When talking about the design of high frequency transformers, there are many things: design of coil parameters, selection of magnetic materials, selection of magnetic core structure, design of magnetic core parameters, selection of transformer structure, etc. Here are five key points for high frequency transformer design.

1. Coil parameter

When we design coil parameter, we should concern about number of coils, wire diameter, wire type, winding arrangement and safety insulation design. The number of primary winding turns is determined by the applied field voltage or the field inductance of the primary winding. The number of circles should not be too many or too few. If the turns number is too much, the leakage inductance increases, and the working time of the winding increases.

If the number of turns is too small, when the external excitation voltage is high, the voltage drop between turns and layers increases. You must strengthen the safety insulation. The number of secondary windings is determined by the output voltage. The wire diameter depends on the current density of the winding. In addition, the wire diameter is also related to strong leakage.

2. Transformer structure

The structure of high frequency transformer is divided into horizontal and vertical type. If you choose a planar core, core, or membrane core, the horizontal assembly structure is adopted. The upper and lower surfaces are large, which is conducive to heat dissipation. The other one is a vertical structure.

In addition, the hardware or terminals used in the assembly structure should use standard equipment as much as possible to facilitate procurement, shorten research and development time, and reduce research and development costs.

3. Magnetic material

Soft magnetic materials are usually used in the cores of high frequency transformers. Soft magnetic materials have high magnetic permeability, low coercive force and high resistivity. When the magnetic permeability is high, and the number of coils is constant, the small excitation current has high magnetic induction. It can withstand higher applied voltage.

Therefore, in the case of constant output power, it decreases without change. If the coercive force is low, the magnetic core hysteresis loop area is small, and the iron loss is small. The higher the resistance, the smaller the eddy current, and the smaller the iron loss.

The ferrite material is a soft magnetic material. Like other soft magnetic materials, this one has the advantages of high resistivity, small AC eddy current loss, relatively cheap price, and easy processing into magnetic cores of various shapes. The disadvantages are low magnetic flux density, low magnetic permeability, large magnetostriction, and sensitivity to temperature changes. Therefore, ferrite materials are usually used as magnetic materials for high frequency transformers.

4. Magnetic core

For the design of high frequency transformers, the factors for selecting the magnetic core are: reducing magnetic leakage, increasing the heat dissipation area of the coil, facilitating shielding, easy winding of the coil, convenient assembly and wiring.

In the core structure design of high frequency transformers, various factors should be considered comprehensively to determine the size of the window area. In order to prevent electromagnetic interference from the inside to the outside and from the outside to the inside of the high-frequency power transformer, there are some semi-closed shells outside the window.

The wiring holes should have good heat dissipation holes. Otherwise, wiring and heat dissipation will be inconvenient. The semi-enclosed shell is used for shielding electromagnetic interference, wiring and heat dissipation. If the window is fully opened, the wiring heat dissipation is convenient. The electromagnetic interference shielding effect is poor.

5. Core ΔB parameters

When choosing the core parameters of a high-frequency transformer, the working flux density is not only limited by the magnetization curve, but also related to the working mode of power transmission.

When it is the unidirectional flux change mode, ΔB is limited by the saturation flux density and loss. When it is the working mode that the magnetic flux changes in two directions: the area surrounded by the working hysteresis loop is much larger than the local flux linkage, and the loss is much larger. ΔB is limited by losses. You should pay attention to DC bias.

In fact, the design of high frequency transformers is also related to a lot of electrical thing. If you want to learn more about transformers, visit our transformer column.