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Maxim > Design Support > Technical Documents > Application Notes > Automotive > APP 3980
Maxim > Design Support > Technical Documents > Application Notes > Temperature Sensors and Thermal Management > APP 3980
Keywords: Automotive Lighting, Power Supplies, LED, CCFL
APPLICATION NOTE 3980
Power Supplies for Next-Generation Automotive
Lighting
Nov 16, 2007
Abstract:
Today's automobiles
are using LED and CCFL lighting sources, and both technologies need a power
supply. This application note discusses power-supply solutions for LED and CCFL light sources that are
optimized for interior and exterior automotive applications.
Introduction
Throughout the history of automobiles light sources always played an important role. Originally cars merely
had front lights to find a way in the dark. Soon other light sources, taillights, and indicators were added for
security and better organization in growing traffic. Warning and fog lights increased functionality for extreme
conditions. Interior light sources such as cluster, dome, map, or courtesy lighting added convenience for the
driver and passengers. Except for the earliest models, all these light sources were electrically powered and
used incandescent light bulbs.
In recent years light-emitting diodes (LEDs) and cold-cathode florescent lamps (CCFLs) have proved useful as
light sources in automobiles. The key advantages of these new light sources are longer lifetime and better
efficiency. Typical lifetimes for incandescent bulbs are specified at 10,000h, while florescent bulbs can reach
50,000h and LEDs up to 100,000h. This extended lifetime is a clear improvement for reliability and necessary
maintenance, which ultimately reduces service costs. Other LED advantages include: low-voltage operation,
low electromagnetic radiation, immunity to mechanical stress, wide operating temperature range, and a wide
dimming range. With the ongoing improvements to LED technology it seems that eventually this technology will
replace the other lighting options. Nonetheless, today CCFL definitely still has clear advantages in certain
applications like backlighting of large areas and wherever high-power unfocussed light is needed.
Incandescent, CCLF, and LED light sources all need an electric power supply, and each technology has its
special requirements. The power supplies must also perform additional application-specific functions. This
article presents power-supply solutions for LED and CCFL light sources. Design approaches are discussed for
various automotive interior and exterior applications.
Applications
Interior Lighting
Interior lighting applications include cluster or instrument backlighting, dome or map reading lights, courtesy
lights at doors or in the trunk, and display backlighting. Since display backlighting has special requirements, it
will be discussed separately below.
All these interior light applications can use LEDs as a light source. While map and dome lighting are often
implemented with one LED, cluster and courtesy lighting normally require more than one LED connected in
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