As the latest lighting technology, LED has its advantages not only in terms of lighting quality, but also greatly surpasses traditional light sources such as incandescent lamps and fluorescent lamps in terms of production, manufacturing and ease of use. Inspired by the principle of fluorescent lighting, LED manufacturers use a blue phosphor to excite phosphors to emit white light by adding a layer of phosphor to the high-brightness blue LED die. In addition, by using different phosphors, a variety of white LEDs with a color temperature of 4500 to 10000K and a color temperature of 2850 to 3800K can be emitted. The luminous efficiency of white LEDs has exceeded 301m/W, and some products have exceeded the level of 50lm/W. It has the basis for formal large-scale practical use. The RGB three-color LED synthetic white light has good comprehensive performance. Under the high color rendering index, the lumen efficiency may be as high as 2001m/w. The main technical problem to be solved is to improve the electro-optical conversion efficiency of the green LED, which is currently only about 13%. For the LED-excited phosphor illuminating, the three-primary color mixing can avoid the disadvantages of discontinuous spectral distribution and poor color rendering of the former, and the comfort of the human eye of the three primary colors can be greatly improved, and can be modulated by the three primary colors PWM. Multi-color and full-color illumination at the same source as needed.
1. Design concept and plan
Designing high-power semiconductor drivers, first of all from the choice of light-emitting chip and light source; drive circuit design, secondary optical design; equipment packaging three aspects.
In the LED lighting, there is a successful design case of monochromatic LED to stimulate phosphor light emission, but considering this scheme is difficult to achieve full spectrum, high color rendering, in this design, RGB three primary color mixed light source, and red The three green and blue monochromatic LED chips are separately driven to realize the completion of the light source. In order to meet the illuminance stability under high-power output, it is necessary to compensate for the LED temperature attenuation, and also to compensate for the unstable fluctuations of the surge pulse and current at startup. In the secondary optical design, the three primary colors are mainly mixed, and the fiber coupling is selected in the comparison of the integrating sphere mixing and the fiber coupling, and the light of the three color chips is coupled and output by the fiber coupling.
2, LED optical characteristics and electrical characteristics
For the characteristics of super bright LEDs, when the forward voltage exceeds a certain threshold (about 2V), that is, the so-called turn-on voltage, it can be approximated that IF is proportional to VF. The current super bright LED has a maximum IF of 1A, while VF is usually 2 to 4V. Since the light characteristics of LEDs are generally described as a function of current rather than a function of voltage, constant current source driving can be used to better control brightness. In addition, the forward voltage drop range of the LED is relatively large (up to lV or more), and a small change in VF causes a large IF change, which causes a large change in brightness. Therefore, the use of constant voltage source drive can not guarantee the consistency of LED brightness, and affect the reliability, life and light decay of LED. Therefore, super bright LEDs are usually driven by a constant current source. The luminous flux of an LED is inversely proportional to temperature. The luminous flux at 85 ° C is half that at 25 ° C, and the light output at -40 ° C is 1.8 times that at 25 ° C. The change in temperature also has a certain effect on the wavelength of the LED. Therefore, good heat dissipation is a guarantee that the LED maintains a constant brightness.
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