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LED electrical characteristics: current control type de […]
LED electrical characteristics: current control type device, the load characteristic is similar to the UI curve of the PN junction. The small change of the forward conduction voltage will cause a large change of the forward current (exponential level), the reverse leakage current is small, and there is a reverse Breakdown voltage. In actual use, you should choose . The LED forward voltage becomes smaller as the temperature increases, with a negative temperature coefficient. The power consumed by the LED is partly converted into light energy, which is what we need. The rest is converted to heat, which causes the junction temperature to rise. The amount of heat (power) emitted can be expressed as .
LED optical characteristics: LED provides a half-width large monochromatic light, because the energy gap of the semiconductor decreases with the rise of temperature, so its peak wavelength emitted as the temperature increases, that is, the spectrum red shift The temperature coefficient is +2~3A/. The LED luminance L is approximately proportional to the forward current: K is the proportionality factor. As the current increases, the luminance of the light also increases approximately. In addition, the luminance of the light is also related to the ambient temperature. When the ambient temperature is high, the composite efficiency is lowered and the luminous intensity is decreased.
LED thermal characteristics: under small current, LED temperature rise is not obvious. If the ambient temperature is high, the main wavelength of the LED will be red-shifted, the brightness will decrease, and the uniformity and consistency of the light will be deteriorated. In particular, the temperature rise of the dot matrix and the large display screen has a more significant effect on the reliability and stability of the LED. So thermal design is critical.
LED life: LED long-term work will cause aging caused by light decay, especially for high-power LED, the light fade problem is more serious. When measuring the life of an LED, it is not enough to use the damage of the lamp as the end of the life of the LED. It is more meaningful to specify the lifetime of the LED by the percentage of light attenuation of the LED, such as 35%.
high-power LED package: mainly consider heat dissipation and light. In terms of heat dissipation, copper-based thermal lining is used to connect to the aluminum-based heat sink, and the solder joint is used as a connection between the die and the thermal lining. This heat dissipation method has better effect and high cost performance. In terms of light output, chip flipping technology is adopted, and the reflective surface is added on the bottom surface and the side surface to reflect the wasted light energy, so that more effective light can be obtained.