Automotive (or super bright) LEDs

[Ioannis]

Yes. Keep it simple!

Ioannis

[ErnieM]

It makes great sense to pulse LEDs, and is well worth the trouble in increased performance.

You have two physics principles working together. First, you can pulse a LED with a high peak current but low average current that will extend battery life. Second, your eye responds as a peak detector. Together this means a LED pulsed with a 10% duty cycle at 10 times a DC level will look brighter then that LED just running a pure DC (for the same power).

So taken together this means you can run a pulsed LED on less power then a DC LED and make it look just as bright (or same power and make it appear brighter).

LEDs are basically current controlled devices. Your driver should control the current and let the voltage be whatever it is; practically you’ll typically use a resistor anyway, but size it to give the LED the desired current. The drawback of a resistor is the intensity will fall as the battery drains, you’ll have to play that against the increased complexity/cost of a true current source or sink driver. LED current driver chips are available (I’ve used one from Maxim).

The goal of any driver scheme here (portable device on a bike needs to use every Joule stored) would be to transmit maximum power to the LED and burn off the minimum (such as in a current limiting resistor): a PWM scheme is not above consideration and doable with a PIC.

LEDs are becoming more popular in factory supplied automotive signals. If you ever noticed some cars seem to flash as they speed by you you’re seeing the pulsed nature of the LED drive.