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What is the reason for R7 in 317 regulator ?

Discussion in 'Electronic Basics' started by little billy, Aug 2, 2004.

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  1. little billy

    little billy Guest


    Does anyone know the 5A COnstant Volatge/Constant Current Regulator
    from the LM117/LM317A/LM317 regulator, it's on page 16 and is
    downloadable from

    I am curious as to the reason from R7=220.
    What will happen if we put R7=0R ?
  2. colin

    colin Guest

    i think it sets the voltage but it looks like theyve got vout and adj pin
    names transposed in that circuit.

    Colin =^.^=
  3. Rich Grise

    Rich Grise Guest

    It clamps the output when in constant current mode: if the load
    wants to be less than 5A, the voltage wants to climb to I * R.
    R7 is there to prevent that.

  4. Roy McCammon

    Roy McCammon Guest

    I haven't analyzed it, but I think it may be necessary
    for stability. Without it, the opamp looks like it
    would be driving a capacitive load.
  5. Rok Sitar

    Rok Sitar Guest

    R7 is in the circuit for Iadj. Take the time end read the instructions!
  6. little billy

    little billy Guest

    Hello my dear half baked engineers of this thread.
    I am afraid you were all wrong. I wonder, shall I
    tell, or shall I let you burn some more midnight
    oil over this one?
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