MXPA97000895A - Video exhibition apparatus including circuit to eliminate unwanted radiation of the catodi ray tube - Google Patents

Abstract

A video display apparatus having a circuit for reducing or eliminating unwanted radiation from a front and / or back part of a cathode ray tube. The apparatus includes a transformer for inducing a waveform of opposite deflection voltage in its secondary winding in accordance with a deflection voltage waveform applied to its primary winding through a deflection coil in response to a switching operation switching on / off of the switching transistor, and a wire wrapped around a periphery of the cathode ray tube and to which the opposite deflection voltage waveform is applied from the transformer. The wire is wound at least once or several times, so that the unwanted radiation emitted from the cathode ray tube by the deflection voltage waveform applied to the anode of the cathode ray tube is deflected by the waveform of opposite deflection voltage applied to the wire

Description

VIDEO DISPLAY APPARATUS INCLUDING CIRCUIT TO ELIMINATE UNDESIRABLE RADIATION OF CATHODIC RAYS TUBE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a video display apparatus such as a television receiver, a computer monitor, etc., and more particularly to a video display facility that has a circuit to reduce or eliminate unwanted radiation emitted forward and / or backward from the apparatus. 2. Description of the Prior Art A common video display apparatus comprises a cathode ray t bo (hereinafter referred to as CRT) having an electronic cannon to generate an electronic beam and an exhibit screen to display a video signal thereon. , and a deflection unit having a transformer for deflecting the electronic beam through the display screen. The transformer generates a high voltage which is required to operate the display apparatus. For this type of device, there are safety regulations that specify that certain electric fields in the vicinity of the device can not exceed certain limits. For example, the alternating electric field in a frequency band comprising horizontal deflection frequencies may not exceed 2.5 V / m at a distance of 0.5 meters from the center of the CRT screen. In general, all parts having a voltage to the suit with a frequency in the frequency band comprising the horizontal deflection frequencies will contribute to the alternating electric field. The electric field emitted from the upper part and sides of the video display apparatus can be easily protected by means of a metallic housing or an electrically conductive shield. However, it is difficult to protect the electric field emitted from the front side of the CFT because this side comprises a glass display screen. Consequently, some methods are well known in the field for eliminating the electric field emitted from the CRT, and one of the methods is shown in Figure 2. In Figure 2, a deflection unit comprises a -transistor Q1 that functions as a connection / disconnection switch depending on a voltage applied from a supply B + of energy, and a transformer FBT1 of recoil. The retrace transformer FBT1 includes a primary winding 62 for generating an alternating current back-off voltage and a secondary winding 64 for inducing a high voltage of alternating current in response to a switching voltage applied to the primary winding 64. The primary winding 62 is connected to a deflection yoke (not shown), and the deflection yoke is driven by the connection / junction switching operation of the transistor Q1. A deflection voltage waveform generated from the deflection yoke is also induced to the secondary winding 64. The electrical field elimination circuit of the foregoing technique comprises a diode DI and a capacitor Cl to rectify and soften the high votivity induced in the secondary winding 64, and a coupling capacitor C2 to apply i opposing pulses which are induced in a third winding 66 of the retrace transformer FBT1 to an anode of the CRT. The high voltage induced in proportion to a winding relay of the second winding 64 of the reversing transformer FBT1 is rectified and smoothed by the diode and the capacitor C1. At this time, the induced high voltage includes the conning form of deflection voltage of the flexion yoke, and this causes unwanted radiation to be emitted from the front and / or the back of the CRT. Meanwhile, the voltage pulses generated from the third winding 66 of the reverse transformer FBT1 have a very similar or equal amplitude and a polarity opposite the deflection voltage pulses. Voting pulses from the third winding 66 are fed through the C2 to the anode of the CRT. Consequently, the unwanted deflection voltage waveform which is being applied from the secondary winding 64 to the anode of the CRT is canceled by the opposing pulses that are applied from the third winding to the anode of the CRT, so that the radiation does not desired caused by the deflection votive waveform is prevented from being issued from the front and / or back of the CRT However, since capacitor C2 to eliminate unwanted radiation emitted from the CRT is not appropriate for use on a high voter scale, it can not sufficiently eliminate unwanted radiation. Consequently, capacitor C2 must be molded of an electrical insulating material, which requires a large amount of capacitance. This causes the increase in the size and cost of manufacturing the capacitor. Furthermore, in order to eliminate the radiation emitted from the CRT, the surface resistance of the CRT has to be reduced, for example to 10, thereby increasing the cost of the CRT. Consequently there is a need for a device that can eliminate the radiation emitted from the CRT without simple structure and low cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a video display apparatus that includes a circuit for effectively reducing or eliminating unwanted radiation emitted from the front and back of a cathode ray tube. In order to achieve the above object, the video display apparatus according to the present invention comprises: a deflection coil for generating a deflection voltage wave form. a transistor for performing a switch-on / switch-off operation in accordance with the deflection voltage waveform generated by the deflection coil; a transformer having a primary winding pulsed by the deflection voltage waveform applied to it in response to the connection / connection conjugation operation of the transistor and a secondary winding to induce an opposite deflection voltage waveform. having a polarity opposite to the deflection voltage waveform and a wire wound around a periphery of the cathode ray beam and to which the opposite deflection vortex waveform is applied from the transformer; wherein the unwanted radiation emitted by the cathode ray tube by means of the deflexi voltage waveform applied to an anode of the cathode ray tube deviates half the waveform of petering deflection voltage applied to the wire. Preferably, the wire is wrapped around an external surface from the front and / or the lower part of the cathode ray bole. According to one aspect of the present invention, the wire is wound at least once or several times in the form of an open loop.

It is also preferable that the video display apparatus in accordance with the present invention further comprises voltage dividing elements for adjusting a level of the opposite deflection voltage waveform provided from the transformer, elements for configuring the waveform of the opposite deflection voltage waveform provided from the voltage divider element, and element for eliminating the peak noise i in the form of the opposite deflection voltage waveform seen from the waveform configuration element.

BRIEF DESCRIPTION OF THE DRAWINGS The above object, other features and advantages of the invention will become apparent by describing the preferred embodiment thereof with reference to the accompanying drawings in which: Figure 1 is a schematic circuit diagram of a video display apparatus including a circuit for eliminating unwanted radiation of co-normity with the present invention. Figure 2 is a schematic circuit diagram of a deflection unit with an electric field elimination circuit of the prior art.

DETAILED DESCRIPTION OF THE PREFERRED MODE Referring now to Figure 1, a circuit is shown to eliminate unwanted radiation in accordance with the present invention, provided to a front and / or post part of the CRT. The circuit for removing the unwanted radiation of the present invention is connected to a secondary coil 24 of the transformer Til. A transformer primary winding 22 is coupled to a collector of a switching transistor 011 which is also coupled in parallel to a deflection coil Dy., a diode D11 and a capacitor C14. Deflection bobbin DY is connected to ground through a capacitor C11. Also, the secondary winding 24 of the transformer T11 is coupled to the resistors R11 and R12, which are a voltage divider circuit. In turn, a waveform configuration circuit composed of a resistor R13 and a capacitor C12, and a noise removal circuit composed of a resistor R14 and a capacitor C13 are coupled to the voltage divider circuit. Specifically, the unwanted radiation removal circuit comprises an open-loop type wire having at least one turn around the front and / or rear periphery of the CRT. With this circuit arrangement as described above, if the power supply B is applied to the primary winding 22 of the transformer T11, the transistor Q11 coupled to the primary winding 22 performs a switching on / off operation. In response to the on / off switching operation of transistor Q11, the deflection coil DY coupled in parallel to diode D11 and capacitor C14 produces a deflection voltage waveform. The deflection voltage ond shape generated from the deflection coil DY is loaded into or discharged from the capacitor C11. In accordance with the switching / disconnecting operation of transistor 011, the deflection voltage waveform is induced in the primary winding 22 of transformer T11, resulting in the opposite d-bend voltage waveform which it has the opposite polarity to the shape of ond of deflection voltage is induced in the secondary winding 24 of the transformer T11. The level of the opposite deflection voltaic waveform induced in the secondary winding 24 of the transformer T11 is adjusted by the split resistors R11 R12 and by the supply voltage B, +, as the expression below Goes: ?? i R12 R11 + R12 xB K1¿ 1 R11 + R12 x negative impulses The opposite deflection waveform adjusted in level is configured in waveform by resistor R13 and citor layer C12. Here, the pulse magnitude of the deflection voltage waveform and its direct current level can be adjusted depending on the resistance values of the resistors R11 and R12.

Therefore, the opposite deflexion voltage waveform passes through the resistor R14 and the capacitor C13, resulting in the reduction or elimination of the peak noise including the opposite deflection voltage waveform. The opposite deflection voltage waveform from the noise removal circuit is applied to the wire Lll of the open, causing its voltage component to be applied to CRT and to affect the electric field emitted from the CRT. It is true, the unwanted radiation, which is emitted from the CRT by the deflection voltage waveform included in the high voltage applied to the CRT anode, is deflected by the opposite deflection voltage waveform applied to the wire. L11 of open loop type, result in the elimination of the unwanted diation emitted from the front and / or psoteri of the CRT. Although the present invention has been described and illustrated herein with reference to the preferred embodiment thereof, it will be understood by those experienced in the field that various changes in form and details may be made therein without abandoning the spirit and scope. of the invention.

Claims (4)

1. - A video display apparatus that includes a circuit for reducing or eliminating unwanted radiation emitted from a front and / or post part of a cathode ray tube, the video display apparatus comprising: a deflection coil to generate a shape wave deflection voltage; a transistor for performing a connection / disconnection operation of coformidity with the deflection voltage waveform generated by the deflection coil; a transformer having a primary winding i pulsed by the deflection votive waveform applied thereto in response to the switching / disconnect switching operation of the transistor and a secondary winding to induce a deflection voltage waveform. opposite having a polarity opposite to the deflection voltage waveform and a wire wound around a periphery of the cathode ray tube and to which the opposite deflection voltage waveform is applied from the transformer; wherein the unwanted radiation emitted from the cathode ray tube by the deflection voltage waveform applied to an anode of the cathode ray tube is deflected by the deflection voltage waveform applied to the ambre.

2. A video display apparatus as claimed in clause 1, wherein the wire is wound around an external surface of the front and / or rear of the cathode ray tube.

3. A video display apparatus as claimed in clause 1, wherein the wire is wound in the form of an open loop and at least once or several times.

4. A video display apparatus as claimed in clause 1, further comprising: a voltage divider element for adjusting a level d of the opposite deflection voltage waveform provided from the transformer; an element for configuring the waveform of the opposite deflection voltage waveform provided from the voltage divider element; and an element for eliminating a peak noise included in the opposite deflection voltage waveform provided from the waveform configuration element.