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voltage controller circuit update

Discussion in 'Electronic Design' started by [email protected], Jul 1, 2007.

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  1. Guest

    I think i fixed some of the problem

    I am using following circuit, made following changes;

    I have replaced R2 resistor with Potentiometer -- 25k.
    like this one

    It's three pint, a, b, c

    a is connected to ground
    b is connected to r1 resistor and adj
    c I don't know where this goes....
    Added 1N4002 diods across voltage regulator -connected to in and out
    Also input capisitor is a big one.

    Finally on output voltage I have added 35v tantalum capacitor.

    I am able to control the voltage, however I am not get zero at all..

    resister for testing current 1kohm
    (measure by dimm) 992ohms

    This is the output.
    input voltage is 15.12 (regulated adaptor)

    current 15.29ma

    minimum voltage 1.281v
    current 1.29mA

    maximum 14.26v+
    current 13.63mA

    I want miminum voltage to be 0, how do i do that? Also my regulated
    adaptor has two output 15v and 30v, and I will be using 30v b/c some
    of the circuit require 20v --- like series, and parallel circuits and
    few more complex circuits -- school work. I am very new to this stuff
    -- like two weeks.
  2. DaveM

    DaveM Guest

    Download the datasheet for the LM317 regulator from
    Look in the suggested applications section of the sheet. There is a schematic
    there that will allow you adjust the output to 0V. It requires a few more
    components but it will get you there.
    Note that the example schematics show use of the LM117, but they are
    functionally equivalent to the LM317; just a wider temperature range.
    Be sure to mount the regulator chip on a good heat sink. The metal chassis of a
    typical construction box should suffice. Use the 30V output of the adapter.
    The regulator can handle it.

    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in the

    "In theory, there isn't any difference between theory and practice. In
    practice, there is." - Yogi Berra
  3. neon


    Oct 21, 2006
    LM317 is a regulator that has a regualtion of 1.2v no matter what i have no idea why 0v shut the power off that will do it. of supply a negative voltage to r2 and then you can go down to 0 volts is the only way.
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