JPH02305091A - Demagnetizing circuit - Google Patents

Abstract

PURPOSE:To perform stable demagnetizing operation by demagnetizing a cathode-ray tube with a magnetic field for demagnetization which is produced by a demagnetizing coil and synchronizing the timing of the demagnetizing operation completely with the timing of a display period and a blanking period. CONSTITUTION:This circuit consists of a 1st monostable multivibrator 2 which is supplied with a synchronizing signal, a 2nd monostable multivibrator 3 whose input connects with the output of the 1st monostable multivibrator 2, and a series resonance circuit 4 where the output of the 2nd multivibrator 3 is connected to the input of a switch element 4a, and the demagnetizing coil 5 which constitutes part of the series resonance circuit 4. Consequently, the demagnetizing operation can be synchronized with the timing of the display and blanking period and a color irregularity phenomenon can be eliminated completely.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a degaussing circuit for a cathode ray tube (hereinafter referred to as CRT) display device.

In a display device using a conventional color CRT, images change in principle due to the influence of the earth's magnetism. In particular, shadow masks, which have the function of accurately applying three electron beams to phosphors that emit three primary colors, are easily magnetized by the earth's magnetism due to their material, and as a result, the electron beams are bent and do not reach the phosphors correctly, so-called Color unevenness may occur.

Therefore, in general, a degaussing circuit is widely used that removes magnetization by applying an alternating current magnetic field with attenuation to a shadow mask or the like for a few seconds after the display device is started up. Once demagnetized, it will not become magnetized again unless the geomagnetic state changes, so this is a very useful method for stationary display devices and the like.

However, in a display device installed in a moving body, such as a vehicle, a ship, an aircraft, etc., or a portable display device, the geomagnetic state changes and the shadow mask etc. may become magnetized again during use. In this case, a manual switch may be installed to operate the degaussing circuit, but if the screen swings unnecessarily during the degaussing operation or the earth's magnetic field changes frequently, the switch must be operated each time. There are many inconveniences.

For this reason, degaussing circuits have been put into practical use that perform demagnetization by periodically applying an alternating current magnetic field with damped oscillation during the flyback period, which does not affect the display.

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

FIG. 3 is a block diagram of a conventional degaussing circuit.

In FIG. 3, 1 is an input terminal for a synchronization signal indicating the retrace period of the display, 6 is an astable microvibrator circuit, and 7 is an AND gate, which receives a synchronization signal and the output of the astable multivibrator 6. A signal is provided. 4 is a series resonant circuit having a switch element 4a;
The output of the AND gate 7 is connected to the input of the AND gate 7. A degaussing coil 5 constitutes a part of the series resonant circuit 4, and a degaussing magnetic field from the degaussing coil 5 demagnetizes the CRT.

Next, the operation of the degaussing circuit shown in FIG. 3 will be explained using FIG. 4. FIG. 4 is a waveform diagram in the conventional degaussing circuit shown in FIG. In FIG. 4, (a) is a binary signal indicating the synchronization signal in FIG. 3, where a high level indicates a retrace period and a low level indicates a display period. (b) is a binary signal indicating the operation of the astable multivibrator 6 in FIG. 3, (C) is a binary signal indicating the operation of the AND gate 7 in FIG. 3, and (d) is a binary signal indicating the operation of the astable multivibrator 6 in FIG. This is an AC signal indicating the operating current of the resonant circuit 4.

As shown in No. 4 (a), the synchronization signal alternately repeats a retrace period of period W1 and a display period of period W2.

On the other hand, as shown in signal (b), the astable multivibrator circuit 6 maintains the high level of W6 for a certain period of time and the high level of W7 for a certain period of time.
cyclically repeating the low level. Here, Wl<W6.
Other than setting the relationship Wl+W2<W6+W7, there is no synchronous relationship between the periods W1 and W2 and the periods W6 and Wl.

The output of the AND gate 7 to which the two signals (a) and (b) are input is the signal (a) as shown in the signal (C).
) and the high level period W of signal (b).
6 occurs at the same timing, the level becomes high. Period W8 is an example. As shown in the signal (d), the series resonant circuit 4 starts oscillating and attenuates at the moment when the signal (C) of the AND gate 7 becomes high level, that is, at the rising edge of the period W8 in the signal (C). While performing the vibration, the vibration is stopped at the instant when the signal (C) of the AND gate 7 becomes low level, that is, at the falling edge of the period W8.

As a result of these series of operations, a damped oscillating current flows through the demagnetizing coil 5 every few times during the repeated retrace period, and demagnetization is performed.

Note that the reason why a damped oscillating current is used as the demagnetizing current is as follows. Generally, to demagnetize a magnetized magnetic material,
This is because a method must be used in which a magnetic field stronger than the amount of magnetization is applied in an alternating current manner, and the field is gradually weakened to converge to a neutral state. This is achieved by converting electrical energy into thermal energy and reducing it by the series resistance of the degaussing coil during series resonant circuit operation.

Furthermore, the reason why demagnetization is performed only during part of the retrace period is that the electrical energy required for demagnetization must be charged from the power supply to the capacitance of the series resonant circuit when the series resonant circuit is not operating. .

Problem to be Solved by the Invention By the way, as mentioned above, the signal (a) in FIG.
Since there is no synchronous relationship between the period Wl-W2 and the period W6-W7 of the signal (b), for example, the signal (C) in FIG.
A shorter than normal high level period, such as period W10, may occur. In this case, the current in the series resonant circuit 4 has a state in which the damped oscillation is interrupted, as shown in the period Wll of the signal (C) in FIG.

Therefore, a current flows through the degaussing coil 5 in a form in which the damped vibration is interrupted. As a result, not only demagnetization, which is the original purpose, is not carried out sufficiently, but also magnetization occurs due to the strong magnetic field. In most cases, this magnetization disappears when the next demagnetization is performed, but until then, the color unevenness phenomenon described above will continue to occur, degrading the quality of the display device. That is undeniable.

As explained above, in conventional degaussing circuits, the interval between degaussing operations is not synchronized with the timing of the display/retrace period, so there is a problem in that it sometimes induces magnetization and causes color unevenness. ing.

Means for Solving the Problems In order to solve these problems, the degaussing circuit in the present invention includes a first monostable multivibrator to which a synchronization signal is supplied, and an output from the first monostable multivibrator. A second monostable multivibrator connected to the switch element, a series resonant circuit in which the output of the second multivibrator is connected to the input of the switch element, and a degaussing coil forming a part of the series resonant circuit. .

Effect By adopting the above configuration, degaussing operation can be displayed and
It is now possible to synchronize with the timing of the retrace period,
The color unevenness phenomenon that occurs in conventional degaussing circuits can be completely eliminated.

EMBODIMENT A degaussing circuit according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a degaussing circuit in one embodiment of the present invention.

In FIG. 1, 1 is a synchronization signal input terminal, which is the same as that already explained in FIG. 2 is an edge-triggered monostable multivibrator that is triggered by the rising edge of an input signal, and a synchronization signal is input to the trigger input. 3 is an edge trigger type monostable multivibrator similar to 2, and the output of the monostable multivibrator 2 is connected to the trigger input. Note that these monostable multivibrators are based on standard logic integrated circuits (for example, 74
LS221 type, etc.) can be used. 4 is switch element 4
A is a series resonant circuit with a, and 5 is a degaussing coil, which are the same as those already explained in FIG.

Next, FIG. 2 will be explained. FIG. 2 is a waveform diagram for explaining the operation of the degaussing circuit in one embodiment of the present invention shown in FIG. In FIG. 2, (a) is a synchronization signal, in which a high level indicates a retrace period and a low level indicates a display period. (b)
is a binary signal indicating the operation of monostable multivibrator 2,
(C) is a binary signal indicating the operation of the monostable multivibrator 3, and (d) is a signal indicating the operating current of the series resonant circuit 4.

The operation of the degaussing circuit in one embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

The synchronization signal (a) alternately repeats a retrace period of period W1 and a display period of period W2. Note that the initial state of the outputs of the monostable multivibrator 2 and the monostable multivibrator 3 is at a low level as shown in the signal (b) and signal (C) at time t1 in FIG. 2. Time t1
At , signal 1 transitions from low level to high level.

That is, since a rising signal is applied to the trigger input of the monostable multivibrator 2, the monostable multivibrator 2 outputs a high level signal during the period W3 after time t1, as shown in signal (b). Here W1+W2<
It is set to be W3. Therefore, since a rising signal is also applied to the trigger input of the monostable multivibrator 3 at time t1, the monostable multivibrator 3 receives a high level signal during the period W4 after time t1, as shown in signal (C). Output. Here, it is set to be W1ξW4. The series resonant circuit 4 receives the signal ω
), at the moment when the signal of the monostable multivibrator 3 becomes high level, that is, at the rising edge of period W4 in signal (C), oscillation imaging is started, and while performing attenuation imaging, the monostable multivibrator 3 Impression is stopped at the moment when the signal of the vibrator 3 becomes low level, that is, at the falling edge of the period W4 in the signal (C).

Now, at time t2, the signal (a) again transitions from low level to high level. However, as shown in signal (b), monostable multivibrator 2 has already outputted a high level signal, so the state does not change.

Therefore, the monostable multivibrator 3 also does not change, and therefore the series resonant circuit 4 also remains stopped.

At time L3, signal (b) ends period W3 and transitions from high level to low level, but since this signal is in the opposite direction to the trigger condition of monostable multivibrator 3, the state of monostable multivibrator 3 changes. do not. That is,
The output of the monostable multivibrator 3 transitions from a low level to a high level only when the output of the monostable multivibrator 2 transitions from a low level to a high level. Similarly, the output of the monostable multivibrator 2 transitions from a low level to a high level only when the synchronization signal (a) transitions from a low level to a high level. Therefore, the series resonant circuit 4 always generates a damped oscillating current due to the signal (a).
is synchronized with the rise time of
Since interruption of the oscillating current as seen in conventional degaussing circuits does not occur, stable degaussing operation can be performed.

Effects of the Invention According to the present invention, since the timing of the degaussing operation can be completely synchronized with the timing of the display period and blanking period, a stable demagnetizing operation can be performed. In addition, rising edge-triggered monostable multivibrators are commercially available at low cost as standard logic integrated circuits in packages of two circuits, and can be used as is, making the entire circuit inexpensive. Moreover, it can be made small and has extremely high practicality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a degaussing circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the degaussing circuit shown in FIG. 1, FIG. 3 is a block diagram of a conventional degaussing circuit, and FIG. This figure is a waveform diagram for explaining the operation of the degaussing circuit shown in FIG. 3. 2...First monostable multivibrator, 3.
...Second monostable multivibrator, 4...
...Series resonant circuit, 5... Demagnetizing coil. Name of agent: Patent attorney Shigegami Awano and one other person

Claims (1)

[Claims] A series resonant circuit consisting of first and second monostable multivibrators that are triggered by the rising edge of an input pulse signal and output a pulse signal of a preset width from an output terminal, a switching element having a control input terminal, and a degaussing coil. A display synchronization signal having a constant period is input to the input terminal of the first monostable multivibrator, and the output terminal of the first monostable multivibrator and the second monostable multivibrator are connected to each other. and the output terminal of the second monostable multivibrator and the control input terminal of the switch element of the series resonant circuit, so that the cathode ray tube is demagnetized by the demagnetizing magnetic field of the degaussing coil. The constructed degaussing circuit.