1, What is the LED junction temperature?
The basic structure of the LED is a semiconductor P-N junction. The research indicates that when current flows through the led power components, the P-N junction temperature will rise in the strict sense, put the P-N junction temperature is defined for the LED junction temperature. Usually due to component chips has a small size, so we can also be the temperature of the LED chip regarded as the junction temperature.
Two reasons to produce the LED junction temperature?
LED Floodlight 80W work, the following five circumstances prompted the rise in junction temperature varying degrees of:
a bad component in the electrode structure, the material of the window layer substrate junction area as well as conductive silver glue, etc. There is a certain resistance value, the resistance base plus each other, constitute a series resistance of the LED components. When current flows through the P-N junction, but also flow through these resistors, resulting in Joule heating, resulting in elevated chip temperature or junction temperature.
b, due to the P-N junction can not be extreme perfection, the injection efficiency of the components will not reach 100%, in other words, LED work except P charge (holes) injected to the N area, N area will injected charge (electrons) to the P region, under normal circumstances, after a charge injection does not produce the photoelectric effect, the form of heat consumed. Even if the useful part of the injected charge, it will not all become light, impurities or defects of the part of the junction area combining, will eventually become hot.
Practice has proved that the limit of the optical efficiency of the LED junction temperature rise. At present, advanced materials growth and device fabrication process has enabled the LED of the vast majority of input power converted to optical radiation, the LED Spotlight 30W chip material with the surrounding medium, however, has a much larger refractive index, resulting in chip internally generated very most of the photons (> 90%) can not be successfully overflow the interface, total internal reflection in the chip and the media interface to return inside the chip, and multiple internal reflection eventually chip material or substrate absorption, and lattice vibrations form into a hot, prompting the rise of junction temperature.
d, apparently, the heat dissipation capacity of the LED components is a key condition for determining junction temperature of high and low. Cooling capacity is strong, the junction temperature drops, on the contrary, poor heat dissipation, junction temperature will rise. Epoxy adhesive is a material of low thermal conductivity, the heat generated by the P-N junction is difficult to upwards through the transparent epoxy released into the environment, most of the heat through the substrate, silver paste, shell and tube, epoxy adhesive layer, PCB and heat sink downward divergence. Obviously, the heat capacity of the related materials will directly affect the components of the heat dissipation efficiency. An ordinary LED, from the P-N junction area to the total thermal resistance of the ambient temperature at 300 to 600 ° C / w, a well-structured power LED components, the total thermal resistance of about 15 to 30 ° C / w. The huge differences in the thermal resistance that ordinary LED components only in a small input power conditions in order to work properly, while the power dissipation of the power components to the watt level or even higher.
3 ways to reduce led driver 120w junction temperature?
a, to reduce the thermal resistance of the LED itself;
b, the second cooling bodies;
c, to reduce the thermal resistance between the LED and second cooling bodies installation interface;
d, control Rated input power;
e, lower ambient temperature
LED input power is the only source of components thermal effects, part of the energy into light energy of the radiation, the rest eventually were turned into heat, thus driving up the temperature of the components. Clearly, reducing the LED Flood light 10W temperature effect, one is trying to improve the components of the electro-optical conversion efficiency (also known as external quantum efficiency), so that as much as possible the input power into light another important way is to try to improve component the heat dissipation capacity, so that the junction temperature of the heat produced and distributed through various channels into the surrounding environment.