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Thread: Looking for cheap boost chip 1.5v for LED

  1. #1

    Default Looking for cheap boost chip 1.5v for LED

    Just looking to drive 1 20ma LED from old batteries that are .7 to 1.5.
    Is there a chip for this or a REAL simple circuit to do it?

    Thanks

  2. #2
    *Flashaholic* mdocod's Avatar
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    Default Re: Looking for cheap boost chip 1.5v for LED

    the little dorcy 1AAA LED flashlight has one in it , not sure how far it can pull down the cells though. Might be cheaper to buy that light for $6 at the store than have something shipped, hard to say though.
    -Eric

  3. #3
    *Flashaholic* Illum's Avatar
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    Default Re: Looking for cheap boost chip 1.5v for LED

    the dorcy 1AAA 2nd gen measures off my multimeter at 240ma
    since its a DC-DC step up, the LED's not getting 240ma, thats for sure...from the output I'd say its around there

    I built this guy from scratch...and I'm out of 150uF electrolytic caps, so I used two 100uF caps
    using a new 1.5V alkaline AA It can boost to 3.3V, sufficient to light up a RX1H luxeon star...at about 100ma
    Last edited by Illum; 07-23-2008 at 09:09 PM.

  4. #4
    *Flashaholic* Gunner12's Avatar
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    Default Re: Looking for cheap boost chip 1.5v for LED

    Joule thief?

    The Dorcy circuit could work too.

  5. #5

    Default Re: Looking for cheap boost chip 1.5v for LED

    Saw that. Can I buy the coil from digi-Key? Which one.

    Thanks
    Quote Originally Posted by Gunner12 View Post
    Joule thief?

    The Dorcy circuit could work too.

  6. #6
    *Flashaholic* Illum's Avatar
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    Default Re: Looking for cheap boost chip 1.5v for LED

    Quote Originally Posted by ken2400 View Post
    Saw that. Can I buy the coil from digi-Key? Which one.

    Thanks

    unfortunately the coil is the most difficult part of the joulethief, and it has to be homemade because the schematics require it to have 4 wires instead of the usual 2, meaning you'll need a ferrite coil and wound one yourself. none of my homemade inductors as per the joulethief instructions actually gave me a light

  7. #7
    Flashaholic* TorchBoy's Avatar
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    Default Re: Looking for cheap boost chip 1.5 V for LED

    Quote Originally Posted by Illum_the_nation View Post
    none of my homemade inductors as per the joulethief instructions actually gave me a light
    That's sad. Don't give up!
    No, a torch does not always mean flames.
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  8. #8
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    Default Re: Looking for cheap boost chip 1.5v for LED


  9. #9

    Default Re: Looking for cheap boost chip 1.5v for LED

    Any idea what the lowest voltage this will do?

    Thanks
    Quote Originally Posted by jtr1962 View Post

  10. #10
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    Default Re: Looking for cheap boost chip 1.5v for LED

    Thank you JTR1962 for posting this circuit. I hadn't thought to ask on here but I wanted a simple low current boost circuit to play with and it looks like this is the ticket

  11. #11
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    Default Re: Looking for cheap boost chip 1.5v for LED

    Quote Originally Posted by ken2400 View Post
    Any idea what the lowest voltage this will do?

    Thanks
    It'll start at about 0.65 to 0.70 volts. Once started, it'll work down to about 0.5 volts.

  12. #12
    Flashaholic* Black Rose's Avatar
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    Default Re: Looking for cheap boost chip 1.5v for LED

    Quote Originally Posted by jtr1962 View Post
    Electronics noob question.

    R1 and R2 are resistors, Q1 and Q2 are transistors.

    What are C1 and L1?

  13. #13
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    Default Re: Looking for cheap boost chip 1.5v for LED

    C1 is a ceramic capacitor. L1 is an inductor.

  14. #14

    Default Re: Looking for cheap boost chip 1.5v for LED

    Thats GREAT!
    What is the volt of C1 and does it matter?

    Thanks

    Quote Originally Posted by jtr1962 View Post
    It'll start at about 0.65 to 0.70 volts. Once started, it'll work down to about 0.5 volts.

  15. #15

    Default Re: Looking for cheap boost chip 1.5v for LED

    Hey jtr, is the inductor in that design commercially available, or does it have to be hand-wound like the Joule Thief's? It looks a little more complex, but if it doesn't require any hand-made components, it could be pretty handy.

  16. #16
    datiLED's Avatar
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    Default Re: Looking for cheap boost chip 1.5v for LED

    The simple two transistor schematic that jtr1962 posted is a winner. I have built several drivers using it.
    Until further notice, I am not accepting new mod requests.

  17. #17

    Default Re: Looking for cheap boost chip 1.5v for LED

    if you have a walmart near they sold a raovac 1AAA LED penlight for cheaper than the dorcy unless you can find one on clearance. My walmart had the nichia dorcy for $4.50 on clearance
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  18. #18
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    Default Re: Looking for cheap boost chip 1.5v for LED

    Quote Originally Posted by TigerhawkT3 View Post
    Hey jtr, is the inductor in that design commercially available, or does it have to be hand-wound like the Joule Thief's? It looks a little more complex, but if it doesn't require any hand-made components, it could be pretty handy.
    It's just a standard commercially available inductor. No hand winding required.

  19. #19
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    Default Re: Looking for cheap boost chip 1.5v for LED

    Quote Originally Posted by ken2400 View Post
    Thats GREAT!
    What is the volt of C1 and does it matter?

    Thanks
    Voltage of C1 doesn't really matter as it sees no more than perhaps 4 volts. Most ceramics are rated at 50V at least.

    BTW, with some tweaking and changing of values it's possible to use this circuit to drive far more than one LED. I made a version which powers two strings of 14 LEDs in series from 4.8 volts (4 AA batteries in series). I don't remember what component values I used offhand as that was about 3 years ago. The circuit as shown drives the LED with an average of roughly 20 mA when powered by a AA cell. You can decrease R2 to increase the drive current, and vice versa.

  20. #20
    *Flashaholic* Illum's Avatar
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    Popcorn Re: Looking for cheap boost chip 1.5v for LED

    Quote Originally Posted by ken2400 View Post
    Just looking to drive 1 20ma LED from old batteries that are .7 to 1.5.
    Is there a chip for this or a REAL simple circuit to do it?

    Thanks

    well...simple as possible you could go down to two components...but I'd prefer to have filter caps on both the in and out
    0.9V- Boost Driver for White LEDs PR4401/4402


    All you need to change is the inductor value to get the appropriate current output.

    I don't think it gets easier than this, my soldering suck so SOT23 is no good for me because its a SMT component. but so far I haven't been able to find one that has it in the easy TO-220 packages

    minimum startup: 0.9V and could operate between 0.7V and 1.9V at 25C
    if the circuit is completed with 10uH inductor + 1 LED Vcc = 1.5V
    LED peak Vf [5.8V], mean current [20ma], mean supply current [70ma], efficiency [77%]

    these values are from a datasheet I have on the hard drive...I haven't been able to locate the right link to post to this post

    EDIT: found the link: http://www.prema.com/pdf/pr4401.pdf
    Last edited by Illum; 07-24-2008 at 02:09 PM.

  21. #21
    Flashaholic Tohuwabohu's Avatar
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    Default Re: Looking for cheap boost chip 1.5v for LED

    Quote Originally Posted by Illum_the_nation View Post
    I don't think it gets easier than this, my soldering suck so SOT23 is no good for me because its a SMT component. but so far I haven't been able to find one that has it in the easy TO-220 packages
    It's not that difficult. It has only 3 pins. You can solder it direcly to the leads of the LED as shown in the last image on this page. The inductor is beneath the PR4401.

  22. #22
    *Flashaholic* Illum's Avatar
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    Default Re: Looking for cheap boost chip 1.5v for LED

    last time I tried soldering a LT1111 in SOT23 was a brutal experience
    knowing that my solder iron's tip is thicker than a Macdonald's straw

  23. #23

    Default Re: Looking for cheap boost chip 1.5v for LED

    hi jtr, can you kindly repost the 2 transistor schematic ? Thank you

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