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Single Supply OPAMP instead of 741

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by tahoka, Sep 26, 2008.

  1. tahoka

    tahoka New Member

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    Please can someone suggest me an alternative to IC 741 in the basic V to I converter and non inverting amplifier circuit as we require an opamp which uses only a single supply.
    The input to V to I converter is 0 to 5 volts and output is 0 to 20 milliamperes.
    the output of amplifier is 0 to 5 volts.
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    What's wrong with just using a 250 ohm resistor?.
     
  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    You can buy V2I ic's, this is one example, single supply
     

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  4. Hero999

    Hero999 Banned

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    Because it isn't a normal standard value?

    Nevertheless it can easily made by connecting 240Ω and 10Ω in series or just use 249Ω which is a 2% value and is only 0.4% out in this case.

    However it seems like a pretty common thing to do so it wouldn't surprise me if you can buy 250Ω resistors specifically made for the purpose
     
  5. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    You can buy HS 250R's

    http://www.rhopointcomponents.com/products.asp?partno=H1L45AL
     
  6. Willbe

    Willbe New Member

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  7. Roff

    Roff Well-Known Member

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    A resistor works well if the load is zero ohms. If he is trying to make a voltage-controlled current source, well, ....
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    The load can't be zero ohms, it couldn't possibly work no matter what you did if it was :D
     
  9. Roff

    Roff Well-Known Member

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    It could be virtual ground. But you just made my point. If the load is other than zero ohms, then the current won't be Vin/250.
     
    Last edited: Sep 26, 2008
  10. Hero999

    Hero999 Banned

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    Last edited: Sep 26, 2008
  11. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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  12. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello,


    It would help if we knew if you need the load to connect to ground or
    not. If the load has to connect to ground the circuit is a little more
    complex than if it does not have to connect to ground.

    There are also sometimes simplifications possible if the input voltage
    generator does not have to connect to ground, so knowing this
    would be good too...if the input voltage source is floating.
     
  13. bnfdvn

    bnfdvn New Member

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    I did a Google search of 'single supply op amp' and came upon this thread. The original post could have been written by me today as this is exactly my dilemma. I implemented a Voltage to Current converter using a 741 Op amp with a single 24 V supply and it is not working correctly. The lower the voltage input, the more incorrect the output current is. I am assuming this is related to the common mode voltage or the single supply operation. (I'm not an analog wizard by any means.) It is good at 4.7 volts on the input. (I only have two input voltages in this application, 1 volt and 4.7 volts).

    Then I read the posts in this thread and realized that the load that I will be driving goes to ground so this won't work for me. So my question becomes, "How do I implement a voltage to current converter with a 24 VDC supply and 5 VDC supply that will drive a grounded load?" The XTR110 is looking better all the time but the cost is more than I had hoped for. Any suggestions will be greatly appreciated!!
     
  14. Willbe

    Willbe New Member

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    Howland Current Pump?
     
  15. Roff

    Roff Well-Known Member

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    How much current do you want with 1V in? How much with 4.7V in?
     
  16. bnfdvn

    bnfdvn New Member

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    I would like a 4-20 mA output proportional to the 1 to 5 volt input.
     
  17. Roff

    Roff Well-Known Member

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    4-20mA into what load?
     
  18. bnfdvn

    bnfdvn New Member

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    500 Ohms maximum but probably more in the neighborhood of 50-100 Ohms. I would like the design to be good for 500 Ohms, though.
     
  19. Roff

    Roff Well-Known Member

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    Sorry for the nitpicking questions, but what accuracy do you need? In other words, when the input is 5V, you want 20mA out. What percentage error can you tolerate?
     
  20. bnfdvn

    bnfdvn New Member

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    The circuit doesn't have to be super accurate. Within 2-3% would be okay.
     

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