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  1. #1
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    general question about LED drivers

    So Iím now very familiar with led drivers. I know they act as current sources, but from there the effectiveness comes from? Is this because they give as much voltage as LED needs with a fixed current, depending on LEDís internal resistance? I have 4 3W ledís bought from Hon Kong the only spec. they had is: If=750mA, Voltage min3V, max3.2V. I will be running them with 12AA rechargeable batteries 3000mAh. I was thinking to run them separately 3x1.2V. Would I benefit from a LED driver, because I only need to drop voltage by 0.4volts? If so is there any cheap DIY one?

  2. #2
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    Quote Originally Posted by zmogedra
    So Iím now very familiar with led drivers. I know they act as current sources, but from there the effectiveness comes from? Is this because they give as much voltage as LED needs with a fixed current, depending on LEDís internal resistance? I have 4 3W ledís bought from Hon Kong the only spec. they had is: If=750mA, Voltage min3V, max3.2V. I will be running them with 12AA rechargeable batteries 3000mAh. I was thinking to run them separately 3x1.2V. Would I benefit from a LED driver, because I only need to drop voltage by 0.4volts? If so is there any cheap DIY one?
    Yes you need a driver of some sort because battery voltage is not constant. For a NiMH it varies from 1.0 to 1.4V.
    You can use a resistor to drop the voltage but efficiency is not so good.
    DIY LED Bike Lights:
    A few Dynamo builds and some Small battery lights

  3. #3
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    Ok, now I know that I need a led driver and Nimh batteries for every 0.1C discharge voltage drops by ~1.25V. Maybe you know a DIY driver? I think it could also include a PWM mode to save some of that juice.

  4. #4
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    Quote Originally Posted by zmogedra
    Ok, now I know that I need a led driver and Nimh batteries for every 0.1C discharge voltage drops by ~1.25V. Maybe you know a DIY driver? I think it could also include a PWM mode to save some of that juice.
    For cheap LM317 is ok and easy to find. I use this for bench testing.
    It needs a 3V overhead which might be ok depending on your LEDs(at 1A Vf varies from 3.25 to 3.7 for different LEDs).
    http://users.telenet.be/davshomepage/current-source.htm

    Heres an intro to drivers and theres a list at the bottom
    http://www.videofoundry.co.nz/ianman...vers_why.shtml

    Check out dealextreme for low cost drivers.
    Check out taskled for high quality.
    DIY LED Bike Lights:
    A few Dynamo builds and some Small battery lights

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