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LEDs - Series or Parallel?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by sjaguar13, Dec 19, 2003.

  1. sjaguar13

    sjaguar13 New Member

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    I need 10 blinking LEDs. What's better, a series or parallel, or doesn't it matter?
     
  2. pike

    pike Member

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    parrallel-they are all the same brightness.
     
  3. panic mode

    panic mode Well-Known Member

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    It depends........

    I would rather try to keep them in series. It's the
    current that dictates the brightness so if you want
    same brightness this is definitelly way to go.

    All diodes are different and have different curve.
    If you put two in parallel, one is always going to draw
    more current than another meanining different brightness.

    It is possible to select diodes with very similar
    characteristic specially if they come out of same batch.
    However this requires patience and maybe quite few LEDs
    to match one perfect pair.

    It is possible but rather unpractical to do this for three or four
    LEDS and very difficult for ten or more and even more so if
    they are different color.

    Sure you can parallel them and if you are lucky all of them
    will also illuminate (even the different color ones) but
    this will stress some of them more than other.

    You can however put resistor in series with each LED
    instead of one resistor for ten LEDs in parallel.

    This way current for each LED can be regulated individually.

    Connecting LEDs in series means less resistors and simpler
    wiring. Only problem is if the supply voltage doesn't allow
    LED string of size you want. In that case, brake it into two
    or more strings (each with one resistor) and put those
    in parallel.

    Resistors should be selected to keep current in reasonable
    limits (14-16mA for classic LED or ca 2mA for Organic LED).
     
  4. dave

    Dave New Member

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  5. sjaguar13

    sjaguar13 New Member

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    I'm not really good with electronics. It took me 7 months to figure out how to make the 10 LEDs blink. I have a 9 volt battery with one resistor total infront of 10 red LEDs. Are you saying to use more resistors or use do it in series? Should I put them in series, but go from resistor to LED to resistor to LED for all 10?
     
  6. dingo

    dingo New Member

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    You should be able to put 5 LEDs in series without any resistor at 9v
    or you can put them in parallel with one resistor in series, or in parallel each with their own resistor. In the long run if you are using identical LEDs it does not matter.
     
  7. Sebi

    Sebi New Member

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    For best efficiency apply this circuit for 9V. The normal red LED forward voltage about 2V, the super-brite about 1,7V.
     

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  8. csaba911

    csaba911 Member

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    as I remember you should always use resistor, even if is only 2 ohm !!
    right ? or no ?!

    STEVE
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I would say so, it's certainly not good practice not to limit the current in some way.
     
  10. sjaguar13

    sjaguar13 New Member

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    The LEDs have to go in a straight line, and space is limited. It would be easier to do them parallel with one resistor total, but I heard that wasn't the best because of battery life. In a couple hours, the battery would be dead. Is that true?
     
  11. ChrisP

    ChrisP New Member

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    In a given series circuit of simple resistances, the current remains constant throughout the series string, while the voltage divides, or is dropped by each successive resistance.

    In a given parallel circuit of simple resitances, the voltage to each parallel branch is the same, with the current s of each branch adding to yield the total circuit current.

    Simply put, 5 15mA LED's in series will, if properly limited, be seen by the souce as a single 15mA load, whereas 5 15mA LED's in parallel, assuming each is properly limited to that current, will be seen by the source as a 75mA load. Hence, the parallel circuit will likely deplete the source (battery) more rapidly...
     
  12. sjaguar13

    sjaguar13 New Member

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    Series it is. How do I get them to be equal in brightness, or doesn't that matter because they are all red? Do I use one resistor at the beginning, or one resistor infront of each LED?
     
  13. ChrisP

    ChrisP New Member

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    Assuming that all of the LED's are the same type and of the same specifications, a single limiting resistor before the series string will do the trick. The current, and therefore the perceived brightness, will be the same through each of the LED's in the series string, and will be limited through that string by the single resistor.
     
  14. sjaguar13

    sjaguar13 New Member

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    So 10 LEDs of the exact same kind with one 330 resistor in series would make all of them the same brightness and use less of the battery?
     
  15. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Yes, bearing in mind that your power supply needs to be high enough to power 10 LED's in series - at about 1.7V each you need 17V for the LED's, plus 3.3V across the 330 ohm (for 10mA through the LED's) - giving a total of 20.3V. At that you would only be wasting 33mW in the resistor, as you are going to flash them it will be less than that - 33mW when on, nothing when off (50/50 would give 16mW wasted). Identical LED's in series should all be the same brightness as they all get the same current.
     
  16. sjaguar13

    sjaguar13 New Member

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    So 1 9 volt battery won't be enough. I'd really need two 9 volt batteries?
     
  17. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Two would just about do it, but it would be close, and the LED's might well stop working as the batteries fade. Best solution is probably that posted above by Sebi - where you have three rows of LED's, you would simply have to choose the series resistor for the row of four to give the same current as the two rows of three.
     

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