0-10vdc to 4-20ma to 0-5vdc loop circuit needed

Discussion in 'General Electronics Chat' started by NathanB919, Sep 8, 2010.

  1. NathanB919

    Thread Starter New Member

    Sep 8, 2010
    2
    2
    I have found several IC examples but this is a school project that requires the circuit to be made from discrete components, i.e. 741 op-amps, transistors, resistors etc. I'll be able to use the IC equivalent later, but not right now.

    Does anyone have any ideas? Any comments will be greatly appreciated.

    Thanks
     
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  2. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    You can use L.D.R. with ic 741 ( light activated switch).
     
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  3. sgardner025

    Active Member

    Nov 5, 2009
    79
    4
    You could probably put the 0-10V into a summing amplifier and go from there to a current source and another summing amp for the 0-5V.
     
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  4. Dyslexicbloke

    Active Member

    Sep 4, 2010
    420
    19
    If your using opamps .. go modern J-Fet or MosFet input so you can dispene with any input bias current, for practical purposes, it just makes things so much easer.

    The opamp examples on this site in Vol3 are great.

    As far as a current loop is concirned if you use an adjustable voltage reg configured as a constant current source but replace the series resistor with a fet you will be able to set the current with a voltage .. simple and loads of examples about.

    The data sheets for the LM317T has a bench PSU application circuit in it which demonstrates the adjustable current limmit using a FET as a variable resistor as well as the negative rail requirement ( -1.2v ) that is required to make the regulator adjust all the way to 0v.

    On that note pick an amp that will run from a single supply and includes, at least, ground in its output range even if it wont swing all the wat to Vcc.

    Obviously there hundreds of other possible solutions, possibly better ones I dont know about, these are just a couple of possible circuit elliments that may help get you started.

    Al
     
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  5. sgardner025

    Active Member

    Nov 5, 2009
    79
    4
    Any luck on this task so far?
     
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  6. NathanB919

    Thread Starter New Member

    Sep 8, 2010
    2
    2
    Thanks for your interest, I'm just now getting back to this project and will keep you informed. From what the instructor says the 4-20ma loop is much used in the industry. When I finish this project, I expect to use this circuit quite a bit. Thanks again for your interest.
     
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