1. What is the junction temperature of the junct […]
1. What is the junction temperature of the junction temperature of high-power LED lamps?
The basic structure of the junction temperature of high-power LED lamps is a semiconductor P-N junction. The experiment indicates that when the current flows through the junction temperature element of the high-power LED lamp, the temperature of the P-N junction will rise. In the strict sense, the temperature of the P-N junction region is defined as the junction temperature of the high-power LED lamp. Generally, because the component chips have a small size, we can also consider the temperature of the junction temperature chip of high-power LED lamps as the junction temperature.
2. What are the reasons for the junction temperature and junction temperature of high-power LED lamps?
When the junction temperature of high-power LED lamps is working, the following five situations may exist to promote the junction temperature to varying degrees:
a. Poor electrode structure of the element, the material of the window layer substrate or the junction area, and the conductive silver glue all have certain resistance values. These resistances add to each other to form the series resistance of the junction temperature components of high-power LED lamps. When a current flows through the P-N junction, these resistors will also flow through it, which will cause Joule heat, which will cause the chip temperature or junction temperature to increase.
b. Since the PN junction cannot be extremely perfect, the injection efficiency of the component will not reach 100%, that is to say, in addition to the charge injection (holes) from the P region to the N region during the junction temperature operation of high-power LED lamps, N The region also injects charge (electrons) into the P region. Generally, the latter type of charge injection does not produce a photoelectric effect, but is consumed in the form of heat. Even if the useful part is injected with electric charge, it will not all become light, and some of it will be combined with impurities or defects in the junction region and eventually become heat.
c. Practice has proved that the limitation of light output efficiency is the main reason for the increase in junction temperature and junction temperature of high-power LED lamps. At present, advanced material growth and component manufacturing processes have been able to convert most of the input power of high-power LED luminaires into light radiation energy. However, due to the high-power LED luminaires, the temperature of the chip material is much larger than that of the surrounding medium. The refractive index of the chip causes a large part of the photons (> 90%) generated inside the chip to not smoothly overflow the interface, but generates total reflection at the chip and dielectric interface, returns to the inside of the chip and is finally rejected by the chip material or substrate through multiple internal reflection Absorbs and becomes heat in the form of lattice vibrations, causing the junction temperature to rise.
d. Obviously, the heat dissipation capability of the junction temperature components of high-power LED lamps is another key condition that determines the junction temperature. When the heat dissipation capability is strong, the junction temperature decreases, and conversely, when the heat dissipation capability is poor, the junction temperature will rise. Because epoxy adhesive is a low thermal conductivity material, it is difficult to dissipate the heat generated at the PN junction to the environment through transparent epoxy. Most of the heat passes through the substrate, silver paste, shell, epoxy bonding layer, PCB and The heat sink radiated downwards. Obviously, the thermal conductivity of related materials will directly affect the heat dissipation efficiency of the component. The junction temperature of a common high-power LED lamp, the total thermal resistance from the PN junction region to the ambient temperature is between 300 and 600 ° C / w. For a well-structured high-power LED lamp junction temperature element, its total The thermal resistance is about 15 to 30 ° C / w. The huge thermal resistance difference indicates that the junction temperature components of ordinary high-power LED lamps can only work normally with a small input power, and the power dissipation of power components Can be as large as watts or higher.
3. What are the ways to reduce the junction temperature and junction temperature of high-power LED lamps?
a. Reduce the thermal resistance of the junction temperature of high-power LED lamps;
b. Good secondary heat dissipation mechanism;
c. Reduce the thermal resistance between the junction temperature of high-power LED lamps and the installation interface of the secondary heat dissipation mechanism;
d. Control the rated input power;
e. Reduce the ambient temperature
The input power of the junction temperature of high-power LED lamps is the only source of the thermal effect of the component. A part of the energy becomes radiant light energy, and the remaining part eventually becomes heat, thereby raising the component temperature. Obviously, the main method to reduce the junction temperature and temperature rise effect of high-power LED lamps is to try to improve the electro-optical conversion efficiency (also known as external quantum efficiency) of the components so that as much input power as possible can be converted into light energy. Another important The way is to try to improve the heat dissipation ability of the component, so that the heat generated by the junction temperature is dissipated to the surrounding environment through various ways.