LED has the advantages of energy preservation and long service life, and has been widely used in various small lamps in the interior of automobiles. With the advent of high-brightness LEDs, LEDs have also been used in various lamps in the exterior of automobiles. This article will show you the development process of headlights and the LED headlight solution introduced by Arrow.
Evolution of headlight design
From the birth of the automobile, kerosene lamps (1886-1904) were originally used for lighting. The design of headlights was just better than nothing. The so-called headlights were simply kerosene lamps hung on the vehicle and had no function as a matter of fact. As the times changed, kerosene lamps were quickly replaced by acetylene lamps (1905-1925) due to the low luminous power of kerosene lamps. With the development of electric lamps and the improvement of bulb durability, acetylene lamps, together with their defects, gradually withdrew from the stage of lamp history and were replaced by increasingly mature incandescent lamps.
However, the luminous power of incandescent lamps is usually not high, so more energy-saving halogen lamps were born and gradually became the mainstream of automotive headlights. However, in view of the shortcomings of the incandescent lamp series such as low brightness, power consumption, and short service life, Hella, a professional lamp manufacturer, brought xenon lamps with higher brightness to the market in the 1990s, improving the tungsten filament luminous principle invented by Edison, and filled the quartz tubes with high-pressure inert gas to replace the traditional filament, making xenon lamps the first choice for high-brightness headlights.
Xenon headlights have been followed by LED headlights that have not been widely used at present. Although LED headlamps were seen on many concept cars, they have been used in cars only in recent years due to factors such as technology, costs, and regulations.
Advantages of LED headlights
At present, the headlights that are still being used mainly include halogen lamps, xenon lamps, and emerging LED lamps. Among them, halogen lamps have disadvantages such as low luminous efficiency, high heat generation, and relatively low brightness, and are generally standard for low-grade cars, so it is difficult to meet the needs of current car owners. In addition, the service life of a halogen lamp is relatively short. Under normal circumstances, the service life of a halogen bulb may last for up to about 1,000 hours. Besides, because of their inflexible appearance, halogen lamps can only be made into double round lamps, thus limiting the shape of lamps.
The xenon lamp with higher brightness is the mainstream headlight currently used in high-end cars. However, because of poor light concentration and an overly high brightness, xenon lamps easily dazzle the drivers of vehicles proceeding in the opposite direction, thus causing accidents. Moreover, their light penetration is poor. In foggy, icy, and snowy weather, the penetration of xenon headlights is very weak. Another defect of the xenon lamp that is the most fatal is the delay effect, which is as a result of the working principle of xenon headlights. It takes 2 to 4 seconds to light a xenon lamp. When the vehicle is running at high speed, the horn is often useless, so it is necessary to use the headlights to "dazzle" the drivers of vehicles proceeding in the opposite direction. However, relying on xenon headlights will be slow to help in an emergency.
The emerging LED lamp has the advantage of very high luminous efficiency. LED lamps directly convert electric energy into light energy through LEDs, so LED lamps are also called cold light sources. Their working temperature is generally 50 to 70℃, and their power consumption is only about 1/10 compared with ordinary automobile bulbs. Therefore, they can better reduce oil consumption and protect the car circuit from being burned out by excessive load current. In addition, LED lamps are similar in brightness to xenon lamps. Moreover, they are stable in energy-saving performance and relatively environmentally friendly. There are no ultraviolet and infrared rays in the spectrum of its light. Besides, a headlight is in a combination of multiple LEDs, therefore, many options are available for design of the shape, which can be cool and aesthetic. In addition, its service life is very long, up to 50,000 hours, and it has a broad color temperature range, from high color temperature to fog lamp. Its high reaction speed allows it to light up without delay, thus becoming the most promising headlamp technology at present.
Dim vision at night is the main cause of car accidents
Headlights are one of the most important parts in a car, because accidents caused by incorrect use of headlights accounted for about 40% of all car accidents. According to incomplete statistics, about 60% of traffic accidents in the world occur at night. In 2013, the death toll from driving accidents at night in China was 50,000, accounting for about 50% of the total death toll in traffic accidents. Among them, during the time period from 7 pm to 6 am the next day, the death toll accounted for more than half of the total. It can be seen that poor vision at night is the main cause of traffic accidents.
The reasons why there were so many car accidents at night include not only human factors of bad driving, but also the impact of car lighting on safe driving. About 22% of traffic accidents occurred under poor visibility, i.e. many accidents were caused due to the limited width and distance of vehicle lighting, dim lighting, drivers’ inability to see the obstacles in front clearly and brake and avoid them in time while driving. Therefore, the adoption of adaptive driving beam (ADB) matrix LED headlights with high brightness and automatic light types that change in accordance with road conditions have become the new development trend of automotive headlights.
Adaptive headlights have smart lighting function
ADB headlights are a smart high-beam control system that can adaptively change the high-beam type according to road conditions. It converts a complete high-beam spot into a high-beam spot composed of multiple optical lighting zones through special optical modules and electronic control. When targets such as vehicles and pedestrians appear on the road, the control system composed of sensors (cameras) and drive circuits will turn off or dim some high-beam lighting zones, thus avoiding dazzling the illuminated targets and ensuring clear high-beam lighting.
In addition, the ADB system can automatically turn the high beam on or off for the driver according to the driving state of the car, the environmental state, and the state of other vehicles on the road. At the same time, in conjunction with the control system in the vehicle, the ADB system can adjust and change the direction of the light while the car is steering, making the light control more convenient and comfortable. It can even set various light modes, such as town mode, country road mode, high-speed mode, curve mode, etc, to meet the needs of more complex road conditions.
Excellent matrix headlight solution
To speed up the customer development of the ADB system, Arrow has introduced a matrix headlight solution, of which the complete software and hardware design was completed in 2020, and the ADB control will be achieved in 2021 (through cooperation with Arrow’s IDH). Up to 60 LED controls are currently supported, with DC 9V to 18V input, up to 60W output, using 5 strings x 12 LEDs, up to 1.5 A per channel, efficiency greater than 82%@1A in high beam mode, boost/buck output voltage set by software, with body control module (BCM) and interconnection through a CAN interface, supporting segment and matrix switching, for comprehensive system diagnosis and LED string protection, and optimized EMI performance. At present, Arrow has built-in 6 sets of demonstration systems, which can be used for preliminary customer evaluation, and intends to manufacture another 30 sets in the first quarter of 2021 to further promote the market.
FS32K144HAT0MLLT
Arrow's matrix headlight solution features NXP's MCU (FS32K144HAT0MLLT), dual-phase boost converter (ASL2507SHN), dual-channel LED buck driver (ASL2417SHN), three-channel LED buck driver (ASL3417SHN), matrix LED controller (ASL5115SHN 5 pieces/set), system basis chip (SBC) (UJA1163 and UJA1164), CAN transceiver (TJA1044T), and CREE LEDs (AP20AW-1E-CZZ-000Q325TTT 60 pieces/set), ADI's surge stopper (LTC4380CDD-1#PBF), and MOLEX connector (5023521200 1393366-1) and other key parts and components, which is the best system design at present.
Conclusion
The emerging ADB matrix LED headlights are the best choice of headlights at present, which can improve the overall safety of the car, provide more flexibility in car modeling design, and enhance the technological sense and value of the car. At present, many car manufacturers have applied them in commercially available car models. With gradual expansion of the market size of LED headlights, the cost is expected to be further reduced. LED headlights will also be gradually popularized among more car models, forming a positive market cycle, with an extremely considerable market prospect.
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