How does the hottest car LED headlights dissipate

2022-08-24
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How can automotive LED headlights dissipate heat in a harsh sealed environment

as we all know, semiconductor materials are greatly affected by ambient temperature when working, especially in the high temperature environment where the materials work. With the booming development of the automobile market with a year-on-year increase of 38.89%, the LED headlights of automobiles have gradually replaced halogen bulbs and become the basic equipment of the new generation of automobiles. From daytime running lights to low beam lights and even high beam lights, LED headlights have been everywhere

this figure is provided by Huo Jing Optoelectronics Technology, and theft must be investigated

Figure 1: common automotive LED headlights are shown in the figure below

assuming that the specification of one of them is roughly: input voltage 12/24v, power 35/45w, LM. In order to meet this specification, led must also adopt high-power products. The photoelectric conversion of high-power LED constitutes a complete laboratory technology prototype, and the efficiency is very low. In the working process, only 10% - 25% of the electric energy is converted into light energy, and the rest is almost converted into heat energy. In addition, automotive headlights are generally installed in the hot engine compartment. The heat generated by the high-temperature water tank, engine and exhaust system places the LED headlights in a harsh working environment. The light output of LED will affect its PN junction temperature stability due to its own heat or the high temperature from the engine compartment, and the LED luminous flux Ф Important parameters such as V and wavelength are directly affected by PN junction temperature. This poor temperature cycle will lead to a sharp decline in luminous efficiency and lifetime. Therefore, heat dissipation has become an important topic in the design of LED as automotive headlamp light source

this figure is provided by Huojing Optoelectronics Technology, Figure 2: the global carbon fiber composite market for automotive LED is 941billion yen (at the current exchange rate, the structural anatomy of the lamp is equivalent to about 49 billion yuan

the yellow part in Figure 2 is a high-power LED device. As can be seen from the above figure, the high-power LED needs to be welded to the circuit board, and then firmly fixed on the radiator for heat dissipation. The heat generated by the LED during operation is transmitted to the aluminum radiator with good heat conductivity through the circuit board through conduction. The fins of the aluminum radiator will contact the air in a large area Heat emanates. The relevant heat conduction diagram is as follows

Figure 3: heat conduction diagram

in order to effectively reduce the thermal resistance between the radiator and the circuit board, the heat conducting medium is filled between them. However, the thermal conductivity of the circuit board itself often restricts the heat dissipation capacity of the whole system. The traditional LED mounting circuit board is made of FR4 material, also known as epoxy glass cloth laminate, with a thermal conductivity of about 0.25-0.4w/m.k. Because of its low thermal conductivity, the heat of high-power LED cannot be effectively transferred to the external radiator. In response to this requirement, Rogers introduced 92ml plate, which is filled with epoxy resin and ceramic, with a thermal conductivity (Z-axis) of 2.0 w/m-k, times that of ordinary FR-4 material. The comparison of characteristics between FR4 and 92ml plates is shown in the figure below

in order to more truly show the good thermal conductivity of 92ml plate compared with FR4 plate, we carried out relevant experiments. The experimental conditions of LED lamp agent

are as follows: weld special chip heating resistors on 92ml and fr4pcb boards, add fixed constant current sources at both ends of the resistors to make them heat, and test and record their temperature with an infrared thermometer one hour later

it can be seen from the above figure that under the same external environment, the temperature of 92ml series plate can be reduced by about 30 ℃ compared with FR4 plate, and the temperature of its bottom can be reduced by about 37 ℃. To sum up, 92ml series of plates can effectively reduce the node temperature of automotive headlamp LEDs, thus greatly increasing the service life and luminous efficiency of LEDs. It is especially suitable for use in environments with high stability requirements, more stringent ambient temperature and sealing. LED car headlights

the above content is provided by Huojing photoelectric technology

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