variable current source

Discussion in 'General Electronics Chat' started by nikomas, May 24, 2011.

  1. nikomas

    Thread Starter New Member

    Mar 31, 2010
    Hi everyone.
    Please can you help me to understand how work this circuit what I have found on internet? Thank you.
  2. BillB3857

    Senior Member

    Feb 28, 2009
    What part of the circuit do you not understand? Left op amp section or right op amp section? Is this homework?
  3. nikomas

    Thread Starter New Member

    Mar 31, 2010
    It is not homework. I just find that on internet. I don't understand circuit in global. I think that I understand how left section work (like current source). But how is that related with right part?
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Both amps are connected to run in a constant current mode.

    Left amp will turn left fet on and keep the voltage across R1 = Vin. This makes the current thru the fet Vin/R1, which flows thru R2.

    Right amp keeps the voltage across R3 same as the voltage across R2 with both referenced to Vcc.

    The current thru R3 that develops will drive Io, thus this is a current SOURCE.

    If you eliminate everything above & to the right of the VN2222 that point is a current SINK.
    nikomas likes this.