For a long time, automobile brake lights, turn signals, reversing lights and rear fog lights have all used tungsten filament bulbs with a brightness of 280 to 570 lumens, ranging from 21W to 27W, as light sources. Car tail lights, parking lights, side display lights and turn signal flashers use 4W to 10W tungsten filament bulbs with a brightness of 40 to 130 lumens, while car headlights use high-brightness xenon fluorescent tubes (HID). But in automotive lighting, LEDs are increasingly used as light sources. The rear central high-mounted brake light is the first car light to use LED. In addition, in the car lighting market, other exterior lighting and indicator lights such as brake lights, turn signals and interior lighting have switched to LED bulbs. In recent years, exterior lighting, such as daytime running lights (DRL) and headlights, have begun to use LED bulbs. It is expected that car headlights will soon switch to high-brightness LED lights. In addition, inside the car body, some in-car display backlights have begun to use LEDs as light sources, such as instrument panels and TFT displays.
Advantages of automotive LED lighting systems
The color temperature of white LED is about 6000K, which is visually almost the same as natural light. Because the human eye's ability to distinguish colors is best under natural background conditions. At night, the human eye can only distinguish between scenery or the edge of the road very well in natural colors.
LED lights have a longer average lifespan than tungsten lamps and high-brightness fluorescent tubes, and are more stable and reliable. For example, it can reduce the chance of failure and eliminate the need to replace light bulbs frequently, saving a lot of trouble. And using LED can save more energy. LED lights are smaller in appearance and easier to install into the lamp holder. While taking up less space, they are easier to match with fashionable lighting designs. More importantly, LED brake lights start up faster. The lighting time of LED brake lights is only about 50ms, which is about 250ms faster than the start-up time of tungsten bulbs, thereby reducing the risk of being hit by a trailing vehicle. In addition, LED is a solid-state light source and can withstand greater vibration.
Technical requirements for driving LED lighting
Since the brightness of an 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 must remain constant to ensure consistent LED brightness. 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 constant current output rather than constant voltage output.
In the LED driver design, a blocking circuit must be added to provide protection against reverse power operation. Another challenge we will encounter is ensuring that the LED can work properly when the car is cold-started or the load is powered off. Under normal operation, the battery supply voltage of a car is between 9V and 16V (such as a 12V system bus), while the battery supply voltage of a large truck is between 18V and 32V (such as a 24V system bus). In the event of load power outage or cold start, the input voltage range of the battery will be greatly different from the normal range.
During the operation of the generator, if the battery power supply is suddenly cut off, the generator will continue to generate electricity, and the voltage of the capacitors and other power consuming parts powered by the generator will suddenly increase. If no protective measures are taken, electrical appliances will be damaged. If the LED is not driven by constant current, the current of the LED will change, causing the brightness of the LED to change. This is why current car lights will flicker.
ANNA