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How to detect transformer saturation?

Discussion in 'Electronic Basics' started by larry moe 'n curly, Feb 9, 2006.

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  1. Is there a way to detect when a switching power supply's isolation
    transformer is starting to saturate? I've read, in a Linear Technology
    application note, that it can be done with a current probe and looking
    at the shape of the ramp -- straight line is OK, curved like a parabola
    is bad. But is there an easier way that doesn't require a current
    probe?
     
  2. Put a series resistor (0.1 ohms or so) in and connect an o-scope across it.
     
  3. n cook

    n cook Guest

    heat?
     
  4. Mark

    Mark Guest

    if you are working on power supplies and you don't have a current
    probe, get one, you'll be glad you did...

    Mark
     
  5. Guest

    Most SMPSes have a current sensing resistor at the emitter or source of
    the main output device. Just scope across that.

    If it doesn't have one, Charles is right, you can add one. You must
    however think about two things, one is that it must be a small
    resistance, and two if the chopper is bipolar, you need to make sure
    that degeneration of the drive current does not occur. What's more if
    the chopper is bipolar, you need to figure that some of what you're
    seeing is base current. It is not advisable to do this at the collector
    or drain, it's a shock hazard and radiates too much. You can't go to
    the AC rectifiers because of the nature of the signal you need.

    I cannot completely agree that the current waveform of the chopper
    being parabolic indicates transformer satuation in every case. Certain
    time constants, snubber schemes and other things chosen by the designer
    could cause an innacurate conclusion on your part. I think you can get
    really meaningful data just from the efficiency. But then you might
    have your own reasons for wanting what you want.

    I'd be interested in the application, or at least the capacity of this
    PS, is it like huge or something or are you trying to miniturize ? Just
    curious.

    JURB
     
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