Digital Flashlight: 800+ Lumens

 This is an early version of a digital flashlight implementing Powered LED's (Luxeons) and a constant current circuit.  With variable levels of current sourcing thanks to a microcontroller.

 

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  • Just some friendly suggestions. Using PWM to achieve variable light output may be a better approach, especially if your uC isn't doing anything else. Advantages? Lower part count and you will extend the battery life of your device since now you are driving the FET fully 'on' or 'off' virtually eliminating power losses in the FET. Another benefit if your frequency is sufficiently fast you are operating the LED's in a pulsed current mode. This means you could put all the LEDs in parallel and won't even need current limiting resistors and your LEDs will actually last longer! A parallel configuration means your circuit will operate at much lower battery voltages, the uC you choose will actually be the limiting factor. Making the frequency fast enough that no flicker is perceivable is pretty easy. Be careful you don't get over zealous and go faster than you need to as you will increase switching losses in the FET. The trick is to go fast enough that you are operating in the pulsed current mode of the LED(with some margin) and not much faster. Disadvantage? Make a mistake in your code which locks your FET 'on' and your expensive LED's blow up.

    Posted by LPM, 19/12/2009 12:21pm (7 years ago)

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