In the past, halogen lamps were often selected for automobile lighting. In recent years, the application of LED in the whole vehicle began to grow rapidly. The service life of traditional halogen lamps is only about 500 hours, while that of mainstream LED headlamps is up to 25000 hours. The advantage of long life almost allows LED lights to cover the entire life cycle of the vehicle.
The application of exterior and interior lamps, such as front lighting headlamp, turn signal lamp, tail lamp, interior lamp, etc., began to use LED light source for design and combination. Not only automotive lighting systems, but also lighting systems from consumer electronics to factory automation equipment. LED designs in these lighting systems are increasingly diversified and highly integrated, which is particularly prominent in automotive lighting systems.
Rapid growth of LED in automobile lighting system
As a lighting source, LED not only has a longer life, but its luminous efficiency also greatly exceeds that of ordinary halogen lamps. The luminous efficiency of halogen lamps is 10-20 Im/W, and the luminous efficiency of LED is 70-150 Im/W. Compared with the disordered heat dissipation system of traditional lamps, the improvement of luminous efficiency will be more energy-saving and efficient in lighting. The LED nanosecond response time is also safer than the halogen lamp second response time, which is particularly evident in the braking distance.
With the continuous improvement of LED design and combination level as well as the gradual lowering of cost, LED light source has been verified in automotive electronics in recent years and began to rapidly increase its share in automotive lighting systems. According to TrendForce data, the penetration rate of LED headlights in the world’s passenger cars will reach 60% in 2021, and the penetration rate of LED headlights in electric vehicles will be higher, reaching 90%. It is estimated that the penetration rate will increase to 72% and 92% respectively in 2022.
In addition, advanced technologies such as intelligent headlights, identification lights, intelligent atmosphere lights, MiniLED/HDR vehicle display have also accelerated the penetration of LED in vehicle lighting. Today, with the development of vehicle lighting towards personalization, communication display, and driving assistance, both traditional car manufacturers and electric vehicle manufacturers have begun to seek ways to differentiate LED.
Selection of LED driving topology
As a light emitting device, LED naturally needs to be controlled by a driving circuit. Generally, when the number of LED is large or the power consumption of LED is large, it is necessary to drive (usually several levels of drive). Considering the diversity of LED combinations, it is not so simple for designers to design a suitable LED driver. However, it can be clear that due to the characteristics of LED itself, it generates large heat and needs to limit the current for protection, so constant current source drive is the best LED drive mode.
The traditional driving principle uses the total power level of LEDs in the system as an indicator to measure and select different LED drivers. If the total forward voltage is higher than the input voltage, then you need to select a boost topology to meet the voltage requirements. If the total forward voltage is lower than the input voltage, you need to use a step-down topology to improve the overall efficiency. However, with the improvement of LED dimming capacity requirements and the emergence of other requirements, when selecting LED drivers, we should not only consider the power level, but also fully consider the topology, efficiency, dimming and color mixing methods.
The choice of topology depends on the specific location of LED in the automobile LED system. For example, on the high beam and headlamp of automobile lighting, most of them are driven by step-down topology. This step-down drive is excellent in bandwidth performance. It can also achieve good EMI performance through the design of spread spectrum frequency modulation. It is a very safe topology choice in LED drive. The EMI performance of boost LED drive is also excellent. Compared with other types of topologies, it is the smallest drive scheme, and it is applied more in the low and high beam lamps and backlights of automobiles.
Post time: Dec-06-2022