Electron gun for color cathode ray tube

Details Electron gun for color cathode ray tube Electron gun for color cathode ray tube

2000-01-12

2002-04-16

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Plural beam generating or control

C313S412000

Reexamination Certificate

active

06373178

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color cathode ray tube(CRT), and more particularly, to an electron gun for a color CRT for generating electron beams.
2. Background of the Related Art
FIG. 1
illustrates a section of a first exemplary related art color CRT with an electron gun. In general, the CRT is a display for displaying a desired image by directing three electron beams
2
to a fluorescent film
3
on an inside surface of a panel
1
, to make the fluorescent film
3
luminescent. The CRT is provided with an electron gun
4
for emitting the electron beams.
The first exemplary related art electron gun is provided with three independent cathodes
40
, and first, second, third, fourth, fifth, and sixth electrodes
41
,
42
,
43
,
44
,
45
, and
46
disposed at intervals in a tube axis direction. There is a shield cup
47
fitted to a screen side of the sixth electrode
46
. Upon application of power to stem pins
5
on the electron gun
4
, heaters heat the cathodes
40
causing them to emit electrons. The amount of emitted electrons is controlled by the first electrode
41
, accelerated by the second electrode
42
, and converged and accelerated by a pre-focus lens formed between the third, fourth, and fifth electrodes
43
,
44
, and
45
. Then, the electron beams
2
are precisely focused onto a preset scan position by a main lens having a strong focusing power formed by a potential difference between the fifth electrode
45
and the sixth electrode
46
.
The diameter of the main lens fixes a spot size of the electron beam
2
. That is, if the main lens has a smaller diameter with a greater spherical aberration, the spot size of the electron beams passing through the main lens becomes greater, and if the main lens has a greater diameter with a smaller spherical aberration, a spot size of the electron beams passing through the main lens becomes smaller, relatively. The diameter of the main lens is dependent on electron beam pass through apertures formed on opposing sides of the fifth and sixth electrodes
45
and
46
. If the size of the electron beam pass through apertures is large, the diameter of the main lens is the larger, and opposite to this, if the size of the electron beam pass through aperture is small, the diameter of the main lens is comparatively smaller.
Therefore, in the electron gun in the first exemplary related art CRT, the three electron beam pass through apertures (not shown) formed in opposing surfaces of the fifth and sixth electrodes
45
and
46
form a main lens proportional to the size of electron beam pass through apertures. Though the size of the electron beam pass through apertures should be formed greater for forming a greater main lens, the size is limited. Accordingly, the electron gun in the first exemplary related art CRT, which has a small main lens diameter, is mostly used in a small sized Braun tube or a Braun tube, requiring a low resolution.
FIG. 2
illustrates a perspective view of key parts of a second exemplary related art electron gun, showing the fifth and sixth electrodes provided for enlarging the main lens. (See U.S. Pat. No. 4,406,970). The second exemplary related art electron gun is a modified version of the first exemplary related art electron gun for enlarging the main lens. That is, the second exemplary related art electron gun is provided with rim portions
45
b
and
46
b
of race track forms on opposing surfaces of the fifth electrode
45
(or focus electrode) and the sixth electrode
46
(or anode electrode), recesses with recess surfaces
45
c
and
46
c
inside of the rim portions
45
b
and
46
b
, and three electron beam pass through apertures
45
a
,
46
a
in each of the recess surfaces
45
c
and
46
c
. Since the recesses
45
d
and
46
d
formed in the opposing surfaces of the electrodes act as apertures, a main lens proportional to the recesses can be obtained between the fifth electrode
45
and the sixth electrode
46
, permitting use of a main lens that is comparatively greater than the first exemplary electron gun.
FIG. 3
illustrates a perspective view of key parts of a third exemplary related art electron gun, showing the fifth and sixth electrodes provided for enlarging the main lens. (See U.S. Pat. No. 4,599,534).
Referring to
FIG. 3
, in order to enlarge the diameter of the main lens, the third exemplary related art electron gun is provided with rim portions
45
b
and
46
b
of race track forms in opposing surfaces of the fifth electrode
45
and the sixth electrode
46
for common pass through of the three electron beams, and field control electrodes
45
e
and
46
e
of plates approx. 0.6~0.7 mm thick and fixed at locations recessed at a depth from the rim portions
45
b
and
46
b
for forming identical lens power for the electron beams
2
. Each of the electric field control electrodes
45
e
and
46
e
has vertically elongated electron beam pass through apertures
45
a
and
46
a
at their centers, which have a horizontal diameter that is shorter than a vertical diameter, and half cut away vertically elongated apertures adjacent to the apertures
45
a
and
46
a
at the centers for pass through of outer electron beams. There is also a correction electrode
48
of an angle form fitted to the shield cup
47
electrically connected to the sixth electrode
46
. End portions of the rim portions
45
b
and
46
b
are curved inwardly by approx. 1 mm. Thus, also in the third exemplary related art electron gun, inside portions of the rim portions
45
b
and
46
b
formed in opposing surfaces of the fifth electrode
45
and the sixth electrode
46
serve as apertures, to provide a large diameter main lens. In comparison to the second exemplary related art electron gun, the third exemplary related art electron gun can provide a uniform lens action to the three electron beams by means of the electric field control electrodes
45
e
and
46
e
formed in the fifth and sixth electrodes
45
and
46
, and can correct the vertical direction strong lens action into a horizontal direction by means of the vertically elongated rim portions
45
b
and
46
b.
FIG. 4
illustrates a perspective view of key parts of a fourth exemplary related art electron gun, similar to the second and the third examples provided for enlarging the main lens.
Referring to
FIG. 4
, the fourth exemplary related art electron gun is provided with rim portions
45
b
and
46
b
of race track forms in opposing surfaces of the fifth electrode
45
and the sixth electrode
46
for pass through of the three electron beams in common, with the insides of the rim portions fully opened, and electric field control electrodes
45
e
and
46
e
having rectangular electron beam pass through apertures
45
a
and
46
a
curved inwardly for the center electron beam at locations inside of opened portions
45
f
and
46
f
. Each of the rim portions
45
b
and
46
b
are curved inwardly by 1 mm for reinforcing the electrodes for preventing distortion of the diameter during fabrication.
FIG. 5
illustrates a section of a fifth exemplary related art electron gun. The fifth exemplary related art electron gun
4
is an electron gun for forming a dynamic quadrupole lens (“DQ”) having a lens action against a deflection yoke. That is, the fifth electrode, a focus electrode, is divided into a
5
-
1
electrode
50
and a
5
-
2
electrode
51
, and the DQ lens is provided between the
5
-
1
electrode
50
and the
5
-
2
electrode
51
. The DQ lens corrects a vertical elongation of a spot of an electron beam in forming a circular spot. This electron gun is used in a Braun tube requiring a high resolution or a large sized Braun tube to prevent distortion of an image along the periphery of a screen.
FIG. 6
illustrates a perspective view of key parts of a sixth exemplary related art electron gun. The sixth exemplary related art electron gun also utilizes a DQ lens, wherein the fifth electrode is divided into a
5
-
1
electrode
50
and a
5
-
2
electrode
52
, three vertically elongated electron beam pa

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