Deflection yoke apparatus with means for reducing unwanted radiation

Abstract: A deflection yoke apparatus comprising pairs of horizontal and vertical deflection coils, a coil separator located between both coils, a deflection core forming a magnetic path for a magnetic flux generated from both deflection coils and auxiliary coil means which is arranged at at least one of positions in a vertical deflection direction outside said deflection core, wherein a horizontal deflection current is supplied to this auxiliary coil means and a magnetic field generated from said auxiliary coil means reduces an intensity of externally leaking magnetic field which radiates outside said deflection core when a horizontal deflection current is supplied to said horizontal deflection coils.

Description: Background of the Invention The present invention relates to a deflection yoke apparatus, which is mounted on a neck of a cathode-ray tube for projecting rasters on a screen by scanning at least one electron beam, comprising a pair of horizontal deflection coils for generating a magnetic field to deflect said electron beam in a horizontal direction, and a pair of vertical deflection coils for generating a magnetic field to deflect said electron beam in a vertical direction, and a coil separator for electrically insulating between said both deflection coils, said coil separator being provided as a front expanded part at its front and a rear expanded part at its rear end, and annular deflection core which forms magnetic parts for a magnetic flux generated when a deflection current is supplied to said horizontal and said vertical deflection coils, thus generating a deflection magnetic field for deflecting said electron beam inside said annular deflection core and an externally leaking magnetic field outside said annular deflection core. A deflection yoke apparatus of such kind is known from the US-A-4 553 120. Such a deflection yoke apparatus is frequently employed in a cathode-ray tube widely used in various types of television equipment such as television receivers and television display units. The deflection of said electron beam is achieved by said magnetic flux generated by supplying a deflection current to said horizontal and vertical deflection coils. Usually a horizontal deflection current of approximately 15.75 kHz to 120 kHz is supplied to the horizontal deflection coils to generate the horizontal deflection magnetic field in order to deflect the electron beam in the horizontal direction. In an analogous way a vertical deflection current of 50 Hz or 60 Hz is supplied to the vertical deflection coils in order to generate a vertical deflection magnetic field deflecting the electron beams in the vertical direction. These deflection magnetic fields are distributed as the leaking magnetic field both inside and outside the deflection yoke. Of these magnetic fields, the leaking magnetic field generated inside the deflection yoke contributes to the deflection of said electron beam and much attention has been paid to the improvement of this internal magnetic field. On the other hand, the leaking magnetic field radiated outside the deflection yoke, that is, the externally leaking magnetic field, does not greatly affect the characteristics of the deflection yoke and the function of the deflection yoke is based on the utilization of the leaking magnetic field. Accordingly, up to now, measures to reduce the externally leaking magnetic field hardly have been taken. Lately, various types of personal computers and electronically controlled office machines have been widely used at various offices and job shops where they are used in many cases in the vincinty of television equipment. Therefore, the externally leaking magnetic fields of the deflection yoke which has not been a problem up to that point in time, was taken under examination: The high frequency magnetic field generated by the horizontal deflection coils has been found to affect other electronic equipment causing these electronic equipment to malfunction due to electromagnetic interferences. An attempt to mitigate this electromagnetic interference caused by the externally leaking magnetic field is described in the DE-A-3 513 216: A magnetism shielding cylinder surrounding the deflection yoke is provided to reduce such electromagnetic interference. However, provision of the magnetism shielding cylinder around the deflection yoke is disadvantageous in that a larger space will be required to result in a large size design of the housing of the television equipment and the magnetism shielding cylinder forms the magnetic path for the externally leaking magnetic field to adversely affect landing and convergence of electron beams. Summary of the Invention An object of the present invention is to provide the deflection yoke apparatus provided with one or more auxiliary coil devices for reducing the externally leaking magnetic field generated from the deflection yoke. Another object of the present invention is to provide the deflection yoke apparatus provided with one or more auxiliary coil devices for reducing unwanted electromagnetic radiation generated from the deflection yoke without adverse effect on landing and convergence of electron beams in the television equipment employing the cathode-ray tube. The deflection yoke apparatus of the present invention comprises a deflection core, a pair of horizontal deflection coils, a pair of vertical deflection coils, a coil separator located between these coils and auxiliary coil devices which are arranged at upper and lower positions or one of upper and lower positions in the Y-axis direction outside the deflection yoke when the horizontal deflection direction of electron beams is assigned as the X axis and the vertical deflection direction as the Y axis. The vertical deflection coils can be a saddle type coil or a toroidal type coil which is wound around the deflection coil. A deflection yoke apparatus according to the invention is defined in claim 1. The auxiliary coil device is generally made up by winding the auxiliary coil around the coil bobbin in a square form or winding it without the coil bobbin, and arranging the auxiliary coil device in the coil case. A magnetic member having high magnetic permeability is inserted into the center space of each auxiliary coil. The auxiliary coils can be made circular and bent in the circumferential direction of the deflection core. The auxiliary coils are connected in series or parallel to the horizontal deflection coils or connected to the horizontal deflection circuit to generate the cancel magnetic field which suppresses part of the externally leaking magnetic field radiated from the deflection core. If the auxiliary coil device is to be arranged only at one of positions in the Y-axis direction outside the deflection core, such adjustment as increasing of the number of turns of auxiliary coils or increasing of the current to be supplied to the auxiliary coils is required. Brief Description of the Drawings Figure 1 is a side view of the deflection yoke apparatus provided with the auxiliary coils in accordance with the present invention, Figure 2 is a sectional view along the one-dotted broken line II-II in Figure 1, Figure 3 is a simplified illustration to show the relative positions of the toroidal coils and the auxiliary coils in the deflection yoke apparatus in accordance with the present invention, Figure 4 shows an example of the connecting circuit for the horizontal deflection coils and the auxiliary coils, Figure 5 briefly illustrates the operation of the deflection yoke apparatus in accordance with the present invention, Figure 6 is a side view showing another embodiment of the deflection yoke apparatus in accordance with the present invention, Figure 7 shows the auxiliary coil which is bent, Figure 8 is a plan view showing another embodiment of the auxiliary coil, Figure 9 shows an example of the case of the auxiliary coils, Figure 10A shows another embodiment of the case of the auxiliary coil, Figure 10B shows an example of the case cover, and Figure 11 shows another embodiment of the deflection yoke apparatus in accordance with the present invention in which the auxiliary coil device is fixed on the deflection yoke. Detailed Description of the Invention In Figure 1, the annular ferrite core 10 can be divided into two semi-annular half cores around each of which vertical deflection coils 11 and 12 are toroidally wound. Inside the deflection core 10, a pair of horizontal deflection coils 14 and 15 shown with the broken line are disposed with the coil separator 13 made of plastic resin material. On the exterior of the deflection core 10, auxiliary coil devices 16 and 17 are slantly arranged in the vertical direction on the drawing and respectively fixed to the engaging portion 36 provided on the front expanded part 13a and the rear expanded part 13b of the coil separator. Figure 2 shows the sectional view along the broken line II-II in Figure 1 and the deflection core 10 is located at the coordinate position where it is divided into four equal portions by X and Y axes. As viewed on this coordinate system, a pair of vertical deflection coils 11 and 12 are respectively arranged at upper and lower sides in reference to the X axis so that they are arranged symmetrically in reference to the Y axis. The auxiliary coil devices are located at the positions in the Y-axis direction equally away from the X axis and the parallel to the X axis. Figure 3 shows the relationship between the deflection core 10 around which vertical deflection coils 11 and 12 are toroidally wound and the auxiliary coil devices 16 and 17. Auxiliary coils 18 and 19 are wound in a rectangular form and its length is almost equal to the length of the deflection core 10 in the axial direction of the core. Magnetic members 20 and 21 with high magnetic permeability made of ferrite, permalloy, silicon steel sheet or other material are inserted into the center hollow spaces or auxiliary coils 18 and 19 to intensify the magnitude of magnetic field generated when a current is supplied to the auxiliary coils. Auxiliary coils 18 and 19 are made up by winding seven times five 0.4mm diameter copper wires which are stranded or bound, and these auxiliary coils are connected in series to horizontal deflection coils 14 and 15 as shown in Figure 4. Accordinglly, the current as large as the current flowing through the horizontal deflection coils is supplied to auxiliary coils 18 and 19. Figure 5 shows the cross section of a part of the deflection yoke apparatus and briefly illustrates the state where the horizontal deflection current flows in horizontal deflection coils 14 and 15 and auxiliary coils 18 and 19. The arrowheads included in the broken line and the said line indicate an instantaneous state of the deflection cycle and the directions of the arrowheads are reversed when electron beams are deflected in the opposite direction. If it is assumed that magnetic flux B flows through the deflection core 10 when the horizontal deflection current is supplied to horizontal deflection coils 14 and 15, the magnetic flux D passes through the internal space of the deflection core 10 to contribute to deflection of electron beams and the remaining magnetic flux R passes through the external space of the deflection core 10. This magnetic flux R forms the externally leaking magnetic field which causes electromagnetic interference. On the other hand, magnetic flux C generated from auxiliary coils 18 and 19 of auxiliary coil devices 16 and 17 has the direction opposite to that of magnetic flux R and forms the cancel magnetic field against the externally leaking magnetic field to suppress a part of the externally leaking magnetic field. In this case, since magnetic members 20 and 21 are inserted into auxiliary coils 18 and 19, the magnitude of the cancel magnetic field is increased by approximately 60% as compared with the auxiliary coils into which the magnetic members are not inserted. Accordingly, the number of turns of auxiliary coils 18 and 19 can be less. The external sizes of auxiliary coils 18 and 19, number of turns of said coils, diameters of conductors used in these coils, etc. are determined taking into account the impedance of the horizontal deflection coils, magnitude of the externally leaking magnetic field, frequency of the current flowing through said coils 18 and 19, etc. Figure 6 shows another embodiment of the deflection yoke apparatus in accordance with the present invention. Auxiliary coil devices 16 and 18 are fixed horizontally to the engaging portion 38 provided on the front expanded part 13a of the coil separator 13. In this case, auxiliary coil devices 16 and 18 can be easily fitted to the coil separator. Figure 7 shows another embodiment of the auxiliary coil device. Auxiliary coils 22 and 23 are bent along the contour of the deflection core 10 and magnetic members 24 and 25 are bent accordingly. In this configuration, the magnetic resistance between magnetic members 24 and 25 and the deflection core 10 becomes uniform and the effect of the cancel magnetic field becomes large. Figure 8 shows another shape of the auxiliary coil device. The auxiliary coil 26 is formed to be circular and a disk-shaped member 27 is inserted. Though not shown, the auxiliary coil can be formed to be trapezoidal and the shape of the auxiliary coil can thus be freely determined in accordance with the shape of the deflection core. Since the horizontal deflection current is supplied to the auxiliary coil, it is necessary to protect workers for assembling television equipment from electrical shock. For this purpose, the auxiliary coil device is made up by housing the auxiliary coils and magnetic members in the insulation case 28 made of a plastic material. Figure 10 shows the more practically designed coil case for the auxiliary coil. The coil case 29 is rectangularly formed to have the internal square wall 29a, the external square wall 29b which is larger than the internal square wall 29a and the bottom 29C which exists between said internal and external square walls. The auxiliary coil is housed in the space formed by the internal wall 29a, external wall 29b and bottom 29c. The magnetic member is inserted and fixed in the center opening 30. The coil case 29 is covered with the case cover 31 as shwon in Figure 10B. The case cover 31 has the edge wall 31a slightly larger than the contour of the external wall 29b of the coil case, top cover plate 31b for closing the auxiliary coil space of the coil case 29, and hook parts 31c for engaging with the engaging parts of the coil separator. Figure 11 shows an example of the auxiliary coil device which employs the coil case and the case cover shown in Figures 10A and 10B and is fixed to the coil separator. The engaging parts 35 are provided at the rear expanded part 32b of the coil separator 32 and engaged with the hook parts 31c. In this case, the front expanded part 32a of the coil separator 32 does not have the engaging means for the auxiliary coil device 31 and the lower part of the auxiliary coil device is fixed with an adhesive agent such as for melt to the vertical deflection coil 11. The auxiliary coil device 31 has the auxiliary coil 34 and the magnetic member 33. For strengthening connection of the auxiliary coil device 31 and the rear expanded wall 33b, the cover 31b is partly expanded in place of the hook part 31C and the expanded portion is directly fixed to the rear expanded wall 33b. As described above, the deflection yoke apparatus in accordance with the present invention can reduce the externally leaking magnetic field having a high frequency radiated from the deflection coil, in other words, an unwanted radiation and minimize electromagnetic interference to other electronic equipment.

Claims: A deflection yoke apparatus, which is mounted on a neck of a cathode-ray tube for projecting rasters on a screen by scanning at least one electron beam, comprising (a) a pair of saddle type horizontal deflection coils (14, 15) which are arranged along the internal surface of the core for generating a magnetic field to deflect said electron beam in a horizontal direction, (b) a pair of toroidal or saddle type vertical deflection coils (11, 12) for generating a magnetic field to deflect said electron beam in a vertical direction, (c) a coil separator (13) for electrical insulation between said pair of horizontal and said pair of vertical deflection coils (11, 12, 14, 15), said coil separator (13) being provided with a front expanded part (13a, 32a) at its front end and a rear expanded part (13b, 32b) at its rear end, (d) an annular deflection core (10) which forms a magnetic path for a magnetic flux (B) generated when a deflection current is supplied to said horizontal (13, 14) and vertical deflection coils (11, 12), thus generating a deflection magneticfield (D) for deflecting said electron beam inside said annular deflection core (10) and generating an externally leaking magnetic field (R) outside said annular deflection core (10), (e) an auxiliary coil means (16, 17) comprising an auxiliary coil (18, 19) with a magnetic member (20, 21), said auxiliary coil being formed in a looped shape and being electrically connected to said horizontal deflection coils (14, 15) and being arranged at at least one of an upper and lower position in said vertical direction outside said deflection core (10) to generate a magnetic field (C) with a direction opposing to the direction of said externally leaking magnetic field (R) when a horizontal deflection current is supplied to said means, (f) an engaging means (35, 36, 37, 38) for fixing said auxiliary coil means (16, 17) to said coil separator (13), (h) said auxiliary coil means (16, 17) is arranged between said front expanded part (13a, 32a) and said rear expanded part (13b, 32b) of said coil separator (13). A deflection yoke apparatus in accordance with claim 1, wherein said engaging means comprises engaging parts (35) provided on at least one expanded part (32b) of said coil separator (32) and hook parts (31c) provided on said auxiliary coil means. A deflection yoke apparatus in accordance with Claim 1, wherein said magnetic member (20, 21) is made of soft magnetic material. A deflection yoke apparatus in accordance with Claim 1, wherein said auxiliary coil means (16, 17) is provided with an auxiliary coil (18, 19), a coil case (29) for housing said coil (18, 19) and a case cover (31) for covering said case (29). A deflection yoke apparatus in accordance with Claim 4, wherein said coil case (29) is formed by an internal square wall (29a), an external square wall (29b) and a bottom (29c) which couples said internal (29a) and external square walls (29b).

Inventors: OHTSU SHINJI, TAKAMATSU YOSHIMITSU, YABUSHITA HARUYASU, OHTSU, SHINJI, TAKAMATSU, YOSHIMITSU, YABUSHITA, YABUSHITA, HARUYASU NO. 1016, 3-3, 2-CHOME
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1987
Main classification: H01J29
IPC codes: H01J29