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Constant current source

Discussion in 'General Electronics Discussion' started by StellenboschStudent, Jun 17, 2010.

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  1. StellenboschStudent

    StellenboschStudent

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    Jun 17, 2010
    I am trying to build a constant current source with the following specs: Current, from 0.5mA to 1mA, load resistance varies from 10k-ohm to over 1M-ohm.
    I have been working on this for a while now, and it works fine for low loads, but as soon as the load gets too large, the current varies too much.

    Any suggestions?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    If you want 1mA through 1Mohm then you need a voltage source greater than 1000 volts.

    Is your input voltage that high?
     
  3. StellenboschStudent

    StellenboschStudent

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    Jun 17, 2010
    Yes, I am aware of that, and yes, my voltage source can handle that (can go up to 3000V)
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Eeek! Then you're going to need seriously high voltage parts and I'm not even going to try to suggest a design.

    What do you need this for?
     
  5. NickS

    NickS

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    Apr 6, 2010
    Out of curiosity what parts are you using? (MFR & MFR P/N)
     
  6. StellenboschStudent

    StellenboschStudent

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    Jun 17, 2010
    It is for a post-grad project. Doing electrodeposition to grown nanowires...

    Jeez, I am not sure now. We bought a digital voltage source, not sure what the specs are.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    How rapidly does your load resistance vary?

    How easily is the voltage source interfaced to?

    Is it possible to monitor the current across a series resistor and use the voltage drop to provide feedback to alter the voltage setting?
     
  8. NickS

    NickS

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    Apr 6, 2010
    Good Idea.
     
  9. StellenboschStudent

    StellenboschStudent

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    Jun 17, 2010
    It does change rather rapidly, but I think this method will work. Will give it a try, thanks.
     
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