Power Supply Calculation

Discussion in 'The Projects Forum' started by krishnan_hari83, Feb 14, 2012.

  1. krishnan_hari83

    Thread Starter New Member

    Feb 11, 2012

    Please clarify my doubt.

    I am having 3 LEDs each of 4 V and 120mA.

    What is the power supply I must give under the following conditions.

    1. 3 LEDs connected in series
    2. 3 LEDs connected in parallel.

    Kindly advice me of the power supply calculation.

  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    In series u will need more than 12V @ 120mA max & one resistor.

    In parallel u will need 4V @ 120 X 3mA
    But I doubt this way would be advisable.
  3. wmodavis

    Well-Known Member

    Oct 23, 2010
    For series - 12 V @ 120mA
    For parallel - 4 V @ 360mA

    But as R! suggests best to have resistors which will limit current.
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    I always wonder how many millions of LED's have been destroyed in the past 10 years because people think you can just hook them up like a light bulb and off you go..

    Your power supply could be rated for 100V @ 50 Amps and still work just fine provided you include some sort of current limiting into your schematic (like a resistor in series with the LED to limit the current or other constant current supply)
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
    You might like to consider a series connection of two parallel pairs.

    That way you can run from a 9V battery and a 4R7 half watt resistor.