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Need info

  1. Jan 30, 2004 #1
    I need help find a good page which talks about the physics of a tranformer. I know all about the b fields and the flux and the ratio of the windings but what I really need is the practical formulea and methods for example calculating the voltage drop on the primary if the secondary has aresistance of so much and there is a resistor in series with the primary. I could experiment with different variations and figure it out but it would be alot safer and quicker to find a reference for this material. I really would appreaciate help in this matter.
     
  2. jcsd
  3. Feb 13, 2004 #2
    I've never seen a specific reference on transformers. I learned the stuff you're asking about in RF design classes. Maybe this will help:

    V2 = N2/N1 * V1
    I2 = N1/N2 * I1
    P1 = P2

    Use an ideal transformer as a circuit element & put the resistances in as circuit elements. For example if the secondary has a resistor of R2 ohms & you look into the primary the above relations will show you see a resistance of

    Rin = (N1/N2)^2 * R2

    This Rin would be added to any resistance in the primary winding to make a practical dc cicruit model. For ac, you apply the same idea to the capacitance of the windings using Zc = 1/(2pifc). It works well for frequencies below the self-resonant freq. of the transformer.

    I think this is covered in a wonderful book by Tom Lee called
    "CMOS RFIC Design".

    mmwave ( writing without his EE211 notes)
     
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