Driving scheme of small size non isolated constant current 18WLED fluorescent la

Into 2013, we personally feel the LED industry development bursts of warmth. There are several trends that are driving the development of the LED lighting market. The first is to improve the efficiency of high brightness LED and high reliability LED constant current drive power continue to emerge, then gradually fade out the global legislation to ban incandescent lighting and energy-saving lamp CFL (it contains harmful mercury). Together, these factors are making LED lighting a long-term trend. More importantly, low cost (including LED lamp, cooling system and LED drive) is the original motivation of consumers widely used in LED general lighting. In addition to the important mission of energy saving and emission reduction, LED is more controllable than other light sources, making it possible to revolutionize people's lighting environment and provide many new light and shade world. The most critical aspect of implementing these applications is driving the brain of the LED light source. Smaller volume, less components, lower cost, and more powerful, these are the "harsh" requirements of the market for LED drive power.

This short circuit 18W LED fluorescent lamp driving scheme introduced in this paper is smaller than a one dollar coin. The cost is about half of the current market mainstream program. It is complied with this "harsh" requirement. Simple, perfect philosophy plays the most part in this scheme.

2.1, third generations of non isolated LED constant current control technology closed loop algorithm TRUEC2 introduction.

In view of the characteristics of LED lighting load, the current structure of non isolated constant current drive power supply is basically BUCK step-down structure. The development of non isolated LED constant current control technology is divided into three generations, from the initial to the fixed frequency mode, fixed turn off time later, strictly speaking, is not the real closed loop constant current, has been developed to today, the use of the third generation of non isolated control technology of closed loop algorithm, called TRUEC2 control strategy. The DU8618 chip of Shanghai duty cycle Semiconductor Corporation, based on TRUEC2 drive technology, is insensitive to various peripheral components, which reduces the cost of the whole scheme while improving reliability and accuracy.

The so-called closed loop, that is, the actual detection of the output current value, as a standard to issue PWM signals. The so-called open-loop, not to detect the output current value to do a reference to the issue of PWM signal. From the circuit topology, there is no difference between the two, are non isolated BUCK buck topology. But there are two benchmarks in the chip, one is the peak reference, and the other is the average reference. The chip detects the inductor current signal and does the patent processing, as shown in Figure 1, TRUEC2, for integral processing and peak control. In this way, the average value of the inductor current is detected, that is, the average value of the output current. The chip achieves closed-loop control for the detected values and controls the output duty cycle. This kind of control structure, the line is very simple, because the current closed-loop control, compared to the open-loop mode, the short circuit is constant. This is very important in production applications, which is equivalent to greatly reducing the risk of system failure. This scheme not only has a qualitative leap in performance, but also greatly improves the reliability. DU8618 integrated high voltage MOSFET 1A, and will simplify the circuit to achieve the ultimate, the low current and high voltage design, reduce loss, let 1A MOSFET integrated package to a small volume of SOP8, can be competent for all non isolated LED within 18W driving demand.

Figure 1: chip internal TRUEC2 part of the module work

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