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planar transformer of switch power supply
Date:2014-05-28 Hits:4149 Source:Novsense

High power density is the main trend of the development of the switching power supply, to do this, we must increase the power density of planar transformermagnetic components because of the close coupled planar structure and windingspecial, so the high frequency parasitic parameters is greatly reduced, greatlyimproved the working state of the switching power supply, so it has been widely used to study several different plane structure and winding making way,introduced a standard design method for planar transformer, which makes the design process more simple, greatly reducing the design cost. Finally, someparameters of planar transformer and traditional transformer are compared, and gives the design guidelines.

0 Introduction

The design of the magnetic components is an important part of switch power supply, because the planar transformer has a lot of advantages in improving theproperties of switching power supply, so it has been widely applied in recent years. For an ideal transformer, magnetic flux generated by the primary coilpasses through the secondary coil, i.e. no leakage flux. While the general transformer, magnetic flux is not generated by the primary coil passes throughthe secondary coil, and thus a leakage inductance, close the electromagnetic coupling can not meet the requirements of. The planar transformer only one turnmesh secondary winding, the winding is also different from the traditionalenameled wire, but a piece of copper sheet, stick around the same size stampingferrite core surface. Therefore, the output voltage depends on number of planar transformer cores, and the output current of planar transformer can be expandedby parallel, in order to meet the design requirements. Therefore, the characteristic of planar transformer is obviously: tightly coupled planar windingleakage are greatly reduced; planar transformer special structure makes it verylow, which makes the converter is conceived in a plate to obtain the realization.However, the very high capacitance effect problem of planar structure, greatly limits its large-scale use, however, these shortcomings in certain applications,may also be converted to an advantage. In addition, the plane of the core structure of the radiating area is enlarged, is conducive to the transformer radiator.

The 1 insertion technique

Insert technology refers to the primary, secondary winding arrangement of the transformer, the primary winding and the secondary winding is arranged alternately, increase the coupling primary, secondary winding to reduce the leakage inductance, the current average distribution, reduce the loss of transformer.

Now the research into the technology is divided into two aspects, insert that is used in transformer (forward circuit) and applied to the inserted connectioninductor (flyback circuit). Therefore, the insertion technique has now been placed in different topology of magnetic components as different to study.

1.1 insert technology applied to planar transformer

The main advantage is applied to the insertion technique in the transformer:

1) the stored magnetic energy in the transformer space reduction, to reduce leakage;

2) the current transfer process on the conductor ideal distribution, leads to a reduction of AC impedance;

3) coupling windings better, leading to lower leakage inductance.

In order to illustrate the characteristic insertion technique, figure 4 shows theapplication of 3 different insertion technique structure, P represents the primary winding, the secondary winding s representative. Tests show that the SPSPstructure is the best, because the primary and secondary windings are insertedin the interval. Figure 5 shows in 500 kHz, AC impedance 3 structures and theleakage inductance of transformer by comparison, can be easily found using theinsertion technique, AC impedance and leakage inductance are greatly reduced.

1.2 in different topological planar transformer in action

In different topologies, magnetics effect is different. Transformer in forward converter, magnetic energy in the main switch tube is opened by the primary winding is transferred to the secondary winding. However, in the flyback converter in "Transformers" is not entirely a transformer, but two connected inductors. In flyback topology "Transformers" in the main switch when the primary winding of storing energy, and in the closing when the energy transfer to the secondary winding. Therefore, the advantages of this insertion technique is different from the above comparison. The following characteristics insertion technique is applied in the transformer::

1) stored in the core energy is not reduced, because the current in a certain timecan only flow in a winding, and no current compensation;

2) current distribution is not ideal, the same reason, so also did not reduce AC impedance;

3) insert makes a good coupling windings, so there is leakage inductance is small.

1.3 plane structure in the advantage of multi winding transformer

Planar transformer is another important advantage is the height is very low, which makes the core can be provided with more number of turns. A converter of high power density requires magnetic element of a smaller, planar transformer is very good to meet this requirement. For example, the number of turns very much inneed of transformer winding, if the transformer will be common cause volume and height is too large, affecting the overall design of power supply, and the planar transformer not to have this problem.

In addition, the transformer winding, winding coupling remained very good very important. If the coupling is not ideal is the leakage inductance value increases,will make the error of secondary voltage. The planar transformer with a very good coupling, which makes it become the best choice.

Study on characteristics of 2 planar transformer

As mentioned before, the advantages of planar transformer is mainly focused on the value and AC impedance leakage inductance and low. Gap winding askbigger mean leakage

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