JPH0950242A - Suppression device for electric field radiation from cathode-ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the electric field radiation from the front surface of a cathode-ray tube to solve anxiety that the electric field radiation in a VDT imparts an inverse influence to human body. SOLUTION: The device suppressing the electric field radiation from cathode- ray tube is intends to cancel the radiation previously. In this device, after the beam current flowing into the high voltage winding of a fly-back transformer 12 is detected from the resistor R 6 connected to a current flow-in port in which a voltage is low and the change of the beam current is amplified in an inversion and amplifier 11, the electric field radiation from the tube 9 is canceled and suppressed by connecting the output of the inversion and amplifier 11 to the outer peripheral graphite part 8 of the tube 9 or the electrically conductive coating applied to the inner surface of the bezel positioning arround the tube 9 or a metallic part, and by combining the output and the tube 9 by utilizing the electric static capacitance existing between the outer peripheral graphite part 8 of the tube 9 or the electrically conductive coating applied to the inner surface of the bezel positioning arround the tube 9 or the metallic part and a high voltage electrode 10 being in the inner part of the tube 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for suppressing electric field radiation from a cathode ray tube.

[0002]

2. Description of the Related Art A display device using a cathode ray tube (VD
The electric field radiation in T), especially the electric field radiation of 5 Hz to 400 kHz, is a problem because it has a bad effect on the human body.

For example, according to the TCO standard (TCO1992) in Sweden, AEF (Alternating El
For ectric Field), Band I (20Hz ~ 2kHz) 1
It is regulated to be 0 V / m, Band Φ (2 kHz to 400 kHz) and 1 V / m or less.

Most of the electric field radiated from the VDT is caused by the retrace pulse of horizontal deflection, and the electric field due to this is
It has been found that it mainly occurs from the deflection yoke attached to the cathode ray tube.

The electric field resulting from such a horizontal deflection blanking pulse exists in a relatively high frequency region in the above-mentioned frequency range.

Further, the electric field radiated from the VDT is caused not only by the above-mentioned deflection pulse of the horizontal deflection circuit but also by the high voltage applied to the anode of the cathode ray tube changing in vertical synchronization. There are also things.

The electric field produced by the voltage that fluctuates in the vertical synchronization appears in the relatively low frequency region in the above-mentioned frequency range.

Radiation of such an electric field can be effectively shielded in a region other than the front surface of the cathode ray tube by a shield material made of a metal plate or the like.

[0009]

However, on the front surface of the cathode ray tube, the image has to be displayed visibly, so that the shield made of a metal plate or the like cannot be simply applied.

On the other hand, a transparent conductive film is disposed in front of the cathode ray tube or in front of the cathode ray tube in order to prevent the front surface of the cathode ray tube from being charged due to the high voltage applied thereto, thereby preventing dust in the air from adhering thereto. The transparent conductive film is formed on a transparent panel, and the transparent conductive film is grounded.

Such a transparent conductive film can be expected to have a certain shield effect against the electric field radiated from the front surface of the cathode ray tube.

However, high cost is required to form such a transparent conductive film.

Another problem is that the apparent focus is worsened.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a device capable of effectively suppressing the electric field radiated from the front surface of a cathode ray tube.

[0015]

The apparatus for suppressing the electric field radiation from the cathode ray tube according to the present invention is intended not to use the shield as described above but to cancel in advance so as not to radiate the radiation, and solves the above-mentioned technical problem. In order to detect the beam current flowing through the high voltage winding of the flyback transformer from the resistance connected to the low voltage inlet, the change in the beam current is inverted and amplified by an amplifier, and then the outer peripheral graphite part of the CRT, or Conductive coating applied to the inner surface of the bezel located around the cathode ray tube or connected to the metal part, and the outer peripheral graphite part of this cathode ray tube or the conductive coating applied to the inner surface of the bezel, or the high voltage electrode inside the metal part and the cathode ray tube By using the electrostatic capacity existing between and, the electric field radiation from the cathode ray tube is canceled and suppressed.

In the present invention, the beam current flowing through the high voltage winding of the flyback transformer is detected from the resistance connected to the low voltage inlet as the original signal for canceling the electric field radiation from the cathode ray tube. The first reason is that it is proportional to the beam current. Second, it is easy to handle because it is not a high voltage.

This method of utilizing the beam current is effective in canceling the electric field component in the relatively low frequency region in the above-mentioned frequency range.

On the other hand, the frequency component having high electric field radiation from the cathode ray tube exits the deflection yoke and the flyback transformer, and is generally a positive polarity pulse having a horizontal period.

The method of canceling this pulse is also effective in canceling the electric field component in the relatively high frequency region in the above-mentioned frequency range by adding and mixing in the inverting amplifier.

[0020]

FIG. 1 shows an embodiment of the present invention.

This embodiment is effective in canceling the electric field component in the comparatively low frequency region in the above-mentioned frequency range which is particularly difficult to cancel in the electric field radiated from the cathode ray tube.

A high voltage is applied to the anode 7 of the cathode ray tube 9 from the high voltage rectifying diode D2 of the flyback transformer 12.

The cathode of the high-voltage rectifying diode D2 has a high-voltage smoothing capacitor C2 and high-voltage bleeder resistors R3, R.
4 and R5 are connected.

The terminal 3 of R3 is a focus voltage extraction terminal for supplying a focus voltage to the cathode ray tube 9.

The terminal 4 of R4 is a screen voltage output terminal for supplying a screen voltage to the cathode ray tube 9.

R5 is a bleeder resistor for detecting the fluctuation of the high voltage of the anode 7, and the flyback transformer 12
Is fed back to the power supply regulator 13 of.

A DC voltage is supplied to the power supply regulator 13 from the power supply voltage input terminal 2.

From the power supply regulator 13, a voltage corresponding to the voltage detected by the resistor R5 is supplied to the primary winding of the flyback transformer 12.

The primary winding of the flyback transformer 12 is connected to the collector of the horizontal output transistor Q1, the damper diode D1 and the resonance capacitor C1.

A horizontal drive pulse is supplied to the base 1 of the horizontal output transistor Q1.

With the above configuration, the voltage of the anode 7 of the cathode ray tube 9 can be made constant. Since the primary winding voltage of the flyback transformer 12 and the high-voltage winding voltage are generally in a proportional relationship, the collector voltage (Vc-peak) of the horizontal output transistor Q1 is also substantially constant.

When a different deflection frequency is handled as in the multi-scan monitor, a DC voltage corresponding to the horizontal drive pulse frequency supplied to the base 1 is supplied from the power supply voltage input terminal 2 to the power supply regulator 13. There is a need. The DC voltage corresponding to the horizontal drive pulse frequency is generally produced by an FV (Frequency-Voltage) conversion circuit.

A resistor R6 is connected in series between the low potential side of the high voltage winding of the flyback transformer 12 and the DC power supply terminal 6.

Anode current of the cathode ray tube 9 (Beam current I
Since b) flows from the DC power supply terminal 6 through the resistor R6, the change in the anode current (Beam current Ib) can be known by detecting the voltage drop across the resistor R6.

D3 is a clamp diode for preventing the voltage drop of the resistor R6 from becoming lower than the ground voltage. C3 is a smoothing capacitor for removing high frequency noise.

The cathode voltage waveform of the diode D3 is shown in FIG.
It is shown in (a). The symbol V in the drawing indicates a vertical scanning period. In the figure, (b) shows the waveform in the horizontal scanning period.

The cathode voltage waveform of the diode D3 is taken out by the coupling capacitor C4, amplified by the signal inversion & amplifier 11, the direct current component is removed by the coupling capacitor C5, and the minimum value of the voltage waveform is regenerated to the ground potential by the clamp diode D5. After that, noise removal coil L1 and capacitor C
It is connected to the outer peripheral graphite part 8 of the cathode ray tube via 6. In addition, the cathode 8 is grounded by a resistor R8 from the outer peripheral graphite portion 8. This resistor R8 may use about several tens k to several hundreds kΩ.

Since the coil L1 and the capacitor C6 are filters for suppressing high-frequency unwanted radiation noise, they may of course be deleted if there is no problem with high-frequency unwanted radiation noise. If a high-pass filter having a cutoff frequency of the noise suppression filter is several tens MHz or more, the noise suppression filter can serve as a noise suppression filter without affecting the detection waveforms shown in FIGS. 2A and 2B.

The diodes D4 and D5 are for electrostatic breakdown protection for preventing signal inversion and element breakdown of the amplifier 11 during discharge of the cathode ray tube 9 in the tube.

If the output port of the signal inversion & amplifier 11 is set to have a low impedance, the above-mentioned direct current regeneration operation by the diode D5 can be effectively performed. Therefore, push-pull amplification should be used. Of course, SEPP, SRPP type push-pull amplification or a cascode amplifier with low impedance is naturally possible.

The resistor R7 is for discharging the coupling capacitor C5 during the direct current regeneration operation.

Although the embodiment of FIG. 1 shows a direct current regeneration type using the coupling capacitor C5, it is of course possible to operate in a direct coupling type as well. At this time, the coupling capacitor C5 and the resistor R are used.
7 is unnecessary.

Since the external graphite portion 8 of the cathode ray tube 9 is coupled with the high voltage electrode portion (the shadow mask and the high voltage electrode portion of the cone portion) inside the cathode ray tube 9 by the electrostatic capacity (thousands of pF), It can be driven from the external graphite part 8 by the output of the inverting & amplifier 11.

FIG. 3 shows the bezel 2 around the cathode ray tube 9.
0, the back cover 21, the tilt table 25, the main board 24 inside the cabinet, and the board 23 at the neck portion of the cathode ray tube 9.

In this embodiment, the outer peripheral graphite portion 8 of the cathode ray tube 9 is used.
Instead of applying and driving the output of the signal inversion & amplifier 11, the conductive coating applied to the inner surface of the bezel or the electrostatic capacity existing between the metal part and the high voltage electrode inside the cathode ray tube is used. It is explanatory drawing of combining by combining. In this case, when the coupling is coarse, the output of the signal inversion & amplifier 11 is large, and when the coupling is dense, the output of the signal inversion & amplifier 11 is small, and the same effect can be obtained. Naturally, the relative relationship of these structures can be designed because they are predetermined.

[0046]

According to the present invention, the beam current flowing through the high voltage winding of the flyback transformer is detected from the resistance connected to the low voltage inlet as an original signal for canceling the electric field radiation from the cathode ray tube. However, since the signal proportional to the beam current is used, the canceling effect is large.

Secondly, since the high voltage circuit is not controlled, the cost is low and the circuit can be easily handled.

The third effect is not only effective in canceling the electric field component in the relatively low frequency region in the above-mentioned frequency range, but also canceling the electric field component in the relatively high frequency region in the above-mentioned frequency range at the same time. It has an effect.

Fourthly, since the high voltage circuit is not controlled, there is little risk of destruction of the circuit element due to discharge within the cathode ray tube.

Fifth, since it is not necessary to form a transparent conductive film on the front surface of the cathode ray tube, it can be realized at a low cost, and has an excellent effect that there is no adverse effect such as apparent focus deterioration. Is.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram of an example of the present invention.

FIG. 3 is an explanatory view showing one embodiment of the present invention.

[Explanation of symbols]

Q1 ... Horizontal output transistor, 10 ... Internal high voltage electrode of cathode ray tube, D1 ... Damper diode,
11 ... Signal inversion & amplifier, D2 ... High-voltage rectifier diode, 12 ... Flyback transformer, 7 ... Anode electrode, 13 ... Power regulator, 8
... peripheral graphite part, R6 ... beam current detection resistor, 9 ... cathode ray tube, C4
C5 ... Coupling capacitor, C1 ... Resonance capacitor,
C2 ... Smoothing capacitor for high voltage.

Claims (2)

[Claims] 1. A beam current flowing through a high voltage winding of a flyback transformer is detected from a resistance connected to an inlet having a low voltage, and a change in the beam current is amplified by an inverting amplifier,
A device for suppressing electric field radiation from the cathode ray tube, which is connected to an outer peripheral graphite portion of the cathode ray tube and is coupled by utilizing an electrostatic capacitance existing between the outer peripheral graphite portion and a high voltage electrode inside the cathode ray tube. . 2. A beam current flowing through a high voltage winding of a flyback transformer is detected from a resistance connected to an inlet having a low voltage, and a change in the beam current is amplified by an inverting amplifier,
Conductive coating applied to the inner surface of the bezel located around the cathode ray tube, or connected to a metal part, and present between the metal part and the conductive coating applied to the inner surface of the bezel, or between the high voltage electrode inside the cathode ray tube. A device for suppressing electric field radiation from a cathode-ray tube, which is characterized in that coupling is performed by using capacitance.