LED Daytime Running Lights: Safe, Stylish, Energy-efficient

Daytime running lights have already been introduced in certain countries to improve road safety.  Their use continues to expand and will become mandatory in all light vehicles throughout Europe starting in 2011.  If special daytime running lights are not fitted to the vehicle, the low beams of the headlamp must be used during the daytime, which have the disadvantage of producing unnecessarily bright lighting in a daytime driving environment.

LED daytime running lights reduce fuel consumption by approx 0.2 liter/100 km, compared to a headlamp low beam.  Using LED technology is ideal for providing the extended use demanded of daytime running lights because LED lamps, unlike halogen, offer a working life equal to that of the vehicle itself.

LED daytime running lamps also offer vehicles a touch of individual style.  Figure 1 shows an example of the LEDs on the Audi A6.  The LEDs take the form of a broken white band across the lighting unit’s lower section, and give the model an individual style signature.



Figure 1: The Audi A6 LED Daytime Running Lights

When Halogen low beams are used for daytime running lights, approximately 200 Watts of electricity are consumed.  The use of Xenon headlamps in the low-beam position reduces this electricity consumption to approximately 170 W.  By using dedicated daytime running lights that utilize LED technology, the electrical power required is drastically reduced to just 10-20 W.  This reduced electrical consumption has a direct effect on the vehicle’s fuel consumption, resulting in a savings of nearly 0.2 liter/100 km.

Benefits

The user benefits of LED daytime running lights include:

Reduced fuel consumption of nearly 0.2 liter/100 km, when compared to Halogen headlamp low beams
LED daytime running lights improve visibility and active safety
LEDs have the same lifetime as the vehicle itself and are maintenance-free
LED daytime running lights give the vehicle a unique style 

System Solution

The block diagram in Figure 2 describes a daytime running light solution with an additional LED Position Light (PL).



Figure 2: Daytime Running Light System with Additional LED Position Light

In the above system, the PIC16F785 microcontroller (MCU) monitors input voltage and temperature, and adjusts the LED current.  Additionally, it performs LED binning, detects whether the daytime running light or PL function has been selected, and synchronizes a low-speed 100 Hz PWM with the input signal.  The PIC16F785 MCU is optimal for this application due to its extensive peripheral integration level, including a Programmable Switch Mode Controller (PSMC) module, two high-speed comparators, an op amp, an internal voltage reference and an Analog-to-Digital Converter (ADC).

Additional feedback channels and more flexibility can be achieved by adding a Pulse-Width Modulation (PWM) controller such as Microchip’s MCP1630.  The MCP1630 enables the development of a scalable DC-to-DC converter and can be used for any kind of topology.  With this design, a generic platform can be developed that is able to address the varying design parameters.  The design can also measure temperature, brightness, voltage and current, and thus adapt to the characteristics of the LED.  Diagnosis capability delivers the state of LED and LED lifetime information.  It also helps to manage the EMC challenge by providing a scalable switching frequency.

Summary

The embedded solutions from Microchip Technology are able to reliably address the challenging requirements of LED daytime running light controls. With the advanced peripheral integration of the PIC16F785 and other PIC MCUs, as well as Microchip’s analog ICs, the system designer has the building blocks for a solution that delivers lower power consumption and reduced board space without compromising functionality.  With the unparalleled flexibility that Microchip’s embedded solutions offer, system designers have the tools to create innovative solutions that meet the expectations of automotive OEMs as they strive to satisfy the market demands, as well as governmental legislative mandates.

LED Daytime Running Lights: Safe, Stylish, Energy-efficient