A CATHODE RAY TUBE SYSTEM COMPRISING AN ELECTROMAGNETIC DEFLECTION UNIT DIRECTLY WOUND ON A SUPPORT AND AN ELETROMAGNETIC DEFLECTION UNIT

Abstract: The electromagnetic deflection unit has a support(4) with a flange (8) at its constricted end (5) which has a transversal groove in which radial grooves (14) merge. Two sets of deflection coils (18, 19) are directly wound on the support (4). Their turns run through radial grooves (14). Thence turns of a set of deflection coils (18) bend into a tangential groove. The coils of the coil system 18 for line deflection are wound in the opposite sense with such a winding sense and are energized during operation in such a manner that the highest voltage in both coils occurs at the plane of separation between the two coils and the lowest voltage occurs as far remote from it as possible.

Description: The invention relates to an electromagnetic deflection unit for a cathode ray tube, comprising: - a hollow, annular support having a constricted and a wide end and a longitudinal axis; - a flange at the constricted and the wide end, respectively, of the support, each flange having at least one tangential groove with a bottom and each having a multitude of substantially radial grooves merging into a said tangential groove; - a first set of deflection coils for line deflection of an electron beam in a first derection at right angles to the longitudinal axis, which deflection coils are directly wound on the inside of the support and whose turns each run through the tangential groove and through radial grooves in the flanges; and - a second set of deflection coils for field deflection of an electron beam in a direction at right angles to the longitudinal axis and at right angles to the first direction, which deflection coils are directly wound on the support and whose turns run through radial grooves in the flanges. A deflection unit of this type is known from EP 0,102,658A1 (PHN 10416). Cathode ray tubes have a neck-shaped portion one end of which accomodates an electron gun and the other end of which merges into a tapered portion with a screen contiguous to it. An electromagnetic deflection unit surrounds the neck-shaped portion and rests against the tapered portion or is positioned at a short distance therefrom. In the case of a colour display tube this deflection unit must be capable of deflecting the electron beams to the corners of the screen while maintaining convergence. This means that both the horizontal deflection field and the vertical deflection field must have a very special distribution. To realize this, the known deflection unit is provided between its ends with an annular body having guide grooves in the inner circumference accomodating the longitudinal segments of the coil turns. This provides a possibility of controlling the wire distribution (and hence the field distribution) : the choice is not restricted to wires running straight from front to back but they may alternatively run in a bend via the grooves in the intermediate ring. The wire location of a coil can therefore be freely modulated as a function of the direction along the longitudinal axis in the direction of the corners and a self-converging deflection coil system can be realized. Since both the wires of the line deflection coil and the field deflection coil are guided on the inside of the intermediate ring and are thus positioned close together, there is a risk of ringing occurring between the line deflection coil and the field deflection coil. Since a limited number of grooves can be provided in the inner circumference of the said ring, there may be a number of grooves, depen­ dent on the coil design, accomodating longitudinal turn segments of both the line deflection coil and of the field deflection coil. During winding, for example, the field deflection coil turns are accomodated in these grooves first and then the line deflection coil turns are accommo­ dated. In addition to the risk of ringing there is also the risk of breakdown between the line and field deflection coils. It is an object of the invention to provide a deflection unit having a construction reducing the risk of ringing and the risk of breakdown between the ione and field deflection coils. In a deflection unit according to the invention this object is realized in that the coils of the first system of coils, viewed in a flared-out form, are wound in the opposite sense with such a winding sence and are connected during oporation to an energizing device in such a manner that the potential distribution in both coils is such that the highest potential is on the side of the plane of separation between the coils and the lowest potential is as far remote from the plane of separation as possible. A preferred embodiment of the deflection unit according to the invention is characterized in that the longitudinal turn portions of the coils of the second system of coils are remote from the plane of separation between the coils of the first system of coils. The following is achieved thereby: For the two line deflection coil halves the high voltage of the line deflection coil is in a position which is not opposite a field deflection coil. Advantages: a. Of the line and field deflection coils are not separated by a separate isolator, this configuration has the advantage that the wire insulation can be dimensioned at a lower voltage than at the total flyback voltage. b. The capacitive currents from the line to the field deflection coil will be lower because the voltage between the line and the field deflection coil is altogether lower. This reduces the intensity of a ringing source. The annular support of the deflection unit according to the invention may be a synthetic material body having synthetic material flanges in which or around which a yoke ring of a soft magnetic material is provided. On the other hand a yoke ring itself may be the support whose constricted and wide ends are connected to a synthetic material flange. Both sets of deflection coils may be of the saddle type, or one set may be of the saddle type and one set may be of the toroidal type. The flange at the constricted end may have a trans­ versal groove for each of the sets of deflection coils, or one groove for the two sets combined, or more than two transversal grooves such as, for example,one for one set of deflection coils and two for the other set, or one for each separate set and one for the two sets combined. An embodiment of a deflection unit according to the invention is shown in the drawing. In this drawing: Figure 1 is a side view of a deflection unit placed around the neck-shaped portion of a cathode ray tube: Figure 2 is a perspective elevational view of the deflection unit of Figure 1; Figure 3 shows an annular component of the deflection unit of Figure 1; Figure 4a shows a winding diagram for the system of line deflection coils of the deflection unit of Figure 1 and Figure 4b shows the associated connection diagram; Figure 5 is a diagrammatical cross-section through the coil systems of the deflection unit of Figure 1 and Figure 4b shows the associated connection diagram. In Figure 1 the electromagnetic deflection unit 1 is placed around the neck-shaped portion 2 of a cathoderay tube whose tapered portion is denoted by the reference numeral 3. The deflection unit 1 has a hollow, annular support 4 having a constricted and a wide end 5 and 6, respectively, and a longitudinal axis 7. In the Figure the support 4 is a yoke ring of a soft magnetic material. The support 4 has flanges 8 and 9 of transparent polycarbonate at the constricted end 5 and the wide end 6, respectively. The flanges 8, 9 each have at least one tangential groove 10, 11 with a bottom and a multitude of substantially radial grooves 14, 15 merging into the tangential grooves 10, 11. In the Figure the flange 8 has a second tangential groove 12. In the flange 8, at the constricted end 5, the radial grooves 14 have a longitudinally extending portion with a width and a depth, which longitudinally extending portions are tangent to an inscribed circle. A first set of deflection coils 18 for line deflection of an electron beam in a first direction at right angles to the longitudinal axis 7 (that is to say: in the plane of the drawing) is directly wound on the inside of the support 4. The turns of the set of coils 18 each run through the tangential grooves 12 and 11 of the flanges 8 and 9, respectively and through their radial grooves 14 and 15, respectively. A second set of deflection coils 19 for field deflection of an electron beam in a direction at right angles to the longitudinal axis 7 and at right angles to the first direction (that is to say: at right angles to the plane of the drawing) is also directly wound on the support and its turns run through radial grooves 14, 15 in the flanges 8, 9. In the Figure the two sets of deflection coils 18, 19 are of the saddle type. Also the second set of deflection coils 19 is wound on the inside of the support 4 and its turns also run through tangential grooves 10 and 11 in the flanges 8 and 9, respectively. The first set of deflection coils 18 is wound first. In an intermediate ring 20 (Figure 2) its turns partly run in the same grooves as the turns of the second set of deflection coils 19 and hence under the turns of the second set 19. The flange 8 the turns of the first set 18 and the second set of deflection coils 19 have their own tangential grooves 12 and 10, respectively. The deflection unit of Figure 1 has the characte­ ristics of the deflection unit according to the invention. These characteristics are explained with reference to Figures 2, 3, 4 and 5. Components shown in Figure 1 have the same reference numerals in these Figures. Figure 2 shows an intermediate ring 20 whose inside is provided with a plurality of grooves. A front view of intermediate ring 20 (Figure 3) shows a substantially non-radial variation of the grooves 21, 21′, 21″ etc. Between the flanges 8 and 9 the wires of the coils run through the grooves 21, 21′, 21″ ... on the inside of the interme­ diate ring 20 (Figure 5) so that not only the wires run free from the inner surface of the support 4 but also the parts of the wires from the one to the other end of the deflection coil support 4 run in different planes (the paths of the wires have a "kink"). With reference to Figure 3 it is to be noted that the grooves 21, 21′, 21″ ... which are provided on the inner circumference of ring 20 have a variation which corresponds to the direction of the wire supplied during the winding process. Since, as already noted herein­ before, a number of wires does not extend straight from the front to the rear of the coil support, but with a kink, the direction of the axis of the grooves 21, 21′, 21″ ... differs from the radial direction. Figure 3 also shows that such a groove must extend in two different directions when the wires of coils of two different sets of coils must be passed through one groove. If the line coil halves with the reverse winding sence are paired to parallel arranged combinations, it can be achieved that there is only a low voltage between the parts of the coil halves which are located close together if at least the connection of the parallel arranged coil halves is connected to the highest voltage of the energi­ zing device, which connection corresponds to the wires of the parts of the coil halves which are closest together. This is further illustrated in Figures 4a, 4b and 5. In Figure 4a the points e are at the highest voltage and the points b are at the lowest voltage (earth in this case). By winding the line coil halves 18 in an opposite sense (Figure 4A) and connecting them in parallel, there is no voltage difference between the two coil halves. The line coil spacer, or line peg (23 in Figur 2), can then be dispensed with. In other words, adjecent turns of the line coil halves may run through the same grooves of the intermediate ring at their plane of separation. If is is also ensured that the winding sense is such that the "hot" side (+ in the drawing) is around the (possibly imaginary) line peg 23, there will have been a voltage division before the field de­ flection coil 19 is reached (see Figure 5). The + connection of the line deflection coil system may then be connected to the flyback voltage and the - connection may be connected to earth (Figure 4b). Ringing be­ tween the line and the field deflection coil is reduced by: the lower voltage between the line and field deflection coils as a result of the voltage division in the line deflection coil; a reduction of the capacitance (by a reduction of the contact surface) between the line deflection coil 18 and the field deflection coil 19 by deliberately keeping the field deflection coil turns far remote from the line peg (See Figure 5). The above-described measures, namely: - opposite sense winding of the line deflection coil halves 18; - selecting the correct winding sense in connection with the "hot" side; - keeping the turns of the field deflection coil 19 remote from the line peg 23 in connection with the voltage division; are also of great importance for the present yoke winding technique if no or only an extremely thin insulation can be used between the line and field deflection coil turns in connection with the dimensioning of this insulating layer with the aid of corona. Breakdown problems can be reduced in an effective manner by using the said measures.

Claims: 1. An electromagnetic deflection unit for a cathoderay tube, comprising: - a hollow, annular support having a constricted and a wide end and a longitudinal axis; - A flange at the constricted and the wide end, respectively, of the support, each flange having at least one tangential groove with a bottom and each having a multitude of substantially radial grooves merging into a said tangential groove. - a first set of deflection coils for line deflection of an electron beam in a first deflection at right angles to the longitudinal axis, which deflection coils are directly wound on the inside of the support and whose turns each run through the tangential groove and through radial grooves in the flanges; and - a second set of deflection coils for field deflection of an electron beam in a direction at right angles to the longitudinal axis and at right angles to the first direction, which deflection coils are directly wound on the support and whose turns run through radial grooves in the flanges; characterized in that the coils of the first system of coils, viewed in a flared-out form, are wound in the opposite sense with such a winding sense and are connected during operarion to an energizing device in such a manner that the potential distribution in both coils is such that the highest potential is on the side of the plane of separation between the coils and the lowest potential is as far remote from the plane of separation as possible. 2. A deflection unit as claimed in Claim 1, characterized in that the longitudinal turn portions of the coils of the second system of coils are remote from the plane of separation between the coils of the first system of coils. 3. A deflection unit as claimed in Claim 1 or 2, characterized in that adjacent turns of the one coil of the first system of coils and of the other coil of the first system of coils run through the same grooves of a coaxial intermediate ring at their plane of separation.

Inventors: MEERSHOEK, HANS, VAN TIEL, ANTONIUS HENRICUS
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1987
Main classification: H01J29
IPC codes: H01J29