EP0142200B1 - Voltage control device for cathode-ray tube electrodes - Google Patents

Description

The invention relates to an adjustable voltage generator device for supplying at least one electrode of a cathode ray tube, device comprising a transformer provided with a winding for supplying at least one voltage to at least one potentiometer on the cursor of which is collected. an adjustable tension, and of a hollow part called "pipe" in which is introduced at least one electric cable and in which the latter is put in connection with the winding.

The invention finds its main application in color television receivers.

In known voltage generating devices, a special potentiometer capable of supporting a voltage of several kilovolts across its terminals is used to supply the adjustable voltage. Such a potentiometer is present for example in the catalog of the PHILIPS Company under the name "FOCUS POTENTIOMETER UNIT".

Such a potentiometer is bulky, difficult to connect, and above all expensive to manufacture because of the insulation constraints required by the high voltages present.

The invention provides a solution to avoid the use of such a specific element, its attachment to the transformer and its connection to the voltage generator element.

The generating devices include a transformer provided with a winding to provide a voltage, and a hollow part called a "pipe" into which an electric cable is introduced and in which the latter is connected to the winding.

The device according to the invention is remarkable in that the potentiometer is produced inside the pipe, the cable directly collecting the adjustable tension therein, because inside said pipe. pipe is arranged at least one resistive layer forming a potentiometer, one end of which is connected to the winding, that the electric cable is provided with means connected to its conductive core for making contact with said layer, and that the insertion of the cable into the pipe is adjustable, thereby moving the point of contact with the resistive layer.

In the device according to the invention, the potentiometer track is constituted by means of a resistive layer placed inside the very pipe of the output of the concentration voltage, and the potentiometer cursor by means of the end of the cable. high voltage introduced into said pipe which can slide in this pipe to adjust the tension.

In order to avoid the use of an additional resistance, the other end of the resistive layer is advantageously connected to another point of the winding.

Advantageously, the means for making contact with the layer consist of the end of the conductive core of the cable folded over its insulating sheath.

Thanks to the device according to the invention, it is possible to provide an adjustable high voltage by using only extremely simple and inexpensive means.

In addition, the device according to the invention advantageously applies to the supply of the concentration voltage as well as to the bias voltage of the second grid of the cathode-ray tube, and for this purpose, its hollow part has two housings, for two cables, housings each provided with a resistive layer.

• Les figures 1A et 1B représentent une vue latérale et une coupe d'un transformateur utilisé dans l'invention.
• Les figures 2A et 2B sont deux schémas électriques de branchement à l'enroulement.
• Les figures 3A et 38 représentent en perspective coupée deux exemples de réalisation de la pipe selon l'invention.
• La figure 4 représente une barrette isolante recouverte d'une couche résistive.
• Les figures 5A et 5B représentent en perspective des moyens pour assurer le contact entre le câble et la couche résistive.
• Les figures 6A, B, C, et D illustrent différents exemples de réalisation de moyens de blocage du câble.
• Les figures 7A à 7C sont respectivement une vue en perspective, une coupe transversale et une coupe longitudinale d'un mode de réalisation particulier de l'invention où la partie creuse comporte deux logements.
• Les figures 8A et 88 représentent en perspective à divers stade de fabrication, des barrettes munies de couches résistives.
• La figure 9 est un schéma de branchement pour deux électrodes d'un tube cathodique.

The description which follows, with reference to the appended drawings given by way of nonlimiting examples, will make it clear how the invention can be implemented.

• Figures 1A and 1B show a side view and a section of a transformer used in the invention.
• Figures 2A and 2B are two electrical diagrams of connection to the winding.
• Figures 3A and 38 show in perspective cut two embodiments of the pipe according to the invention.
• FIG. 4 represents an insulating strip covered with a resistive layer.
• FIGS. 5A and 5B show in perspective means for ensuring contact between the cable and the resistive layer.
• Figures 6A, B, C, and D illustrate different embodiments of cable locking means.
• Figures 7A to 7C are respectively a perspective view, a cross section and a longitudinal section of a particular embodiment of the invention where the hollow part has two housings.
• FIGS. 8A and 88 show in perspective at various stages of manufacture, bars provided with resistive layers.
• Figure 9 is a connection diagram for two electrodes of a cathode ray tube.

In Figure 1, a high voltage television transformer is shown. The latter is usually provided with several windings, or windings, providing various voltages, placed around a ferrite core 8. The winding 20 which provides the focusing voltage is shown. The transformer has a protruding and hollow part 10 called a "pipe", into which an electrical cable 9 is introduced and into which the latter is connected to the winding 20.

Inside said pipe 10, a resistive layer 2 is arranged, one end of which is connected by connection 7 to a point of the winding. The electric cable 9 is provided with means for making contact with said layer and its insertion into the pipe is adjustable by hand or by some mechanical means which is easy to carry out.

The other end of the resistive layer 2 is connected, for example by means of a clip 12, to a conductor 11. FIG. 2A, where the winding 20 and the resistive layer 2 are found, shows that said other end is connected by the conductor 11 to a heel resistor 23, itself connected to ground.

This diagram also includes rectifier diodes not described here, which can be connected in different ways, described for example in the book "The new guide to color television" at Editions CHIRON in Paris, pages 229 to 240 These diodes are generally incorporated in the molding of the winding, for example in the manner described by patent FR 2 146 419. A diode can thus be placed in series in connection 7.

The diagram in FIG. 2B represents another possibility of connecting the potentiometer. This possibility is not used in the prior art because it requires the presence of a second pipe to ensure the connection, at point 22, of the other end of the potentiometer. This connection is on the other hand advantageous in the context of the invention since it makes it possible to eliminate the conductor 11 and the resistor 23. The two ends of the resistive layer, located in the same pipe 10, are connected to the sockets 21, 22 of the 'winding.

The pipe of FIG. 3A comprises a resistive layer 2 deposited directly inside the pipe. This deposition can be carried out under plasma, this well-known technique making it possible to metallize inaccessible surfaces. On the two ends 5, 6 a conductive layer is deposited by masking the central part of the layer 2 during the deposition. The conductive pads 5, 6 allow the connection with, respectively, the connection 7 and the clip 12.

The pipe of FIG. 3B is provided with an internal prefabricated part 100. This part has a groove 4 in which is fixed an insulating strip covered with a resistive layer.

FIG. 4 represents such a bar covered with the resistive layer 2 on one side, a conductive layer 1, 3 being deposited at each end. These layers are preferably deposited by screen printing in a thick layer on a ceramic substrate which has a large quantity of bars and which is then cut into unitary bars. On the end layers 1 and 3, connections 7 and 70 are fixed, the connection 70 being for example folded behind the bar. The bar is then fixed in the part 100, the connections 7, 70 passing through the holes 24, then the connections 7, 70 are connected to the winding 20 and, finally, all of the winding and the part 100 is overmolded to form a block provided with the pipe 10.

The cable 9 of FIG. 5A is provided at its end with a ferrule 14 welded to the central conductor 13 of the cable. This tip comprises one or more stamped cutout (s) each constituting an elastic blade 25 intended to ensure good contact with the resistive layer. In a simplified version represented by FIG. 5B, the end of the rigid central conductor 13 of the cable is folded over its insulating sheath to ensure contact with the resistive layer. This arrangement is suitable for the pipe shown in FIG. 3B, the groove 4 then being deeper than the thickness of the bar, so that after fixing it in the bottom of the groove, the resistive layer remains in shrinkage with respect to the inner wall of the pipe, thus further constituting a groove into which the end 13 of the cable enters into contact with the bar, thus preventing the cable from turning around its longitudinal axis. Instead of a narrow bar housed in the groove, it is also possible to use a relatively wide bar, housed in a suitable recess next to the housing intended for the cable, with a slot between said recess and said housing, slot through which the conductive end of the cable, such an arrangement is represented by FIGS. 7A, B, C which will now be described.

To provide both the concentration voltage and the second grid voltage of a color television cathode ray tube, the pipe seen in perspective in FIG. 7A comprises two housings for two cables 9, 29, housings each provided with a resistive layer.

This arrangement enables the electrical diagram shown in FIG. 9 to be produced. The winding 20 provides a voltage of approximately 8 kV via a conductor 33 at one end of a resistive track 2 on which the cable 9 supplying the electrode contacts. focusing, track followed by a track 23 forming resistance-heel, and a resistive track 28 on which makes contact with cable 29 supplying the second grid of the cathode-ray tube. The end, opposite to track 23, of track 28 is connected by a conductor 36 to an outlet of the transformer winding, outlet providing approximately 0.5 kV; it could also be brought back to earth via a heel resistance.

Figure 7B is a cross section through the pipe of Figure 7A. It shows two cables 9, 29 in two cylindrical housings, and two bars 31, 32 with which the ends 13, 30 respectively of the cables 9, 29 are in contact. The bars 31, 32 are placed together in a suitable recess 27 placed between the two housings for the cables, and passages parallel to the axes of the cables make said housings communicate with said recess 27 by allowing the ends of the cables to pass 13.30. Of course a contact tip like that shown in Figure 5A could as well be used here.

FIG. 7C, which is a perspective view in section along C of the pipe of FIG. 7A, makes it possible to perfectly understand the arrangement of the cables 9, 29, and the bars 31, 32.

FIG. 8a represents bars 31 and 32 seen from the side which carries the resistive tracks 2 and 28 and conductive connecting tracks 33 to 36. The bars are cut from an alumina plate and the tracks are produced according to the so-called "technique". in thick layers "by screen printing and baking.

Track 28 is wider than track 2, because for the same cable sliding length, it must provide a voltage variation of approximately 400 volts, while track 2 provides a variation of approximately 2 kilovolts. The Resis part heel counter 23 which extends the track 28 is offset laterally so that, in the event of insufficient penetration of the cable, it is no longer in contact with the resistor, so that the second grid cannot be brought to a tension too high.

Before being placed in the pipe 10, the wafer 32 is turned back to back against the wafer 31, as indicated by arrow 37, and the assembly of bars represented by FIG. 8B is then obtained. A clip 26 provides the electrical connection between the conductive tracks 34 and 35 of FIG. 8A, and the tracks 33 and 36 are connected to taps of the winding as explained above with reference to FIG. 9.

Figure 6A shows the outer end of a pipe provided with slots 15 around a cable passage. The slots 15 allow tightening by constriction. One uses for example a plug 17 shown in Figure 6B, screwed onto the thread 16 of the pipe, so as to cause tightening. One can also use a ring 18 shown in Figure 6C, forced into the frustoconical end of the pipe. It is also possible to use a transverse screw 19, as shown in FIG. 6D, to tighten the cable. Although FIGS. 6A and D represent a pipe with a cable, it is obvious that the means described with reference to these figures and more particularly in FIG. 6D apply equally well to a pipe with two cables.

One can use to block the cable (s), a wedge-shaped piece which is slid until locked between the two cables, or between a cable and a stop provided on the end of the pipe. It is thus possible to replace part of the conductive track 36 (FIG. 8A) with a resistive track so as to produce a heel resistance.

Claims (10)

1. A device for generating a variable voltage for powering at least one electrode of a cathode-ray - tube, which device comprises a transformer having a winding for applying at least one voltage, to at least one potentiometer (2) whose wiper carries a variable voltage, and at least one hollow portion (10), referred to as "pipe", into which at least one electrical cable (9) is inserted and in which said cable is brought into contact with the winding, characterized in that the potentiometer is realized inside the pipe, the cable receiving directly the variable voltage therein in that at least one resistive layer (2) which forms the potentiometer is arranged inside said pipe, one end of said layer being connected to the winding (20), the electrical cable being provided with means which are connected to its core for establishing contact with said layer, the insertion depth of the cable in the pipe being adjustable, thus shifting the point of contact with the resistive layer.

2. A device as claimed in Claim 1, characterized in that the means for establishing contact with the layer are formed by the end (13) of the conductive core of the cable, folded back onto its insulating sheath.

3. A device as claimed in Claim 1, characterized in that the means for establishing contact with the layer are formed by a ferrule (14) comprising at least one elastic strip.

4. A device as claimed in any one of the preceding Claims, characterized in that the resistive layer is provided in a groove in the wall of the pipe.

5. A device as claimed in any one of the preceding Claims, characterized in that the other end of the resistive layer is connected to another point of the winding (20).

6. A device as claimed in any one of the preceding Claims, characterized in that at least one insulating strip on which there is provided a resistive layer is arranged in the pipe.

7. A device as claimed in any one of the Claims 1 to 5, characterized in that the resistive layer is deposited directly on the inner wall of the pipe.

8. A device as claimed in any one of the preceding Claims, characterized in that its hollow portion comprises two recesses for two cables (9, 20), each recess being provided with a resistive layer supplying the focussing voltage and the voltage for the second grid of the cathode-ray tube, respectively.

9. A device as claimed in any one of the Claims 1 to 6, characterized in that its hollow portion comprises two recesses for two cables, each recess being provided with an insulating strip (31, 32) on which there is provided a resistive layer (2, 28), said strips being arranged back-to-back between the two recesses, their resistive layers being connected in series.

10. A device as claimed in any one of the preceding Claims, characterized in that it is provided with cable-locking means.

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