Abstract:
The iron core ( 2 ) and the windings ( 3, 4 ) of a transformer ( 1 ) are held together by a coil former ( 21 ) which is arranged in an injection mould in such a way that it comes into contact with said mould only with small parts at its surface, whereas the transformer ( 1 ) is a distance away from its walls. A plastic shell ( 22 ) is then moulded on to complete a small and light integral casing ( 7 ) enclosing the transformer all round and in an abutting manner. Joints between the coil former ( 21 ) and the shell ( 22 ) are essentially at the bottom of indentations which separate cooling fins ( 20 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a mains adapter and a method for its production. Mains adapters are used for stepping down the mains voltage so that electrical equipment requiring low voltage, such as, for example, chargers, can be operated thereon. 
     DESCRIPTION OF THE RELATED ART 
     European Patent No. EP-A-0 485 341 discloses a mains adapter of the generic type, in which the transformer held together by an integrally moulded holder is surrounded by a mould sleeve, which however leaves large parts of the surface of the transformer free. To ensure that the transformer is completely encased, the mains adapter of the generic type therefore additionally comprises a housing which surrounds the partly encased transformer in part with a spacing. The mains adapter therefore has a relatively large volume. Its production requires insertion of the transformer into the housing after preliminary injection moulding steps, in which, on the one hand, the transformer was completed and, on the other hand, the parts of the housing were produced, and is therefore relatively complicated. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to provide a mains adapter of the generic type which can be designed to be very small and can be produced simply and cheaply. This object is achieved by an integral plastic casing completely enclosing the transformer in an abutting manner, so as to permit only contact elements and connections to extend through the casing and connect to the transformer. In addition, the present invention intended to provide a particularly suitable, very simple and cheap method for the production of a mains adapter. These exemplary objects the invention. This object are achieved by the steps providing a transform including an iron core, a primary winding, and a secondary winding; providing a coil former configured for supporting the iron core, the primary winding and the secondary winding of the transformer; providing an integral shell shaped for covering at least one portion of an outer surface of the transformer; arranging the transformer and the coil former in an injection mould while the coil former supports the iron core, primary winding and secondary winding of the transformer; and moulding the integral shell onto the transformer and the coil former so as to form an integral plastic casing completely enclosing the transformer in an abutting manner, thereby permitting only contact elements and connections to extend through the casing and connect to the transformer. 
     The advantages achieved by the present invention lie essentially in the fact that no additional housing is required. As a result the mains adapter according to the invention is very small and light and hence easy to accommodate and convenient to transport. Moreover, the mains adapter of the present invention is not only extremely stable, with regard to mechanical or structural properties, but also meets the usual safety requirements with regard to its electrical properties. The mains adapter of the present invention also removes heat in an improved manner. In addition, the present invention includes manufacturing such a main adapter in an extremely simple manner and consuming materials in an efficient matter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in more detail below with reference to Figures, which represent merely an embodiment. 
     FIG. 1 a  shows a perspective view of a mains adapter according to the invention, 
     FIG. 1 b  shows a plan view of the mains adapter according to FIG. 1 a , with the cover removed, 
     FIG. 2 a  shows a horizontal section along the plane A through the mains adapter according to FIG. 1 a,    
     FIG. 2 b  shows a vertical section along the plane B through the mains adapter according to the invention and according to FIG. 1 a,    
     FIG. 2 c  shows a horizontal section along the plane C through the mains adapter according to the invention and according to FIG. 1 a,    
     FIG. 2 d  shows a vertical section along the plane D through the mains adapter according to the invention and according to FIG. 1 a,    
     FIG. 3 shows a section through a transformer and coil former of a slightly modified embodiment of the mains adapter according to the invention and according to FIG. 1 a,    
     FIG. 4 shows a section through the transformer with coil former corresponding to FIG. 3 in an injection mould and 
     FIG. 5 shows a section corresponding to FIG. 3 through a mains adapter according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The mains adapter has a transformer  1  with an iron core  2  consisting of E-shaped and I-shaped laminations and with a primary winding  3  and a secondary winding  4  which, axially in succession, surround a central yoke  5  of the iron core  2 , which is flanked by outer yokes  6   a, b.    
     The transformer  1  is completely enclosed by a plastic casing  7  which rests against its entire outer surface. Only various wired connections in the form of connecting pins, namely a primary connection  8   a  and secondary connections  9 , are led through the casing  7 . One end of the primary winding  3  is connected to a first contact pin  11   a  via the primary connection  8   a  and a fuse  10  connecting thereto, while a second contact pin  11   b  is connected directly to a primary connection  8   b , a piece of winding wire drawn from the other end of the primary winding  3 . The secondary winding  4  is connected to a cable  13  via the secondary connections  9  and a circuit  12 . The circuit  12  may comprise, for example, a rectifier and a smoothing capacitor. 
     The connections  8   a ,  9  are led out on the same side from the housing  7 , where they enter an indentation  14  in which the fuse  10  and the circuit  12  are also arranged. The indentation  14  is surrounded by an all-round side wall  15 . In addition, the primary connection  8   a  is separated from the secondary connections  9  by an approximately U-shaped partition  16 , the ends of which adjoin the side wall  15 . The indentation  14  is closed by a cover  17  through which the cable  13  is led. The cover  17  has an opposite wall  18  which, when the cover  17  is mounted, runs a small lateral distance away from the cover inside the partition  16  and overlaps with it. As a result of this separation of the primary side from the secondary side, arc-overs or leakage currents between them are virtually ruled out. On the back, the casing  7  has continuous cooling fins  19  and further cooling fins  20 , running transversely thereto, on opposite edges. 
     The casing  7  is composed of two parts. The first part is a coil former  21 , a prefabricated one-piece injection moulded part, which is wound with the primary winding  3  and the secondary winding  4  and into which thereafter an E-shaped lamination is inserted alternately from each of two sides and an I-shaped lamination from the other side for the formation of the iron core  2 . It also carries the contact pins  11   a,b , which are anchored in it and project from the casing  7  below the side wall  15  of the indentation  14 , parallel to the plane defined by its edge. The second part is a shell  22  which covers the larger part of the outer surfaces of the iron core  2  and of the windings  3 ,  4  and also forms the predominant part of the outer surface of the casing  7 , but also separating layers between the primary winding  3  and the secondary winding  4  on the one hand and the outer yokes  6   a,b  of the iron core  2  on the other hand. The coil former  21  and the shell  22  are fused together at the joints so that the finished casing  7  is integral. It hermetically seals the transformer  1 , and does so by being directly adjacent to its outer surface all round, and, apart from the cover  17  and the contact pins  11   a,b , forms the total outer surface of the mains adapter. It is therefore very compact and the space it requires is very small. Thanks to the compact design and the close connection of its parts, the mechanical stability of said mains adapter is excellent. For the same reasons, it is also not susceptible to oscillations so that pulsed delivery of the output power is possible without problems. Owing to the close encasing which does not enclose air layers, the heat removal too is excellent and permits high power density. 
     The coil former forms only one small part of the outer surface of the casing  7 , in particular at the base of the three middle cooling fins of the further cooling fins  20 , alternatively referred to as the three cooling fin base portions, and at the intermediate spaces between them and at points on the opposite side of the casing  7 , i.e. in the indentation  14  (FIG. 1 b ). The joint between the coil former  21  and the shell  22  is therefore evident only in lower-lying, poorly visible areas and in areas concealed by the cover  17 . The coil former  21  and the shell  22  consist of the same material, e.g. polyamide, polycarbonate or ABS. 
     For the production of the mains adapter according to the invention (FIGS. 3 to  5 ), the transformer  1 , which is shown in FIG. 3 in a section corresponding sectional plane of FIG. 2 a , for example is first assembled by winding the coil former  21 , inserting the connecting pins for forming the primary connections  8   a,b  and secondary connections  9  therein and soldering them to the ends of the windings  3 ,  4  and then mounting the contact pins  11   a,b  and the iron core  2 . The iron core and windings are connected to the coil former  21  so that there is no mutual shifting of these parts in the following production steps. 
     The transformer  1  is then placed in an injection mould having a base  23 , an upper slide  24  and lateral slides  25  and the injection mould is closed. It rests in each case only with small parts of the coil former  21  against the walls of the injection mould, while the iron core  2  and the windings  3 ,  4  are a distance away therefrom. In particular, the bases of the middle cooling fins among the further cooling fins  20  rest on the base  23  while small sections of the opposite surface of the coil former  21  are in contact with the upper slide  24  and are held down by it (cf. FIG. 1 b ) so that the transformer  1  is fixed nondisplaceably in the injection mould. The fixing is further reinforced by the fact that the connections  8   a ,  9  are held in corresponding recesses in the wall of the upper slide  24  and the contact pins  11   a,b  in recesses of the appropriate lateral slide  25 . 
     Finally, the shell  22  is moulded on and the casing  7  is thus completed. The coil former  21  is slightly fused on at the joint with the shell  22  and connects tightly thereto. Only those sections of the surface of the coil former  21  which are in contact with the wall of the injection mould and have already been described further above rest against the outer surface of the casing  7 , while the predominant part thereof is formed by the shell  22 . The connecting pins and contact pins arranged in a protected manner in recesses remain bare. Finally, the injection mould is opened again (FIG. 4) and the virtually ready mains adapter is removed (FIG.  5 ). 
     It is also possible to fix the coil former by retractable retaining parts, in particular retaining pins in the injection mould and to retract said parts after the shell has been moulded on and to carry out subsequent injection moulding. In this case, the coil former—apart from connecting pins and contact pins—is completely encased and its outer surface is formed entirely by the shell. 
     The cover  17  is produced separately, likewise by the injection moulding method. Finally, the mains adapter is assembled by connecting the fuse  10 , the circuit  12  and the cable  12  and mounting the cover  17  on the casing  7  and welding it or screwing it to said casing. Because the connections led out are all arranged on one side, not only is the injection moulding process facilitated but also the steps mentioned are all carried out from this single side so that they can be effected without changing the position and can easily and quickly be performed manually as well as automatically. The same casing can be used to connect covers of different heights, so that the available space can be adapted to the space requirement of the wiring.