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The Problem of Led Automotive Headlights

Mar. 03, 2020

For a long time, the problem of LED heat dissipation has plagued the entire industry, and in the face of a headlight market, they do not want to miss it. The custom heat sink extrusion supplier will share with you how to overcome the heat dissipation problem in the small space of the car headlights, and then reach the national standard 50°C ambient temperature of the car lights. The maximum junction temperature cannot exceed 80°C.

At present, the power of low-beam and high-beam lights of cars is concentrated between 40 ~ 60W, and high-end cars reach more than 80W. In addition, the width of the lights, direction lights, etc., the heat generated by ultra-high power It is not easy to think that the temperature does not exceed 80°C, so solving the heat dissipation problem will be a problem for engineers.

Heat and space are inseparable. Under the condition of large space, the cheapest cooling solution can be selected. For example, a street lamp can be easily solved by increasing the aluminum led street light heat sink.

Aluminum Led Street Light Heat Sink

Aluminum Led Street Light Heat Sink

With the concept of space in mind, understand the heat source and the required upper temperature. The heat source transmits the temperature to the surface and then to the gas through solid heat conduction. Gas convection is slow and passive, so it is especially important to solve the overall packaging material and heat source first.

It is well known that LED chips are converted from electricity to light, and the efficiency is generally only 30%, and the remaining 70% are turned into heat. If the heat is not released in time, the light efficiency will be reduced. The CSP structure used in automotive headlights is related in this structure. The first is how much wattage generates how much heat; the second is the thermal conductivity of the upper and lower materials, which affects the overall temperature uniformity; the third is these materials.

Although the car headlights are large enough, there is not much room for heat dissipation, and in the pursuit of brightness, more and more car manufacturers use high-power and multiple LEDs. The front of the lamp beads is reserved for light and mirrors, and the rear can be reserved for heat dissipation. The simplest and most effective way to dissipate heat is to install a fan and a heat pipe. However, each additional component has the risk of failure and cost. Therefore, the uniformity of the LED package has become the direction of efforts of various manufacturers.

Uniform temperature is the most important issue for heat dissipation in a small area, and how to transfer the junction temperature in the shortest time. Figure 3 shows the relationship between junction temperature and life.

How can the junction temperature not exceed the customer's specifications? The following is an analysis of the thermal structure of the LED package with different driving currents. At a current of 150mA, the temperature difference between the two is not large. The thermally conductive ceramic fluorescent sheet is 2.5°C lower than glass. However, when the current reaches 800mA, the gap is widened to 20.1°C.

Therefore, it is inferred that the thermal conductivity ratio is an important method for analyzing the heat dissipation of LEDs. Under the driving of a small current, the temperature will not constitute the quenching and aging of the LED lamp. However, the temperature effect is very large at high currents. Therefore, a good packaging material is the most direct and effective way to achieve high-quality LED car lights.

A comparative analysis of the materials in the packaging layer structure found that the chip and the phosphor layer material have the highest proportion of heat dissipation, and the cost of changing the chip is too large, and it is more cost-effective to change the phosphor layer material. The quality of a lamp bead is inseparable from heat dissipation, and the key focus of heat dissipation lies in the material and its proportion.

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