Sinrace Power Supply Technology (Shenzhen) Co., Ltd.

Advantages of planar transformers are mainly concentrated in the lower leakage inductance and impedance. The larger gap of winding means larger leakage inductance, it produces a higher energy loss. Planar transformer uses joint connection between copper foil and the circuit board, to make a small gap among adjacent turns layers , so the energy loss is also small.

In the planar transformers, the "winding" is done on flat conductive guide line of  printed-circuit board printed circuit board or directly the copper mooring. Flat geometry reduce loss of skin effect when switching frequency is high, that is the eddy current loss. Therefore, effectively use the surface conductivity of copper conductor, much higher efficiency than conventional transformers. A profile map of flat transformer, and make use of the different distance between two windings, to obtained leakage inductance and impedance values under the different gap 5vdc 1a adapter.

The change of leakage inductance and AC impedance in the different gap, it is evident that the greater the gap, the greater the leakage inductance, the smaller the impedance is. Add 1mm to the gap , leakage inductance increased more than 5 times. Therefore, in the condition of meeting the electrical insulation, you should use the thinnest insulation to get the minimum leakage value.

However, the capacitive of a 5vdc 1a adapter effects is very important in the planar transformer, the tightly rolling wire in the printed circuit board make the capacitive effect be obvious. And the selection of the insulation materials has a very big impact on capacitive value, the higher the dielectric constant of insulating materials is, the higher the capacitive value of the transformer is. The capacitive effect will cause EMI, because from the primary to the secondary winding, only a capacitive loop winding spread such interference.

Insert technology is namely that when the layout of the transformer primary, secondary winding, the primary winding and secondary windings are placed alternately, increasing the coupling of original, the secondary windings to reduce leakage inductance, and at same time making the current average distribution, reduce transformer losses for a 5vdc 1a adapter.

Technology research is now divided into two aspects, namely, applied to the transformer insert (forward circuit) and inductors insert (flyback circuit). Therefore, the insertion technique has now been placed in a different topology as different magnetic components to study.

As mentioned above the advantages of planar transformers, same as it also has disadvantages, its main drawback is that the design process is very complex, and the design costs are very high.

Here introduce a standard design procedure of planar transformer; it is designed by providing a standard turns model, so that it can be used in different planar transformer, thus making the design process greatly simplified, greatly reduce the cost .

In each layer of the double-sided PCB board is winded by a and many windings, and all layers have maintained the same physical characteristics: the same shape and the same external connection points. In some multi-turn level, this external connection point is electric point between the different turns. If there is only one turns in some layer, it can also be printed on both sides of the PCB to reduce the impedance. Using the copper foil directly printed on the PCB to replace traditional wire, even though many switching power supply need a lot of turns , the transformer is still able to maintain a small volume, which would greatly reduce the size of the machine. Detailed design steps and attentions see also docu. For example of top-level turns standard design, which use the pot (RM) core for the 5vdc 1a adapter.

Copper foil height is according to skin depth selection of the maximum switching frequency, this could make all the parts of a copper be current path, greatly reducing the skin effect. Therefore, we should make every switching frequency corresponding to different copper level.

To compare the planar transformers and conventional transformer ,separately make the two kind models of transformer, one use a flat structure and insert technology, and the other use copper wire winding made at the primary and secondary. Two kinds of transformers are used in a complementary-controlled half-bridge converter. Two transformer parameters are as follows:

Primary 12 turns: Secondary two winding of two l-turns (1:1 center-tap). Traditional transformer use enameled wire as winding wire, although the current density of these coils are not the same, current density is chosen less than 7.5A/mm. Planar transformer primary winding is made to four layers, there are four parallel sub. The final structure of the transformer shown in Figure 7.

Two kinds of transformers both use the same core RM10, compared leakage impedance and the occupied area inductance of two transformers.

The leakage inductance of plat transformer is only 1/5 of that of conventional transformer, AC impedance is only l / 3 of it , we can see that this will greatly enhance the operating characteristics of the converter. Moreover, since the structure is more compact, so you can use a smaller RM8 core.

Conclusion

The aspects of reducing leakage inductance AC impedance of planar transformers, has a very big advantage, and because of the small size, which makes it a very good magnetic components. Giving a standard method of planar transformer design, making it easier to design planar transformers, the cost will be greatly reduced. Can be expected, planar transformers will have a very good prospect.