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Short circuit protection with differential amp?

Discussion in 'General Electronics Discussion' started by eem2am, Nov 3, 2012.

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  1. eem2am

    eem2am

    422
    0
    Aug 3, 2009
    Hello,

    I wish to do load short circuit protection with a differential opamp (please see link)

    http://www.2shared.com/document/8HsEwxb1/s...ircuit_SCM.html

    (also attached)

    Do you think this will work?.....it just has to catch the flyaway short circuit current and stop it reasonably quickly.......if short circuit happens, then there will be periodic high current pulses from the battery , but this is better than high current all the time........the FET keeps getting switched back on to allow resumption of operation when the short is removed

    Battery current when load is short circuit....
    http://i48.tinypic.com/116ne68.jpg


    LTC1841 opamp DATASHEET
    http://cds.linear.com/docs/Datasheet/184123f.pdf

    The differential opamp doesnt have to be particularly accurate......but it does have to work....will common mode effects stop it from working suitably in this application?
     

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
    2,837
    Jan 21, 2010
    Any reason you don't use the output of the 555 to drive the gate of the mosfet directly?

    I think the circuit may be more complex than is required.

    Curiously enough, you've almost got a current limited switch-mode power supply there.
     
  3. eem2am

    eem2am

    422
    0
    Aug 3, 2009
    Thanks Steve,

    yes it does act like a current limited SMPS when theres a short......unfortunatley at the moment it never really allows the circuit to start up because it keeps tripping the fet off with startup inrush current.

    I didnt have the 555 directly control the fet because on the real circuit, a microcontroller also can switch the FET on , and keep it on throughout inrush..........oh i see what you mean.....maybe i can still do this and loose some of those BJT's......will look into it.
     
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