Driving LED to full brightness

Discussion in 'General Electronics Chat' started by Cyberduke, Mar 5, 2011.

  1. Cyberduke

    Thread Starter Active Member

    Mar 5, 2011
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    HI, I am kind of new to electronics but 'n am very eager to learn. I am looking for a simple cuircut to drive a LED to full brightness using only one AA cell. Any help or suggestions will be appreciated. ps. Sorry for any launguge or spelling mistakes English is not my first language,
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Hmmm, it can be done, but not simply. You didn't mention color, different colors of LEDs need different voltages to turn on, after that it is the current that is important. Once a LED is conducting, the current determines the brightness.

    Red LEDs typically need at least 2.2V, sometimes up to 2.6V depending on the part.

    Blue LEDs start at around 3.3V, and go up to 3.7V. White are modified blue LEDs.

    See the problem? You don't have enough voltage.

    There is a solution, make a simple joule thief. A Joule Thief boosts the voltage from a single battery using several transistors, but maximum brightness is not predictable anymore.

    Your call, how do you want to go?

    I have a tutorial on LEDs and more advanced projects...

    LEDs, 555s, Flashers, and Light Chasers

    BTW, Welcome to AAC!
     
  3. Cyberduke

    Thread Starter Active Member

    Mar 5, 2011
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    Thank you for suck a quick reply I would like to power an ultra bright yellow LED.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Do you have specs? A datasheet answers a lot of questions before they're asked.

    Right now I'm tentatively assuming 3.0Vf at 20ma, maybe 30ma.

    Check out Chapter 7 - The Joule Thief, Figure 7.1

    There are much better designs out there though.
     
  5. Cyberduke

    Thread Starter Active Member

    Mar 5, 2011
    33
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    Hi here is what I did: 'n build this execact joule thief

    http://trailfriendlyradio.blogspot.com/2008/12/ki6sn-trail-friendly-joule-thief.html

    But it is not working correctly.('n have used a blue LED) When 'n plug the wire that came from the bead(I have used a small ferrite bead-about a 1cm in diameter) the Led stays off but when 'n plug the wire out it flickers quick. I am not shure where my mistake lay. Any help would be appreciated.
     
  6. Cyberduke

    Thread Starter Active Member

    Mar 5, 2011
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    Here is an unclear picture of my build:
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    The picture is not really viewable. The most likely problem is the coil you've made, as it is polarity sensitive. The wire arrangement from the coil is critical, connect it wrong and it will not work.

    The other thing is you really should use magnet wire. Make sure the base is not shorted anywhere else.

    The only advantage of my design (yours is better) is there is no polarity issues with the coil.
     
  8. Cyberduke

    Thread Starter Active Member

    Mar 5, 2011
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    I have got it right (it was the polarity of the coil) but then I unfortunatly pushed it off the table and the wires came loose so now I can't get it to work I have gone tru the cuircut a lot of limes but still nothin...
     
  9. Cyberduke

    Thread Starter Active Member

    Mar 5, 2011
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    I would like to know what type of wire should I use on my ferrite bead I dont exacly know what you mean by magnetic wire should Enameld copper wire work?
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Yeah, enameled wire, aka magnet wire. Wire wrap wire also has thin insulation, which is what you really need.
     
  11. Cyberduke

    Thread Starter Active Member

    Mar 5, 2011
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    I got it working for one moment but then it stopped again. Too bad. HAHA Could you please give me a discripsion of Wire wrap wire?
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    It is solid core wire with a thin, easy to remove insulation.

    You need insulation on the wire, but not so much as to interfere with the winding being close and tight on the core. The wire needs to be tight, maybe superglue? As I mentioned before, polarity is critical.

    Don't assume your transistor is still good. I'm betting it is good, but you don't know for sure.
     
  13. Cyberduke

    Thread Starter Active Member

    Mar 5, 2011
    33
    1
    I know this post is overdue but but I was busy with schoolwork and exams. I finally got it 100% right the problem was the polarity. Thank you for the help I appreciate it.
     
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