Energy saving and emission reduction has become a major strategic issue in the world today. LED is known as “green energy†because of its energy saving, environmental protection, high luminous efficiency and long life. It is gradually replacing traditional light sources [1]. With the advancement of science and technology and the improvement of the quality of life, people have higher and higher requirements for the control level of LED lighting. In order to achieve secondary energy saving, people hope to achieve brightness adjustment and freely adjust the brightness of the light. In order to create a different atmosphere, people hope to achieve color temperature adjustment and personalize the lighting environment [2].
Related studies have shown [3] that two dimming power supplies are used to drive white LED arrays of high and low color temperature respectively. Color temperature adjustment can be achieved by adjusting the ratio of driving currents of the two power supplies. However, this method has low reliability and cannot be realized. Independent dimming.
The conventional color temperature adjustment method uses two dimming power sources to drive high and low color temperature white LED arrays, and adjusts the color temperature by adjusting the ratio of the driving currents of the two LEDs. This method can only achieve color temperature adjustment, and can not achieve linear dimming. Therefore, based on the analysis of the problems existing in the conventional method of LED color temperature adjustment, this paper proposes a new method of LED color temperature adjustment, which is discussed with everyone. The new method only uses one LED dimming power supply, after the LED dimming power supply. Only adding a few devices can realize the color temperature adjustment and brightness adjustment of the LED lamps without mutual interference, which is beneficial to reducing the cost and improving the reliability of the power supply, and has application value for the control of the LED.
First, the conventional method of LED color temperature adjustment
1. Conventional method of LED color temperature adjustment
The LED color temperature adjustable lamp adopts white LED array with high and low color temperature. The two LED arrays are densely arranged alternately to make the two color temperatures fully mixed, and the overall color temperature adjustment can be realized by adjusting the driving current ratio of the two LEDs [3]. Figure 1 shows the block diagram of this method. The PWM1 signal is used to adjust the output current I1 of the dimmable power supply P1, I1 drives the warm white LED array; the PWM2 signal is used to adjust the output current I2 of the dimmable power supply P2, and I2 drives the cool white LED array. The brightness ratio of the warm white LED array and the cool white LED array is adjusted by adjusting the duty ratio of the PWM1 signal and the PWM2 signal, and the overall temperature adjustment of the lamp is achieved due to the sufficient mixing of the two LEDs.
Figure 1 block diagram of the conventional method system
2. Problems with the conventional method of LED color temperature adjustment
People often do not want to change the brightness of the light when the color temperature is adjusted or the color temperature is significantly shifted when dimming, which means that the color temperature and the dimming do not interfere with each other, so that it can be configured by different combinations of dimming and color temperature. More light environment. However, the above scheme is difficult to meet this requirement.
(1) It is difficult to achieve brightness adjustment
In most mature LED dimmable drive power solutions, the power management chip usually only provides one dimming pin. When the color temperature is adjusted by the above conventional method, in order to adjust the ratio of the output current of the dual power supply, the dimming pins of the two power supplies are occupied, so that the hardware resources for independently dimming while adjusting the color temperature are not realized.
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