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Enabling high power automotive LED headlamps

Posted: 05 Nov 2014     Print Version  Bookmark and Share

Keywords:HB LED  headlights  LED driver  synchronous buck-boost DC/DC  LT3791 

The market size for high brightness (HB) LEDs is expected to reach Rs.1.22 lakh crore ($20.2 billion) by 2015 (source: Strategies Unlimited). One of the key application areas driving this growth is the LEDs used in automobile designs. Applications range from headlights, daytime running lights and brake lights; to instrument cluster display backlighting, as well as all kinds of in-cabin vanity lighting.

This impressive growth rate is driven by not only by LED's high reliability, reduced power consumption and more compact form factors, but also by enabling innovative designs such as steerable headlights and antiglare dimming. Furthermore, in an automotive environment, all of these improvements must be optimised while also withstanding the rigors of the relatively caustic automotive electrical and physical environment. It goes without saying that these solutions must offer very low profile, compact footprints while simultaneously enhancing overall cost effectiveness.

Although LEDs have been used in daytime running lights, brake lights, turn signals and interior lighting for several years; it's relatively recent that a handful of headlamp specific applications have emerged such as the Audi A8 and R8 and Lexus's LS600h. However, in the past year, several automotive manufacturers have introduced LED headlamps in their most popular models. In 2014, Toyota offered LED headlamps in their bestselling car, the Toyota Corolla. Additionally, several other models of Toyotas, Hondas, Nissans, Porsches and Audis offer LED headlamps in most of their upcoming models. Most estimate that the current LED headlamp market will surpass $3B in 2014.

One of the biggest challenges for automotive lighting systems designers is how to optimise all the benefits of the latest generation of HB LEDs. HB LEDs generally require an accurate and efficient DC current source and a means for dimming. The LED driver IC must be designed to address these requirements under a wide variety of conditions. As a result, power conversion solutions must be highly efficient, robust in features and reliability while being very compact and cost effective. Arguably, one of the most demanding applications for driving HB LEDs is found in automotive headlamp applications as they are subjected to the rigors of the automotive electrical environment, must deliver high power (typically between 50W to 75W) and must fit into thermally and space constrained enclosures, all while maintaining an attractive cost structure.

Automotive LED headlamps
Benefits, such as small size, extremely long life, low power consumption and enhanced dimming capability are the catalyst for the wide spread adoption of HB LED headlights. Years ago, most manufacturers, such as Audi, Daimler and Lexus have used LEDs to design very distinctive driving lights or "eyebrows" around their headlights as part of their distinctive branding. There is a similar trend in LED headlamp designs with Acura's Jewel Eye design, Porsche's four quadrant design as well as numerous emerging designs.

The benefits of using LEDs in automotive headlights have several positive implications. First, they never need to be replaced, since their solid state longetivity of up to 100K+ hours (11.5 service years) surpasses the useful life of the vehicle. This allows automobile manufactures to permanently embed them into headlight designs without requiring accessibility for replacement. This enables their styling to be dramatically changed as LED lighting systems do not require the depth or area as do the HID or halogen alternatives.

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