FR2825508A1 - Telecommunications signal transmitter, has transformer coils of conductor wire in thick synthetic sleeves embedded in insulating material - Google Patents

Abstract

Telecommunications signal transmitter, has transformer coils of conductor wire in thick synthetic sleeves embedded in insulating material. The transmitter (1), having input (2, 3) and output (4, 5) terminals, contains an insulating transformer (6) with its primary circuit (7a, 7b, 15) connected to the input terminals and its secondary circuit (8a, 8b, 16) to the output terminals, and an insulating chopper (9). At least some of the transformer windings are made from conducting wire inside thick synthetic sleeves, embedded in a synthetic insulating material. The transformer windings are on ferrite cores, with adjacent portions separated by an insulating film material.

Description

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La présente invention est relative à un transformateur à isolement galvanique amélioré et à un transmetteur de télécommunications équipé d'un tel transformateur. Telecommunications transmitter incorporating a transformer with improved galvanic isolation

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The present invention relates to a transformer with improved galvanic isolation and to a telecommunications transmitter equipped with such a transformer.

 The technical field of the invention is that of the manufacture of terrestrial telecommunications transmission devices enabling high galvanic isolation to be ensured.

 Such devices are made necessary in particular for connecting a telephone terminal located in a room containing generators and / or electrical conductors at medium or high voltage, with a wired telecommunications network.

 In such devices, galvanic isolation can be obtained by an optical, radio or magnetic link; the present invention applies to the latter case where a first transformer is used to transmit, from a first winding to a second winding of the transformer, the telecommunications signals.

 In such devices, a second transformer is generally also used in a DC-DC converter used to transmit a DC supply voltage to the terminal.

 The present invention relates to said first transformer.

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 The development of telecommunications traffic requires the creation of such transmitters whose bandwidth is increasingly wide; for more and more applications of these transmitters, the frequency of the signals to be transmitted can vary from a few hundred hertz to several tens or hundreds of kilohertz, and the phase shift of the signals in this range, induced by the inductance of the windings, must be limited: in particular the leakage inductance must be limited to allow correct transmission at high frequencies.

 Furthermore, a high dielectric strength must be obtained between the windings and the mass (transformer carcass) and between the windings themselves, in particular a stiffness of the order of 5 to 10 kilovolts at 50 hertz.

 In accordance with the invention, it has been discovered that these contradictory constraints can be satisfied by winding, for the production of at least part of the windings, a wire surrounded by a thick sheath of synthetic insulating material, and by drowning the windings by overmolding of a second synthetic insulating material.

 Optimal results both in terms of dielectric strength and of bandwidth have been observed by using a conductive wire sheathed in PTFE and by at least partially embedding the windings in a polyurethane resin.

 In order to increase the linearity at high frequencies, the windings are preferably wound on a ferrite core.

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 In addition, performance can be improved in certain cases by dividing the primary winding into two portions and by dividing the secondary winding into two portions, by nesting the portions alternately, and by separating two adjacent winding portions by a insulating sheet material.

 Preferably, the device according to the invention maintains between 300 hertz and 5000 hertz a phase shift not exceeding more or less 10 degrees, in particular more or less 5 degrees.

 According to another aspect, the invention consists of a method of manufacturing said device, in which the transformer is overmolded with an insulating polymeric material, and preferably in which the transformer is placed in a sealed enclosure maintained at a pressure below the pressure atmospheric, preferably during at least part of the polymerization of the insulating material.

 Other characteristics and advantages of the invention appear in the following description which refers to the appended drawings, which illustrate without any limiting character the preferred embodiments of the invention.

 Figure 1 schematically illustrates a high isolation telecommunications transmitter according to the invention.

 FIG. 2 schematically illustrates a preferred embodiment of the transformer of the transmitter of FIG. 1.

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 The device 1 illustrated in FIG. 1 allows the connection of a telecommunications terminal to a network; for this purpose, the terminal is connected to the output terminals 4.5 of the device, the input terminals 2.3 of which are connected to the telecommunications network.

 The telecommunications signals are transmitted by the transformer 6 of the device 1 ensuring the galvanic isolation between the input and the output as well as with the ground.

 The DC component supplying the terminal via the network is transmitted from terminals 2.3 to terminals 4.5 by a chopper 9 also provided with a second isolation transformer.

 The primary circuit of the transformer 6 comprises two winding portions 7a and 7b which are connected in series with a capacity 15 connecting these two portions; similarly, the secondary circuit of the transformer 6 comprises two portions 8a, 8b of winding connected in series with a capacity 16 connecting these two portions; the inputs of the chopper 9 are connected to the terminals of the capacity 15 while the outputs of the chopper are connected to the terminals of the capacity 16.

 Referring to Figure 2, the transformer 6 extends substantially in a symmetry of revolution about the axis 18 along which extends the core 13 of the transformer.

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 It can be seen in this figure that the winding portions 7a, 8a, 7b, 8b have been successively wound around the core, and are separated in pairs by a sheet insulator 14.

 Each winding portion comprises two layers of juxtaposed turns formed with a wire 10 coated with a thick sheath 11; the wire turns 10, 11 and the insulating sheets 14 are embedded in a resin 12 inside which the transformer can be completely included.

 Preferably, a polymerizing resin is used at a temperature in the region of 100 to 300 ° C. in about one hour, the polymerization being carried out under a partial vacuum.

Claims (10)

1. Device (1) for transmitting telecommunications signals between input terminals (2,3) and output terminals (4,5), which comprises an isolation transformer (6) including a primary circuit (7a , 7b, 15) is connected to the inputs (2,3) and of which a secondary circuit (8a, 8b, 16) is connected to the outputs (4,5), and further comprising a chopper (9) with galvanic isolation, characterized in that at least part of the windings (7a, 7b, 8a, 8b) of the transformer (6) consists of a conducting wire (10) surrounded by a thick synthetic sheath (11) and is embedded in a material synthetic insulation (12).  2. Device according to claim 1, wherein the conductive wire (10) is sheathed with PTFE.  3. Device according to any one of claims 1 or 2, in which the primary and secondary windings (7a, 7b, 8a, 8b) are embedded in a polyurethane resin 12.  4. Device according to any one of claims 1 to 3, in which the windings (7a, 7b, 8a, 8b) are wound on a ferrite core (13).  5. Device according to any one of claims 1 to 4, in which adjacent portions of the windings are separated by an insulating sheet material (14). <Desc / Clms Page number 7>  6. Device according to any one of claims 1 to 5, wherein the primary windings (7a, 7b) and secondary (8a, 8b) are wound by alternating nested portions.  7. Device according to any one of claims 1 to 6, which maintains between 300 hertz and 5000 hertz a phase shift not exceeding more or less 10 degrees, in particular more or less 5 degrees.  8. A method of manufacturing a device according to any one of claims 1 to 7, in which the transformer (6) is overmolded with an insulating polymeric material (12).  9. The method of claim 8, wherein the transformer is placed in a sealed enclosure maintained at a pressure below atmospheric pressure, preferably during at least part of the polymerization of the material (12).  10. The method of claim 8 or 9, wherein a polymerizing resin is used at a temperature in the region of 100 to 30 C.