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Hello can somebody tell me, how come 10mA this current source

Discussion in 'General Electronics Discussion' started by michael1978, Jan 8, 2018.

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  1. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    can somebody tell me this circuits calculations, how come 10mA
    please
    1.gif
     
  2. Audioguru

    Audioguru

    3,305
    703
    Sep 24, 2016
    The base-emitter voltage of the 2N5401 Q6 is about 0.62V when it begins to turn on. When Q6 turns on it begins to cutoff Q7 so the current in R9 and Q7 is constant at 0.62V/62 ohms= 10mA.
     
  3. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    ooohh thank you very much
     
  4. Terry01

    Terry01

    206
    48
    Jul 5, 2017
    I guessed the answer was to do with the transistors before I got to see Audioguru's detailed answer to the question.
    I didn't know the exact numbers but I guessed that was where the 10mA reading was coming from.
    I am learning :)
     
  5. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    yes 10mA audioguru
    answer
     
  6. Terry01

    Terry01

    206
    48
    Jul 5, 2017
    We will learn a lot from the more experienced guys Michael. I have learned a lot by just reading other peoples posts. :)
     
  7. AnalogKid

    AnalogKid

    2,501
    719
    Jun 10, 2015
    Note that the schematic in post #1 has a problem. The high impedance and high compliance 10 mA output point is not the emitter of Q7. It is between the collector of Q7 and ground. If you want the 10 mA to go off and do something like light an LED, that is where to connect it.

    ak
     
  8. michael1978

    michael1978

    388
    2
    Mar 17, 2012
    yes that is ture, thnx the forums
     
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