JPH02230884A - Degaussing device for cathode ray tube - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cathode ray tube degaussing device that uses a degaussing coil to demagnetize the residual magnetism of the cathode ray tube.

[Conventional technology]

In conventional cathode ray tubes, as is well known, a degaussing coil is installed on the front panel of the cathode ray tube, and by passing an alternating current that gradually attenuates through this degaussing coil when the power is turned on, residual magnetization in the shadow mask, etc. is removed. It is designed to demagnetize magnetism.

Figure 2 shows the vertical deflection current X and the degaussing current Y of the degaussing coil in a conventional cathode ray tube.
indicates the negative half cycle of C, E, G. I is the demagnetizing current Y
Positive half cycle of D, F, H. J indicates the negative half cycle of the demagnetizing current Y.

Next, the operation will be explained. When a 50 or 60 Hz AC power source is applied to a display device using a cathode ray tube, the drive circuit that drives the degaussing coil is activated, causing the degaussing coil to have COD>E>... as shown in Figure 2. A demagnetizing current Y that gradually attenuates by K flows. Then, the magnetism due to part C is canceled by the magnetism due to part K of D, and then the magnetism of part D is canceled by part E, and so on, and demagnetization is performed. .

On the other hand, when the power is turned on, the vertical deflection circuit is also activated, and the second
A vertical deflection current X of 5o or 60}IZ as shown flows through the vertical deflection coil of the cathode ray tube.

[Problem to be solved by the invention]

Conventional cathode ray tube degaussing devices operate as described above, so if the degaussing current Y and vertical deflection current The magnetic field interferes with the demagnetizing effect of the demagnetizing current Y, and therefore C, D, E. The magnetism is supposed to be canceled sequentially in each part, but the vertical deflection current
The magnetism from the B portion is superimposed, and this causes the magnetism to remain in the shadow mask, etc., resulting in problems such as color unevenness on the screen.

This invention was made to solve the above-mentioned problems, and its purpose is to obtain a demagnetizing device for a cathode ray tube that can suppress the interference between vertical deflection and demagnetization and reduce the residual magnetic field. do.

[Means to solve the problem]

In the cathode ray tube degaussing device according to the present invention, the vertical deflection frequency is changed to a frequency that does not interfere with the degaussing action while the degaussing circuit is in operation.

[For production]

In the cathode ray tube degaussing device according to the present invention, the interference of the vertical deflection current during the period when the degaussing current is flowing is reduced, and the degaussing effect is improved.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, reference numeral 1 denotes a degaussing circuit, which includes a known degaussing coil provided in a cathode ray tube (not shown) and its drive circuit.

Reference numeral 2 denotes a switch for operating the degaussing circuit 1, which is turned on, for example, when the cathode ray tube display device is powered on, and turned off after a predetermined period determined by the drive circuit has elapsed. 3
4 is a horizontal deflection circuit that supplies the horizontal deflection current to a horizontal deflection coil (not shown), 4 is a vertical deflection circuit that supplies the vertical deflection current X to a vertical deflection coil (not shown), and 6 is separated from the video signal. 7 is a vertical synchronizing signal separated from the video signal; 8 is a deflection control circuit; based on the horizontal and vertical synchronizing signals 6 and 7, horizontal and vertical control of the horizontal and vertical deflection circuits 3 and 4 is performed; Create a signal that determines the deflection frequency.

A control circuit 9 controls the deflection control circuit 8 to change the vertical deflection frequency. In the control circuit 9, 10 is a control signal that becomes "H" when the switch is on, and 11
are controlled by the control signal 10 and supply or cut off the vertical synchronization signal 7 to the deflection control circuit 8; 12.13.
14 is a variable resistor for adjusting the vertical deflection frequency produced by the deflection control circuit 8; 15 is the variable resistor 12, 1;
3. An analog switch that selectively connects 14 to the deflection control circuit 8, 16 is a switch that selects whether or not to change the vertical deflection frequency, and has an ON contact on the 1B power supply side, an OFF contact on the ground side, and a K switch. It will be done. 17 is the above switch 16
The analog switch 15 is controlled by the AND output.

Next, the operation will be explained. When the cathode ray tube display device is powered on, the switch 2 of the extinction circuit 1 is turned on.
This degaussing circuit 1 is operated. As a result, a gradually attenuating demagnetizing current Y as shown in FIG. 2 flows through the demagnetizing coil. At the same time, the rHJ control signal 10 is output, the switch 11 is turned off, and the vertical synchronization signal 7 is cut off.

If the switch 16 is on at this time, the AND gate 17 receives the signal from this switch 16 and the control signal 1.
Since 0 is added, the AND output becomes rHJ. Therefore, the analog switch 15 operates and the variable resistor 1
2, 13, and 14 selected and adjusted in advance are connected to the deflection control circuit 8. From the above K, the vertical deflection portion of this deflection control circuit 8 includes variable resistors 12, 13,
The free running frequency is determined by the resistance value of the connected one of the 14, and this free running frequency becomes the vertical deflection frequency and is applied to the vertical deflection circuit 4.

Therefore, this free-running frequency is set in advance by the variable resistors 12 and 13.
, 14 to a value different from the frequency of the demagnetizing current (for example, the power supply frequency), it is possible to reduce the interference between the vertical deflection current and the demagnetizing current, and improve the demagnetizing effect. can.

When the degaussing current flows through the degaussing coil for a predetermined period, switch 2
is turned off, and the control signal 10 becomes rLJ. As a result, the switch 11 is turned on, the vertical synchronizing signal 7 is supplied to the deflection control circuit 8, and the output of the AND gate 17 becomes rLJ, the analog switch 15 is turned off, and the variable resistors 12, 13 , 14 that were connected are disconnected. As a result, the deflection control circuit 8 is operated at a regular vertical deflection frequency synchronized with the vertical synchronization signal 7.

In the above embodiment, only the vertical synchronization signal 7 is cut off during the degaussing period, but in order to prevent screen distortion,
Both the video signal and the horizontal synchronization signal 60 may be cut off to turn off the screen.

Furthermore, in the above embodiment, the switch 16 is used to manually select whether or not to change the vertical deflection frequency, but it is also possible to use a microcomputer or the like to automatically perform the operation in accordance with the synchronization signal. You can.

〔Effect of the invention〕

As described above, according to the present invention, since the configuration is such that the vertical deflection frequency can be changed during the degaussing period, mutual interference between the degaussing current and the vertical deflection current can be reduced, and color unevenness can therefore be eliminated. This has the effect of improving image quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a degaussing device for a cathode ray tube according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing the vertical deflection current and degaussing current of the cathode ray tube. 1 is a degaussing circuit, 2 is a switch, 4 is a vertical deflection circuit, 7 is a vertical synchronization signal, 8 is a deflection control circuit, 9 is a control circuit, 10
is a control signal, 11 is a switch, 12, 13.14 is a variable resistor, 15 is an analog switch, 16 is a switch, 1
7 is and gate. Patent applicant: Mitsubishi Electric Corporation (2 others)

Claims (1)

[Claims] a degaussing circuit including a degaussing coil provided in the cathode ray tube; a deflection control circuit that controls the vertical deflection frequency of the cathode ray tube to a frequency according to a vertical synchronizing signal; and when the degaussing circuit operates, the vertical deflection frequency is set to the A degaussing device for a cathode ray tube, comprising: a control circuit for controlling the deflection control circuit so that the frequency is different from a frequency according to a vertical synchronization signal.