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The overview of the LED dimming technology

Dec 27, 2016

Dimming is a major direction of LED driver technology development. There are 2 ways to realize dimming from technology aspect , which are PWM and Triac. Triac has more advantages in the replaceable project. But PWM meets human’s LED dimming requirement of accuracy, efficiency and affection better. So design adjudgement is different base on different principle between them. 

There are 3 kinds needing of Dimming: 1. Needing of function adjustment line, such as entrance, meeting room and so on; 2. Reflection of lifestyle and life comfortability, which not only could adjust the light brightness according to environment, but also could foil atmosphere. 3. Needing of environmental protection and energy saving, meanwhile it is the newest needing of “Energy Star”. Energy saving is the most prominent advantages and the important basis of government issued a policy to promote the technology application. If dimming technology be used for daily lighting, it would play a greater energy saving advantage of LED lighting. 

There are 3 main ways of LED dimming in the market currently: 1. linear dimming; 2. Triac dimming; 3. PWM dimming. The three ways has their own advantages and disadvantages. Linear dimming mainly bases on simple voltage separation principle. The advantages are the application is simple and no interference. And the disadvantages are not only Inflexible and inefficient, But also makes white light LED offset to yellow light while low the LED electronic current. Besides, there will be overheated because of voltage separation.

Triac dimming is the widely-used dimming way of application for incandescent and energy-saving lamps currently. Its working principle is to input voltage waveform through the conduction angle after the cut-wave, resulting in a tangential to the output voltage waveform. Application of tangential principle can reduce the output voltage RMS to reduce the ordinary load (resistive load) power. The advantages of Triac dimming is efficiency and stable. But base on the working principle, there are some design disadvantages when applied. Such as when load big power, conduction angle will easily unstable and the output waveform will be uneven, and the vibration and spikes will occur. These unstable output makes LED flicker. The reason of previous Incandescent lamp hasn’t flicker is because it is Linear loading and the working current normally up to 50mA. So the Triac dimmer in the market currently, which is suitable for Incandescent lamp, is not suitable for LED products. It is needed to be improved to fit in LED characteristic. 

Under the premise of LED Light market great replacement potential , terminal system manufacturers mainly prefer Triac. Since they view from the angle of convenience of lamp replacement. There are many LED dimming products based on Triac, and they are also optimized for power factor correction (PFC), accurate output, wide range, flicker-free and so on. However, it is generally accepted that the technology is only a transitional technology: Triac is designed for incandescent, with the characteristics of LED to adapt to the characteristics of Triac, which limiting the further development of LED dimming technology .

PWM dimming technology is currently considered as the most promising LED dimming technology. While dim by pulse width PWM, it is necessary to provide an additional pulse width adjustment signal source. Through changing the input pulse signal duty cycle to modulate the LED driver chip on the power FET gate to control signal, so as to achieve the purpose of adjusting the LED current. There are 3 advantages of PWM diming:1. color temperature of white light LED will be offset with the driving current size, which is the shortcoming of linear dimming. And PWM diming will not have the problem; 2. PWM control accuracy is much higher than linear dimming; 3. base on PWM digital dimming has much more long-term technology expansibility, It is better for the future intelligent LED technology Integrated development.