How to Select the Driving Power Supply for LED Bar Dimming Application

LED is more and more widely used in lighting and lighting, which is superior to traditional lighting. Apart from improving the quality of life, improving the efficiency of light source and prolonging the life of lamps and lanterns, it uses its unique dimmable function to change the color temperature and brightness of lamps, and fully achieves the biggest advantage of energy saving application.

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

Generally speaking, LED light sources can be simply divided into two categories: single LED diode light source or LED diode light source with resistance. In application, sometimes led light sources will be designed as a module containing DC-DC converter. Such complex modules are not within 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 LED input current. Therefore, this characteristic should be referred to in the selection of LED driving power supply. The HLG / ELG family of Mingwei company is characterized by adjustable current The modulation of output current can be controlled by external 1-10vdc * or 10vpwm pulse width modulation, or even only through an external simple variable resistor.

Another LED diode light source with resistor (generally referred to as LED strip or ledtrip). LED strip is widely used. It has a resistance in series with LED diodes, so the voltage is relatively stable. Therefore, users can use any commercially available constant voltage power supply to drive LED strip. Common LED strips are usually driven by 12VDC or 24VDC, but it may be a little difficult in the dimming application of LED strips.

This paper describes the application of current amplitude dimming driver in LED light bar, discusses some common dimming problems, and introduces the dimmable LED power driver with output pulse width (PWM) modulation.

Common poor LED dimming conditions:

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

Table 1: common dimming problems

Deadtravel is a common problem when using LED power driver with adjustable output current to dimming LED lamps. Although the LED drive power supply can operate well when it is in the full load state (as shown in Fig. 1-A), it is obvious that the dimming is not smooth when the LED driver is not in the full load state.

Figure 1: Mingwei LED driver hlg-100 is connected to LED light bar under different load (length): (a) 100% full load - can produce the best dimming performance; (b) Load 70% -- shows imperfect dimming effect; (c) Load 30% - shows poor dimming results because the dimmable range is too narrow.

Output pulse width modulation (PWM) solution

If the LED driving power supply is used for LED strip dimming application under full load, there is no deadtravel problem. The above argument is true, but it is 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. Therefore, the simplest and best application solution is to correctly select the LED driving power supply with output pulse width PWM dimming function to meet the dimming requirements of LED strips.

The output brightness reduces the dimming change of brightness by means of the load cycle of dimming signal. The important parameters for selecting the driving power supply are dimming analysis and output pulse width modulation PWM frequency. The minimum dimming capacity should be as low as 0.1%, so as to achieve an 8bit dimming resolution to meet all LED strip dimming applications, The output pulse width modulation PWM frequency should be increased as much as possible to prevent the light flicker problem mentioned in table (I). According to the relevant technical research literature, the frequency is recommended to be at least higher than 1.25khz to reduce the ghost flicker visible to human eyes.

The best LED light bar dimming scheme is to use the output pulse width modulation PWM dimming function to solve the common deadtravel dimming problem.

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