Current source circuit

Discussion in 'General Electronics Chat' started by someonesdad, Jun 22, 2010.

  1. someonesdad

    Thread Starter Senior Member

    Jul 7, 2009
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    The attached schematic is from an older Maxim application note that showed how to construct a current source for measuring low resistances. U1 was a voltage reference and U2 is a single-ended supply op amp. The recommended parts are no longer available from Maxim.

    1. I'm planning on building one of these. Do you experienced folks see any potential problems with the circuit?

    2. I will use an LM385 for the voltage reference, as I have one around somewhere. However, I'd appreciate a recommendation for a suitable op amp. My preference would be for a micropower one so that the 9 V battery lasts a long time.
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    Last edited: Jun 22, 2010
  3. someonesdad

    Thread Starter Senior Member

    Jul 7, 2009
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    Thanks, retched; looks like a good choice.
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
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    I guess every one agrees, Im surprised there has not been a hundred replies of peoples favorite op-amps. Or maybe they just realized for micropower, that is a pretty good way to go. And still in a pdip. Thats really great of Analog Devices.
     
  5. cjdelphi

    New Member

    Mar 26, 2009
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    oh so with one of these, you have to provide the voltage you want it to compare to? I figured you used some kind of resistor to specify the voltage you wish to compare it to, to say charge a battery? check for 4.2v but you have to supply 4.2v to the op amp?
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
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    Well, you are thinking of a comparator. opamps can be used as comparators, but for a mission critical, or more accurate comparison, a stand alone comparator is the way to go. Then you dont need a reference voltage, the comparators have them built in.

    You still can add a reference voltage if you prefer however.
     
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