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How to decide input filter specifications for linear power supply design

Discussion in 'Power Electronics' started by Farukh Khan, Aug 10, 2021.

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  1. Farukh Khan

    Farukh Khan

    160
    2
    Jun 12, 2015
    Hello,

    I am trying to design a precision linear power supply and I have already chose a transformer which will meet my output requirements. Now, I am not sure how to figure out what parts should I use for EMC/EMI filters for the input of the transformer from main's AC. I have basic knowledge about X and Y rated caps and common mode chokes but I am not sure what specification or ratings parts should I choose to go with a simple ac filter input stage before hitting the primary winding of the transformer. The transformer I am using is: https://my.mouser.com/ProductDetail/Triad-Magnetics/VPM18-2780?qs=bdQtRzgkM2RlDm/tY2Kgow==

    Also, planning to use HRC Fuses for both the live and neutral mains input but not sure how to select the HRC fuses. What specifications I need in terms of trip current and time delay etc. Any help would be really appreciated. Thank You.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,667
    2,700
    Nov 17, 2011
    Designing an EMC filter can be tricky.
    Even more complex is measuring the effectivity of such a filter as it requires expensive equipment.
    I suggest you use a commercially available filter.
    One form is built into an IEC inlet, possibly the least space consuming method and in the ideal position next to the inlet. No long wires that can pick up EMC and radiate it to the outside.
    [​IMG]
    Another form is sealed modules that can be placed anywhere convenient. Here you'll have at least some additional wiring to do which can act as an antenna.
    [​IMG]

    Why HRC fuses? If your power supply isn't an extremely high power unit, standard glas tube fuses will suffice. These can be used with conveniently placed fuse holders for easy repair.
    upload_2021-8-10_6-46-45.png

    Fuses on both live and neutral are only required if reversal of the two is possible.
     
  3. crutschow

    crutschow

    119
    27
    May 7, 2021
    And what are your requirements for this "precision" supply?
    Does it have a regulator?
     
  4. Farukh Khan

    Farukh Khan

    160
    2
    Jun 12, 2015
    The goal is to learn how to design EMC filter for specific power supply use case and that's why buying a premade one is not an option here. @Harald Kapp Also, I was planning to put HRC fuses to avoid the arching problem of normal glass tube fuse. Want to use the best quality items possible for the supply.

    @crutschow Yes the supply does have a regulator. But I am trying to design the primary side first and then move on towards the secondary part of the supply.
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    11,667
    2,700
    Nov 17, 2011
    Do you have access to the necessary EMV testing tools to verify your design is doing what it's supposed to do? Without these tools your effort is imho wastedas you can't verify the effectivity of your design.

    Anyway, this website offers some webinars on EMC filter design, see under the heading "EMC Components".
     
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