Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Reexamination Certificate
2003-01-13
2004-11-30
Williams, Joseph (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
C335S213000
Reexamination Certificate
active
06825602
ABSTRACT:
BACKGROUND OF THE INVENTION
This nonprovisional application claims priority under 35 U.S.C. §119(a) on patent application Ser. No. 2002-0024939 filed in KOREA on May 7, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube having a deflection yoke which can decrease a leakage magnetic field.
2. Description of the Related Art
In general, a television set or other image display devices using a cathode ray tube include a deflection yoke for deflecting an electron beam generated from an electron gun.
Here, a black and white cathode ray tube needs one electron gun, but a color cathode ray tube includes three in-line electron guns aligned in a row on a horizontal surface in order to reproduce color images with the mixture of red R, green G and blue B.
The color cathode ray tube employs a self-converging deflection yoke using an irregular magnetic field so as to converge three electron beams R, G and B emitted from the in-line electron guns into one point of a phosphor screen.
Here, the three electron beams emitted from the electron guns are deflected in a horizontal or vertical direction by a pincushion type horizontal deflection magnetic field or a barrel type vertical deflection magnetic field of the deflection yoke.
The beams deflected by the deflection yoke can be landed on the phosphor screen through a shadow mask.
FIG. 1
is a structure view illustrating a general cathode ray tube. Referring to
FIG. 1
, the cathode ray tube includes a panel unit
1
, a funnel unit
2
connected to the panel unit
1
, and a neck side
3
incorporating with the funnel unit
2
.
A phosphor screen
5
coated with three dot or stripe-shaped color phosphor layers emitting R, G and B lights is installed on the inner surface of a panel
4
of the panel unit
1
. In addition, a shadow mask
6
which is a color sorting electrode having a plurality of pores or slits is aligned at the inside portion to face the phosphor screen
5
. The shadow mask
6
is connected to a frame
7
, elastically supported by an elastic member
8
, and also supported by the panel
4
through a stud pin
9
. An inner shield
10
is fixed to the frame
7
in order to intercept an external magnetic field of electron beams deflected by a deflection yoke
13
to prevent the path of the electron beams from being changed.
Electron guns
14
are built in the neck side
3
for receiving a voltage and emitting R, G and B electron beams. Preferably, the electron guns
14
are in-line type electron guns aligned in a row on the same plane in the color cathode ray tube, for emitting three electron beams. In addition, convergence purity correction magnets (CPM) for converging the electron beams
12
emitted from the electron guns
14
into one point are positioned at the front end of the electron guns
14
.
The deflection yoke
13
for horizontally or vertically deflecting the electron beams from the electron guns
14
is disposed on the outer surface of the funnel unit
2
at the rear end of the funnel unit
2
, namely the front end of the neck side
3
.
As illustrated in
FIG. 2
, the deflection yoke
13
includes a round-shaped holder
35
for forming a first flange
25
and a second flange
27
comprising a screen side
21
and a neck side
23
, fixing horizontal deflection coils
29
a
and
29
b
, a vertical deflection coil
31
and a ferrite core
33
to predetermined positions, and insulating the vertical deflection coil
31
and the horizontal deflection coils
29
a
and
29
b
, the horizontal deflection coils
29
a
and
29
b
wound between the first flange
25
and the second flange
27
at the inside portion of the holder
35
, for deflecting the electron beams emitted from the electron guns in the horizontal direction, the vertical deflection coil
31
wound between the first flange
25
and the second flange
27
at the inside portion of the holder
35
, for deflecting the electron beams in the vertical direction, and the conical ferrite core
33
for improving magnetic efficiency by decreasing loss of the horizontal/vertical deflection magnetic field generated by the horizontal deflection coils
29
a
and
29
b
and the vertical deflection coil
31
.
In general, the deflection yoke
13
generates the leakage magnetic field in the screen side
21
and the neck side
23
. The leakage of the magnetic field is harmful to humans.
In order to prevent leakage of the magnetic field, cancel coils
37
a
and
37
b
are installed at the upper and lower portions of the first flange
25
of the deflection yoke
13
. Here, a fetch line
41
fetched from a terminal plate
39
is connected to the horizontal deflection coils
29
a
and
29
b
through the cancel coils
37
a
and
37
b.
As shown in
FIG. 4
, the upper horizontal deflection coil
29
a
is connected in series to the pair of cancel coils
37
a
and
37
b
, and the lower horizontal deflection coil
29
b
is connected in series to a resistor R and a condenser C, which are re-connected in parallel. A saw tooth wave horizontal deflection current is applied to both ends H+ and H−, thereby generating the horizontal deflection magnetic field. Accordingly, the electron beams emitted from the electron gun are horizontally deflected due to the horizontal deflection magnetic field.
In general, the conventional deflection yoke applies a current having a frequency of at least 15.76 kHz to both ends H+ and H− of the horizontal deflection coils
29
a
and
29
b
, and deflects the electron beams of the funnel unit
2
in the horizontal direction by using the thusly-generated pincushion type horizontal deflection magnetic field. On the other hand, the deflection yoke applies a current having a frequency of about 60 Hz to the vertical deflection coil
31
, and deflects the electron beams in the vertical direction by using the thusly-generated barrel type vertical deflection magnetic field.
In addition, the self-converging type deflection yoke has been developed to converge the three electron beams onto the screen by using an irregular magnetic field due to the horizontal deflection coils
29
a
and
29
b
and the vertical deflection coil
31
, without requiring a special additional circuit or device.
That is, the self-converging type deflection yoke adjusts the wiring distribution of the vertical deflection coil
31
and the horizontal deflection coils
29
a
and
29
b
, generates the barrel or pincushion type magnetic field to each portion, (for example the screen side
21
, intermediate side
22
and neck side
23
) in order for the three electron beams to have deflection force that differs according to their positions, and converges the electron beams to the same point in spite of a different distance between a starting point and ending point (namely, phosphor screen), thereby precisely hitting the corresponding phosphors.
In the case that the horizontal deflection magnetic field and the vertical deflection magnetic field are generated by transmitting the current to the horizontal deflection coils
29
a
and
29
b
and the vertical deflection coil
31
, the horizontal/vertical deflection magnetic fields generated due to the horizontal/vertical deflection coils, it is difficult to deflect the electron beams toward the whole surface of the panel. Therefore, the ferrite core
33
of high magnetic permeability is used to minimize loss on a feedback path of the magnetic fields, thereby increasing magnetic efficiency and magnetic force.
On the other hand, as described above, the screen side
21
and the neck side
23
of the deflection yoke unnecessarily generates the leakage magnetic field in addition to the main deflection magnetic field for deflecting the electron beams in the horizontal or vertical direction. The leakage magnetic field may be harmful to humans. Particularly, leakage magnetic fields having extremely low frequencies (ELF) ranging from 5 Hz to 2 kHz or a very low frequency (VLF) ranging from 2 to 400 kHz are considerably harmful to humans. Ther
Birch & Stewart Kolasch & Birch, LLP
LG. Philips Displays Korea Co. Ltd.
Williams Joseph
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