Need help in controlling Voltage and Current

Discussion in 'The Projects Forum' started by plmrguest, Nov 20, 2015.

  1. plmrguest

    Thread Starter New Member

    Nov 20, 2015
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    0
    I am trying to control voltage range from 1.5 to 34 using LM338 voltage regulator with 1000u capacitor at the input 430u capacitor at the output with
    potentiometer @ the adjustment terminal.

    I have 37v and around 5 Amps current at the Vout but when i try to reduce the voltage using potentiometer,resistor 120 ohms burns out. Please suggest me how to control and get constant Voltage & Current.
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,988
    3,226
    You can get constant voltage or constant current, pick one, you can't control both at the same time.

    Post the schematic of what you have.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
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    Sounds like your 120 ohm pot is the constant current regulation resistor,better post your circuit for further assistance.
     
  4. plmrguest

    Thread Starter New Member

    Nov 20, 2015
    2
    0
    Here is my schematic for you reference i have both voltage and current , since we can't control both voltage & current
    so i need to keep the voltage constant 32V and current should be adjustable.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Last edited: Nov 20, 2015
  6. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    You can never have a higher voltage on the output of the regulator.
    There will be a dropout voltage of 1.5 to almost 3 volts depening on the drawn current:

    LM338_dropout_voltage.png

    Bertus
     
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