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Regulator noise

Discussion in 'Electronic Basics' started by Michael, Aug 7, 2005.

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  1. Michael

    Michael Guest

    I'm wanting to put together an xmtr and rcvr pair using some Linx modules
    (ES series 916mhz) and it's a very simple straightforward process to get it
    done but....

    I'd like to learn some more about the power supply requirements and the
    issue of regulator noise.

    I see alot of suggestions for using a LDO regulator like a Micrel part and
    it seems that it's not just the fact that's low drop out but also has a good
    "noise figure". (The spec sheet says the module needs a supply with noise
    and hash below 20 mv).

    I'd like to use one of my LM317 parts if possible (because I have a ton of
    them).

    I know any circuit generates noise but where are the concerns with power
    supply regulators? What is going on in the regulator and what is the freq
    spectrum of particular concern?

    Sure, I know all about fighting 60hz ripple...but I'd like to hear about the
    higher freq components that are in the mix.

    I suppose the fact that the 317 requires a larger input voltage (compared to
    a LDO) is a factor in noise generation as well?

    THANKS for help.
     
  2. Andrew Holme

    Andrew Holme Guest

    The LM317 is perfectly adequate for your application. The datasheet quotes
    internally generated regulator noise as a percentage of output voltage. The
    frequency spectrum of concern is low to audio frequency.

    Higher frequencies are dealt with using passive power supply filtering and
    decoupling e.g. using 100nF decoupling capacitors, and - if necessary - RF
    chokes.
     
  3. Michael

    Michael Guest

    The LM317 is perfectly adequate for your application. The datasheet
    Which is something I've always done......OK, thanks.
    I just looked at the datasheet on the 317 and see they show it as a
    percentage (.003) from 10hz to 10khz.

    (15mv for a 5v output?)

    If it's audio be choosy and use good design but if it's RF
    again, use good design but...
    the internal noise isn't a factor?
     
  4. Andrew Holme

    Andrew Holme Guest

    ..003% of 5V is 0.15mV
    Low frequency noise on the power supply can be a problem in any application.
     
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