BACKGROUND ART There are known transformers having primary and secondary coils carried out by windings made of electric wire and impregnated insulators.

A drawback of said known transformers consists in that, because of the wire winding, the characteristics of primary and secondary coils are not reproduceable with the needed precision.

Other drawback consists in that during the operation of known transformer windings there are very high voltage gradients which increase the effect of the parasitic capacitances and which practically annul the energy transfer between primary and secondary coils, particularly during the high frequency operation.

Further drawback consists in the lack of homogeneity of insulators, for instance due to blisters, which can cause harmful electrical discharges.

DISCLOSURE OF THE INVENTION An object of the present invention is to propose an electric transformer having characteristics, which can be industrially repeated with high precision and stable during the operation.

Other object is to propose a transformer minimizing the effect of the parasitic capacitances, reliable and with perfectly and homogeneously insulated turns.

Further object is to propose an electric transformer, particularly for high voltage and high frequency, having efficiency higher than the known transformer efficiency and having economic manufacture, since the application of insulators and the wire winding is eliminated.

The above-mentioned objects are achieved according to the claim content.

BRIEF DESCRIPTION OF THE DRAWINGS The characteristics of the present invention are underlined in the following with particular reference to the attached drawings, in which: figure 1 shows a schematic axonometric view of the transformer of the present invention; - figure 2 shows an axonometric exploded view of transformer of figure 1; - figure 3 shows a plan view of an element of a winding of figure 1 transformer.

BEST MODE OF CARRYING OUT THE INVENTION With reference to figures I to 3, numeral 1 indicates the electric transformer of the present invention.

The transformer I is provided with a primary coil 2 and of two secondary coils 3,4 whose outlets can be connected in series or in parallel.

Each secondary coil includes a defined number of winding elements 5, each one provided with a plate means 6 having a spiral conductor 8 whose ends have respective contacts 9,10 of mutual in series electric connection among the winding elements 5.

The number of winding elements 5 of each secondary coil 3,4 depends on the turn number of the spiral conductor 8 of the respective winding element, on the total number of turns of the respective secondary coils 3,4, on the total number of turns of primary coil 2 and on the ratio of transformation of transformer 1.

The plate means 6 is carried out from a plate made of high dielectric strength insulating material having, at a face 7 thereof, the spiral conductor 8 added or carried out from a metallic layer; for instance, said plate means 6 consists of a board made of vetronite with a layer of photoengraved copper in order to carry out the spiral conductor 8 and at least a portion of the respective contacts 9, 10.

The thickness of the metallic layer and the track width of spiral conductor 8 decide the value of

maximum current of secondary coils 3,4, while the distance between the coils and the thickness and the material of the plate means 6 defines the insulation.

One or both contacts 9,10 extend, for instance by means of a metallized hole and/or a metallic track, at the face of the plate means 6 opposed to the face having the spiral conductor 8, for the mutual connection among the winding elements 5.

Each plate means 6 is centrally provided with an opening 11 for the ferrite core 12 of the transformer 1 from which the opening 11 is isolated by first insulator means 15 having a tubular shape end made of solid insulating material with high dielectric strength.

The winding elements 5 have holes 13 for linking means, consisting of screws and nuts and the like, for mutual fixing. The terminal winding elements 5 of each secondary coil 3,4 have respective terminal insulating plates 14 made of solid insulating material and fixed by the linking means.

The core 12 is provided with second insulating means 16 mating the edges of the winding elements 5.

The primary coil 2 is carried out by a conductive wire made of copper winded in a respective seat carried out in the first insulated means 15; in alternative, the invention provides that the primary coil also can be carried out by means one or more winding elements 5, having conductors 8 with suitable section and suitable number of coils.

The spiral conductors 8 of winding elements 5 of secondary coils can be identical or can be provided with different numbers of turns in order to obtain predetermined ratios between the turn number of the primary coil 2 and the turn numbers of secondary coils 3,4.

The number of said secondary coils can be one or greater than two in order to obtain more outlets or voltage or current values, multiple of those provide by a single secondary coil.

Particularly, it is provided that each secondary coil 3,4 can supply a maximum voltage of about 46. 000 V.

Furthermore, according to the invention, each winding element 5 can be provided with a spiral conductor 8 on each face of plate 6 and the winding elements 5 are spaced apart by insulating

means made of vetronite plates or other electric insulators.

The main advantage of the present invention is to provide an electric transformer stable during the operation and having characteristics, which can be industrially repeated with high precision.

Further advantage is to provide an electric transformer, particularly for high voltage and high frequency, having efficiency higher than the known transformer efficiency and having cheap manufacture, since the application of insulators and the wire winding is eliminated.

Other advantage is to provide a transformer minimizing the effect of the parasitic capacitances, reliable and with perfectly and homogeneously insulated coils.