Design points of high frequency transformer
Design points of high frequency transformer
There is no difference between the High frequency transformer and the ordinary transformer. Both of them transmit energy through electromagnetic induction, but the difference in operating frequency is caused by the difference in magnetic materials used. Therefore, the design process of the high-frequency transformer and the transformer process are basically the same, including: parameter calculation, winding method, selection of core material and core structure, wire diameter, etc. The following small series will be elaborated from various aspects.
1. Calculation and selection of parameters
The coil parameters of the high-frequency transformer include: core cross-sectional area, number of coil turns, primary current, wire form, wire diameter, winding arrangement and insulation arrangement.
2. The winding method of the high-frequency transformer is: sequential winding method and sandwich winding method.
The order of winding of the sequential winding is: primary winding Np - secondary winding Ns - auxiliary power winding Nb. The winding process is simple, easy to control various parameters of the magnetic core, convenient for the insulation arrangement of the magnetic core, and the cost of the winding is low.
Sandwiches are divided into two types of winding: primary clamp secondary, secondary clamp primary.
(1) The winding sequence of the primary clip secondary is the primary winding Np/2 - the secondary winding Ns - the primary winding Np/2 - the power winding. Such winding method is beneficial to the coupling of primary and secondary, reducing the leakage inductance and distributed capacitance of the high-frequency transformer; improving the flatness of the high-frequency transformer winding, and the common-mode interference current can also be reduced. The last advantage is that the voltage of the power supply winding changes. It is less affected by the secondary load and has better stability.
(2) The winding sequence of the secondary clamp primary is the secondary winding Ns / - primary winding Np - secondary winding Ns / 2 - auxiliary power winding Nb. Such a winding method has the advantages of reducing the copper loss and heat generation of the high-frequency transformer, making the winding more compact and improving the primary coupling condition to reduce the high-frequency interference of the magnetic core.
3. Selection of magnetic core material for high frequency transformer
Commonly used magnetic cores are soft magnetic materials (amorphous, nanocrystalline, permalloy, manganese zinc ferrite, silicon steel sheets), which have high magnetic permeability, low remanence, low coercivity, and high Resistivity and high Curie temperature points. At the same time, according to different parameters, uses, size requirements, in the production process, the ratio of raw materials and additives can be changed, and the characteristics of the products can be adjusted within a certain range.
4, high-frequency transformer selection core structure should consider factors: parameter use, reduce leakage and leakage inductance, increase coil heat dissipation area, shielding effect, winding technology, assembly wiring and so on.
(1) Laminated magnetic core, usually composed of ferrite, silicon steel or nickel steel sheet, such as E, I, F, O, etc., stacked into a transformer core.
(2) The toroidal core is generally composed of O-shaped sheets, and is also commonly formed by winding long and narrow silicon steel and alloy steel strips.
(3) The C-shaped magnetic core is constructed by butting two C-shaped cores. This structure has high saturation magnetic induction, high magnetic permeability, low loss characteristics, and good temperature stability.
(4) The pot-shaped magnetic core has a structure in which the core portion is outside and the coil portion is inside, such a structure is convenient for winding; the disadvantage is that the internal temperature is stable and the temperature rise is high.
(5) Square core, the advantage is that the resistance is large, the current is small; the second is the hysteresis loss, the narrower the curve enclosing area is, the smaller the loss is.
5, high-frequency transformer wire diameter calculation method: According to the formula wire diameter D = 1.13 (I / J) ^ 1/2 can be calculated, J is the current density, I is the current size.
With the wide application of electronic intelligence and industrial automation, the original high-frequency transformer design scheme to design transformers has gradually failed to meet the needs of increasingly advanced products. In the future, the volume, frequency, cost of high-frequency transformers, Environmental protection and other aspects put forward more stringent requirements. In order to meet this demand, every company should start researching new high-frequency transformers.