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Developing constant current regulation for automotive LED lighting

Posted: 17 Jun 2010     Print Version  Bookmark and Share

Keywords:LED lighting  automotive LED  current regulation 

By using a simple value process, it is possible to speed up the analysis and help identify the best approach to take when developing a constant current regulation scheme for automotive interior LED lighting systems. Various approaches exist to address this particular design challenge that may result in a slowdown of the design process, while engineering analysis can be performed to consider the advantages and disadvantages of the different options.

Convenience lighting for passengers during entry and exit is a standard feature on all modern passenger cars. The typical method of operation is to power the lighting system when a door is open, via a manual push button, or from other vehicle body functions such as RF keyless entry. Usually located in the overhead trim and perhaps in the lower door trim to illuminate the threshold into the car, these relatively basic lighting systems feature simple optical arrangements to focus the light on specific areas inside and outside the vehicle.

Compared with incandescent lighting, LED based lighting systems offer longer life, lower power consumption and greater design flexibility. These characteristics make them a good fit for interior vehicle lighting applications. In addition, advancing technology that has seen the emergence of lower cost, higher light output per Watt white LEDs has enhanced the compatibility of LEDs to automotive interior lighting applications.

One system requirement that applies to LEDs but not to incandescent technology is that they require a current limit. In its simplest form, this can be achieved by the use of a resistor connected in series. The resistor acts to fix the current in the LED at a particular battery voltage. However, this is a crude approach and it is well proven that an attempt to regulate a constant current independent of battery voltage is a more efficient way of driving LEDs. A regulated constant current drive scheme provides a more balanced light output in a form factor and at a cost that can be easily integrated into the vehicle's interior trim system.

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