EE13 high frequency transformer
The high frequency transformer is the most important part of the switching power supply。 There are many topologies in switching power supplies。 For example, a half-bridge power conversion circuit, in which two switching transistors are turned on in turn to generate a high-frequency pulse wave of 100 kHz, and then transformed by a high-frequency transformer to output an alternating current, and the ratio of the turns of each winding of the high-frequency transformer is determined。 What is the output voltage?
The most prominent of the typical half-bridge transformer circuits are three high-frequency transformers: the main transformer, the drive transformer, and the auxiliary transformer (standby transformer). Each transformer has its own measurement standard in the national regulations, such as the main transformer. As long as it is more than 200W, its core diameter (height) must not be less than 35mm.
The auxiliary transformer, when the power of the power does not exceed 300W, the core diameter of 16mm is enough.
Increased efficiency is a common requirement in today's power and electronic equipment, and traditional transformers cannot meet today's efficiency requirements。
This is due to the magnitude of the induced potential of the transformer, which depends on how much the magnetic flux changes in a unit, that is, the faster the flux changes, the larger the induced potential. Although the core of the high-frequency transformer is small, the maximum magnetic flux is not large, but he works at high frequency, and the magnetic flux changes rapidly. Therefore, it is possible to generate a sufficient potential when the core is small and the number of turns is small, and the low frequency is The opposite.
The design and calculation of the high-frequency low-frequency transformer show that under the same power condition, the higher the frequency, the smaller the core and the fewer the number of turns per volt. Designing a high frequency transformer should start with the core。 The magnetic core of the switching power supply transformer is mostly a soft magnetic material used in a low magnetic field, which has high magnetic permeability, low coercive force and high electrical resistivity. The magnetic permeability is high, and when a certain number of turns of the coil is used, a relatively high applied voltage can be withstood by a small excitation current, and therefore, the core volume can be reduced under the requirement of outputting a certain power.