Led analog and digital dimming

LED Dimming signals can be divided into ： Analog dimming 、 Digital dimming

Analog dimming

The transistor base or... Is modulated according to the change of response load MOS The bias reference of the tube gate is used to realize the transistor or MOS Change of conduction time , So as to realize the change of switching power supply output , Adjust the LED brightness

Digital dimming

By width 、 Narrow different digital pulses , Repeatedly cut off 、 closed LED electric current , If the frequency is higher than 120Hz, The human eye will appreciate these pulses , And produce a perceptible average brightness , The output current is controlled by adjusting the pulse duty cycle , Adjust the LED brightness , Also known as PWM Dimming

Analog dimming VS  Digital dimming

Analog dimming does not produce low noise when dimming , Therefore, it is not easy to produce ripple and flicker when taking photos in the face of digital equipment , But in the analog dimming scheme ,LED Not working at rated current , Long term work will shorten LED service life , And because LED As the current of the driver decreases, the conversion efficiency decreases rapidly , Therefore, it will increase the power loss of the power supply system .

Digital dimming has extremely high dimming accuracy , Compared with analog dimming, its dimming range is larger , And it doesn't produce LED Chromatographic shift . but PWM When the working frequency of dimming is too low, human eyes will feel flickering , And the noise caused by dimming is easy to fall within the hearing range of human ears , Cause dimming noise ; When the frequency is too high , Although it can reach the standard of no stroboscopic , But in the dimming gray level range will be reduced , And it is easy to flicker at low brightness .

A good dimming power supply ：

1. Dimming does not affect LED Optical index ;

2. Wide dimming range , The dimming depth is lower than 1% following , It can meet the requirements of more scenario applications ;

3. Look with the naked eye , There is no visual flicker when the light is still and adjusted , The dimming is even and delicate ;

4. Take pictures with camera and other photographic equipment without ripple or flicker ;

5. Test with professional stroboscope , Meet the standard requirements , No effect on human health

——《 Rett T-PWM Ultra deep dimming technology 》

In order to overcome the disadvantages brought by a single way of dimming , At present, the mainstream dimming method combines the two , namely ：CCR（ simulation ）+ PWM Dimming

When the brightness is low PWM Dimming , Ensure that the accuracy of the dimming range extends to low brightness ,

Use analog dimming when the brightness is not low , Try to overcome the dimming stroboscopic

With crystal Feng Mingyuan BP2876D Take dimming as an example , Its full range dimming is divided into two sections ：

1. When external PWM The duty cycle of the signal is less than 33% when , It's using PWM Dimming mode , Inside PWMO The duty cycle of the signal varies with the external PWM The duty cycle of the signal changes linearly ;

2. When external PWM The duty cycle of the signal is greater than 33% when , Analog dimming method is adopted ,CS The reference voltage varies linearly with the duty cycle of the external signal

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