JPS6220491A - Television receiver - Google Patents

Abstract

PURPOSE:To obtain a normal image surface in a short time when the power source is turned on by controlling a switching element by a capacitive element which has a different charging and discharging time constant when the power source is turned on and off and setting the correcting voltage for the DC level of a primary color video signal to a specific value forcibly. CONSTITUTION:The time constant of the capacitor 62 of a control circuit 60 is equal to the time up to when a normal beam current flows to a color cathode- ray tube 40, so when a power switch 80 is turned on, output voltages Vr, Vg, and Vb of a cutoff characteristic detecting circuit 50 fall to 0 during the period and DC level correcting circuits 20R, 20G, and 20B lower pedestal levels of primary color video signals Rc, Gc, and Bc, so that no fly-back line appears in an image surface. When the normal beam current flows to the color cathode- ray tube 40, an automatic cutoff function operates. When the discharging time constant of the capacitor 62 is large, the normal image surface is projected in a short time by turning on the power switch 80 after the power switch 80 is turned off for a long time.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Field of industrial application B. Overview of the invention C. Prior art D. Problem to be solved by the invention E. Means for solving the problem F. Effect G. Embodiment G-1 Configuration (Figure 1) G-2 Operation (Fig. 3) Effect A of the Invention H Industrial Field of Application The present invention provides a red, green, and blue color cathode ray tube that drives a color cathode ray tube using pilot signals inserted into red, green, and blue primary color video signals. The present invention relates to a television receiver having a so-called automatic cutoff adjustment function that corrects the DC level of a primary color video signal according to the cutoff characteristics of the red, green, and blue cathodes of a color cathode ray tube.

B. Summary of the Invention The present invention provides a television receiver having an automatic cutoff adjustment function, which is charged with a first time constant when the power is turned on, and discharged with a second time constant when the power is turned off. It includes a capacitive element and a switching element whose switching is controlled by the terminal voltage of the capacitive element. When the terminal voltage of the capacitive element is below a predetermined value, the switching element is set to one state, for example, an on state, and the primary color video signal is output. By providing a control circuit that forcibly sets the correction voltage of the DC level to a predetermined value, for example, zero, the retrace line will not appear on the screen when the power is turned on (the retrace line will shine), and the return line will be as low as possible. This allows the screen to return to normal in a short period of time.

C. Prior Art A television receiver having an automatic cutoff adjustment function as shown in FIG. 4 has been considered.

The terminals 10R, IOG, and IOB are connected to the 21st, 22nd, and 23rd horizontal periods H21 and 23 of the vertical retrace period, respectively, as shown in the first, second, and third stages of FIG.
In H22 and H23, pilot signals Pr, Pg, P
Red with b inserted.

Green and blue primary color video signals Rp, cp, and Bp are supplied.

The pilot signals Pr, Pg, and Pb are signals having arbitrary constant levels higher than the pedicle levels of the primary color video signals Rp, cp, and Bp, respectively.

These primary color video signals Rp, cp, and Bp are supplied to DC level correction circuits 20R, 20G, and 20B, respectively, and their respective DC levels are corrected as described later. The primary color video signals Rc, Gc, and 13c whose DC levels have been corrected are supplied to video output circuits 30R, 30G, and 30B, respectively, and are amplified in the video output circuits 30R, 30G, and 30B, and are output to the color cathode ray tube 40. , green, and blue cathodes 41R, 41G, and 41B. The video output circuits 30R, 3CG, and 30B each include, for example, an amplifier circuit 31 and a transistor 32 whose output is supplied to the base, and the emitter of the transistor 32 is connected to the cathode 41R of the color cathode ray tube 40 via a resistor 33. ,41G,
41B, and a resistor 34 is connected to the collector,
configured.

The anodes of diodes Dr, Dg, and Db are connected to the collectors of the transistors 32 of the video output circuits 30R, 30G, and 30B, respectively.
A resistor Rd is connected between the cathode of and ground. Therefore, the beam current of the color cathode ray tube 40 is detected as a voltage Vd across the resistor Rd, as shown in the bottom row of FIG. In the bottom row of Fig. 2, ■ is the detection voltage of the beam current, that is, the leakage current, flowing at the beddeskle level in the 20th horizontal period H20 in which the pilot signal of the vertical blanking period of the primary color video signal is not inserted. Yes, ■2 is the 21st, 2nd vertical retrace period of the primary color video signal.
This is the detection voltage of the beam current flowing in the portions of the pilot signals Pr, Pg, and Pb in the second and 23rd horizontal periods H21, H22, and H23. Voltage V2 is 21st, 2
The video output circuits 30R, 30G, and 30B are set to be equal in the second and 23rd horizontal periods H21, H22, and H23.
The value of the resistor 34 is adjusted.

The terminal voltage Vd of this resistor Rd is supplied to the cutoff characteristic detection circuit 50, and from the cutoff characteristic detection circuit 50, the cathodes 41R, 41G, 4 of the color cathode ray tube 40 are connected to each other.
Voltages Vr, Vg, according to the cutoff characteristics at 1B
Vb is obtained. That is, the voltage Vd is supplied to one end of the switch 52 via the buffer amplifier circuit 51 with a gain of 1, the other end of the switch 52 is grounded via the resistor 54 and the capacitor 55, and the vertical return is caused by the switching signal S20. In the 20th horizontal period H20 of the line period, the switch 52
is turned on and the 20th horizontal period H of the vertical retrace period
In step 20, the leak current detection voltage ■1 described above is charged in the capacitor 55, and the leak current detection voltage ■1 charged in the capacitor 55 is applied to the voltage comparison circuits 56R and 56.
The output side of the buffer amplifier circuit 51 is connected to the positive side of a power supply 53 with a voltage Vf corresponding to the difference Vp between the voltage 2 and the voltage 1. A voltage lower than the voltage ■d by Vf is obtained on the negative side, and this voltage is applied to the voltage comparator circuits 56R, 5.
6G and 56B, respectively, and a switch 5 is connected to the output side of the voltage comparator circuits 56R, 56G, and 56B.
7R, 57G.

Capacitors Cr and Cg via 57B respectively.

cb are connected respectively, and switching signals S21 and S are respectively connected.
22.323, the switches 57R, 57G, and 57B are turned on in the 21st, 22nd, and 23rd horizontal periods H21, H22, and H23 of the vertical blanking period, and the switches 57R, 57G, and 57B are turned on in the 21st, 22nd, and 23rd vertical blanking periods, respectively. In the 23rd horizontal period H21°H22, H23, the voltage comparison circuit 5
Leak current detection voltage ■1 by 6R056G and 56B
and the detection voltage V2 of the beam current in the pilot signal portion of the red, green, and blue primary color video signals mentioned above are compared, and the voltages Vr, Vg, and Vb corresponding to the difference are applied to the capacitors Cr and C.
g, obtained in Cb.

Output voltages Vr, Vg of this cutoff characteristic detection circuit 50
, Vb are supplied to the DC level correction circuits 20R, 20G, and 20B, respectively, and the DC level correction circuits 20R, 20G
, 20B, the primary color video signal Rp from terminals 10R, 10G and IOB is output by voltages Vr, Vg and Vb, respectively.
, Gp, and Bp are corrected. For example, the DC level correction circuits 20R, 20G, and 20B are clamp circuits, and the pedestals of the primary color video signals Rp, Gp, and Bp are clamped using voltages Vr, Vg, and Vb as clamp voltages, respectively.

D Problems to be Solved by the Invention In the above-mentioned conventional television receiver having the automatic power/gutter-off adjustment function, when the power is turned on after being turned off for a relatively long time, the color cathode ray tube 4
While it takes time for a normal beam current to flow to zero, the capacitor 55 is quickly charged with the leakage current detection voltage. , the output voltages Vr, Vg, and Vb of the cutoff characteristic detection circuit 50 become high voltages, and in the DC level correction circuits 20R, 20G, and 20B, the pedestals of the primary color video signals Rp, Gp, and Bp are clamped by these high voltages. Primary color video signals Rc, Gc, Bc
Since the Bedeskler level is lifted, there is an inconvenience that a retrace line appears on the screen (the retrace line shines).

However, if the charging of the leakage current detection voltage to the capacitor 55 is delayed, the retrace line will not appear on the screen (the retrace line will shine) like this. However, if you do so, there will be a delay in getting the normal screen, especially if the power is turned on immediately after the power is cut off. The drawback is that it takes much longer than a receiver.

In view of this, the present invention is designed to prevent a return line from appearing on the screen (retrace line shines) when the power is turned on, and to return to a normal screen in as short a time as possible.

E. Means for Solving the Problems In the present invention, in the television receiver having the above-mentioned automatic cut-off adjustment function, when the power is turned on, the first
It has a capacitive element that is charged with a time constant of In the following cases, a control circuit is provided in which the switching element is brought into one state, for example, an on state, and forcibly sets the DC level correction voltage of the primary color video signal to a predetermined value, for example, zero.

F action According to the above configuration, when the power is turned on after being cut off for a relatively long period of time, the capacitive element of the control circuit is charged from zero with the first time constant; By appropriately selecting , the terminal voltage of the capacitive element is below a predetermined value until a normal beam current flows through the color cathode ray tube, the switching element is turned on, and the DC level of the primary color video signal is corrected. Since the voltage becomes zero, the bed scale level of the primary color video signal is not raised in the DC level correction circuit, and no retrace line appears on the screen (retrace line shines). In addition, if the power is turned on immediately after the power is cut off, a normal beam current will flow through the color cathode ray tube in a short time, but in this case, the capacitive element will be set to a predetermined value due to the power being cut off. Although the capacitive element discharges from a value exceeding 1 to zero at a second time constant, by selecting an appropriately large second time constant, the terminal voltage of the capacitive element will be close to the predetermined value at the time the power is turned on. , when the power is turned on, the terminal voltage of the capacitive element reaches a predetermined value in a short time and the switching element turns off, so compared to when the power is turned on after being cut off for a relatively long time. A normal screen appears in a short time.

G Example G-1 Configuration (FIG. 1) FIG. 1 shows an example of a television receiver according to the present invention.

A luminance signal and red and blue color difference signals (not shown) are supplied to the matrix circuit 11, and the matrix circuit 11 generates red, green, and blue primary color video signals R, G.

B is obtained. These primary color video signals R, G, and B are supplied to synthesis circuits 12R, 12G, and 12B, respectively, and the pyro signal P obtained from the pilot signal generation circuit 13 is
r, Pg, and Pb are respectively supplied to the combining circuits 12R, 12G, and 12B, and the 21st, 22nd, and 23rd signals of the vertical retrace period are supplied from the combining circuits 12R, 120, and 12B, respectively.
Primary color video signal R into which pilot signals Pr, Pg, and Pb are inserted in the th horizontal period H21, H22, and H23
p, cp, and Bp are obtained, respectively. Pilot signal P
As described above, r, Pg, and Pb are signals having arbitrary constant levels higher than the level of the basic color of the primary color video signals Rp, Gp, and Bp, respectively.

These primary color video signals Rp, Gp, and Bp are supplied to DC level correction circuits 20R, 20G, and 20B, respectively, and the output voltage Vr of a cutoff characteristic detection circuit 50, which will be described later, is
, Vg, and Vb, the respective DC levels are corrected. For example, DC level correction circuits 20R, 20G, 20
B are clamp circuits, respectively, with voltages Vr and Vg.
, Vb as the clamp voltage and the primary color video signals Rp, Gp.

The pedestal of Bp is clamped. The primary color video signals Rc, Gc, and Bc whose DC levels have been corrected are supplied to video output circuits 30R, 30G, and 30B, respectively.

The signal is amplified at 30B and supplied to cathodes 41R, 41G, and 41B of a 4° color cathode ray tube.

The video output circuits 30R, 30G, and 30B have the same configuration as that shown in FIG. 4 described above, for example.

As described above, diodes pr, Dg, and Db and a resistor Rd are connected to the video output circuits 30R, 30G, and 30B, and the beam current of the color cathode ray tube 40 is detected as a voltage Vd across the resistor Rd. The terminal voltage Vd of this resistor Rd is supplied to the cutoff characteristic detection circuit 50, and from the cutoff characteristic detection circuit 50, voltages Vr and Vg corresponding to the cutoff characteristics at the cathodes 41R, 4, IC, and 41B of the color cathode ray tube 40, respectively. , Vb are obtained.

The cutoff characteristic detection circuit 50 itself is the same as that shown in FIG. However, the capacitance of the capacitor 55 is made sufficiently small so that the capacitor 55 is quickly charged with the leakage current detection voltage. Note that the above-mentioned switching signals S20°521, S22. S23 is supplied respectively.

The output voltage Vr of this cutoff characteristic detection circuit 50.

Vg and Vb are DC level correction circuits 20R and 20G.

20B! DC level correction circuit 20
At R, 20G, and 20B, voltages Vr and Vg, respectively.
, Vb, as mentioned above, the primary color video signals Rp, cp, B
The DC level of p is corrected.

In the present invention, a control circuit 60 is provided for the cutoff characteristic detection circuit 50. The control circuit 60 includes, for example, a capacitor 62 and a resistor 63 connected in series between a power supply line 61 and a ground, and a resistor 64 . A diode 65 and a resistor 66 are connected in series, the base and emitter of a transistor 67 are connected between both ends of the resistor 66, a resistor 68 is connected between the collector of the transistor 67 and the power supply line 61, and the collector of the transistor 67 is connected to the base emitter of the transistor 67. The cathodes of the diodes 69R, 69G, and 69B are connected, and the anodes of the diodes 69R, 69G, and 69B are connected to the capacitors Cr, Cg, and the cutoff characteristic detection circuit 50, respectively.
Cb respectively, and are configured. power line 6
1, when the power switch 80 is turned on with the power plug 70 inserted into the outlet, the power circuit 9
The power supply voltage Vcc is obtained from 0.

G-2 operation (FIG. 3) With the above configuration, when the power switch 80 is turned on after being turned off for a relatively long time, the capacitor of the control circuit 60 is turned on. 62 is the power supply voltage Vc from zero as shown by curve 1 in FIG.
Capacitance of capacitor 62 and resistance 63, 64.6 toward c
6, and the terminal voltage of the capacitor 62 is lower than the predetermined voltage Vx, which is lower than the power supply voltage Vcc by the sum of the forward voltage of the diode 65 and the base-emitter forward voltage of the transistor 67. , the transistor 67 is turned on, and the diodes 69R, 69G,
, 69B are turned on, and the terminal voltages of the capacitors Cr, Cg, and Cb of the cut-off characteristic detection circuit 50, that is, the output voltages Vr, Vg, of the cut-off characteristic detection circuit 50,
Vb is forced to zero. Therefore, if the charging time constant is appropriately selected to make the time required for the terminal voltage of the capacitor 62 to reach the predetermined voltage Vx equal to the time required for a normal beam current to flow through the color cathode ray tube 40, the color cathode ray tube 40 Until a normal beam current flows, the output voltages Vr, Vg, and Vb of the cutoff characteristic detection circuit 50 become zero, and the Bedeskle level of the primary color video signals Rc, Gc, and Bc becomes zero in the DC level correction circuits 20R, 200, and 20B. Because it is lowered, a retrace line appears on the screen (the retrace line lights up)
Never. When a normal beam current begins to flow through the color cathode ray tube 40 and the terminal voltage of the capacitor 62 exceeds a predetermined voltage Vx, the transistor 67 is turned off and the diodes 69R and 69G are turned off.

69B is turned off, and the automatic cutoff adjustment function comes into operation.

From this state, if the power switch 80 is turned off at time t2 and then turned on again at time t3 immediately after, first the power switch 80 is turned off at time t2.
When the power switch 80 is turned off at , the capacitor 62 is discharged from the power supply voltage Vcc toward zero with a time constant determined by the capacitance of the capacitor 62 and the value of the resistor 63, as shown by curve 2 in FIG. By selecting a suitably large discharge time constant, the terminal voltage of the capacitor 62 at time t becomes close to the predetermined voltage Vx, and at time t, the power switch 80 is turned on and the transistor 67 and the diodes 69R, 690, 6
When 9B is turned on, capacitor 62 is charged as shown by curve 3 in FIG.
2 reaches the predetermined voltage Vx, and the transistor 67 and the diodes 69R, 69G, and 69B are turned off. Therefore, the power switch 80 is turned off from the state where the power switch 80 has been off for a relatively long time as at time t1. A normal screen will be displayed in a shorter time than when it is turned on.

H Effects of the Invention According to the present invention, as described above, in a television receiver having an automatic power-off adjustment function, a retrace line does not appear on the screen (return line shines) when the power is turned on. At the same time, the screen returns to normal in the shortest possible time.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of a television receiver according to the present invention, FIG. 2 is an example of the television receiver according to the present invention shown in FIG. 1, and an example of a conventional television receiver shown in FIG. 4. 3 is a diagram showing the operation of the control circuit of an example of the television receiver according to the present invention shown in FIG. 1, and FIG. 4 is a diagram showing the connections of an example of the conventional television receiver. It is a diagram.

Claims (1)

[Claims] Red, green, and blue primary color video signals with pilot signals inserted in the first, second, and third horizontal periods within the vertical retrace period are amplified and supplied to a color cathode ray tube. a video output circuit, and the first, second, and third primary color video signals of red, green, and blue;
The beam current of the color cathode ray tube that flows in the horizontal period of the color cathode ray tube and the color that flows in the horizontal period other than the first, second, and third horizontal periods within the vertical retrace period of the red, green, and blue primary color video signals. A cutoff characteristic detection circuit compares the beam current of the cathode ray tube and obtains an output voltage according to the difference, and the output voltage of this cutoff characteristic detection circuit determines the DC level of the primary color video signals of red, green, and blue. a DC level correction circuit that corrects the voltage, a capacitive element that is charged with a first time constant when the power is turned on and discharged with a second time constant when the power is turned off, and a switching device that uses the terminal voltage of this capacitive element. The switching element has a controlled switching element, and when the terminal voltage of the capacitive element is below a predetermined value, the switching element is brought into one state to forcibly set the output voltage of the cut-off characteristic detection circuit to the predetermined value. A television receiver equipped with a control circuit and.