Invert current direction

Discussion in 'General Electronics Chat' started by talhaali, Jun 28, 2012.

  1. talhaali

    Thread Starter New Member

    Nov 24, 2011
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    i have made a voltage controlled current source , on its input if i give negative voltage then i get my required current direction but sumhow in my circuit i am unable to get this negative voltage , i have to make use of positive voltage instead , now please guide me how can i invert direction of my output current using this positive voltage at input.
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    And we are supposed to divine how this voltage controlled current source of yours works....how? ESP?

    Depending on how you implemented it, it may not be able to provide current in the opposite direction.

    It would sure help to have a schematic.
     
  3. talhaali

    Thread Starter New Member

    Nov 24, 2011
    19
    0
    i have attatched the achematics
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    Is there any reason you can't just follow the transimpedance amplifier that produced your control voltage with a unity-gain inverting amplifier to invert the signal?

    It sounds like you only need your current source to produce current in one direction, it's just that the present circuit is doing it in the wrong direction. Is that correct? If so, then I believe there are common variants of the Howland current pump that you are using (if I'm recognizing it correctly) that changes the polarity of the transfer function. If nothing else, you can also use a current mirror.
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,014
    3,234
    The Howland circuit has a differential input so you can ground R23 and feed the voltage into R22 to invert the signal polarity.
     
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