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Power a Luxeon Star with two AA batteries?

Discussion in 'Electronic Basics' started by BruceW..1, Sep 6, 2004.

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  1. BruceW..1

    BruceW..1 Guest

    I'd like to power a 1-watt Luxeon Star
    with two AA batteries.

    And I'd like to be able to dim the light. I've found that the Luxeon
    Star puts out useable light down to 50mA, or up to about 350 mA.

    This is for a headlamp to be used for camping and backpacking. Most
    manufacturers of these headlamps use 3 batteries and a voltage dropping
    resistor. IMHO, this is pretty cheesy and besides I'd like to mod one
    of my existing AA headlamps.

    Actually I'd like to make it run off of a single AA battery because I'd
    rarely use full brightness.

    Has Maxim come out with any new IC'c in the last year that might be
    right for the job? I just ran across this, don't know what's inside,
    but it doesn't dim:

    I'm no electronics expert but I'm smarter than the average bear in this
    respect and I can solder.

    Can anyone recommend a circuit?

    Thanks for your help.
  2. Build a switcher. There are lots of circuits available. Here is one:

    (View with courier font)

    VCC = .8 to 3V
    | | |
    .-. | C|
    470R| |<-' C| L1
    p1 | | C|
    '-' |
    | ___ || | D2
    | R1 | || | | |
    | | C1 | | |
    | | |/c | |
    o------------|----------| Q2 | |
    | | |> | .----'----.
    | | | | | |
    c\| | | --- | Luxon |
    Q1 |----------o | C2 --- | Star |
    <| | | | '----.----'
    | - D1 | | |
    | ^ | | |
    | | | | |

    C1 = 220pF
    C2 = 100uF electrolytic
    R1 = 10k
    Q1,Q2 = 2N4401
    D1 = 1N4001
    D2 = Schottky Diode
    L1 = 33uH High Q inductor, at least 1A rating.

    Put a 100 ohm resistor where your Luxon goes
    Then, adjust voltage to minimum value before putting on star

    You might want to use a power transistor for Q2. This circuit puts
    more than rated current across it

    created by Andy´s ASCII-Circuit v1.25.250804

    Its a simple boost switcher, based on a two transistor oscillator. The
    input voltage should be less than the forward voltage of the luxon +
    Schottky, or it won't oscillate, and the luxon and inductor will fry.

    I'm not sure it'll get all the way up to 350mA.

    Bob Monsen
  3. You might want to check out

    Streamlight makes a 2 AA Luxeon flashlight
    and a dimmable 3 AAA Luxeon headlight. I believe the flashlight
    has a DC-DC voltage converter, so it runs well on NiMH rechargeables.

  4. Spork

    Spork Guest

  5. Ken Smith

    Ken Smith Guest

    I'm making a small change:
    R2 gives Q2 a little protection. If a huge current tries to go through
    Q2, R2 will develop more than 2 diode drops of voltage and cut the "on"
    part of the cycle short.

    It doesn't add many parts (one) but its protection is not all that good.

    I'd use something faster for D1
    This is a good idea. Over current spikes can slowly kill a transistor.
  6. nospam

    nospam Guest

    The Linear Technology LT1618

    Looks like a useful part for this application. Unfortunately like most
    switchers for portable applications it is only available in tiny surface
    mount packages.
  7. Ian Stirling

    Ian Stirling Guest

    It'll put out a lot more light at low average currents if you keep the
    peak current at 350ma.
    For most of the SMPS chips available, they are significantly more efficient
    at a battery voltage of 2.4V, rather than 1.2V.
    You can probably get away with a step-up only device, 2 fresh alkaline AA
    cells won't provide enough current at ~3.5V to kill the luxeon device, even
    neglecting diode drops.
    Synch rectification will buy you a little bit, but not much.
  8. Ian Stirling

    Ian Stirling Guest

    What may also be useful would be a 3 cell device.
    2 AA 1.5V cells, and 1AA 3V cell, for emergencies.
  9. I have found the efficiency of red, orange and yellow Luxeons to be
    maximized at instantaneous currents somewhat less, maybe around 200 mA.
    For white and blue ones, the efficiency is maximized at even lower
    instantaneous currents around 100 mA or less.
    If your average current is around or over 50 mA and the Luxeon is a
    white one, I recommend steady rather than pulsating current. But if the
    average current is only a few milliamps, then you are better off using
    pulses with a higher instantaneous current - perhaps 50-100 mA.

    - Don Klipstein ()
  10. Zetex ( have a range of single and double cell LED
    constant current drivers that are used in many commercial LED

    Dave :)
  11. dan

    dan Guest

    What's that Lassie? You say that BruceW..1 fell down the old
    sci.electronics.basics mine and will die if we don't mount a rescue by
    Mon, 06 Sep 2004 00:33:27 GMT:

    Ask here:

    Search in the electronics forum.
  12. Check or reviews before buying the Argo
    headlamp. One review alleged the 3 AA batteries lasted only an hour.
    Would be very costly, if NiMH rechargeable batteries weren't used. The
    new model Argo may have an improved (more efficient) driver.

    What is the cost of building a LS 2-AA headlamp?
  13. Well, the 1W LS with lens, AKA -NW98, is about $16 or maybe a bit less.
    So I'd say that that's the most expensive part. You can also buy a kit
    of a LS and a Micropuck for about $25 and put into yout own case. I
    bought two of them from LED Supply and put them each in its own project



    Just make sure you heatsink the LS to some copper or aluminum.

    In my humble opinion, the candlepower guys are a bunch of elitists,
    trying to make some bucks. They make these good looking flashlights,
    but they all use CR123 lithium cells which cost up to $10 each or more,
    and are hard to find. I think the only way to go is the two AA cells,
    and use rechargeables if you use it a lot. Two AA cells are only fifty
    cents on sale. See
  14. dan

    dan Guest

    What's that Lassie? You say that Watson A.Name - "Watt Sun, the Dark
    Remover" fell down the old sci.electronics.basics mine and will die if
    we don't mount a rescue by Thu, 23 Sep 2004 05:02:14 -0700:
    You can get them for $1.00 at
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