Why is LM7805 output 4.94 volt only instead of 5 volt?

Discussion in 'General Electronics Chat' started by dante_clericuzzio, Jun 12, 2016.

  1. dante_clericuzzio

    Thread Starter Member

    Mar 28, 2016
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    Hi i would like to ask opinion from any experience/experts here...I am testing the LM7805 that i just purchased and using 9.6 volt battery...based on the datasheet it should produce at least 5 volt or a little more like 5.2 volts..However the output i see is only 4.94 volt my questions is

    Is the LM7805 defect or am i missing something here?

    Zoom Pictures - 02016-57-12-10-57-11.jpg
    Zoom Pictures - 02016-56-12-10-56-53.jpg
     
  2. dl324

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    Mar 30, 2015
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    Unless you're buying a screened part, tolerance is 5%.
     
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Electronic components have a tolerance. The LM series of voltage regulators are not precise devices, and 4.94 V is within the guaranteed range. Check the datasheet for its exact tolerances. There are other regulators that are more precise and there are ways to add some components to fine tune the output of the LM7805; again, this is described in the datasheet.
     
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  4. dante_clericuzzio

    Thread Starter Member

    Mar 28, 2016
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    Thank you for all the feedback now i understand
     
  5. bushrat

    Member

    Nov 29, 2014
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    4.94V is not bad for 7805.
    If you need precision, consider using LM317 (or LM338 if you need high cirrent)
    [​IMG]
     
  6. dl324

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    From a TI datasheet:
    upload_2016-6-12_8-20-19.png
     
  7. tracecom

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    The Fairchild datasheet specifices +/- 4%. And for good regulation, you need a .33uF cap from the input to ground and a .1uF cap from the output to ground.
     
  8. Nykolas

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    Aug 27, 2013
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    And who said your meter is accurate? E
     
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  9. ISB123

    Well-Known Member

    May 21, 2014
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    That meter has 0.5% accuracy.7805 is working fine since its within the 5% tolerance.
     
  10. dante_clericuzzio

    Thread Starter Member

    Mar 28, 2016
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    Thank you for the suggestion actually i am trying to find a circuit diagram that uses 9 volt to output 5 volt and 1.5 amp to 2 amp current. But i couldn't find any....do you have suggestion or this is not possible to use 9 volt battery?
     
  11. ISB123

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    9V battery wont live long enough with 1-2A current draw.
     
  12. tracecom

    AAC Fanatic!

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    An ordinary 9V battery will be depleted very quickly with a 1.5 to 2 amp drain. What are you trying to power?
     
  13. dante_clericuzzio

    Thread Starter Member

    Mar 28, 2016
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    It's okay if it is doesn't live long enough - but if it is possible would you mind to share the circuit diagram how it can be done
     
  14. ISB123

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    May 21, 2014
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    [​IMG]

    LM7805 will require a heat sink if high currents are drawn.
     
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  15. dante_clericuzzio

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    Mar 28, 2016
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    Thank you very much ISB123 i will try this and see how it goes
     
  16. ISB123

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    Diode is not needed if you make sure to connect the battery correctly.
     
  17. dl324

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    Assuming alkaline battery chemistry, you'd be lucky to get 5 or 10 minutes before the regulator dropped out.
    RAYOVAC 9V Alkaline Battery:
    upload_2016-6-12_8-54-26.png
     
  18. eetech00

    Active Member

    Jun 8, 2013
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    LM7805 is only good for 1A max...
     
  19. ISB123

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    They can go above 1A with a beefy heat sink.
     
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  20. bushrat

    Member

    Nov 29, 2014
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    LM338 is your best choice, it has max 5A output. (provided you have sufficient source to power it up)
    LM317 only has 1.5 A and you need heatsink.
    7805 can only provide 1A and you need heatsink if you are going over 0.5A
    Driving 2A from 9V battery will last you for few minutes before voltage starts to drop.
     
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