Isolation Transformer Question

Discussion in 'General Electronics Chat' started by danielb33, Jan 18, 2016.

  1. danielb33

    Thread Starter Member

    Aug 20, 2012
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    I have never seen a tranformer used this way. Can someone explain? Looks like isolation.

    upload_2016-1-18_12-51-12.png
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    That is called a balun. Differential signals enter on 1 and 2 and exit on 3 and 4. The coupled inductors act as a common mode choke, exhibiting high inductance (and impedance) to common mode signals while have relatively little effect on the differential signals. This is a common technique to filter radiated noise from RF and other high frequency signals.

    ak
     
  3. danielb33

    Thread Starter Member

    Aug 20, 2012
    105
    0
    Thanks!
     
  4. Ramussons

    Active Member

    May 3, 2013
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    The explanation of working is fine, but the term "Balun" is not. It is a Series Filter.
    "Balun" is a short form of the "Balanced" to "Unbalanced" transformer used to interface Balanced Transmission Lines to Unbalanced. Like a 75 Ohm Coax feeder to a 300 Ohm Antenna.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    its called a common mode filter, used in filtering noise off power lines. very common in switching power supplies.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Yup. My bad. A while ago I combined the two in three straight projects, and they got compounded in my little brain.

    ak
     
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