JP2000125147A - Video display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the video display device that can activate a spot killer circuit without being affected by a load change in a ternary winding of a flyback transformer. SOLUTION: A spot killer circuit 30 detects a trailing of a DC voltage V3 that is an output of a regulator circuit 3, and decreases a cathode voltage of a picture tube 12 so as to allow the cathode voltage to reach a cut-off voltage or below when the result of detection indicates a fall of the DC voltage. When a power switch of a television receiver is switched from on to off, a 1st DC power voltage Vl outputted from a main power supply 1 descends and the output of the regulator circuit 3 also decreases, and a transistor(TR) 31 of the spot killer circuit 30 is conductive. Thus, the spot killer circuit 30 decreases the cathode voltage of the picture tube 12 to the cut-off voltage or below and supplies a cathode current so as to prevent a fluorescent screen of the television receiver from being baked due to beam spots.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device provided with a spot killer circuit for preventing a bright spot from burning a fluorescent screen of a picture tube due to a high brightness spot.

[0002]

2. Description of the Related Art In a conventional television receiver, when the power is turned off, even if the deflection of the picture tube is stopped, a beam is applied to the phosphor screen without reducing the cathode voltage of the picture tube. However, this resulted in high-luminance spots, which caused bright spot burns on the phosphor screen. In response to this, in recent color television receivers using a cathode ray tube, a spot killer circuit is provided to prevent a bright spot from burning on a fluorescent screen due to a high brightness spot when the power is turned off.

FIG. 2 is a circuit diagram showing a main part of a color television receiver provided with such a conventional spot killer circuit.

In FIG. 2, reference numeral 61 denotes a flyback transformer, which generates a flyback pulse during a retrace period of the sawtooth current flowing through the horizontal deflection coil, rectifies the flyback pulse, and rectifies the anode voltage V21 and the focus voltage. V22 and a screen voltage V23 are created and supplied to the anode electrode, focus electrode, and screen electrode of the picture tube 62, respectively. In addition, flyback transformer 61
The flyback pulse generated at the first
And a voltage generating circuit 6 for generating a second DC voltage.
3 and the voltage generation circuit 64.

A voltage generating circuit 63 generates a power supply voltage for a video signal output circuit, and includes a rectifying diode D6.
1 and a smoothing capacitor C61. The anode of the diode D61 is connected to the tertiary winding of the flyback transformer 61, and the cathode of the diode D61 is connected to the reference potential point via the smoothing capacitor C61. Thus, a voltage V24 for the video signal output circuit is obtained from the connection point between the cathode of the diode D61 and the smoothing capacitor C61.

The voltage generating circuit 64 is provided with another circuit, for example, I
It generates a power supply voltage for the C device 65, and includes a rectifying diode D62 and a smoothing capacitor C62. The anode of the diode D62 is connected to the tertiary winding of the flyback transformer 61. Thereby, the cathode of the diode D62 and the smoothing capacitor C6
The power supply voltage V25 is obtained from the connection point with the power supply voltage V2. This power supply voltage V25 is supplied to the IC device 65 and to the spot killer circuit 80.

The video signal output circuit 70 includes resistors R71 to R71.
76 and NPN transistors Tr71, Tr72, Tr
73.

The input terminals 71, 7 of the video signal output circuit 70
The color difference signals (RY) and (G-
Y) and (BY) are supplied. Transistor Tr
Bases of 71, Tr72, Tr73 are input terminals 71,
72, 73, respectively, and the collector is connected to the voltage generating circuit 6 via resistors R71, R72, R73, respectively.
3 is connected to the cathode of the diode D61.

The transistors Tr71, Tr72, T
The emitter of r73 is connected to the reference potential point via resistors R74, R75, R76, and the transistors Tr71, T71
Y72 from the video amplifier circuit is applied to the emitters of r72 and Tr73.
The signal is being led. With such a configuration, RGB video signals are obtained from the collectors of the NPN transistors Tr71, Tr72, and Tr73, and these RGB signals are supplied to the RGB cathodes of the picture tube 62, respectively. Further, the transistors Tr71, Tr72, Tr73
Are connected to the anodes of the diodes D81, D82 and D83 of the spot killer circuit 80, respectively.

The spot killer circuit 80 includes a diode D
81, D82, D83, D84, capacitors C81, C
82, a transistor Tr81, and a resistor R81.

The cathodes of the diodes D81, D82 and D83 are connected to a reference potential point via the collector-emitter path of the transistor Tr81 and the diode D84, and the base of the transistor Tr81 is connected to the reference potential point. The emitter of the transistor Tr81 is connected to a reference potential point via a capacitor C81.
It is connected to the cathode of a diode D62 of the voltage generation circuit 64 via a series connection of a capacitor C82 and a resistor R81.

The spot killer circuit 80 detects the fall of the power supply voltage V25 from the voltage generation circuit 64, and lowers the cathode voltage of the picture tube 62 so as to be lower than the cutoff voltage.

Such a conventional spot killer circuit 80
The operation of is described below.

When the power switch of the television receiver is turned on, the power supply voltage V25 from the voltage generation circuit 64 also has a stable predetermined value, so that the transistor Tr81 of the spot killer circuit 80 is turned off. The cathode voltage based on the RGB signal from the video signal output circuit 70 is guided to the RGB cathode of the picture tube 62.

When the power switch of the television receiver is switched from on to off, the power supply voltage V25 from the voltage generation circuit 64 falls, so that the spot killer circuit 80
From the series connection of the capacitors C81 and C82 to the resistor R81.
, The emitter voltage of the transistor Tr81 decreases, and the transistor Tr81 is turned on. As a result, the diodes D81, D82 and D83 are turned on, the cathode voltage of the picture tube 62 is reduced to a cut-off voltage or less, and a cathode current is supplied to prevent burning of the fluorescent screen due to a high brightness spot.

However, in such a conventional technique, the on / off of the power switch is detected by detecting the fall of the voltage from the voltage generating circuit 64 coupled to the tertiary winding of the flyback transformer 61. Because
When the state of the load of the IC device 65 or the like is different, the fall characteristic of the power supply voltage V25 changes due to the load fluctuation, and the operation of the spot killer circuit is delayed, and a high-luminance spot is often generated on the phosphor screen.

[0017]

In the above-mentioned conventional television receiver, the spot killer circuit is operated by detecting the fall of the voltage from the voltage generating circuit coupled to the tertiary winding of the flyback transformer. Therefore, when the state of the load changes, the spot killer circuit does not operate even when the power switch is turned off, and a high-luminance spot is often generated.

An object of the present invention is to eliminate the above-mentioned problems and to provide a video display device capable of operating a spock-tailer circuit without being affected by a load change of a tertiary winding of a flyback transformer.

[0019]

SUMMARY OF THE INVENTION A spot killer circuit according to the present invention comprises a video signal output circuit for supplying a video signal to a cathode electrode of a picture tube, and a horizontal oscillation circuit driven by a DC power supply voltage output from a main power supply circuit. A regulator circuit that creates and outputs a necessary DC voltage, and detects the fall of the output of the regulator circuit, and when this detection result indicates a fall, lowers the cathode voltage of the picture tube,
And a spot killer circuit for setting the cut-off voltage or lower.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a case where an embodiment of a video display device according to the present invention is applied to a television receiver.

In FIG. 1, reference numeral 1 denotes a main power supply circuit. The operation of the main power supply circuit 1 is controlled by turning on / off a power switch. When the main power supply circuit 1 is turned on, an AC power supply voltage from a commercial AC power supply 2 is supplied. The first and second DC power supply voltages V1 and V2 are generated by rectification. These DC power supply voltages V
1 and V2 are supplied to the regulator circuit 3 and the flyback transformer, respectively.

The regulator circuit 3 includes resistors R1, R2
, A transistor Tr1, and a Zener diode ZD1
And a capacitor C1.

One end of each of the resistors R1 and R2 is connected to a first output terminal of the main power supply circuit 1. The other end of the resistor R1 is connected to the horizontal oscillation circuit 4 via the collector-emitter path of the transistor Tr1. The other end of the resistor R2 is connected to the base of the transistor Tr1 and the cathode of the Zener diode ZD1, and the anode of the Zener diode ZD1 is connected to a reference potential point.

With such a connection, the regulator circuit 3 stabilizes the first DC power supply voltage output from the main power supply circuit 1, generates the DC voltage V3, and
1 is output from the connection point of the emitter C1 and the capacitor C1.

The horizontal oscillation circuit 4 is driven by the DC voltage V3 from the regulator circuit 3, and oscillates and outputs horizontal frequency pulses.

The horizontal drive circuit 5 shapes the pulse from the horizontal oscillation circuit 4 and outputs it.

The horizontal output circuit 6 supplies a deflection current to the horizontal deflection coil 7 of the picture tube 12 in response to a pulse from the horizontal drive circuit 5, and supplies a flyback transformer 1
A horizontal output pulse is supplied to one primary winding.

The flyback transformer 11 rectifies the flyback pulse generated in the secondary winding, and converts the anode voltage V11, the focus voltage V12, and the screen voltage V1.
3 are supplied to the anode electrode, focus electrode, and screen electrode of the picture tube 12, respectively. The flyback pulse generated in the tertiary winding of the flyback transformer 11 is used to generate relatively low-voltage first and second DC voltages.
To supply.

The voltage generating circuit 13 generates a power supply voltage for a video signal output circuit, and includes a rectifying diode D1.
1 and a smoothing capacitor C11. The anode of the diode D11 is connected to the tertiary winding of the flyback transformer 11, and the cathode of the diode D11 is connected to the reference potential point via the smoothing capacitor C11. Thereby, the power supply voltage V14 for the video signal output circuit is obtained from the connection point between the cathode of the diode D11 and the smoothing capacitor C11.

The voltage generation circuit 14 includes another circuit, for example, I
A power supply voltage for the C device circuit 15 is generated. The power supply voltage V15 is created and supplied to the IC device circuit 15.

The video signal output circuit 20 includes resistors R21 to R21.
26, and transistors Tr21, Tr22 and Tr23.

The input terminals 21 and 22 of the video signal output circuit 20
Color difference signals (RY) and (G-
Y) and (BY) are supplied. Transistor Tr
The bases of 21, Tr22, Tr23 are input terminals 21,
The collector is connected to the voltage generating circuit 13 via the resistors R21, R22, and R23, respectively.

The transistors Tr21, Tr22,
The emitter of Tr23 is connected to resistors R24, R25,
The transistor T is connected to the reference potential point via R26.
The Y signal from the video amplifier circuit is led to the emitters of r21, Tr22, and Tr23. With such a configuration, RGB video signals are obtained from the collectors of the transistors Tr21, Tr22, and Tr23.
The signals are respectively supplied to the RGB cathodes of the picture tube 12. In addition, transistors Tr21, Tr22, T
The collector of r23 is a spot killer circuit 3
0 are connected to the anodes of the diodes D31, D32 and D33.

The spot killer circuit 30 includes a diode D
31, D32, D33, D34, capacitors C31, C
32, a transistor Tr31, and a resistor R31.

The cathodes of the diodes D31, D32 and D33 are connected to a reference potential point via the collector-emitter path of the transistor Tr31 and the diode D34, and the base of the transistor Tr31 is connected to the reference potential point. The emitter of the transistor Tr31 is connected to a reference potential point via a capacitor C31.
It is connected to the emitter of the transistor Tr1 of the regulator circuit 3 through the series connection of the capacitor C32 and the resistor R31.

The spot killer circuit 30 detects the fall of the DC voltage V3, which is the output of the regulator circuit 3, and when the detection result indicates the fall, the picture tube 1
2, the cathode voltage is lowered so as to be equal to or lower than the cutoff voltage.

The operation of the television receiver of the present invention will be described below.

When the power switch of the television receiver is turned on, that is, when the main power supply circuit 1
When the DC power supply voltages V1 and V2 of the spot killer circuit 30 are generated, the output DC voltage V3 of the regulator circuit 3 also has a stable predetermined value.
Reference numeral 31 denotes a transistor Tr3
1 is turned off, and the RGB signal from the video signal output circuit 20 is guided to the RGB cathode of the picture tube 12.

When the power switch of the television receiver is switched from on to off, that is, the first and second DC power supply voltages V1 and V2 from the main power supply circuit 1 fall, and the output of the regulator circuit 3 also falls. Therefore, a current flows from the series connection of the capacitors C31 and C32 of the spot killer circuit 30 toward the resistor R31, and the transistor Tr3
The emitter voltage of No. 1 decreases, and the transistor Tr31 is turned on. Thereby, the diodes D31, D32, D
33 turns on, the cathode voltage of the picture tube 12 is reduced to a cut-off voltage or less, and a cathode current is supplied to prevent burning of the phosphor screen due to a high-brightness spot.

According to such an embodiment of the present invention, the spot killer circuit 30 detects the fall of the output of the regulator circuit 3 which is operated by the DC power supply voltage from the main power supply circuit 1, and the detection result rises. If it shows down,
Since the cathode voltage of the picture tube 12 is lowered to be equal to or lower than the cutoff voltage, the operation of the spockerler circuit 3 can be performed without being affected by the load change of the tertiary winding of the flyback transformer. Therefore, even if the load is changed, the malfunction of the spot killer circuit can be prevented, so that the degree of freedom in circuit design of the television receiver can be improved.

In the embodiment of the invention shown in FIG. 1, the present invention is applied to a television receiver as a video display device, but may be applied to a monitor device without a built-in television broadcast tuner.

[0043]

According to the present invention, the spock killer circuit can be operated without being affected by the load change of the tertiary winding of the flyback transformer, and the spot killer circuit can be reliably operated when the power is turned off. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a video display device according to the present invention.

FIG. 2 is a perspective view showing a conventional video display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main power supply circuit 3 Regulator circuit 4 Horizontal oscillation circuit 5 Horizontal drive circuit 6 Horizontal output circuit 7 Horizontal deflection coil 11 Flyback transformer 12 Picture tube 13 Voltage generation circuit 14 Voltage generation circuit 15 IC device circuit (load) 20 Video signal output circuit 30 spot killer circuit

Claims (2)

[Claims] 1. A video signal output circuit for supplying a video signal to a cathode electrode of a picture tube, and a regulator for generating and outputting a DC voltage necessary for driving a horizontal oscillation circuit from a DC power supply voltage output from a main power supply circuit And a spot killer circuit that detects a fall of the output of the regulator circuit, and when the detection result indicates a fall, lowers the cathode voltage of the picture tube to reduce the cathode voltage to a cut-off voltage or less. A video display device characterized by the above-mentioned. 2. The spot killer circuit includes: a diode having an anode connected to a video signal supply path to the cathode electrode; a collector connected to a cathode of the diode; a base connected to a reference potential point; 2. The video display device according to claim 1, further comprising a transistor connected to an output potential point of said regulator circuit.