4 reasons for the junction temperature phenomenon of LED lamp beads
The p-n junction of the semiconductor is the basic structure of the LED lamp bead! Expansion After the experimental research on the LED, the final conclusion is: when the LED is in normal operation, when the current flows through the LED, the temperature of the pn junction will gradually rise, so the evil phenomenon is called the junction temperature of the LED lamp bead! The chip size of LED lamp beads is very small, so we can also call the temperature of the chip as the junction temperature! There are several reasons for the junction temperature of LED lamp beads:
Reason one:
There are many resistances in the motor structure of the LED lamp bead. When the resistances are added to each other, the series resistance of the LED lamp bead will be formed! When the current flows through the pn junction, at the same time, it also flows through these resistors, resulting in Joule heat, and finally the chip junction temperature rises.
Reason two:
The pn section cannot be perfect, and the injection efficiency of LED lamp beads will not reach 100%! This effect means that when the LED lamp bead is working, both the p region and the n region will inject charges into each other. Under normal circumstances, the latter type of charge injection will not produce a photoelectric effect and will be consumed in the form of heat dissipation! Even if part of the charge is injected, it will not all become a light source. There will always be a part of it combined with the intercepted impurities or defects, which will eventually form heat!
Reason three:
It has been proved by experiments that the limitation of luminous efficiency is the main factor that leads to the formation of high junction temperature of LED lamp beads. At present, there are advanced LED material growth and electronic component manufacturing processes that allow LED lamp beads to input most of the electrical energy. After conversion, finally Switch to photovoltaics. Since the material of the chip inside the LED lamp bead has a higher number of refraction coefficients than the surrounding valence, most of the photons (90%) generated inside the lamp bead cannot flow out of the interface smoothly. The interface between the chip and the ring produces an emission phenomenon. After many internal emission, it is finally absorbed by the chip material or the bottom of the ring, and generates heat through lattice vibration, which causes the junction temperature to gradually increase!
Finally, the heat dissipation capability of the LED lamp bead is a key condition that determines its own junction temperature! If the heat dissipation effect is good, the junction temperature will naturally drop. And if the heat dissipation capacity is checked, the junction temperature will rise! Since the epoxy resin is a low thermal conductivity material, the possibility of the heat generated at the pn junction being dissipated to the environment through the transparent epoxy is almost zero. Most of the heat energy is dissipated through the bottom, shell, silver paste, epoxy bonding process, bottom and PCB or heat sink. Obviously, the thermal conductivity of related materials also determines the thermal conductivity of LEDs. an influencing factor!
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