What is a current source?

Discussion in 'General Electronics Chat' started by JStitzlein, Jan 30, 2012.

  1. JStitzlein

    Thread Starter Member

    Dec 6, 2010

    I'm trying to measure current using a transimpedance amplifier like this circuit:


    What I dont understand is how to wire a current source from a power supply. If i short the leads I see the current limit, but how can I use the power supply to replace the current source from this circuit?

    Perhaps I don't understand what a current source is.
  2. panic mode

    Senior Member

    Oct 10, 2011
    in theory opamp has no voltage difference between inputs.
    since one input is connected to ground, the other can be assumed to be at zero potential as well.
    this means you can replace current source with fixed voltage source and adjustable resistor (potentiometer).
    but 10uA is fairly small so assumptions on ideal opamp may not give you desired accuracy of the model.

    current source is source that maintains named current regardless what is connected to it. if open circuit (infinite resistance) in theory it would produce infinite voltage. real current sources are more down to earth. basically they measure current and if it deviates from target, it adjusts potential difference so that ratio of voltage and load resistance is constant.