LM317 basic adj regulator help

Discussion in 'The Projects Forum' started by Al Vince, Feb 24, 2015.

  1. Al Vince

    Thread Starter New Member

    Feb 24, 2015
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    For the life of me I cannot seem to get this simple circuit to work... I have created similar circuits in the past without any issues. I simply want to bring in 13v and output to an adjustable 2-12 volts. Seems simple right.

    I have tried multiple LM317s, multiple resistors, multiple pots, multiple breadboards... no matter what I do the volts out will only adjust between 10-12volts. Any help would be appreciated. I initially had the setup with the capacitors, but removed them to trouble shoot my issue.

    My layout with LM317, 240 resistor, 5k pot... LM317-issue.jpg

    Reference... variable voltage power supply.png
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    what happens if you short out the pot to ground?
     
  3. Al Vince

    Thread Starter New Member

    Feb 24, 2015
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    The pot is connected to the ground (-) already... can you explain what you mean. Sorry I am just a hobbyist ;)
     
  4. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I think I see a 750 ohm on the board. The regulator would like that to be 120 or at most 240 ohms.
     
  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    He means what is the output V when you add a wire right across your pot.
     
  6. ScottWang

    Moderator

    Aug 23, 2012
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    Th pins of LM317 shows in the circuit was wrong, if count the pins of LM317 from left are 1,2,3 then the 1--adj, 2-- Vout, 3-- Vin, so you have to recheck the circuit, the pins should be like this way, Vin=3, Adj=1, Vout=2, please check this.
     
  7. Al Vince

    Thread Starter New Member

    Feb 24, 2015
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    Yes I noticed half of the diagrams online don't show the correct pin numbers... if you check the photo, I got the right pins connected to the rights components... I think anyways.
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    I don't think the wiring on breadboard is right, please recheck it.
     
  9. ScottWang

    Moderator

    Aug 23, 2012
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    Is the front of lm317 facing the camera?
    Another problem is that the LM317 needs 3V drop voltage between Vin and Vout, so when you want a 12V output then you should input 15V.
     
  10. Al Vince

    Thread Starter New Member

    Feb 24, 2015
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    Yes that is the front of the LM317... even if I set the Vin to 15V then I get a range of 13V-14V. I have spent all day on this simple circuit. I have rechecked. The photo shows a different resistor, but even with a 240 I get the same results. I don't know how many diagrams I have downloaded, and printed out for reference.

    This is driving me crazy haha. I have built power regulators before.
     
  11. Al Vince

    Thread Starter New Member

    Feb 24, 2015
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    Rechecked... this time I added the caps... still, with about 13Vin.... I get a range of about 11V-12V

    WP_20150224_19_08_58_Raw__highres[1].jpg

    25V-Adjustable-Voltage-Regulator-Schematic.png
     
  12. Patrick Joseph

    New Member

    Feb 23, 2015
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    If you have an ohm meter then remove the trimmer pot and check the resistance between the terminals that you are using.
    As someone else mentioned, you stated that the fixed resistor that you are using is 240 Ω, but the picture shows a 560 Ω.
    That would throw off the LM317 resistor formula if you were using 240.
     
  13. ScottWang

    Moderator

    Aug 23, 2012
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    Please check R2, R3(pot) using multimeter.
    Do you have another LM317?
     
    Patrick Joseph likes this.
  14. Patrick Joseph

    New Member

    Feb 23, 2015
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    Rechecked... this time I added the caps... still, with about 13Vin.... I get a range of about 11V-12V

    Al, I hate to ask, but have you considered that your LM317 may be defective? Do you have others that you can try?
    I once burned one and it was nearly a dead short.
     
  15. Al Vince

    Thread Starter New Member

    Feb 24, 2015
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    In the new photo I have the 240 installed... removed the pot and checked the resistance between the two pot connectors... I got -7.5 on the 20k voltmeter setting. I am guessing that is 7500? Not sure if the negative symbol means anything.
     
  16. Al Vince

    Thread Starter New Member

    Feb 24, 2015
    27
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    R2 = 240
    R3 Pot = 5000
    I have retried another LM317... same results.
     
  17. Patrick Joseph

    New Member

    Feb 23, 2015
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    Al said "In the new photo I have the 240 installed... removed the pot and checked the resistance between the two pot connectors... I got -7.5 on the 20k voltmeter setting. I am guessing that is 7500? Not sure if the negative symbol means anything"

    You can't check resistance on the voltage setting. What brand and model of meter do you have? I might be able to help you with the dial settings
    so that you can measure resistance.
     
  18. ScottWang

    Moderator

    Aug 23, 2012
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    Is it possible the LM317 is not a real LM317?
     
  19. WBahn

    Moderator

    Mar 31, 2012
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    Replace the pot with a 1kΩ resistor and see what you get.

    Also, your photo labels indicate that you are running this between +12V and -12V. Are you?
     
    Patrick Joseph likes this.
  20. ScottWang

    Moderator

    Aug 23, 2012
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    I just thought the means of -12V is GND.
     
    Last edited: Feb 24, 2015
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