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LED in series and parallel

  1. Apr 26, 2014 #1
    If i have a LED which drops 3V, and 30mA through each LED and i need 8 LED in series.. does it mean that i need a total of 24V and 30mA from power supply or less?
    And if i use the same circuit in parallel, does it mean i will use 3V but much more current like 0.24A?? or least current?
     
  2. jcsd
  3. Apr 26, 2014 #2

    psparky

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    For your series circuit, I believe you would need at least 24 volts at 30 ma.

    That's 720 mwatts from your source.

    For parallel, 3 volts will work with 240 ma coming from source, yet each branch will get it's 30ma.

    That's also 720 mwatts from your source.
     
  4. Apr 26, 2014 #3

    mfb

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    Why less? You'll need 24V and 30mA. It is safer to use a voltage a bit above 24V together with a suitable resistor in series.

    8*30mA of course. The same advice: use a resistor in series.
     
  5. Apr 26, 2014 #4

    Baluncore

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    LED current is highly sensitive to applied voltage and temperature.
    Each parallel path will require a resistor to stabilise the current in that path.

    Consider a 12.00 volt DC supply for 8 LEDs.
    4 LEDs in series would give no control of current at varying temperatures.

    3 LEDs and a 100 ohm resistor in each series chain would stabilise the current at 30 mA. One of the three chains will need an extra 100 ohm resistor or a hidden LED to make 8 visible LEDs total.

    2 LEDs with 200 ohms in series will be less efficient than 3 LEDs with 100 ohms.
     
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