10.7 The Transformer
The transformer is a device designed to transform voltages and currents (and, therefore, impedances). It is an AC device and
operates on the principles of Faraday’s law. The transformer consists of two or more coils and a magnetic path that links the
coils. There is a variety of transformers with different types of paths, but they all operate on the same principles. Power
transformers are designed primarily for voltage transformation and operate at relatively high currents. The magnetic path is
made of a ferromagnetic material like iron to produce a low-reluctance magnetic path (see Figure 10.13). Typically, the iron
core of the transformer is laminated to reduce induction of currents in the core which contribute to losses. Impedancematching
transformers are normally designed for low-power applications. There are other types of transformers, some with
iron cores, some without a core (air-core transformers), and still others with ferrite cores. There are also transformers which
do not look like transformers but act as such. For a device to be considered a transformer, it must have two or more coils,
coupled together by a common flux, whatever the physical construction of the device.