DC power supply LED dimming technology depth discussion
Release time:
2024-08-28 13:20
OFweek semiconductor lighting net news with the method of adjusting the forward current to adjust the brightness to change the brightness of the LED, is very easy to achieve. The first thing that comes to mind is to change its drive current, because the brightness of the LED is almost directly proportional to its drive current.
1, the method of adjusting the forward current
The simplest 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, is the detected voltage and the chip's internal reference voltage compared to the control of the current constant. But the value of this detection resistor is usually very small, only a few ounces, if you want to install a few ounces of potentiometer on the wall to adjust the current is unlikely, because the lead resistor will also have a few ounces. So some chips provide a control voltage interface, change the input control voltage can change its output constant current value.
2, adjust the forward current will make the colour spectrum shift
However, the method of adjusting the forward current to adjust the brightness will produce a problem, that is, in adjusting the brightness at the same time will also change its spectrum and colour temperature. Because the current white LED are used to excitation of yellow phosphor LED yellow phosphor and produce, when the forward current decreases, the blue LED brightness increases and the thickness of the yellow phosphor is not proportionally thin, so that the main wavelength of the spectrum growth. For example: when the forward current is 350mA, the colour temperature is 5734K, and the forward current increases to 350mA, the colour temperature is shifted to 5636K. When the current is further reduced, the colour temperature will be changed to a warm colour.
Of course these issues may not be a big problem in general practical lighting. However, in LED systems using RGB, it will cause a colour shift, and the human eye is very sensitive to colour deviations, and therefore cannot be allowed.
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