JPH09214865A - Crt display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode-ray tube(CRT) display device with which the stability of image can be improved by stabilizing the black level of a CRT irrespective of the brightness of a picture. SOLUTION: A detection circuit D detects the current of a flyback transformer FT1 fluctuated in proportion to a change in the beam current of a CRT B1 and a voltage provided corresponding to the fluctuation of this current is outputted as the controlled variable of a screen voltage. Based on this controlled variable of the screen voltage, a control circuit C stabilizes the screen voltage of the CRT B1 by operating the impedance, which is changed in proportion to the controlled variable of the screen voltage, by feeding it back to a circuit composed of divider resistors R1, R2, R3 and R4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CRT display device for displaying and driving a CRT used in a television receiver or the like.

[0002]

2. Description of the Related Art Conventionally, a television receiver has been provided with a cathode ray tube display device for displaying and driving a cathode ray tube. The cathode ray tube display device rectifies the high voltage generated in a flyback transformer to obtain a DC voltage. , A voltage divided by a plurality of resistors and a volume is supplied as the screen voltage of the cathode ray tube.

FIG. 2 shows a circuit example of a conventional cathode ray tube display device used in a television receiver or the like. As shown in FIG. 2, the screen circuit SC1 of the cathode ray tube B1 in this cathode ray tube display device has a focus volume (hereinafter referred to as VR) from a midpoint of the high voltage winding TH1 of the flyback transformer FT1 through a rectifying diode D1. R2, screen VRR
4. A plurality of resistors R1, R3 and R5 are connected and configured.

A screen circuit SC having such a configuration
As shown in FIG. 2, 1 supplies the screen voltage applied to the screen electrode of the cathode ray tube B1 from the screen VRR4, and by adjusting this screen VRR4, the screen voltage of the cathode ray tube B1 can be changed.
Adjust the display status of the image on the screen.

[0005]

However, in the conventional cathode ray tube display device as described above, as the screen voltage of the cathode ray tube, the voltage generated in the high voltage winding of the flyback transformer is used by the screen circuit as shown in FIG. Since a voltage based on the DC voltage obtained by rectification is supplied, the screen voltage fluctuates greatly due to changes in the beam current when the screen brightness is adjusted. There is a problem that the image becomes stable and the stability of the image displayed on the screen decreases.

The present invention solves the above-mentioned conventional problems and can stabilize the black level in a cathode-ray tube regardless of the brightness of the screen, thus improving the stability of the image displayed on the screen of the cathode-ray tube. Provided is a cathode ray tube display device.

[0007]

In order to solve the above problems, a cathode ray tube display device of the present invention is a cathode ray tube display in which a DC voltage obtained by rectifying a high voltage generated in a flyback transformer is divided by voltage dividing means. In the CRT display device which supplies the screen voltage as a screen voltage, a control circuit for controlling the screen voltage supplied by the voltage dividing means and a detection circuit for detecting the control amount of the screen voltage proportional to the current of the CRT And the control circuit is configured to control the screen voltage by causing an impedance changed in proportion to the control amount of the screen voltage detected by the detection circuit to act on the voltage dividing means. According to this configuration, the detection circuit detects the current of the flyback transformer that fluctuates in proportion to the change in the beam current of the cathode ray tube, and outputs the voltage obtained in response to this fluctuation of the current as the control amount of the screen voltage. To do.

Based on the control amount of the screen voltage,
The control circuit stabilizes the screen voltage by feeding back the impedance changed in proportion to the control amount of the screen voltage to the voltage dividing means to act.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A cathode ray tube display device showing an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a screen circuit SC2 of a cathode ray tube B1 in the cathode ray tube display device of this embodiment. In FIG. 1, R1, R2, R3, R4 and R5 are
It is a dividing resistor provided in the flyback transformer FT1 as a voltage dividing means for obtaining the focus voltage and the screen voltage, and is connected from the terminal 4 to the ground via the resistor R7. On the other hand, flyback transformer FT1
One side of the high voltage winding TH1, which is the secondary winding of the above, is connected to the ground from the terminal 3 via the capacitor C1. Further, the same terminal 3 is also connected to the + B power source via the resistor R6. Further, the resistors R8, R9, R10 and the transistor Q1 constitute a screen voltage stabilizing circuit for stabilizing the screen voltage of the cathode ray tube B1.

Here, the capacitor C1 and the resistor R8,
Based on the beam current of the cathode ray tube B1 by R9,
A detection circuit D that detects a control amount of the screen voltage proportional to the beam current is configured, and a control circuit C that controls the screen voltage of the cathode ray tube B1 supplied from the resistor R4 through the terminal 5 by the resistor R10 and the transistor Q1. Is configured.

The operation of the CRT display device configured as described above will be specifically described below. FIG.
As shown in, the beam current flows through the cathode ray tube B1 through the terminal 7 of the flyback transformer FT1. By the flow of this beam current, the flyback transformer F
Due to the large internal impedance at T1, both the high voltage and the screen voltage supplied to the cathode ray tube B1 drop. On the other hand, at the terminal 3, the beam current of the cathode ray tube B1 flows from + B through the resistor R6, so that the voltage of the terminal 3 decreases in inverse proportion to the beam current. This voltage is divided by the resistors R8 and R9, and the transistor Q is used as a control amount of the screen voltage proportional to the beam current.
Fill in the base of 1.

Here, the emitter of the transistor Q1 is connected to the ground via the resistor R10, and the collector is connected to the terminal 4 of the flyback transformer FT1. By connecting in this way, the voltage of the terminal 3 is inverted. When the beam current flows through the cathode ray tube B1, the transistor Q1 raises the voltage of the terminal 4 to prevent the screen voltage from decreasing.

By the above operation, the black level in the CRT can be stabilized regardless of the brightness of the screen, and the stability of the image displayed on the screen of the CRT can be improved.

[0015]

As described above, according to the present invention, the detection circuit detects the current of the flyback transformer which fluctuates in proportion to the change of the beam current of the cathode ray tube and obtains it in response to the fluctuation of the current. The voltage is output as the control amount of the screen voltage, and based on the control amount of the screen voltage, the control circuit operates by feeding back the impedance changed in proportion to the control amount of the screen voltage to the voltage dividing means. , The screen voltage can be stabilized.

Therefore, the black level in the CRT can be stabilized regardless of the brightness of the screen, and the stability of the image displayed on the screen of the CRT can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a cathode ray tube display device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional CRT display device.

[Explanation of symbols]

 Q1 transistor R6, R7, R8, R9, R10 resistance

Claims (1)

[Claims] 1. A cathode ray tube display device, in which a DC voltage obtained by rectifying a high voltage generated in a flyback transformer is divided by a voltage dividing means to be supplied as a screen voltage of a cathode ray tube, and a screen voltage supplied by the voltage dividing means. And a detection circuit for detecting a control amount of the screen voltage proportional to the current of the cathode ray tube based on the current of the cathode ray tube, and the control circuit, the control amount of the screen voltage detected by the detection circuit. A cathode ray tube display device configured to control the screen voltage by causing an impedance changed proportionally to the voltage dividing means.