The application of LEDs in lighting fixtures is becoming more and more extensive, coupled with the uniqueness that is superior to traditional lighting methods, in addition to improving the quality of life, improving the efficiency of the light source and extending the life of the lamp, it uses its unique dimming function to adjust the color temperature and brightness The greatest advantage of energy-saving applications is fully achieved.

　　The dimming efficiency of LED lighting fixtures depends on the LED light source and driving power used.

　　Generally speaking, LED light sources can be simply divided into two categories: single LED diode light sources or LED diode light sources equipped with resistors. In application, sometimes LED light sources are designed to include DC-DC conversion. A module of the device, such a complex module is beyond the scope of this article. If the LED light source or module is a separate LED diode itself, the common dimming method is to adjust the amplitude of the LED input current. Therefore, the selection of LED driving power should refer to this feature. The characteristics of MEAN WELL's HLG/ELG family That is, the current can be adjusted, and the output current can be adjusted by external 1-10VDC* or 10VPWM pulse width modulation or even by connecting a simple variable resistor. And another kind of LED diode light source equipped with resistor (generally called LED light bar or LEDSTRIP), LED light bar is widely used to have LED diode series resistance, so the voltage is relatively stable, so users You can use any commercially available constant voltage power supply to drive the LED light bar. Common LED light bars are generally driven by 12VDC or 24VDC, but it may be a little difficult to dimming the LED light bars. This article explains the application of current amplitude dimming method drivers in LED light strips. It also discusses some common dimming problems. It also introduces dimmable LED power drivers that use output pulse width (PWM) modulation. The PWM family series launched by MEAN WELL and won the National Technology Innovation Product Award is the most appropriate and simplest LED light bar dimming solution on the market.

　　Common poor LED dimming conditions:

　　Dimming sounds like a simple thing. In fact, many factors need to be considered to have a good and smooth dimming performance. There are many common LED dimming situations, as shown in the following table (1):

　Table (1): Common dimming problems

　　When using LED power drivers with adjustable output current to dimming LED lights, deadtravel is a common problem. Although the LED drive power supply can operate well when it is at full load (as shown in Figure 1-a), when the LED drive is not at full load, the dimming is not smooth.

   Figure 1: MEAN WELL LED driver HLG-100 is connected to the LED strip under different load (length) conditions: (a) Full load 100%-can produce the best dimming performance; (b) Load 70%-display In order to achieve an imperfect dimming effect; (c) 30% load-showing poor dimming results because the dimming range is too narrow.

　　Output pulse width modulation (output PWM) solution

　　If the LED driver power supply is used for LED light bar dimming applications under full load conditions, there is no deadtravel problem. The above argument is correct, but not very practical. In fact, LED strips are often used in various applications (decorative lighting/auxiliary lighting/advertising lighting) because the length cannot be accurately estimated, so the simplest and best The application solution is to correctly select the LED drive power supply with output pulse width PWM dimming function to realize the LED light bar dimming requirements. The output brightness relies on the duty cycle of the dimming signal to achieve the dimming change that reduces the brightness. The important parameters for selecting the driving power supply are the dimming resolution and the output pulse width modulation PWM frequency. The minimum dimming ability should be as low as 0.1 %, to achieve 8bit dimming resolution to meet all LED light bar dimming applications, the output pulse width modulation PWM frequency should be as high as possible to prevent the light flicker problem mentioned in Table (1), according to the relevant Technical research literature reports that the frequency is recommended to be at least 1.25kHz to reduce the ghost flicker visible to the human eye.

　　in conclusion

　　The best LED light bar dimming solution is to use the output pulse width modulation PWM dimming function to solve the common deadtravel dimming problem. The PWM models provided by MEAN WELL cover four series such as 40/60/90/120W, which are very suitable for LED drive power supply for various LED light bar dimming applications.