LM317 Calculator

Discussion in 'General Electronics Chat' started by chrissyp, Sep 18, 2008.

  1. chrissyp

    Thread Starter Active Member

    Aug 25, 2008
    82
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    Hi All
    I am new to the forum. i am a electronics troubleshooter for a uk company,specialising in power supplies and led lighting control.One of the regular transistors i use is the good old LM317. I have an EXCEL file to calculate R1 and R2.You can either key in the voltage you require and one of the resistor values or both resistor values and it will tell you the voltage you will get. The problem is either i am being thick of it's this b****y vista but it will not let me import it into a thread. If anybody can help me i will import it as i think there will be members that will find it useful.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    It's because .xls is not an allowed format for file attachments.

    You will need to use a file compression utility like WinZip or ZipGenius to create a .zip file, which you can then upload.
     
  3. raptor30

    New Member

    Oct 15, 2008
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    also, LM317 is not a transistor.
     
  4. chrissyp

    Thread Starter Active Member

    Aug 25, 2008
    82
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    OOooHHH Lets be picky
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    For windows I use 7-zip for zipping stuf.
    http://www.7-zip.org/

    • Supported formats:
      • Packing / unpacking: 7z, ZIP, GZIP, BZIP2 and TAR
      • Unpacking only: RAR, CAB, ISO, ARJ, LZH, CHM, MSI, WIM, Z, CPIO, RPM, DEB and NSIS

    Greetings,
    Bertus
     
  7. chrissyp

    Thread Starter Active Member

    Aug 25, 2008
    82
    10
    Hi SGTwookie and bertus
    Don't mis understand my response ,i am downloading a zip program and thank you for the help both now and back then when the question was first posted.
    My earlier response was aimed at Raptor30 for his pointless and unhelpfull post.I appologise to sgt wookie and bertus if there was any mis understanding
     
  8. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Where is the file my friend?
     
  9. chrissyp

    Thread Starter Active Member

    Aug 25, 2008
    82
    10
    Hi
    hopefull I will post it tomorrow, it is on my memory stick which I have left in my office at work , doh!!
     
  10. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    Honestly, it wasn't that pointless. The LM317 contains much circuitry (reference, opamp, pass transistor, etc) and shouldn't be confused with a transistor, as it often is, due to the typical TO-220 package.

    Steve
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Well, here's a version I whipped up.

    It won't flag all error conditions, but it's not bad. One needs to watch their power dissipation when Vin vs Vout differential is high with higher current loads.
     
  12. chrissyp

    Thread Starter Active Member

    Aug 25, 2008
    82
    10
    LM371 Calculator.zip

    here is the calculator.if you fill in the values in any of the blue rows(2,5,8) the grey box will give you the missing answer.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    You'll get slightly different values for R2 with my calculator than chrissyp's; that's because my version accounts for Iadj (current from the ADJ terminal) current flow through R2 where chrissyp's does not.

    In most cases it makes just a very small difference, perhaps 4mV to 10mV per 1V of output, depending upon actual Iadj.

    The LM317L requires a minimum of 5mA load to provide guaranteed regulation. Since Vref may vary as low as 1.2v and still be within specifications, in datasheets manufacturers may show a 240 Ohm resistor being used in some typical applications schematics. A 120 Ohm resistor is typically used for the standard versions of the LM317 if the load may occasionally be less than 10mA.

    If you will always have a minimum of 10mA load on the output, you can use a much larger value for R1. However, this will make Iadj much more significant in the selection of R2.
     
    Last edited: Oct 16, 2008
  14. Duxthe1

    New Member

    Sep 27, 2008
    9
    0
    Great post, I'm using the lm317 in a project but don't have Excel on my computer. Can someone calculate the values for me? I'm using a 5v supply and want a 3v output. I'm going to use a potentiometer for R2 so that I can trim the output +- a little. I have a 47k mini trim pot that would fit my board well but think it's value is way too high. Is it possible to use it with the right value for R1? If not what values are reccomended?

    Apologies for the somewhat relevant hiack.
     
  15. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    You can get free excel viewers, do a search.

    Steve
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    You should be able to read it with OpenOffice as well.
    http://www.openoffice.org/
    OpenOffice is a suite of tools that are more or less compatible with Microsoft Office, but it's freeware.
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    I wouldn't use your 47k pot. Even a 1k pot would be too large for this application, but a 1k 10-turn pot could be used.

    If Vref=1.2, R1 should be 120 and R2 should be 178.9 Ohms.
    If Vref=1.25, R1 should be 120 and R2 should be 167 Ohms.
    If Vref=1.3, R1 should be 120 and R2 should be 156 Ohms.
     
  18. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    Since we are exchanging spreadsheets here are my efforts at a ML317 calc (I think anyone who has ever used an LM317 has written a spreadsheet to work out the resistor values) and a rough and ready spread sheet for working out the minimum value of filter capacitor for any given rectified voltage and load.

    Both spreadsheets were written in Open Office. The Excel versions have not been tested on Excel software but in theory should work ok.
     
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