JP2000032289A - Method for driving cathode ray tube device and cathode ray tube device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent production of stray emission with an inexpensive circuit means by forcibly decreasing a 2nd grid voltage in the case of power-off and video frequency switching so as to suppress emission of stray electrons from a foreign material such as a cathode material deposited on a 1st grid or the like. SOLUTION: When a cathode ray tube is in operation, a flyback transformer 31 applies a voltage VG2 of about 300-700 V to a 2nd grid. In the case of power- off and video frequency switching, a command signal pulse voltage 26 reaches 0 V, a base level of a transistor(TR) 1 is decreased via a resistor R1 and the TR 1 is turned off. TRs 2, 3 are both turned on attended therewith and a current from the flyback transformer 31 flows to GND via resistors R6, R7, then a 2nd grid voltage is decreased by a voltage division ratio by the resistors R6, R7. In the case of video frequency switching, since the command signal pulse voltage restores to +5 V in 1 to 2 sec, the 2nd grid voltage is restored.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for preventing a stray emission phenomenon occurring when a cathode ray tube used for a color television or a computer monitor is turned off or when a video frequency mode is switched.

[0002]

2. Description of the Related Art As shown in FIG. 1, a cathode ray tube apparatus comprises an envelope 3 comprising a front panel 1 and a funnel 2, a fluorescent screen 4 formed on the inner surface of the front panel 1, and a funnel 2
And a deflection yoke 6 mounted on the funnel 2. The electron beam 7 emitted from the electron gun 5 is scanned by a deflection magnetic field formed by the deflection yoke 6 to form a shadow. The fluorescent screen 4 passing through the mask 8
Shoot at.

As shown in FIG. 2, the electron gun 5 has a so-called triode comprising a cathode 21, a first grid 22, and a second grid 23, and adjusts the balance of these three relative voltages. By doing so, the current value of the electron beam is adjusted. Generally, a negative voltage is applied to the first grid 22 to function as an electron beam barrier, and a voltage of + several hundred [V] is applied to the second grid 23 to accelerate the electron beam. Further, a focusing voltage of + several [kV] is applied to the third grid 24 and the fourth grid (not shown). On the other hand, an anode voltage of about +30 [kV] is applied to the fluorescent screen 4, and functions as an anode for capturing an electron beam.

By the way, when the cathode ray tube device is turned off, weak light emission may be observed at the center of the fluorescent screen 4 or the like, even though the emission of the electron beam from the cathode 21 is cut off. Such a phenomenon is called stray emission.
The stray emission phenomenon occurs for the following reasons. If a foreign substance is attached to a portion other than the cathode 21 inside the cathode ray tube, the work function at that portion is reduced, so that electrons are easily emitted. Immediately after the cathode-ray tube device is turned off, the anode voltage applied to the phosphor screen 4 cannot be sufficiently reduced, so that electrons emitted from places other than the cathode 21, so-called stray electrons, are attracted to the phosphor screen by the anode voltage. Then, the fluorescent screen 4 is excited to emit light. At this time, since the scanning of the electron beam by the deflection yoke 6 has already been stopped, the central portion of the phosphor screen 4 emits light.

In addition, with the recent high performance of the cathode ray tube device and the complicated structure of the electron gun, foreign matter such as ionized fine dust and scattered cathode material is reduced to the second grid such as the first grid.
There is a problem that it adheres to a portion on the cathode side of the grid and becomes an electron emitting portion, causing a stray emission phenomenon. Since the stray electrons generated from the foreign matter adhering to the first grid are attracted to the second grid voltage and fly, the more stray electrons are generated as the potential difference between the first grid and the second grid increases.

When an impregnated cathode having a high ability to emit an electron beam current per unit area is used to realize a high brightness of a cathode ray tube, barium as a cathode material is ionized and released. There is a problem that it easily adheres to one grid. As described above, when foreign matter attached to the first grid is a radiation source of stray electrons,
Even if the cathode voltage or the first grid voltage is controlled, the second material is removed from the cathode material attached to the first grid surface.
Extraction of electrons by the grid voltage or the anode voltage cannot be prevented.

[0007] Such a stray emission phenomenon is as follows.
Not only occurs when the cathode-ray tube device is turned off, but also when displaying the screen, if the display screen is sufficiently dark, it can be visually recognized and become background noise.

Conventionally, in order to prevent the stray emission phenomenon, Japanese Patent Application Laid-Open No. Hei 5-276466 discloses that when the cathode ray tube device is powered off, the discharge of the charge / discharge unit is used as a driving voltage to drive the high voltage unit of the cathode ray tube and GND. It has been proposed to close the circuit between them to quickly discharge the high voltage remaining in the cathode ray tube. Japanese Patent Application Laid-Open No. Hei 5-48921 proposes that a drive current of a horizontal deflection circuit is smoothly attenuated to prevent a stray emission phenomenon when a cathode ray tube is turned off.

[0009]

In recent years, a so-called multi-scan system capable of displaying a plurality of video frequency modes has become the mainstream of cathode ray tube devices for computer monitors and the like. For example, for a television compatible with multimedia, the frequency is about 15.75 to 50 [kHz], and for a computer monitor, it is 31.5 to 115 [kHz].
z], the horizontal deflection frequency is switched. In a multi-scan cathode ray tube device, when the video frequency mode is switched, the display screen is momentarily darkened, and the deflection of the electron beam stops instantaneously, so electrons generated from places other than the cathode are focused on one point on the phosphor screen. It is drawn and it is in a state where it is easy to collide. Therefore, the stray emission phenomenon occurs both at the time of power-off and at the time of switching the video frequency mode.

However, the conventional stray emission preventing means prevents the stray emission phenomenon from occurring only when the power is turned off. Therefore, the stray emission phenomenon cannot be prevented from occurring when the video frequency mode is switched. there were.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent a stray emission phenomenon caused by emission of stray electrons from a foreign substance such as a cathode material attached to a first grid or the like, among stray emission phenomena. Further, it is an object of the present invention to provide a driving method of a cathode ray tube device and a cathode ray tube device which can prevent the occurrence of a stray emission phenomenon not only when a video frequency mode is switched but also when the cathode ray tube device is turned off. In addition, a stray emission phenomenon is prevented by inexpensive, highly reliable and stable circuit means using an off-the-shelf semiconductor element.

[0012]

According to the driving method of the cathode ray tube apparatus of the present invention, the voltage of the second grid of the electron gun of the cathode ray tube is forcibly reduced when the cathode ray tube is turned off or the video frequency mode is switched. By doing so, it is possible to prevent the emission of electrons in the direction of the phosphor screen from the electron emission portion located on the cathode side of the second grid (claim 1).

According to such a driving method, it is possible to prevent electrons from being extracted from the cathode material attached to the first grid by the second grid voltage. Further, since the second grid voltage is about several hundreds [V], the voltage can be reduced more quickly than the third and fourth grids to which several [kV] voltages are applied. As the circuit components, lower-voltage and lower-cost components can be used.

Further, in the driving method of the cathode ray tube device according to the first aspect, it is preferable that the voltage of the second grid is reduced to a GND level or the same voltage as the voltage of the first grid.

As described above, if the second grid voltage is reduced to 0, the extraction of electrons by the second grid voltage can be more effectively prevented, and the voltage can be further reduced to the same negative voltage as that of the first grid. Then, since the second grid voltage acts as a barrier against emission of electrons, it is possible to prevent the extraction of electrons from the first grid by the anode voltage.

Further, the cathode ray tube device of the present invention has a cathode ray tube having an electron gun and a phosphor screen in an envelope, and a circuit means for forcibly reducing the voltage of the second grid of the electron gun. (Claim 3).

[0017]

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

FIG. 1 is a schematic diagram of a cathode ray tube device of the present invention. The cathode ray tube device of the present invention has circuit means 11 for forcibly reducing the voltage of the second grid of the electron gun 5. The other parts are the same as those of the conventional cathode ray tube device, and the description is omitted.

FIG. 2 is a conceptual diagram showing a state where the circuit means 11 is connected to the second grid 23 of the electron gun 5.
The electron gun 5 has a first grid 2 in front of the cathode 21.
2, a second grid 23, and a third grid 24, and the circuit means 11 is connected to the second grid 23. When the cathode ray tube device is powered on and operated, the switch 25 in the circuit means 11 is opened, and the voltage _VG2 is applied to the second grid. When the cathode ray tube device is turned off and the video frequency mode is switched, a command signal pulse 26 is input to the circuit means 11, the switch 25 is closed to close the circuit between the second grid 23 and GND, and the second grid voltage is changed to GND. Lower to the level. In this case, the second grid voltage may be reduced to the same voltage as the first grid voltage.

[0020]

FIG. 3 shows an example of a specific circuit configuration of the circuit means 11. In FIG. The circuit means 11 includes a resistor, a capacitor, a transistor, a diode, and the like. The resistance R1 is 100 [kΩ], the resistance R2 is 10 [kΩ], the resistance R3 is 1 [kΩ], the resistance R4 is 100 [Ω], and the resistance R5 is 10 [Ω].
[KΩ], the resistance R6 is 1 [MΩ], and the resistance R7 is 44 [MΩ].
Ω]. The capacitor C1 is 100 [μF] (withstand voltage 1).
6 [V]) and the capacitor C2 is 2700 [pF] (withstand voltage 2 [kV]). The diodes D1 and D2 are switching diodes, the transistors TR1 and TR2 are switching transistors, and the transistor TR3 is a high-withstand-voltage switching transistor. As a command signal for switching the transistor, a video-off signal generated from a driving circuit of the cathode ray tube device at the time of switching the video frequency mode was used.

Next, the operation of the circuit means 11 will be described. During power-on and operation of the cathode ray tube device, the command signal input to the base of the transistor TR1 is +5.
[V] Since it is constant, the transistor TR1 is on and T
R2 and TR3 both remain off, and a predetermined voltage _VG2 is applied to the second grid 23. This voltage is
Screen volume 32 of flyback transformer 31
Is usually set in the range of about 300 to 700 [V].

On the other hand, when the video frequency mode is switched, a TTL level command signal pulse 26 whose voltage level becomes 0 [V] is input to the transistor TR1 via the resistor R1, so that the transistor TR1 is turned off, and the transistors TR2 and TR3 are turned off. Are turned on. Since the current from the flyback transformer flows to GND via the resistor R7 and the resistor R7 connected to the collector of the transistor TR3, the second grid voltage decreases to a voltage corresponding to the voltage dividing ratio between the resistors R6 and R7. I do. Since the command signal pulse 26 returns to +5 [V] in about 1 to 2 seconds when the video frequency mode is switched, the predetermined voltage _VG2 is applied to the second grid again. When the power is off, the command signal is 0 [V].
And the power supply of +12 [V] drops to 0 [V], so that the second grid voltage quickly drops to 0 [V].

[0023]

As described above, according to the present invention, the second grid voltage is forcibly reduced both at the time of power-off of the cathode ray tube device and at the time of switching the video frequency mode. First
It can prevent the stray emission phenomenon caused by the emission of stray electrons from foreign substances such as the cathode material attached to the grid, etc., and can stray not only when the cathode ray tube device is turned off but also when switching the video frequency mode. Provided are a driving method of a cathode ray tube device and a cathode ray tube device capable of preventing the occurrence of an emission phenomenon. In addition, the stray emission phenomenon can be prevented by using inexpensive, highly reliable and stable circuit means using off-the-shelf semiconductor elements.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a cathode ray tube device of the present invention.

FIG. 2 is a conceptual diagram of the same electron gun and circuit means.

FIG. 3 is a circuit diagram showing an example of the circuit means.

[Explanation of symbols]

 Reference Signs List 3 envelope 4 phosphor screen 5 electron gun 11 circuit means 21 cathode 22 first grid 23 second grid

Claims (3)

[Claims] When the power of a cathode ray tube is turned off or when a video frequency mode is switched, the voltage of a second grid of an electron gun of the cathode ray tube is forcibly reduced, so that the second grid is reduced.
A method for driving a cathode ray tube device, comprising: preventing electron emission from an electron emitting portion located closer to a cathode side than a grid toward a fluorescent screen. 2. The method according to claim 1, wherein the voltage of the second grid is reduced to a GND level or the same voltage as the voltage of the first grid. 3. A cathode ray tube device comprising: a cathode ray tube having an electron gun and a phosphor screen in an envelope; and a circuit means for forcibly reducing the voltage of a second grid of the electron gun.