Dimming technology using DC power LED
It is easy to change the brightness of the LED by adjusting the forward current to adjust the brightness. The first thought is to change its drive current, because the brightness of the LED is almost directly proportional to its drive current.
1.1 Method of adjusting forward current
The easiest way to adjust the current of the LED is to change the current detection resistor connected in series with the LED load. Almost all DC-DC constant current chips have an interface to detect the current. Constant current. However, the value of this detection resistor is usually very small, only a few ohms, if you want to install a potentiometer on the wall to adjust the current is unlikely, because the lead resistance will also have a few ohms. Therefore, some chips provide a control voltage interface. Changing the input control voltage can change the output constant current value.
1.2 Adjusting the forward current will shift the chromatogram
However, using the forward current method to adjust the brightness will cause a problem, that is, it will change its spectrum and color temperature while adjusting the brightness. At present, white LEDs are produced by exciting blue phosphors with blue LEDs. When the forward current decreases, the brightness of blue LEDs increases and the thickness of yellow phosphors does not decrease proportionally, thereby increasing the dominant wavelength of its spectrum. For example, when the forward current is 350mA, the color temperature is 5734K, and when the forward current increases to 350mA, the color temperature shifts to 5636K. When the current is further reduced, the color temperature will change to warmer colors.
Of course, these problems may not be a big problem in general actual lighting. However, in the RGB LED system, it will cause color shift, and the human eye is very sensitive to color deviation, so it is also not allowed.