JPH05130626A - Display device - Google Patents

Abstract

PURPOSE:To prevent the generation of a landing deviation due to magnetization such as a shadow mask due to earth magnetism and to enable effective display in a display device using a cathod-ray tube(CRT) and a demagnetizing coil. CONSTITUTION:A synchronous signal polarity detecting circuit 6 connected to a deflecting circuit 1 detects the polarity of a synchronous signal, a synchronous signal period judging circuit 7 judges a change in the synchronous signal and when an operation mode is changed, current necessary for demagnetizing operation is allowed to flow into the demagnetizing coil 3 to automatically execute demagnetizing operation. Even when a CRT in using generates color slippage due to magnetization, demagnetizing operation is automatically executed when the synchronous signal is changed and the operation mode is also changed, so that an always effective display state can be obtained during the using of the device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device such as a computer display.

[0002]

2. Description of the Related Art In a television or a computer display using a cathode ray tube, a positive temperature coefficient thermistor or the like is used for a degaussing coil provided around the cathode ray tube in order to prevent deviation of landing due to magnetization of a shadow mask due to geomagnetism. Thus, a degaussing current, which decays with time when the power of the device is turned on, is supplied for degaussing, or an independent degaussing switch is provided to degauss as necessary.

FIG. 3 is a block diagram of a conventional display device.
Is a deflection circuit of the cathode ray tube 2 for display, 3 is the cathode ray tube 2
The degaussing coil for degaussing the shadow mask 4 is a positive temperature coefficient thermistor 4 connected in series with the degaussing coil 3, and the degaussing switch 5 is also used as a power switch of a display device for supplying a degaussing current to the degaussing coil 3. The conventional display device is shown in FIG.
Will be explained. An AC power source is connected to a degaussing coil 3 provided around the cathode ray tube 2 via a positive temperature coefficient thermistor 4 and a degaussing switch 5, and control is performed so that the degaussing switch 5 is turned on when the display device is powered on. Alternatively, when the degaussing switch 5 is turned on as necessary, a degaussing current that decays with time flows to the degaussing coil 3 by the positive characteristic thermistor 4 to degauss a shadow mask or the like.

[0004]

However, in the above-mentioned conventional configuration, a system in which the positive temperature coefficient thermistor 4 and the degaussing coil 3 are connected in series is connected to an AC power source and degaussed when the power of the display device is turned on is used. In this case, the usage time becomes long, and especially in the case of a computer display or the like, when the installation direction is changed by the twist and swivel device attached to the device after the power is turned on, it is demagnetized once and good landing is obtained. It may happen that the color of the object deteriorates and uneven coloring occurs. At this time, even if the power switch is turned off and then turned on again, if the power switch is turned off for a short time, the PTC thermistor 4 is not sufficiently cooled and the temperature of the PTC thermistor 4 is high and the resistance value is large. Since a sufficient degaussing current does not flow in the degaussing coil 3, the magnetization cannot be eliminated, causing a problem. As a countermeasure against this, a dedicated independent degaussing switch 5 is provided. However, the operation becomes complicated, it may interfere with the design of the display device, or the display device may not be operated when placed at a distance.

In order to solve the above problems, the present invention provides a display device which has good operability and can always obtain good landing.

[0006]

In order to solve the above problems, the present invention provides a circuit for detecting a change in a sync signal and a degaussing coil for degaussing by passing a current through a degaussing coil when the sync signal changes. And a degaussing means for performing the degaussing.

[0007]

According to the present invention, the degaussing operation can be automatically performed when the synchronizing signal changes due to the above configuration.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram of a display device according to an embodiment of the present invention. 1 is a deflection circuit, 2 is a cathode ray tube, 3 is a degaussing coil, and 4 is a positive temperature coefficient thermistor. Is omitted. Reference numeral 6 is a polarity detection circuit for a sync signal input to the display device, 7 is a cycle signal determination circuit for the sync signal input to the display device, and 8 is a one-shot multi-purpose timer that determines the time for which the degaussing current flowing through the degaussing coil 3 flows. A vibrator circuit 9 is a drive circuit of the relay 10 for turning on and off the degaussing current flowing through the degaussing coil activated by the one-shot multivibrator circuit 8. 2A is a circuit diagram of the polarity detection circuit 6, FIG. 2B is a circuit diagram of the cycle determination circuit 7, and in FIG. 2A, 11 is an inverter IC,
12 is a diode, 13 is a first integrating capacitor, 14
Is a discharge resistance, 15 is an integration resistance, 16 is a second integration capacitor, and 17 is an exclusive OR IC. In FIG. 2B, 18 is a one-shot multivibrator IC, 19 is a resistor that determines the pulse width of the one-shot multivibrator IC 18, 20 is a capacitor that determines the pulse width of the one-shot multivibrator IC 18, and 21 is a first integral. A resistor, 22 is a first integration capacitor, 23 is a comparator IC, 24 is a comparison reference power source of the comparator IC 23, 25 is a second integration resistor, 26 is a second integration capacitor, and 27 is an exclusive OR IC.

The operation of the display device according to the embodiment of the present invention will be described below. The polarity of the sync signal is detected by the sync signal polarity detection circuit 6 connected to the deflection circuit 1 in FIG. 1, for example, as shown in FIG. 2A, and it is determined that the sync signal has changed, and the signal is degaussed. It is output to the one-shot multivibrator circuit 8 which determines the time for which the degaussing current flowing in 3 flows. Further, the period of the synchronizing signal inputted by the period discriminating circuit 7 is discriminated, and it is detected that the period of the synchronizing signal is changed and the operation mode thereof is changed, and it is outputted to the one-shot multivibrator circuit 8. The one-shot multivibrator circuit 8 is activated by these output signals to generate a relay drive signal for the time required for the degaussing operation to conduct the relay 10 through the drive circuit 9 to pass a current through the positive temperature coefficient thermistor 4 and the degaussing coil 3 to degauss. The degaussing operation is performed when the synchronizing signal changes due to the operation. In addition, the degaussing operation is performed when the display device is started up, so that the one-shot multivibrator circuit 8 is used.
A power activation detection circuit 28 is provided which is interlocked with a power switch of the display device for activating the display device. When the display device is activated, the one-shot multivibrator circuit 8 is activated to perform the degaussing operation.

The operation of the sync signal polarity detection circuit 6 shown in FIG. 2A will now be described. First, a synchronizing signal having a smaller duty ratio is input from point A, inverted by the inverter IC 11, and then integrated by the diode 12, the first integrating capacitor 13, and the discharging resistor 14, and the synchronizing signal is applied to both ends of the first integrating capacitor 13. High and low voltages are generated depending on the polarity. This voltage is applied to the integration resistor 15 and the second integration capacitor 1
6 and the exclusive OR I together with the voltage delayed by the time
When input to C17, the two inputs of the exclusive OR IC 17 are different during the time delay generated by the integrating resistor 15 and the second integrating capacitor 16 when the polarity of the synchronizing signal changes, and the output is as shown in FIG. 3 (c). The detection signal of the polarity change as shown is obtained, and the change of the polarity of the synchronization signal can be detected. At this time, the same operation is performed regardless of whether the synchronizing signal is a horizontal synchronizing signal or a vertical synchronizing signal. Next, the operation of the sync signal cycle determination circuit 7 of FIG. 2B will be described. First, a sync signal having a duty ratio smaller than that of point B is input to the one-shot multivibrator IC 18 whose pulse width is narrower than the cycle of the sync signal by the resistor 19 and the capacitor 20. Since the output of the one-shot multivibrator IC 18 is constant regardless of the cycle of the synchronizing signal, it is integrated by the first integrating resistor 21 and the first integrating capacitor 22, and the cycle of the synchronizing signal is across both ends of the first integrating capacitor 22. High and low voltages are generated in response to each. When this voltage is input to the comparator IC 23 together with the reference voltage 24, a signal whose output is high or low is obtained according to the cycle of the synchronization signal input to the display device. This voltage is applied to the second integrating resistor 25 and the second integrating capacitor 2
6 and the exclusive OR I together with the voltage delayed by the time
When input to C27, the period of the output changes because the two inputs of the exclusive OR IC 27 are different during the time delay generated by the second integrating resistor 25 and the second integrating capacitor 26 when the period of the synchronizing signal changes. And the change in the cycle of the synchronization signal can be detected. At this time, the same operation is performed regardless of whether the synchronizing signal is a horizontal synchronizing signal or a vertical synchronizing signal.

In this embodiment, the relay 10 is used for explanation, but it is constituted by an electronic circuit using a triac or the like, and a demagnetizing current is obtained by using a self-resonant current without using a positive temperature coefficient thermistor. Alternatively, it is clear that the detection of the synchronization frequency has the same effect even if the frequency of the deflection signal is detected. Further, the present invention is particularly effective in a multi-scan rate display that operates by switching some deflection frequencies, because demagnetization is performed at the same time when the deflection frequencies are switched.

[0012]

As described above, the present invention is provided with the circuit for detecting the change of the synchronizing signal, and the degaussing means for degaussing the shadow mask of the cathode ray tube by passing a current through the degaussing coil when the synchronizing signal changes. By doing so, it is possible to perform a degaussing operation when the sync signal changes, and to provide a display device that is degaussed when the operating mode of the computer in use changes and that can always obtain a good display state. You can

[Brief description of drawings]

FIG. 1 is a block diagram of a display device according to an embodiment of the present invention.

FIG. 2A is a circuit diagram of a sync signal polarity detection circuit of a display device according to an embodiment of the present invention. FIG. 2B is a circuit diagram of a sync signal cycle determination circuit of a display device according to an embodiment of the present invention.

FIG. 3 is a block diagram of a conventional display device.

[Explanation of symbols]

 1 Deflection Circuit 2 CRT 3 Degaussing Coil 4 Positive Characteristic Thermistor 5 Degaussing Switch 6 Polarity Detection Circuit 7 Cycle Discrimination Circuit 8 One-Shot Multivibrator Circuit 9 Drive Circuit 10 Relay 11 Inverter IC 12 Diode 13 First Integrating Capacitor 14 Discharge Resistance 15 Integral Resistance 16 Second integration capacitor 17 Exclusive OR IC 18 One-shot multivibrator IC 19 Resistance 20 Capacitor 21 First integration resistance 22 First integration capacitor 23 Comparator IC 24 Comparison reference power supply 25 Second integration resistance 26 Second Integration capacitor 27 Exclusive OR IC 28 Power supply start-up detection circuit

Claims (4)

[Claims] 1. A display device for displaying a period on a Braun tube by a periodic signal sent thereto and degaussing the Braun tube with a degaussing coil, comprising: a sync signal detecting means for detecting a change in a sync signal; A degaussing means for degaussing by causing a degaussing current to flow through the degaussing coil when the synch signal detecting means detects a change in the synch signal. 2. The display device according to claim 1, wherein said sync signal detecting means detects at least one of a polarity and a cycle of the sync signal. 3. The display device according to claim 1, wherein degaussing is performed by the degaussing means when the power of the device is turned on. 4. The display device according to claim 1, wherein the display device is a multi-scan rate display.
Display device described.