Analyze the cause of LED junction temperature and

Analyze the cause of LED junction temperature and how to reduce the junction temperature

the basic structure of LED is a semiconductor p-n junction. The experiment points out that when electricity flows through the LED element due to the high aspect ratio of the longer fiber segment, the temperature of the p-n junction will rise. Strictly speaking, the temperature of the p-n junction region is defined as the LED junction temperature. Usually, because the component chips have very small sizes, we can also regard the temperature of LED chips as the junction temperature

2. What are the reasons for the LED junction temperature

when the LED is working, there are five situations that can promote the junction temperature to rise to varying degrees:

a, there are certain resistance values in the poor electrode structure of the element, the material of the window layer substrate or junction area, and the conductive silver glue. These resistances are stacked with each other to form the series resistance of the LED element. When the current flows through the p-n junction, it will also flow through the compressive strength resistance of these building material test blocks, which are mainly used to test concrete, cement, high-strength bricks, refractories and other building materials, resulting in Joule heat, resulting in the rise of chip temperature or junction temperature

b. Because the p-n junction cannot be extremely perfect, the injection efficiency of components will not reach 100%, that is to say, when the LED works, in addition to the charge (hole) injected into the n area of the automation zone where local enterprises appear in the bright spot, the n area will also inject charge (electron) into the P area. Generally, the charge injection of the latter type will not produce photoelectric effect, but will be consumed in the form of heating. Even the useful part of the injected charge will not all become light, and some will eventually become heat when combined with impurities or defects in the junction region

c. Practice has proved that the limitation of light output efficiency is the main reason for the rise of LED junction temperature. At present, advanced material growth and component manufacturing processes have been able to convert most of the input electrical energy of led into light radiation energy. However, due to the fact that the LED chip material has a much larger refractive index than the surrounding medium, a large part of photons (90%) generated inside the chip cannot smoothly overflow the interface, and total reflection occurs at the chip and medium interface, It returns to the inside of the chip and is finally absorbed by the chip material or substrate through multiple internal reflections, and turns into heat in the form of lattice vibration, promoting the junction temperature to rise

d. Obviously, the heat dissipation capacity of LED components is another key condition to determine the junction temperature. When the heat dissipation capacity is strong, the junction temperature decreases, on the contrary, when the heat dissipation capacity is poor, the junction temperature will rise. As epoxy adhesive is a low thermal conductivity material, p-universal testing machine is also applicable to the biomaterial industry. The heat generated at the n junction is difficult to be dissipated upward to the environment through transparent epoxy. Most of the heat is dissipated downward through the substrate, silver paste, tube shell, epoxy bonding layer, PCB and heat sink. Obviously, the thermal conductivity of related materials will directly affect the heat dissipation efficiency of components. The total thermal resistance of a common led from the p-n junction area to the ambient temperature is between 300 and 600 ℃/w. For a power LED element with good structure, the total thermal resistance is about 15 to 30 ℃/w. The huge thermal resistance difference shows that ordinary LED components can work normally only under the condition of small input power, and the dissipated power of power type components can be as large as watt level or even higher

3. What are the ways to reduce the LED junction temperature

a, reduce the thermal resistance of LED itself

b, good secondary heat dissipation mechanism

c, reduce the thermal resistance between the LED and the installation interface of the secondary heat dissipation mechanism

d, control the rated input power

e, reduce the ambient temperature

led input power is the only source of the thermal effect of the element. Part of the energy turns into radiant light energy, and the rest eventually turns into heat, thus raising the temperature of the element. Obviously, the main way to reduce the LED temperature rise effect is to try to improve the electro-optical conversion efficiency (also known as external quantum efficiency) of the element, so that as much input power as possible can be converted into light energy. Another important way is to try to improve the heat dissipation capacity of the element, so that the heat generated by the junction temperature can be distributed to the surrounding environment through various ways