Development and future of high power LED lighting dimming technology

With the development of global industry, in the process of industrialization of carbon emissions increase, global climate deterioration, flood drought, hail storms around a record trend, a serious threat to human survival. To jointly deal with the threat, in December 2009, the heads of state gathered in Copenhagen to discuss energy-saving emission reduction plan, actively develop and implement low-carbon programs around the country. As a green, environmental protection and energy saving LED lighting, more and more favored by all countries, China's Ten City million, the United States, Losangeles, the one hundred and forty thousand plan is in full swing. The successful application of dimming technology in LED lighting will further improve the effect of energy saving and emission reduction.

The necessity and dimming

As a kind of green energy, electric energy is becoming more and more important in the field of energy application. According to the Chinese Academy of Engineering Chen Lianghui survey concluded that in 2010, the country's electricity consumption will reach 2 trillion and 700 billion degrees, of which the lighting power consumption will be more than 300 billion degrees. Because LED lighting power consumption is only the traditional incandescent lamp and HID lamp 1/3, if the use of LED lamps to replace the existing traditional lamps, will be expected to save electricity 2/3. Its energy saving effect is evident.

Dimming technology will further reduce energy consumption, saving lighting electricity. At present, the public lighting accounts for 1/3 of the entire field of lighting, up to 100 billion degrees. In China, the city from 5:30 or 6:00 to start the evening lights, however small city at night after 9, large and medium-sized city in the middle of the night after 12 o'clock, the roads were scarce, even in Beijing, Shanghai and Guangzhou City, 2 in the morning, after 3, the road also rare pedestrians and vehicles. From this period of time to start at 6 in the morning lights out, in the low traffic flow on the road to maintain a high degree of illumination is obviously not very necessary. If the dimming technology, so that the output power LED lamp at 12 midnight with reduced traffic decreased to half, will save electricity up to 50 billion degrees, equivalent to about 5/8 of the 2009 annual saving of Three Gorges power station generating capacity (Three Gorges power station in 2009 79 billion 850 million kilowatt hours of electricity), the energy saving effect is very significant.

Dimming technology, reducing output power, will significantly improve the working environment of LED lamps, extend lamp life, improve reliability. The key factor affecting the reliability of LED lamps is the temperature. Whether it is LED power supply or LED chip, the higher the ambient temperature, its life and reliability will decline sharply. Figure 1 for the LED power supply life and temperature, when the ambient temperature of 25 degrees C LED power supply life of up to 320000 hours, and when the temperature rises to 60 degrees C, LED power supply life will be shortened to only 35000 hours.

Figure 1 LED drive power life and temperature curve

The higher the temperature, the LED chip also declined significantly increased. Such as the LED light decay curves of Figure 2 of Cree company. It can be seen from the figure, LED light and is closely related to its junction temperature, the junction temperature is a semiconductor pn junction temperature, the higher the junction temperature, LED light source is the first light, life is short. As can be seen from the chart, if the junction temperature is 105 DEG C, LED light source life brightness to 70% only more than 10 thousand hours; junction temperature at 95 DEG LED source life have 20 thousand hours; and reduce the junction temperature to 75 degrees Celsius, life can be up to 50 thousand hours, 65 degrees more life can be extended to 90 thousand hours. To sum up, the key to prolong the life of LED is to reduce the junction temperature.

Decay curves of figure two Cree, LED

With the dimming technology, the power loss will be reduced with the decrease of the output power, and the shell temperature will also decrease. As shown in Figure three 200W LED drive power output power and temperature curve of the shell. When the ambient temperature is 25 DEG C, the temperature of the shell is at the temperature of 50 DEG C, and the temperature of the shell is reduced to about 40 DEG C, the life of the shell is reduced to about 50% DEG C, and the reliability can be increased by 25%-40%.

Figure three LED drive power output power and temperature curve of the shell

Traditional incandescent or HID due to the inability to light, in 70s the Japanese energy crisis, had tried to use interval lighting energy saving. However, due to the uneven illumination of the road, leading to the visual problems of passers-by, public security and road traffic accidents rose sharply, and finally had to give up interval lighting. With the rapid development of dimming technology, LED lighting dimming system will be brought into a new field, which will be a wide range of green environmental protection and energy saving LED lighting applications and promotion.

Two, the main LED lamp dimming technology.

In the beginning of LED applied to roads and other public lighting, in the early promotion, some LED dimming lamp factory in order to achieve the purpose of energy saving, the interval lighting ideas, the LED chip LED lights into two parts, respectively control the driving current on and off, in the middle of the night before 12, all LED all light, 12 points after breaking in half, to achieve the purpose of saving energy. This kind of dimming mode can achieve a certain energy saving effect, and the uniformity of illumination is obviously improved compared with the traditional way of lighting, but it will affect the light distribution curve of LED lamps. In order to further improve the LED lamps light efficiency and light distribution curve, some LED lamp factory and consider the LED chip with interval arrangement, in light and see only the bright intervals or out, improve the uniformity and light distribution in a certain extent.

The brightness of the LED chip and the LED drive current into a proportional relationship, so you can adjust the LED drive current to achieve the dimming of the LED lamp, the second dimming is often referred to as analog modulation