JPH04330894A - Degaussing method - Google Patents

Abstract

PURPOSE:To degauss with low cost and in a short time by using the commercial alternating current power signal of the prescribed frequency for a degaussing action and changing a vertical synchronizing signal to the frequency sufficiently away from the frequency of the commercial alternating current power signal during the degaussing action. CONSTITUTION:The title method is the degaussing method of an image display to perform the scanning in correspondence to horizontal and vertical synchronizing signals and display an image, and a multi television signal generating circuit 33, when the start of the degaussing action is commanded, changes the vertical scanning number supplied through a terminal 22 to a television set circuit 23 to the frequency different from the frequency of an AC power 11. Next, it is awaited that the television set circuit 23 is synchronized to the changed vertical synchronizing signal, when the synchronizing locking is performed, a switch 32 is turned on, and an outside-fitted posistor 31 is connected through a terminal 21 to a degaussing coil 13. Thus, the degaussing current flows through the channel of the degaussing coil 13, the posistor 31, the switch 32 and the AC power 11 from the AC power 11. Then, the dispersion occurrence of the degaussing effect is suppressed and the waiting time is minimized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degaussing method suitable for use in degaussing image display devices such as television receivers.

0002

2. Description of the Related Art As shown in FIG. 3, an electron beam is influenced by the earth's magnetism and may misland on a phosphor 1 at a different position. When this mislanding occurs, color unevenness occurs. To prevent this, television receivers and the like have a built-in degaussing circuit as shown in FIG.

That is, when the AC power supply 11 is turned on, a signal of the power supply frequency is caused to flow to the degauss coil 13 via the POSISTOR 12. POSISTOR 12 has a relatively low resistance before current flows, and therefore a large level of current flows. However, as time passes and heat is generated, the resistance value gradually increases. As a result, the value of the current flowing therethrough is limited. In this way, for example, as shown in FIG. 5, a sinusoidal attenuation current whose envelope gradually attenuates flows through the degauss coil 13. This allows CRT
Magnetic transfer is performed on the internal and external metal covers (magnetic shields) and shadow masks (aperture grilles) that cancel out the earth's magnetic field.

[0004] The frequency of this AC power supply 11 is 50Hz in the Kanto area and 60H in the Kansai area.
z, which almost matches the vertical scanning frequency in the PAL system or the NTSC system, respectively. Therefore, the vertical scanning magnetic field from the deflection yoke of the television receiver and the magnetic field from the degauss coil 13 may resonate, causing variations in the demagnetization effect.

[0005] In order to prevent this, conventionally, for example, the following method has been adopted.

The first method is to use a frequency conversion AC-AC converter that can set a frequency different from the vertical scanning frequency as an AC power source for the digauss.

[0007] The second method is to turn off the power to the television receiver in advance when degaussing is performed externally.

[0008]

[Problems to be Solved by the Invention] However, in order to realize a device with a capacity that can withstand the inrush current at the start of the degaussing operation, this first method requires a very expensive frequency conversion AC-AC converter. There is an issue that could lead to this.

Furthermore, in the second method, once the power is turned off, even if the power is turned on again, it takes several seconds for the image to stably emit light, which increases the idle waiting time on the production line. There was an issue where productivity decreased.

[0010] The present invention has been made in view of the above situation, and it is an object of the present invention to enable a demagnetizing operation to be performed at low cost and in a short time.

[0011]

[Means for Solving the Problems] The degaussing method of the present invention is a method for degaussing an image display device that displays an image by scanning in response to horizontal and vertical synchronizing signals, and in which a commercial AC power supply signal of a predetermined frequency is used. is used for the degaussing operation, and during the degaussing operation, the vertical synchronization signal is changed to a different frequency sufficiently distant from the frequency of the commercial AC power signal.

0012

[Operation] In the degaussing method with the above configuration, during the degaussing operation,
The frequency of the vertical synchronization signal is set to a value different from the frequency of the commercial AC power signal. Therefore, the occurrence of variations in the demagnetizing effect is prevented.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a block diagram showing the structure of an embodiment of a degaussing apparatus using the degaussing method of the present invention, and parts corresponding to those in FIG. 4 are given the same reference numerals. In addition to the digauss coil 13 and the posister 12, a television set circuit 23 including horizontal and vertical deflection circuits is built into the main body of the television receiver. This main body is provided with a terminal 21, and an external POSISTOR 31 is connected to a switch 32.
It can be connected in parallel with the built-in POSISTOR 12 via the POSISTOR 12. Also, from the terminal 22 to the television set circuit 23
A predetermined external synchronization signal can be supplied to the

On the degaussing device side, a multi-television signal generation circuit 33 is provided, and is configured to supply a predetermined synchronizing signal to the television set circuit 23 in the television receiver via the terminal 22. Further, the multi-TV signal generation circuit 33 is adapted to control the operation of the switch 32.

Next, the operation will be explained with reference to the flowchart shown in FIG. When the multi-television signal generation circuit 33 receives a command to start the degaussing operation, it converts the vertical scanning frequency supplied to the television set circuit 23 via the terminal 22 into an AC
Change the frequency to a frequency different from that of the power source 11. That is, N
In the case of the TSC system, the frequency is changed from 60 Hz, and in the case of the PAL system, the frequency is changed to a sufficiently distant frequency from 50 Hz (step S1). Next, it waits for the television set circuit 23 to synchronize with the changed vertical synchronization signal (step S2).

When the vertical synchronizing signal of the television set circuit 23 is locked to the changed vertical synchronizing signal, the switch 3
2 is turned on, and the external POSISTOR 31 is connected to the digauss coil 13 via the terminal 21 (step S3). As a result, a degaussing current flows through the path from the AC power source 11 to the degauss coil 13, the POSISTOR 31, the switch 32, and the AC power source 11.

This posister 31 has almost the same characteristics as the posister 12 built into the television receiver. Therefore, as in the case described above, immediately after the start of demagnetization, a relatively large level of current flows through the POSISTOR 31 having a small resistance value, but as the resistance value increases over time, the current value flowing through the POSISTOR 31 is limited. Ru. As a result, a degaussing current as shown in FIG. 5 flows through the degauss coil 13.

Then, the process waits until the current flowing through the degauss coil 13 (POSISTOR 31) becomes almost zero (step S4). When the equilibrium point temperature is reached and the current flowing through the POSISTOR 31 becomes almost zero, the demagnetization operation is completed. Therefore, the multi-TV signal generation circuit 33 connects the TV set circuit 2 to the TV set circuit 2 via the terminal 22 at a timing when a predetermined time has elapsed after the start of the degaussing operation (at a timing when the time when the current flowing through the POSISTOR 31 becomes almost 0 has elapsed). The frequency of the vertical synchronizing signal supplied to the NTSC or PAL system is set to the original frequency of the NTSC system or PAL system (step S5). Furthermore, a period of time is waited until the signal of the television set circuit 23 is phase-locked to the changed vertical synchronization signal, and when that period of time has elapsed, the degaussing operation is ended (step S6).

[0019]

[Effects of the Invention] As described above, according to the demagnetization method of the present invention,
The frequency of the vertical synchronization signal during degaussing is changed to a value different from the frequency of the commercial AC power signal.
Variations in the demagnetizing effect are suppressed. Furthermore, the cost is lower than when using an AC-AC frequency conversion power source. Furthermore, the waiting time is reduced compared to the method of turning off the television receiver during the degaussing period.
It becomes possible to increase the productivity of the line.

[Brief explanation of drawings]

FIG. 1 is a flowchart explaining the operation of the embodiment shown in FIG.

FIG. 2 is a block diagram showing the configuration of an embodiment of a degaussing device to which the degaussing method of the present invention is applied.

[Figure 3] Diagram explaining the influence of the earth's magnetism on electron beams

[
Figure 4: Block diagram showing the configuration of an example of a degaussing device built into a television receiver

[Figure 5] Diagram showing the waveform of the degaussing current in Figure 4

[Explanation of symbols]

11 AC power supply 12 Posistor 13 Digauss coil 23 TV set circuit 31 External Posistor 32 Switch 33 Multi TV signal generation circuit

Claims (1)

[Claims] 1. A degaussing method for an image display device that displays an image by scanning in response to horizontal and vertical synchronizing signals, the method comprising: using a commercial AC power signal of a predetermined frequency for the degaussing operation; A degaussing method characterized in that the vertical synchronization signal is changed to a frequency sufficiently distant from the frequency of the commercial AC power signal.