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Problem with voltage regulator

  1. Aug 24, 2013 #1
    So I need to use this LM117t 3.3v voltage regulator and I asumed the pins were the same as most regulators where you have in/ground/ and out. But it is not working that way, does anyone know the in and outs of this regulator or have an alternative?
  2. jcsd
  3. Aug 24, 2013 #2


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    hey t-dude :smile:

    not its not ...
    its never safe to assume anythig in electronics... always test, measure and in this case check the datasheet


    page 3 gives the pin out configuration for the various package forms

    the output as you will see is the centre pin

    hope that's helpful :smile:

  4. Aug 24, 2013 #3


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    lm117 is an adjustable regulator. It works by generating an output voltage such that the voltage at the reference input (what was ground in a fixed output regulator) reaches 1.25V. So it you have R1/R2 divider with equal values the output will go to 2.5V producing 1.25V at the "center" pin. If you connect the output to the reference input you will get 1.25V.

    The datasheet that davenn linked to is for an LM1117 (different number, 3 1's) that is a family of fixed output regulators.
  5. Aug 24, 2013 #4


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    that's interesting as it was also saying 117 at that page

    LM1117T-3.3 - LM1117 3.3V Low Drop-Out Voltage Regulator
    Technical Information - National Semiconductor LM117T Datasheet

    I wonder if the TD typoed and was meant to say LM1117t-3.3 and not the 117t-3.3 that he did ???
    cuz he was pretty specific with the rest of the info. he wasnt referring to setting up an adj regulator huh

    so I will stick with the info I gave till TD reports back in
  6. Aug 24, 2013 #5
    MY BAD!


    The datasheet also says ground output input and I just tried that and i am getting the exact same output as I have input (9v)
  7. Aug 24, 2013 #6


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    show me a pic of you circuit digram and also a pic of your actual construction
    to see if you boo boo'ed :)

    that V-reg is different pinned to the LM78xx series fixed regulators where the GND pin is the centre pin

  8. Aug 24, 2013 #7
    those are the 2 ten caps shown in datasheet circuit

    Attached Files:

  9. Aug 24, 2013 #8


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    Hi TD

    through the dark blurryness :wink: it looks ok
    assuming you have put the electro caps in the correct way around ?

    you didnt have this connected incorrectly originally did you ?
    your opening comment
    indicates you probably did. you may have damaged the regulator, do you have another one to try ?

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