All along, the brake lamps , turn signal lamps , reversing lights and rear fog lamps are used 21W to 27W, 280-570 lumens brightness of the incandescent light bulb as a light source . Car tail lights, parking lights , side lights and turn signal flashing display uses 4W to 10W, 40-130 lumens brightness of incandescent light bulbs , car headlights xenon high- intensity fluorescent tubes (HID). But in automotive lighting , more and more use of LED as a light source . Central tail brake light is the first car with LED lights . In addition, the lighting market , exterior lighting and other indicators such as brake lights, turn signals and interior lights are switched LED bulbs. In recent years, vehicle lights, such as daytime running lights (DRL), as well as near the front lights are beginning to switch to LED bulbs. Expected car headlights will soon switch to high-brightness LED lights. In addition, inside the body , some of the interior of the display backlight are beginning to use LED panel lighting wholesale as a light source , such as dashboards and TFT displays.
Advantages automotive LED lighting systems
The color temperature of the white LED is about 6000K, visually almost identical to natural light. Because the human eye 's ability to distinguish colors under natural background conditions are best. In the evening, the human eye color only in the case of natural scenery or road edge to have a good ability to distinguish .
The average life expectancy of LED lights than incandescent light and high brightness fluorescent tube length , but more stable and reliable . If you can reduce the probability of failure , but do not need frequent replacement bulbs , save a lot of trouble. And the use of LED can save more energy. LED lamp shape is smaller and easier to mount the holder, at the same time take up less space , is easier with stylish lighting design . More importantly, the startup speed LED brake lights faster. LED brake lights lighting time is only about 50ms, fast start-up time than incandescent light bulbs around 250ms, thereby reducing the risk of collision trailing vehicles. In addition , LED is a solid state light source , can withstand greater shock.
Technical requirements of the LED driver
Since the brightness proportional to the current flowing through the LED , it needs a constant current source to drive the LED. In any case , the current flowing through the LED to maintain a constant brightness LED to ensure consistency. Also in any case need to be able to control the ripple current at an acceptable level. So the LED driver design belongs power conversion circuit design, which is characterized by constant voltage constant current output rather than output .
In LED driver design , the need to increase the blocking circuit to provide power protection to prevent reverse operation. We will encounter another challenge is to ensure that the LED can work properly in the case of automotive cold start or load off of . Under normal operating conditions , the car 's battery supply voltage between 9V and 16V ( eg 12V system bus ) , and a large truck battery supply voltage is between 18V and 32V ( eg 24V system bus ) . In case of power failure or load cold start when the battery input voltage range with the normal range is very different .
During generator operation , if the battery power is suddenly cut off , then the generator will continue to generate electricity , using generator power capacitors and other electrical parts of a sudden increase in voltage will appear the phenomenon , if you do not take protective measures will be damaged by appliances. If the LED driver is not constant current drive LED will change, resulting in changes in the brightness of the LED , which is why the presence of current automotive lamp flicker . Here is a test of a defined load power , used to mimic some cases sudden load off . Different car manufacturers use different standards , so the load off test definitions are not the same , Figure 1 is just one case .
Automotive design and breakthrough LED lighting systems
Although the load dump will cause the load voltage increases, but most advanced alternator are equipped with central control , load power clamp circuit. 12V reference level bus system will be limited to between 35V 42V, 24V and the reference level of the bus system will be clamped between 50V to 60V.
In cold weather , start the device will make the battery supply voltage dropped , Figure 2 shows the "cold start" typical waveform testing.
Automotive design and breakthrough LED lighting systems
As the input power supply terminal connected to a battery LED driver inputs , and therefore such as brake lights of the car involved in safe driving lights must not affect the load off and cold start , or even to be able to continue to operate normally in this case . In a typical case , 12V input range of the bus system is 6V to 42V, 24V input voltage range of 12V bus system to 60V.
LED drive technology
LED current limiting resistor is one of the driving method , the advantage of low cost, simple design ; drawback is that current will vary with the forward voltage and the driving voltage is changed , the luminance of the LED panel lighting wholesale. When the battery voltage is relatively high , the driving efficiency is poor , because the most of the power is dissipated in the resistor . In addition, the current limiting resistor will produce great heat, resulting in heat dissipation problems. So this is a simple, but it is not the most efficient way .
The second method is a linear current regulator , also called constant current source. Its advantages are simple in design , constant current ; drawback is inefficient , and with the input voltage increases , the voltage drop linear chip bearing the greater , so the linear chip will have a great heat. But it improves the shortcomings of the current limiting resistor method fluctuations .
In addition to the above two methods , there are a method of driving the power switch type . Table 1 is a comparison of three different methods of switching power supply as the LED -driven approach with high efficiency and constant current . Since opening higher efficiency of the power converter , so it is more and more manufacturers to use headlights . Its biggest drawback is that the design lines more complicated , and the cost is relatively high.
Automotive design and breakthrough LED lighting systems
Why use in automotive lighting to Boost / Buck LED Driver do ? This is because the battery voltage fluctuations in the voltage fluctuation, we need to maintain a constant current through the LED Boost / Buck LED driver can ensure that regardless of the input voltage is higher or lower than the output voltage and current can be kept constant. This ensures that the load off and cold startup, and security-related lighting can maintain a constant brightness. In addition , a variety of LED automotive lighting applications also require different LED driver topologies. Some car manufacturers want to be able to light a LED driver platform for different LED configurations of different lighting systems. Boost / Buck LED Driver is the ideal drive most high brightness automotive lighting system solutions.
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