The advantage and high price of the hottest LED ca

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Advantages, reasons for high price and system design analysis of LED automotive headlights

although there are some shining examples of LED applications in automotive headlights, its adoption rate is still not growing as fast as solid-state lighting (SSL). Automotive applications present a unique design challenge, and the cost is still relatively high. However, LED will add unique functions to the headlights. In this paper, we will introduce a design that can produce a powerful headlamp system

you can make a comparison between general lighting and automotive lighting. We all remember the traditional tungsten bulb. At the end of 2013, 40W and 60W incandescent bulbs commonly used by most American households were banned from being manufactured or imported in the United States; But even so, they can still be purchased. It should also be noted that 75W and 100W bulbs have been phased out in 2012

the reason why they are eliminated is that the US Environmental Protection Agency (EPA) needs better electro-optic output efficiency. The main reason for the transition is that residential lighting accounts for about 14% of power consumption (source: US Energy Information Administration), which helps to reduce power consumption. While solid-state LED lights only need about one eighth of the power to produce the same amount of lumen output, so LED lights have entered our modern world

the evolution process from incandescent bulbs to solid-state electronic lamps is very similar to the evolution of vehicle lighting in the automotive industry. Although red LED lamps have been used in tail lamps for more than ten years, the changes in the interior and forward lighting system of cars have made significant progress in the adoption rate of LED lamps. For example, more than 70% of internal indicator lights and more than 45% of instrument display backlights use LED lights. In contrast, more than 55% of daytime running lights (DRLs) and about 5% of headlights now use LED lights. Ironically, although headlights (low beam, high beam, fog lights) represent the greatest opportunity, they have the least penetration! One of the main reasons is that the implementation cost of automobile manufacturers is too high, and consumers are unwilling to pay

automotive headlights

before we discuss the reasons for the low adoption rate of lighting lamps, it is necessary to continuously upgrade the industry and know why many drivers and even original equipment manufacturers prefer LED lighting products. These include but are not limited to the following:

performance and design flexibility. LED provides design flexibility due to its shape factors, and provides the dimming function of free maintenance in Guangdu. Remember that the human eye is very sensitive to small deviations in light output

energy conservation, emission reduction and low carbon dioxide emissions. Led not only has better power efficiency, which reduces the energy required to power it, but also has a longer life cycle

cost. This may seem counter intuitive, but in non headlamp applications, the continuous cost reduction, durability improvement and high quality make LEDs a new standard of end customer value

regulations. Many government regulations clarify the requirements of DRL, headlamp and other lighting applications, increasing the demand for LED lighting

Audi is generally regarded as the leader in the application of LED automotive exterior lighting, and no one will be surprised. Anyone who sees Audi's famous "eyebrow" white sky running lights in the rearview mirror will be very conspicuous. In addition, Audi used LED headlights for the first time in its 2004 R8. In addition, Audi is famous for its matrix headlights that can guide the beam (an example of beam steering can be seen in Figure 1)

Figure 1 This figure shows how the matrix LED headlights diffuse light

then why are LED headlights not as popular as other forms of automotive LED lighting? The answer, of course, is cost. In the headlamp, the alternative of LED is incandescent lamp, halogen lamp or hid xenon lamp. Comparable LEDs may cost 100% more than halogen headlamps and 1.5 times more than HID xenon lamps

Where is led suitable

generally speaking, in terms of its light emission, LED headlights are between halogen lamps and HID lamps, but LED headlights provide more focused rays and can also be controlled to produce different shapes. In addition, due to its small size and good operation of LEDs, automobile manufacturers can manufacture various shapes and components to match their models perfectly

although the LED will not emit heat when it is illuminated, when the current passes, a certain amount of heat will be generated at the bottom of the transmitter, which will cause potential risks to adjacent components and connecting cables. Therefore, LED headlamps need a cooling system, such as a radiator or fan, to prevent them from melting. In addition, these cooling systems are located in the engine compartment, which is a less cool area for some other systems to maintain the appropriate temperature. This is another reason why LED headlights are difficult to design and implement in vehicles, so they are more expensive than HID lamps

led may not be the only choice for the next generation of headlights. A recent article in American trade said that Audi introduced an optional laser high beam in its high-performance R8. The system is very excellent. It won't shine light on the vehicle in front, so the high beam can remain on and adjust itself, even if there are eight cars in front. Compared with LED high beam, Audi's laser spotlight can project a beam twice the distance along the road (500 feet), so that the driver can see farther

ic promotes the adoption of LED

now let's solve the challenge of driving LED. Incandescent lamp produces light output, provided that current passes through its filament; LED is different. Led needs special integrated circuit (IC) to drive (Figure 2)

Figure 2 Lt3956 IC can drive a series of LED light strings with wide dimming range

today, manufacturers are taking price reduction measures to maintain a profitable situation. A key performance feature of LED Driver IC is the ability to properly dim the LED. Because the LED is driven by a constant current, its DC current level is proportional to the brightness of the LED. In order to change the brightness of the led by controlling the LED current, there are two dimming methods

the first method is analog dimming, which reduces the LED DC current level proportionally by reducing the constant LED current level. Reducing the LED current may lead to changes in LED color or inaccurate LED current control. The second method is digital or pulse width modulation (PWM) dimming. PWM dimming turns on and off the LED at a frequency of 100Hz and above, which is imperceptible to the human eye. The PWM dimming duty cycle is proportional to the LED brightness, and the LED current when turned on remains at the same level as the LED Driver IC setting, maintaining a constant LED color during high dimming ratio. In some applications, this PWM dimming method can use a ratio of 3000:1

let's have a more detailed understanding of a special LED Driver IC in a typical headlamp circuit. The new lt3965 has 80V input and output capabilities, and can realize a constant current and constant voltage converter. This topology enables it to drive high current LEDs (Figure 3). It has an internal low side n-channel power MOSFET, rated at 84v, 3.3a, driven by an internal regulated 7.15v power supply. The fixed frequency and current mode architecture can work stably under a wide range of power supply and output voltage. The ground based voltage FB pin is used as the input of multiple LED protection functions, which can also make the converter generate a constant voltage source. The frequency adjustment pin allows the user to adjust the frequency from 100 kHz to 1 MHz to optimize efficiency, performance or external component size

Figure 3 shows the I2C 8-switch matrix dimming LED Driver IC

lt3956 senses the output current at the high voltage side of the LED string (usually referred to as high voltage side current detection). This is the most flexible scheme to drive the LED, which can support the configuration of step-up, step-down or step-down boost mode

although the popularity of LED headlights is low at present, the progress of performance is too attractive for automobile manufacturers. The reasons include improving the safety of drivers, flexibility. According to the statistical data of the lithium industry branch and field research, it can be determined that China's salt lake brine lithium extraction process has achieved new breakthroughs in body shape, energy saving and pure appearance. We all know that the appearance of a car is very important. It looks good, so we want to buy it. When you drive, please pay attention to matrix lighting, because when you look at the rearview mirror, you will see a significant increase in the use of matrix lighting and LED headlights

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