Making a 20w+ led driver

Discussion in 'General Electronics Chat' started by peck68, Aug 10, 2010.

  1. peck68

    Thread Starter Member

    Nov 27, 2009
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    Right, my birthday coming up soon and i want to treat myself - so I want to get myself a pretty bright torch, since I am a torch fanatic. :)

    I can get a 1000 lumen LED torch (around £30) or a 4000 lumen LED for around the same price.

    So i was thinking to myself, how about make my own? :D

    Now the thing is, supplying 50 watts is one task to keep things cool to a minimum, and also supplying 25v @ 2.2A sustained is another.

    Since this is a torch, its going to need a few cells - 18650's are popular i hear over the web as supplies for these sort of things, since they have a large capacity. But that means i am going to need a DC to DC booster (10v ish to 25v) - I have never yet discovered these things yet so I need a few refs to teach me (if anybody has any guides it would be amazing :))

    Also, supplying/limiting the amperage with minimal heat build up etc. How do i go about that? I could simply use a resistor, but its going to be bloody huge to withstand supplying 50w... Any simpler solutions? (or complex.. as i should say)

    If its a too big of a task for me to learn and figure then i shall stick to the ol' prebuilt - but i think it would be a good learning experience for me to do :)

    Thanks
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    and by a "torch" you mean a "flashlight" right?
     
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Start out with a PWM LED driver IC setup, you may also find that an LED pulsed at a high frequency with a low duty cycle can be a lot brighter than just giving it direct drive.
     
  4. peck68

    Thread Starter Member

    Nov 27, 2009
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    Yeah sorry, english lingo lol :)

    ----

    Hmm sounds sensible, what about the boost converter though? And would it need huuge resistors?

    Edit: found this nifty website :) http://www.ladyada.net/library/diyboostcalc.html
     
    Last edited: Aug 11, 2010
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Well, if the boost circuit is 90% efficient with a 10v supply, you'll need about 6.12A to operate the LED.

    (25v/10v)/0.9 = 2.778 ; 2.778 x 2.2A ~= 6.12A

    90% may be achievable, but it'll be tough. Somewhere in the vicinity of 80%-85% is more likely.
     
  6. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Not if you utilize an LED driver IC designed just for this function and there are a ton of them.

    I've got a device in use that sends an IR pulse to control something across the room. The IR LED is only rated for 100 mA continuous but will gladly deal with 2A pulses provided the duty cycle is less than 10%. Although only used on a semi-regular basis the little transmitter module just has 4 AA cells in it and they seem to last forever.

    I just didn't feel wireless that day. The transmitter is mounted on a forklift and the receiver is used to trigger a door opener. Even without optics it has no problem working over a 100' range.
     
  7. campeck

    Active Member

    Sep 5, 2009
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    please let me know how this turn out for you! I am currently fitting a 1W 300ma 70lm LED into a small "torch".

    What is the beam width on the LED that you are looking at? any plans to use optics to narrow the beam? This is something I haven't looked into yet but need to as my LED has a 120deg viewing angle.
     
  8. marshallf3

    Well-Known Member

    Jul 26, 2010
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  9. peck68

    Thread Starter Member

    Nov 27, 2009
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    http://cgi.ebay.co.uk/HIGH-POWER-50...LM-24-26V-/390224706604?pt=LH_DefaultDomain_0 -> this is the baby ;) (obviously not this precise one, there are loads others on ebay)

    The beam angle is 150°, so i am probably going to need a reflector or lens - it the only trouble of finding a reflector that is suitably large enough to fit the size of the led :p

    ---

    Marshallf3 you are amazing ;) but can this only go up to 1A no higher? Or is it "moddable" to use higher rated components?
    Thanks
     
  10. bertus

    Administrator

    Apr 5, 2008
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  11. marshallf3

    Well-Known Member

    Jul 26, 2010
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    It's a new part series I haven't bothered to look into yet. It was just meant to be used as an example but I'm sure as already noted above current specs will rise as demand dictates. Usually once you get to know the circuit it becomes easy to customize the ouput stage(s) to your needs which is the least they can ask after doing all the difficult control circuitry for you. :)
     
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