90 led's circuits

Discussion in 'Homework Help' started by myosff, Aug 18, 2013.

  1. myosff

    Thread Starter New Member

    Aug 18, 2013
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    dear all
    i need full diagram circuits for 90 led's sheet led's 5 mm blue and white and power supply 12 v

    many thanks
     
    Last edited: Aug 18, 2013
  2. LDC3

    Active Member

    Apr 27, 2013
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    JoeJester and Metalmann like this.
  3. myosff

    Thread Starter New Member

    Aug 18, 2013
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    no things please advice

    any help please
     
    Last edited by a moderator: Aug 19, 2013
  4. LDC3

    Active Member

    Apr 27, 2013
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    How can we help if we do not know anything about what you want. It's like saying, build me a car!
     
  5. myosff

    Thread Starter New Member

    Aug 18, 2013
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    need help to define all part for circuits
     
  6. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    You're not making any sense. I am guessing you are not a native English speaker. In that case, I suggest you try translate.google.com. It might help you to better explain what you want, and help us to better understand you.

    Matt
     
  7. absf

    Senior Member

    Dec 29, 2010
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    You have to tell us more about the LED. How many are blue and how many are white. How much current and voltage is required for each color of your LED......etc

    Allen
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    And let's not forget that this is the HOMEWORK Help forum. You need to show what efforts YOU have made to at least attempt a solution for YOUR homework problem.
     
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  9. myosff

    Thread Starter New Member

    Aug 18, 2013
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    all led's are 3.6 volt 75 mA and power supply 12 volt
     
  10. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    You didn't answer our questions.
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    Still waiting to see this "attempt" thing.
     
  12. myosff

    Thread Starter New Member

    Aug 18, 2013
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    now i don't need any help
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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  14. myosff

    Thread Starter New Member

    Aug 18, 2013
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    many thanks max
     
  15. WBahn

    Moderator

    Mar 31, 2012
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    So, either you figured it out on your own once you decided to make the attemp -- which is a great thing; or you concluded that we weren't going to just do your work for you and gave up -- which is a great thing.
     
  16. ScottWang

    Moderator

    Aug 23, 2012
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    If you want to light up the 90 LEDs, then you should doing as this:
    12V/3.6V=3.333, 90V/3=30 strings, the power only has 12V, so you only can using 3 LEDs in a string, and then you have to calculate the limited resistor for LED current limitation.
     
  17. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    Don't now what r u doing are u making light system??
    anyway just make 4 or 3 led series with series resistance of 100/220ohm 1/4watt as per requirement of intensity.
    and then connect all these series in parallel to 12v source...
     
  18. WBahn

    Moderator

    Mar 31, 2012
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    How do you figure that the OP will be able to power 3 LEDs in series if they are using 12 V and each LED has a forward drop of 3.6 V?

    At the requested intensity of 75 mA, a 100 Ω resistor will drop 7.5 V and dissipate well over 500 mW while a 220 Ω resistor will drop 16.5V and dissipate nearly 1.25W. So just where did you come up with the recommendation of using "100/220ohm 1/4watt" resistors?

    With three LEDs in a string, the voltage that needs to be dropped across the current limiting resistor would be

    Vdrop = 12 V - 3 x 3.6 V = 1.2 V

    To do this at a current of 75 mA would require a 16 Ω resistor and would dissipate about 90 mW. This may work just fine, but small variations in the forward LED voltage or the supply voltage could move the actual current around by perhaps 50%. If that's acceptable, then this is probably the way to go.

    But if the OP needs a more consistent and uniform current, it would probably be better to go to two LEDs in a string, meaning that the resistor would have to drop

    Vdrop = 12 V - 2 x 4.6 V = 4.8 V

    which would require a 64 Ω resistor (use a 62 Ω if you need it close or a 56 Ω or a 68 Ω if you can be a little loose) capable of dissipating 360 mW. So two 1/4 W 33 Ω resistors in series might be a way to go. With this, it is probably unlikely that the current will vary more than about 10% from the nominal value.
     
    Last edited: Aug 20, 2013
  19. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    OK, if there are 8 Led white in series with 220ohm at 1/2 or 1/4 watt resistor(in paraallel there are more than 1000's led) driving from 26V source is not giving good brightness, increasing voltage to 46V will damage the led?
     
  20. WBahn

    Moderator

    Mar 31, 2012
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    What, on Earth, are you rambling about? Who said anything about 8 LEDs in series? Or thousands of LEDs? Or about 26 V sources? Or about 46 V sources?

    Are you sure you are in the right thread on the right plane of existence?
     
    DerStrom8 likes this.
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