Pirahna LED High brightness LED flashlight - Page 1
Forum section: electronics / projects

author: ElectroElvis
author_rank: Regular Contributor
timestamp: January 28, 2013, 07:07:55 pm
content: Hello,recently I have build small project flashlight using Pirahna FLUX LED which are very bright individually. I connected 16 of them trough 5V regulator which is thermaly glued to heatsink. Problem I have is that after 10 min of constant use whole back side where heatsink is mounted gets very very hot. Is there any other way except reducing power to dissapte heat better? And any reasonable solutions how to make this portable without changing batteries evry few mins:DFor rest of picture please refere to my blog since pictures are big and there are many of them:www.electroelvis.com

author: ConKbot
author_rank: Super Contributor
timestamp: January 28, 2013, 09:28:58 pm
content: Heat has to go somewhere once its generated. A nice easy to cut/machine plastic enclosure is a rather poor thermal conductor, and youre using a linear circuit instread of a switchmode circuit, so youre going ot have more heat to deal with.Also, both your questions will be answered with the same answer, make it more efficient, and it will run long enough on batteries, and it will be cooler in your hand.Also, Pirahna LEDs on a 5v regulator? 5V isnt enough to run 2 in series, which means you presumably have all 16 in parallel with a dropping resistor in there? If youre running at the typical 50mA/LED for Pirahna leds, thats 800mA * (Vsupply-3.2V) watts of heat where the 3.2 V is the nominal Vf of the LEDs (varies from 3.2-3.8 on white LEDS.)Match your supply voltage to your load voltage better so youre burning up less heat, use a LDO instead of a 7805 or similar which has a high dropout voltage. AMC7135 chips are commonly used flashlight constant current LED driver boards, if your LEDs are matched well enough, a 750mA 7135 based regulator board (available for cheap from a variety of chinese direct ship sites, i.e. deal extreme, and kaidomain) and a 4-series Ni-Mh pack would run strong until the batteries were depleted at 0.9v/cell (usually <0.2v dropout on the 7135 chips)With just a current limiting/balancing resistor (no driver board) you could probably get away with a 3-series Ni-Mh pack too, it would dim as it goes, so your wouldnt be left suddenly without light. like would probably happen with the 4-Series pack and the driver board.At 750mA, an AA Ni-MH cell based pack would last for over 2 hours, and a AAA based pack would run for about an hour.

author: Corporate666
author_rank: Unknown
timestamp: January 29, 2013, 05:28:05 am
content: The whole setup is horribly inefficient... you are burning up power in the regulator, in the resistors, and in the LED's.You should switch to a constant current supply (this lets you get rid of the resistors). You should also move to a switching regulator, which gets rid of almost all of the heat lost in your linear regulator. Really, you should switch to a switching boost regulator and run all your LED's in 2 or 4 strings (or maybe even in 1 string).There is no free lunch... but in your case you can kill two birds with one stone - drop the heat and extend battery life.