Electric lamp and discharge devices: systems – Cathode ray tube circuits – Power supply from deflection circuit source
Reexamination Certificate
1998-12-29
2001-11-27
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Power supply from deflection circuit source
C315S399000, C315S407000
Reexamination Certificate
active
06323607
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from the utility model application entitled Horizontal Drive Circuit in Display Apparatus filed with the Korean Industrial Property Office on Dec. 30, 1997 and duly assigned Serial No. 97-42950 by that Office.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device, and more particularly, to a horizontal drive circuit including means for preventing a surge voltage from occurring in a switching operation, and a method therefor.
2. Description of the Related Art
A monitor (or “display”), which is a peripheral device for a computer, exhibits as a picture a varying visual display of a signal received from a computer, so that a user can recognize the visual display.
FIG. 1
is a block diagram of a display. Referring to
FIG. 1
, the monitor includes a microcomputer
20
for receiving a horizontal synchronizing signal H-Sync and a vertical synchronizing signal V-Sync from a video card
10
contained within a computer (not shown). The microcomputer
20
generates a control signal for controlling a monitor picture. The monitor also includes vertical and horizontal deflection circuits
30
and
40
for receiving the vertical and horizontal synchronizing signals V-Sync and H-Sync, respectively. The vertical and horizontal deflection circuits
30
and
40
perform vertical and horizontal deflections, respectively, so that an electron beam generated by an electron gun of a cathode ray tube
80
is sequentially deflected from the upper left portion of the cathode ray tube
80
to its lower right portion by a defection yoke (DY in FIG.
1
), to thereby form the picture.
The display also includes a high voltage circuit
50
for supplying a high voltage to an anode of the cathode ray tube
80
. The high voltage circuit
50
uses a retrace line pulse generated by the output of the horizontal deflection circuit
40
. A video pre-amplifier
60
is also included in the monitor, for amplifying a low level of a video signal (R,G,B) transmitted from the video card
10
using a low-voltage amplifier, to thereby maintain a predetermined voltage level. The display further includes a video main amplifier
70
for amplifying the voltage amplified by the video pre-amplifier
60
to a signal of 40 to 60 Vpp, and for supplying energy to each pixel of the display.
This display device forms an image using the electron beam projected to its fluorescent screen. Here, a circuit for deflecting the electron beam is called a deflection circuit. Generally, the deflection mode is divided into electrostatic deflection, using an electric field, and electromagnetic deflection, using a magnetic field. Electromagnetic deflection is used, for example, in a TV in which a sawtooth current flows through horizontal and vertical coils to form pictures.
A general configuration of the horizontal deflection circuit (or “horizontal deflector”)
40
is shown in FIG.
2
. Referring to
FIG. 2
, the horizontal deflection circuit
40
includes a horizontal oscillation circuit
41
which generally uses a blocking oscillation circuits A horizontal drive circuit
42
of the horizontal deflection circuit
40
provides one-stage or two-stage current amplification using a transistor TR or a field effect transistor FET. The horizontal drive circuit
42
provides a gate current sufficient for turning on/off an output transistor of a horizontal output circuit
43
and performs waveform correction.
The horizontal output circuit
43
of the horizontal deflection circuit
40
generates a sawtooth current which flows through a deflection coil using a switching operation of a transistor. The horizontal deflection circuit
40
also includes a horizontal size controller
44
, connected to the horizontal output circuit
43
, to maintain a specific horizontal size of the picture of the display device.
The image resolution of a video display is determined by the bandwidth of the horizontal and vertical frequencies. Therefore, the horizontal deflector for deflecting the horizontal frequency is especially important when designing a high resolution video display. In particular, the transistor used for the horizontal output should be operated within a safe operation limit, considering the condition of the gate drive, the current and voltage of the collector, switching, etc. At the same time, to enhance the resolution of the monitor, the horizontal drive circuit requires a large current and high voltage together with a short rising time and falling time.
FIG. 3
illustrates the horizontal drive circuit
42
and horizontal output circuit
43
described above. The output of the horizontal oscillation circuit (or “horizontal oscillator”)
41
is amplified by a field effect transistor (FET) Q
1
whose output is supplied, through the horizontal output transformer “T,” to a gate of the horizontal output transistor Q
2
.
The horizontal drive circuit
42
includes an FET Q
1
, an R-C circuit, a resistor R
2
, and the transformer T. The gate of the FET Q
1
is connected to the output of the horizontal oscillator
41
. The R-C circuit includes a resistor R
1
and a capacitor C
1
for regulating the peak pulse of the switching signal generated by the FET Q
1
. The resistor R
2
introduces a source voltage Vcc. The transformer T induces the source voltage Vcc, supplied through the resistor R
2
, according to the switching signal of the FET Q
1
. The peak pulse of the switching signal is regulated by the R-C circuit with the resistor R
1
and the capacitor C
1
.
The horizontal output circuit
43
includes a horizontal output transistor Q
2
, capacitors C
2
and C
3
, a damping diode D
1
, and a deflection yoke DY. The horizontal output transistor Q
2
performs a switching operation according to the voltage level supplied from the horizontal drive circuit
42
. The capacitors C
2
and C
3
perform a charging and discharging operation in response to the switching of the horizontal output transistor Q
2
. The damping diode D
1
serves as a damper according to the charging and discharging of the horizontal output transistor Q
2
. The deflection yoke DY generates a sawtooth current according to the charging and discharging of the capacitors C
2
and C
3
.
The horizontal drive circuit
42
requires an enhanced specification of the FET Q
1
to prevent the FET Q
1
from being destroyed by an over-specification voltage.
SUMMARY OF THE INVENTION
It is an object of the present invention to protect a horizontal drive transistor of a horizontal drive circuit from an unexpected surge voltage.
It is another object of the present invention to provide a stabilizing drive circuit having a surge protect element without a high performance switching element.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention.
The above and other objects of the present invention are achieved by providing a horizontal drive circuit for a video display. The horizontal drive circuit includes switching means, a driving transformer, and a surge protector. The switching means switches according to a horizontal oscillation frequency generated by a horizontal oscillator. The driving transformer has a primary winding connected the switching means and a secondary winding, the secondary winding providing an amplified current according to the status of the switching means. The surge protector is connected between the switching means and the primary winding of the driving transformer.
In a preferred embodiment of the invention, the surge protector is a diode.
REFERENCES:
patent: 5059874 (1991-10-01), Oliver
patent: 5691890 (1997-11-01), Hyde
patent: 5952795 (1999-09-01), Kofune et al.
patent: 5969486 (1999-10-01), Webb et al.
Chen Shih-Chao
Samsung Electronics Co,. Ltd
Staas & Halsey , LLP
Wong Don
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