Voltage regulator issue

Discussion in 'General Electronics Chat' started by TheBellows, Apr 5, 2010.

  1. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    I bought a couple of 3.3V voltage regulators called LD1117v33, now i wonder why it says 3.3V on the chip and only about 0.6V on my multimeter?

    I've tried different power supplies and two vr's, but they always show 0.6V.
    Something like this has never happened to the other types of vr's i've used, which always show correct voltage output, so can anyone explain me what's happening here?
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Did you add the capacitors at in and output?

    [​IMG]

    What is the input voltage?

    Greetings,
    Bertus
     
  3. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Yes i did, like i always do with voltage regulators.
    There has never been a problem like this before, so i'm clueless...
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Helo,

    As you see the output capacitor is larger as with "normal" regulators.
    At the 78XX you will see 0.1 uF at the output, but here it is 10 uF.

    What is the input voltage?

    Bertus
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    For clarification, 100nF = 0.1uF.

    Your input voltage must be 4.3v or higher. I suggest 5v to 7v. Not too high, or the regulator will get quite hot.

    If you omit either capacitor, the regulator will likely oscillate at high frequency, and the output voltage will be very low. Low-dropout regulators are very sensitive to the presence or absence of the proper amount of capacitance. If your caps are too large, the regulator may shut down.
     
  6. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    I've used the right capacitor values and tried different power supplies.
    My intention is to use a 9V (unregulated psu, shows about 13V with no load).

    I use a ceramic 100nF at the input and a 10uF electrolytic at the output.

    Are these chips very sensitive to static or something?
     
    Last edited: Apr 5, 2010
  7. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    One of the PSU's i tried (may have been the one i tried first), i found out was actually a 6V battery charger, may this have destroyed the regulator?
     
  8. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
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    Are you aware that the input and GND pins are swapped relative to the LM78XX regulators?
     
  9. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    What do you mean, isn't the above illustration (figure 4.) showing the front view of the vr?
     
  10. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Omg, i just noticed that the pin layout in the figure does not correspond to the actual chip...
    Sorry for this, i'm feeling stupid.

    Thanks for the help guys, i should get myself a reading class.


    TheBellows
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The ground pin is at the middle at the 78XX and on the side at the LM1117.

    See the illustrations:
    For the 78XX:

    [​IMG]

    For the LM1117:

    [​IMG]

    Greetings,
    Bertus
     
  12. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Yes, my poor datasheet reading skills didn't pick that up.
    A stupid mistake, but it's almost like the manufacturer does it on purpose just to bamboozle hobbyists.

    Thanks guys, i won't do this mistake again.

    TheBellows
     
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