LED is recognized as the fourth generation of green light source. It is a solid cold light source with many advantages such as high efficiency, long life, safety and environmental protection, small size, high reliability and fast response. At present, the same lighting effect is achieved. The power consumption of LEDs is about 1/10 of incandescent lamps and 1/2 of fluorescent lamps. The LED driver circuit is very important for the LED, and the LED dimming control can save energy. The driving and dimming of the high-brightness white LED is a hot spot in recent years. In this paper, the research on this aspect, designed a novel LED lamp driving circuit with dimming function for the deficiency of existing circuits. LED characteristics The theoretical luminous efficacy of LEDs is 300 lm/W. At present, the laboratory level is 260 lm/W, and the market level is above 120 lm/W. The high-brightness LED has a typical turn-on voltage of about 3.0 to 4.3V, and its core is a PN junction, which has the same volt-ampere characteristics as a normal diode. Its current-voltage relationship is as shown in equation (1): Where, VF is the forward voltage of the diode, I0 is the reverse saturation current, which is a fixed value, q is the electron charge 1.6 & TImes; 1019, k is the Boltzmann constant, the size is 1.38 & TImes; 10-23, T is the thermodynamics The temperature, the constant β is approximately 2 . When the voltage applied to the LED is less than its turn-on voltage, almost no current flows through the LED. However, when the LED is turned on, its forward current changes exponentially with the forward voltage, and a small voltage fluctuation causes a large current change. When the conduction region voltage rises from 80% of the rated value to 100%, the current rises from 0% of its rated value to 100%. Figure 1 shows the relationship between the relative luminous flux of a certain LED and its forward current IF. The relationship between the luminous flux of other types of high-power LEDs and the forward current is different, but the difference is very small. It can be seen that the white LED can effectively emit light when the forward current of the white LED is greater than a certain value, and the luminous flux of the LED is proportional to its forward current. Therefore, the light can be controlled by controlling the forward current of the LED. brightness. If the LED is driven by a constant voltage source, a small voltage change will cause a large current change. Therefore, the constant voltage drive is only suitable for low-power applications where high requirements are required. In high-demand applications and high-power applications, LEDs must be used. Constant current drive. The research shows that the brightness of LED light decreases with the working time. After the brightness decreases, the light effect decreases with the increase of current. The brightness of the LED is saturated with the driving current. After the current of the LED reaches 70%~80% of its rated current, a large proportion of the current is converted into thermal energy, so the driving current of the LED should be 70%~80% of the rated current of the working current. Kadena public chain is the world's first and only Layered -1 PoW blockchain that can be segmented and extensible.
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