JP2587521Y2 - Display device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly to a display device suitable for a television receiver having a zoom function for increasing a vertical amplitude.

[0002]

2. Description of the Related Art At present, television broadcasting in the NTSC system is being carried out in Japan, and high-definition television broadcasting with a large screen and high definition is about to be started. In this high-definition television broadcast, NTS
The aspect ratio of the screen is different from that of the C system.
Aspect ratio (1) wider than SC television system
6: 9). The cinema size is also N
The aspect ratio is wider than that of the TSC system. When displaying images with these wide aspect ratios on an NTSC television receiver, it is not possible to display all the images without distortion over the entire area of the screen.
That is, it is necessary to provide a method of displaying blank images at the top and bottom of the screen to display the entire image, or to extend the vertical amplitude of the image and display the center of the image over the entire screen.

[0003] If an image memory or the like is used to obtain such a function of displaying on the entire screen (hereinafter referred to as a zoom function), the cost becomes extremely high. Therefore,
Normally, the zoom function is enabled by extending the vertical amplitude of the video.

A picture tube (hereinafter, also referred to as a CRT) is formed by a funnel-shaped glass bulb.
The glass bulb consists of a thin cylindrical neck with an electron gun at the end and a cone coated with phosphor.
The electron beam emitted from the electron gun is deflected by the deflection yoke when passing through the neck, and collides with the phosphor surface of the cone portion to cause the phosphor to emit light. In zoom mode,
By setting a large amount of vertical deflection by a vertical deflection circuit, a wide-aspect image is projected over the top and bottom of the screen.

In this case, a large amount of overscan is performed in the vertical direction in consideration of a video period which was originally a blank portion. Therefore, if an electron beam is emitted during an image period corresponding to a blank portion (hereinafter referred to as an overscan period), the electron beam hits the neck and damages the neck. Therefore, the electron beam is not emitted by blanking the video signal during the overscan period.

Incidentally, the amount of the electron beam of the CRT is determined by the grid voltage or the cathode voltage.
As the cathode voltage is reduced, the amount of electron beam gradually increases and the raster becomes brighter. For this reason, when the power supply voltage of the video output stage drops abnormally, even if the video output stage that drives the cathode of the picture tube is blanked by giving a black level signal, the electron gun will There has been a problem that a large amount of electron beams are emitted and the neck of the CRT is damaged in the zoom mode.

[0007]

As described above, in the above-mentioned conventional display device, when the power supply voltage of the video output stage is abnormally reduced in the zoom mode for some reason, the electron beam hits the neck of the CRT. CR
There is a problem that T is damaged.

The present invention has been made in view of such a problem, and a display device capable of preventing a CRT from being damaged by detecting that a power supply voltage of a video output stage has abnormally dropped during zooming. The purpose is to provide.

[0009]

According to a first aspect of the present invention, there is provided a display apparatus having a zoom function for increasing a vertical amplitude by increasing a deflection amount of a cathode ray tube. A power supply circuit for supplying a power supply voltage for video output to a video output stage for supplying a video signal to the cathode ray tube; a standby power supply circuit for receiving the commercial AC power supply voltage to generate a standby power supply voltage; A voltage dividing means for dividing the power supply voltage for video output, an output of the voltage dividing means is supplied to a base, the standby power supply voltage is supplied to a collector, and a reference voltage based on the standby power supply voltage is supplied to an emitter. A first transistor which is turned off when the output of the voltage dividing means falls below the reference voltage; A thyristor having a node connected to a reference potential point, and a constant voltage circuit connected between the collector of the first transistor and the gate of the thyristor and turning on the thyristor only when the first transistor is off. A switching circuit provided on a supply path of the commercial AC power supply voltage to the power supply circuit and turned on / off by a control signal supplied to a control input terminal; a base connected to the cathode of the thyristor and a collector-emitter path connected to the switching circuit; A second transistor connected between a control input terminal of the circuit and a reference potential point to turn off the switching circuit when the thyristor is turned on.

[0010]

In the present invention, the voltage dividing means divides the power supply voltage for video output and supplies the divided voltage to the base of the first transistor. The reference voltage is supplied to the emitter of the first transistor. When the power supply voltage for video output drops abnormally, the first transistor is turned off. Then, a high voltage is supplied to the gate of the thyristor and the thyristor is turned on, and the second transistor turns off the switching circuit by controlling a control signal given to the control terminal of the switching circuit. As a result, the supply of the power supply voltage for video output from the power supply circuit is stopped, and no electron beam is emitted from the CRT.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of a display device according to the present invention.

A CRT 2 is connected to the CRT drive board 1, and a cathode K of the CRT 2 is connected to a power terminal 3 provided on the board 1 via a resistor R1, a coil L1 and a resistor R2. The connection point between the resistor R2 and the coil L1 is connected to the resistor R3 and the coil L constituting the video output stage 4.
2, a collector-emitter path of the transistor Q1, a collector-emitter path of the transistor Q2, a variable resistor R4, and a resistor R5. The base of the transistor Q1 is supplied with a voltage of 12V, and the base of the transistor Q2 is supplied with an R (red) signal via a resistor R6. G (green), B
The video output stage for the (blue) signal is similarly configured, but only the video output stage for the R signal is shown as a representative in the figure. The power supply terminal 3 is connected to the terminal 8 of the main board 7 via the electric wire 5, and a power supply voltage for video output of about 210 V is supplied. The video output stage 4 is supplied with a power supply voltage from the power supply terminal 3 and supplies a video signal based on the R, G, B signals to the cathode K of the CRT 2.

On the other hand, a rectifier circuit 9, a power supply circuit 10, a horizontal output circuit 11, a flyback transformer FBT, and a rectifier circuit 12 are formed on the main board 7. The rectifier circuit 9 rectifies the 100 V commercial AC power supply voltage from the plug 13 to
Give to. The power supply circuit 10 converts the DC voltage from the rectifier circuit 9 into a predetermined constant voltage (hereinafter referred to as a set power supply voltage) and supplies it to one end of a primary winding L3 of a flyback transformer FBT. Flyback transformer FBT 1
The other end of the next winding L3 is connected to a series circuit of a deflection coil L4 and a capacitor C1 constituting a horizontal output circuit 11, and a capacitor C2.
, A damper diode D1 and a collector / emitter path of the horizontal output transistor Q3. The horizontal pulse HD is input to the base of the horizontal output transistor Q3.

The secondary side of the flyback transformer FBT forms a voltage doubler circuit 14, one end of which is connected to the anode of the CRT 2 and the other end of which is an automatic brightness limiting circuit (ABL) not shown.
It is connected to the. The middle of the primary winding L3 of the flyback transformer FBT is connected to a terminal 8 via a diode D2 constituting a rectifier circuit 12, and the anode of the diode D2 is connected to a reference potential point via a smoothing capacitor C3.
The power supply voltage of about 210 V is supplied to the power supply terminal 8 by the rectifier circuit 12.
Is to be given.

Further, in this embodiment, the commercial AC power supply voltage is supplied to the rectifier circuit 9 via the relay 15,
The main board 7 also has a circuit for controlling the ON / OFF of the relay 15. The commercial AC power supply voltage from the plug 13 is also supplied to the rectifier circuit 17 via the transformer 16. Rectifier circuit
Reference numeral 17 denotes a diode D3 and a capacitor C4, and a predetermined standby power supply voltage is supplied from an output terminal 18.

The output terminal 18 of the rectifier circuit 17 is connected to a reference potential point via the relay 15 and the collector-emitter path of the transistor Q4, and is connected to a microcomputer (hereinafter referred to as a microcomputer).
It is also connected to 19). The microcomputer 19 supplies a high-level (hereinafter referred to as "H") signal to the base of the transistor Q4 to turn on the relay 15 when the set power-on is instructed by a user operation. .

Further, the output terminal 18 of the rectifier circuit 17 is connected to a resistor R7,
It is connected to a reference potential point via a series circuit of a thyristor 20 and a resistor R8, and is connected to a reference potential point via a resistor R9, a collector-emitter path of a transistor Q5 and a Zener diode D4. Zener diode D4
Is also connected to the output terminal 18 of the rectifier circuit 17 via the resistor R14. The base of the transistor Q4 is connected to a reference potential point via the collector-emitter path of the transistor Q6, and the base of the transistor Q6 is a thyristor.
Connected to 20 anodes. The gate of the thyristor 20 is connected to the anode through a parallel circuit of a resistor R10 and a capacitor C5, and has a Zener diode D5 and a resistor R5.
11 and connected to the collector of the transistor Q5 via the diode D6. When the transistor Q5 is turned on, the collector voltage is changed to the diode D6 and the Zener diode D.
5, the voltage is lower than the voltage of the constant voltage circuit 21, and the thyristor 20 is turned off. Conversely, when the transistor Q5 is turned off, the collector voltage of the transistor Q5 becomes high and the thyristor 20 is turned on.

On the other hand, the CRT drive board 1 has a detection terminal
The detection terminal 22 is connected to one end of the resistor R2. The detection terminal 22 is a terminal of the main board 7 via the electric wire 6.
Connected to 23. Terminal 23 is resistor R12, diode D
The connection point of the resistor R12 and the diode D7 is connected to the base of the transistor Q5.

The output terminal 18 of the rectifier circuit 17 is also connected to a reference potential point via a capacitor C6, a resistor R15 and a diode D8. The connection point between the resistor R15 and the diode D8 is connected to the base of the transistor Q7, and the collector of the transistor Q7 is connected to the resistor R11 and the diode D8.
6 and the emitter is connected to the reference potential point. When the transistor Q7 is turned on, the thyristor 20 is turned off regardless of whether the transistor Q5 is on or off.

Next, the operation of the embodiment configured as described above will be described.

When the user instructs to turn on the set power supply voltage, the microcomputer 19 supplies an "H" signal to the base of the transistor Q4. This allows
The relay 15 is turned on, and a DC voltage from the rectifier circuit 9 is supplied to the power supply circuit 10. The horizontal output circuit 11 operates according to the set power supply voltage from the power supply circuit 10, and a flyback pulse is generated in the primary winding L3 of the flyback transformer FBT. The rectifier circuit 12 rectifies and smoothes the flyback pulse to obtain a power supply voltage of about 210 V for video output. This power supply voltage is supplied to the video output stage 4 of the CRT drive board 1 via the terminal 8, the electric wire 5, and the power supply terminal 3.

The power supply voltage for video output is supplied to a detection terminal 22.
And the terminal 23 of the main board 7 via the electric wire 6. The voltage appearing at terminal 23 is divided by resistors R12 and R13 and supplied to the base of transistor Q5. When a normal power supply voltage of about 210 V is supplied to the power supply terminal 3, the base voltage of the transistor Q5 is higher than the reference voltage generated by the resistor R14 and the Zener diode D4, and the transistor Q5 is turned on. In this case, the collector voltage of the transistor Q5 is
Thyristor 20 is off. Therefore, transistor Q6 is off and transistor Q6 is off.
The base of 4 maintains "H".

On the other hand, when the power supply voltage of the power supply terminal 3 drops abnormally, the base potential of the transistor Q5 becomes lower than the reference voltage, and the transistor Q5 turns off. Then, the collector voltage of the transistor Q5 becomes higher than the voltage of the constant voltage circuit 21, and the thyristor 20 is turned on. This turns on transistor Q6,
The base potential of the transistor Q4 is lowered. That is, even if the standby power supply voltage is supplied from the output terminal 18 of the rectifier circuit 17 to the microcomputer 19 and the relay 15, the relay 15 is turned off by turning on the transistor Q6, and the AC voltage to the rectifier circuit 9 is reduced. Supply stops. Thyristor 20
Keeps the ON state because the standby power supply voltage is supplied. Thus, the set power supply voltage is turned off, and C
The emission of the electron beam from RT2 stops, and CRT2 is protected.

When the power is turned on to turn on the AC power, a charging current flows from the output terminal 18 of the rectifier circuit 17 to the capacitor C6. While the charging current is flowing through the capacitor C6, the transistor Q7 is turned on and the thyristor 20 is turned off. In other words, when the power is turned on,
Even when the power supply voltage for video output has not yet reached about 210 V, the thyristor 20 is turned off and the supply of the commercial AC power supply voltage to the rectifier circuit 9 is continued. As a result, malfunction at power-on can be prevented.

As described above, in this embodiment, when an abnormal decrease in the power supply voltage for video output is detected, the relay 15 is turned off to stop the supply of the commercial AC power supply voltage to the rectifier circuit 9, and the zoom is performed. Even if the power supply voltage drops abnormally in the mode, it is possible to prevent the electron beam from being emitted and the CRT 2 from being damaged.

[0026]

As described above, according to the present invention, when the power supply voltage of the video output stage 4 drops abnormally, the supply of the power supply voltage from the power supply circuit is stopped. This has the effect of preventing damage to the surface.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a display device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... CRT drive board 2 ... CRT 4 ... Video output stage 5, 6 ... Wire 7 ... Main board 9,12,17 ... Rectifier circuit 10 ... Power supply circuit 15 ... Relay 20 ... Thyristor 21 ... Constant voltage circuit Q1-Q7 ... Transistor R1 to R15: resistance

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H04N 3/223 H04N 3/18 H04N 3/27 H04N 5/46 H04N 5/68

Claims (1)

(57) [Scope of request for utility model registration] 1. A display device having a zoom function for increasing the vertical amplitude by increasing the deflection amount of a cathode ray tube. A video output stage to which a commercial AC power supply voltage is applied and which supplies a video signal to the cathode ray tube is provided. A power supply circuit for supplying a power supply voltage of the power supply; a standby power supply circuit for receiving the commercial AC power supply voltage to generate a standby power supply voltage; a voltage dividing means for dividing a power supply voltage for video output of the video output stage; The output of the voltage dividing means is supplied to the collector, the standby power supply voltage is supplied to the collector, a reference voltage based on the standby power supply voltage is supplied to the emitter, and the output is turned off when the output of the voltage dividing means falls below the reference voltage. A thyristor whose anode is supplied with the standby power supply voltage and whose cathode is connected to a reference potential point; A constant voltage circuit that is connected between the collector of the first transistor and the gate of the thyristor and turns on the thyristor only when the first transistor is off; A switching circuit provided on the supply path and turned on / off by a control signal given to a control input terminal; a base connected to the cathode of the thyristor and a collector-emitter path provided between the control input terminal of the switching circuit and a reference potential point A second transistor connected to turn off the switching circuit when the thyristor is turned on.