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Help choosing +15V reg: L7815CV or LM340T-15?

Discussion in 'Electronic Design' started by [email protected], Jan 25, 2008.

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  1. Guest

  2. Guest

  3. PeterD

    PeterD Guest

    Define 'better'...

    Describe your application and its parameters...
     
  4. Guest

    Better would be more stable and clean output voltage under, say, 20%
    to 50% load conditions. This reg is for the analog supply to the
    opamps of a Delta 1010 soundcard/audio interface which has 8 analog
    inputs A/D, 8 analog outputs D/A, 1 S/PDIF stereo input, and 1 S/PDIF
    stereo output. The input voltage to the reg is 23V with a ripple of
    about 1.2V. Thanks.
     
  5. ehsjr

    ehsjr Guest

    The 340 has better line & load regulation shown on the
    datasheet than the 7815. For load: The 340 shows 35 mV,
    5mA to 1.5A. The 7815 datasheet shows 150 mV for the same
    range. For line: the 340 shows 22 mV, the 7815 shows 150 mV

    It may be that "better" as you defined it does not matter
    in your circuit.

    Ed
     
  6. Guest

    I think you are comparing the LM340A. This is what confuses me about
    the datasheet. On the ordering info page, it lists the LM340A as
    available only for 5V. However, on the LM340A electrical
    characteristics (page 4) you can also see 12V and 15V. I did some
    searching on National's site and Newark, and it looks like the 12V and
    15V of the LM340A are no longer in production. Only the LM340 without
    "A" is available for 12V and 15V. Therefore, the plain LM340 is what
    I would like to compare. Looking at the LM340 electrical
    characteristics on page 5 of the datasheet, it seems that the LM340
    has inferior specs compared to the LM340A. Compared to the L7815, the
    LM340 has slightly inferior output noise voltage and ripple rejection
    specs. Based on this, I would like to confirm if you also think that
    the L7815 is superior, however slightly, to the LM340. Thanks.
     
  7. Fred Bloggs

    Fred Bloggs Guest

    Why don't you get a sample of both and compare their performance in the
    actual circuit...I hope you have advanced measurement methodology
    experience.
     
  8. ram27

    ram27 Guest

    u could go for a +12V supply than a 15V
    ram
     
  9. ram27

    ram27 Guest

  10. Eeyore

    Eeyore Guest

    Use an LM317. You can decouple the sense input ( 10uF cap with 220R in
    series from sense to GND) which helps reduce ripple, although I bet that
    won't matter much anyway to your circuitry, but it'll keep you happy
    perhaps.

    Graham
     
  11. Eeyore

    Eeyore Guest

    WHY ?

    Graham
     
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