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Discussion in 'General Electronics Discussion' started by Soundzman, Mar 27, 2013.

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  1. Soundzman

    Soundzman

    11
    0
    Feb 21, 2013
    I am designing a small led panel .

    I used the led calculator to design the circuit for me .
    [​IMG]

    r = 1 ohm


    But the led's burns out in few seconds .

    I'm using normal led's and 12v( 3 amps ) as source .


    Please help
     
    Last edited: Mar 27, 2013
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    Beware calculated values with very small resistances like this.

    Repeat the process, except this time specify only 2 LEDs in each string.
     
  3. Soundzman

    Soundzman

    11
    0
    Feb 21, 2013
    Can you explain as in what i can do to make it work .

    Thanks a lot Steve
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
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    Jan 21, 2010
    What colour LEDs are these (I presume they're white) and what current do you want to run them at? (I assume 20mA)

    You have 4 strings of 3 LEDs. What you need is 6 strings of 2 LEDs.

    The resistor for each string of LEDs is about (12 - 2*3.5)/0.02 = 5/0.02 = 250 ohms. Use a 270 ohm resistor.
     
  5. Soundzman

    Soundzman

    11
    0
    Feb 21, 2013
    I 'm sorry , i new to all these things .

    I'm using Red Led for testing ( The board has all three colours connected as a different arrays ) .

    The storekeeper where i got the LEd from said , its 3 volts and 200 mA each.

    So ill try , 2 led and 270 ohm in series and 6 strings .

    Thanks steve . i'll try and get back to you .
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    You'll need to show us a picture.

    Are these LEDs on headsinks? (a picture will answer that question)

    Different colours have different forward voltages and will require different resistors.

    If they are really 200mA, then these are high power LEDs and are best used with a current source (now it's getting complicated)

    For more information go to the tutorials section (on the bar at the top ^^^) and look for the one that answers LED questions.
     
  7. Soundzman

    Soundzman

    11
    0
    Feb 21, 2013
    Thanks a lot Steve . I'll sure check out and make it work....
     
  8. gorgon

    gorgon

    603
    24
    Jun 6, 2011
    If the LEDs are 3V you may use 3 in series as in your drawing, but you need at least 15 ohms in series for the 200mA limit. Personally I would start with 150 ohm and look how bright they are with 20mA. You should be aware that red LEDs only drop around 1.7V, and this explains the burnout.
     
  9. Soundzman

    Soundzman

    11
    0
    Feb 21, 2013
    Thank you so much for the reply .



    Will this work for RED . Will i get maximum brightness with the following
    [​IMG]


    R = 10 ohm




    What about green ? what is the voltage drop ?
     
  10. gorgon

    gorgon

    603
    24
    Jun 6, 2011
    All depends on the LEDs you use. You need to look into the data
    sheet for the different parameters.
    Absolute max pulsed current is not the same as nominal continuous current, so the datasheet is the answer.

    This just an estimate:
    If you use normal small red LEDs with this circuit, you'll burn them out. Use R=100 ohm, this should give you a safe current at 12V.
     
  11. Raven Luni

    Raven Luni

    798
    8
    Oct 15, 2011
    Your calculator is crap. No other way to say it.
     
  12. gorgon

    gorgon

    603
    24
    Jun 6, 2011
    I think mine is working ok? :D
     
    Last edited: Apr 6, 2013
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