Structure of electron gun for color cathode ray tube

Details Structure of electron gun for color cathode ray tube Structure of electron gun for color cathode ray tube

2003-02-27

2004-12-21

Le, Hoanganh (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Cathode-ray deflections circuits

C313S414000, C313S412000

Reexamination Certificate

active

06833680

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure of an electron gun for a color cathode ray tube. More particularly, the invention relates to a structure of an electron gun for a color cathode ray tube capable of reducing a drive voltage by creating an optimum relation among a cathode, a first electrode, and a second electrode mounted in the electron gun, and preventing degradation in responsiveness to input signals on a high-resolution screen and a focus characteristic.
2. Background of the Related Art
FIG. 1
is an explanatory diagram of a structure of an electron gun for a cathode ray tube in a related art, and
FIG. 2
is an explanatory diagram of an outward appearance of the electron gun in FIG.
1
.
To give more details on the structure and functions of the electron gun for the cathode ray tube with reference to
FIGS. 1 and 2
, the electron gun includes three mutually independent cathodes
62
, a first electrode (G
1
)
64
positioned spaced apart for a predetermined distance from the cathode
62
, a second electrode (G
2
)
65
, a third electrode (G
3
)
66
, a fourth electrode (G
4
)
67
, a fifth electrode (G
5
)
68
, and a sixth electrode (G
6
)
69
, the second through sixth electrodes being arranged at regular intervals from the first electrode
64
in a tube axis (or in-line) direction wherein a shield cup
70
with a bulb space contact (BSC)
71
adhered thereto is disposed on an upper portion of the last electrode, namely the sixth electrode
69
for electrically connecting the electron gun with a funnel
2
of the cathode ray tube as well as fixing the electron gun to a neck portion
2
a
of the funnel
2
.
Also, a deflection yoke
4
for deflecting an electron beam
5
onto the entire screen is installed outside of the neck portion
2
a
of the funnel
2
where the electron gun is mounted on.
Based on the above construction, the electron gun emits electrons when a heater
63
built in the cathode
62
is heated up using the power supplied by a stem pin
61
. The electrons existing as the beam shape (i.e. electron beam) are preliminarily converged by a pre-focus lens formed between the first electrode
64
and the second electrode
65
, converged later by a pre-main lens formed by a potential difference among the third electrode
66
, the fourth electrode
67
and the fifth electrode
68
, and finally converged and accelerated when passing a main lens formed by a potential difference between the fifth electrode
68
and the sixth electrode
69
.
Basically, an image is formed on the screen when the electron beams
5
are deflected onto the entire screen by the deflection yoke
4
and passes a shadow mask
3
at a predetermined distance from the panel
1
and strikes a fluorescent screen
1
a
formed on an inner surface of the panel
1
.
FIG. 3
diagrammatically explains the structure of a part of the electron gun where the electron beam is formed.
As represented in
FIGS. 1 through 3
, the electron beam
5
is formed on the cathode
62
, the first electrode
64
at a predetermined distance from the cathode
62
, and the second through fourth electrodes
65
,
66
, and
67
. Normally, the intensity of the electron beam
5
modulates in accordance with image signals applied from an external drive circuit
30
, that is, red (Sr), green (Sg), and blue (Sb) colors.
As aforementioned, the first electrode
64
is disposed at a predetermined distance from the cathode
62
. And, an electron beam passing hole (or through-hole) with a diameter D is formed on the first electrode
64
.
In addition, a thing point
28
is formed between the first electrode
64
and the second electrode
65
where the two electrodes are spaced out by a constant distance B.
Upon application of a constant potential ranging from 400V to 1000V to the second electrode
65
, the heater
63
heats the cathode
62
, consequently emitting electrons therefrom. The emitted electrons are accelerated toward the first electrode
64
in which they form three electron beams
5
, and these three electron beams
5
pass an electron beam passing hole
64
A of the first electrode
64
and further an electron beam passing hole
65
A of the second electrode
65
. Later, these electron beams
5
are preliminarily converged by the pre-focus lens
40
formed between the second electrode and the third electrode
66
to which a 5 to 10 kV high voltage is applied.
The pre-focus lens
40
or the diameter of the pre-focus lens is controlled by the size of the electron beam passing hole
6
A of the first electrode
64
, the size of the electron beam passing hole
65
A of the second electrode
65
, a thickness T of the first electrode
64
, and the gap B between the first and second electrodes
64
and
65
.
Also, a pre-main lens
41
is formed between the third electrode
66
and the fourth electrode
67
.
FIG. 4
illustrates another related art cathode ray tube particularly comprising a coining part in the second electrode for reinforcing the pre-focus lens effect.
For instance, a Japanese Patent Publication No. 1999-288664 discloses a cathode ray tube comprising a coining part
65
C for adjusting the gap between the second electrode
65
and the third electrode
66
, ther by reinforcing the pre-focus lens effect and preventing difficulty of assembly or deterioration in an assembly precision within a limited design system based on an automatic process not necessarily using additional parts.
More specifically, the second electrode
65
is provided with the coining part
65
C with a diameter
2
R and a thickness t in the vicinity of the electron beam passing hole
65
A, and a slot part
65
B with a predetermined thickness t
1
−t
2
for improving a focus characteristic of the electron beam.
On the other hand, a drive voltage and a cutoff voltage are different as follows. Usually, the drive voltage from the external drive circuit
30
is applied to respective cathodes corresponding to three-color fluorescent substances through the stem pin
61
. When the drive voltage varies, the variation synchronizes with deflection and resultantly the amount of the electron beam
5
emitted from each cathode
62
is controlled thereby. At this time, the voltage right before the electron beam
5
is emitted from the cathode
62
is called a cutoff voltage. Normally, the cutoff voltage is obtained when the brightness of the screen is at zero level (dark point).
To be short, the cutoff voltage clan be expressed by the following equation:
Cutoff=
K×S
3
/C×T×B
)
×Vg
2
  Equation (1)
In the equation, K is a proportional constant; S is an area of the electron beam passing hole
64
A of the first electrode
64
; C is a gap between the cathode
62
and the first electrode
64
; T is a thickness of the electron beam passing hole
64
A of the first electrode; B is a gap between the first electrode
64
and the second electrode
65
; and Vg
2
is an applied voltage to the second electrode
65
.
Given the applied voltage to the second electrode
65
is 260V, the cutoff voltage for a color monitor cathode ray tube is approximately 55V.
According to Japanese Patent Publication No. 53-18866, a color cathode ray tube for a color television typically has a 0.6 mm diameter first electrode for the electron gun, and the drive voltage for a cathode ray tube particularly in a data processing monitor, e.g. a computer, is approximately 50V, and a current capacity a cathode emits is about 0.3 mA.
This corresponds when the screen of the cathode ray tube is at its recommended brightness level, namely 100 cd/m
2
.
When brightness, resolution and contrast values are substantially high, it is more likely to get a desirable display area for the color cathode ray tube.
Accordingly, as for the cathode ray tube for a monitor which requires all the above characteristics, one needs to reduce a beam spot size at a high brightness and increase the number of pixels, conforming to the increase in the resolution of a dot pitch of each color for composing the fluorescent screen and the

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