The main function of the LED drive circuit is to convert the AC voltage to a constant current power supply, and to complete the matching of the LED voltage and current in accordance with the requirements of LED devices. In addition to the LED driver circuit to meet the safety requirements, the other basic functions should be two aspects:
One is as far as possible to maintain the current characteristics, especially in the supply voltage of 15% of the changes, it should be able to maintain the output current in the range of + 10%.
1, to avoid the driving current exceeds the maximum rating, affecting its reliability.
2, to obtain the expected brightness requirements, and to ensure the consistency of each LED brightness, chroma.
Two is the drive circuit should maintain a low power consumption, so as to make the LED system efficiency is maintained at a higher level.
PWM (pulse width modulation) technique is a kind of traditional dimming mode. It uses a simple digital pulse, repetitive switch LED driver, the system only needs to provide a wide and narrow different digital pulse can simply achieve change the output current, to adjust the LED brightness. The advantages of this technology is capable of providing a high quality white and the application of simple, high efficiency, but a fatal disadvantage is prone to electromagnetic interference, and sometimes even produce the human ear can hear the noise.
Boost is an important task of the LED drive circuit, and the inductor boost and charge pump boost are two different topologies. & quot; because the LED is driven by the current, and the inductance current conversion efficiency is the highest, and it boost inductor maximum advantage is high efficiency, if properly designed, can be more than 90%; but its disadvantages are equally obvious is electromagnetic interference is very strong, the system requirements of mobile phones and other communication products is very high. With the appearance of the charge pump, the efficiency of the charge pump is lower than that of the inductor.
Whether in lighting applications or backlight applications, to improve the conversion efficiency of the drive circuit is the product designers have to face the problem. To improve the conversion efficiency, is not only beneficial for portable devices to extend the standby time, but also solve the problem of the heat radiation of the LED's important means. In the field of lighting, as a result of the use of high power LED, it is particularly important to improve the efficiency of conversion.