WO1996021935A1 - Planar transformer for a switched-mode power supply used for producing low voltages and a method of manufacturing the said transformer - Google Patents

Abstract

The proposed planar transformer (1) for a switched-mode power supply used for producing low voltages comprises two or more plastic carrier plates (2) on which are printed helical primary or secondary coils, the carrier plates form a sandwich with an insulating layer between them and are provided with a magnet core; a central limb of the magnet core protrudes through a central aperture in the carrier plates and each carrier plate (2) is provided on both faces with an imprinted coil (3a, 3b), the coils being connected in series by a plated-through interconnection. To improve potential separation with a view to adapting the coils to low-power outputs and simplifying manufacture, the coils (3a, 3b) are imprinted on a 10-100 micron thick plastic film (12). Two coil ends (3c, 3d) lie exposed over a notch (10) in the plastic film (12) and the plastic film (12) provided with the two coils (3a, 3b) has an insulating thermoplastic synthetic material (11) sprayed around it, said material pressing the two coil ends (3c, 3d) firmly together in the region of the notch (10). During manufacture of the carrier plates (2), the coil ends (3c, 3d) are made to lie exposed above the notch (10) in the plastic film (12) and the plastic film (12) provided with the coils (3a, 3b) is provided with a surrounding insulating thermoplastic synthetic material (11) which is sprayed under high pressure. To assemble a planar transformer (1), two or more carrier plates (2) provided with surrounding material (11) are stacked, the magnet core is fitted and the components are fixed with a sprayed insulating thermoplastic synthetic substance.

Description

Planar transformer for switching power supplies for the generation of low voltages and method for its production

The invention relates to a planar transformer for switched-mode power supplies for generating extra-low voltages, consisting of two or more plastic support plates provided with spirally printed primary or secondary windings, which are sandwiched with an electrically insulating layer and are provided with a magnetic core with a middle leg protrudes through a central opening of the carrier plates, each carrier plate having a printed winding on both surfaces, the winding ends of which are electrically connected in series by means of a plated-through hole. Furthermore, the invention is concerned with methods for the production of such a carrier plate for the production of a planar transformer.

A planar transformer corresponding to the preamble of claim 1 can be found in electronics practice no. Nov. 21-3, 1994, pp. 61-62. Planar transformers of this type are generally equipped with approximately 0.25 mm thick carrier plates made of plastic, a perforation and a mostly sleeve-shaped contact element formed by electroplating being arranged in the carrier plate for through-contacting the winding ends. Similar sleeve-shaped contact elements are also used for through-plating two or more carrier plates connected in series. The printed windings must have a certain minimum distance to ensure adequate protection against breakdown. In addition, the perforation for the plated-through hole, because of the spiral guidance of the windings at the edge of the For reasons of strength, the carrier plate lies at a minimum distance from the edge of the carrier plate which must at least correspond to the hole diameter. However, these measures disadvantageously cause enlarged dimensions of the planar transformer. The through-contacting is also very complex. Another disadvantage is that the known planar transformers are only suitable for power above about 60 W because of the necessary electrical isolation between the primary and secondary circuits and due to the necessary air and creepage distances of the windings to the magnetic core.

From DE-PS 906 831 an induction coil is also known, in which windings are printed on both sides of a band-shaped plastic film, two opposite spirals having their inner ends in contact with one another through a small opening in the insulating material. The tape is folded in a zigzag pattern, the spirals being covered by a layer of lacquer for insulation or insulating plates being inserted between them. Finally, in DD-PS 205 578 a isolating transformer is described, on each of the surfaces provided with a conductor track layer, a winding is applied according to the sealing layer technique; the entire winding arrangement is covered with a highly insulating synthetic resin coating.

In contrast, the object of the invention is to improve the potential separation between the primary and secondary circuits, to make the planar transformer accessible even for powers below 60 W and to simplify its manufacture.

The object is achieved by the features specified in the characterizing part of claim 1.

The use of a particularly thin plastic film as the carrier plate initially has the advantage of a substantially smaller thickness, which results in a substantial reduction in the Dimensions of the planar transformer is reached. Furthermore, the extremely small thickness of the plastic film allows a much easier through-contacting by mechanical means. The two bare winding ends are pressed together in the area of a cutout in connection with a plastic extrusion coating in order to achieve the desired series connection of the two windings. The cutout and the plated-through hole can be placed much closer to the edge. The extrusion coating finally creates insulation which is an integral part of the carrier plate or plastic film provided with the windings, so that no special insulating foils need to be interposed when the carrier plates are stacked. This also improves the dielectric strength and electrical isolation so that the planar transformer, depending on the switching frequency, is also suitable for smaller powers of approximately 10 W and below.

The carrier plate built into the planar transformer can be produced in a particularly simple manner by printing the spiral-shaped windings onto the two surfaces of an approximately 10 to 100 μm thick film made of plastic, the winding ends being bare over a cutout in the plastic film lie and the plastic film provided with the windings is overmolded under high pressure with an electrically insulating thermoplastic material such that the two winding ends are pressed firmly against one another in the region of the cutout. The plastic mass is expediently encapsulated at a pressure greater than 50,000 hPa and applied in such an amount that the coating is less than 0.2 mm thick.

A method which is particularly suitable for producing a planar transformer provides that the plastic films overmolded with the electrically insulating plastic compound are stacked, fitted with the magnetic core and the components of the Unit can be mechanically fixed by extrusion coating with another electrically insulating thermoplastic material.

An embodiment of the invention is shown in the drawing; it shows

1 shows a planar transformer in a perspective view,

2 shows the object of FIG. 1 in a schematic exploded view,

3 shows a partial cross section through a carrier plate in the area of the plated-through hole in a schematic representation,

4 shows a partial cross section through a planar transformer with three carrier plates in a schematic representation and

5 shows the process steps in the manufacture of planar transformers in connection with a carrier film.

The planar transformer 1 shown in FIG. 1 is essentially composed of three carrier plates 2 consisting of thin plastic films, each of which is provided on its two surfaces with a spirally printed conductor track-like winding 3 and with connecting lugs 4 and the like Training is described in more detail below. In addition, a two-part magnetic core 5 is provided which is designed as a jacket core. The upper part of the magnetic core 5 has, as shown in FIG. 2, two side legs 6, a middle leg 7 and a lower yoke 8. The carrier plates 2 are provided with a central opening 9 through which the middle leg 7 of the magnetic core 5 protrudes. In the area of the inner ends of the printed windings 3 a cutout 10 is provided, which serves for through-contacting the winding ends 3c, 3d. In addition, the carrier plates 2 are coated with an insulating plastic compound 11. The windings 3 of the three carrier plates 2 are switched so that they form the primary or secondary windings of the planar transformer 1.

The carrier plates 2 consisting of a very thin flexible plastic film 12 made of a temperature-resistant plastic such as polyamide or the like. The film thickness is between approximately 10 and 100 μm depending on the intended performance. The plastic film 12 is printed on its two surfaces with a spiral, conductor track-like winding 3 made of copper or the like. Depending on the application, the thickness of the copper coating varies between a few micrometers and 200 μm, preferably between 20 and 200 μm. 3 shows the upper winding 3a and the lower winding 3b, the winding ends 3c and 3d of which are arranged bare above the cutout 10 in the plastic film 12 and are pressed against one another by means of an overmolded plastic compound 11, so that the upper and lower windings 3a, 3b are connected in series. An electrically insulating thermoplastic is suitable as the plastic compound 11. The thickness of the extruded plastic compound 10 should be less than 0.2 mm. The injection molding of the plastic mass 11 takes place under such a high pressure that the winding ends 3c, 3d are pressed firmly against one another in the cutout. For example, the injection molding can take place at a pressure of 50,000 hPa. In this way, a carrier plate 2 is formed, which consists of a plastic film 12 with plated-through windings 3a, 3b and an insulating coating made of plastic compound 11.

Depending on the application, two or more carrier plates 2 are stacked and assigned to a planar transformer 1 as primary or secondary windings. The arrangement of three carrier plates 2 is illustrated in FIG. 4. Thieves- Layering of plastic mass 11 isolates the carrier plates 2 from one another and brings about potential isolation. To form a planar transformer 1, the stacked three carrier plates 2 are provided with the magnetic core 5. In order to fix the components of the planar transformer 1 in their position, the assembled structural unit can be extrusion-coated with an insulating thermoplastic material.

5 shows the production of planar transformers 1 in connection with a film-like plastic film 12, which is transported through a plurality of processing stations I to VIII by means of an edge perforation 13a. First, at station I the plastic film 12 is provided with openings 9 and cutouts 14 for the passage of the side legs 6 and the middle leg 7 of the magnetic core 5 and with the cutout 10 for through-contacting the winding ends. The stations II and III are used to print the plastic film 12 with the two windings 3a, 3b. The plastic film 12 with the printed windings 3a, 3b is overmolded with the plastic mass 11 on station IV, the winding ends 3c, 3d being pressed against one another in a current-conducting manner. Station V includes stacking two or more carrier plates 2. The magnetic cores 5 are installed in station VI and in station VII the assembly unit is extrusion-coated with an insulating plastic compound 15. Finally, the planar transformers 1 are isolated at station VIII. This method advantageously allows fully automatic production, which can also be carried out continuously.

Although the exemplary embodiment provides three carrier plates 2, planar transformers 1 with two, four or more carrier plates 2 can of course also be produced. Reference list

1 planar transformer

2 carrier plates

3 windings

3a upper winding

3b lower winding

3c winding ends

3d winding ends

4 connecting lugs

5 two-part magnetic core

6 side legs

7 thighs

8 yokes

9 opening

10 cutout

11 plastic mass

12 plastic film

13 perforation

14 cutouts

15 plastic mass

Claims

claims 1. Planar transformer for switched-mode power supplies for generating extra-low voltages, consisting of two or more plastic carrier plates provided with spirally printed primary or secondary windings, sandwiched with an electrically insulating layer and provided with a magnetic core with a middle leg protrudes through a central opening of the carrier plates, each carrier plate having a printed winding on both surfaces, the winding ends of which are electrically connected in series by means of a plated-through hole, characterized in that the windings (3a, 3b) are 10 to 100 μm thick Foil (12) made of plastic is printed, two of the winding ends (3c, 3d) are arranged bare above a cutout (10) in the plastic film (12) and the plastic film (2, 3a, 3b) is provided with 12) with an electrically insulating thermoplastic material It is overmolded in such a way that the two winding ends (3c, 3d) are pressed firmly against one another in the region of the cutout (10). 2. Planar transformer according to .Anspruch 1, characterized in that the windings made of copper (3a, 3b) have a thickness between 20 to 200 μm. 3. Planar transformer according to .Anspruch 1 or 2, characterized in that the thickness of the molded plastic materials (11) is less than 0.2 mm. 4. A method for producing a support plate provided on both surfaces with a printed spiral winding and made of plastic for the formation of primary or secondary winding for planar transformers for generating low voltages, the winding ends being plated through, characterized in that the spiral Windings are printed on the two surfaces of a 10 to 100 μm thick film (12) made of the plastic, the winding ends (3c, 3d) coming to lie bare over a cutout (10) in the plastic film (12) and those with the windings (3a, 3b) provided plastic oil (12) under high pressure with an electrically insulating thermoplastic material (11) - in such a way that the two winding ends (3c, 3d) firmly in the region of the cutout (10) be pressed against each other. 5. The method according to claim 4, characterized in that the plastic mass (11) with a pressure greater than 50,000 hPa is overmolded. 6. The method according to claim 4 or 5, characterized gekennzeich¬ net that the plastic mass (11) is applied in a thickness less than 0.2 mm. 7. A method for producing a planar transformer for switching power supplies for generating extra-low voltages according to one of claims 1 to 6, characterized in that two or more plastic foils (12) overmolded with the electrically insulating plastic compound (11) are stacked with the magnetic core (5) and the components of the assembly are mechanically fixed by extrusion coating with another, electrically insulating thermoplastic material (15).