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Low noise power supply - linear?

Discussion in 'Power Electronics' started by Cirkit, Feb 6, 2020.

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  1. Cirkit

    Cirkit

    122
    10
    Oct 28, 2015
    Is it possible to design a low noise, low ripple power supply using a switching design with an LDO?

    One typical application is for use with sensitive pre-amp circuits typically measuring pA/nA currents?

    The preference by many is to just use a linear power supply.
     
  2. HellasTechn

    HellasTechn

    1,524
    212
    Apr 14, 2013
    My opinion on this would be to use a linear PSU. The classic transformer with full wave rectifier and smoothing capacitor. Why would you use SMPS for such low currents? Unless if you wish to make it tiny in size.
     
    hevans1944 and Harald Kapp like this.
  3. Cirkit

    Cirkit

    122
    10
    Oct 28, 2015
    I'm just thinking power consumption if it were left on continuously.

    At what threshold would you consider using a switching design with an LDO?
     
    Last edited: Feb 7, 2020
  4. Ylli

    Ylli

    324
    84
    Jun 19, 2018
    Definitely a linear supply. Or if you really want a quiet supply, then use batteries.
     
    hevans1944, (*steve*) and davenn like this.
  5. davenn

    davenn Moderator

    13,575
    1,864
    Sep 5, 2009

    Maybe it would be helpful if you told us what you are doing, then you would get better answers, eg.

    voltage needed
    current needed
    run time needed
     
    HellasTechn likes this.
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,374
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    Jan 21, 2010
    I've looked at a number of designs for pA meters. There's more issues than just ripple, you want to avoid noise coming from all sources. Batteries can be contained within a shielded enclosure, once you go to mains operation, you note need to filter the noise coming in through your power supply and deal with capacitive (or direct) coupling via the power supply.

    Most pA meters don't require lots of power, and an alternative option is to use several small lipo cells in series. The charger for these will likely be noisy (as well as introducing coupling issues) so don't use it when you're charging.

    There's a very simple pA meter design that runs from a 9v battery and has a resolution down to 100's of fA. Have you seen that?
     
    bertus, hevans1944 and Cirkit like this.
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