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LED Circuit Question

Discussion in 'General Electronics Discussion' started by jaftwo, Oct 14, 2019.

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  1. jaftwo


    Oct 14, 2019
  2. Audioguru


    Sep 24, 2016
    The website you found says no details. The LED has a maximum allowed current and has a range of forward voltage that are shown on its datasheet.

    If the forward voltage of the blue LED is 3.3V then the current in the LED and in the 10 ohms resistor is (3V - 3.3V)/10 ohms= ZERO and the LED will not light or it will be very dim.
    If the forward voltage of a red LED is 1.8V then the current is (3V - 1.8V)/10 ohms= 120mA and the LED will blow up.
    Most 5mm diameter LEDs are spec'd to use a current of 20mA. Then a 1.8V red LED with a 3V battery will use a resistor that is (3V - 1.8V)/20mA= 60 ohms.
  3. bertus

    bertus Moderator

    Nov 8, 2019

    The led resistor can be calculated:
    Rled = ( Vsupply - Vfled ) / Ifled
    The Vfled will be different for each color.
    The attached PDF will show you rough figures for the colors.


    Attached Files:

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