Abstract:
It is an object of the present invention to provide an image display apparatus which enables cost reduction while being free from electromagnetic interference problems. 
     A power supply circuit comprises, on a single circuit board, an AC inlet to which a power cord is connected from an external AC power supply, a filter circuit to which an inductance element is connected to suppress leakage of electromagnetic waves to the outside of the image display apparatus, and a switch which switches on/off an AC output supplied from the filter circuit. The circuit board of the power supply circuit is entirely covered by electromagnetic shielding means to shield electromagnetic waves. The electromagnetic shielding means is composed of, for example, a first shielding section which surrounds the lateral side of the circuit board and a second shielding section which covers the upper side of the circuit board. The second shielding section is formed of a part of the flat section of a rear cover of the image display apparatus.

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese application serial No. P2006-009472, filed on Jan. 18, 2006, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a power supply circuit for an image display apparatus. More particularly, the present invention relates to a technique for preventing leakage of electromagnetic waves generated in the apparatus to the outside of the apparatus. 
     Conventionally, electronic apparatuses have been requested to comply with the requirements of the EMC (Electromagnetic Compatibility) standards, i.e., the EMI (Electro Magnetic Interference) measures for preventing unintended emission of electromagnetic waves and the EMS (Electro Magnetic Susceptance) measures for preventing malfunction upon reception of electromagnetic waves. In Japan, the VCCI (Voluntary Control Council for Interference by Information Technology Equipment) was established and self-imposed regulations are conducted based on recommendations of the CISPR (International Special Committees on Radio Interference). This also applies to the U.S. and Europe. Image display apparatus, such as a display apparatus with a plasma display panel, are subjected to the regulations since they generate electromagnetic waves from a display unit such as a plasma display panel. The regulations demand that leakage of the electromagnetic waves to the outside of the apparatus be reduced to a predetermined level. A power supply unit of the apparatus is one of paths which electromagnetic waves leak to the outside. Since electromagnetic waves leak to the side of a commercial power supply, etc. through a power cord or the like, measures are taken so that electromagnetic waves are attenuated by a filter circuit in the power supply unit. 
       FIG. 6  is a schematic diagram showing a circuit configuration of a conventional display apparatus with a plasma display panel. The circuit shown in  FIG. 6  comprises: a power supply circuit including a circuit board  13   a   1 ′ with a power cord  30 ′ directly connected thereto and a filter circuit A′ formed thereon which includes an inductance element; a circuit board  13   a   2 ′ with a fuse  60 ′ connected thereto and a filter circuit B′ formed thereon; and a circuit board  13   a   3 ′ with a switch circuit formed thereon which switch on/off the connection between the fuse  60 ′ and the filter circuit B′. The circuit shown in  FIG. 6  further comprises: a circuit board  13   b ′ with a power supply unit S′ formed thereon which includes a filter circuit C′ with inductance elements connected thereto; a circuit board  12   a ′ with a drive circuit D 1 ′ formed thereon which drives a plasma display panel  11 ′ as a display unit based on an image signal; a circuit board  12   b ′ with a drive circuit D 2 ′ formed thereon; and a rear cover  16 ′ for covering the rear side of the display apparatus. 
       FIG. 7  is a diagram showing an example of the configuration of a display apparatus with a plasma display panel using the circuit shown in  FIG. 6 . In  FIG. 7 , a retaining fitting  14 ′ for retaining a circuit boards  13   a   1 ′,  13   a   2 ′ and  13   a ′, a circuit board  13   b ′, and circuit boards  12   a ′ and  12   b ′ are arranged between the plasma display panel  11 ′ and the rear cover  16 ′. A front filter  15 ′ is arranged at the front of the plasma display panel  11 ′. In the above configuration, electromagnetic waves in the power supply circuit and the power supply unit S′ shown in  FIG. 6  are attenuated by use of filter circuits A′, B′ and C′. 
     One of conventional arts relevant to the present invention is described, for example, in Japanese Patent Laid-open No. 2004-29264. This patent gazette describes a configuration in which a noise filter circuit installed at the rear side of a plasma display panel is covered by a cover of magnetic metal material and a portion of the cover close to the noise filter circuit is secured to a chassis member in order to provide a plasma display apparatus which does not generate audible noise sound. 
     Japanese Patent Laid-open No. 2004-29264 
     SUMMARY OF THE INVENTION 
     In order to further popularize display apparatus with a plasma display panel or the like, further remarkable cost reduction is demanding while predetermined performance is ensured. With the conventional configuration shown in  FIG. 6  and  FIG. 7 , electromagnetic waves are prevented from leaking from the power supply unit to the outside of the apparatus. However, since the power supply circuit is composed of three circuit boards, circuit boards  13   a   1 ,  13   a   2 , and  13   a   3 , it is necessary to prepare connecting sections for connecting these circuit boards with each other, connect between these connecting sections when assembling the apparatus, and separately manufacture each of the circuit boards, resulting in cost increase. Further, the above-mentioned Japanese Patent Laid-open No. 2004-29264 discloses a noise filter circuit having a noise filter and a cover. However, since the invention disclosed in this patent gazette aims at suppressing audible noise sound generated by the strength of absorption force between the noise filter and the cover based on the strength of leakage flux due to an AC current in conjunction with an AC power frequency, the patent gazette only describes a configuration in which the noise filter circuit is covered by a cover for entirely covering the rear side of the apparatus. 
     In view of the situation of the above-mentioned conventional art, a subject of the present invention is to prevent electromagnetic waves generated in the display unit from leaking to the outside of an image display apparatus such as a display apparatus with a plasma display panel, thereby resulting in cost reduction of the power supply circuit. 
     The present invention provides a display apparatus which solves the above-mentioned subject and achieve the cost reduction while being free from electromagnetic interferences. 
     According to the present invention, an image display apparatus comprises, on a single circuit board, an power supply circuit having an AC inlet to which a power cord is connected from an external AC power supply, a filter circuit to which an inductance element is connected to attenuate electromagnetic waves, and a switch which switches on/off an AC output supplied from the filter circuit. The circuit board of the power supply circuit is entirely covered by electromagnetic shielding means to shield electromagnetic waves. The electromagnetic shielding means is composed of, for example, a first shielding section which surrounds the lateral side of the above-mentioned circuit board and a second shielding section which covers the upper side of the circuit board, wherein the second shielding section is formed of a part of the flat section of the rear cover of the display apparatus. 
     According to the present invention, it is possible to provide an image display apparatus which achieves cost reduction while being free from electromagnetic interferences. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, objects and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a diagram showing a configuration of a display apparatus with a plasma display panel according to the embodiment of the present invention; 
         FIG. 2  is a schematic diagram showing a circuit configuration in the display apparatus with the plasma display panel shown in  FIG. 1 ; 
         FIG. 3  is a perspective diagram of the appearance of a power supply circuit and electromagnetic shielding means in the display apparatus with the plasma display panel shown in  FIG. 1 ; 
         FIG. 4  is a diagram showing an example of the configuration of the power supply circuit and a power supply unit in the display apparatus with the plasma display panel shown in  FIG. 1 . 
         FIG. 5  is a diagram showing an example of the configuration of a switch used in the power supply circuit shown in  FIG. 4 . 
         FIG. 6  is a schematic diagram of a circuit configuration of a conventional display apparatus with a plasma display panel. 
         FIG. 7  is a diagram showing an example of the configuration of a conventional display apparatus with a plasma display panel. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be explained below with reference to the accompanying drawings. 
       FIGS. 1 through 5  are diagrams explaining the embodiment of the present invention.  FIG. 1  is a diagram showing an example of the configuration of a display apparatus with a plasma display panel according to the embodiment of the present invention.  FIG. 2  is a schematic diagram of a circuit configuration in the apparatus shown in  FIG. 1 .  FIG. 3  is a perspective diagram of an appearance of a power supply circuit and electromagnetic shielding means of circuits in the apparatus shown in  FIG. 1 .  FIG. 4  is a diagram showing an example of the configuration of the power supply circuit and a power supply unit of circuits in the apparatus shown in  FIG. 1 .  FIG. 5  is a diagram showing an example of the configuration of a switch used in the power supply circuit shown in  FIG. 4 . 
     In  FIG. 1 , reference numeral  1  denotes a display apparatus with a plasma display panel according to the embodiment of the present invention;  11 , a plasma display panel used as a display unit which display an image by means of electric discharge between electrodes arranged in a matrix form;  12   a  and  12   b , circuit boards each having a drive circuit formed thereon which drives the electrodes of the plasma display panel  11  based on an image signal;  13   a , a circuit board with a power supply circuit (not shown) mounted thereon which supplies an AC input from an external AC power supply, eliminates noise components, and outputs a current;  13   b , a circuit board with a power supply unit (not shown) formed thereon which allows conversion of AC power into DC power;  14 , a retaining fitting to which the circuit board  13   a  is secured;  20 , a shielding frame member made of metal material, used as a first shielding section of the electromagnetic shielding means which surrounds the lateral side of the circuit board  13   a ;  16 , a rear cover made of metal material, arranged at the rear (X-axis direction side) of the plasma display panel  11 , which covers the plasma display panel  11 , circuit boards  12   a ,  12   b ,  13   a , and  13   b ; and  15 , a front filter arranged at the front (−X-axis direction side) of the plasma display panel  11 . 
     On the circuit board  13   a  installed are an AC inlet (not shown) to which a lead wire (power cord) is connected from an external AC power supply, a filter circuit (not shown) with an inductance element connected thereto which attenuates electromagnetic waves, a switch (not shown) which switches on/off an AC output from the filter circuit, and a fuse (not shown) which protects the circuit from overcurrent. Further, the rear cover  16  is combined with the shielding frame member  20  in such a manner that a part of the flat section thereof shuts an opening on the Z-axis direction side of the shielding frame member  20 , wherein a part of the flat section of the rear cover  16  forms a second shielding section of the electromagnetic shielding means which covers the upper side of the circuit board  13   a  of the power supply circuit. The drive circuits (not shown) mounted on the circuit boards  12   a  and  12   b  operate with power supplied from a power supply unit mounted on the circuit board  13   b . The AC power is supplied to the power supply unit from a power supply circuit mounted on the circuit board  13   a  through a switch in the power supply circuit. 
     In the following explanations, same numerals are assigned to the same components as those in  FIG. 1 . Further, in the following drawings, the same coordinate axes as those in  FIG. 1  are used. 
       FIG. 2  is a schematic diagram of a circuit configuration in the display apparatus  1  with a plasma display panel shown in  FIG. 1 . 
     In  FIG. 2 , reference numeral  131  denotes a filter circuit A formed on the circuit board  13   a  of the power supply circuit, which includes an inductance element to particularly attenuate high-frequency components of electromagnetic waves generated in the plasma display panel  11 ;  132 , a filter circuit B connected to the filter circuit A 131 , which includes capacitors to particularly attenuate low-frequency components of electromagnetic waves generated in the plasma display panel  11 ;  133 , a filter circuit C formed on the circuit board  13   b  of the power supply unit S, which includes inductance elements to particularly attenuate high-frequency components of electromagnetic waves generated in the plasma display panel  11 ;  12   a , a circuit board with a drive circuit D 1  formed thereon which drives electrodes of the plasma display panel  11  based on an image signal;  12   b , a circuit board with a drive circuit D 2  similarly formed thereon;  30 , a power cord;  40 , an AC inlet to which the power cord  30  is connected;  50 , a switch which switches on/off an AC output from the filter circuit B;  60 , a fuse which protects the filter circuit A 131  and filter circuit B 132  from overcurrent. Other reference numerals are the same as those in  FIG. 1 . The filter circuit B is connected to the filter circuit C  133  of the power supply unit S through the switch  50 . For the circuit board  13   a  of the power supply circuit, the lateral side is surrounded by the shielding frame member  20  used as a first shielding section of the electromagnetic shielding means and the upper side is covered by a part of the flat section of the rear cover  16  used as a second shielding section of the electromagnetic shielding means. 
     With the above-mentioned configuration, the AC input is supplied from the power cord  30  into the circuit board  13   a  through the AC inlet  40  and then inputted to the filter circuit A 131  through the fuse  60 ; the filter circuit A 131  attenuates high-frequency components of electromagnetic waves generated in the plasma display panel  11  and entered to the power supply unit; and the filter circuit B 132  attenuates low-frequency components of electromagnetic waves generated in the plasma display panel  11 . 
     The AC output from the filter circuit B 132  is inputted to the filter circuit C on the circuit board  13   b  of the power supply unit S through the switch  50 . The filter circuit C also attenuates high-frequency components of electromagnetic waves. Electromagnetic waves generated in the plasma display panel  11  are transmitted from the power supply unit S to the power supply circuit, i.e., from the filter circuit C  133  to the filter circuit B 132  and then to the filter circuit A 131 . Accordingly, electromagnetic waves that are not sufficiently attenuated by the filter circuit C  133  are attenuated by the filter circuit B 132  and then by the filter circuit A 131 . The output of the power supply unit S is inputted to the drive circuit D 1  mounted on the circuit board  12   a  and the drive circuit D 2  mounted on the circuit board  12   b . The drive circuits D 1  and D 2  form drive signals based on the image signal, and the plasma display panel (display unit)  11  is driven by the drive signals to display an image. 
     In the following explanations, same numerals are assigned to the same components as those in  FIG. 2 . 
       FIG. 3  is a perspective diagram showing an appearance of the electric wave circuit and electromagnetic shielding means in the display apparatus  1  with a plasma display panel shown in  FIG. 1 . 
     In  FIG. 3 , reference numerals  70   a  to  70   d  denote screws for combining the rear cover  16  with the upper side (X-axis direction side) of the shielding frame member  20 . Other reference numerals are the same as those in  FIG. 1  and  FIG. 2 . The circuit board  13   a  with the AC inlet  40 , the fuse  60 , the filter circuit A 131 , the filter circuit B 132 , and the switch  50  installed thereon is secured on the surface of a retaining fitting  14 . The lateral side of the circuit board  13   a  is surrounded by the shielding frame member  20 . The shielding frame member  20  is also secured on the surface of the retaining fitting  14 . By electrically coupling the rear cover  16  with the upper side (X-axis direction side) of the shielding frame member  20 , the circuit board  13   a  is covered by the shielding frame member  20  and the rear cover  16  to shield electromagnetic waves radiated from the plasma display panel. The AC inlet  40  is provided with pins and holes for connection. 
       FIG. 4  is a diagram showing an example of the configuration of the power supply circuit and the power supply unit of circuits in the apparatus shown in  FIG. 1 . 
     In  FIG. 4 , reference numerals C 1 , R 1 , and L 1  denote a capacitor, a resistor, and an inductance element, respectively, which form the filter circuit A 131 ; C 2 , C 3 , and C 4 , capacitors that form the filter circuit B 132 ; C 5  to C 8  and L 2  to L 3 , capacitors and inductance elements, respectively, which form the filter circuit C  133  of the power supply unit S. The circuit boards  13   a  and  13   b  are connected by lead wires  83  and connectors  81  and  82 . 
       FIG. 5  is a diagram showing an example of the configuration of the switch  50  used in the power supply circuit shown in  FIG. 4 . 
     In  FIG. 5 , reference numeral  50   a  denotes a main unit (hereafter referred to as a switch main unit) of the switch  50 ;  50   b , an arm (hereafter referred to as a switch arm) of the switch  50 ;  50   c , an operating section (hereafter referred to as a switch operating section) at which an external force for operation is applied to the switch  50 . The switch operating section  50   c  is arranged substantially at the lateral side or the display unit side of the plasma display panel (display unit)  11  from the view point that the user performs an operation thereof. With this arrangement, the switch operating section  50   c  and the switch main unit  50   a , which is installed on the circuit board  13   a  at a position separated from the position of the plasma display panel (display unit)  11  in the X-axis direction, are connected by the switch arm  50   b . For example, when an external force added in the ±Z axis direction is applied to the switch operating section  50   c , the external force acts on the switch main unit  50   a  through the switch arm  50   b  to switch on/off a contact in the switch main unit  50   a . When the contact is switched on/off, the connection between the filter circuit B mounted on the circuit board  13   a  and the filter circuit C mounted on the circuit board  13   b  is turned on/off. 
     According to the above-mentioned embodiment of the present invention, the power supply circuit includes the AC inlet  40 , the fuse  60 , the filter circuit A 131 , the filter circuit B 132 , and the switch  50  and is mounted on a single circuit board  13   a , which reduces the manufacturing cost of circuit boards and the assembly cost of the power supply circuit. In addition, the circuit board  13   a , which forms the power supply circuit on the power cord side, is covered by the shielding frame member  20  and the rear cover  16 , making it possible to effectively shield electromagnetic waves that leak from the power supply unit to the outside. 
     While we have shown and described several embodiments in accordance with our invention, it should be understood that disclosed embodiments are susceptible to changes and modifications without departing from the scope of the invention. Therefore, we do not intend to be bound by the details shown and described herein but intend to cover all such changes and modifications as fall within the ambit of the appended claims.