LED backlighting in portable products, the position has been unwavering, even in the large-size LCD backlight source which, LED also began to challenge CCFL (cold cathode fluorescent lamp) in the mainstream status; while in the field of lighting, LED as a semiconductor lighting the most critical component, but also because the withstand energy-saving, environmental protection, long life, maintenance-free, and many other ring and sought after by the market. Drive circuit is a LED (light-emitting diodes) products, an important component in terms of lighting, backlighting or the display panel area, drive the choice of circuit technology infrastructure should be matched to specific applications.

    LED light-emitting principle is that it ends with a positive voltage, so that the semiconductor in the minority carrier and majority carrier compound occurs, release excess energy, causing photon emission. LED driver circuit is the main function of AC voltage is converted to constant-current power supply, while in accordance with the requirements of LED devices to complete the LED voltage and current match. LED driver circuit in addition to meet the safety requirements, the other basic functions should be two-fold:

    First, as far as possible to maintain constant current characteristics, especially in the power supply voltage of ± 15% change occurs when the output current should be able to keep within ± 10% change. With the LED as a display or other lighting equipment or backlight source, need to be constant-current drive, the main reasons are:
    1, to avoid the drive current exceeds the maximum rating, affecting its reliability.
    2, to obtain the desired brightness requirements, and ensure that all the LED brightness, color consistency.

    Second, the drive circuit itself should be kept low power consumption, in order to make LED's to keep at a high level of system efficiency.

    PWM (Pulse Width Modulation) technology is a traditional dimming mode, which uses a simple digital pulse, repeated switching LED driver, the system only need to provide a wide, narrow of different digital pulse, can be achieved simply changing the output current, to adjust LED brightness. The technology is its ability to provide high-quality white light, and the application of a simple, high efficiency, but a fatal drawback is prone to electromagnetic interference, and sometimes will produce the human ear can hear the noise.

    Boost LED driver circuit is an important task, while the boost inductor boost and charge pump are two different topological models. "As the LED is a current drive, while the inductor current conversion during the highest efficiency inductive boost mode so the biggest advantage is high efficiency, if properly designed, can be more than 90%; However, its disadvantages are also obvious that the electromagnetic interference strong, mobile phone and other communication products for the system requirements very high. With the emergence of charge-pump, most current mobile phones are no longer using inductive step-up approach. Of course, the boost mode charge pump efficiency will be lower than the inductance boost.

    Both in lighting applications, or backlighting applications, to improve the conversion efficiency of drive circuits are product designers have to face problems. Improve the conversion efficiency is not only beneficial to extend the standby time of portable products, but also to solve an important means of LED heat problem. In the lighting field, due to the use of high-power LED, thus increasing conversion efficiency becomes particularly important.