LED flashlight help

Discussion in 'The Projects Forum' started by sheffner, Feb 24, 2012.

  1. sheffner

    Thread Starter New Member

    Oct 2, 2009
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    Hello! I'm wanting to create a high powered LED flashlight but I have a few questions. I've worked with electronics before, but am definitely not a pro so please keep that in mind with explanations or if I ask a dumb question. Currently I'm working with the 10mm super bright leds (3.2-3.5v, 20ma). I have 3 powered by 12 volts and a 220 ohm, half watt resistor, but it isn't nearly as bright as I would like it. Do I need more leds? Are there better, brighter leds that would be more suited for a flashlight? Can I do something to increase the voltage using capacitors? Keep in mind I am only working with 12 volts(though I can increase if necessary). Any ideas?
     
  2. #12

    Expert

    Nov 30, 2010
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    You're only putting 7 to 11 ma through them. Try increasing the current by using 120 ohms.

    If that doesn't suit you, you can use 2 groups of 2 LEDS with 2 current regulator chips. That will hold them steady as the battery gets tired.
     
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  3. Wendy

    Moderator

    Mar 24, 2008
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    There are new LEDs that are as bright as incandescent bulbs. Your LEDs take 0.02A, these are 3W, and take 0.7A. Not sure you knew about them.
     
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  4. sheffner

    Thread Starter New Member

    Oct 2, 2009
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    Bill_Marsden: What brand/model regulator chips and how do you wire them?

    #12: What brand/model leds are you talking about? What is the minimum forward voltage on them?

    Thanks to both of you for your help!
     
  5. #12

    Expert

    Nov 30, 2010
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    I was talking about the LEDs you described. You gave the specs, I calculated the resistor.

    LM317 would be a regulator chip. Use a 62 ohm resistor to get it to deliver .02 amps, as long as there is enough voltage available.
     
  6. sheffner

    Thread Starter New Member

    Oct 2, 2009
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    Is the LM317T from radioshack ok? Where would I put the 62 ohm resistor?
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    There are several ways to power the high wattage models. The one I was referring to is a 3W LED, as with conventional LEDs you can get them in a wide range of colors, including white. Last I heard they come in 1W, 3W, 5W, and 20W. I am sure there are others, but those are the ones I'm familiar with.

    They can use a conventional resistor same as regular LED, but as you've probably figured out that is extremely wasteful.

    Another way is to get a current regulated (as opposed to voltage regulated) switching mode power supply (SMPS) regulator to feed them current. A common brand name is buck puck, you can google it. The neat thing about these kinds of regulators is their efficiency is much higher. If the LED drops 3.4VDC, and uses 0.7A, the 12V only has to provided just over 0.2A. This is because it is a conversion circuit, and explains why it is considered better. The trade off is complexity and cost.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    [​IMG]

    I have an article about LEDs you might find handy, Chapters 1 and 2 are for beginners.

    LEDs, 555s, Flashers, and Light Chasers

    I also have a prototype SMPS regulator I have build but never tested. I really need to get off my duff and do so.
     
  9. sheffner

    Thread Starter New Member

    Oct 2, 2009
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    Awesome! Thanks so much for the diagram! So with this regulator I could maximize efficiency and successfully use it with 3 watt leds or is this for the ones I currently have?
     
  10. sheffner

    Thread Starter New Member

    Oct 2, 2009
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    And would where would I then connect the led in the diagram?
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    The regulator shown is for low power LEDs. With a 62Ω resistor it will limit the current to 0.02A, which is where you need to be.

    The article I linked explains how LEDs work, but does not cover the higher wattage models. They (high wattage) have been out for a while, but they have a lot of unique requirements, such as heat sinks. They are much more efficient than light bulbs or fluorescent lights.

    My suggestion, work with the ones you have now. Use 20ma (0.02A) for them. If you want to get into the really bright models later you can pick it up then.

    And yes, I have helped several people make grow lights using LM317's and 3W or better LEDs. It gets hot though.

    As for how I hook the LEDs up, read the link. It does explain it. It has the schematics.

    LEDs, 555s, Flashers, and Light Chasers
     
  12. sheffner

    Thread Starter New Member

    Oct 2, 2009
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    Cool. Thanks again!
     
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