While you probably don’t even think about your car’s headlights and rear lights when driving in the dark, I am fascinated by the many smart minds that are involved in the design of these lighting systems:
With so many disciplines involved in the design of lights, there are obviously many permutations of design choices available to create the end product. I would like to shed light on one of these choices: LED lights.
Let there be . . . LED light
Just like lights in homes, exterior lighting in cars were traditionally based on incandescent bulbs. Just as Light Emitting Diode (LED)-based lights are becoming popular in homes, LED-based based lights in automotive are gaining popularity as well. One such application for LEDs as the light source is in car taillight and brake light function. Designers often utilize one shared set of LED strings as the light source for both these light functions. The light from the LED becomes bright when the driver applies the brakes and is otherwise dimmed for taillight function. Designers accomplish this with the help of dimming features implemented in the electronics that drive the LED light source.
Figure 1 shows a block diagram of the electronics for driving LED lights in automotive headlight and rear lights.
Figure 1: Block diagram showing a typical architecture for driving LEDs in automotive lighting.
A few key considerations of dimming in automotive LED headlight and rear light systems include:
Figure 2: Block diagram showing the addition of feedback to improve the accuracy of the PWM signal generated by the TI 555-based timer circuit.
I’m sure you’re asking: Does this really work? The answer is yes! The precision PWM dimming LED driver reference design for automotive lighting includes design details and test results showing that this solution actually works.
I hope I have given you one more trick (in a bag of many) available to automotive lighting designers. I believe this trick of employing feedback to improve duty cycle accuracy is simpler and has cost advantage compared to alternate approaches. Now, use it and give me your feedback!
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