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Variable Current Limit with Steady Voltage

Discussion in 'General Electronics Discussion' started by ag273n, Feb 28, 2017.

  1. ag273n

    ag273n

    74
    4
    Nov 24, 2016
    several months ago, i created my variable power supply using an LM317 - it was working great and I have been using just about on every electronics experiment I do... but that PSU can only output 1.5A max and cannot limit the current output.

    now i have the LM338 - which can do 7A max, and i want it to include a way to limit the current output (variable) with a steady output.
    so how do you make a variable limit to the current draw - with the same voltage?

    upload_2017-2-28_16-10-45.png
    the above diagram is what i'm hoping to build...
    i tried looking up online for any tutorials, but i could hardly find one thats worth reading...
     
  2. Audioguru

    Audioguru

    2,613
    590
    Sep 24, 2016
    When you limit the current then the voltage drops according to Ohm's Law.
    A second LM338 can be used as a current limiter ahead of the voltage regulator. A current limiter and a current regulator are shown on the datasheet of the LM338.
     
    ag273n likes this.
  3. ag273n

    ag273n

    74
    4
    Nov 24, 2016
    i found this from the datasheet:

    upload_2017-3-1_10-34-18.png

    so i'm guessing just connect this in series to the earlier schematic i have... correct?
     
  4. Audioguru

    Audioguru

    2,613
    590
    Sep 24, 2016
    Of course. Probably ahead if the voltage regulator.
    This current limiter has a voltage drop so the input voltage must add it to the voltage regulator input requirement.
     
    ag273n likes this.
  5. ag273n

    ag273n

    74
    4
    Nov 24, 2016
    Thanks a lot :)
     
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