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Advice on LEDs for the hard of thinking

Discussion in 'Electronic Basics' started by J T Pearson Outdoor Training, Jul 14, 2004.

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  1. I am looking for some advice and a basic circuit to convert a conventional
    torch to LED. I want to use 6-10 white LEDs or possibly a mixtire of blue,
    white & amber. Guidance greatly appreciated.

    Jane Pearson & Bill Wheeler
    J T Pearson Outdoor Training
    12 Mountfort Street
    New Zealand
    Tel. 643 486 1363
  2. Probably better to buy one, like don't re-invent the wheel :)
    However if it's a personal 'Quest', basically if you are using the high
    output white leds there are several approaches. You can drive combinations
    of LED's by connecting them in parallel with a current limiting resistor in
    series with each.
    Many designs for 'pulsed current' circuits have been advanced.
    Really you have not given much information like how many cells and type you
    plan to use.
    There are many combinations and battery styles out there !!
  3. What I'm trying to do is convert an old Petzl head torch to LED. They take a
    4.5v MN1203 battery as standard but I also have an adaptor to use 3no AA
    cells instead.

    Jane Pearson & Bill Wheeler
    J T Pearson Outdoor Training
    12 Mountfort Street
    New Zealand
    Tel. 643 486 1363
  5. Fred Stevens

    Fred Stevens Guest

    There are special ICs to power multiple LEDS with equal brightness -
    have a look at the Linear Technology and Maxim/Dallas websites for

  6. Nichea white LEDs (model NSPW515BS) have a forward voltage drop of
    around 3.6V, with a test current of 20mA. If you use 6 to 10 of them,
    your torch will require between 120mA and 200mA. With a 4.5V supply,
    each LED will need a 47 ohm resistor. The resistor can be on either
    side of the LED.

    These NSPW515BS LEDs cost about $1 US each. You can get cheaper ones
    on EBAY, but according to recent experiments, they aren't going to
    last as long.

    Bob Monsen
  7. dan

    dan Guest

    What's that Lassie? You say that J T Pearson Outdoor Training fell
    down the old sci.electronics.basics mine and will die if we don't
    mount a rescue by Wed, 14 Jul 2004 20:47:56 +1200:
    Look here:
  8. Nichia NSPW500BS white LEDs are available from for
    a dollar each. This 500 is different from the 515 in that the beam is
    narrower, which is more appropriate for flashlights/torches. I've
    bought several hundred from him with no problems. The Hong Kong ones
    from Ebay are junk. :-(

    I use 33 ohm resistor in series with each for three AA cells because the
    voltage drops a bit when several LEDs are connected in parallel.
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