The transformer allows you to increase the voltage due to the loss in current strength, or vice versa. In all cases, the law of conservation of energy applies, but some of it inevitably turns into heat. Therefore, the efficiency of the transformer, although usually close to unity, is less than it.
Instructions
Step 1
The transformer is based on a phenomenon called electromagnetic induction. When a conductor is exposed to a changing magnetic field, a voltage arises at the ends of this conductor, which corresponds to the first derivative of the change in this field. Thus, when the field is constant, no voltage arises at the ends of the conductor. This voltage is very small, but it can be increased. To do this, instead of a straight conductor, it is sufficient to use a coil consisting of the desired number of turns. Since the turns are connected in series, the voltages across them are summed up. Therefore, all other things being equal, the voltage will be greater than a single turn or straight conductor in the number of times corresponding to the number of turns.
Step 2
You can create an alternating magnetic field in different ways. For example, rotating a magnet next to the coil will create a generator. In the transformer, for this, another winding is used, called the primary winding, and a voltage of one form or another is applied to it. A voltage arises in the secondary winding, the shape of which corresponds to the first derivative of the voltage waveform in the primary winding. If the voltage on the primary winding changes in a sinusoidal manner, on the secondary it will change in a cosine manner. The transformation ratio (not to be confused with the efficiency) corresponds to the ratio of the number of turns of the windings. It can be either less or more than one. In the first case, the transformer will be step-down, in the second - step-up. The number of turns per volt (the so-called "number of turns per volt") is the same for all transformer windings. For power frequency transformers, it is at least 10, otherwise the efficiency drops and heating increases.
Step 3
The magnetic permeability of air is very low, therefore, coreless transformers are used only when operating at very high frequencies. In power frequency transformers, cores made of steel plates covered with a dielectric layer have been used. Due to this, the plates are electrically isolated from each other, and eddy currents do not occur, which can reduce efficiency and increase heating. In transformers of switching power supplies operating at increased frequencies, such cores are not applicable, since significant eddy currents can occur in each individual plate, and the magnetic permeability is excessive. Ferrite cores are used here - dielectrics with magnetic properties.
Step 4
Losses in the transformer, which reduce its efficiency, arise due to the emission of an alternating electromagnetic field by it, small eddy currents that still arise in the core despite the measures taken to suppress them, as well as the presence of active resistance in the windings. All these factors, except the first, lead to heating of the transformer. The active resistance of the winding should be negligible compared to the internal resistance of the power supply or load. Therefore, the greater the current through the winding and the lower the voltage across it, the thicker the wire is used for it.
