Deflection yoke for a CRT

Details Deflection yoke for a CRT Deflection yoke for a CRT

2002-04-18

2004-02-03

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Cathode-ray deflections circuits

C313S440000

Reexamination Certificate

active

06686709

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a deflection yoke for a cathode ray tube (CRT), more particularly, a color CRT.
2. Background of the Related Art
An in-line type electron gun generally used in a color CRT has red ‘R’, green ‘G’, and blue ‘B’ color electron beams arranged horizontally in a line. A self-converging type deflection yoke is required in the CRT to converge the three electron beams onto one point on a fluorescent surface using a non-uniform magnetic field.
FIG. 1
of the present application shows a related art color CRT. The color CRT of
FIG. 1
is provided with a panel
1
at a front of the CRT. A fluorescent surface
3
formed of red R, green G, and blue B fluorescent materials is coated on an inside surface of the panel
1
. A shadow mask
2
is positioned adjacent the fluorescent surface
3
and selects a color of the electron beams incident on the fluorescent surface. A funnel
6
is attached to the back of the panel
1
and provides an inner space under vacuum. An electron gun
5
is fitted inside a tubular neck part of the funnel and emits the electron beams. A deflection yoke
4
is provided around an outer circumference of the funnel
6
. The deflection yoke
4
deflects the electron beams in the horizontal or vertical direction.
Referring to
FIG. 2
, the deflection yoke
4
is provided with one pair of horizontal deflection coils
41
that deflect the electron beams emitted from the electron gun
5
inside of the CRT in a horizontal direction, one pair of vertical deflection coils
42
that deflect the electron beams in a vertical direction, and a ferrite core
44
that reduces a loss of magnetic force caused by currents in the horizontal and vertical deflection coils. A holder
43
fixes the physical relative positions, fastens, and couples the horizontal deflection coils, the vertical deflection coils, and the ferrite core, provides insulation between the horizontal deflection coils and the vertical deflection coils, and facilitates coupling of the yoke
4
to the CRT. A COMA free coil
45
fitted to a neck side of the holder improves a COMA aberration caused by a vertical barrel type magnetic field. A ring band
46
fitted to the neck side of the holder mechanically couples the CRT with the deflection yoke. Magnets
47
fitted to an open end of the deflection yoke correct a raster distortion (hereafter called distortion) on the picture.
The horizontal deflection coils of the deflection yoke
4
include upper and lower deflection coils connected in parallel, as shown in
FIG. 3B. A
horizontal deflection current, as shown in
FIG. 3A
, is applied to the upper and lower deflection coils to form a horizontal deflection magnetic field, which deflects the electron beams from the electron gun
5
in the horizontal direction.
The deflection yoke
4
may be categorized depending on the shapes of the horizontal and vertical deflection coils
41
and
42
, and the ferrite core
44
, as set forth in table 1 below. That is, as shown in
FIGS. 4 and 5
, if the horizontal and vertical deflection coils are circular, the ferrite core is circular. As shown in
FIG. 6
, if the horizontal and the vertical deflection coils
41
and
42
are rectangular, the ferrite core is rectangular.
TABLE 1
Kind of DY
Horizontal DY
Vertical DY
Ferrite core
Circular DY
Circular coil
Circular coil
Circular core
RAC DY
Rectangular coil
Rectangular coil
Rectangular core
*DY: deflection yoke
Since the RAC type CRT deflection yoke
4
has a rectangular deflection coil and ferrite core, in the RAC type CRT deflection yoke
4
there is a shorter distance to the electron beams compared to the circular deflection yoke
4
, which provides better deflection sensitivity.
In general, the related art deflection yoke
4
has a current having a frequency equal to, or higher than, 15.75 KHz flowing through the horizontal deflection coil
41
. This current deflects the electron beams in the horizontal direction using a magnetic field formed as the current flows through the horizontal deflection coil
41
. The related art deflection yoke
4
generally has a current having a frequency equal to 60 KHz flowing through the vertical deflection coil
42
. This current deflects the electron beams in a vertical direction using a magnetic field formed as the current flows through the vertical deflection coil
42
.
In most cases, a self-convergence type deflection yoke
4
is used, in which the three electron beams are converged on the screen using a nonuniform magnetic field formed by the horizontal and vertical deflection coils without providing additional circuitry and device(s). That is, distributions of the windings of the horizontal deflection coil and the vertical deflection coil are adjusted to form a barrel or pin-cushion type magnetic field at respective parts (the opening part, the middle part, and the neck part) of the CRT so that the three electron beams undergo different deflection forces according to the positions of the three electron beams to converge the electron beams from different starting points to the same arrival point on the screen
1
.
If the magnetic field formed by the current through the deflection coil is not adequate for deflecting the electron beams to all parts of the screen, the ferrite core
44
, which has high permeability, is employed to minimize the loss of the magnetic field on the returning path, and to enhance a magnetic field efficiency and force.
Referring to
FIG. 7
, each of the one pair of horizontal deflection coils
41
has a rectangular upper horizontal deflection coil and a lower horizontal deflection coil, connected in parallel as shown in
FIG. 3B
, in which horizontal deflection currents in a saw tooth form are formed, forming a pin-cushion type horizontal deflection magnetic field.
There are two kinds of deflection yokes. As shown in
FIGS. 4 and 5
, since a circular deflection yoke
4
, with circular horizontal and vertical deflection coils
41
and
42
and a circular ferrite core
44
, has a ratio of inside surface areas of the neck part to the opening part of at least greater than 10 times, a deflection center of the deflection coil is deviated toward the neck part. Thus, it is necessary to arrange the deflection yoke inclined toward the screen in order to avoid a BSN (Beam Strike Neck) characteristic, a phenomenon in which the electron beams from the electron gun land on an inside surface of the funnel, which results in poor deflection sensitivity.
As shown in
FIGS. 6 and 7
, the RAC type deflection yoke
4
, with rectangular horizontal and vertical deflection coils
41
and
42
, and a rectangular ferrite core
44
, deflects electron beams in the horizontal direction by a force inversely proportional to a third power of a distance between an inside surface of the horizontal deflection coil and the electron beams, according to Flemming's left hand rule, as the three electron beams (i.e., red, green, and blue) from the electron gun
5
pass through the horizontal deflection magnetic field. Accordingly, the rectangular horizontal and vertical deflection coils have horizontal and vertical deflection sensitivities enhanced by approx. 20-30% as the distances between the electron beams and the deflection coils are shorter by a range of 20% compared to the related art circular deflection yokes.
However, the related art CRT deflection yoke
4
has the following problems. First, the circular deflection yoke with the circular deflection coils is unfavorable because of its poor deflection sensitivity due to the unnecessary distance between the electron beams and the deflection coil, and is particularly unfavorable in the case of a wide angle deflection yoke. The wide angle deflection yoke is not applicable to a high definition and high frequency deflection yoke.
Second, the ferrite core
44
used in the RAC type deflection yoke has a shrinkage rate of up to 20%, requiring a fabrication tolerance to be ±2% due to limitations in the fabrication process. Further, the related art ferrite core
44
having a recta

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