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LED Confusion

Discussion in 'LEDs and Optoelectronics' started by jpinc, Mar 17, 2014.

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  1. jpinc

    jpinc

    9
    0
    Oct 2, 2013
    For my situation, I am interested in the brightest LED output I can achieve with AA batteries, as size/profile is a sticking point. After trial and error, I came across the small LED MAG flashlight, that is powered by 2 AA batteries.

    I discovered they used Luxdrive LEDs to get this optimal output. I ordered a few different color LEDs and when I directly connected them to AA batteries, I achieved the same brightness.

    However, as I was informed by the distributor and also posts to my thread here, this is unsafe and unreliable. Ledsupply told me the Micropuck Driver was ideal for my situation.

    My problem- When using driver, the output of the LED is now greatly reduced, thus losing all the brightness I sought out.

    My question- How do I use the driver and still achieve the full brightness potential of the LED. The MAG light is able to produce a very bright output with just 2 AA batteries and I need to accomplish the near same result. Have I improperly wired the driver or is there something I am missing. I am very entry level with this stuff.

    Thank you for taking the time to read and help me out in advance

    Joe
     
  2. kpatz

    kpatz

    301
    80
    Feb 24, 2014
    It's possible that the maglite isn't using a driver or series resistor, and just relying on the voltage drop of the LED (white LEDs usually are between 3 and 4V) along with the internal resistance of the batteries to keep the LED from blowing itself up. Perhaps you could take the flashlight apart and see if there's any series resistor or driver?

    They are right though, directly wiring the LED to the batteries can cause shortened LED life. I wonder what Maglite did.

    Looking at the Micropuck, it should be able to drive the LEDs brighter than the batteries alone, since it boosts the voltage and controls the current. Are your batteries fresh alkalines? Check the application notes here: http://www.luxdrive.com/content/MicroPuck-Applications.pdf They have different ways of wiring it up. For use with 2 AAs, choose the boost driver circuit.

    Which Luxdrive LEDs are you using? So we can look at the datasheet? Maybe the modules you chose have a driver built-in already.
     
    Last edited: Mar 17, 2014
  3. jpinc

    jpinc

    9
    0
    Oct 2, 2013
    Thank you for your quick response.

    The red LED is found here.Luxeon Rebel - Endor Star 1-Up Green High Power LED
    http://www.ledsupply.com/leds/cree-xpe-indus-star-1-up-red-high-power-led

    And the Green is the Cree XPE - Indus Star 1-Up Red High Power LED.

    I am interested in the brightest colored leds I can find that will operate on 2 or 4 AA batteries.

    Also to note, for this circuit, either light will go on for a maximum of just over a second. And there will be hours until the next time its engaged. So I believe the heat wont be an issue?

    I will rewire the micropuck in the next hour to see if that improves the output. If you need any more specifics let me know.

    Thank you again.
     
  4. kpatz

    kpatz

    301
    80
    Feb 24, 2014
    The Micropuck 2009A can drive up to 350 mA, while your LED is rated for up to 700 mA.

    When you drove the LED directly from the AAs, the internal resistance of the batteries likely kept the current below the 700mA maximum (so your LED didn't burn out), but higher than 350 mA. If you have a multimeter, measure the current both with and without the Micropuck.

    To get the max brightness and retain the reliability of the LEDs, I'd find a boost driver that can supply ~600-650 mA of current. You'll also need something beefier than AA batteries. With the short durations the LEDs will be on, a large capacitor would allow AA batteries to work.

    If you can use a higher supply voltage (4-6 AAs instead of 2), you could get by with just a series resistor or a constant current driver to limit the current. The green LED has a minimum forward voltage of 3.4V so without a boost driver you'll never get that LED to light very bright on two AAs.
     
    Last edited: Mar 17, 2014
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