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What is LED PN Junction Temperature
The basics of LED is one PN junction semiconductor; where the current flows, the temperature around this area shall rise up. So temperature in this realm is regard as LED PN junction temperature. Yet, since LED chip dimension is very small, the temperature of LED chip usually can be taken as LED PN junction temperature.
As a rule, higher as LED PN junction temperature becomes, lower is the intensity of light; and vice verse. Under whatever occasion will LED PN junction temperature increase? Here are four conditions to be accounted for.
There exists electrical resistance of the defective electrode structure, of the substrate, of material in PN junction area and of epoxy, which forms series electrical resistance. When current goes through PN junction field, it will run through these cascade resistors; thus LED temperature increases eventually.
(2) Thermal loss
PN junction is not so perfectly made as it was, so input efficiency can hardly reach up to 100%. That is because while the electricity in P-zone injects into N-zone, charge in N-zone shall also transfuse into P-zone, the latter of which can not engender photoelectric effect but cause thermal loss.
(3) Defection of Conversion Efficiency
Defection of conversion efficiency is the key point that affects PN junction temperature. By far, advanced material growth technology and manufactured condoms make LED high conversion efficiency come true. However, in that the refractive index of LED chip is much higher than ambient medium, few of the radiogenic photons can overbrim the surface but reflect between chip surface and ambient medium, finally absorbed by chip material and substrate; turn into heat, only to cause internal temperature go up.
(4) Heat conductivity
The last man is heat management system of LEDs. Epoxy resin is with low heat conductivity. It is not without difficulty for heat to dissipate above through epoxy resin, but below through substrate，elargol, PCB and housing for heat sink. So that heat conductivity of relevant substances should influence lighting efficiency. The entire thermal resistances for general LEDs could come to 300-600℃/W. While well-performed LEDs can be able to restrict among 15-30℃/W. The great difference between the two suggests that only under miniwatt condition can ordinary-size LEDs perform normally; while power LEDs can work with high power supply.