The dimmers for adjusting the brightness of LED lighting fixtures are currently very important in LED lighting, and are also the links that ED lamps and displays must pay attention to. Nowadays, LED lighting has become a new mainstream technology in the 21st century. One of the signs is that a large number of LED lighting standards and specifications have been introduced. At present, the lighting needs to use dimmers for incandescent lamps to realize dimming control functions, and high power factor performance. For the adjustment of LED brightness, it is mainly divided into analog dimming and PWM dimming. The relevant situation of dimming is introduced.
First, the technical principle of LED self-dimming lighting system
The LED self-dimming system is designed and developed based on the dynamic characteristics of public lighting and the concept of “on-demand lightingâ€. It integrates three parts of the pyroelectric infrared motion detector, dimming controller and LED light source to realize the silent control of the brightness of the lighting place. When the person (vehicle) is moving near the lamp, the pyroelectric infrared motion detector installed on the lamp transmits the collected signal to the dimming controller, and the dimming controller controls the LED light source to generate a highlight according to the received signal. And delay for a certain time. If the delay time elapses, the detector will not receive the signal of the person (vehicle) activity, and the LED light source will change from high to low (or off). If the detector can still collect the signal of the person (vehicle) activity within the delay time, the LED light source will continue to be highlighted, thus ensuring that the "ineffective lighting" time is greatly reduced without reducing the lighting quality. The lighting effect of “on-demand lighting†in public places is very obvious.
Due to the transition between low light and high brightness every day, and most of the time is in the low light state, the lightning strike is less than four hours per day, which avoids the light decay caused by the high temperature operation of the LED light source for a long time. Therefore, the LED light source has little light decay and the life is greatly extended.
Second, the main dimming method of LED
The dimming function can reduce the cost for incandescent lamps. With the development of LED lighting products, the advantages of dimming control applications can be lost when switching to LED lighting. The most important and common dimming methods for LED lamps are three. These three dimming skills are all dimmed based on changes in the LED drive current input. According to different circuit systems, it can also be divided into analog dimming and PWM dimming.
The first type: This dimming method is to dim the LED lamp by modulating the LED driving current. Since the brightness of the LED chip is proportional to the LED driving current, we can control the LED driving current to control the LED lamp. Light and dark.
Second: This dimming method is called a simulated dimming method or a linear dimming method. The advantage of this dimming method is that when the driving current linearly increases or decreases, the influence of the driving current overshoot on the lifetime of the LED chip is reduced, and the anti-noise of the dimming circuit is strong. The defect is that the process of changing the magnitude of the driving current definitely has a certain influence on the color temperature of the LED chip.
Third: This dimming method is called pulse width modulation (PWM). The method is adjusted so that the driving current is square wave-shaped, and the pulse width is variable. After the modulation of the pulse width is converted into a time for modulating the continuous lighting of the LED lamp, the input power is also converted, thereby achieving energy saving and dimming. aims. The frequency is about 200Hz~10KHz as usual; because of the hysteresis of the human eye, it will not feel the sparkle of the light source during the dimming process. The advantage of this dimming method is that it can improve the heat dissipation performance of the LED. The defect is that the overshoot of the driving current must have a certain influence on the life of the LED chip.
Third, summary
In general, analog dimming can usually be done very simply. However, since the characteristics of the LED light are shifted with the average drive current. For a monochrome LED, its dominant wavelength will change. For white LEDs, the associated color temperature (CCT) will change. Dimming with PWM ensures that the LEDs emit the colors that the designer needs. PWM dimming also improves output current accuracy. Analog dimming with linear adjustment reduces the accuracy of the output current. In general, PWM dimming can be more accurate than linearly controlled light output relative to analog dimming. In terms of energy saving, there is no comparability. Since PWM is a measure of current (light intensity) in the case of CCT and color, analog dimming does not exist. If you want to sacrifice energy to consider energy saving, you need to measure the data. However, it is estimated that PWM will have an advantage in achieving the same illumination. In terms of dimming response time, PWM dimming is faster because of its fast response and more precise dimming. It is the most widely used in practical use.
Edit: Bober
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