Abstract:
An AC adapter has a synthetic resin case, a switching regulator circuit assembly with an AC input terminal in the synthetic resin case, a synthetic resin name plate, and a metallic Bsheet for heat radiation separate from the resin name plate. A surface of the case has a first concave portion for the name plate and a second concave portion for the metallic sheet in the first concave portion, the metallic sheet being attached in the second concave portion with the name plate attached in the first concave portion and covering the attached metallic sheet.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an AC adapter for a portable device. 
   2. Description of the Related Art 
     FIG. 1  is a perspective view showing a conventional AC adapter  1  with an AC cord. The AC adapter  1  includes a switching regulator circuit embedded in a synthetic resin case  4  prepared by combining a lower half case  2  with an upper half case  3 . An AC cord  11  having an AC plug  10  at a tip thereof extends from one side of the case  4  and a DC cord  21  having a plug  20  at a tip thereof extends from the other side of the case  4 . And a name plate  22  is attached to a surface of the case  4 . 
   The name plate  22  includes a synthetic resin sheet in a front surface thereof and an aluminum sheet portion  23  for diffuse radiation in the whole area of a back surface thereof. The name plate  22  has substantially the same size as that of the surface of the case  4 . The aluminum sheet portion  23  covers substantially the whole area of the surface of the case  4 . 
   The AC adapter  1  is used by inserting the AC plug  10  into an outlet and connecting the plug  20  to a portable device. A noise is generated in each on/off operation repeatedly performed by a switching regulator circuit. Such a noise may be partially transmitted to the AC plug  10  via the AC cord  11 . The noise transmitted via the AC cord  11  is referred to as “noise terminal voltage”. This noise terminal voltage is transmitted to other electronic devices via the outlet and home wiring and affects the electronic devices connected to other outlets. Thus, it is preferable to reduce the noise terminal voltage in the AC adapter  1  as much as possible. 
   In the conventional AC adapter  1 , the aluminum sheet portion  23  covers substantially the whole area of the surface of the case  4  and a portion of the aluminum sheet portion  23  reaches a portion for an AC input terminal to which the AC cord  11  is connected. 
   In  FIG. 2 , line I indicates the result of measurement of noise terminal voltage in the conventional AC adapter  1  using a spectrum analyzer and a receiver. The horizontal axis indicates frequency and the vertical axis indicates noise levels. As the test conditions, Vin is 120V/60 Hz and Io is  2 A. In  FIG. 2 , line II indicates an average noise terminal voltage (AV) determined by the standards and line III indicates a quasi peak value (QP) of a peak noise terminal voltage. 
   As shown in  FIG. 2 , although the noise terminal voltage meets the standards, a margin thereof, such as a margin M relative to the peak noise terminal voltage is relatively small. 
   Accordingly, in the AC adapter, it is required to enlarge the aforementioned margin by further reducing the noise terminal voltage in order to improve the quality of the AC adapter. 
   SUMMARY OF THE INVENTION 
   In light of such requirement, the present invention has been made. 
   It is a general object of the present invention to provide an improved and useful AC adapter in which the above-mentioned problem is eliminated. 
   A more specific object of the present invention is to provide an AC adapter by which the quality thereof is improved in terms of the noise terminal voltage. 
   The present invention provides an AC adapter comprising: a synthetic resin case; a switching regulator circuit assembly having an AC input terminal and a DC output terminal, the switching regulator circuit assembly being housed in the synthetic resin case; a synthetic resin name plate; and a metallic sheet for heat radiation separate from the resin name plate, wherein the metallic sheet is attached to a surface of the case except for a portion for the AC input terminal. 
   According to the present invention, the metallic sheet does not exist in the portion for the AC input terminal, so that the noise terminal voltage is not propagated to the AC input terminal via the metallic sheet. Thus, the quality of the AC adapter is improved in terms of the noise terminal voltage. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing a conventional AC adapter having a name plate on a top surface thereof; 
       FIG. 2  is a chart showing the generation of noise terminal voltage in the conventional AC adapter in  FIG. 1 ; 
       FIG. 3  is a perspective view showing an AC adapter according to an embodiment of the present invention when viewed from below, including an exploded view of an aluminum sheet and a name plate; 
       FIG. 4  is a plan view showing the AC adapter in  FIG. 3  without an upper half case; 
       FIG. 5  is a cross-sectional view of the AC adapter in  FIG. 3 ; 
       FIG. 6  is a chart showing the generation of noise terminal voltage in the AC adapter in  FIG. 3 ; and 
       FIG. 7  is a chart showing the characteristics of heat radiation in the AC adapter in  FIG. 3 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following, an embodiment of the present invention will be described with reference to the accompanying drawings. 
     FIG. 3  is a perspective view showing an AC adapter  30  with an inlet plug for a portable device according to the embodiment of the present invention when viewed from below, including an exploded view of an aluminum sheet and a name plate.  FIG. 4  is a plan view showing the inside of the AC adapter  30  without an upper half case. And  FIG. 5  is a cross-sectional view of the AC adapter  30 . X 1 -X 2  indicates a width direction, Y 1 -Y 2  indicates a longitudinal direction, and Z 1 -Z 2  indicates a height direction. 
   As shown in  FIGS. 3 to 5 , the AC adapter  30  includes a switching regulator circuit assembly  40  embedded in a synthetic resin case  34  prepared by combining a lower half case  32  with an upper half case  33 . An inlet plug  45  is exposed on a surface  34 Y 2  positioned on a Y 2  side of the case  34 , a DC cord  61  having a plug  60  at a tip thereof extends from a surface  34 Y 1  positioned on a Y 1  side of the case  34 , and an aluminum sheet  70  and a synthetic resin name plate  71  are attached to a surface  34 Z 2  positioned on a Z 2  side of the case  34 . 
   In the switching regulator circuit assembly  40 , as shown in  FIGS. 4 and 5 , a transformer  42  and the like are mounted on a top surface of a printed board  41 , an AC input terminal  43  is disposed on the Y 2  side of the printed board  41 , and a DC output terminal  44  is disposed on the Y 1  side of the printed board  41 . The inlet plug  45  is connected to the AC input terminal  43  and the DC cord  61  is connected to the DC output terminal  44 . Further, a line filter  46  and a film capacitor  47  are mounted between the AC input terminal  43  and the transformer  42 . The line filter  46  and the film capacitor  47  are configured to prevent a noise mainly generated in the transformer  42  from propagating to the AC input terminal  43 , the noise being generated in each on/off operation repeatedly performed by the switching regulator circuit. Also, three Schottky diodes (SBD)  48 - 1 ,  48 - 2 , and  48 - 3  are mounted between the transformer  42  and the DC output terminal  44 . The Schottky diodes  48 - 1 ,  48 - 2 , and  48 - 3  generate heat in particular and become main heat sources. The printed board  41  is fixed at the bottom of the lower half case  32 . 
   A shallow concave portion  50  for the name plate  71  having a size in accordance with the size of the name plate  71  is formed on the whole area of the surface  34 Z 2  positioned on the Z 2  side of the case  34  and a deep concave portion  51  for the aluminum sheet  70  having a size in accordance with the size of the aluminum sheet  70  is formed on a portion of the Y 1  side having about a half of the whole area. The concave portion  51  has steps relative to the surface  34 Z 2  and the concave portion  50 . 
   (Regarding the Aluminum Sheet  70 ) 
   The aluminum sheet  70  is a separate member having a thickness of 50 μm and a size of substantially the half of the surface  34 Z 2  of the case  34 . The aluminum sheet  70  is positioned and attached in accordance with the concave portion  51 . As shown in  FIG. 5 , the aluminum sheet  70  is placed within the concave portion  51 . Also, as shown in  FIG. 4 , the aluminum sheet  70  covers an area for the Schottky diodes  48 - 1 ,  48 - 2 , and  48 - 3 . 
   The name plate  71  has a thickness of 50 μm and positioned and attached in accordance with the concave portion  50 . As shown in  FIG. 5 , the name plate  71  is placed within the concave portion  50  and covers the aluminum sheet  70 . A surface of the attached name plate  71  is flat and equal to the surface  34 Z 2 . 
   The aluminum sheet  70  is not extended to a portion for the line filter  46 , the film capacitor  47 , and the AC input terminal  43 . The aluminum sheet  70  does not exist beneath the line filter  46  to the AC input terminal  43 . Thus, although the noise generated in each on/off operation repeatedly performed by the switching regulator circuit is propagated in the aluminum sheet  70 , the propagation is restricted to a portion positioned substantially on the Y 1  side relative to the AC input terminal  43 . The noise propagated in the aluminum sheet  70  is prevented from reaching the inlet plug  45  via the AC input terminal  43 . In other words, the “noise terminal voltage” resulting from the aluminum sheet  70  is not generated. 
   In addition, if the name plate  71  is integrated with the aluminum sheet  70 , it is difficult to manufacture the name plate  71  since the size of the aluminum sheet  70  is different from that of the name plate  71 . In the present embodiment, the aluminum sheet  70  is a separate member, so that it is easy to manufacture the name plate  71 . 
   (Characteristics and the Like of Noise Terminal Voltage in the AC Adapter  30 ) 
   In  FIG. 6 , line IA indicates noise terminal voltage in the aforementioned AC adapter  30  measured using the same test conditions mentioned above. As shown in  FIG. 6 , a margin MA is enlarged and MA&gt;M in comparison with  FIG. 2 . 
   In  FIG. 7 , line X indicates the result of measuring the temperature of a portion of the aluminum  70  for lower portions of the Schottky diodes  48 - 1 ,  48 - 2 , and  48 - 3  when the AC adapter  30  is used in an environment where ambient temperature Ta is about 28 degrees, Vin is 120V/50 Hz, and Io is  2 A. Line XI indicates the result of measuring the temperature of a portion of the bottom of the lower half case  32  for lower portions of the Schottky diodes  48 - 1 ,  48 - 2 , and  48 - 3  when the test is conducted without attaching the aluminum sheet  70 . 
   After 60 minutes has elapsed, when the aluminum sheet  70  is not attached, the temperature reaches 69.4° C. and the difference of temperature ΔT from the ambient temperature Ta is 41.2° C. By contrast, when the aluminum sheet  70  is attached, the increase of the temperature is limited to 60° C. and the difference of temperature ΔT from the ambient temperature Ta is controlled to 31.8° C., thereby reducing the difference of temperature ΔT by about 10° C. in comparison with the case where the aluminum sheet  70  is not attached. In other words, although the size of the aluminum sheet  70  is substantially a half of that of the surface  34 Z 2  of the case  34 , the aluminum sheet  70  is capable of radiating heat in a diffuse manner. 
   The size and arrangement of the aluminum sheet  70  are not limited to the aforementioned size and arrangement. The aluminum sheet  70  has certain effects when an end thereof is distanced from the AC input terminal  43 . 
   The structure of the aluminum sheet  70  attached as mentioned above can be applied to an AC adapter with an AC cord and the same effects are obtained. 
   The present invention is not limited to the specifically disclosed embodiment, and variations and modifications may be made without departing from the scope of the present invention. 
   The present application is based on Japanese priority application No. 2005-192403 filed Jun. 30, 2005, the entire contents of which are hereby incorporated herein by reference.