The transformer has appeared throughout the text in a number of
described applications, from the basic dc supply to the soldering gun to the flyback transformer of a simple flash camera.
Transformers were used to increase or decrease the voltage or current level, to act as an impedance matching device, or in some cases to play a dual role of transformer action and reactive element.
They are so common in such a wide variety of systems that one should make an effort to be very familiar with their general characteristics. For most applications their design
today is such that they can be considered 100% efficient. That is, the power applied is the power delivered to the load. In general, however, they are frequently the largest element of a design and because of the nonlinearity of the B-H curve can cause some distortion of the transformed waveform.
By now it should be clear that they are useful only in situations where the applied voltage is changing with time. The
application of a dc voltage to the primary will result in 0 V at the secondary, but the application of a voltage that changes with time, no matter what its general appearance, will result in a voltage on the secondary.
Always keep in mind that even though it can provide isolation
between the primary and secondary circuits, a transformer can transform the load impedance to the primary circuit at a level that can significantly impact on the behavior of the network. Even the smallest
impedance in the secondary can be made to appear very large in the primary when a step-down transformer is used.
Transformers, like every other component you may use, have power ratings. The larger the power rating, the larger the resulting transformer, primarily because of the larger conductors in the windings to handle the current.
The size of a transformer is also a function of the frequency involved. The lower the frequency, the larger the required transformer, as easily recognized by the size of large power transformers (also affected by the current levels as mentioned above). For the same power level the higher the frequency of transformation, the smaller the transformer can be.
Because of eddy current and hysteresis losses in a transformer, the design of the core is quite important. A solid core would introduce high levels of such losses, whereas a core constructed of sheets of high-permeability steel with the proper insulation between the sheets would reduce the losses significantly.
Although very fundamental in their basic structure, transformers are recognized as one of the major building blocks of electrical and electronic systems. There isn’t a publication on new components published that does not include a new design for the variety of applications developing every day.