(1) Principle of LED illumination
The light-emitting diode is a working principle diagram of a strong light flashlight made of a III-IV compound such as GaAs (gallium arsenide), GaP (gallium phosphide), GaAsP (phosphorus gallium arsenide), and the core thereof is a PN junction. Therefore, it has the IN characteristic of a general PN junction, that is, forward conduction, reverse cutoff, and breakdown characteristics. In addition, it has luminescent properties under certain conditions. At the forward voltage, electrons are injected into the P region from the N region, and holes are injected into the N region from the P region. A part of the minority carriers (small children) entering the other area is combined with the majority carriers (multiple sub-) to emit light, as shown in Fig. 1.
Assuming that luminescence occurs in the P region, the injected electrons directly composite with the valence band holes to emit light, or are first captured by the luminescent center and then condensed with the holes. In addition to this luminescent composite, some electrons are trapped by the non-luminous center (this center is near the middle of the conduction band and the intermediate band), and then recombined with the holes, and the energy released each time is not large, and visible light cannot be formed. The greater the ratio of the composite amount of luminescence to the non-luminous composite amount, the higher the photon efficiency. Since the recombination emits light in the minority carrier diffusion region, light is generated only within a few μm of the PN junction surface.
Theory and practice have proved that the peak wavelength λ of light is related to the forbidden band width Eg of the semiconductor material in the light-emitting region, ie
????λ≈1240/Eg(mm)
The unit of Eg in the formula is electron volt (eV). If visible light (wavelength between 380 nm and 780 nm red) is produced, the Eg of the semiconductor material should be between 3.26 and 1.63 eV. Light longer than the wavelength of red light is infrared light. There are now infrared, red, yellow, green and blue light-emitting diodes, but the blue light diodes are expensive and expensive, and are not commonly used.
(two) the characteristics of LED
1. The meaning of the limit parameters
(1) Allowable power consumption Pm: The maximum value of the product of the forward DC voltage applied to the LED and the current flowing through it. Above this value, the LED is hot and damaged.
(2) Maximum forward DC current IFm: The maximum forward DC current allowed to be applied. Exceeding this value can damage the diode.
(3) Maximum reverse voltage VRm: The maximum reverse voltage allowed to be applied. Above this value, the LED may be damaged by breakdown.
(4) Working environment topm: The ambient temperature range in which the LED can work normally. Below or above this temperature range, the LED will not work properly and the efficiency will be greatly reduced.
Nowadays, the light flashlight with LED as the light source has been constantly entering our lives. With the emergence of LED diode flashlights in previous years, the emergence of single-lamp high-power 1W and 3W has continuously enriched everyone's choice of flashlight. In particular, the emergence of metal flashlights for aviation aluminum alloys has made many buyers feel excited.
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