Transformer impedance question

Discussion in 'Homework Help' started by ddickey, Nov 11, 2011.

  1. ddickey

    Thread Starter Member

    Sep 28, 2011
    55
    1
    Primary has 100 turns.
    Secondary #1 has 50 turns and a 10 ohm impedance.
    Secondary #2 has 25 turns and an impedance of 25 ohm.
    What is the primary impedance. I know the answer but don't know how it was derived. Any help would be appreciated.
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    I think you calculate the primary impedance from each secondary (using the turns ratio) and then parallel the two values on the primary side. I can't remember if the impedance reflects back using the turns ratio or the turns ratio squared? I suspect the latter.

    Is the answer about 36?
     
    Last edited: Nov 12, 2011
  3. jegues

    Well-Known Member

    Sep 13, 2010
    735
    43
    Use impedance matching to match the impedance on secondary #2 to secondary #1. Combine the two impedances and match that impedance to the primary winding.

    Impedance matching is related to the square of the two turns ratio through which you are matching.
     
  4. ddickey

    Thread Starter Member

    Sep 28, 2011
    55
    1
    The formula that my textbook taught number of windings primary/by number of secondary, square the answer and x the secondary impedance so my answer was coming up 62 ohms. Bounty Hunter, your answer is correct.
     
  5. ddickey

    Thread Starter Member

    Sep 28, 2011
    55
    1
    Got it, thanks guys.
     
  6. jegues

    Well-Known Member

    Sep 13, 2010
    735
    43
    You should understand that the formula you mentioned above is only valid if your are matching impedances to the primary winding.
     
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