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Shim Inductor in Phase Shifted Full Bridge topology

  1. Feb 24, 2017 #1
    What is the purpose of the shim inductor and how exactly does it function in PSFB topology? I noticed that I had dramatically improved efficiency when I added a shim inductor to my circuit, not too sure how or why this works though.
  2. jcsd
  3. Feb 24, 2017 #2


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    Could you please post a schematic and link to more information about what you are asking? That would help a lot. Thanks.
  4. Feb 24, 2017 #3


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  5. Feb 25, 2017 #4

    Here in this document, on page 2. Ls is (plus Db and Dc). Made my circuit have much better efficiency.
  6. Feb 25, 2017 #5
    Hmmm, so it's really just to increase inductance? How does that help with efficiency? How strange. Also, how strange that I've never seen this application sheet and the 28950 is the controller I've been using! Thanks for the reply.
  7. Feb 25, 2017 #6


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    I think the problem is that the “leakage inductance” of a transformer primary is in parallel with and so is effectively short circuited by the (backward transformed) output load. That makes it “hard” to drive. By adding series inductance sufficient to cancel switch capacitance it relieves the switches of that in-phase charge transfer twice per cycle. It turns the real losses into a resonant energy circulation without real power losses.

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  8. Feb 25, 2017 #7

    Thanks, that makes sense. I'll keep trying to understand your post better. Here is the picture (hopefully it makes it)
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