Brake lights, turn signals, reversing lights and rear fog lamps have been used as light sources for 21W to 27W and 280 to 570 lumens. The taillights, parking lights, car side lights and turn signal flashes use 4W to 10W tungsten lamps with a brightness of 40 to 130 lumens, while the car headlights use a high-intensity xenon fluorescent tube (HID). However, in automotive lighting, LEDs are increasingly used as light sources. The tail center high position brake light is the first car light to adopt LED. In addition, in the lamp market, other exterior lighting and indicators such as brake lights, turn signals and interior lights have been converted to LED bulbs. In recent years, exterior lighting, such as daytime running lights (DRL), and headlights, have begun to switch to LED bulbs. It is expected that car headlights will soon switch to high-brightness LED lights. In addition, inside the body, the backlight of some in-car displays has also begun to use LEDs as light sources, such as instrument panels and TFT displays.
Advantages of automotive LED lighting systems
White LEDs have a color temperature of approximately 6000K and are visually equivalent to natural light. The ability to distinguish colors by the human eye is best under natural background conditions. In the evening, the human eye only has a good ability to distinguish between the scene or the edge of the road in the natural color.
The average life of LED lamps is longer than that of tungsten lamps and high-intensity fluorescent tubes, and it is more stable and reliable. If you can reduce the chance of failure, and do not need to change the bulb frequently, it saves a lot of trouble. And using LEDs can save more energy. LED lights are smaller and easier to fit into the lamp holder, making it easier to work with stylish lighting designs while taking up less space. More importantly, LED brake lights start faster. The LED brake light has a lighting time of only about 50ms, which is about 250ms faster than the start time of the tungsten bulb, thus reducing the risk of collision with the trailing vehicle. In addition, LEDs are solid-state light sources that can withstand greater vibration.
Technical requirements for driving LED lights
Since the brightness of the LED is proportional to the current flowing through it, a constant current source is required to drive the LED. In any case, the current flowing through the LED should be kept constant to ensure the brightness of the LED. It is also necessary to control the ripple current to an acceptable level under any circumstances. Therefore , the design of the LED driver belongs to the power conversion circuit design, which is characterized by a constant current output instead of a constant voltage output.
In LED driver designs, blocking circuits must be added to protect against reverse power operation. Another challenge we will encounter is to ensure that the LEDs work properly in the event of a cold start or load outage. In normal operation, the car's battery supply voltage is between 9V and 16V (for example, 12V system bus), while the large truck's battery supply voltage is between 18V and 32V (for example, 24V system bus). In the event of a load outage or cold start, the battery's input voltage range will vary greatly from the normal range.
During the operation of the generator, if the power supply of the battery is suddenly cut off, the generator will continue to generate electricity at this time, and the power consumption of the capacitor-powered part will suddenly increase. If no protective measures are taken, it will be damaged. Electrical appliances. If the LED driver is not driven by a constant current, the current of the LED will change, causing the brightness of the LED to change, which is why the current car light will flicker. The following is a definition of a load power-down test that mimics some cases of load breaks. Different car manufacturers use different standards, so the definition of load power-off test is also different. Figure 1 is only one case.
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