Will high-power LED generate heat when working?
Publish：Shenzhen Teng Jie Optoelectronics Technology Co., Ltd. Time：2023-10-24
Many people believe that high-power LEDs do not have heat, but high-power LEDs do have heat. Problems occur during extensive thermal use. Many people who have just used high-power LEDs are not familiar with thermal issues, and how to effectively solve them makes product reliability the main issue. Today, Tengjie Optoelectronics will talk to you about related issues.
Under forward voltage, electrons in LEDs obtain energy from the power supply, and under the driving force of the electric field, they overcome the electric field of the PN junction and transition from the N region to the P region. These electrons recombine with the holes in the P region. Due to the fact that free electrons drifting into the P region have higher energy than valence electrons in the P region, electrons return to low energy states during recombination, and excess energy is released in the form of photons. The wavelength of emitted photons is related to the energy difference Eg. It can be seen that the luminescent region is mainly near the PN junction, and the luminescence is the result of the recombination of electrons and holes to release energy. A semiconductor diode encounters resistance throughout the entire journey of electrons entering and leaving the semiconductor region.
Simply put, from a principle perspective, the physical structure of a semiconductor diode is that the number of electrons emitted from the negative electrode and returned to the positive electrode is equal. In the case of electron hole pair recombination in ordinary diodes, due to the energy level difference Eg, the emitted photon spectrum is not within the visible light range.
The electrons in the internal path of a diode will consume power due to the presence of resistance. The power consumed conforms to the basic laws of electronics: P=I2 R=I2 (RN++RP)+IVTH. In the equation, RN is the N-region body resistance VTH is the opening voltage of the PN junction RP is the power consumed by the P-region body resistance. The heat generated is Q=Pt. In the equation, t is the time when the diode is energized.
Essentially, an LED is still a semiconductor diode. Therefore, when the LED is working in the forward direction, its working process conforms to the above description. The electrical power it consumes is: P LED=U LED × In the I LED formula, U LED is the forward voltage at both ends of the LED light source, and I LED is the current flowing through the LED. The consumed electrical power is converted into heat and released: Q=P LED × In the formula t, t is the power on time.
In fact, the energy released by electrons when recombining with holes in the P region is not directly provided by an external power source, but rather due to the fact that when the electron is in the N region, without an external electric field, its energy level is Eg higher than the valence electron level in the P region. When it reaches the P region and recombines with holes to become the valence electrons in the P region, it releases so much energy. The size of Eg is determined by the material itself and is independent of the external electric field. The effect of an external power source on the electron is only to drive it to move in a directional direction and overcome the effect of a PN junction.
The heat production of LED is independent of light efficiency; There is no relationship between the percentage of electrical power that generates light and the remaining percentage that generates heat. By understanding the concepts of thermal generation, thermal resistance, and junction temperature of high-power LEDs, deriving theoretical formulas, and measuring thermal resistance, we can study the actual packaging design, evaluation, and product application of high-power LEDs. It should be noted that heat management is a key issue in the current stage of low luminous efficiency of LED products. Fundamentally improving luminous efficiency to reduce the generation of heat energy is the ultimate solution, which requires technological progress in various stages of chip manufacturing, LED packaging, and application product development.
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