biggest driving force of the LED common applications include automotive and aircraft instrument panel display and instructions, traffic lights, cell phones, flat panel display backlight, miners lamps, buildings and outdoor large-scale stadium lighting, and the current and future years, the LED market growth from the flat panel display backlighting requirements. These displays use LCD screen for TV sets, navigation systems, portable media players, digital billboards, and computer monitors. However, the LED facing the challenges of thermal management technology. Although LED Unlike other light sources, as so much heat radiation, but depending on the output power, some LED may require a suitable heat sink, so that light output will not reduce the life expectancy is not shortened. For example, the power light output for the the 25lm high brightness LED is generally consumed more than 1W. This means that the white LED driver IC with high efficiency must be converted so that it can not become the main cause of heat problems. In addition, in many cases there are space-constrained problem, the LED driver solutions to small footprint, and small size.
Mobile phone, for example, most cell phones today have built-in digital camera that can shoot high-resolution photos and videos. Camera improved performance has also led to the demand for high-power white light, the camera indoors or in dim environments need to use this light, the white LED main light source for a camera phone. Because the white LED has a wide range of modern cell phone designers want the features: small size, high light output, can provide the “Flash” and “video” object of continuous illumination. Has been specifically developed for the integrated camera lighting the high output power LED.
Although the use of high-power LED visible light is very simple, but if the wrong has been designed to improve, to form a high-performance power supply and current control solution is very difficult. Linear Technology’s LTC3454 is a new product designed specifically for high-current camera lighting applications to improve power conversion efficiency and accuracy, and optimize the control of LED current.