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  • high efficient and easy to modify

    posted by Tobias on 12/30/2007
    0

    Involvement:Expert (understands the inner workings) - Ownership:1 week to 1 month

    Pros:

    This board has a good efficiency. Out of stock I measured maximum 92% at input voltage at which switch mode starts (3,5..4V depending on Vf) and minimum 76% (at 9V).
    It's easy even to improve this good efficiency to 95..82% with two cheep SMD capacitors on the board only.
    For applications providing enough space around the board, it is possible to flatten the output current upon input voltage and to make the device dimmable.

    Cons:

    1) The output current is NOT regulated and depends strongly upon the input voltage.

    2) Additionally the output current depends upon Vf of the LED used.

    3) There is no automatic switch down, so be carefull when using rechargeable batteries: You can destroy unprotected Li-Ion in case you take 2 of them in series and use it until light goes dark!

    OtherThoughts:

    First I bought 2 boards (8 pieces). Than I tested them and made many experiments modifying them.

    My aims were

    1) Constant current of about 350mA independent from input voltage.

    2) Additional possibility to dimm the board to about 35mA at any input voltage.

    3) Additional boost mode, not neccessarily constant but limited to about 800mA.

    At the end I found that this can be realized with only a few cheep external components.

    Now I ordet 10 boards (40 pieces) to start my first generation of headlamp for cavers.



    I can provide circuit diagrams and measurement results (diagrams), but I dont know how to upload pdf documents to this place. So I will upload for first a jpeg of one single side of such a document as an example.

    Bottomline:

    This device is good for modders and unbeatable at this price!

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