What is a transformer? What is the principle of voltage transformation?

The main components of a transformer are the primary winding N1, the secondary winding N2, and the core. Its main functions are voltage conversion, current conversion, isolation, impedance transformation, and voltage regulation.
When AC current passes through the primary winding of the transformer, electricity generates magnetism. The function of the core is to guide the magnetic field path of the primary and secondary windings, conducting the magnetic field to the secondary winding, forcing the movement of charges Q within the coil, thereby generating electromotive force ε, producing current I, and obtaining energy W.

Transformer losses are divided into iron losses (core) and copper losses (coils). Losses are converted into heat energy, causing temperature rise. The role of the core is to strengthen the coupling between the two coils. To reduce iron losses, it is necessary to reduce hysteresis losses and eddy-current losses in the core.
Hysteresis losses are related to the core material. When electricity generates magnetism and the magnetic field of the core changes, the magnetization intensity also changes. This can be judged from the B-H curve; the larger the curve area, the greater the hysteresis loss.
The relationship between the magnetic field strength (H) and magnetic induction intensity (B) of magnetic materials is non-linear. Under enhanced magnetic field conditions, the relationship between the two will rise along a curve to a certain point. After reaching this point, even if the magnetic field strength H continues to increase, the magnetic induction intensity B will no longer increase. This situation is called magnetic saturation.
BR represents residual magnetism, which refers to the certain magnetization intensity that remains in the direction of the original external magnetic field after a magnet is magnetized to saturation and the external magnetic field is removed.
HC is the coercive force, which is the magnetic field strength required to reduce the magnetization intensity of a magnetic material to zero after it has been magnetized to saturation. Ferromagnetic materials with low coercive force are called soft magnetic materials.