LEDs are fast becoming much more popular within the automotive industry and nowhere more so than in the use of front lighting. There are many cars out there already using LEDs for daytime running lights and even some high end vehicles out there which have a full LED headlight or advanced matrix headlight installed.
We will be looking at the most common automotive front lighting architectures and what possible developments there are for this area.
A typical front lighting system will consist of a low beam lamp, high beam lamp, turn light, daytime running light and a fog lamp. Apart from the daytime running lights, most of them will be using incandescent, xenon or HIDs (High Intensity Discharge) lamps. The easiest and most straight forward way to replace these lamps in headlights with LEDs is to apply an individual LED driver to each function and to connect an adequate number of high brightness LEDs. Architectures such as this is known as a single stage, due to the fact there is a DC/DC LED driver that is regulating a constant current and handling each individual lighting function.
For a single stage architecture, the converter will need to handle broad input voltage variations coming from the vehicles battery in extreme conditions such as crank and load dump. It is also common to have a boost or a buck boost conversion topology and although some manufactures will prefer to implement the position lamp function with the daytime running lights, it is also desirable to have a dimming function to go with the LED driver as well.
A recent trend in how to implement a full LED headlight: the platform approach uses an intermediate boost converter that handles all of the battery’s voltage variations and gives a high output voltage, such as 48V that is able to manage the range of LED string lengths that are used for various headlight functions. So long as the LED string voltage isn’t above 48V, the DC/DC buck converters will be able to act as LED driver.
You could call this platform approach, a two stage architecture, the advantage of this architecture is that it has a boost converter handling the battery’s input voltage variations, while the buck LED driver, which are able to be modularized are handling the individual headlight functions.
Adaptive headlights are something that could vastly improve road safety and a two stage architecture is easily adoptable as an adaptive headlight by introducing matrix manager devices to individual LEDs, depending on different function of the headlight.
A matrix manager device will control an individual LEDs brightness/on/off through a microcontroller unit that is running on a digital protocol. This technique is able to realize various advanced lighting features, from a simple welcome or turn light to a more complicated anti-glare function. Due to a LEDs brightness/on/off changing dynamically based on road situations, the buck driver should be able to work fast enough so as not to cause any voltage/current overshoot events that will damage the LEDs.
Designing with LEDs can allow us to create better automotive front light systems, with vehicles on the road not only having beautiful looking lights but also headlights than will improve and enhance road safety.