Basic Limitations of the Conventional Transformer

The conventional transformer consists of two coils (see Figure 2-71) placed so a magnetic field in one coil links the other coil, mostly via a magnetic core [4, 5, 37, 38].

Figure 2-71: Physical schematic of conventional transformer.

The voltages induced in the primary and secondary coils are proportional to the number of turns in that coil; the currents through the coils are inversely proportional to the number of turns. For an ideal transformer (that is, a transformer with perfect magnetic coupling and no loss of energy), the resistance seen across the primary winding (see Figure 2-72) is given by

2.105

where

2.106

is the turns ratio.

Figure 2-72: Conventional transformer.

Because the number of turns in both primary and secondary coils may be arbitrary, the conventional transformer may be used to assure a broadband matching of any impedance value. However, the use of a conventional transformer for broadband impedance matching raises difficulties due to its frequency limitations.

Figure 2-73: Complete T equivalent circuit (referred to the primary winding) of a conventional transformer.