Abstract:
An opening is formed in a case. Air is caused to flow through the interior of the case. A panel closes the opening. A printed circuit board is disposed behind the panel within the case. A plurality of components, including a control device which can be operated on the front surface of the panel and a display device providing a display viewable on the front surface of the panel, are mounted on the printed circuit board. The printed circuit board is enclosed in a closed receptacle disposed within the case.

Description:
This invention relates to a power supply apparatus and, more particularly, to an arrangement of printed circuit boards used in the power supply apparatus. 
   BACKGROUND OF THE INVENTION 
   A power supply apparatus, e.g. a power supply apparatus for a welder, may have a control panel on its outer surface. An example of a power supply apparatus with such control panel is disclosed in Japanese Patent Application Publication No. 2003-136241 (JP 2003-136241 A). The power supply apparatus disclosed in JP 2003-136241 A includes a control panel on an outer surface of a case, and the control panel includes setting devices for setting currents and voltages the power supply apparatus may supply, switches for selecting operating modes of the apparatus, and indicator lamps indicating the operating states. Also not explicitly stated in the publication, the setting devices, the switches and the lamps are mounted on a printed circuit board. This printed circuit board may be packed with high density. In such case, the distance between printed conductors on the circuit board is very small, e.g. less than 0.5 mm. The densely packed printed circuit board is fixed to the rear, or inside surface of the control panel. Plural openings are formed through the control panel, through which controls for the setting devices and switches and the indicator lamps are exposed to enable an operator to externally operate the setting devices and switches and to confirm the operating states by means of the indications by the lamps. 
   Frequently, in order to cool the interior of the case of the power supply apparatus, outside air is taken into the case, and, in such case, both of opposing major surfaces of the densely packed printed circuit board for the control panel is exposed to the air taken into the case. 
   A power supply apparatus for a welder is sometimes used in an environment where electrically conductive dust and/or corrosive gas are present. Such conductive dust and corrosive gas will enter into the case of the power supply apparatus and adversely affect printed circuit boards inside the case. In particular, the printed circuit board for the control panel is affected by dust and corrosive gas more than other printed circuit boards, because it is more densely packed. Electrically conductive dust sticking to the printed circuit board degrades insulation of the circuit board, and corrosive gas corrodes components mounted on the circuit board and printed conductors, which would cause malfunction of the power supply apparatus. 
   Therefore, an object of the present invention is to protect a printed circuit board for a control panel from surrounding air to avoid influence of the air on the printed circuit board. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the present invention, a power supply apparatus includes a case through the interior of which air can flow. In order to make air flow through the interior of the case, an air intake port and an air outlet port may be desirably formed in the case at different parts thereof. It is also desirable to dispose a fan within the case to help air flow through the interior of the case. An opening is formed in the case and is closed by a panel. The panel can cover the opening from inside the case or from outside the case. A first printed circuit board is disposed within the case behind the panel. A plurality of components are mounted on the first printed circuit board. The components include a control device operable on the front side of the panel, and a display device providing a display viewable on the front-side of the panel. The control device has a controller to be used for operating the control device, which desirably extends outward through the panel. The display device has its display desirably appearing on the front side of the panel. The first printed circuit board is housed in a closed receptacle within the case. 
   With the above-described structure of the power supply apparatus, the first printed circuit board does not contact with electrically conductive dust and/or corrosive gas which could be contained in the air flowing through the interior of the case because the first printed circuit board is placed in the closed receptacle. Accordingly, it occurs neither that the insulation of the first printed circuit board degrades, nor that the components mounted on the first printed circuit board or the printed conductors could be corroded. 
   The distance between adjacent ones of a plurality of conductors printed on the first printed circuit board may be small. If any electrically conductive dust adheres to the printed circuit board with conductors spaced from each other by a small distance, it tends to degrade the insulation between the conductors. However, according to the invention, the first printed circuit board is housed in a closed receptacle, degradation of the insulation of the first printed circuit board does not occur. 
   It is desirable that the receptacle should include a wall unit extending inward into the interior of the case from the inner surface of the panel and having an opening in its distal, or innermost, end, and a lid closing the opening. It is desirable that the wall unit and the panel are formed integral. Since the wall unit is formed on the panel, the end of the wall unit on the panel side is closed by the panel, and, therefore, no extra member is required to close that end, which makes the structure of the power supply apparatus simple. 
   The lid closing the rear opening formed by the wall unit may be a second printed circuit board. This eliminates the need to prepare a lid for dedicated use, so that the structure of the power supply apparatus can be simple. 
   The first printed circuit board may be disposed in close proximity to the rear or inner surface of the panel. A securing member for securing the first printed circuit board is disposed on the inner surface of the wall unit, and the securing member desirably extends inward of the outer peripheral edges of the rear surface of the first printed circuit board. This arrangement eliminates the need for use of screws or adhesive for securing the first printed circuit board, which makes it easier to manufacture the power supply apparatuses. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partially broken-away, longitudinal cross-sectional view of a power supply apparatus according to one embodiment of the present invention. 
       FIG. 2  is an exploded view of a control panel of the power supply apparatus shown in  FIG. 1 . 
       FIG. 3  is a partially broken-away, cross-sectional view of a power supply apparatus according to another embodiment of the present invention. 
       FIG. 4  is a partially broken-away, cross-sectional view of a power supply apparatus according to still another embodiment of the present invention. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   A power supply apparatus for welding according to one embodiment of the present invention is shown in  FIGS. 1 and 2 . As is seen from  FIG. 1 , the power supply apparatus has a case  12 , which may be made of, for example, synthetic resin and houses a power supply circuit, e.g. a power supply circuit for a welder (not shown). In order to cool down components of the power supply circuit generating a large amount of heat, external air is introduced into the case  2 . The introduced air flows through the interior of the case  2  and is discharged. For this purpose, a plurality of air intake openings  4   a  are formed in a front panel  2   a  of the case  2 , and a plurality of air discharge openings  4   b  are formed in a rear panel  2   b , which faces the front panel  2   a  with a spacing disposed therebetween. In order to help air to be taken in and discharged, a blower  6  is disposed near the rear panel  2   b  within the case  2 . Power supply apparatuses for welding may be used in an environment where electrically conductive dust and/or corrosive gas exist. Such conductive dust or corrosive gas tends to enter into the case  2  through the air intake openings  4   a.    
   On the case  2 , a control and display unit  8  is mounted, which is used to set various parameters for operation of the power supply apparatus and to display operating states of the power supply apparatus to enable an operator to know the current operating state. The control and display unit  8  includes a control panel  10 , which closes an opening  14  in the bottom of a recessed portion  12  formed in an upper part of the front panel  2   a . The control panel  10  closes the front of the opening  14 . In other words, the outer peripheral portion of the control panel  10  overlies the front surface of the portion of the front panel  2   a  around the opening  14 . The opening  14  is rectangular, for example, and the control panel  10  is also rectangular and is slightly larger than the opening  14 . The control panel  10  is formed of a planar plate  10   a , which may be formed of synthetic resin, for example, and a display sheet  10   b  bonded to the front surface of the plate  10   a.    
   A printed circuit board  16 , for example, a printed circuit board for the control panel, is disposed on the inner surface of the plate  10   a  inside the case  2 . The control panel printed circuit board  16  has a rectangular shape and is in contact with the plate  10   a . A plurality of conductors are printed on the circuit board  16  with a small spacing of, for example, less than 5 mm, disposed between adjacent conductors. 
   Also, plural components are mounted on the printed circuit board  16  for the control panel. The components on the printed circuit board  16  include control devices  18 , for example, rotary encoders and switches for setting operating conditions of the power supply apparatus. A display device  20  is also mounted on the printed circuit board  16 , for displaying the operating state of the apparatus. At least one of the control devices  18  has a controller  18   a  which enables an operator to operate the control device  18  from outside the case  2 . The controller  18   a  extends outward into the recessed portion  12  through openings (not shown) formed in the plate  10   a  and the display sheet  10   b . The display device  20  has a display section  20   a  displaying the operating state of the power supply apparatus. The display section  20   a  extends outward into the recessed portion  12  through openings (not shown) in the plate  10   a  and the display sheet  10   b.    
   The control panel printed circuit board  16  is enclosed in a receptacle  22 . As shown in  FIG. 2 , the receptacle  22  has a wall unit  24 , which is in the shape of a hollow, short, rectangular prism, extending generally perpendicularly from the inner surface of the plate  10   a  into the case  2 . The wall unit  24  is formed of a synthetic resin and is formed integral with the plate  10   a . The wall unit  24  has longer-side walls  24   a  and  24   b  in parallel with each other, and also shorter-side walls  24   c  and  24   d  extending in parallel with each other and perpendicular to the longer-side walls  24   a  and  24   b . The longer-side and shorter-side walls  24   a - 24   d  are disposed in proximity to the peripheral edges of the control panel printed circuit board  16 . The wall unit  24  has an opening at its innermost end. 
   The opening of the wall unit  24  is closed with a lid. Another printed circuit board  26  is used as the lid in the illustrated embodiment. Part of the power supply circuit is arranged on the printed circuit board  26 . The shape of the printed circuit board  26  is substantially the same as that of the rear opening in the wall unit  24 . The receptacle  22 , thus, is formed by the wall unit  24  and the printed circuit board  26 . 
   The control panel printed circuit board  16  is secured to the plate  10   a  by means of securing members  28   a  and  28   b  formed on the inner surfaces of the longer-side walls  24   a  and  24   b . The securing members  28   a  and  28   b  are integral with the wall unit  24  and located at the midpoints of the longer-side walls  24   a  and  24   b , respectively. The securing members  28   a  and  28   b  extend over part of the inner, or rear, surface of the printed circuit board  16  so as to press the board  16  against the plate  10   a.    
   Slits  30   a  and  30   b  are formed in the longer-side walls  24   a  and  24   b  at locations on the opposite sides of the respective securing members  28   a  and  28   b , so that tongue-like pieces  32   a  and  32   b  are formed, with the securing members  28   a  and  28   b  formed thereon, respectively. For mounting the control panel printed circuit board  16 , the board  16  is first placed inside the wall unit  24  through the opening in the innermost end of the wall unit  24 , and bend the tongue-like pieces  32   a  and  32   b  outward as indicated by arrows in  FIG. 2  so that the securing members  28   a  and  28   b  are also displaced outward. With the tongue-like pieces  32   a  and  32   b  kept in this position, the printed circuit board  16  is moved over the thus displaced securing members  28   a  and  28   b  onto the inner surface of the plate  10   a . Thereafter, the tongue-like pieces  32   a  and  32   b  are released, which causes the securing members  28   a  and  28   b  to return to their original positions shown in  FIG. 1  where they are in contact with the rear surface of the control panel printed circuit board  16  and urge the printed circuit board  16  against the plate  10   a.    
   Screws (not shown) are used to fix the printed circuit board  26  to the wall unit  24 . For that purpose, ribs  34  are formed at the four inner corners of the wall unit  24 . The ribs  34  extend across the entire width of the wall unit  24  between the rear surface of the plate  10   a  and the rear end opening in the wall unit  24 . Screw holes are formed in the rear end surfaces of the respective ribs  34 , into which screws (not shown) are screwed through screw holes  38  formed in the four corners of the printed circuit board  26 , to thereby mount the printed circuit board  26  to close the opening in the wall unit  24 . 
   With the above-described arrangement, the printed circuit board  16  for the control panel is placed in the receptacle  22  formed by the wall unit  24  and the printed circuit board  26 . Accordingly, if the air taken into the case  2  through the intake openings  4   a  contains electrically conductive dust and/or corrosive gas, the printed circuit board  16  is shielded from and does not contact with such dust and/or corrosive gas. The spacing between adjacent ones of the printed conductors on the printed circuit board  16  is small, and, therefore, if electrically conductive dust adheres to the printed circuit board  16 , insulation between adjacent conductors is degraded. However, with the above-described arrangement, such insulation degradation can be suppressed. Also, since the control devices  18  and the display device  20  do not directly contact corrosive gas, if any, in the cooling air, they are hardly corroded. 
   Since the wall unit  24  of the receptacle  22  is formed integral with the plate  10   a  which is part of the control panel  10 , with the printed circuit board  26 , which is part of the power supply circuit, used also as the lid to close the rear opening of the wall unit, the power supply apparatus according to this invention is easy to manufacture. Furthermore, the securing members  28   a  and  28   b  for securing the printed circuit board  16  in the receptacle  22  are formed integral with the wall unit  24 , there is no need to use any screws to fix the printed circuit board  16 . 
   Part of a power supply apparatus according to a second embodiment of the present invention is shown in  FIG. 3 . The power supply apparatus according to the second embodiment differs from the apparatus according to the first embodiment in the manner of fixing the printed circuit board  26 . Since the remainder is the same as the power supply apparatus shown in  FIGS. 1 and 2 , the same reference numerals are used for the same or similar parts and components, and no further description is given about them. Spacers  40  are formed integral with the plate  10   a  at spaced locations on the rear surface of the plate  10   a . The spacers  40  extend through the control panel printed circuit board  16  to the rear opening of the wall unit  24 . Screw holes  42  are formed in the rear end surfaces of the spacers  40 , and screws (not shown) are screwed through the printed circuit board  26  into the screw holes  42 , so that the printed circuit board  26  is fixed to the wall unit  24  and closes the rear opening of the wall unit  24 . 
   Part of a power supply apparatus according to a third embodiment is shown in  FIG. 4  The power supply apparatus shown in  FIG. 4  differs from the one shown in  FIGS. 1 and 2  in the manner of fixing the printed circuit board  26 . Since the remainder is the same as the apparatus shown in  FIGS. 1 and 2 , the same reference numerals are used for the same or similar parts and components and no detailed description is given about them. The printed circuit board  26  according to this embodiment is electrically connected to the printed circuit board  16  for the control panel. For that purpose, a connector  44  is mounted on the printed circuit board  16  and a connector  46  is mounted on the printed circuit board  26 . The lengths of the connectors  44  and  46  are so determined that, when they are connected together, the printed circuit board  26  can be located at the rear opening of the wall unit  24  to thereby close the rear opening. 
   In the above-described embodiments, the printed circuit board  26  is used as a lid for closing the rear opening of the wall unit  24 , but any one of various suitable members may be used instead. For example, a plate for mounting components of the power supply apparatus can be used. Also, in the embodiments described above, the shape of the wall unit  24  is a hollow-short rectangular prism so as to conform with the rectangular shape of the printed circuit board  16 , but, if the shape of the printed circuit board  16  is different, for example, circular, the wall unit may have a cylindrical shape. The securing members  28   a  and  28   b  may be formed on the shorter-side walls  24   c  and  24   d  instead of the longer-side walls  24   a  and  24   b.