1、 LED development history

 

 

 

2、 LED classification

 

 

 

3、 LED driving technology principle

 

 

 

4、 LED driver design skills

 

 

 

5、 LED driver design reference cases and selection guidance

 

 

 

6、 LED cooling solution

 

 

 

7、 List of LED industry chain manufacturers

 

 

 

8、 Design reference index

 

 

 

 

 

LED development history

 

 

 

 

 

In 1907, Henry Joseph Round observed the electroluminescence phenomenon in a piece of silicon carbide for the first time. Because its yellow light is too dark, it is not suitable for practical application; More difficult is that silicon carbide and electroluminescence can not adapt well, and the research has been abandoned.

 

 

 

In the late 1920s, Bernhard Gudden and Robert Wichard used yellow phosphorus extracted from zinc sulfide and copper to emit light in Germany. Once again, it stopped because the light was dim.

 

 

 

In 1936, George Destiau published a report on the emission of light from zinc sulfide powder. With the application and wide recognition of current, the term "electroluminescence" finally appeared. In the 1950s, British scientists used semiconductor gallium arsenide in the experiment of electroluminescence to invent the first LED with modern significance, which was launched in the 1960s. It is said that in the early test, LEDs need to be placed in liquefied nitrogen, and further operation and breakthrough are needed to work efficiently at room temperature. The first commercial LED can only emit invisible infrared light, but it is rapidly applied in the field of sensing and optoelectronics. In the late 1960s, the first visible red LED was invented using phosphide on the GaAs substrate. The change of gallium phosphide makes LED more efficient, emitting brighter red light, and even producing orange light.

 

 

 

By the mid-1970s, gallium phosphide was used as a light source, and then it gave off gray and green light. LED adopts double-layer gallium phosphide chip (one red and the other green) to emit yellow light. At this time, Russian scientists used carborundum to produce LED emitting yellow light. Although it is not as efficient as LED in Europe. But in the late 1970s, it could emit pure green light.

 

 

 

The use of gallium arsenide and aluminum phosphide in the early and middle 1980s led to the birth of the first generation of high-brightness LEDs, first red, then yellow, and finally green. By the early 1990s, indium aluminum gallium phosphide was used to produce orange, orange, yellow and green LEDs. The first blue LED with historical significance also appeared in the early 1990s, and once again made use of emery metal, the obstacle of the early semiconductor light source. By today's technical standards, it is as dim as the previous yellow LED in Russia.

 

 

 

In the mid-1990s, ultra-bright GaN LEDs appeared, and then Indium GaN Led, which can produce high intensity green light and blue light, was produced. Ultrabright blue light chip is the core of white light LED. Apply fluorescent phosphor on this luminescent chip, and then the fluorescent phosphor will be converted into white light by absorbing the blue light source from the chip. It is to use this technology to produce light of any visible color. Today, we can see new colors produced in the LED market, such as light green and pink. Readers with scientific thoughts may realize that the development of LED has gone through a long and tortuous historical process. In fact, the recently developed LED can not only emit pure ultraviolet light but also emit real "black" ultraviolet light. It is unclear how far LED has gone in its development history. Maybe LED that can emit X-ray can be developed one day. Early LED can only be applied to indicator lights, early calculator displays and digital watches. Now it begins to appear in the field of ultra-brightness. It will continue in the next period of time.

 

 

 

LED classification

 

 

 

 

 

Classification of common LEDs

 

 

 

 

 

1. It is divided into red, orange, green (subdivided into yellow-green, standard green and pure green), blue light, etc. In addition, some light-emitting diodes contain chips of two or three colors. According to whether the light-emitting diode is doped with or without scattering agent, colored or colorless, the light-emitting diodes of the above colors can also be divided into four types: colored transparent, colorless transparent, colored scattering and colorless scattering. Scattered LED is not suitable for indicator light.

 

 

 

2. According to the characteristics of the light-emitting surface of the light-emitting tube, it can be divided into round light, square light, rectangular light emitting tube, surface light emitting tube, lateral light emitting tube, surface mounting micro-tube, etc.

 

 

 

Circular lamps are divided into φ 2mm、 φ 4.4mm、 φ 5mm、 φ 8mm、 φ 10mm and φ 20mm, etc. In foreign countries φ 3mm LED is recorded as T-1; Put φ 5mm is recorded as T-1 (3/4); Put φ 4.4mm is recorded as T-1 (1/4) [6-8].

 

 

 

The angular distribution of circular luminous intensity can be estimated from the half-value angle. According to the luminous intensity angle distribution diagram, there are three types:

 

 

 

1) High directivity. Generally, it is a pointed epoxy package, or a package with a metal reflection cavity, without scattering agent. The half-value angle is 5 °~20 ° or less, with high directivity, which can be used as a local lighting source or combined with a light detector to form an automatic detection system.

 

 

 

2) Standard. It is usually used as an indicator light with a half-value angle of 20 °~45 °.

 

 

 

3) Scattering type. This is an indicator with a large angle of view. The half-value angle is 45 ° - 90 ° or more, and the amount of scattering agent is large.

 

 

 

3. According to the structure of LED, it can be divided into full epoxy encapsulation, metal base epoxy encapsulation, ceramic base epoxy encapsulation and glass encapsulation.

 

 

 

4. According to the luminous intensity and working current, there are LED with ordinary brightness (luminous intensity is less than 10mcd); Ultra-high brightness LED (luminous intensity greater than 100mcd); The luminous intensity between 10 and 100 cd is called high brightness LED. Generally, the working current of LED is between 10 mA and 10 mA, while the working current of low current LED is below 2 mA (the brightness is the same as that of ordinary LED).