ภาพรวมเทคโนโลยี LED
First, LED history
Second, LED classification
Third, LED drive technology principle
Fourth, LED driver design skills
5. LED driver design reference cases and selection guidance
Six, LED cooling solutions
Seven, LED industry chain manufacturers
8. Design reference index
History of LED
Electroluminescence was first observed in 1907 by Henry Joseph Round in a piece of silicon carbide. Because the yellow light emitted by it is too dark, it is not suitable for practical application; More difficult is that silicon carbide and electroluminescence can not be well adapted, the study was abandoned.
In the late 1920s Bernhard Gudden and Robert Wichard in Germany used yellow phosphorus from zinc sulfides and copper for luminescence. Once again it stopped because the light was dim.
In 1936, George Destiau published a report on the emission of light from zinc sulfide powders. With the application and widespread understanding of electric current, the term “electroluminescence” eventually appeared. In the 1950s, British scientists used the semiconductor gallium arsenide in electroluminescence experiments to invent the first LED with modern significance, and it was introduced in the 1960s. It is said that in early tests, leds need to be placed in liquefied nitrogen, and further operations and breakthroughs are needed to work efficiently at room temperature. The first commercial LED could only emit invisible infrared light, but it was quickly applied to induction and optoelectronics. In the late 1960s, the first visible red LED was invented using phosphide on a gallium arsenide matrix. Changes in gallium phosphide make leds more efficient, emit brighter red light, and even produce orange light.
By the mid-1970s, gallium phosphide was being used as a light source, which subsequently gave off a grey-green light. Leds use a double-layer gallium phosphide core (one red and the other green) that emits yellow light. At this time, Russian scientists used emery to produce yellow leds. Although it is not as efficient as European leds. But in the late ’70s, it glowed pure green.
The use of gallium arsenide and aluminum phosphide in the early to mid-1980s LED to the birth of the first generation of high-brightness leds, first red, then yellow, and finally green. By the early 1990s, the use of indium aluminum gallium phosphide produced orange, orange, yellow and green leds. The first historic blue leds also appeared in the early 1990s, once again using gold sand – an obstacle to early semiconductor light sources. According to today’s technical standards, it is as dim as the previous yellow leds in Russia.
In the mid-1990s, super-bright gallium nitride leds appeared, and then indium gallium nitride leds were produced to produce high intensity green and blue light. The ultra-bright blue core is the core of the white LED, which is coated with fluorescent phosphorus, and then converted into white light by absorbing the blue light source from the core. This is the technique used to create light of any visible color. Today in the LED market you can see the production of novel colors, such as light green and pink. Scientifically minded readers may now realize that the development of LED has gone through a long and tortuous historical process. In fact, recently developed leds emit not only pure UV light but also true “black” UV light. So LED development history to low energy to go far, it is unknown. It may one day be possible to develop leds that emit X-rays. Early leds could only be applied to indicators, early calculator displays and digital watches. And now it’s starting to appear in the field of super brightness. Will continue for some time to come.
Classification of LED
Classification of common leds
1. According to the luminous color of the luminescent tube, it is divided into red, orange, green (and subdivided into yellow green, standard green and pure green), blue light, ฯลฯ. In addition, some leds contain chips of two or three colors. According to the light-emitting diode doped or not doped scattering agent, color or colorless, the above various colors of light-emitting diodes can also be divided into colored transparent, colorless transparent, colored scattering and colorless scattering four types. The scattering LED is not suitable for use as an indicator.
2. According to the characteristics of the luminous surface of the luminescent tube, it is divided into round lamp, square lamp, rectangle, surface luminescent tube, side tube, surface mounted micro-tube and so on.
The circular lamp is divided into φ2mm, φ4.4mm, φ5mm, φ8mm, φ10mm and φ20mm according to its diameter. In foreign countries, φ3mm LED is usually recorded as T-1; Let’s call phi 5mm T-1 (3/4); Let’s call phi 4.4mm T-1 (1/4) [6-8].
The angular distribution of circular luminous intensity can be estimated by the half-value Angle. There are three categories from the luminous intensity Angle distribution diagram:
1) High directivity. Generally, it is a pointed epoxy package, or a metal reflection cavity package, and no scattering agent is added. The half value Angle is 5° ~ 20° or smaller, with high directivity, and can be used as a local lighting source, or combined with a light detector to form an automatic detection system.
2) Standard type. Usually used as an indicator, its half value Angle is 20° ~ 45°.
3) Scattering type. This is a large Angle of view of the indicator light, the half value Angle of 45° to 90° or larger, the amount of scattering agent is larger.
3. According to the structure of the LED, there are full epoxy encapsulation, metal base epoxy encapsulation, ceramic base epoxy encapsulation and glass encapsulation.
4. LED with ordinary brightness according to luminous intensity and working current (luminous intensity less than 10mcd); Ultra-high brightness LED (light intensity greater than 100mcd); The luminous intensity between 10 ~ 100mcd is called high brightness LED. The working current of the general LED is more than ten mA to dozens of mA, while the working current of the low-current LED is below 2mA (the brightness is the same as that of the ordinary light emitting tube).