FIELD OF THE INVENTION

The present invention relates generally to a line circuit connection adapted for a telephone exchange, and more particular¬ ly to such a line circuit connection that includes a predeter¬ mined number of line circuits, for instance thirty line circuits, of which each can be allocated to a telephone exchange subscrib- er, wherein the line circuits are coordinated on a printed circuit board, a printed circuit board assembly or the like, that carries a plurality of discrete components belonging to respec¬ tive line circuits.

Each of the line circuits includes discrete components in the form of subscriber line resistances, each of said components being adapted to provide high heat dissipation.

DESCRIPTION OF THE BACKGROUND OF THE INVENTION

Several different embodiments of telephone-exchange-adapted line circuit connections of the aforedescribed kind are known to the art, and with regard to subscriber-line associated resistances, it is also known to mount the resistances on a circuit board in the form of discrete components.

It is also known that each of these resistances must be dimensioned to provide high heat dissipation. To this end, it is necessary to place the resistance body or resistance unit at an

adapted long distance from the outer surface of the circuit board, and preferably in the close vicinity of a casing that encases the circuit board, so that heat will be dissipated to the casing through a narrow air gap.

It is also known that the line circuit resistances may have a resistance value of 2 x 250, 2 x 400 or 2 x 800 ohms, depending on the circuitry concerned.

With regard to features of the present invention, it can be mentioned that it is known to form a resistance body from a foil having resistance conductors orientated in a loop. The foil can be given an adhesive layer for application to a heat-conducting material. Referenses are made to foils manufactured and sold through Casco Foil AB in Kolback, Sweden, as an example of foils of this kind.

SUMMARY OF THE INVENTION

TECHNICAL PROBLEMS

When considering the known state of the art as described above, it will be seen that a technical problem resides in providing with the aid of simple means and within a given arrangement conditions that will enable heat to be dissipated from subscrib¬ er-line allocated resistances directly to a well-adapted heat- absorbing surface in the absence of any appreciable air gaps, so as to achieve effective heat transfer and heat transport from the circuit board.

It will also be seen that a technical problem is one of realizing the significance of and the advantages afforded by physically separating the subscriber-line associated resistances from the circuit board or circuit board assembly.

Another technical problem is one of finding suitable mounting locations for the line circuit resistances, two for each line

circuit, such that heat will be effectively transferred to cooling flanges and like devices without deleteriously affecting the temperature of the circuit board assembly or circuit board concerned.

Another technical problem is one of realizing the significance of providing said resistances in the form of one or more resistance-exhibiting conductors applied to and/or formed by a foil, and to be able to readily relate said foil directly to a hea -absorbing surface separate from the circuit board assembly or circuit board.

In this regard, a technical problem resides in realizing the conditions required and the advantages that are afforded by connecting the conductors in said set of foils to a contact device which is related to said heat-absorbing surface and which is adapted for coaction with corresponding board-related contact devices.

Another technical problem is one of realizing the advantages that are afforded by enclosing said circuit board in a divided casing, such as a two-part or a three-part metallic or metalized casing in a known manner, and fastening said foils to one or more of the inner surfaces of the casing.

It will also be seen that a technical problem is one of realizing the significance of and the advantages afforded by fastening a plurality of foil-pairs for a plurality of line circuits on the casing surface or surfaces, with the foil conductors connected to a set or an array of contact devices, said contact devices conveniently being placed in a row to form a terminal unit.

In this regard, the printed circuit board shall also include a row of contact devices in a terminal unit, and the contact devices in respective terminal units shall coact mutually when the circuit board is in place and enclosed by the casing.

It will also be seen that a technical problem is one of realizing the significance of creating adapted heat dispersion with the aid of foil-like, line-circuit-associated resistances, and to allow at least one surface, preferably the two mutually opposing inner surfaces of the two parts of the casing, to form foil carriers.

It will also be seen that a technical problem is one of allowing all or a chosen number of said foils to be fastened to one or more frame-related U-bars or the like, such as U-bars for guiding the insertion and the withdrawal of a casing and enclosed circuit board, as an alternative and/or as a complementary feature.

Another technical problem is one of dimensioning the surface extension of the foil to exhibit an adapted resistance value and to be adapted to the number of line circuits on the circuit board and to effect adapted heat transport to the casing and/or the frame.

SOLUTION

The present invention takes as its starting point a telephone- exchange adapted line circuit connection of the aforedescribed kind and, with the intention of solving one or more of the aforesaid technical problems, suggests that subscriber-line associated resistances present in the line circuit connection are comprised of a conductor having an adapted resistivity, which is applied to a foil in a previously known manner, that the foil is related to a heat-absorbing surface for effective direct heat transfer, and that said conductor in said foil is connected to a surface-related contact device adapted for coaction with corresponding card-related contact devices.

It is proposed in accordance with embodiments that fall within the scope of the inventive concept that the circuit board is enclosed in a divided casing, and that the foil is fastened to an inner surface of the casing and/or on mutually opposing inner surfaces thereof.

It is also proposed that a plurality of foils are fastened to said surface (surfaces) with the conductors connected to an array of contact devices provided in a terminal unit or contact strip. The contact devices and terminal unit may conveniently be positioned in a row.

It is also proposed that the circuit board includes a terminal unit comprising a row of contact devices, and that the contact devices are in electrical and mechanical coaction with one another when the circuit board is placed in and enclosed by the casing.

It is also proposed that two mutually opposing inner surfaces of the casing parts are used as foil carriers.

One or more foils may be fastened to one or more frame-related U-bars that function to guide the insertion and withdrawal of a metallic casing and enclosed circuit board.

In one practical application of the present invention, each foil will have for a selected resistance value a surface extension measuring 10-20 mm x 40-120 mm with end-related exposed contact surfaces.

The foil may also conveniently be provided with an adhesive surface for fastening the foil to said heat-absorbing surface.

ADVANTAGES

Those advantages that are primarily characteristic of a tele¬ phone-exchange adapted line-circuit connection in accordance with the present invention reside in the provision of conditions that enable subscriber-line associated resistances that possess high heat dissipating properties to be placed directly against heat- absorbing surfaces in the absence of air gaps, said surfaces being comprised of cooling flanges, or in effective thermal contact with such flanges, therewith providing effective heat

transport without excessive heating of the line-circuit connec¬ tion devices on the printed circuit board or printed circuit board assembly concerned.

The main characterizing features of a telephone, exchange adapted line circuit connection in accordance with the present invention are set forth in the characterizing clause of the following Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of an inventive telephone-exchange associated and adapted line-circuit connection arrangement will now be described in more detail with reference to the accompany¬ ing drawings, in which

Figure 1 illustrates a cabinet having features significant of the present invention and adapted to accommodate a plurality of line circuit-board associated blocks in one perspective;

Figure 2 illustrates the cabinet shown in Figure 1 in an opposite perspective;

Figure 3 illustrates from above a block having a surface enlargement in the form of a cooling flange, wherein subscriber-line associated resistances are, in known manner, mounted on a casing-enclosed circuit board, and also illustrates in side view on a larger scale mounting of one such resistance;

Figure 4 is a perspective view of opposing U-bars for receiving a block with the U-bars mounted directly on respective

cooling flanges and with the resistance-exhibiting foils mounted on the U-bars;

Figure 5 is an exploded view of a casing and enclosed circuit board, with subscriber-line associated resistances in the form of foils mounted on mutually opposing inner surfaces of the casing in accordance with the inven¬ tion; and

Figure 6 is a perspective view of a resistance-exhibiting foil with an adhesive layer partially attached to a heat- absorbing surface.

DETAILED DESCRIPTION OF PROPOSED EMBODIMENTS

Figures 1 and 2 are different perspective views of a cabinet that accommodates a telephone-exchange associated cross-connection arrangement, among other things.

The cabinet is referenced 1 and includes a frame having two mutually parallel opposing sides la, lb and a cross-connection associated side lc.

The frame also includes a side Id from which a number of blocks, such as the block 10, can be inserted and withdrawn in a manner described in more detail hereinafter.

According to the invention, each block 10 shall be able to enclose a circuit board 10', which may include a plurality of line-circuit connections, for instance thirty connections, adapted for a telephone exchange.

As illustrated in Figure 1, the frame has mounted thereon one or more terminal units having coordinated subscriber-associated connection pins, of which the uppermost block is referenced 2a. The connection pins are disposed in superimposed rows to form a column 2, and a plurality of telephone-exchange related line-

circuit-associated connection pins 3a are coordinated in one or more terminal units fixedly mounted on the frame, and structured in rows such as to form a column 3.

As illustrated in Figure 1, each subscriber-associated terminal unit 2a is positioned in a column 2 that is located externally of the column 3 of line-circuit associated terminal units 3a.

The arrangement will normally include a relatively large number of cross-connection conductors, so-called jumpers, since each connected subscriber must have two physical conductors in an electrical connection with an own line circuit.

One such jumper 23 is shown in Figure 1 in a simplified manner, with the jumper connected to its pin in a manner described in more detail in the patent application filed this day by the same Applicant, and entitled "Cross-Connection Arrangement".

A predetermined number, in the illustrated case thirty, tele- phone-exchange related line circuits of principly known kind are coordinated in a block 10 that carries a printed circuit board assembly 10' .

With regard to a telephone exchange application, the invention requires access to a large number of subscriber-associated conductors available for connection to a subscriber-allocated line circuit through the medium of a cross-connection arrangement and conductors 23.

The cross-connection arrangement used will require a plurality of such blocks when applied in practice. However, because the remaining blocks are generally identical to the block 10, only the block 10 will be described hereinafter.

Each block 10 has an externally divided, e.g. a two-part or three-part, metal casing 10c, such as an aluminium casing, which encloses a printed circuit board 10' that coacts electrically

with the surroundings, line-circuit-associated connection pins and terminal units 3 through the medium of associated connection pins lOd.

Although the circuit board may have diverse functions, the following description is concerned solely with circuit boards that carry line circuits.

Each of the blocks 10 can be inserted and withdrawn along mutually parallel U-bars 11, 12 attached to the frame in a known manner, and then particularly to the frame sides la and lb, these sides being comprised of cooling flanges 13, 14.

The leading part of the block 10, as seen in the insertion direction, has mounted thereon a terminal unit lOe that includes line-circuit allocated connection pins lOd which, when the block 10 is fully inserted, make electrical and mechanical contact with telephone-exchange related connection pins in a terminal unit, such as the block 3a.

It is important that the connection pins lOd of a block are in direct, or indirect, electrical coaction with the connection pins of the terminal unit 3 and therewith externally accessible for connection of subscriber lines through the medium of jumpers 23.

The block 10 and the U-bars 11, 12 coact mechanically so that heat generated in the block by the components mounted therein will be conducted to the frame sides la, lb and to the cooling flanges 13, 14 mounted on said sides.

Discrete heat-generating components 10a, 10b, such as transform¬ ers, diodes, transistors, will preferably be placed on the printed circuit board 10' and in regions proximal to the U-bars 11, 12, depending on power development.

The thickness or thickness distribution of material within the casing or within the block are adapted for satisfactory transpor¬ tation of heat via the U-bars 11 and 12.

In this regard, the casing 10c may be given different thicknesses and the U-bars 11, 12 different lengths and widths.

The casing thickness, etc., may be chosen so that temperature rises will lie within given limit values even during high loads of shorter duration, for instance shorter than 30 min.

The casing 10c may conveniently be fully sealed, so as to provide an effective EMC protection.

The block may also be provided with one or more surface enlarge¬ ments.

Such a surface enlargement may have the form of cooling flanges 10g' provided on the edge lOg of the block 10 that lies distal from the terminal unit lOd.

It will be evident that the line-circuit related terminal unit lOe belonging to the block 10 shall be able to coact with a corresponding terminal unit lOh in a further block 15, this terminal unit having, in turn, a terminal unit 15a that coacts electrically with the line-circuit-associated terminal unit 3a.

The further block 15 may have the form of a simple connection between the connection pins of the terminal units lOe and 15a, or include circuit connections and/or circuit arrangements, such as overvoltage protectors.

Mutually opposing U-bars 11, 12 are fastened directly to adjacent cooling flanges in a known manner, and the legs Ila, lib of the U-bars are given a length (300 mm) and a width (150 mm) that provides the desired heat transfer.

The vertical distance between mutually adjacent legs Ila, lib shall only slightly exceed the thickness of the block 10.

Figure 1 is intended to illustrate that subscriber cables are arranged in a space 51 and that cable conductors shall be fastened to the rear side of the terminal unit 2a in a known manner, so as to leave the front sides free for requisite jumpers.

In the case of the practical embodiment, mutually adjacent blocks will be placed closer together than is shown in the Figure.

The inventive arrangement thus includes a telephone-exchange adapted line-circuit connection with a predetermined number of line circuits, each of which can be allocated to a telephone- exchange associated subscriber, wherein the line circuits are coordinated on a printed circuit board 10' or the like on which a plurality of discrete components 10a, 10b or line circuits are mounted, and wherein each of the line circuits includes discrete components in the form of subscriber-line associated resistances 31, 31' which are each dimensioned for high heat dissipation.

The enlarged view in Figure 3 illustrates a known method of applying such resistances 31, in which the resistance body is located in the immediate proximity of the casing part 10c and at an adapted long distance from the circuit board 10' , so as to enable heat to be transferred to the casing or to the block 10 via a small air layer.

According to the invention, each of the resistances 31 shall comprise a conductor 70 of adapted resistivity and resistance mounted on a foil 71 (according to Figure 6).

The foil 71 is related directly to a heat-absorbing surface 80 in the absence of an air gap, for effective heat transfer.

The conductor 70 in the foil 71 is connected to a contact device 72 adapted for coaction with corresponding board-related contact device 73.

As will be evident from Figure 5, the circuit board 10' is enclosed in a two-part metallic casing 60 with each of the parts 61, 62 located on a respective side of the board 10' and with each of the foils 71 being fastened to the inside surfaces 61a, 62a of the part 61 and 63.

In a preferred embodiment, a plurality of foil parts are fastened to said surface with the conductors 70 connected to a central row of contact devices 72.

The board 10' has a centred row of contact devices 73, wherein contact devices 72, 72", 73, 73' coact when the board 10' is placed in the casing 60.

Figure 5 illustrates an embodiment in which the foils 70, 71, 70', 71' are mounted on one or both of the two mutually opposing inner surfaces 61a, 62a of the two casing parts 61, 62.

As evident from Figure 4, one or more foils 71 can be fastened to one or more frame-associated U-bars 11, 12 that guide a casing 10 and enclosed circuit board 10' .

In this embodiment, the foils are placed in channels Ila', lib' in the parts Ila, lib of the U-bars, with a contact device 72" placed in one end-part of the U-bar 12 for coaction with a corresponding contact device 73" on the printed circuit board.

A foil that provides an adapted resistance value may have a surface extension that measures 10-20 mm x 40-120 mm with end- related contact surfaces 74, 75, said contact surfaces 74, 75 being connected to contact elements in the terminal unit 72 in a known manner.

The foil 71 may also include an adhesive surface 71a for fasten¬ ing the foil to said heat-absorbing surface 80.

Since the present invention enables heat-generating line-circuit resistances to be placed selectively and as desired, it will be endeavoured to place said resistances close to the U-bars 11, 12 and/or to the cooling flanges 12, 13.

It is particularly proposed that the resistances are placed in the U-bar-part lib, wherein one or more foils 71 may be placed over one another with an adapted air gap to the casing 10, so as to reduce the transportation of heat to the casing 10 and increase said transportation towards the cooling flanges 12, 13.

In the case of thirty line circuits, 2 x 30 resistance-exhibiting foils are required, of which only a few have been shown in the drawings.

Figure 4 illustrates an arrangement in which double foils are placed on one another in the U-bars 21a, with a depth adapted to the channel Ila'.

It will be understood that the invention is not restricted to the illustrated and described exemplifying embodiment thereof and that modifications can be made within the scope of the inventive concept illustrated in the following Claims.