Current Injector Question

Discussion in 'General Electronics Chat' started by Engr, Jul 27, 2011.

  1. Engr

    Thread Starter Member

    Mar 17, 2010
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    Hello Everyone,

    I want to ask what is the purpose of a current injector. I saw a current injector circuit but I don't know the purpose of a current injector.
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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  3. Engr

    Thread Starter Member

    Mar 17, 2010
    114
    5
    I have already read the article on the url mentioned above, I still don't get how a current injector works and when is this kind of circuit needed. As I look at this circuit, it is just like a current source.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Ok, I agree it's not described, HOW it works. But the WHY it needs to be implemented is explained in the article. "to reduce the turn-OFF switching transient of power bipolar semiconductor devices (like IGBTs)"

    Could you please post the circuit you saw?
     
  5. Engr

    Thread Starter Member

    Mar 17, 2010
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    Attached file is the current injector circuit that I saw. This circuit is from the TI's "Handbook of Operational Amplifier Applications"
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Ok, forget everything I wrote before. You where talking about an opamp current injector. :)

    One of its purposes can be for example to determine the resistance value of a component. The circuit provides a constant (known) current which passes through the unknown resistance. By measuring the voltage drop over the component one can determine its resistance.
    The ""Handbook of Operational Amplifier Applications" mentions also another purpose of the current injection on page 44.

    In your particular case however it's not clear, it seems to have a different purpose, because if we assume the input voltage as constant, the current through the resistor changes with its resistance value...
     
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