5 volt regulator problem

Discussion in 'General Electronics Chat' started by yonitsubery53, Jan 21, 2014.

  1. yonitsubery53

    Thread Starter New Member

    Jan 21, 2014
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    I hooked up my 5 volt regulator (LM2940CT) to a 9 volt battery, but for some reason the output voltage is 6.5(approx.). I checked everything but i couldn't find the problem, I also tried different regulators but I still had the same problem.
    So if someone can tell me what might be the problem it would be great.
     
    Last edited: Jan 21, 2014
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    What is the full part number. Does it say, LM2940CT5.0? Or does it say LM2840CT9?

    The LM2940 comes in various voltage output versions.
     
    Last edited: Jan 21, 2014
  3. yonitsubery53

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    Jan 21, 2014
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    I said it was 5 volts
     
  4. t_n_k

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    Mar 6, 2009
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    Did you connect a load to the regulator output?
     
  5. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    That is awfully rude. Gopher is just trying to help and make sure you have the right part. What is wrong with providing the full part number that you are using? And a schematic for that matter?

    And you never answered the question on a load. Are you measuring the supply with a load?
     
  6. yonitsubery53

    Thread Starter New Member

    Jan 21, 2014
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    Yes a 130 ohm resistor which should be a big enough load according to the data sheet.
     
  7. yonitsubery53

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    Jan 21, 2014
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    Sorry, I didn't mean to be rude.
     
  8. yonitsubery53

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    Jan 21, 2014
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  9. tshuck

    Well-Known Member

    Oct 18, 2012
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    Do you have the capacitors connected?

    A schematic would answer a number of questions without having to ask them...
     
  10. yonitsubery53

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    Jan 21, 2014
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    Aren't capacitors needed just for smoothing out the voltage for frequency stuff ? (sorry if my questions are dumb)
     
  11. spinnaker

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    But does not answer if everything is wired correctly. :) Which should be checked, double checked, triple check and quadruple checked. ;)
     
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  12. crutschow

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  13. crutschow

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    Mar 14, 2008
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    No. They also stabilize the device to prevent oscillations (which can appear as a change in voltage when measure with a DC meter).
     
    Last edited: Jan 21, 2014
  14. yonitsubery53

    Thread Starter New Member

    Jan 21, 2014
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    Yes I checked a couple of times and I also changed the regulator and still I had the same problem.
     
  15. BillB3857

    Senior Member

    Feb 28, 2009
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    All of these responses and still not letting us now the FULL PART NUMBER!
     
  16. yonitsubery53

    Thread Starter New Member

    Jan 21, 2014
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    Yea, but don't you thing a 1.5 volt oscillation is a bit much
     
  17. yonitsubery53

    Thread Starter New Member

    Jan 21, 2014
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    Lm2940ct-5.0
     
  18. BillB3857

    Senior Member

    Feb 28, 2009
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    Carefully read the opening 3 paragraphs on Page 13 of the data sheet. They pretty well say it all.
     
  19. spinnaker

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    And no schematic. Two of the very first things that should have been posted.
     
  20. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    The 2940 and 2941 series are notorious for oscillating if you don't have the right input and output capacitors. When they do, a DMM will read the wrong output voltage because there is an AC component and it is peak reading that along with the DC level.
     
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