JPH0463067A - Display device - Google Patents

Abstract

PURPOSE:To prevent a spot from being obstructively left on a display screen by providing a continuing means which continues the oscillating operation of a horizontal oscillating circuit for a prescribed time at the time of power-off and a changing means which forcibly changes the luminance of a display picture to the white level in this oscillation continuation period and forcibly reducing the high voltage applied to a cathode-ray tube at the time of power-off. CONSTITUTION:A display device 1 where a picture is displayed with a cathode- ray tube 10 is provided with a continuing means 9 which continues the oscillating operation of a horizontal oscillating circuit 12 for the prescribed time at the time of power-off and changing means 4 and 5 which forcibly change the luminance of the display picture to the white level in the oscillation continuation period. At the time of power-off, the oscillating operation of the horizontal oscillating circuit 12 is continued for the prescribed time by the means 9 and the luminance of the display picture is changed to the white level by means 4 and 5 to forcibly flow a beam current to the cathode-ray tube 10; and thus, the high voltage applied to the cathode-ray tube is reduced in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a display device, and is particularly suitable for application to a display device using a cathode ray tube.

B. Summary of the Invention The present invention provides a display device using a cathode ray tube, in which the high voltage applied to the cathode ray tube can be reduced in a short time by forcing a beam current to flow when the power is turned off. , it is possible to prevent a spot from remaining on the display screen such that a part of the display screen lights up when the power is turned off.

C. Prior art In conventional display devices using cathode ray tubes such as television receivers, a high voltage of about 20 CkVE is applied to the anode of the cathode ray tube (hereinafter referred to as CRT), and the cathode of the electron gun is heated by a heater. By heating, an electron beam is emitted from the cathode side to the screen side.

Here, when the luminance level of the color signal input to the CRT is a white level, the display screen becomes white (bright) by being irradiated with a large number of electron beams.

On the other hand, when the luminance level of the color signal input to the CRT is a black level, the display screen becomes black (dark) because the amount of electron beam irradiation decreases.

When more electron beams are irradiated, more beam current flows, and the high voltage applied to the CRT becomes a relatively small value.

On the other hand, when the amount of electron beam irradiation decreases, the beam current flows less, so that the high voltage applied to the CRT becomes higher.

In this way, the color signal is adjusted according to the brightness level of the color signal input to the CRT (that is, the brightness of the CRT display screen).
The high voltage applied to RT changes.

Problem to be Solved by the Invention D However, as shown in FIG. 2(C), when the luminance signal SY is relatively close to the black level (time 2 to t3),
When the power switch of the display device is turned off (at that point), the horizontal oscillation circuit provided in the horizontal deflection circuit stops its oscillation operation, and the oscillation output of the horizontal oscillation circuit as shown in FIG. 2(D) increases. Signal S. , C no longer forms an oscillation waveform at the time point t.

At this time, as the high voltage remains applied to the CRT, a discharge occurs inside the electron gun due to dust mixed into the electron gun, and a so-called spot remains that partially shines on the display screen. There was a problem.

In addition, when the collar is open and the brightness signal SY is at the black level, the display screen is dark and the beam tfL flowing through the CRT is small, the user may turn off the main power or turn off the ta.
If the main power is turned off by unplugging the cord, etc., as shown in Figure 3 (C)
The W degree adjustment signal S that determines the brightness of the display screen as shown in
Since the signal level of I1 exhibits the same adjacent characteristics as the power supply voltage level, the luminance signal Sv, which is a negative polarity signal, gradually drops as shown in FIG. 4(C).

Therefore, if the power is turned off while the display screen is dark,
Since the display device is turned off without the display screen becoming white (bright) again, the high voltage applied to the CRT remains without being immediately discharged.

According to experiments, the high voltage (19.5 (kV)) applied to the anode of a CRT when the power is turned off is 1
The time it takes to drop to 0 (kV) is about 6 seconds.

Therefore, when the power is turned off, the residual high voltage causes discharge due to dust and the like to occur inside the electron gun of the CRT, resulting in a problem that a spot remains on the display screen.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a display device that can prevent unsightly spots from remaining on the display screen when the power switch is turned off.

E Means for Solving the Problems In order to solve the problems, in the first invention, a display device 1 that displays images using a cathode ray tube 10 includes:
The i! #Forcibly lower the high voltage applied to the cathode ray tube 10 when it is off.

Further, in the second invention, in the display device l in which the brightness of the image displayed by the cathode ray tube 10 is adjusted by a predetermined brightness adjustment means 8, the drop characteristic is longer than the drop characteristic of the power supply voltage B3 when the power is turned off. Time constant means C that lowers the brightness adjustment signal level (S□,) according to a time constant
1, the beam current is forced to flow through the cathode ray tube 10 when the power is turned off, and the high voltage applied to the cathode ray tube tlo is forced to drop.

F action In the first invention, the oscillation operation of the horizontal oscillation circuit 12 is sustained for a predetermined period of time by the sustaining means 9 when 26 is off, and the brightness of the display screen is changed to a white level by the changing means 4 and 5. A beam current can be forced to flow through the cathode ray tube 10, thereby making it possible to drop the high voltage applied to the cathode ray tube in a short time.

In this way, it is possible to prevent an unsightly spot from remaining on the display screen when the power is turned off.

Further, in the second invention, by providing the time constant means C1 having a predetermined capacity in the brightness adjustment means 8, the brightness adjustment signal level can be lowered by a time constant longer than the drop characteristic of the t source voltage when the power is turned off. can.

Therefore, by making the brightness adjustment signal level relatively higher than the power supply voltage level, the display screen can be changed to a white level, and thereby a beam current can be forced to flow through the cathode ray tube IO.

In this way, the high voltage applied to the cathode ray tube 10 can be lowered in a short time, and it is possible to prevent unsightly spots from remaining on the display screen when the power is turned off.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, reference numeral 1 indicates a display device using a CRT as a whole, and a video signal S sent out from a video signal generation circuit 3.
v is input to the adder circuit 4.

In the adder circuit 4, the switch circuit 5 composed of a microcomputer is in the ON state; at this time, by inputting the DC output of the voltage #B1, this is superimposed on the luminance signal Sv in the video signal Sv, and the video signal processing circuit Send on 7.

The video signal processing circuit 7 is activated by a predetermined power supply B2, and adjusts the brightness by inputting a brightness adjustment signal S□a output from a brightness adjustment circuit 8 consisting of a trAB3, a variable resistor R1, and a capacitor C1. After amplifying the signal Sv to a predetermined luminance level, a color signal Sc is obtained based on the luminance signal SV and sent to the CRTIO.

On the other hand, when the switch circuit 5 is in the on state, the horizontal oscillation circuit 12 transfers the output voltage of the power supply B to the diode D1.
, a time constant circuit 9 consisting of a resistor R2 and a capacitor C2 performs an oscillation operation, and outputs an oscillation output signal s osc synchronized with the horizontal synchronization signal SN sent from the synchronization signal generation circuit 11 to the transistor Q1. send out to the base of

The output transistor Q1 has its collector side connected to the power source B4, and in addition to the voltage source E, the deflection coil LL, and the resonant capacitor C3, the oscillation output signal S is inputted to the base. , C to generate a sawtooth wave current in the deflection coil L1.

Further, the primary winding L2 of the flyback transformer 14 is connected between the collector side of the output transistor Ql and the voltage #84, and the high voltage side winding L3 of the flyback transformer 14 is connected based on the collector current of the output transistor Q1. The generated high voltage output is sent to CRTIO via rectifier diode D2.
is sent to the anode terminal 10A of the

Thus, in the CRTIO, the electron beam emitted from the electron gun 10B is attracted to the high voltage anode side and collides with the phosphor screen 10C, thereby causing the phosphor screen 10C to emit light.

Here, the capacitor C4 connected to the anode terminal 10A side of the CRTIO is generally the capacitance (
2000 (pF)).

In addition, in the display device 1, when the user turns on or off the power using a remote commander or the like, the switch circuit 5 operates on and off accordingly, and at this time, the main taB, , B2, Bt and B4 is kept in the on state.

On the other hand, if the user turns off the main power supply or pulls out the power cord to turn the power on or off, the main power supplies B, , B2, B, and B4 will be in the off state, and the power supply will be turned off. has been made to stop.

In the above configuration, when the user turns off the t'g switch of the display device 1 using a remote commander or the like, the switch circuit 5 is turned off and the main power supplies B, ,
B, , B, and B4 remain on.

Therefore, when the switch circuit 5 is turned off, the DC output B1 that has been superimposed on the brightness signal SV in the video signal SvO is no longer supplied in the adder circuit 4, so that the brightness signal SV changes as shown in FIG. As shown in A), at the point in time when the switch circuit 5 is turned off, the signal level is at the white level (in this embodiment, it is a negative polarity signal; the lower the signal level is, the whiter the displayed image is (
brighten) and maintain this.

On the other hand, in the horizontal oscillation circuit 12, at time L3 when the switch circuit 5 is turned off, the time constant τ (0.2 to 0.3 in this embodiment) is determined by the resistor R2 and the capacitor C2. seconds) later at time t4
At this point, the supply from the power source B is stopped, and at this time, the sawtooth wave current is no longer supplied to the deflection coil L1, and no high voltage output is supplied to the high voltage circuit side of the flyback transformer 14.

Therefore, after the switch circuit 5 is turned off at time τ and until the horizontal oscillation circuit 12 is stopped operating at time L4, a sawtooth wave current is supplied to the deflection coil Ll and the brightness is By keeping the signal SY at the white level, the amount of electron beams emitted from the CRTIO increases, and a white (bright) screen is displayed on the display screen 10D of the CRTIO.

Therefore, by increasing the beam current, the CRT's capacity C
4 enters a discharge state, thereby making it possible to reduce the high voltage remaining between the flyback transformer 14 and the CRTIO.

By thus preventing the generation of discharge in the electron gun 10B of the CRTIO, it is possible to prevent a spot from remaining on the display screen 10D after the power switch is turned off.

If the power switch of the display device 1 is turned off using the remote commander etc. (i.e. main power supply B+, Bz
, B3 and B4 maintain the power supply state), but on the other hand, for example, if the user unplugs the power outlet of the display device 1, the main power supply B,
, B, , B, and B4, when the power supply is stopped, the capacitor C1 connected to the brightness adjustment circuit 8
The brightness adjustment signal S is determined by the brightness adjustment signal S. By slowing down the fall of T, no spot remains on the display screen 10DJ:.

In other words, as shown in FIG. 3(A), when the main power supply B3 is turned off, the signal level of the brightness adjustment signal SIIIT falls more slowly than the fall of the power supply potential, so that the relative The brightness adjustment signal S! The IRT signal level increases.

Therefore, as shown in Figure 4 (A), after turning off the power, the
By obtaining the state T,1 in which the luminance signal SY is forcibly changed to the white level for 100 [ms], a white (bright) screen can be displayed on the display screen lOD of the CRTIO, and this This allows the beam to flow.

At this time, T1. If! Since B a is in the off state, no output is supplied from the high voltage side of the flyback transformer 14 and the capacitor IC 4 of the CRTIO is in a discharge state, which causes the flyback transformer 14 and the CRTIO to be in a discharge state.
The high voltage remaining between O can be lowered in a short time.

According to experiments, the capacitor CI is 221μF]
If the connection is made, the high voltage (19,5,' k V =.

) was reduced to a voltage (105 to ■) at which no spot residue was generated, and the time required was 0.7 seconds, which was extremely short compared to the conventional method.

In this way, it is possible to prevent discharge from occurring in the electron gun 10B of the CRTIO, and thus it is possible to prevent a spot from remaining on the display screen 10D after the power switch is turned off.

Incidentally, if the capacitance of the capacitor CI provided in the brightness adjustment circuit 8 is 470 [μF], the signal level of the brightness adjustment signal S□7 will be higher than the voltage level of the power supply B3, as shown in FIG. 3(B). As a result, as shown in FIG. 4(B), the time required to change the luminance signal S7 to the white level becomes much shorter, making it impossible to sufficiently discharge the capacitor C4 of the CRT.

Therefore, as described above with respect to FIG. 3(A), approximately 22 [μ
Brightness adjustment signal S by providing a capacitor C1 of about F]. It is sufficient that T falls so as not to exceed the voltage level of electric [B,.

According to the above configuration, by forcing the beam current to flow when the power switch is turned off, it is possible to prevent an unsightly spot from remaining on the display screen.

In the above embodiment, the oscillation duration τ of the horizontal oscillation circuit 12 was set to 0.2 to 0.3 seconds, but the present invention is not limited to this, and the resistor constituting the time constant circuit 9 It is also possible to set the time to another time by changing R2 and capacitor C2 to other values and changing the time constant.

Further, in the above embodiment, 2 is used as the capacitor CI.
Although the case where a capacitor of 2 [μF] is used has been described, the present invention is not limited to this, but it is possible to use a capacitor of other capacitance as long as it has a time constant that allows the beam current to flow forcibly. May be used.

Further, in the above-described embodiment, the present invention was applied to a television receiver configured to display images on a display screen provided on a cathode ray tube, but the present invention is not limited to this. For example, it can be widely applied to other display devices using cathode ray tubes, such as projector devices.

Effects of the Invention As described above, according to the present invention, when the power is turned off, the shadow 8i
By forcing the beam current to flow through the cathode ray tube, the high voltage applied to the cathode ray tube can be lowered in a short period of time, thereby eliminating unsightly spots on the display screen. Therefore, it is possible to realize a display device that can prevent this from occurring.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing an embodiment of a display device according to the present invention, and FIG. 2 is a signal waveform diagram for explaining when the horizontal oscillation output is sustained and the display screen is forcibly changed to a white level.
Figure 3 is a signal waveform diagram showing the drop characteristics of the brightness adjustment signal level due to the capacitance of the capacitor provided in the brightness adjustment circuit, and Figure 4 is a signal waveform diagram showing the drop characteristics of the brightness signal level due to the capacitance of the capacitor installed in the brightness adjustment circuit. FIG. 1...Display device, 4...Addition circuit, 5
...Sinch circuit, 7...Video signal processing circuit, 8...Brightness adjustment circuit, 9...
Time constant circuit, 10... negative 8i ray tube, 12...
...Horizontal oscillation circuit.

Claims (2)

[Claims] (1) In a display device that displays images using a cathode ray tube, a sustaining means for sustaining the oscillation operation of the horizontal oscillation circuit for a predetermined period when the power is turned off, and forcibly reducing the brightness of the displayed image to white during the oscillation duration period. 1. A display device comprising: changing means for changing the level, and forcibly lowering the high voltage applied to the cathode ray tube when the power is turned off. (2) In a display device in which the brightness of an image displayed by a cathode ray tube is adjusted by a predetermined brightness adjustment means, the brightness of an image displayed by a cathode ray tube is adjusted by a time constant longer than the drop characteristic of the power supply voltage when the power is turned off. A time constant means is provided for lowering the brightness adjustment signal level, and the beam current is forced to flow through the cathode ray tube when the power is turned off, and the high voltage applied to the cathode ray tube is forcibly lowered. A display device characterized by: