Now LED lighting lamps and lanterns has become the new mainstream technology of the 21st century, the logo is one of a large number of LED lighting lamps and lanterns of standards and norms developed.The current lighting should not only use for incandescent dimmers to realize dimming control function, and to achieve high power factor performance, for the LED brightness adjustment, at present mainly divided into analog dimming and PWM dimming, the following will introduces the related situation of LED light.
A, LED dimming technology principle of lighting system
LED the dimming system is based on the dynamic characteristics of public lighting and design research and development of the concept of "on-demand lighting".It integrates move pyroelectric infrared detector, dimming controller and the LED light source of three parts as a whole, realize the brightness of the mute control lighting places.When the person (car) in the vicinity of lamps and lanterns, lamps and lanterns is installed on the moving pyroelectric infrared detector will be passed to the collected signals, dimming controller, dimming controller according to the received signal, control LED light source highlighting, and delay time.
If the delay time, the detectors do not gather the signals of the person (car) activities, the LED light source will be highlighted to low light (or destroy).If the detector is still in the delay time can collect to the person (car) of signal, will continue to be highlighted LED light source, thus ensuring the under the premise of not lower the quality of lighting, reduce the "effect" lighting time, "on-demand lighting", implements the public power saving effect is very obvious.
Due to the conversion between low light and highlight every day, and most of the time are in low light condition, highlighting time lightning under four hours a day, to avoid the LED light source for a long time high current work to produce the light failure phenomenon caused by the high temperature, so the LED light source the light failure is small, greatly extend the service life.
Second, LED dimming method mainly
Callback function for incandescent light can achieve lower costs, with the development of LED lighting products, in the transformation to the LED lighting doesn't want to lose the dimming control application advantages, the main LED lamps and lanterns that move light method, there are three kinds of common, these three skills that move light are according to the change of the LED drive current input for dimmer.According to the different circuit system can also be divided into imitation dimmer and PWM dimming.
First: this kind of dimming method is done through modulation of LED drive current LED lamp dimming, due to the brightness of the LED chip and LED drive current into a certain proportion to do, so we can adjust the LED drive current control LED lamp shade.
The second: the dimming method called imitation method that move light or linear dimming method.The advantages of this kind of dimming method is: when the drive current linear growth or decrease hours, reduced the drive current overshoot in the process of impact on life of the LED chip, and the dimming circuit nuisance resistance stronger.Its defect is the size of the drive current change process is sure to color temperature of LED chip has certain influence.
The third: this dimming method is called pulse width modulation (PWM).This kind of method is through adjusting the drive current square shaped, the variable pulse width, the modulation of pulse width modulation into continuous light LED lights, also changed the input power at the same time, thus reach energy-saving and dimmer.Frequency as usual in about 200 hz to 10 KHZ;Because people's eyes visual lag, don't feel light source in the process of that move light shine.This method has the advantage of that move light LED heat dissipation performance can be improved and the overshoot is drive current defects on must have a certain effect on the lifespan of the LED chip.
In general, analog dimming can often be very simple to implement.But due to the nature of the LED light to offset with average drive current.For monochrome leds, its main wavelength can be changed.For white LED, its associated color temperature (CCT) will change.
With the LED PWM dimming, a designer need to color.PWM dimming can also improve the precision of output current.With linear analog dimming adjustment can reduce the precision of output current.Generally speaking, relative to the analog dimming, PWM dimming can accuracy than linear control light output.
From the energy saving, no comparison.Because PWM is to ensure that CCTS and color measuring current (intensity), analog dimming is the premise.If you want to sacrifice the premise to consider energy saving, need the measured data.But in the implementation under the condition of same illumination, PWM will have an advantage.From the dimming response time, PWM dimming due to its fast response speed, and can more precisely the dimming.The most widely applied in the actual use.