Deflection yoke for braun tube and fabrication method thereof

Details Deflection yoke for braun tube and fabrication method thereof Deflection yoke for braun tube and fabrication method thereof

2001-04-19

2003-09-09

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Beam deflecting means

C313S441000, C335S213000, C335S210000, C335S299000

Reexamination Certificate

active

06617780

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a deflection yoke for a Braun tube, and more particularly, to an improved deflection yoke for a Braun tube having a secondary 4-pole convergence yoke for correcting a misconvergence caused by the primary 4-pole convergence yoke, and to a fabrication method thereof.
2. Description of the Background Art
FIG. 1
shows a partial sectional view of a general color Braun tube, which includes an electron gun
4
emitting three electron beams from the rear side of a funnel
3
, a screen
1
on which the electron beams collide to produce light, a shadow mask
2
discriminating the three electron beams and a deflection yoke
30
deflecting the electron beams to determined points of the screen
1
.
The Braun tube serves to receive an electric signal from an external source for an image, changes it to a light signal and displays it as an image having a spatial position on the screen
1
and a functional content (color, luminosity).
Accordingly, in the Braun tube, the content signal having information of the color of an image to be displayed on the screen
1
is applied to the electron gun
4
so that a desired color is shown on the screen
1
through the appropriate color combination of R, G and B electron beams and R, G and B phosphors on the screen, and the position signal of the image is applied to the deflection yoke
30
so that the position points of the screen
1
that the R, G and B electron beams emitted from the electron gun
4
reach are controlled to display a desired image.
The deflection yoke
30
includes a horizontal deflection coil
31
deflecting the electron beams emitted from the electron gun of the Braun tube in the horizontal direction, a vertical deflection coil
33
deflecting the electron beams in the vertical direction, a conical ferrite core
34
for reducing loss of a magnetic force generated from the horizontal and the vertical deflection coils
31
and
33
to heighten the magnetic efficiency, and a holder
32
fixing the horizontal and the vertical deflection coils
31
and
33
and the ferrite core
34
at pre-set positions with respect to the Braun tube.
A primary 4-pole convergence yoke
35
and a ring-shaped permanent magnet
36
are installed at a neck portion
31
of the funnel
31
to correct a misconvergence caused due to a fabrication error of the deflection yoke
30
and the Braun tube.
As for the Braun tube, by varying the distance between the R beam and the B beam emitted from the electron gun
4
, the curvature of the shadow mask
2
can be considerably reduced more than the inner curvature of a panel forming the screen
1
, and thus, the hawling and doming characteristics of the Braun tube can be improved.
As shown in
FIG. 2A
, the primary 4-pole convergence yoke
35
is constructed such that coils are wound in the 2 o'clock, 5 o'clock, 7 o'clock and 10 o'clock positions to form magnetic fields as shown in FIG.
2
B.
As shown in
FIG. 3
, in order to correct a misconvergence of a screen varied due to the primary 4-pole convergence yoke
35
, a secondary 4-pole convergence yoke
40
, on which auxiliary coils
41
are wound in the 12 o'clock, 6 o'clock, 3 o'clock and 9 o'clock positions, is provided at the ferrite core
34
.
As shown in
FIG. 4
, in the deflection yoke, in order to apply a driving current to the primary and the secondary 4-pole convergence yokes
35
and
40
, an amplifying circuit is connected in parallel with the vertical deflection coil
33
and an integrating circuit is connected in series with the vertical deflection coil
33
. And in order to prevent an induced current from being generated in the secondary 4-pole convergence yoke
40
, an induced current preventing circuit is provided to synchronize the parallelly connected horizontal deflection coil
31
and the serially connected horizontal compensation coil
51
to a vertical compensation coil
53
.
The vertical compensation coil
53
is connected in series with the amplifying circuit and the integrating circuit and also connected in series with the secondary 4-pole convergence yoke
40
.
The deflection yoke
30
constructed as described above supplies current generally having a frequency of 15.75 kHz or more to the horizontal deflection coil
31
which generates a deflecting magnetic field that deflects the electron beam in the Braun tube in the horizontal direction.
The deflection yoke
30
is formed to have a self-convergence form which is capable of converging the electron beams on a screen by applying a non-uniform magnetic field by the horizontal and vertical deflection coils
31
and
33
even when the three electron beam guns do not use any supplemental circuit or device.
In other words, in the deflection yoke, the winding distributions of the horizontal deflection coil
31
and the vertical deflection coil
33
are adjusted to form a barrel type or a pin-cushion type magnetic field by regions (an opening portion, a middle portion and a neck portion). Then, each of the three electron beams has a different deflection force according to its position, and thus, the electron beams are converged to the same point on the screen even from different distances of each beam from a starting point to an arrival point.
In addition, in the case where a magnetic field is formed by applying a current to the horizontal and the vertical deflection coils
31
and
33
, it is difficult to deflect the electron beams over the entire screen only with the magnetic field applied by the horizontal and the vertical deflection coils
31
and
33
. Thus, the ferrite core
34
is used to minimize the loss in the return path of the magnetic field, thereby heightening the magnetic field and increasing the magnetic force.
In the Braun tube, the howling and the doming characteristics of the shadow mask
2
may be degraded due to the planarization of the screen
1
. Thus, after the primary 4-pole convergence yoke
35
is installed at the neck portion
3
a
of the funnel
3
to be symmetrical horizontally and vertically as shown in
FIGS. 1 and 2
, when the vertical deflection current (the current indicated by a dotted line in
FIG. 5
) supplied by the circuit illustrated in
FIG. 4
is applied thereto, the magnetic fields B
1
and B
2
shown in
FIG. 2B
are formed at the primary 4-pole convergence yoke
35
, so that the R beam receives a force in the 3 o'clock direction at the point ‘A’ and the B beam receives a force in the 9 o'clock direction.
At this time, on the screen
1
″, the paths of the R beam and the B beam are not changed at the points ‘B’ and E′, However, as shown in
FIG. 5
, at the points ‘C’ and ‘F’, the upper and lower end portions of the screen
1
″, since the current flows in the opposite direction, a magnetic field is formed in the opposite direction to that of the magnetic field as shown in FIG.
2
B. Accordingly, the R beam receives a force in the 9 o'clock direction and the ‘B’ beam receives a force in the 3 o'clock direction, and thus, the positions of the R and the B beams are changed in the horizontal directions. As the beams trace other points of the screen
1
″, the applied magnetic field is changed in proportion to the change in the beam position at the A-F points.
When the primary 4-pole convergence yoke
35
is operated, the distance between the R beam and the B beam at the center of the deflection yoke
30
is the longest at the point ‘A’ and the shortest at the points ‘C’ and ‘F’.
Meanwhile, the changes in the positions of the R beam and the B beam in the horizontal direction signify the change of the angle at which the R and the B beams are made incident on the shadow mask. In this respect, a small incident angle is called a grouping and a large incident angle is called a degrouping.
With reference to
FIG. 7
, the degree (G) of grouping is expressed by the following equation:
G
=(3
SQ/PhL
)  (1)
wherein ‘S’ indicates a distance between the R and the B beams at the deflection ce

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