LED Drivers for Automotive Applications
While the basic operating requirement for an LED driver is to supply a constant current to LEDs in order to produce consistent lighting, automotive application - unlike other market segments - have more stringent guidelines in regards to temperature and humidity range, voltage, ability to withstand harsh chemicals, electromagnetic interference and electromagnetic compatibility (EMI) as well as protection circuitry.
This article describes the different options designers have to integrate a LED driver solution. ROHM has expanded its range of highly integrated LED Driver ICs to provide a variety of design options with integrated or externally switched outputs, parallel/series control and extensive protection and fault detection functions in small surface mount packages.
Automotive applications for LED include interior lighting (such as dome, dash and footwell lighting), indicator and telltale lights and infotainment backlighting as well as exterior (signalling) functions such as tail lights, turn signals, brake lights including CHMSL (center high-mount stop lamps), parking lights, side marker lights, fog lamps and daytime running lights (DRLs).
A few car manufacturers have introduced LED headlamps on production models based on high-brightness (HB) LEDs. In some cases, the capabilities of an LED driver can enable more than one application to be addressed with the same LEDs. With leading automotive headlamp manufacturers providing prototypes with HB-LEDs, almost all carmakers have displayed concept vehicles with LED headlights and it is predicted that several standard vehicles will have LED headlights in 2012. As LEDs continue to improve in efficiency and reduce in cost (the light output levels from packaged LED devices roughly doubles every 18 months), an increasing amount of LEDs and LED drivers will be used in vehicles. With the low power consumption of LEDs compared to conventional lighting, an estimated 0.2 liters of fuel per 100 km and about 4 grams lower CO2 emissions/km are being cited as the ultimate advantage of replacing incandescent lighting with LEDs in the DRL application alone. In electric and hybrid vehicles, an 85% reduction in energy consumption from LED usage instead of incandescent bulbs translates into increased range. As a result, there are several compelling reasons to implement LEDs in automotive applications. One essential part is the power management provided by the IC drivers.
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