Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2001-07-09
2003-07-22
O'Shea, Sandra (Department: 2875)
Electric lamp and discharge devices
Cathode ray tube
Envelope
Reexamination Certificate
active
06597101
ABSTRACT:
BACKGROUND OF THE INVENTION
1 Field of the Invention
The present invention relates to a color cathode-ray tube, and more particularly, to a wire structure in which a natural frequency of a wire itself and a vibration damping force are improved to prevent a vibration of a neck glass caused due to an electrostatic force between the neck glass and a dynamic voltage focusing electrode.
2. Description of the Background Art
Generally, as shown in
FIG. 1
, a color cathode-ray tube includes a bulb-shaped funnel
1
, a panel
2
with a fluorescent material coated on the inner surface thereof and being attached on the front surface of the funnel, an electron gun
4
encapsulated in a neck glass
3
formed at a rear side of the funnel
1
, a stem pin
15
installed at the rear side of the neck glass
3
, for applying a power to the electron gun
4
, and a deflection yoke
5
installed at an outer periphery of the front side of the electron gun
4
, that is, at an outer periphery of the rear side of the funnel
1
.
In the color cathode-ray tube having the above-described structure, when a power is applied through the stem pin
15
to the electron gun
4
, an electron beam is focused and accelerated to be injected toward the panel
2
. At this time, an injection position of the electron beam is adjusted by the deflection yoke
5
to emit the fluorescent material coated on the inner surface of the panel
2
.
The construction of the electron gun
4
for generating electron beams will now be described in detail with reference to
FIGS. 2 and 3
.
The stem portion is fused with the neck glass and sealed so that it may receive a voltage from an external source as being inserted inside the neck glass
3
at the rear side of the funnel
1
, and a plurality of terminals are installed at the stem portion to make a stem pin
15
.
A heater
41
is disposed connected to the stem pin
15
. A cathode
42
is positioned at the front side of the heater
41
. A first grid electrode
43
is disposed forwardly at a distance from the cathode
42
. A second grid electrode
44
, a third grid electrode
45
and a fourth grid electrode
46
are sequentially installed spaced apart from the first grid electrode
43
. A static voltage focusing electrode
47
, a dynamic voltage focusing electrode
48
and an anode
49
are disposed forwardly spaced apart from the fourth grid electrode
46
.
Lower portions of each electrode are fixed to a bead glass
9
so that each electrode can be maintained at certain intervals, and a shield tap
7
is positioned in the middle of the upper and the lower faces of the bead glass
9
.
A shield cup
14
for shielding a leakage magnetic field is installed at the end of the front side of the anode
49
, and a bulb space connector (BSC)
50
for supporting the electron gun is connected at the front side of the shield cup
14
.
Generally, in order to improve an image quality of a color cathode-ray tube, a dynamic voltage current is applied to one of the focusing electrodes
47
and
48
of the electron gun
4
and a static voltage current is applied to the other, or a dynamic voltage current is applied to at least two grid electrodes.
Thus, in order for the dynamic voltage current to be applied to the focusing electrodes
47
and
48
, a wire
8
is connected between the stem pin
15
and the dynamic voltage focusing electrode
48
. As shown in
FIG. 4
, the wire
8
is made of one-strand metal of which a rear end portion or a central portion is bent to rest on the upper surface of the bead glass
9
.
In the conventional electron gun, as the heater
41
is heated upon receipt of the static voltage current through the stem pin
15
, electron beams are injected from the cathode
42
. The electron beams are controlled by the first grid electrode
43
and accelerated by the second grid electrode
44
.
After being controlled and accelerated, the electron beams are focused and accelerated by a potential difference between the dynamic voltage applied to the dynamic voltage focusing electrode
48
and the constant-voltage applied to the static voltage focusing electrode
47
, which passes through a slot of a shadow mask so as to be color-sorted and land on the fluorescent material coated on the inner surface of the panel
2
to emit the fluorescent material.
However, in the conventional electron gun, due to the dynamic voltage applied to the dynamic voltage focusing electrode
48
intended initially to improve the image quality, a large amount of dynamic voltage is induced at each point outside the neck glass
3
.
At this time, the voltage applied to the electrode is defined by the following equation [1].
V=V
DC
+V
AC COS &ohgr;t
[1]
wherein V
DC
indicates a static voltage applied to the cathode, the heater, the first, the second and the third grid electrodes or the like of the electron gun, V
AC COS &ohgr;t
indicates a dynamic voltage applied to the dynamic voltage focusing electrode, ‘V’ indicates a voltage applied to the electrode, &ohgr; indicates an angular frequency, and ‘t’ indicates time.
Accordingly, an electrostatic force is generated between the neck glass and the dynamic voltage focusing electrode as obtained in the following equation [2].
F
(
t
)
=
(
σ
b
/
2
ϵ
0
)
CV
D
C
+
(
1
/
2
)
(
dC
/
dZ
)
{
V
D
C
2
+
(
1
/
2
)
V
A
C
2
}
+
(
σ
b
/
2
ϵ
0
)
DV
AC
COS
ω
t
+
(
dC
/
dZ
)
V
D
C
V
AC
COS
ω
t
+
(
1
/
4
)
(
dC
/
dZ
)
V
A
C
COS
2
ω
t
2
[
2
]
wherein F(t) indicates an electrostatic force, &sgr;
b
indicates a surface charge density, ∈
0
indicates a dielectric constant in vacuum, and ‘C’ indicates an electrostatic capacity between the neck glass and the focusing electrode to which a dynamic voltage is applied.
When such a force is at work, the force according to third, fourth and fifth items of the above equation (2), not the static voltage, shows changes of
COS &ohgr;t
. When it is simplified, the electrostatic force can be expressed by the following equation [3].
F
(
t
)=∈
0
·S·
(
dV
)
2
/(2
D
2
) [3]
That is, dV indicates a potential difference between electrodes, ‘D’ indicates a distance between the electrodes, ‘S’ indicates a facing area between the electrodes.
The electrostatic force vibrates the dynamic voltage focusing electrode
48
, and the vibration of the dynamic voltage focusing electrode
48
is transmitted along the wire
8
to the stem pin
15
connected to the wire
8
, to vibrate the neck glass
8
.
Meanwhile, even though the dynamic voltage focusing electrode
48
is not vibrated by the electrostatic force, the wire
8
is vibrated owing to the change of the static electricity generated between the neck glass
3
and the dynamic voltage focusing electrode
48
. This vibration makes the neck glass
3
vibrate, causing increased noise.
In addition, the vibration transmitted from the dynamic voltage focusing electrode
48
or the vibration occurring in the wire
8
generates a resonance if it is identical to the natural frequency of the neck glass
3
, causing a high frequency noise which degrades the sensitivity characteristics of the cathode-ray tube.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an electron gun for a color cathode-ray tube in which a wire structure and form connected to apply a current to a focusing electrode are changed to vary a natural frequency of a wire and a vibration is prevented from being transmitted to a neck glass by improving a vibration damping capability, thereby restraining occurrence of a high frequency noise.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and b
Krishnan Sumati
LG Electronics Inc.
O'Shea Sandra
LandOfFree
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