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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 http://en.wikipedia.org/wiki/Image:Pot-pic.jpg

    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
    pins.
    --------------------------
    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
    http://www.national.com/ds.cgi/LM/LM117.pdf
    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
    address)

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

    neon

    1,325
    0
    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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