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Help Identifying a transformer and it's use from a PC power supply

Discussion in 'Power Electronics' started by Kain6622, Dec 24, 2020.

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  1. Kain6622

    Kain6622

    11
    1
    Jul 14, 2020
    Good evening everyone,

    I've recently been disassembling my old PC for parts that I can use and on opening the PSU I came across multiple transformers but one stood out to the others due to its location (fixed to the size of the PSU shell) and also the fact it only has two cables connected to a two pin plug for the pcb.

    My first thoughts were that it might of been used as a large inductor but on closer inspection I'm not sure as one cable goes to each coil and there is tape covering the rest (maybe both coils are joined in series? will take a multimeter to it in a bit (not wanting to open or remove anything off it in case i damage it).

    Does anyone know what it's function is in this unit and shed some light on what it is used for or can be? (Pictures below)

    I've tried searching the web for it but i can't seem to find a PSU that has this in it.

    Any help will be much appreciated.

    Kind regards (and Merry Christmas)
    Dave

    (Update: On taking a multimeter to it, it would be apparent that the coils are connected together with a resistance of 1.7Ω, so it seems like it might be used for energy storage... maybe?)

    PSU1.jpg PSU2.jpg PSU3.jpg
     
  2. Martaine2005

    Martaine2005

    3,103
    851
    May 12, 2015
    These transformers are high frequency. Typically in SMPS. Some look exactly the same as common mode chokes.
    There would be several of these in a SMPS.
    Covered in tape is also typical.
    Just two wires? I’d guess an inductor too, but it sure doesn’t look like one.
    Your picture has two coils. Both common ground?.
    Who knows.

    Martin
     
  3. Kain6622

    Kain6622

    11
    1
    Jul 14, 2020
    when i connect the probes of the multi-meter across them

    Thanks for the reply, looking further into it, there doesn't seem to be any other connection ( I had thought that the common ground may be the screws that held the transformer to the PSU shell but on checking the conductivity of then with wires i have available nothing and they were just for holding the screws in place and have no relation to the transformers function).

    As in my update in the first post I get a resistance of ~1.7Ω, unfortunately I didn't take a photo of the transformer before i disconnected it and desoldered everything but the only connection that i had to remove was the one in the photo from the pcb:
    DSC_1522.JPG

    I'm totally lost with what function this would serve apart from an over-sized inductor,and from the cables each going to a difference coil would seem like they are paired (only guessing in series) with the resistance value i'm getting, interested to know what one would do with such a configuration/ why it would be needed hence why I came here in hope someone might be able to shed some light on the matter.

    Regards
    Dave
     
  4. Martaine2005

    Martaine2005

    3,103
    851
    May 12, 2015
    Well Dave, probably nothing you can do or use it for.
    It was designed specifically for its intended purpose.

    Unless anybody else can add something here.

    Martin.
     
  5. Bluejets

    Bluejets

    4,424
    938
    Oct 5, 2014
    Less the meter and leads resistance of approx. 0.4 in most instances.
     
  6. Kain6622

    Kain6622

    11
    1
    Jul 14, 2020
    The only thing I've found so far is What is this transformer-like component with only two leads. which helps and doesn't help at the same time, yes we gathered that it pretty much was an inductor but i'll need to look up techniques used for power factor correction to understand why it's needed in some smps units and not others and also get ideas on what i can used it for myself (I've used inductors for joules thief circuits and other oscillators but can think why i would need to use something so extreme just yet)
     
  7. davenn

    davenn Moderator

    13,722
    1,913
    Sep 5, 2009

    99% probability that it is a choke winding ....
    With only one winding (untapped) it cannot be a transformer
     
    hevans1944 and Harald Kapp like this.
  8. ramussons

    ramussons

    374
    71
    Jun 10, 2014
    From which part of the board did you unplug it from? A photo will give us some idea whether it's a choke or a transformer.
     
  9. davenn

    davenn Moderator

    13,722
    1,913
    Sep 5, 2009
    As I said prior, it cant be a transformer with only 1 winding
     
  10. Kain6622

    Kain6622

    11
    1
    Jul 14, 2020
    Yes I've accepted it is just a oversize inductor, it measures about 26.75mH (could be a margin of error as my oscilloscope is a handheld and I rushed finding the highest amplitude before solving for L in an LC circuit but will revisit when i think i might want to use it to make sure i have it as accurate as possible). Thank you for the help (and sorry for referring to it as a transformer, it just looked like one initially when i made the post).

    Kind Regards
    Dave
     
    davenn likes this.
  11. ColKlonk

    ColKlonk

    12
    2
    Dec 22, 2020
    It is a choke winding, most likely on the output of one of the voltage lines (5V or lower), physical configuration minimise noise.
    Switch Mode Power Supplies (SMPS) use these things all the time.

    The PC PSU is a Buck-Converter (Step Down) used at a fairly high frequency frequency.

    If you follow the AC input line you'll come across a filter section, with chokes (4 lead 'anti-phase') and other surge protectors.
    Followed on by a fairly large Full Bridge rectifier, Caps, feeding into this coil and a power fet.
    At the 'side' of this lot is the control section.

    Depending on the PSU design, you might see a mult-wound (different voltage outputs) isolation transformer instead of this coil, but the operation is basically the same - High frequency switching, with voltage control.

    Then again I could be mistaken and this might just be an input filter.;)
     
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