Power dissipation of 7805. how to calculate?

Discussion in 'Physics & Math' started by cato, Sep 4, 2006.

  1. cato

    cato less hate, more science Registered Senior Member

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    hey everyone,

    hey, does anyone know how to calculate the power dissipated by a 7805 voltage reg? if I know what the input and output voltages are, and the current being drawn through it, how would you calculate the power dissipation?

    would it be the difference between the input and output voltage times the current through it?
     
    cato, Sep 4, 2006
    #1

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  3. DaleSpam

    DaleSpam TANSTAAFL Registered Senior Member

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    Yes, exactly.

    -Dale
     
    DaleSpam, Sep 4, 2006
    #2

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  5. cato

    cato less hate, more science Registered Senior Member

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    ok, thanks. I could not remember, but that seemed like the way you would do it. it just makes sense =]
     
    cato, Sep 4, 2006
    #3

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  7. cato

    cato less hate, more science Registered Senior Member

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    yeah, I just figured I would check before I just assumed it was correct.
     
    cato, Sep 4, 2006
    #4
  8. Pete

    Pete It's not rocket surgery Registered Senior Member

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    Strictly speaking you should also add the no-load power, which is the input voltage times the current through the ground terminal. This appears to be 5 to 10mA for the 78xx regulators.

    It's not a big deal. For 8V in, 5V out at 1A, it changes the dissipation from 3W to maybe 3.08W.
     
    Last edited: Sep 5, 2006
    Pete, Sep 5, 2006
    #5

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