Abstract: based on characteristics of the LED, LED light radiant energy depends entirely on the drive current and junction temperature. Therefore, a good thermal management system is a prerequisite for good performance of LED applications. In the field of automotive light-guided daytime running lights, due to the small size of the light source and the constraints of the less efficient optical system, high power LEDs must be used to cause heat concentration. Therefore, a good thermal management solution must be used in light-guided daytime running light applications.
This paper uses Osram Opto Semiconductors QFN package LED KWH2L531.TE as the light source, considering the high performance thermal management system. The thermal performance of various PCBs was compared, the influence of the heat sink was analyzed, and the selection of PCB materials and the importance of heat sink design were emphasized.
Introduction of light-guided daytime running lights
A light guide is a light guide device based on the principle of total reflection of light. When light is transmitted from a light-tight medium to a light-diffusing medium, according to Snell's law and total reflection law, when the incident angle is larger than the critical angle, light does not When the light-tight medium is emitted to the light-diffusing medium, a total reflection phenomenon occurs at the boundary between the two mediums; therefore, when the light is transmitted in the light guide (light-tight medium) at a larger critical angle, total reflection occurs so that the light is The light guide is continuously forwarded. If some corrugation or sawtooth structure is applied to the surface of the light guide, the total reflection condition of the light is destroyed, so that a part of the light escapes the light guide tube, and the uniform brightness distribution of the light guide surface can be realized by adjusting the ripple and the saw tooth. Since the efficiency of the light guide is lower relative to the reflector and the lens, the efficiency is different depending on the shape of the light guide. To achieve the minimum 400 cd DRL requirement for ECE R87, usually a light guide requires about 500 lm of light flux. According to the current LED efficiency, at least two chips are needed. Since the diameter of the light guide is usually only 6mm to 8mm, the size of the LED particles is very high. At present, each LED manufacturer has released a small package (Fig. 1). At 700mA, each chip can reach about 200lm; so usually Two separate LED particles are required and can be achieved with increased current;
OSRAM Opto Semiconductors' latest QFN package LED KWH2L531.TE (Figure 2), single rated power 6.5W, maximum drive current is 1.2A, maximum operating junction temperature 150 °C, short-time operation can reach 175 °C, so it is especially suitable for temperature Higher forward light applications are required. The two chips of the LED are packaged together, and the chip pitch is only 0.1 mm, which greatly reduces the pitch compared with the two separate LEDs, thereby improving the coupling efficiency of the light guide. At present, KWH2L531.TE can reach 560lm under the driving current of 1A and 25°C; even considering light decay, one LED can realize the requirement of single light guide daytime running light, but due to the concentrated concentration of chips, heat accumulation occurs. Therefore, the heat dissipation performance of the entire system is relatively high. Taking the OSRAM KWH2L531.TE LED as an example, this paper analyzes and compares the performance of the whole heat dissipation system from the perspective of heat dissipation, and gives appropriate suggestions for the heat dissipation system of the light guide type DRL.
Figure 1 LUW CEUP
Figure 2 KWH2L531.TE
Analysis of the heat dissipation system of light-guided daytime running lights
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