LED backlighting in portable products, the status can not be shaken, even in which the large-size LCD backlight, the LED also began to challenge the CCFL (cold cathode fluorescent lamp), the mainstream position; in the lighting field, LED as a semiconductor lighting the most critical components, but also wore the halo of the energy saving, environmental protection, long life, maintenance-free, and many other sought after by the market. The drive circuit is an important part of the LED (light emitting diode) lighting, backlighting or the board areas, the choice of the drive circuit architecture should match the specific application.
LED light-emitting principle is that it ends with a positive voltage, the semiconductor minority carrier and majority carrier complex, and release excess energy, causing the emission of photons. The main function of the LED driver circuit to convert AC voltage constant current power supply, in accordance with the requirements of the led 1w devices to match with the voltage and current of the LED. LED driver circuit to meet the safety requirements, and other basic functions should have two aspects:
First, as far as possible to maintain constant current characteristic, especially in the power supply voltage of ± 15% change should still be able to maintain the output current changes in the range of ± 10%. Using LED as a display or lighting or backlighting, the need for constant current drive, mainly due to:
1, to avoid the drive current exceeds the maximum rating, affect its reliability.
2, the expected brightness requirements, and to ensure that each led power 50w brightness, color consistency.
Second, the drive circuit should be kept lower power consumption, so as to enable the efficiency of the LED system to maintain at a high level.
PWM (Pulse Width Modulation) technology is a traditional way of dimming it using a simple digital pulse repeatedly switch the LED driver, the system need only provide a wide, narrow different digital pulse, you can simply change the output current, so as to adjust the brightness of the LED. The advantages of the technology is able to provide high-quality white light, and the application of simple, high efficiency, but a fatal flaw is prone to electromagnetic interference, and sometimes will produce the human ear can hear the noise.
Boost High Power LED 50W circuit, the inductive boost charge pump boost two different topologies. "As the led 10w is driven by the current and the inductor current conversion efficiency inductive boost mode of the biggest advantages of high efficiency, if properly designed, can be more than 90%; but its disadvantages are also obvious, is the electromagnetic interference strong, the system requirements of mobile phones and other communications products is very high. With the advent of the charge pump, most cell phones are no longer inductive boost, of course, the charge pump boost its efficiency will be lower than the inductance boost.
Improve the conversion efficiency of the drive circuit are the product designers must face in terms of lighting applications, or the backlight applications. Improve the conversion efficiency is not only conducive to portable products to extend the standby time and it's also an important means of LED heat dissipation problem. , Due to the use of high-power LED lighting in the area, thereby increasing the conversion efficiency is particularly important.
LED at work steady flow regulator components, such components should have to bear the costs of partial pressure high power consumption, but much smaller features will keep the high efficiency of the LED drive circuit power The consumption of too large to make the overall system efficiency is greatly reduced, contrary to the purpose of energy efficiency. So as far as possible do not use resistance or series regulator circuit as the main circuit of the LED drive current limit, but should be efficient circuits of capacitors, inductors or active switching circuit so as to ensure the high efficiency of the LED system. Tandem integration constant power output circuit, you can make the led power 10w output remains constant within a wide range of power, but the IC circuit will be leaving the efficiency decline. Active switching circuit to ensure high conversion efficiency to achieve substantial changes in the supply voltage, constant power output.