JPH02311888A - Video output circuit - Google Patents

Abstract

PURPOSE:To decrease charges which are discharged from the anode electrode of an image receiving tube and to prevent an afterimage from remaining on the human retina by turning on a switching element while a power source is turned on and short-circuiting a load resistance, and raising the emitter voltage of a video output transistor(TR) and cutting off the electron beam of the image receiving tube. CONSTITUTION:The collector and emitter of the switching element 26 are connected to both ends of the load resistance 34 of a blanking TR 36 and a low and a high signal are applied to the switching element 76 associatively with the ON/OFF operation of a power switch to turn on the switching element 76 and short-circuit the load resistance 34 while the power source is turned off and then raise the emitter voltages of video output TRs 42, 49, and 56, thereby cut off the electron beam of the image receiving tube 61. Consequently, when a power-off instruction is inputted from a key pad to a control part, an image plane is prevented from sparkling owing to the discharge of charges accumulated in the anode of the image receiving tube and remaining on the human retina.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video output circuit for a display monitor used as a captain's terminal.

Conventional technology Conventionally, in video output circuits, when the picture tube is operating during the retrace period of vertical and horizontal deflection, a white retrace line appears on the screen. Horizontal and vertical pulses are applied to the cathode or first grid of the picture tube so that no retrace line appears on the screen. Generally, the horizontal blanking signal is taken out from a flyback transformer, and the vertical blanking signal is taken out from a vertical output circuit.

A conventional video output circuit will be described below with reference to the drawings.

FIG. 2 is a block diagram of a conventional monitor-integrated captain terminal, and FIG. 3 is a circuit diagram of a portion of the monitor.

In Fig. 2, 1 is an AC voltage input terminal, 2 is a power supply section,
3 is a key bat, 4 is a control section, and 5 is a monitor part. The power supply part 2 supplies the control part 4 with DC voltage and the monitor part 5 with AC voltage, respectively. The key bat 3 is an input device that gives commands to the control unit 4. For example, the control unit 4 demodulates a signal sent from an information center through a telephone line into a data signal using a modem, and then, depending on the type of data, if it is photographic information, it is compressed for efficient transmission within the Videotex communication network. If it is code information, the character font is read from the character font ROM and written into the image memory together with the color information 2 display operation information. Then, these pieces of information are sequentially read out, code information, photographic information, and other information previously handled separately are superimposed, display operations such as flashing are performed, and the signals are converted into analog signals and sent to the monitor part 5. are doing. The monitor section 5 displays signals sent from the control section 4 on its screen.

Next, in FIG. 3, 6 is a monitor power supply, and 7.8 is a smoothing capacitor. 11 is a deflection signal processing circuit. A resistor 9 and a smoothing capacitor 10 apply a DC voltage to the deflection signal processing circuit 11. 12 is a synchronization signal input terminal that supplies a synchronization signal to the deflection signal processing circuit 11. 15 is a horizontal drive transistor, 16 is a horizontal drive transformer, 17 is a resistor, the collector of the horizontal drive transistor 15 is the primary winding of the horizontal drive transformer 16, and the resistor 1
7 to the output (+81) of the monitor power supply 6. 13 and 14 are resistors whose midpoints are connected to the base of the horizontal drive transistor 15, and horizontal drive pulses are supplied from the deflection signal processing circuit 11. 18
is a horizontal output transistor, the base of which is connected to the secondary winding of the horizontal drive transformer 16. 19 is a resonant capacitor, 20 is a damper diode, 22 is a horizontal winding of the deflection yoke (hereinafter abbreviated as DY), 23 is a figure-8 correction capacitor, and the resonant capacitor is 19° damper diode 20
．． A series circuit of the DY horizontal winding 22 and the figure-8 correction capacitor 23 is connected between the collector and emitter of the horizontal output transistor 18, respectively. 24 is a vertical output circuit to which a vertical drive output signal is supplied from the deflection signal processing circuit 11. 21 is a flyback transformer (hereinafter abbreviated as FBT), 26 is a rectifier diode, and 27 is a smoothing capacitor.
The output of the low voltage winding of BT21 is connected to the rectifier diode 26. The leading value is rectified by the smoothing capacitor 27 and the DC voltage (+82)
is produced and supplied to the vertical output circuit 24. 25 is D
It is connected to the vertical output circuit 24 by a Y vertical winding. 2
8.31° 33.34 is a resistor, 29 is a coupling capacitor,
30° 32 is a diode, 36 is a blanking transistor, 35 is a DC voltage (+83) application terminal, and resistor 28 is FB
A coupling capacitor 29. connected to the low voltage winding of T. A horizontal retrace pulse is connected to a resistor 33 through a diode 30, and a resistor 31 is connected to a vertical output circuit 24, and a vertical retrace pulse is connected to a resistor 33 through a diode 32.
Furthermore, it is connected via a resistor 33 to the base of a blanking transistor 36. Resistor 34 is DC voltage (+83)
It is connected between the application terminal 35 and the emitter of the blanking transistor 36. 37, 38, 39 are R, G, B video signal input terminals, 42, 49° 56 are R, G, B video output transistors, 40° 47.54 are R, G, B load resistors, 41. 48°55 is the combination resistance of R, G, B, 6
1 is a picture tube with R, G, and B video signal input terminals 37 and 38
．． 39 is connected to the base of each R, G, B video output transistor 42.49.56, and R, G, B load resistance 40.47.54 is connected to the output of the monitor power supply 6 (+B 1
) and R, G, B video output transistors 42.49.
56 collectors, and each collector is connected to R,
Picture tube 61 via G and B coupling resistance 41.48°55
It is also connected to each of the R, G, and B cathodes. 43 is a drive adjustment volume resistor (hereinafter abbreviated as VR) of R;
44 is a resistor, 45 is R cutoff adjustment VR146 is R
The R drive adjustment VR43 is connected between the emitter of the blanking transistor 36 and the emitter of the R video output transistor 42, and the R high-frequency compensation capacitor 46. A series circuit of a resistor 44 and an R cutoff adjustment VR is connected between the emitter of each R video output transistor 42 and ground. 50 is G drive resistance, 51 is resistance, 52 is G cutoff adjustment VR153
is a G high-frequency compensation capacitor, a G drive resistor 50 is connected between the emitter of the blanking transistor 36 and the emitters of the four G video output transistors, and a G high-frequency compensation capacitor 53 . A series circuit of a resistor 53 and a G cutoff adjustment VR is connected between the emitter of each G video output transistor 49 and ground. 57 is the drive adjustment VR1 of B, 59 is the resistor, and 59 is the cutoff adjustment VR1 of B.
60 is B's high frequency compensation capacitor and B's drive adjustment VR
57 is connected between the emitter of the blanking transistor 36 and the emitter of the B video output transistor 56, and is connected to the B high frequency compensation capacitor 60. A series circuit of a resistor 58 and a B cutoff adjustment VR 59 is connected between the emitter of each B video output transistor 56 and ground.

The operation of the captain terminal integrated with the display monitor configured as described above will be explained below.

In FIG. 2, when an AC voltage is supplied from the AC power supply input terminal 1 to the power supply section 2, the output terminal of the power supply section 2 is supplied to the control section 4.
A DC voltage is applied to the controller 4, and the controller 4 operates. Next, when a command to turn on the power is input from the key bat 3 to the control unit 4, the control unit 4 sends a power control signal (hereinafter referred to as P) to the power supply unit 2.
An alternating current voltage is applied to the monitor part 5 to which the C signal is supplied. At this time, a video signal and a synchronization signal are also supplied from the control section 4 to the monitor section 5, and information is displayed on the monitor section 5.

Next, the monitor part 5 will be explained using FIG.

In FIG. 3, the AC voltage applied to the monitor part 5 is a DC voltage (+81
) and is smoothed by smoothing capacitor 7.8,
Deflection signal processing circuit 11 via resistor 9. The primary winding of the horizontal drive transformer 16 and the FBT 21 .
It is applied to R, G, and B load resistances 40, 47, and 54, respectively. At the same time, a synchronization signal is sent from the synchronization signal input terminal 12 to the deflection signal processing circuit 11, and from the R, G, B signal input terminals 37, 38.39 to the R, G, B video output transistors 42, 49, 56. A video signal is supplied to each. As a result, in the deflection signal processing circuit 11, the synchronizing signal is separated into horizontal and vertical components and supplied to each of the horizontal and vertical oscillation circuits. And the horizontal synchronization signal is
It is supplied to the base of the horizontal drive transistor 15 via the resistor 13 through the buffer circuit of the deflection signal processing circuit 11, and is inverted by the horizontal drive transformer 16, and then supplied to the base of the horizontal output transistor 18, and is then supplied to the base of the horizontal output transistor 18. 18 is operated for switching. and,
Horizontal output transistor 18, resonant capacitor 19. Damper diode 20, DY horizontal winding 122. At the same time, the horizontal output circuit consisting of the S-shaped correction capacitor 23 causes a sawtooth wave current to flow through the horizontal winding 22 of the DY, and at the same time, the horizontal winding 22 of the DY has a small resistance component (close to pure inductance, so the sawtooth wave current flows through the coil). A very high voltage pulse occurs during the retrace period when FB suddenly becomes zero.
At T21, this horizontal pulse voltage is taken out by the low voltage winding of FBT21, and the rectifier diode 26. A smoothing capacitor 27 rectifies the leading value to create a DC voltage (+82) and applies it to the vertical output circuit 24. The high voltage applied to the anode electrode of the picture tube 61 is obtained by boosting a horizontal flyback pulse and rectifying it to its peak value. On the other hand, the vertical synchronization signal is supplied to the vertical output circuit 24 as a vertical drive output via the vertical drive circuit of the deflection signal processing circuit 11, and causes a vertical deflection current to flow through the vertical winding 1s25 of DY. next,
R,G.

The video signal input from the B signal input terminal is RlG,B
The voltage is applied to the bases of the video output transistors 42, 49, and 56 respectively, amplified to several tens of volts, and displayed on the screen applied to the cathode of the picture tube 61. Also, the output of the low voltage winding of the FBT 21 is connected to the resistor 28 as a horizontal blanking signal. The vertical blanking signal from the vertical output circuit 24 is also connected to the resistor 31. It is applied to the base of the blanking transistor 36 via the diode 32, and is taken out as a blanking signal from the emitter of the blanking transistor 36, and is applied to the R, G, B video output transistors 42, during the blanking period of horizontal and vertical deflection. The emitter voltage of 49.degree.

Problems to be Solved by the Invention However, in the above configuration, when a command to turn off the power is input from the key bat 3 to the control section 4, a PC signal is supplied from the control section 4 to the power supply section 2, and the monitor is turned off. Part 5
The alternating current voltage is cut off, and at the same time, the video signal, signal, and synchronization signal supplied from the control section 4 to the monitor section 5 are also stopped.

Therefore, the monitor power supply 6 is also stopped, and the charge accumulated in the smoothing capacitor 10 of the smoothing filter that applies the DC voltage (+81) to the deflection signal processing circuit 11 causes horizontal and vertical The output circuit performs free oscillation and connects the DY horizontal winding 22. A deflection current flows through the vertical winding 25, and at the same time, the charges accumulated in the anode electrode of the picture tube 61 are discharged and displayed as a white raster on the screen.As the voltage of the smoothing filter 10 decreases, the amplitude decreases and the operation stops. . Therefore, after a command to turn off the power is input from the key bat 3 to the control section 4, the screen glows white, the deflection area of which becomes smaller and disappears, leaving an afterimage on the human retina.

Means for Solving the Problem In order to solve this problem, the video output circuit of the present invention has the following features:
A switching element is connected across the load resistor of the blanking transistor, and the switching element goes low in conjunction with the on/off of the power switch.

This device has a configuration in which a high control signal is applied to turn on the switching element and short-circuit the load resistance when the power is turned off.

According to the above-described configuration, the present invention prevents the smoothing capacitor of the filter circuit applying DC voltage (+81) to the deflection signal processing circuit from discharging when a power-off signal is input from the key bat to the control unit. Due to the time lag until the oscillation circuit stops, the charge on the anode electrode of the picture tube is discharged, causing the screen to turn white (glowing), which remains as an afterimage on the human retina. By applying low and high signals to the switching element in conjunction with the on and off of the power switch, it becomes conductive at the same time as the power is turned off, short-circuiting the load resistor, increasing the emitter voltage of the video output transistor, and increasing the voltage of the picture tube's electrons. By blocking the beam, the charge discharged from the anode electrode of the picture tube is reduced, and it is prevented from remaining as an afterimage on the human retina.

Embodiments Hereinafter, video output circuits according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a video output circuit in one embodiment of the present invention.

In Figure 1, 6 is a monitor power supply, 7°8.10.
27 is an electrolytic capacitor, 9,13°14.1? , 28.
31,33,34.40°41.44,47.48.5
0, 51, 54° 55.58 is a resistor, 11 is a deflection signal processing circuit, 12 is a synchronization signal input terminal, 15, 18, 36° 42.49.56 is a transistor, 16 is a horizontal drive transformer, 19 is a horizontal common 20 is a damper diode, 21 is an FBT, 22 is a DY horizontal winding, 2
3 is a figure 8 correction capacitor, 24 is a vertical output circuit, 25 is a DY vertical winding, 26.30.32 is a diode, 29
, 46° 53.60 is a ceramic capacitor, 43,4
5°51.57.59 The VR 161 has the same structure as shown in FIG. 3 except for the picture tube.

62 is a controller IC 163 is a PC signal output terminal, 6
4.65 is a resistor, 66 is a transistor, 67 is a +5V voltage terminal, and the PC signal output terminal 63 is connected to the base of the transistor 66 via a resistor 64. Further, the collector of the transistor 66 is connected to the +5V voltage terminal via the resistor 65, and the above circuit is configured in the control section 4.

68, 69, 71, 72 are resistors, 70, 73 are transistors, 74 is a DC voltage (+84) application terminal, and resistor 68 connects the collector of transistor 66 to the base of transistor 70. Further, the collector of the transistor 70 is connected to a DC voltage (+B4) application terminal 74 via a resistor 69 and to the base of a transistor 73 via a resistor 71. The collector of the transistor 73 is connected to a DC voltage (+84) application terminal via a resistor 72, and the above circuit is configured in the power supply section 2.

75 is a resistor, 76 is a transistor which is a feature of the present invention, and the resistor 75 connects the collector of the transistor 73 to the base of the transistor 76, and the collector and emitter of the transistor 76 are connected to both ends of the load resistor 34 of the transistor 36. , the above circuit is configured in the monitor part 5.

The operation of the video output circuit configured as described above will be described below with reference to FIGS. 1 and 2.

First, when a power-on command is input from the key bat 3 to the control unit 4, a high signal is output from the PC signal output terminal 63 of the CRT controller IC 62, and the transistor 66
On, 70 off, 73 on. Therefore, the collector voltage of transistor 73 becomes Vcg73 (sat),
The voltage is applied to the base of the transistor 76 via the resistor 75, and the transistor 76 is turned off. Therefore, the horizontal and vertical blanking signals taken out from the FBT 21 and the vertical output circuit 24 are applied to the base of the blanking transistor 36 and taken out from the emitter of the blanking transistor 36 as blanking signals, and the The emitter voltage of the video output transistors 42, 49, 56 is increased, thereby increasing the cathode voltage of the picture tube 61, thereby blocking the electron beam and performing blanking. Next, when a command to turn off the power is input from the key bat 3 to the control unit 4, a low signal is output from the PC signal output terminal 63 of the CRT controller IC 62, and the transistors 66 are turned off, 70 is turned on, and 7
3 is turned off, and a voltage is applied from the DC voltage (+84) application terminal 74 to the base of the transistor 76 via the resistor 72.75. Therefore, in conjunction with the power off command from the key bat 3, the transistor 76 becomes conductive and is instantaneously short-circuited by the load resistor 34 of the blanking transistor 36, and the emitter voltage of the blanking transistor 36 becomes (DC voltage (+B
3)-VcI! 76 (sat)l, R, G, B
The emitter voltage of the video output transistor 42, 49, 56 increases, the cathode voltage of the picture tube 61 also increases, the electron beam is blocked, and the discharge of the charges accumulated in the anode electrode of the picture tube 61 can be reduced.

As described above, according to this embodiment, immediately after a command to turn off the power is input from the keypad, by shorting the load resistance of the blanking transistor, the emitters of the R, G, and B video output transistors are reduced. Increase the voltage and the picture tube 6
By increasing the cathode voltage of 1, it is possible to reduce the instantaneous white flashing of the screen due to discharge of charge from the anode electrode of the picture tube 61, and to prevent it from remaining as an afterimage on the human retina. can.

Effects of the Invention According to the present invention, the collector and emitter of a switching element are connected to both ends of a load resistance of a blanking transistor, and low and high signals are transmitted to the switching element in conjunction with on and off of a power switch. When the power is turned off, the switching element is made conductive and the load resistance is short-circuited, the emitter voltage of the video output transistor is increased, and the electron beam of the picture tube is cut off. When a command is input, the electric charge accumulated in the anode electrode of the picture tube is discharged, causing the screen to glow white and preventing it from remaining as an afterimage on the human retina, which has a great practical effect. It is.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a part of the monitor of a captain terminal with integrated monitor according to an embodiment of the present invention, and Figs. 2 and 3 are a block diagram and a circuit diagram of part of the monitor of a conventional captain terminal with integrated monitor. It is. 2...Power supply section, 3...Key bat, 4
・Old...control unit, 5...part of monitor, 9,28
,31,33゜34.64,65,68.69.71,
72゜75... Resistor, 10... Electrolytic capacitor, 11... Deflection signal processing circuit, 24...
... Vertical output circuit, 29 ... Ceramic capacitor, 30.32 ... Diode, 36
．． 42.49.56...Transistor, 35.
...DC voltage (+B3) application terminal, 61...
...Picture tube, 62...CRT controller IC
163...PC signal output terminal, 67...
・+5V voltage terminal, 74...DC voltage (+84
) application terminal.

Claims (1)

[Claims] By connecting a switching element to both ends of the load resistance of the blanking transistor and applying low and high signals to the switching element in conjunction with turning on and off the power switch, the switching element can be turned on at the same time as the power is turned off. A video output circuit characterized in that the video output circuit is configured to conduct, short-circuit a load resistor, increase an emitter voltage of a video output transistor, and block an electron beam from a picture tube.