JPH09325726A - Leakage electric field reducing device in crt display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce a leakage electric field from a CRT display device by constituting an anode lead with a main conductor and a subconductor and detecting the intensity of a radiated electric field based on a voltage signal to be induced on the subconductor. SOLUTION: The anode lead 21 of a flyback transformer is constituted of a coaxial shielded wire and the center conductor of the lead 21 is used as a main conductor for supplying the anode voltage of a CRT and the shielding conductor of it is used as a subconductor having a fixed static electric capacitance in between time main conductor and the subconductor and the subconductor of the anode lead is connected to the end part of the flyback transformer side. Then, an electric field level detecting circuit 13 detects a voltage signal to be induced on the subconductor of the lead 21 as the intesity of a rediated electric field due to the influence of the flyback transformer. Moreover, a canceling signal generating circuit 14 generates a signal for canceling the electric field rediated in the inside of a CRT display device in accordance with the voltage signal detected by the electric field level detecting circuit 13 to impress it on an electrode for caceling signal injection 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leakage electric field reduction device for reducing an electric field leaked to the outside in a CRT display device used for a display device of a computer or a TV receiver.

[0002]

2. Description of the Related Art Conventionally, users of CRT display devices,
Considering the effect on the health of workers nearby,
Measures are taken so that the intensity of electromagnetic waves leaked from the CRT does not exceed a certain standard.

The main sources of electromagnetic waves leaking from CRT display devices are deflection yokes and flyback transformers.
Various shields are provided to prevent the electromagnetic waves radiated from these components from leaking to the outside of the CRT display device. However, since the display surface of the CRT cannot be covered with a metal plate or the like, the leakage electric field from the display surface of the CRT becomes a problem.

As a method of reducing a leakage electric field in such a CRT display device, a transparent and highly conductive film (so-called AR panel) is attached to the display surface of the CRT, or a metal plate or an antenna lead is attached inside the bezel. Circulate,
A method of applying a pulse voltage of opposite polarity to the radiated electric field, or a method of connecting a large-capacity capacitor between the anode of the CRT and the ground to increase the electric field shielding effect of the aperture grill (shadow mask), etc. are adopted. It was being done. However, in these methods, an expensive and special CRT is used, or the entire CRT display device is complicated,
There was a problem that the cost increased as a whole. Therefore, JP-A-6-
In 289801, a circuit for generating a pulse voltage for canceling the electric field radiated from the high voltage generating circuit and the deflection circuit in the CRT display device and a circuit for superimposing a canceling pulse on the output voltage of the high voltage generating circuit are provided. A device has been proposed.

[0005]

However, in the above-mentioned Japanese Patent Laid-Open No. 6-289801, a pulse for canceling a radiation electric field is taken from a winding provided in a flyback transformer or a horizontal output transformer, and the phase thereof is adjusted. Since it is only superimposed on the output voltage of the high voltage generation circuit,
There is a problem that the cancellation of the radiated electric field does not work well for the following reasons.

For example, if the luminance of the display screen changes, the anode current changes accordingly. In the case where the anode voltage stabilizing circuit is provided, a pulse generated on the secondary side of the flyback transformer according to the change in luminance. The peak value of the pulse changes, and the voltage / current of the pulse generated on the secondary side of the flyback transformer fluctuates due to these interactions. For example, since the anode voltage generation circuit using a flyback transformer has peak rectification, it is well smoothed at low brightness and the horizontal scanning frequency ripple included in the anode voltage is small, but at high brightness, the anode current becomes large, resulting in smoothness. Of the horizontal scanning frequency included in the anode voltage increases. Therefore, for example, if an image like vertical stripes is displayed, a change in ripple occurs during horizontal scanning, and if an image like horizontal stripes is displayed, the amount of the ripple changes with vertical scanning, Further, for example, when a blinking image or the like is displayed, the amount of the ripple varies according to the blinking. For this reason,
The pulsed voltage (hereinafter referred to as “FBT pulse”) superimposed on the anode voltage changes according to the display content of the screen and the brightness change, and the radiated electric field changes due to the influence of the flyback transformer. Further, the pulse voltage applied to the deflection yoke for deflection (hereinafter referred to as "DY pulse") is not always constant, but changes due to the action of the distortion correction circuit, for example. Therefore, the intensity of the electric field radiated from the deflection yoke or the conductor capacitively coupled to the deflection yoke changes.

Therefore, the radiation electric field cancels well if the radiation electric field canceling pulse is taken from the winding provided in the flyback transformer or the horizontal output transformer and the phase thereof is adjusted so as to be superimposed on the output voltage of the high voltage generating circuit. However, a leakage electric field will be generated.

An object of the present invention is to provide a leakage electric field reducing device in a CRT display device capable of appropriately reducing the leakage electric field even in response to changes in brightness without using a special and expensive CRT. .

[0009]

The present invention provides a CRT display device in which a high voltage generated by a flyback transformer is applied to the anode of a CRT through the anode lead, and the anode lead is provided as described in claim 1. A main conductor that supplies an anode voltage and a sub-conductor that causes a constant electrostatic capacitance between the main conductor and the main conductor, and detects a radiation electric field strength based on a voltage signal induced in the sub-conductor, A means for generating a signal for canceling the radiated electric field and applying it to an electrode provided at a predetermined location of the CRT is provided.

As described above, the anode lead for guiding the high voltage generated by the flyback transformer to the anode of the CRT is provided between the main conductor supplying the anode voltage and this main conductor, such as a coaxial shield wire. Since it is composed of a sub-conductor that produces a certain capacitance, a signal corresponding to a change in the anode voltage is induced in this sub-conductor. As described above, the anode voltage includes ripples, and the FBT pulse and the DY pulse are superposed by the jump, so that the intensity of the electric field radiated by these is detected from the sub conductor. Therefore, even if there is a change in the brightness of the screen, the intensity of the radiated electric field to be canceled is detected accordingly, and the electric field leaked from the CRT display device is always effectively reduced.

According to a second aspect of the present invention, the anode lead is composed of a main conductor for supplying an anode voltage and a sub-conductor for producing a constant electrostatic capacitance between the main conductor. , An electrode is arranged at a predetermined position of the CRT, and the radiant electric field strength is detected based on the voltage signal induced in the electrode,
Means for generating a signal for canceling the radiated electric field and applying it to the sub conductor of the anode lead is provided.

Since the radiation electric field intensity is detected based on the voltage signal induced in the electrode arranged at the predetermined location of the CRT as described above, the radiation electric field intensity which fluctuates according to the change in the brightness of the screen is detected, and further, , The anode lead is composed of a main conductor and a sub-conductor that produces a certain capacitance between the main conductor, such as a shield wire, and a signal for canceling the radiated electric field is applied to the sub-conductor of the anode lead. By doing so, it is not necessary to provide a circuit for injecting a signal for canceling the radiation electric field in the circuit for generating the anode voltage in the flyback transformer, and it is possible to configure at a low cost with a simple structure.

[0013]

1 is a block diagram showing the configuration of a leakage electric field reducing device in a CRT display device according to a first embodiment of the present invention.
This will be described below with reference to FIGS.

FIG. 1 is a block diagram showing the configuration of the entire CRT display device. In FIG. 1, an inner graphite film 3 and an aperture grill (shadow mask) are provided on the inner surface of the CRT 1.
4 is provided, and an exterior graphite film is provided on the surface.
A deflection yoke 6 is attached to the neck portion of the CRT 1,
The offset signal injection electrode 5 is provided between the deflection yoke 6 and the CRT 1. The high voltage generation circuit 10 of FIG. 1 is composed of a flyback transformer or the like, and supplies a high voltage to the anode 2 of the CRT 1 via the anode lead 21. The deflection circuit 11 applies a deflection pulse voltage to the deflection yoke 6. The video circuit 12 gives a video signal to the cathode of the CRT 1. The electric field level detection circuit 13 detects the voltage signal induced in the shield conductor (sub conductor) of the anode lead 21 as the radiated electric field strength due to the influence of the flyback transformer. The cancellation signal generation circuit 14 is an electric field level detection circuit 13
In accordance with the voltage signal detected by, the canceling signal for canceling the electric field radiated inside the CRT display device is generated, and this is applied to the canceling signal injecting electrode 5.

FIG. 2 is a perspective view showing the structure of the flyback transformer and the anode lead. As shown in FIG. 2, the anode lead 21 of the flyback transformer 20 is composed of a coaxial shield wire, and its center conductor is a CRT. It is used as a main conductor for supplying an anode voltage, the shield conductor is used as a sub conductor having a constant capacitance with the main conductor, and the anode sub conductor lead 22 is connected to the end portion on the flyback transformer side. are doing.

FIG. 3 is a circuit diagram showing configurations of the high voltage generating circuit, the deflection circuit, the electric field level detecting circuit and the canceling signal generating circuit shown in FIG. In FIG. 3, the transistor Q1
By driving the current in the primary winding of the flyback transformer 20, a high voltage is generated from the secondary winding of the flyback transformer 20, and this is applied to the anode of the CRT via the anode lead 21. This anode voltage is smoothed by the capacitance between the internal graphite film and the external graphite film of the CRT and the smoothing capacitor provided in the flyback transformer 20. One of the secondary side outputs of the flyback transformer 20 is connected to an ABL circuit (auto brightness limiter circuit). Also, in FIG.
Is a horizontal output transformer, to the primary side of which a drive transistor Q2, a damper diode Dd, a deflection yoke 6 and resonance capacitors Ct and Cs are connected. A capacitor C1 is connected between the anode sub-conductor lead 24 drawn from the shield conductor 23 of the anode lead 21 and the ground, and the amplifier circuit A1 is arranged between the center conductor 22 of the anode lead 21 and the shield conductor 23. The voltage signal divided by the generated capacitance and the capacitor C1 is input. Since the DY pulse is superimposed on the anode voltage of the CRT due to the jump from the deflection yoke, the amplifier circuit A1 inverts and amplifies the signal corresponding to the change in the anode voltage on which the DY pulse is superimposed. An amplifier circuit A2 is connected to the secondary side of the horizontal output transformer 25.
Amplifies a voltage signal substantially equal to the signal applied to the deflection yoke. The amplifier circuit A3 synthesizes the output voltages of the amplifier circuits A1 and A2 and supplies a canceling signal to the canceling signal injection electrode. The gains of the amplifier circuits A1, A2, A3 are set according to the ratio of the radiated electric field due to the influence of the flyback transformer and the radiated electric field due to the influence of the deflection yoke, and the level of the conductivity of the CRT surface. As a result, the radiation electric field due to the influence of the flyback transformer and the radiation electric field due to the influence of the deflection yoke are effectively canceled by the cancellation signal injected into the cancellation signal injection electrode, and the leakage electric field from the CRT display device is reduced.

FIG. 4A is an equivalent circuit diagram of a leakage electric field reducing device including a CRT. (B) is a diagram showing a correspondence relationship between each capacitor and resistor shown in (A) and each part of the CRT. Further, (C) is a perspective view showing a configuration of an offset signal injection electrode. In the figure, C _DY is the capacitance between the deflection yoke and the offset signal injection electrode, Cc is the capacitance between the offset signal injection electrode and the internal graphite film of the CRT, and Ri is the CRT.
It is the internal graphite film resistance of. Further, C _FBT and R _FBT are circuits of capacitors and resistors by a flyback transformer, Cg is a capacitance between the exterior graphite film of the CRT and the interior graphite film, and Rg is an exterior graphite film resistance of the CRT. Also, Cp
Is a CRT aperture grill (shadow mask) and C
Capacitance with the RT surface, Rp is the surface resistance of the CRT. The DY pulse is injected through the electrostatic capacity C _DY , and the FBT pulse is injected into the resistor Ri. C _A is the electrostatic capacitance between the center conductor and the shield conductor of the anode lead, and C 1 is the same capacitor as that of C 1 shown in FIG. 3, which is provided between the shield conductor of the anode lead and the ground. Here, the amplifier circuit A1 is represented as an inverting amplifier circuit by an open amplifier in which a reference voltage is input to the non-inverting input terminal. The amplifier circuits A2 and A3 are the same as those shown in FIG. 3, and the cancellation signal output from the amplifier circuit A3 is injected between the electrostatic capacitances C _DY and Cc. The cancellation signal output from the amplifier circuit A3 cancels the DY pulse and the FBT pulse, and suppresses the leakage electric field due to these. As shown in (C) of the figure, the canceling signal injecting electrode 5 is provided with radial slits in order to prevent the generation of eddy currents.

Although the canceling signal injection electrode is provided between the deflection yoke and the CRT in the above-described embodiment, the canceling signal injection electrode is provided in the peripheral portion (frame portion) of the CRT 1 as shown in FIG. 5, for example. 7 may be provided and a cancellation signal may be applied to this.

Next, FIG. 6 shows a circuit diagram of the leakage electric field reducing device in the CRT display device according to the second embodiment. In the first embodiment, the cancel signal injection electrode is provided on the CRT side, and the cancel signal is applied to the electrode. However, in the second embodiment, the circuit for generating the anode voltage in the flyback transformer is used. The cancellation signal is superimposed on. That is,
In FIG. 6, a smoothing high voltage capacitor Ch and a discharge resistor Rh are provided inside the flyback transformer 20, and a canceling signal output from the amplifier circuit A3 is applied via the capacitor C2. Other configurations are the same as those shown in FIG. By thus applying the canceling signal to the circuit that generates the anode voltage in the flyback transformer, the canceling signal is superimposed on the anode of the CRT, and the radiation electric field due to the FBT pulse and the DY pulse is canceled.

Next, C according to the third embodiment of the present invention.
FIG. 7 is a circuit diagram of the leakage electric field reducing device in the RT display device.
Shown in In each of the above-described embodiments, the anode lead is used for detecting the radiation electric field intensity, but in the third embodiment, conversely, the anode lead is used for injecting the canceling signal. That is, in FIG. 7, the leakage electric field detection electrode is, for example, the same as that shown by 5 in FIG.
It should be provided between T1 and the deflection yoke 6, or 7 in FIG.
It is provided around the CRT 1 in the same manner as the one shown in. The amplifier circuit A1 inverts and amplifies the voltage induced in the leakage electric field detection electrode. The configuration of the horizontal deflection circuit portion is similar to that shown in FIG. 3, and the amplification circuit A2 amplifies a voltage signal substantially equal to the signal applied to the deflection yoke. The amplifier circuit A3 combines the output voltages of the amplifier circuits A1 and A2 and applies the combined output voltage to the shield conductor 23 of the anode lead 21 via the anode sub-conductor lead 24. In this case, unlike the case shown in FIG. 3, the capacitance between the center conductor 22 and the shield conductor 23 of the anode lead is smaller than the capacitance of the smoothing capacitor in the flyback transformer, and the capacitor voltage division ratio is The cancellation signal requires a high voltage because it is small. In this way, the cancellation signal is superimposed on the anode voltage for the CRT, and the leakage electric field due to the FBT pulse and the DY pulse is canceled.

[0021]

According to the first aspect of the invention, the anode lead for guiding the high voltage generated by the flyback transformer to the anode of the CRT is supplied with the anode voltage like a coaxial shield wire. It consists of a main conductor and a sub conductor that creates a certain amount of capacitance between the main conductor and the radiation field strength is detected based on the voltage signal induced in this sub conductor. Even if there is a change or the like, the intensity of the radiated electric field to be canceled out is detected accordingly, and the electric field leaked from the CRT display device is always effectively reduced.

According to the second aspect of the present invention, the radiation electric field intensity is detected based on the voltage signal induced in the electrode arranged at a predetermined position of the CRT. The radiant electric field intensity is detected, and
The anode lead is composed of a main conductor and a sub-conductor that causes a certain capacitance between the main conductor, such as a shield wire, and a signal that cancels the radiated electric field is applied to the sub-conductor of the anode lead. Therefore, it is not necessary to provide a circuit for injecting the signal for canceling the radiation electric field in the circuit for generating the anode voltage in the flyback transformer, and the simple structure can be realized at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram of an entire CRT display device.

FIG. 2 is a perspective view showing a configuration of a flyback transformer and an anode lead.

FIG. 3 is a circuit diagram of a leakage electric field reducing device.

4A and 4B are diagrams showing an equivalent circuit of a leakage electric field reducing device including a CRT, in which FIG. 4A is an equivalent circuit diagram thereof, and FIG. 4B is a diagram showing a relationship between each element in FIG.
(C) is a figure which shows the structure of the cancellation signal injection electrode.

FIG. 5 is a diagram showing another configuration example of the cancellation signal injection electrode.

FIG. 6 is a circuit diagram of a leakage electric field reducing device according to a second embodiment.

FIG. 7 is a circuit diagram of a leakage electric field reducing device according to a third embodiment.

[Description of Reference Signs] 1-CRT 2-Anode 3-Interior graphite film 4-Aperture grill (shadow mask) 5,7-Cancellation signal injection electrode 6-Deflection yoke 20-Flyback transformer 21-Anode lead 22-Center conductor 23-Shield conductor 24-Anode sub-conductor lead 25-Horizontal output transformer

Claims (2)

[Claims] 1. In a CRT display device in which a high voltage generated by a flyback transformer is applied to an anode of a CRT through an anode lead, the anode lead is provided between a main conductor feeding the anode voltage and the main conductor. A sub-conductor that produces a certain capacitance, detects the radiant electric field strength based on the voltage signal induced in the sub-conductor, and generates a signal that cancels the radiated electric field to generate a signal at a predetermined location on the CRT. A leakage electric field reducing device in a CRT display device, comprising means for applying to the provided electrode. 2. In a CRT display device in which a high voltage generated by a flyback transformer is applied to an anode of a CRT through an anode lead, the anode lead is provided between a main conductor feeding the anode voltage and the main conductor. A signal that is composed of a sub-conductor that produces a certain capacitance, an electrode is arranged at a predetermined location of the CRT, the radiation electric field strength is detected based on the voltage signal induced in the electrode, and the radiation electric field is canceled. A leakage electric field reducing device in a CRT display device comprising means for generating and applying to the sub-conductor of the anode lead.