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small voltage regulator?

Discussion in 'Electronic Basics' started by Rick J., Jan 17, 2006.

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  1. Rick J.

    Rick J. Guest

    I want to power a small 3V LED blinky device for a week or so. Normally
    it runs off watch batteries, so I tried building a little
    flashlight-like container to hold it and a couple of AAA batteries.
    Maybe not too surprisingly, it starts to fade significantly in a day or
    so. After a couple months it's still blinking, but I'd much rather it
    have a shorter, brighter life.

    How can I use say, 3 AAA batteries to guarantee that the thing will run
    at full brightness as long as possible? The blinky light is very close
    to the diameter of the batteries, so of course I'd like something that
    could fit into the same tube. For that matter it would be OK to have it
    pulse at full brightness with 2 batteries as long as it doesn't take too
    long to charge up.

    Thanks,
    Rick
     
  2. ehsjr

    ehsjr Guest

    Use a circuit based on a TL499 or similar.
    http://focus.ti.com/lit/ds/symlink/tl499a.pdf
    As the battery voltage decreases, the output voltage remains
    unchanged, down to 1.1 volts on the battery. With 2 AAA's in
    series, 1.1 volts total is long after the batteries would
    normally be called dead. Whether you'll get a week with
    the circuit is anybody's guess, but you will get a solid 3V
    output right up almost to the end, and you'll get more total
    energy out of the batteries by using them after they would
    normally be called dead. *However*, if you use rechargeables,
    running them that way is not good for them.

    Ed
     
  3. Rick J.

    Rick J. Guest

    That looks like the way to go! Thanks, I'll try it.

    Cheers,
    Rick
     
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