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 LM7805 - What's wrong? 

Last post Tue, Nov 20 2012 3:06 PM by borntonag. 2 replies.
Started by borntonag 31 Oct 2012 12:32 PM. Topic has 2 replies and 1252 views
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  • Wed, Oct 31 2012 12:32 PM

    • borntonag
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    LM7805 - What's wrong? Reply

     Hi,

    I'm trying to simulate a adjustable current source (from 4mA to 20mA) but something is wrong with the circuit and I can't identify what I'm doing wrong.
    Can someone please help me?

    Best regards.

    Note: Circuit  attached.The middle one is where I need help, the other two are just for reference.


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    • Post Points: 20
  • Wed, Oct 31 2012 2:02 PM

    • oldmouldy
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    • Joined on Tue, Jul 15 2008
    • Woking, Surrey
    • Posts 1,446
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    Re: LM7805 - What's wrong? Reply
    There is no return from the input to output. You probably want the 7805 GND terminal to go between the right hand resistors and the lower end of the right hand resistor to go back to the 0 node. You will probably need to adjust the resistor values......
    • Post Points: 20
  • Tue, Nov 20 2012 3:06 PM

    • borntonag
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    Re: LM7805 - What's wrong? Reply

    oldmouldy thank you for your very quick response, but it's seems this circuit doesn't work for what I'm looking for, which is a adjustable current source (from 4mA to 20mA).

    This adjustable current source is to replace the current source on the circuit attached.

    The goal of the circuit is to simulate a sensor which output range is from 4mA to 20mA, and convert that output current to an interval from 0V to 5V.

     This is working fine with a current source but I can't use one, so I need to replace it with a similar circuit, that's why I was trying to use a LM7085 but I came to the conclusion it won't work as it is supposed to, with such low values of current.

    Any suggestions of an equivalent circuit I can use to replace the current source?

    Best regards

     


    • Post Points: 5
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Started by borntonag at 31 Oct 2012 12:32 PM. Topic has 2 replies.