WO1997001177A1 - Selv-generating transformer for supply switches - Google Patents

Abstract

A compact flat transformer for supply switches allows the supply switch into which the transformer is integrated to be designed in such a way that it fits into a panel, in particular a presspahn panel, having 19 mm or less standardised thickness, without protruding out of the panel. In spite of its reduced height, this transformer can transmit a power of at least 60 watts. The transformer has a maximum height of 19 mm and includes a coil body (11) in a single piece that carries a single flat primary winding (13) and at least one equally flat secondary winding (14a, 14b) so that the windings are located directly next to each other and separated by an airgap and leakage path that are accurately defined only by a thin circular wall (11b, 11c) of the coil body (11). In one preferred embodiment, insulating washers (11b, 11c) that form an integral part of the coil body (11) are arranged on both sides of the primary winding (13) and a spiral, self-supporting secondary winding (14a or 14b) made of a single layer lies on the side of the insulating washers (11b, 11c) opposite to the primary winding (13). The coil body (11) and windings (13, 14a, 14b) are spray-coated with an insulating mass (15) so that the insulating washers (11b, 11c) on both sides of the primary winding are molecularly joined without gaps to the sprayed coating (15) at least around their circumference. The sprayed coating is preferably made of the same material as the coil body (12).

Description

 description

Switching power supply transformer for generating a SELV voltage

The invention relates to a transformer for a switching power supply for generating a SELV voltage (Safety Electric Low Voltage), in particular for operating one or more halogen lamps.

The object of the invention is to make the transformer so flat that it is possible to install it together with the appropriately sized switching power supply completely in a plate, in particular chipboard, of the type used in furniture and housing construction at least from a thickness of 19 mm , although it should be capable of transmitting a power of a few 10 watts despite its small height, should have a high degree of efficiency in order to avoid heat development that is particularly critical in this application and, moreover, should be able to be produced automatically in a simple manner while ensuring the prescribed safety distances.

The above object is achieved by the features mentioned in claim 1.

Switched-mode power supplies can be produced with the transformer according to the invention, which at least fit into boards with a thickness of 19 mm or more and thereby enable a power transmission of 60 watts and more. Despite this high level of functionality, the transformer is easily mechanically vol.automatically and with a high level

ORIGINAL DOCUMENTS Accuracy, especially with regard to compliance with the prescribed air and creepage distances and material thicknesses between the primary winding and the secondary winding (s) can be produced.

With the intended use for the transformer according to the invention, it is important to keep the heat development in general and in particular also in the case of a short circuit on the secondary side low. In this regard too, the transformer according to the invention exhibits very advantageous operating behavior. The use of a single secondary winding on the side next to one or at most between two secondary windings on the one hand brings about a certain reduction in the coupling between the primary side and the secondary side and thus a corresponding short-circuit strength, while on the other hand the length of the middle leg specified by the prescribed thickness of insulation material between the individual windings of the core, at least the total insulation thickness to be provided is optimally small, so that even relatively thick wires can be used for the windings within the specified, relatively low maximum overall height of the transformer, which is very beneficial for the undesirable heat development due to the ohmic winding resistance. In any case, the achievable coupling between the primary side and the secondary side is completely sufficient for the desired high power transmission capacity, that is to say that the transformer according to the invention achieves a very good compromise in every respect.

Attempts have already been made to produce transformers for switching power supplies that are so flat that the switching power supply fits into a furniture building board.

In a first known type, the transformers have a toroid on which the primary winding is wound.

The core and primary winding are in a double-shell casing completely encapsulated from plastic. This sheath has a center hole insulated from the core and primary winding, and the secondary winding is wound through the center hole on the outside over the sheath. These known transformers require a considerable amount of machinery to manufacture, and the achievable production speed leaves something to be desired.

In contrast, as already explained above, in the available dimensions of the transformer structure according to the invention, a leakage inductance which is sufficient for short-circuit protection can also be readily achieved, but with a sufficiently good coupling between the primary winding and the secondary winding, in order to achieve high power transmission with low heat losses.

Other known transformers (Patent Abstracts of Japan: 5- 166646 A., E-1447, October 14, 1993, Vol. 17, No. 568; DE 37 18 383 AI) have several primary windings in the form of disks and several, also in the form of disks Secondary windings, which are pushed onto the middle leg of an EE core in an alternating sequence with the interposition of insulating washers. In DE 37 18 383 AI, the several primary windings have their own bobbin and are pushed together with the inherently rigid secondary windings and loose insulating washers onto a sleeve-shaped further bobbin, which is pushed onto the central leg of the core under this multi-part arrangement. In the aforementioned Japanese prior publication, all windings are designed as dimensionally stable, self-supporting loose elements and are arranged on the center leg of the core together with the loose insulating disks without an intermediate insulating sleeve. In both cases, the large number of individual winding and insulation elements present in the direction parallel to the center leg of the core results in compliance with the prescribed minimum insulation thicknesses between the individual L

Windings and when setting up a sufficient transmission of power for halogen lamps of a few tens of watts inevitably such a large height that it cannot be accommodated in a particle board of 19 mm thickness or less. In addition, the coupling between the primary side and the secondary side would be so great in both cases with a disk thickness that was optimized with regard to the prescribed insulation thickness between the windings that there would not be sufficient short-circuit strength, so that thicker insulation washers would have to be used between the windings for this purpose, as a result of which the achievable minimum height of the transformer would be further increased.

The subordinate claims relate to advantageous developments of the transformer according to patent claim 1. The design according to patent claim 6 is of particular importance here. This enables the transmission of particularly high electrical power from the power network to low-voltage consumers, as well as dimensions that are optimally small in the lateral direction enable the required safe separation between the primary and secondary sides. With regard to the desired molecular connection between the bobbin wafers at least on their circumference and the encapsulation, it is particularly advantageous to use the same material for the encapsulation and the bobbin according to claim 7. In a transformer according to the invention with the features according to patent claims 6 and 7, the bobbin washers do not need to protrude much around the primary winding and the secondary windings, because even under thermal movements due to the same temperature behavior of the bobbin and the insulating material due to the use of the same material, no creepage and clearance between the surroundings - circumferential side of the primary winding and on both sides next to the Spu¬ lenkörperscheiben adjacent thereto secondary windings may arise, so that relatively small distances between the primary winding and the secondary windings zuläε ^'are ig. In addition, the Primary winding and secondary windings can be realized with the same diameter, whereby an optimal coupling can be achieved. For example, a practical transformer for a power transmission of 105 watts has a height of only about 12 mm and a maximum lateral extension of 35 mm.

The invention is explained in more detail below with the aid of exemplary embodiments.

The drawing shows:

1 is an exploded view of a first exemplary embodiment of the transformer according to the invention in side view,

2 shows the transformer according to FIG. 1 in a side view in a position rotated by 90 ° with respect to FIG. 1, the core being shown in section along the section line II in FIG. 2,

3 shows the transformer according to FIGS. 1 and 2 in a view from above,

Fig. 4 shows the entire switching power supply with a transformer according to the invention in a schematic representation, seen from the side.

5a to 5c a further embodiment of the transformer according to the invention before the encapsulation with an insulating compound, u. 5a partly in cross-section and partly in side view along the section line Va-Va in FIG. 5b, in FIG. 5b with respect to FIG. 5a in a view from below and in FIG. 5c with respect to FIG. 5a in

Top view, and 6a to 6c the transformer according to Fig. 5a-5c after overmolding with the insulating compound in the finished state, namely in

Fig. 6a in cross section along the section line Vla-Via in Fig. 6b, in Fig. 6b with respect to Fig. 6a in

View from below and in Fig. 6c with respect to Fig. 6a in

View from above.

In the embodiment shown in FIGS. 1-3, the transformer has a coil former 1 which, as can be seen in FIGS. 1 and 2, has two flat winding spaces 1d and le between relatively thin outer walls 1a and 1b and a likewise thin middle wall 1c limited, of which one (ld) has a smaller height than the other (le), the former receiving the secondary winding ld 'and the latter the primary winding le'. A bore lg extends through the central part 1f of the coil former 1.

The core 2 of the transformer consists of two identical halves 2a and 2b, which have an E shape, the side legs 2c and the yoke sections 2d have a rectangular cross section and the center leg 2e is circular in cross section.

The outer walls la and lb of the coil former 1 are provided on the outside with groove-like recesses lh extending perpendicular to the plane of the drawing in FIG. 2, into which the core halves 2a, 2b with their yoke sections 2d can be inserted. In the assembled state of the transformer, the middle leg sections 2e of the core 2 engage in the central bore 1g of the coil former 1, the side legs 2c colliding on the end faces essentially without a gap, so that the total height x of the transformer is twice the height x / 2 of the side legs 2c corresponds to the core halves 2a, 2b.

For easy removal of one end of the Secondary winding ld ^'', the outer wall la has the coil body 1 a in Fig. 3 to be seen segment li on from which one end of the single-layer secondary winding ld 'from the inside to the out in Fig. 3 to be seen associated connection contact 3a is The other, outer end of the secondary winding ld 'is connected to the connection contact 3b.

The primary winding le 'is connected to the contact pins 4 shown in FIG. 1.

In a practical embodiment of a transformer according to FIGS. 1 to 3, the total height x of the core composed of the core halves 2a and 2b is approximately 10 mm. A power of approx. 60 W can be transmitted via this core.

The entire switching power supply consists, for example, as shown schematically in FIG. 4

a) the transformer Tr,

b) the switching power supply electronics SE,

c) a flat carrier arranged adjacent to a broad side of the transformer Tr and preferably designed as a circuit board P for the latter and the switching power supply electronics SE,

d) the line connections (3a, 3b, 4), and

e) a thin-walled envelope U surrounding the aforementioned parts,

the switched-mode power supply electronics SE being arranged laterally next to the transformer Tr in the region of its height, ie for

Total height of the switching power supply does not contribute. In the case of a baus in a chipboard of 16 mm thickness thus remains for the board P arranged immediately adjacent to a broad side of the transformer Tr including the line connections 3a, 3b, 4 and the sheath U a height of 6 mm. This height is sufficient. The circuit board P is preferably arranged on the transformer side on which the winding connections 3a, 3b and 4 are located.

The center disk lc of the coil former 1 projects beyond the primary coil and the secondary coil to such an extent that the prescribed length of the clearance and air gap between the primary coil and the secondary coil, including the connections of the latter, is present.

In the exemplary embodiment of the transformer according to the invention shown in FIGS. 5a to 6c, it has a coil former 11, a core 12, a primary winding 13, two secondary windings 14a, 14b and an outer extrusion coating 15.

The core 12 has an E-E shape with a central leg 12a with a circular cross-section and side legs 12b with a rectangular cross-section, which extend outside the coil former 11 and the windings 13, 14a, and 14b.

The coil former 11 has a tubular middle part 11a, two of which are parallel to one another at a mutual distance

Extend discs llb and 11c radially outward. The disks 11b and 11c delimit the multi-layer wound between them

Flat winding chamber 11k receiving primary winding 13 and are each on their broad side facing away from primary winding 13 in a winding space 111 which is open to the side and which can be regarded as a flat chamber open to the side, with a

Secondary winding 14a and 14b occupied, which is wound from thick wire spirally self-supporting in one layer. The

Secondary windings 14a and 14b are fixed in the radial direction circumferentially on the outside in their position on the respective disk 11b and 11c by means of projections 11d that extend from the outside protrude broad sides of the discs llb and llc. The secondary windings each surround a collar Ile, which is formed by the central coil body part 11a protruding somewhat beyond the outer broad side of the relevant disk 11b or 11c and fixes the associated secondary winding in the radially inward direction.

The disks 11b and 11c have projections 11f and 11g which extend outward from them at diametrically opposite locations for fixing the ends 13a and 13b of the primary winding 3 on the one hand and 11h and 11i for fixing the ends 14al, 14a2 as well as 14bl and 14b2 of the secondary windings 14a and 14b on the other hand.

The ends 14al, 14a2, 14bl, and 14b2 of the secondary windings 14a and 14b are bent toward the side of the coil former 11 located at the bottom in FIG. 1a parallel to its central axis M and protrude somewhat from the shoulder III as contact pins, the ends 14al and 14a2 of the secondary winding 14a penetrate the shoulder 11h on the adjacent disk 11b through a hole.

The ends 13a and 13b of the primary winding 13 are each fastened to a contact pin 16a and 16b, which is fastened in the lateral extension 11f of the disk 11c and extends parallel to the coil core central axis M and which the respective end 13a or 13b wraps around. The winding end 13a coming from an outer turn of the primary winding 13 is first guided over the lateral extension 11g of the coil former disc 11b and only then to the pin 16a in order to achieve a particularly reliable position fixation. The core webs 12c on both sides crossing the secondary windings 14a and 14b are each provided with a recess 12d, which creates space for the respective inner end of the adjacent primary winding 14a or 14b, which is led outward over the spiral winding to the fixing attachment assigned to it. After the assembly of the individual parts of the transformer, which can be seen from FIGS. 5a-5c, the latter is extrusion-coated in the manner best seen in FIG. 6a with an insulating compound, which consists of the same material as the coil body 11, preferably of thermoplastic polyester. The encapsulation is carried out in such a way that in the finished encapsulation 15 insulating compound from the latter and the coil former 11, at least along the edge region of the coil former disks 11b and 11c, have formed a molecular connection with one another without gaps, so that the dividing line drawn in FIG. 6a between these parts at least there largely or completely disappears and thus the primary winding 13 is reliably encapsulated without the possibility that an air gap is formed towards the one and / or other secondary winding 14a, 14b under thermal movements. In addition, the extrusion coating 15 also covers the secondary windings 14a, 14b up to the core webs 12c.

The encapsulation of the coil body provided with the windings is preferably carried out without the core of the transformer, because the pressure on the core could change μ, as was the case with the simple casting of the coil body with the windings in a shell together with the core, which has been frequently practiced up to now can happen.

The drawing shows on a scale of about 2: 1 a practical embodiment of a transformer according to the invention according to FIGS. 5a-6c, via which a power of 105 watts can be transmitted, the secondary windings 14a, 14b being dimensioned such that they are each for have an output voltage of approximately 12 volts, so that the secondary voltage of the transformer is approximately 12 volts when the secondary windings are connected in parallel and approximately 24 volts when the secondary windings are connected in series.

Overmolding with an insulating compound that connects unusually intimately to the coil body also favors this

Heat dissipation to the outside, which is particularly considering which, compared to the embodiment according to FIGS. 1 to 3, has a larger coupling between the primary side and the secondary side, particularly in the case of a short circuit on the secondary side.

Claims

claims 1. Transformer for a switching power supply for generating a SELV voltage, in particular for operating one or more halogen lamp (s), the transformer as a flat transformer with a magnetic core made of ferrite material (2; 12) essentially in EE or EI Form is executed and a flat primary winding (le ', * 13) surrounding the middle leg (2e; 12a) of the core (2; 12), at least one the middle leg of the core (2; 12) in its axial direction next to the primary winding (le ', 13) surrounding flat secondary winding (ld'; 14a, 14b) and one each from the central leg (2e; 12a) of the core (2; 12) to at least the outer contour of the primary winding (le ¹ ; 13) reaching insulating disc (lc, * llb, llc) on both sides of the primary winding (Ile ¹ ; 13), characterized in that a) each insulating disk (lc, * llb, llc) is part of a one-piece coil former (1; 11) which surrounds the central leg (2e, * 12a) of the core (2; 12) and at least two each by a disk (lc, * llb, llc) forms separate, flat chambers (le, ld; 11k, 111), in one (le; 11k) of the primary winding (le ¹ , * 13) is kept insulated from the core (2; 12) and in the other (ld; 11k)) a secondary winding (ld '; 14a, 14b) is arranged, and b) the transformer without taking into account the connecting pins (4; 14a _1; 14a ₂ , 14b- _. , 14b ₂ ) one by the total length of the essentially gap-free Core outer leg (2c, * 12b) has a maximum height of 19 mm. 2. Transformer according to claim 1, characterized in that the material of the core (2, -12) and its dimensions are chosen so that a power of at least 60 watts can be transmitted via the transformer at a transmission frequency of at least 45 kHz. 3. Transformer according to claim 1 or 2, characterized in that the transformer has a maximum height of 16 mm. 4. Transformer according to one of the preceding claims, characterized in that each the flat winding chamber (le) for the primary winding (le ¹ ) from a flat winding chamber (ld) for a secondary winding (ld ') separating disc (lc) of the coil former (1) has an outer diameter which is at least 3 mm larger than that of the primary winding (le ¹ ). 5. Transformer according to one of the preceding claims, characterized in that the at least one Secondary winding (ld ') adjacent to the primary winding (le ¹ ) receiving at least one chamber (ld) on the side facing away from the primary winding (le ¹ ) is delimited by a wall (la) corresponding to the safety regulations. 6. Transformer according to claim one of claims 1 to 3, characterized in that a) on the side of each disk (11b, 11c) of the coil former (11) facing away from the primary winding (13), a spiral-shaped, self-supporting secondary winding (14a, 14b) is arranged and fixed in the radial direction, and b) the coil former (11) with the secondary windings (14a, 14a, 14b) is overmolded with an insulating compound (15) which overlaps the disks (11b, 11c) with the primary winding (3) and the secondary windings (14a, 14b) and each disk (11b, 11c) at least along the extent of which has a complete molecular connection. 7. Transformer according to claim 6, characterized in that the Isoliermaεεe (15) consists of the same material as the coil former (11). 8. Transformer according to claim 6 to or 7, characterized in that the coil body (11) and the Isolierma¬ εεe (15) consist of thermoplastic polyester. 9. Transformer according to one of claims 6 to 8, characterized in that the secondary windings (14a, 14b) are wound in a self-supporting manner from thick wire and for their fixing in the radial direction on the respective disk (11a, 11b) on the outer circumferential projections ( Ild) are provided, which protrude outwards from the disk broad sides facing the secondary windings (14a, 14b), and that the central middle part (lla) of the coil former (11) protrudes slightly beyond each disk (11b, llc) and there in each case forms a collar (le) which centrally aligns and fixes the relevant secondary winding (14a or 14b). 10. Transformer according to one of claims 6 to 9, characterized by peripheral projections (11g, 11h, 11f, lli) on the bobbin washers (llb, llc) for fixing the winding ends, the ends (14al, 14a2) of one secondary winding (14a) through bores in the lugs (11h, lli) assigned to them to the other secondary winding (14b) occupied disk broadside and, like the ends (14bl, 14b2) of the latter secondary winding (14b), form contact pins for connection to an external circuit.