A high-frequency transformer is the most important component of a switching power supply. There are many topologies in switching power supplies. For example, the half-bridge power conversion circuit operates by having two switching transistors alternately conduct to generate a 100kHz high-frequency pulse wave. Then, it is stepped down through a high-frequency transformer to output alternating current. The number of turns in each winding of the high-frequency transformer determines the output voltage. In a typical half-bridge power conversion circuit, the most prominent ones are three high-frequency transformers: the main transformer, the driver transformer, and the auxiliary transformer (standby transformer). Each type of transformer has its own measurement standards as stipulated by the country. For example, for the main transformer, as long as the power supply is above 200W, the diameter (height) of the magnetic core must not be less than 35mm. While for the auxiliary transformer, when the power of the power supply does not exceed 300W, its magnetic core diameter of 16mm is sufficient.
Working principle

A transformer is a device that changes alternating voltage, current and impedance. When an alternating current flows through the primary coil, an alternating magnetic flux is generated in the iron core (or magnetic core), inducing a voltage (or current) in the secondary coil.
A transformer consists of an iron core (or magnetic core) and coils. There are two or more windings in the coils, among which the winding connected to the power source is called the primary coil, and the remaining windings are called the secondary coils.