1 Introduction Led Point Light emit
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With the maturity of LED technology, LEDs of various colors have been developed, and the cost has also dropped significantly. The LED drive circuit with output current above 300mA has an inductive switching power supply and a linear power supply. It is also a combination of a switching power supply and a linear power supply. There is almost no ground bounce and ripple in the linear power drive circuit, and the interference generated by the circuit is small, and it is often used in places where electromagnetic compatibility is required.
The backlight technology of multi-color LED mixed color complementary color is a hot spot of current research. As early as 2000, Japan has produced multi-chip LED backlight products. Subsequently, major companies have introduced high-performance LCDs with multi-chip LEDs as backlights. However, there are few published documents on how to mix and match complementary colors.
Although the red, green and blue color LED lights are mixed with a wide backlight gamut, there is a red edge phenomenon. In this paper, the white LED lamp is used as the main light source, and then the orange light and the blue light are used as the complementary light source. The color temperature of the screen white field is within (6 500±100)K, the color coordinate u' is within 0.198±0.01, and v' is at 0.468. Standard white light within ±0.01.
2, complementary color circuit block diagram
The white light LED uses blue light to excite the phosphor to obtain white light. Since the attenuation of the short-wave component by the liquid crystal screen is greater than the long-wave component, the light emitted by the white light LED is yellowish after being screened out, and it is necessary to supplement the blue light and also make up Red light.
In the case of a typical current of 20 mA, the orange lamp voltage is 2V at normal temperature, the blue lamp voltage is 3V, and the white lamp voltage is 3V.
The three lights are all eight strings. The orange lamp only needs about 16V to work under the typical current condition. The linear constant current source efficiency of the drive circuit is less than 60%. Since the orange lamp is complementary color, the power loss is less than 1W; the linearity of the white light and the blue light. Power efficiency is over 85%.
Each of the three kinds of LED lamps is driven by a linear constant current source, and the total current is set to 200 mA per channel to ensure that the current of each string of LED lamps is 20 mA of its typical current, as shown in Fig. 1. Each linear constant current source independently uses PWM dimming signals of the same frequency, their frequencies are fixed, and the duty time varies with the dimming brightness.
Using FPGA as the controller, adjust the PWM duty ratio according to the dimming command of the host computer to control the brightness of the backlight; sample the data of the color sensor, fine-tune the PWM duty ratio of the orange and blue lights, and ensure that the color temperature does not change when the temperature changes. change.
Figure 1 Block diagram of LED orange light and blue light complementary circuit.