Summary:
      In order to improve the quality of lighting LED modules, LED modules to achieve adjustment of the color temperature, by analyzing the driving circuit technology LED module, a design scheme is proposed full-color LED drive circuit HSI color model. The driving circuit uses the three-color ratio adjustment to achieve the required color, and adopts PID adjustment mode to ensure the stability of the adjustment. In addition, the color temperature and light intensity of the output light can be adjusted to achieve a good lighting effect.
0 Preface
A Light Emitting Diode (LED) is a solid-state semiconductor device that converts electrical energy into visible light. It can directly convert electricity into light. As LEDs become more widely used, the requirements for their driving circuits are also increasing. The higher it is. For most occasions, it is necessary to use a constant-current output switching power supply. For a full-color LED lamp, the conventional RGB separately drive has obvious defects in the face of both the color temperature and the brightness adjustment. Based on this, The improved HSI model is designed to be suitable for driving circuits with full-color LEDs. The traditional RGB model needs to be adjusted separately for R, G, and B. The HSI model mainly separates the luminance and chrominance, and adjusts the three parameters of H, S, and I respectively, H (chroma), S (saturation), and I ( brightness). The driving circuit under the HIS model defines the I parameter (brightness) by controlling the bus driving current by the single chip microcomputer, and adjusts the comprehensive ratio (H parameter) of R, G, and B through the R, G, and B terminals, and obtains the brightness of the light through the light sensor. The S-parameter of saturation degree achieves the purpose of adjustment of the drive circuit.
1 overall design
Figure 1 shows the overall design of a full-color LED driver circuit under the HIS model. The hardware part adopts the constant current driving chip PT4115, adopts the total one-point mode for RGB driving, and obtains the R, G, B three-way current signal feedback through the sampling circuit to adjust the ratio of R, G, B. The software adopts STC series single-chip microcomputer as the main adjustment module, adjusts the color ratio of three colors by obtaining A/D conversion, and adopts PID adjustment mode to ensure the stability of adjustment.
2 LED driver circuit hardware design
2.1 Constant current drive principle
As shown in FIG. 2, two tubes VT0 and VT1 having the same characteristics are formed here, and the emitters of the two tubes are respectively connected to the resistors Re0 and Re1. The current in resistor R is the reference current and its expression is:
So the collector current is:
Since the relationship between Ic1 and Ir is changed in this way, the work Ic1 and Ir are proportional, thereby overcoming the shortcomings of the mirror constant current source circuit. Theoretical deduction proves:
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