The invention relates to a transformer comprising a primary with a coil structure and a core structure, and a secondary with a coil structure and a core structure, in which transformer the primary is divided into parts.

The invention relates to transformers used in alternating current technology (AC technology). The transformer is composed of a structure with at least two coils with mutual inductance. There may or may not exist a gal¬ vanic, i.e. conducting coupling between the coils. The transformer coil into which energy is fed is called the primary. The secondary delivers energy to the load. A ferromagnetic core is often employed to couple the magnetic flux gen¬ erated by the current carried in the primary to the secondary. The path of the magnetic power lines generated by the coil is always closing. The ferromag¬ netic core provides the magnetic flux with a low-loss and natural way to return to the primary, from where it originates. At the same time the majority of the magnetic flux generated by the primary circles through the secondary resulting in an efficient inductive coupling.

Transformers are used for a variety of purposes. By means of a transformer, electric energy can be transferred from one electric circuit to an- other without a conductive, i.e. galvanic coupling between the circuits. When electric energy is transferred from one electric circuit to another, the voltage level and the current can be transformed from one value to another by e.g. transforming a 220 V input into a 12 V output voltage. The transformer can be used to influence the voltage levels and currents of electric circuits, and can consequently also be used as an impedance transformer.

A transformer with an I shaped core with the primary and the sec¬ ondary wound on top of each other on a common I shaped core is previously known. A transformer with an E shaped core with the primary and the secon¬ dary wound upon different legs of a common core is also previously known, the advantage of such a transformer structure being a smaller capacitive cou¬ pling between the primary and the secondary. Furthermore, a transformer with a toroid core is previously known. A toroid transformer comprises a ring made of ferromagnetic material, upon which the primary and the secondary are wound. A toroid transformer provides a good inductive coupling between the primary and the secondary. A transformer with one winding divided into two parts is also known, the structure being such that one coil, operating as the

primary, is wound on the core. A part of the primary coil is used as the secon¬ dary so that energy is delivered to the load by "pinning" from the primary coil. The disadvantage of such a transformer structure is that the secondary volt¬ age is always lower than the primary voltage. In a transformer electric power is also transformed into heat and hence transformer performance is always less than 100%. The series resistors formed by the bobbin threads of the coils and the whirling currents of the transformer core cause electric power to transform into heat in a transformer. Situations where high primary voltages have to be followed by significantly lower secondary voltages, or vice versa, are the most difficult as to transformer performance. In these cases the transformation ratios have to be made either high or low, and the number of turns of the primary or the secondary of known transformers has to be made high. This again causes increased resistive losses in the transformer. Structures allowing a minimal number of turns for the windings would also be advantageous in transformers where transforma¬ tion ratios are nearer to the value one.

German publication 4,404,551 discloses a transformer structure in which the secondary is divided into several parts. The transformer comprises a group of coils in the form of "a Greek cross". In said publication a single cross shaped coil group comprises four secondary coils (one at each of the four ends of the cross) coupled either in series or in parallel. The primary coil is in the middle. The above problems arise, however, in this solution.

U.S. publication 4,156,222 discloses the closest prior art solution which describes a primary divided into two parts. The primary is in two parts, i.e. in connection with two transformer legs, the secondary being in connection with the third leg. The above problems arise, however, in this solution. This solution does not sufficiently contribute to the possibility of using coils with a small number of turns.

It is the object of this invention to provide a new type of transformer that eliminates the problems with known solutions.

This object is achieved with the transformer of the invention, which is characterized by that the coil structure and the core structure of the divided primary are such that the primary comprises at least three primary units, each comprising a core and two or more coils in connection with the core, arranged as a circle around the secondary.

The transformer conforming with the invention is based on the idea that the primary, which is divided into parts, is arranged around the secondary in at least three portions, each comprising at least two coils.

The transformer conforming with the invention offers several ad- vantages. It can be implemented using coils with a small number of turns. It is possible to achieve a high transformation ratio with relatively small number of primary and secondary coil turns. Hence the resistive losses and the induc¬ tances of the primary and secondary coils in the transformer remain low. The preferred embodiments of the invention emphasise its advantages. In the following the invention will be described in greater detail with reference to the accompanying drawings, in which

Figure 1 shows a top view of a transformer core, Figure 2 shows a side view of a transformer core, Figure 3 shows a wound transformer from an obliquely upward po- sition,

Figure 4 is a transformer wiring diagram, Figure 5 shows a first embodiment of a primary unit, Figure 6 shows a second embodiment of a primary unit, Figure 7 shows a secondary. Firstly, with reference to Figures 1 to 3 in particular, it is stated that the invention concerns a transformer A for transforming electric energy and comprising a primary 1 to 6 with a coil structure 11 to 16 comprising coils, i.e. windings, and a core structure 21 to 26 comprising cores 21 to 26. The trans¬ former A additionally comprises a secondary 31 with a coil structure 41 com- prising at least one coil 41 , and a core structure 51. The core structure also comprises a base 101 and a cover 102.

The primary 1 to 6 comprises at least three primary units, e.g. six primary units 1 to 6, each comprising at least one coil and one core. At least three, e.g. six primary units 1 to 6, are placed around the secondary 31 as a circle, as best observed from Figures 1 and 3.

The coil structure and the core structure of the divided primary of the transformer conforming with the invention are such that the primary 1 to 6 comprises at least three primary units 1 to 6, each comprising a core 21 to 26 and two or more coils 111 to 116, 121 to 126, 131 to 136, 141 to 146, 151 to 156, 161 to 166 in connection with the core, arranged around the secondary

31 as a circle As the numerals imply, the number of primary units can be e.g six, and each primary unit can in turn comprise e.g six coils

In a transformer conforming with a preferred embodiment of the in¬ vention said at least three primary units 1 to 6 are essentially at the same dis- tance from the secondary 31. In a further preferred embodiment said at least three primary units are arranged at regular intervals on the periphery of a cir¬ cle, as best observed from Figures 1 and 3 These preferred embodiments make the transformer structure symmetric thus improving its performance. As a result, the magnetic flux is coupled more efficiently from the primaries 1 to 6 to the secondary 31

In a transformer conforming with a preferred embodiment of the in¬ vention the cores 21 to 26, 51 of the coil structure 11 to 16 of the primary and the coil structure 41 of the secondary are of ferromagnetic material, and that the coil cores 21 to 26 and 51 of the primary and the secondary are arranged between the ferromagnetic end pieces 101 and 102 of the transformer and are in contact with the end pieces 101 , 102. In a way, the end pieces 101 , 102 form the base 101 and the cover 102 of the transformer. The coil structure 11 to 16 of the transformer is wound around vertical pins 21 to 26, i.e. cores 21 to 26, arranged between the cover 102 and the base 101 Preferably the cores 21 to 26 of the primaries 1 to 6 are pin-like Preferably the upper and lower ends of the pin-like cores 21 to 26 are in contact with the cover 102 and the base 101 so that the magnetic flux has free access through the connections Then, the magnetic flux can efficiently circle between the primary and the sec¬ ondary. In a preferred embodiment the cores 21 to 26 of the coils 11 to 16 are formed of separate pin-like pieces and they are in contact with the end pieces 101 , 102, e.g. being supported by the end pieces, as such a structure is sim¬ plest to manufacture A preferred embodiment is also a structure made for ex¬ ample by casting, in which a first end of one or more pins is fixedly fastened to one end piece and the other ends of the pins are supported by the other end piece A structure in which part of the pins are of the same casting piece as the base and part of the pins are the same casting piece as the cover can also be used. Instead of casting, other methods can also be used, with which a one-piece structure is achieved. In a one-piece structure achieved by casting or other methods the magnetic flux flows efficiently and the structure is easy to build.

In a preferred embodiment of the invention, one or more primary units 1 to 6 can each comprise a plurality of coils. In the example shown in the Figures, the coil structures 11 to 16 of all six primary units 1 to 6 comprise a plurality of coils, i.e. in accordance with Figure 4, six coils per each primary unit. In the first primary unit 1 the core 21 has a coil structure 11 comprising coils 111 to 116, in the second primary unit 2 the core 22 has a coil structure 12 comprising coils 121 to 126, in the third primary unit 3 the core 23 has a coil structure 13 comprising coils 131 to 136, in the fourth primary unit 4 the core 24 has a coil structure 14 comprising coils 141 to 146, in the fifth primary unit 5 the core 25 has a coil structure 15 comprising coils 151 to 156, in the sixth primary unit 6 the core 26 has a coil structure 16 comprising coils 161 to 166.

Figure 5 shows a first embodiment of a primary unit. Let the primary unit shown in Figure 5 be primary unit 1 , for example. The primary unit 1 com- prises a coil structure 11 comprising for example six coils 111 to 116. In addi¬ tion, the primary unit 1 comprises a core 21 upon which the coils 111 to 116 are wound. In the example of Figure 5, the coils 111 to 116 in the same pri¬ mary unit, e.g. primary unit 1 , are coupled electrically apart. In this example, six threads have been wound around the core pin 21 of the primary unit 1 as parallel windings, i.e. coils. Thus, each thread forms its own coil 111 to 116. Built in this way, six switching points 1a to 6a are formed in the upper portion of the vertical pin, and correspondingly six switching points 1b to 6b in the lower portion. The coupling is mainly inductive between the equivalent points 1a to 1b, 2a to 2b, etc. The number of parallel windings does not necessarily have to be six, it can be anything, but must be at least two. It should be noted, that in Figure 4 all primary units 1 to 6 are of the same type as in Figure 5, i.e. the coils in the same coil structure are coupled apart.

Figure 6 shows a second embodiment of a primary unit; a version where one primary unit 1 comprises at least four coils coupled together in pairs. That is, coils on a vertical pin on the periphery can also be coupled to¬ gether. E.g. twelve threads are wound around the core pin 21 of the primary 1. The coils formed of these threads are e.g. in pairs or otherwise coupled in se¬ ries, resulting in six switching points 1a to 6a in the upper portion of the verti¬ cal pin 21 and six switching points 1b to 6b in the lower portion of the vertical pin. The coupling between the formed equivalent points 1a to 1b, 2a to 2b, etc. is mainly capacitive. In Figure 6, the second and the fifth tread at the upper

end of the primary pin are coupled together, the sixth and the ninth tread are also coupled together, and further the tenth and the twelfth tread are coupled together. In Figure 6, the first (twelfth lowest) and the third thread at the lower end of the primary pin are coupled together, the fourth and the seventh are also coupled together, as are the eight and the eleventh.

Thus, in a transformer of the preferred embodiment the coils 111 to 116, 121 to 126, 131 to 136, 141 to 146, 151 to 156, 161 to 166 of the primary units 1 to 6 comprise first coupling points 1a to 6a and second coupling points 1b to 6b. Then, the transformer is preferably such that the first coupling points of coils in different primary units 1 to 6, e.g. coupling points 1a, are coupled together by a first coupling means, e.g. coupling means 221a. Correspond¬ ingly, second coupling points of coils in different primary units 1 to 6, e.g. cou¬ pling points 1b, are coupled together by a second coupling means, e.g. cou¬ pling means 221b. Primary coils coupled together in the different primary units 1 to 6 surrounding the secondary 31 improve the performance of the trans¬ former.

In a more developed version shown in the Figures, the primary units 1 to 6 each comprise a plurality of coils, for example six coils each. In a pre¬ ferred embodiment the transformer comprises a first coupling means 211a to 216a combining the first coupling points of the coils in the different primary units 1 to 6, and a second coupling means 211b to 216b combining the sec¬ ond coupling points of the coils in the different primary units 1 to 6.

As far as the first coupling points 1a to 6a of the coils 1 to 6 are concerned, the structure, as shown in Figure 4, is such that a circling thread formed by the first coupling means 211a to 216a combines first the coupling points 1a of the coils 111 , 121 , 131 , 141 , 151 , 161 in the different primary units 1 to 6, then the coupling points 2a, then the coupling points 3a, then the coupling points 4a, then the coupling points 5a and then the coupling points 6a. As far as the second coupling points 1 b to 6b of the coils 1 to 6 are concemed, the structure, as shown in Figure 4, is such that a circling thread formed by the second coupling means 211b to 216b combines first the cou¬ pling points 1 b of the coils 111 , 121 , 131 , 141 , 151 , 161 in the different pri¬ mary units 1 to 6, then the coupling points 2b, then the coupling points 3b, then the coupling points 4b, then the coupling points 5b and then the coupling points 6b.

A transformer primary input IN, into which the alternating voltage or current to be transformed is fed, is formed between the coupling means 211a and 211b.

The above usage of a plurality of coils in the same primary unit and coupling together the coils in the different primary units improves the efficiency and performance of the transformer.

It is especially clear from Figures 3 and 4 that in a preferred em¬ bodiment the coupling means 211a to 216a and the coupling means 211 b to 216b are arranged around the transformer on a periphery formed by the pri- mary units 1 to 6. The coupling means are preferably formed of conductor wire.

Figure 7 shows the secondary 31 comprising a coil structure 41 and preferably a pin-like core 51. In a preferred embodiment the whole of the coil 41 of the secondary 31 is arranged on the centre pin 51 of the transformer. One or more, for example three parallel windings 411 to 413 can be wound on the ferromagnetic centre pin 51. In Figure 7, the first coil 411 comprises con¬ nections 10a and 10b, between which a first output OUT1 is formed. The sec¬ ond coil 412 comprises connections 11a and 11b, between which a second output OUT2 is formed. The third coil 413 comprises connections 12a and 12b, between which a third output OUT3 is formed

It may be seen from Figure 4 that the primary 1 to 6 of the trans¬ former comprises an input IN into which the voltage/current to be transformed is fed. The secondary 31 of the transformer comprises one or more, for exam¬ ple three, outputs OUT1 , OUT2 and OUT3. Feeding AC voltage into the input IN of the primary 1 to 6 results in the primary coil structure 11 to 16 with its coils 111 to 116, 121 to 126, 131 to 136, 141 to 146, 151 to 156, 161 to 166 producing a variable magnetic flux which is coupled by means of the ends 101, 102 of the core structure and/or directly to the coil structure of the secon¬ dary 31 and induces an AC voltage into the coils 411 to 413 of the coil struc- ture 41 of the secondary 31. An AC voltage is induced between the ends of each separate coil 411 to 413 upon the core 51 , i.e. the centre pin 51 , of the secondary 31. If the numbers of turns of the coils 411 to 413 of the secondary are unequal, the induced voltages are also unequal.

Owing to the symmetry of the transformer structure, the magnetic fluxes generated by the coil structures 11 to 16 of all vertical pins 21 to 26 on the periphery of the primary 1 to 6 return most preferably via the ferromagnetic

centre pin 51 , that is the core 51 , of the secondary 31. Because of the ferro¬ magnetic material of the cover 102 and the base 101 , the magnetic flux re¬ mains in the core structure of the transformer with practically no leakage to the outside.

Thus a voltage (V _secondary ) whose magnitude can be estimated from the formula (1) is induced between the ends of the secondary coils 411 to 413 of the secondary coil structure 41 wound around the centre pin 51 of the pri¬ mary 31 ;

' " ' 'secondary v " secon „dary = * K ^, * M "" * V ' primary π V ')/

N * _π pπmary

in which 5 N _secondary = number of turns of the centre pin of the secondary winding

N _pπmary ⁼ number of turns of one parallel primary winding on the vertical pin

V _pπmary - primary voltage coupled to the input

K = number of vertical pins on the periphery

M = number of coils wound in parallel on the vertical pin 0 A coupling as shown above in the Figures allows a number K*M of coils to be connected in parallel. Thus the wasteful resistance is small as the coils are in parallel. Owing to the symmetrical structure, the same current passes through each coil. As the coefficients K and M increase the value of the transformation ratio, the above formula (1) shows that a high transforma- 5 tion radio can be achieved with a relatively small number of turns of the coils of the primary and the secondary. This results in small resistive losses in the transformer, and small inductances in the primary and the secondary coils.

In a transformer conforming with a preferred embodiment of the in¬ vention at least nearly all primary units 1 to 6 comprise two or more coils. In 0 the example of the Figures, the primary units equal six, each comprising two or more coils. Said embodiment improves the performance of the invention and further increases the possibility of using coils with a small number of turns.

In a transformer conforming with a preferred embodiment of the in¬ vention the core structure 51 of the secondary 31 surrounded by the primary 5 units 1 to 6 is one-piece, i.e. the whole coil structure 41 , i.e. coils 411 to 413, of the secondary 31 are around the core 51 of the secondary, In addition, the

cores 21 to 26 of the primary units 1 to 6 are parallel, and preferably parallel also with the core 51 of the secondary 31. This embodiment improves the performance of the invention and provides a simpler transformer structure.

The invention can be applied to a variety of purposes, i.e. the trans- former conforming with the invention is a transformer employed for transform¬ ing voltage or current, or a transformer used as an impedance transformer, which in practice also deals with transformation of voltage levels or currents.

Even though the invention has been explained in the above with reference to examples in accordance with the accompanying drawings, it is obvious that the invention is not restricted to them but can be modified in vari¬ ous ways within the scope of the inventive idea disclosed in the attached claims.