How to Design Ferrite Transformers

It is important to verify the customer’s requirements and the exact application before designing a ferrite transformer. It may include input voltage, output voltage, current, and operating frequency, among others.Other factors to consider include physical size, spacing, mounting style, isolation, leakage current, and temperature.

The design steps for ferrite transformers :

1. Core material
2. Core structure
3. Core parameter
4. Coil parameter
5. Assembly structure
6. Temperature rise check

Core material

A ferrite core consists of three metal elements, iron (Fe), manganese (Mn), and zinc (Zn), and is often referred to as a manganese-zinc ferrite. Due to its uniform cross-sectional area and no air gap, the toroidal ferrite core has a high magnetic effect.

Ferrite cores are composed of dense and homogeneous ceramic structures with low coercivity, also called soft ferrite. Iron oxide (Fe2O3) and one or more other metals, such as manganese, zinc, nickel, magnesium, form oxides or carbonates. In comparison with other types of magnetic materials, ferrite has a high magnetic permeability and low eddy current losses even over a wide frequency range. Ferrite is pressed, sintered at a high temperature of 1300°C, and finally processed into a finished magnetic core. As a result of these properties, ferrites are ideal for applications such as high frequency transformers, broadband transformers, tunable inductors, and other high frequency circuits.

Core structure

There are four main types of ferrite cores: E core, pot core, U core, and torodial core

1.E core

CUT core has small size, high inductance, easy winding, high inductance per unit space, magnetic

2.POT core

CUT core has small size, high inductance, easy winding, high inductance per unit space, magnetic

3.U Core

There are two types of U cores: UU and UI. UU core has small impedance deviation big output current, high inductance. Ul core has wide distributing permeability

4.Torodial core

Low noise, low magnetizing current.

Core parameter

When designing magnetic core parameters, special attention should be paid to the working magnetic flux density that is not only limited by the magnetization curve, but also by the loss factor. In addition, it relates to how power is transferred when the magnetic flux changes direction:ΔB=Bs-Br B=Bs-Br；It is limited by the saturation flux density and more primarily by the loss, magnetic flux density at work Bm=0.6 =0.6~ ΔB an open air gap can reduce noise Br, Increasing magnetic flux density ΔB。 When the air gap is opened, the excitation current increases, but the magnetic core volume can be reduced: The maximum magnetic flux density that can be used Bm,ΔB=2Bm B=2Bm；A small air gap can be added in the magnetic core or a spacer can be added in the circuit design if the DC bias problem occurs when changing the working mode in both directions.

Coil parameter

It is recommended to wind the primary winding close to the magnetic core, and the feedback winding of the secondary winding gradually outward.

1. The secondary winding can be used close to the magnetic core if the voltage of the primary winding is high (for example, 220V) and the voltage of the secondary winding is low.
2. You can reduce leakage inductance by winding the outermost layer around half of the primary winding to increase the coupling between the primary and secondary windings.

Assembly structure

There are horizontal and vertical sections to the ferrite transformer assembly.

Temperature rise check

The temperature rise check can be carried out by calculation and sample test. If the temperature rise is lower than the allowable temperature rise by more than 15 degrees, the current density should be appropriately increased and the cross-section of the wire should be reduced. If the diameter is increased, the window cannot be wound around, and the magnetic core must be enlarged to increase its heat dissipation area.