JPH09154029A - Ac electric field radiation suppressing device for cathode-ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease AC electric field radiated from the front face of fluorescent face. SOLUTION: A coil L1 wound around the secondary side of flyback transformer 13 detects a pulse, which is generated during the flyback period of horizontally deflected current let flow to a deflecting yoke 11, and outputs the detected pulse. In response to the detected pulse, the cancel voltage of polarity inverse to that of synthetic ripple is outputted by a cancel voltage generating circuit 20 connected to the coil L1 . A capacitor C4 inserted between the cancel voltage generating circuit 20 and a high tension line 15 injects the cancel voltage to the high tension line 15 so that the synthetic ripple superimposed on a high DC voltage on the high tension line 15 can be canceled.

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 alternating electric field radiation from a cathode ray tube.

[0002]

BACKGROUND OF THE INVENTION As is well known, cathode ray tubes (CRTs) are
Generally, it is also called a cathode ray tube after the inventor's name.
A cathode ray tube is a display device which has the widest application in various fields such as a television receiver, an oscilloscope and radar observation. The cathode ray tube is basically for displaying information by applying an electron beam emitted from an electron gun to a phosphor to emit light.

Explaining in a little detail, the cathode ray tube comprises a vacuum vessel, an electron gun, a deflection system, and a fluorescent screen. The vacuum vessel is made of a glass valve having a high X-ray absorption rate.
The electron gun forms, accelerates and focuses an electron beam to form a spot on the fluorescent screen and modulates the amount of the electron beam according to an input signal. The deflection system deflects the electron beam and draws a television screen (raster) or an observed waveform on the phosphor screen. The deflection system includes electromagnetic deflection that deflects by a magnetic field generated by flowing a sawtooth current through a deflection yoke (which changes the direction of an electron beam by a magnetic field generated by causing a current to flow in a coil) and electrostatic deflection that deflects by static electricity. is there. Electromagnetic deflection is used in a cathode ray tube of a TV receiver or the like, and a sawtooth current is passed through two sets of horizontal and vertical deflection yokes (deflection coils) to scan the screen. The phosphor screen emits light according to the intensity of the incident electron beam to display a visible image.

The fluorescent screen is defined by an electrode (anode), and this electrode (anode) has an anode voltage (high DC) of about 20 kV obtained by a high voltage power supply circuit called a horizontal output circuit.
Voltage) is applied. Deflection includes horizontal deflection and vertical deflection corresponding to horizontal scanning and vertical scanning, respectively. A circuit for supplying a sawtooth current (horizontal deflection current, vertical deflection current) necessary for the corresponding deflection yoke is provided with a horizontal deflection circuit and a vertical deflection circuit, respectively. It is called a deflection circuit. The horizontal output circuit outputs an anode voltage by using a pulse generated in a blanking period of a horizontal deflection current in the horizontal deflection circuit. That is, the horizontal output circuit boosts the pulse with a horizontal output transformer called a flyback transformer (FBT), rectifies the high voltage by a rectifier circuit, and applies a high DC voltage to an electrode (anode) through a high voltage line. To do. Rectifier circuits generally consist of diodes and smoothing capacitors. Further, this electrode (anode) is capacitively coupled to the deflection yoke via a parasitic capacitance and is also grounded via another capacitor.

[0005]

By the way, such a cathode ray tube (CRT) emits an alternating electric field from the front surface of its fluorescent screen. This radiated electric field is said to cause various health problems. For example, in Sweden and the United States, it has been reported that this alternating electric field radiation particularly adversely affects pregnant women. Therefore, it is desired to suppress this alternating electric field radiation.

Therefore, an object of the present invention is to provide a device for suppressing alternating electric field radiation from a cathode ray tube in view of the above-mentioned conventional problems.

[0007]

It is believed that the alternating electric field radiation is caused by the ripple superimposed on the high DC voltage (anode voltage). This ripple consists of two components. That is, the main component (first component) is a high-voltage ripple caused by capacitive coupling of parasitic capacitance between the electrode and the deflection yoke, and the second component is a sawtooth waveform caused by charging / discharging of the smoothing capacitor included in the rectifier circuit. Is the rectification ripple of.

Therefore, the present inventor can reduce the ripple by canceling the ripple superimposed on the high DC voltage on the high voltage line, thereby reducing the alternating electric field radiation radiated to the front surface of the phosphor screen. I thought I could do it.

That is, according to the present invention, the electron beam emitted from the electron gun is electromagnetically deflected by the deflection yoke and projected on the fluorescent screen to form an image on the fluorescent screen. Is a device for suppressing the alternating electric field radiation, and a high DC voltage is applied to the electrode that defines the phosphor screen from the flyback transformer through the rectifier circuit and the high voltage line, and is superimposed on the high DC voltage on the high voltage line. In a device that suppresses alternating electric field radiation radiated to the front surface of the phosphor screen by the generated ripple, a detection unit that detects a pulse generated during a blanking period of a horizontal deflection current flowing in a deflection yoke and outputs a detection pulse, A cancel voltage generation circuit that generates a cancel voltage of the opposite polarity to the ripple in response to the detection pulse, and injects the cancel voltage into the high voltage line. And a capacitor, a cathode ray tube for alternating electric field radiation suppression device, characterized in that to cancel the ripple superimposed on the high DC voltage on the high-pressure line is obtained by canceling voltage.

According to the first aspect of the present invention, the cancel voltage generating circuit reverses the polarity of the detection pulse and outputs a reverse pulse, and the polarity inverting circuit adjusts the amplitude of the reverse pulse to adjust the amplitude. The amplitude adjusting circuit outputs an adjusted inverted pulse, and the capacitor injects the amplitude adjusted inverted pulse into the high voltage line as a cancel pulse.

According to a second aspect of the present invention, the cancel voltage generating circuit responds to the detection pulse by generating a sawtooth wave having a polarity opposite to that of the rectification ripple.
The amplitude adjusting circuit adjusts the amplitude of the sawtooth wave and outputs the sawtooth wave with the adjusted amplitude. The capacitor injects the sawtooth wave with the adjusted amplitude as a canceling sawtooth wave into the high voltage line.

Further, according to the third aspect of the present invention, the cancel voltage generating circuit inverts the polarity of the detection pulse to output an inversion pulse, and adjusts the amplitude of the inversion pulse. , A first amplitude adjusting circuit that outputs an amplitude-adjusted inverted pulse, a sawtooth wave creating circuit that creates a sawtooth wave having a polarity opposite to that of the rectification ripple in response to the detection pulse, and an amplitude of the sawtooth wave are adjusted, The second which outputs the sawtooth wave whose amplitude is adjusted
And an amplitude adjusting circuit, and a waveform synthesizing circuit for synthesizing the amplitude-adjusted inverted pulse and the amplitude-adjusted sawtooth wave and outputting the cancel voltage.

The detecting means may be a coil wound around the secondary side of the flyback transformer.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Referring to FIG. 1, a cathode ray tube (CRT) to which the apparatus for suppressing alternating electric field radiation according to the first embodiment of the present invention is applied has an electron beam (not shown) emitted from an electron gun (not shown). (1) is electromagnetically deflected by the deflection yoke 11 and projected onto the phosphor screen 12 to draw an image on the phosphor screen 12. The alternating electric field radiation suppressing device according to the present embodiment is a device for suppressing alternating electric field radiation from the cathode ray tube.

An electrode (anode) 12a defining the phosphor screen 12
A high DC of about 20 kV from a flyback transformer (FBT) 13 via a rectifier circuit 14 and a high voltage line 15.
Voltage (anode voltage) is applied. The flyback transformer 13 boosts a pulse generated during a blanking period of a horizontal deflection current in a horizontal deflection circuit (not shown). Electrode 12
a and the deflection yoke 11 are capacitively coupled via a parasitic capacitance C ₁ of several tens pF. In addition, the electrode 12a is about 200
0 pF or 1000-2000 pF capacitor C ₂
Grounded. Rectifier circuit 14 is a diode D
And a smoothing capacitor C ₃ of about several thousand pF.

As described above, the high D on the high pressure line 15
A ripple is superimposed on the C voltage (anode voltage). This ripple is composed of a high ripple (main component) caused by capacitive coupling of the parasitic capacitance C ₁ and a sawtooth rectification ripple (second component) caused by charging / discharging of the smoothing capacitor C ₃ which is a synthetic ripple. . This alternating electric field radiation suppressor
This is a device that suppresses the alternating electric field radiation radiated to the front surface of the phosphor screen 12 by the synthetic ripple.

The alternating electric field radiation suppressing apparatus shown in the figure has a coil L ₁ wound around the secondary side of the flyback transformer 13 and a cancel voltage generating circuit 20 connected to this coil L _1.
And the cancel voltage output circuit 20 and the high voltage line 15
And a capacitor C ₄ inserted between and. The coil L _{1 functions} as a detection unit that detects a pulse generated during the blanking period of the horizontal deflection current flowing through the deflection yoke 11 and outputs a detection pulse. The cancel voltage generation circuit 20
In response to this detection pulse, a cancel voltage having a polarity opposite to that of the synthetic ripple is generated. The capacitor C ₄ injects this cancel voltage into the high voltage line 15. That is, the alternating electric field radiation suppressor cancels the combined ripple superimposed on the high DC voltage on the high voltage line 15 by this cancel voltage.

FIG. 2 shows the signal waveform of each part in FIG. The configuration and operation of the cancel voltage output circuit 20 will be described below with reference to FIGS. 1 and 2. The cancel voltage generating circuit 20 includes a polarity reversing circuit 21 and a sawtooth wave creating circuit 22 connected to the coil L ₁ , and first and second amplitude adjusting circuits connected to the polarity reversing circuit 21 and the sawtooth wave creating circuit 22, respectively. 23 and 24, and a waveform synthesizing circuit 25 connected to the amplitude adjusting circuits 23 and 24.

The polarity reversing circuit 21 and the sawtooth wave generating circuit 22
A detection pulse a as shown in FIG. 2A is supplied from the coil L ₁ . This detection pulse a has the same shape as the high voltage ripple caused by the capacitive coupling of the coupling capacitor C ₁ . The polarity inversion circuit 21 inverts the polarity of the detection pulse a and outputs an inversion pulse. Sawtooth wave creation circuit 22
Produces a sawtooth wave having a polarity opposite to that of the rectification ripple in response to the detection pulse a. The first amplitude adjusting circuit 23 adjusts the amplitude of the inversion pulse and outputs the amplitude-adjusted inversion pulse b as shown in FIG. On the other hand, the second amplitude adjusting circuit 24 adjusts the amplitude of the sawtooth wave as shown in FIG. The sawtooth wave c whose amplitude is adjusted is output. The waveform synthesizing circuit 25 synthesizes the amplitude-adjusted inverted pulse b and the amplitude-adjusted sawtooth wave c, and outputs a cancel voltage d as shown in FIG. The cancel voltage d is injected into the high voltage line 15 via the capacitor C _4, and the cancel ripple d cancels the composite ripple superimposed on the high voltage line 15.

The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and variations can be made without departing from the spirit of the present invention. For example, when the rectification ripple (second component) can be ignored, the sawtooth wave creating circuit 22, the second amplitude adjusting circuit 24, and the waveform synthesizing circuit 25 in the cancel voltage generating circuit 20 are deleted, and as shown in FIG. In addition, the cancel voltage generation circuit 20A may be composed only of the polarity inversion circuit 21 and the amplitude adjustment circuit 23. On the contrary, when the high voltage ripple (main component) can be ignored, the polarity reversing circuit 21, the first amplitude adjusting circuit 23, and the waveform synthesizing circuit 25 in the cancel voltage generating circuit 20 are deleted and shown in FIG. As described above, the cancel voltage generating circuit 20B may be configured by only the sawtooth wave creating circuit 22 and the amplitude adjusting circuit 24.

[0022]

As is apparent from the above description, according to the present invention, the detecting means for detecting the pulse generated during the blanking period of the horizontal deflection current flowing through the deflection yoke and outputting the detection pulse, and the detecting means. By adding a cancel voltage generating circuit that generates a cancel voltage having a polarity opposite to that of the ripple in response to the pulse and a capacitor that injects the cancel voltage to the high voltage line, it is superimposed on the high DC voltage on the high voltage line. The ripples can be canceled (suppressed), and the alternating electric field radiation emitted from the front surface of the phosphor screen can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a cathode ray tube (CRT) including an alternating electric field radiation suppressor according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing waveforms of respective parts of the alternating electric field radiation suppressing device shown in FIG.

FIG. 3 is a block diagram showing a main part of a cathode ray tube (CRT) including an alternating electric field radiation suppressor according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a main part of a cathode ray tube (CRT) including an alternating electric field radiation suppressor according to a third embodiment of the present invention.

[Explanation of symbols]

11 Deflection yoke 12 Phosphor screen 12a Electrode (anode) 13 Flyback transformer (FBT) 14 Rectifier circuit 15 High voltage line 20, 20A, 20B Cancel voltage generation circuit 21 Polarity inversion circuit 22 Sawtooth wave generation circuit 23, 24 Amplitude adjustment circuit 25 Waveform Combined circuit C ₁ Parasitic capacitance C _{2 to} C ₄ capacitor D diode L ₁ coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiichiro Kakeya 1-44-2 Jomi, Chuo-ku, Osaka-shi, Osaka NEC Home Electronics Co., Ltd.

Claims (4)

[Claims] 1. An alternating electric field radiation from a cathode ray tube in a cathode ray tube for displaying an image on the fluorescent surface by electromagnetically deflecting an electron beam emitted from an electron gun by a deflection yoke and projecting the electron beam onto the fluorescent surface. In the suppression device, a high DC voltage is applied to the electrode defining the phosphor screen from a flyback transformer via a rectifier circuit and a high voltage line, and the electrode and the deflection yoke are connected via a parasitic capacitance. A high voltage ripple resulting from capacitive coupling of the parasitic capacitance is superimposed on the high DC voltage on the high voltage line and suppresses alternating electric field radiation radiated to the front surface of the phosphor screen by the high voltage ripple. In the device, a detecting means for detecting a pulse generated during a blanking period of a horizontal deflection current flowing through the deflection yoke and outputting a detection pulse; A polarity inversion circuit that inverts the polarity of the inversion pulse and outputs an inversion pulse, an amplitude adjustment circuit that adjusts the amplitude of the inversion pulse and outputs an amplitude-adjusted inversion pulse, and the amplitude adjustment inversion pulse as a cancellation pulse A capacitor for injecting into the high-voltage line, wherein the high-voltage ripple superimposed on the high DC voltage on the high-voltage line is canceled by the cancel pulse, and an alternating electric field radiation suppressing device for a cathode ray tube. 2. An alternating electric field radiation from a cathode ray tube in a cathode ray tube for drawing an image on the fluorescent surface by electromagnetically deflecting an electron beam emitted from an electron gun by a deflection yoke and projecting the electron beam onto the fluorescent surface. In the suppression device, a high DC voltage is applied to an electrode defining the phosphor screen from a flyback transformer via a rectifying circuit including a smoothing capacitor and a high voltage line, and the high DC voltage on the high voltage line is applied. A sawtooth rectification ripple caused by charging / discharging of the smoothing capacitor is superposed on the deflection yoke in the device for suppressing the alternating electric field radiation radiated to the front surface of the phosphor screen by the rectification ripple. Detection means for detecting a pulse generated during the blanking period of the horizontal deflection current and outputting the detection pulse, and the rectification resistor in response to the detection pulse. A sawtooth wave creating circuit that creates a sawtooth wave having a polarity opposite to that of the pull, an amplitude adjusting circuit that adjusts the amplitude of the sawtooth wave and outputs the sawtooth wave whose amplitude is adjusted, and a sawtooth wave for canceling the sawtooth wave whose amplitude is adjusted. And a capacitor for injecting into the high voltage line, and the rectifying ripple superimposed on the high DC voltage on the high voltage line is canceled by the canceling sawtooth wave, and an alternating electric field radiation suppressing device for a cathode ray tube. 3. An alternating electric field radiation from a cathode ray tube in a cathode ray tube for displaying an image on the fluorescent surface by electromagnetically deflecting an electron beam emitted from an electron gun by a deflection yoke and projecting the electron beam onto the fluorescent surface. In the suppression device, a high DC voltage is applied to an electrode defining the phosphor screen from a flyback transformer through a rectifying circuit including a smoothing capacitor and a high voltage line, and the electrode and the deflection yoke are parasitic. The high DC voltage on the high voltage line, which is coupled via a capacitor, is combined with a high voltage ripple resulting from the capacitive coupling of the parasitic capacitor and a sawtooth rectification ripple resulting from charging and discharging of the smoothing capacitor. In the device for suppressing the alternating electric field radiation radiated to the front surface of the phosphor screen by the combined ripple, the deflected deflection is overlapped. Detecting means for detecting a pulse generated during the blanking period of the horizontal deflection current flowing through the output pulse, and outputting a detection pulse; a polarity inversion circuit for inverting the polarity of the detection pulse and outputting an inversion pulse; A first amplitude adjusting circuit that adjusts the amplitude of the pulse to output an amplitude-adjusted inverted pulse; and a sawtooth wave creating circuit that creates a sawtooth wave having a polarity opposite to that of the rectification ripple in response to the detection pulse. A second amplitude adjusting circuit that adjusts the amplitude of the sawtooth wave and outputs the sawtooth wave whose amplitude is adjusted, and the inversion pulse whose amplitude is adjusted and the sawtooth wave whose amplitude is adjusted are combined to output a cancel voltage. A waveform synthesizing circuit and a capacitor for injecting the cancel voltage into the high voltage line, and canceling the synthesized ripple superimposed on the high voltage line by the cancel voltage. Cathode-ray tube an alternating electric field radiation suppression device according to symptoms. 4. The alternating electric field radiation suppressing device for a cathode ray tube according to claim 1, wherein the detecting means is a coil wound around a secondary side of the flyback transformer.