SMPS switching Transformer

Discussion in 'General Electronics Chat' started by kevco, Oct 24, 2009.

  1. kevco

    Thread Starter New Member

    Sep 24, 2009
    8
    0
    Hi all, any one know the best way to test a SMPS transformer in or out of circuit?

    Checking windings, core...

    Thanks,

    Kevin
     
  2. Thav

    Member

    Oct 13, 2009
    82
    0
    You probably want it out of the circuit. If there's a manufacturer's name and part number on there you should at least check their website or call them to try to get information about it. Falco and Pulse are pretty good about handling requests like that, and Renco has a fairly standardized product range.

    If that doesn't work, get it out of the circuit. The first thing you can test is just the turns ratio with a frequency generator and an oscilloscope. The other things you might want to know are leakage and magnetizing inductance. If you have a good bench LCR meter, this is easy.

    To find leakage inductance, solder the secondary leads short and measure L across the primary leads. Depending on the application this could be 1-5uH. More or less is possible! Leakage is a function of uncoupled flux between the two windings.

    To find magnetizing inductance, open the secondary leads and measure L across the primary leads. If the transformer has more than say ten turns to a winding, I would expect this to be the 300-700uH range. This is a function of the primary winding's inductance and is unaffected by the secondary.

    To check self resonance, use the same setup as above and do a frequency sweep. The impedance of the primary should stay relatively constant until some point where it will drop. This is where the parasitic winding capacitance swamps out the magnetizing inductor. This should be at least 10x your switching frequency.

    I don't know of any good way to test core losses, but it is dependent on frequency and ΔB, which is proportional to the V-s product. This link has some info on how you might measure this. http://web.mit.edu/6.013_book/www/chapter9/9.4.html
    I've never done this one. The loss in the core is basically the energy stored minus the energy recovered. You can read that off the B-H curve as in the attached picture.

    Here's some info on saturation. If you measure the B-H curve, you should be able to get a handle on this one as well. There are other methods, but if you've already got the B-H curve, why bother?
    http://www.coilws.com/index.php?main_page=page&id=104

    Good luck!
     
  3. @android

    Member

    Dec 15, 2011
    178
    9
    Does trafo the winding gets heated? And what is the effect of increased temperature on the trafo? Any failures??
     
  4. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    what is the smps from?
     
  5. @android

    Member

    Dec 15, 2011
    178
    9
    SMPS transformer!
     
  6. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    let me ask the same question in a different way-what is your power supply out of?tv dvd pc or electric toaster?
     
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