Guidelines for a super stable linear PSU?

Discussion in 'General Electronics Chat' started by TheLaw, Jan 16, 2011.

  1. TheLaw

    Thread Starter Member

    Sep 2, 2010
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    Hello everyone,

    I'm trying to build a super stable power supply. I've been roaming the internet for just about an eternity but I can't find exactly what I am trying to figure out.

    My question is mostly about capacitors.

    What kind of capacitors do I use? Where in the circuit do I use the capacitors? What value capacitors is best?



    This section is me asking every possible question about power supplies and capacitors. Reader beware.

    So to explain that further. I should have a high value electrolytic before the voltage regulator. Should any other type of capacitor be used before the regulator? I've heard a ceramic should be on the input and output of a regulator. Should I use a metalized polypropylene film instead? Or strictly ceramic?

    On the secondary side of the voltage regulator, I should have another high value electrolytic. What other types of capacitors should be there? More films? Ceramics? What do different types of capacitors do? How do I determine the value? What order should the capacitors be in? Electrolytic, film, ceramic? Does it matter?


    Okay, I recognize that I just asked about 6,000 questions. That's just me belting out all of my problems that I've been trying to figure out.

    If you can answer just one or two, I'd be very happy. Please don't be bewildered by my questions.

    I appreciate it.

    Thanks.
     
  2. bertus

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  3. radbrad

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    Jan 17, 2011
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  4. timrobbins

    Active Member

    Aug 29, 2009
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    TheLaw, it seems that you're really just after a standard regulated power supply from a generic constant voltage regulator (aka 7805), and need to read thoroughly the application notes available from manufacturers of the regulators. Or do you have some super special application?

    Ciao, Tim
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    What's the difference between a Regulated PSU and a stable PSU or/and a Super Super stable PSU.

    I dunno what the OP wants but what I built is far better than anything I can buy here.
     
  6. TheLaw

    Thread Starter Member

    Sep 2, 2010
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    Hehe. I just meant...More stable than the average regulated linear supply.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    You might look at the uA723. It's been around for quite awhile. Much better than your typical LM317 regulator.
     
  8. bertus

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  9. TheLaw

    Thread Starter Member

    Sep 2, 2010
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    Wow, those look lovely. Too bad they can't push too much current. For a 5V regulator, is the Texas Instruments TL780-05 better than a standard LM7805. By specification, it seems to have better line/load regulation, but I can't be sure.
     
  10. TheLaw

    Thread Starter Member

    Sep 2, 2010
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  11. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    What do you mean by stable? The 7805 isn't unstable.
     
  12. TheLaw

    Thread Starter Member

    Sep 2, 2010
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    Stable probably wasn't the right word. I mean: Ultra low ripple and good voltage regulation.
     
  13. TheLaw

    Thread Starter Member

    Sep 2, 2010
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    And where do you find these application notes that have the component selection guides? These voltage regulator datasheets don't include much of that. I've seen component selection guides on switching regulators and op-amps, but none on linear regulators.
     
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U don't seem to understand.
    The IC regulates and the transistor handles any current u desire.
     
  15. TheLaw

    Thread Starter Member

    Sep 2, 2010
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    Oh you are <snip> right. I was about to say....this beautiful regulator with 150uA max? What a shame.

    I understand it now...Hmm....It's a possibility.
     
    Last edited by a moderator: Jan 17, 2011
  16. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    A stock 7805 is a 1A regulator, the 78S05 is 1.5A

    What do you need ultra low ripple for? What are you powering?
     
  17. TheLaw

    Thread Starter Member

    Sep 2, 2010
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    It's just a theoretical question. I don't really have anything to power as of now. Maybe a small amp or something later on.
     
  18. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    That greately depends on what you mean by low ripple. For a 5v regulator it could be 10mV for someone, 1uV for another.

    Also the speed at which it can regulate makes a difference. You could want 100ns settle time after a severe change in current, or you could do with much slower response.

    So lets get some practical numbers in here, what amount of regulation do you need?.
     
  19. tom66

    Senior Member

    May 9, 2009
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    Generally you shouldn't worry about any less than 20mVp-p ripple on a 5V supply as it's not going to make a significantly audible noise.
     
  20. Wendy

    Moderator

    Mar 24, 2008
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    Most IC regulators (such as the 7805) are very good. Look at the data sheet, going from memory I believe it is 60db, which is in the nanovolt region. As long as the ripple going into the regulator is above the power up range of the regulator you should have nothing to worry about.
     
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