need some help

Discussion in 'General Electronics Chat' started by zeyad, May 31, 2014.

  1. zeyad

    Thread Starter New Member

    Jul 7, 2013
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    0
    i am looking to design a circuit that gives continious 20 mA DC output using battery source
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    An LM317 3-pin regulator with a resistor chosen to give 1.25v @ 20mA (R=E/I, R=1.25/0.020, R=62.5 ohms) will make a constant current source.

    Headroom will be approx 2.75v when it is regulating, so a 9v battery will produce 20mA up to about 6.25v.
     
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