Deflection Yoke With Auxiliary Coils for Stray Line Radiation Suppression

1. Field of the Invention

The present invention relates to a deflection yoke which is mounted on a cathode-ray tube, and more particularly, to a deflection yoke which is capable of suppressing the generation of unnecessary radiant magnetic fields.

2. Description of the Related Art

Conventional deflection yokes have been proposed in the specification of, for example, Japanese Patent Unexamined Publication No. 63-26928. This deflection yoke (the first conventional technique) has a pair of upper and lower loop-shaped cancelling coils for suppressing the generation of unnecessary radiant magnetic fields externally on a core and in the vicinity of a vertical axis. Japanese Patent Unexamined Publication No. 63-76245 discloses a deflection yoke (the second conventional technique) with two pairs of auxiliary coils for suppressing the generation of unnecessary radiant magnetic fields disposed along the sides of the horizontal deflection coil. Part of each of the coils is covered by a conductive shielding member.

In the first conventional technique, when the numbers of turns for the auxiliary coils are selected such that an unnecessary radiant magnetic field is completely cancelled on the side of the deflection yoke which is close to a fluorescent surface (hereinafter referred simply to as "in front of the deflection yoke"), the auxiliary coils generate an unnecessary radiant magnetic field having a polarity opposite to that of the unnecessary radiant magnetic field of the deflection yoke on the side of the deflection yoke which is close to an electron gun (hereinafter referred simply to as "at the back of the deflection yoke"). In the second conventional technique, shielding of the auxiliary coils makes the structure of the deflection yoke complicated. Furthermore, since the size of the auxiliary coils is large, the resultant deflection yoke requires a large space in an image display apparatus which employs it.

An object of the present invention is to provide a deflection yoke provided with an auxiliary means which is capable of suppressing the generation of unnecessary radiation simultaneously in front of and at the back of the deflection yoke, which has a simple configuration, and which requires only small space.

The above-described object of the present invention is achieved by the provision of a deflection yoke in which a first pair of upper and lower auxiliary coils provided on the side of the deflection yoke which is close to a fluorescent surface and a second pair of upper and lower auxiliary coils provided on the side of the deflection yoke which is close to an electron gun are separated from each other in the direction of the axis of a cathode-ray tube. A horizontal deflection current is supplied to the first pair of auxiliary coils in the direction in which the intensity of the unnecessary radiant magnetic fields generated in front of and at the back of the deflection yoke is decreased, and a horizontal deflection current is supplied to the second pair of auxiliary coils in the direction in which an unnecessary radiant magnetic field generated at the back of the deflection yoke is intensified.

The above-described object of the present invention is also achieved by the provision of a deflection yoke in which a pair of upper and lower auxiliary coils, whose loops are formed such that the central axes of the windings are deviated from each other, are disposed externally on the deflection yoke in such a manner that the loops of the auxiliary coils are inclined with respect to a horizontal plane. A horizontal deflection current is supplied to the auxiliary coils.

In the present invention, the first pair of auxiliary coils generate, in front of and at the back of the deflection yoke, correction magnetic fields in the direction opposite to that of the unnecessary radiant magnetic fields caused by high-frequency horizontal deflection magnetic fields. As a result, the unnecessary radiant magnetic field generated in front of the deflection yoke is substantially cancelled, and the unnecessary radiant magnetic field generated at the back of the deflection yoke is excessively corrected, resulting in the generation of an unnecessary radiant magnetic field having a polarity opposite to that of the original unnecessary radiant magnetic field. At the same time, the second pair of auxiliary coils generate, in front of the deflection yoke, a correction magnetic field which substantially affects no unnecessary radiant magnetic field. The second pair of auxiliary coils also generate, at the back of the deflection yoke, a correction magnetic field in the same direction as that of the unnecessary radiant magnetic field caused by the horizontal deflection magnetic field. In consequence, the unnecessary radiant magnetic field remaining at the back of the deflection yoke as the consequence of the correction by the first pair of auxiliary coils can be corrected by the second pair of auxiliary coils, thereby enabling unnecessary radiant magnetic fields to be cancelled in front of and at the back of the deflection yoke.

In a case where the auxiliary coils, whose loops are formed such that the central axes of the windings are deviated from each other, are disposed in such a manner that the loops of the coils are inclined with respect to a horizontal plane, the auxiliary coils generate magnetic fields having intensities substantially the same as those of the unnecessary radiant magnetic fields generated by the deflection yoke in front thereof and at the back thereof, and being in the direction opposite to that of the unnecessary radiant magnetic fields. The unnecessary radiant magnetic field generated in front of the deflection yoke has a large intensity, and the unnecessary radiant magnetic field generated at the back of the deflection yoke has a small intensity. In consequence, the unnecessary radiant magnetic fields generated in front of and at the back of the deflection yoke can be cancelled.

FIG. 1A is a perspective view of a deflection yoke showing a first embodiment of the present invention;

FIG. 1B is a plan view of the deflection yoke of FIG. 1A;

FIG. 2 is a cross-sectional view taken along the line II--II of FIG. 1B;

FIG. 3 is a graph showing distribution of a magnetic field generated by horizontal deflection coils of a conventional deflection yoke;

FIG. 4 is a cross-sectional view of a deflection yoke showing a second embodiment of the present invention;

FIG. 5A is a side-elevational view of a deflection yoke showing a third embodiment of the present invention;

FIG. 5B is a perspective view of the essential parts of the deflection yoke of FIG. 5A;

FIG. 6 is a cross-sectional view of the third embodiment of the present invention;

FIGS. 7A and 7B show another example of the auxiliary coil employed in the third embodiment; and

FIG. 8 is a side-elevational view of a cathode-ray tube showing a fourth embodiment of the present invention.

A first embodiment of the present invention will now be described with reference to FIGS. 1A and 1B. In FIGS. 1A and 1B, a reference numeral 1 denotes a deflection yoke, 2: a horizontal deflection coil, 3: a vertical deflection coil, 4: a magnetic core, 5: a separator, 6a: a first pair of auxiliary coils, 6b: a second pair of auxiliary coils, 7: a terminal cover, 8: a core clamp, 9: a tightening band, and 10: an arrow indicating the front of the deflection yoke.

In this embodiment, a pair of upper and lower auxiliary coils 6a are provided on the side of the deflection yoke which is close to a fluorescent surface, and a pair of upper and lower auxiliary coils 6b are provided on the side of the deflection yoke which is close to an electron gun, as shown in FIGS. 1A and 1B. Each of the auxiliary coils 6a and 6b is wound around a bobbin 20. The auxiliary coils 6a and 6b are mounted on the deflection yoke in such a manner that transverse conductors 2a and 2b of the horizontal deflection coil are located within the loops of the auxiliary coils, and that the loops of the auxiliary coils 6a and 6b are substantially in a horizontal plane.

As shown in FIG. 2, when a horizontal deflection current flows through the horizontal deflection coil 2, a horizontal deflection current which flows in the directions indicated in FIG. 2 is supplied to the auxiliary coils 6a and 6b, which may be connected in series with the horizontal deflection coil 2. Alternately, the auxiliary coils 6a and 6b may be connected in parallel with the horizontal deflection coil 2 if the impedance of the auxiliary coils 6a and 6b is high. At that time, the horizontal deflection coil 2 generates a downward deflection magnetic field 11a. The horizontal deflection coil 2 also generates downward leakage magnetic fields 11b and 11c in front of and at the back of the deflection yoke, respectively. The intensity of the leakage magnetic field 11b generated in front of the deflection yoke is large, while that of the leakage magnetic field 11c is small, as shown in FIG. 3. The first pair of auxiliary coils 6a generate upward magnetic fields 12a and 12b in front of and at the back of the deflection yoke, respectively. The magnetic field 12a has an intensity larger than that of the magnetic field 12b. As a result, the leakage magnetic field generated in front of the deflection yoke is cancelled, whereas the leakage magnetic field generated at the back of the deflection yoke is corrected excessively, resulting in the generation of an upward magnetic field. The second pair of auxiliary coils 6b generate downward magnetic fields 13a and 13b in front of and at the back of the deflection yoke, respectively. The magnetic field 13b has an intensity larger than that of the magnetic field 13a. In consequence, the leakage magnetic fields generated in front of and at the back of the deflection yoke can be cancelled by setting the numbers of turns for the first and second pairs of auxiliary coils 6a and 6b to optimal values, and generation of the unnecessary radiant magnetic fields from the deflection yoke caused by leakage of the high-frequency horizontal deflection magnetic field can thereby be suppressed simultaneously in front of and at the back of the deflection yoke. The auxiliary coils 6a and 6b have a simple loop-shaped configuration, and requires no large space for installation.

Next, a second embodiment of the present invention will be described below with reference to FIG. 4. Like the first embodiment shown in FIG. 2, a first pair of upper and lower auxiliary coils 6a are provided on the side of the deflection yoke 1 which is close to the fluorescent surface. A second pair of upper and lower auxiliary coils 6c are provided on the side of the deflection yoke which is close to the electron gun in such a manner that the loops thereof are perpendicular to the axis of the tube (z axis). A horizontal deflection current which flows in the directions indicated in FIG. 4 is supplied to the auxiliary coils 6a and 6c. Hence, when the horizontal deflection coil 2 generates the downward horizontal deflection magnetic field 11a as well as the downward leakage magnetic fields 11b and 11c in front of and at the back of the deflection yoke respectively, the first pair of auxiliary coils 6a generate the magnetic fields 12a and 12b in the direction in which the leakage magnetic fields 11b and 11c are cancelled. As a result, the leakage magnetic field is cancelled in front of the deflection yoke, and the leakage magnetic field is corrected excessively at the back of the deflection yoke, resulting in the generation of an upward magnetic field. The second pair of auxiliary coils 6c generate a downward magnetic field 14b at the back of the deflection yoke, and an upward magnetic field 14a having a slightly small intensity in front of the deflection yoke. In consequence, the leakage magnetic fields from the deflection yoke can be cancelled by setting the numbers of turns for the first and second pairs of auxiliary coils 6a and 6c to optimal values, and generation of the unnecessary radiant magnetic fields can thereby be suppressed in front of and at the back of the deflection yoke.

In the second embodiment, the second pair of auxiliary coils 6c generate, in front of the deflection yoke 1, the magnetic field 14a having a polarity opposite to that of the leakage magnetic field 11b of the deflection yoke. In consequence, the numbers of turns for the first and second pairs of auxiliary coils 6a and 6c can be reduced from those of the first embodiment when unnecessary radiant magnetic fields are to be suppressed in front of and at the back of the deflection yoke.

A third embodiment of the present invention will be described below with reference to FIGS. 5A, 5B and 6. A pair of upper and lower auxiliary coils 6d are provided externally on the deflection yoke 1. The vertical cross-section of the loop of the auxiliary coils 6d substantially has the form of a parallelogram, so as to allow the centers of the windings to be deviated from each other. Each of the auxiliary coils 6d is formed as follows. A wire is wound substantially in the form of a parallelogram. This coil is mounted on a retaining member 15, and the outer surface of the coil with the retaining member 15 is covered by an insulating member 16. Each of the auxiliary coils 6d is disposed such that the loop formed by the auxiliary coil 6d is inclined at an angle .theta. with respect to the axis of the tube (z axis). A horizontal deflection current having a polarity shown in FIG. 6 is supplied to the auxiliary coils 6d, and this generates an upward magnetic field 17a in front of the deflection yoke and a magnetic field 17b whose direction changes from upward to downward, as the angle .theta. increases, at the back of the deflection yoke. In consequence, when the numbers of turns and the angle .theta. for the auxiliary coils 6d are set to optimal values, the magnetic fields 17a and 17b generated by the auxiliary coils 6d have intensities substantially equal to those of the magnetic fields 11b and 11c generated in front of and at the back of the deflection yoke 1 by the horizontal deflection coil 2 and have a polarity opposite to those of the magnetic fields 11b and 11c. As a result, leakage magnetic fields can be cancelled, and generation of the unnecessary radiant magnetic fields can be thereby suppressed. In this embodiment, unnecessary radiant magnetic fields can be prevented by one pair of auxiliary coils which require a small space for installation.

FIGS. 7A and 7B show another example of the auxiliary coils 6d. In this example, the vertical cross-section of the loop of the coil has stages. The use of such auxiliary coils ensures the same effect as that of the third embodiment.

A fourth embodiment of the present invention will be described below with reference to FIG. 8. A first pair of upper and lower auxiliary coils 6e for generating magnetic fields 18a and 18b which cancel the leakage magnetic fields 11b and 11c generated in front of and at the back of the deflection yoke are mounted on a cathode-ray tube 19. The second pair of auxiliary coils 6b for generating the magnetic fields 13a and 13b in the same direction as that of the leakage magnetic fields 11b and 11c are mounted on the side of the deflection yoke which is close to the electron gun in the same manner as that in the first embodiment shown in FIG. 2. A horizontal deflection current is supplied to the auxiliary coils 6b and 6e. The intensity of the magnetic field 18a is larger than that of the magnetic field 18b, and the intensity of the magnetic field 13b is larger than that of the magnetic field 13a. In consequence, when the numbers of turns for the auxiliary coils 6b and 6e are set to optimal values, the magnetic fields generated by the auxiliary coils 6b and 6e have intensities substantially the same as those of the leakage magnetic fields 11b and 11c from the deflection yoke 1 and a direction opposite to that of the magnetic fields 11b and 11c. As a result, the leakage magnetic fields 11b and 11c can be cancelled and generation of the unnecessary radiant magnetic fields can thereby be suppressed in front of and at the back of the deflection yoke. In this embodiment, the first pair of auxiliary coils 6e, having a large loop which ensures a small inductance and the same effect, are provided on the cathode-ray tube 19 where there is less limitation to the space for installation. In consequence, only one pair of auxiliary coils 6b are mounted on the deflection yoke 1, and this is effective in reducing the overall size of the deflection yoke as well as the horizontal deflection power.

It is clear that the auxiliary coils employed in this invention may be one in which the number of turns or the surface area thereof is reduced by inserting a magnetic material within the loop formed by the auxiliary coils.

As will be understood from the foregoing description, according to the present invention, since the auxiliary coils generate the magnetic fields having intensities substantially the same as those of the leakage magnetic fields generated in front of and at the back of the deflection yoke by the horizontal deflection coil in the direction opposite to that of the leakage magnetic fields, the leakage magnetic fields can be cancelled and generation of the unnecessary radiant magnetic fields can thereby be suppressed simultaneously in front of and at the back of the deflection yoke. Furthermore, since the auxiliary coils for generating magnetic fields which cancel unnecessary radiant magnetic fields can be shaped in the form a small loop and no shielding is necessary, they have a simple configuration and require no large space for installation.