Abstract:
In a power conversion adapter which is connected to an AC power supply receptacle to convert AC power supplied therefrom to DC power, a casing body has a first principal face, a second principal face which extend in parallel with each other, and at least one pair of connection passages extending from the first principal face to the second principal face. Conductive members are disposed within the casing body so as to elastically protrude into the respective connection passages while being electrically connected to an AC/DC converter. At least one plug member each includes a base portion, and a pair of plug pieces extended from the base portion so as to have a length which is longer than a length of the connection passages. The plug member is detachably combined with one of the first principal face and the second principal face of the casing body such that the plug pieces are inserted into the connection passages while being electrically connected with the conductive members. A portion of each plug piece protruded from the other one of the first principal face and the second principal face is inserted into each plug fitting hole of the AC power supply receptacle.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a power conversion adapter (hereunder referred to as an AC adapter) connected to an AC power supply and adapted to perform power conversion by a built-in alternating current-direct current (AC-DC) conversion circuit and to output DC power to equipment connected thereto.  
           [0002]    AC adapters are used, for example, in the case of using a charger, which charges a rechargeable battery, and electronic equipment, which employs a DC power source as a power supply, by connecting the charger and the electronic equipment to a commercial power supply. Further, AC adapters convert DC to AC and supply AC to equipment connected thereto. As shown in FIG. 7, a first related AC adapter  50  is constructed so that a circuit board (not shown), on which a power transformer (not shown) and components of a power supply circuit (not shown) are mounted, is built in a casing  51 , that a pair of plug pieces  52   a ,  52   b  to be respectively plugged into plug holes  61   a  and  61   b  of a power supply receptacle  60  is provided on one of side faces of the casing  51  in such a way as to protrude therefrom, and that a connection code  53  to be connected to equipment (not shown) is drawn out of the casing  51 .  
           [0003]    As portable telephones, various kinds of mobile equipment, and notebook personal computers come into wide use, it has been often that a user carries an AC adapter so as to charge a rechargeable battery, which is used as a power supply therefor, at a place away from home. As described above, a power transformer, which is relatively large in weight and size, is built in the first related AC adapter  50 . Therefore, the first related AC adapter  50  has a drawback in that this related AC adapter is large in size and weight, and that it is difficult to carry this related AC adapter as a portable one. Moreover, the AC adapter  50  has another drawback in that the plug pieces  52   a ,  52   b  are bent or damaged when carelessly dropped while carried.  
           [0004]    Meanwhile, the reduction in size and weight of the AC adapter  50  can be achieved by, for example, employing thin film devices as various components of the AC-DC conversion circuit. However, as described above, the plug pieces  52   a ,  52   b  are provided in such a way as to be orthogonal to the side face of the casing  51  and as to project therefrom, so that the thickness of the entire AC adapter  50  cannot be reduced. Therefore, regarding AC adapters, for instance, a second related AC adapter  55 , in which each of the base portions of the plug pieces  52   a ,  52   b  is supported by a rotating mechanism as shown in FIG. 8, and a third related AC adapter  57 , in which the plug pieces  52   a ,  52   b  freely go in and out of the casing  51  as illustrated in FIG. 9, have been provided.  
           [0005]    The second related AC adapter  55  is constructed so that when unused, the plug pieces  52   a ,  52   b  are accommodated in slits  56  formed in the casing  51 , as represented by arrows in FIG. 8. Conversely, when used, the plug pieces  52   a ,  52   b  are plugged into plug holes  61  of the power supply receptacle  60  by being rotated and operated in such a manner as to be orthogonal to the casing  51 , as represented by solid lines in this figure. Thus, the AC adapter  55  can be carried by accommodating, when unused, the plug pieces  52   a ,  52   b  in the casing  51  so that the plug pieces  52   a ,  52   b  are not hindrances to carrying the AC adapter  55 .  
           [0006]    On the other hand, the third related AC adapter  57  is constructed so that when unused, the plug pieces  52   a ,  52   b  are respectively accommodated in mounting holes formed in the casing  51 , as represented by arrows in FIG. 9, and that when used, the plug pieces  52   a ,  52   b  are drawn out of the casing  51  and plugged into plug holes  61  of the power supply receptacle  60 , as represented by solid lines in this figure. With such a configuration, the adapter  57  can be carried so that the plug pieces  52   a ,  52   b  are not hindrances to carrying the AC adapter  57 .  
           [0007]    However, the second related AC adapter  55  has a drawback in that because a bearing mechanism for rotating and supporting the plug pieces  52   a ,  52   b , and a contact mechanism for connecting these plug pieces  52   a ,  52   b  to the circuit board, or a lock mechanism for holding the plug pieces  52   a ,  52   b  in a rotating position are provided therein, the number of components thereof is large, and the structure thereof is complex.  
           [0008]    Further, the AC adapter  55  has a drawback in that because the slits  56 , in which the plug pieces  52   a ,  52   b  are respectively accommodated, are formed in the casing  51 , a dead space is produced in the casing  51 , so that it is difficult to considerably reduce the size thereof. Furthermore, the AC adapter  55  has another drawback in that because the plug pieces  52   a ,  52   b  are formed from metal pieces each having a certain amount of thickness, the width of each of the slits  56  increases, so that the size of the casing  51  increases.  
           [0009]    On the other hand, the third related AC adapter  57  requires a lock mechanism for holding the plug pieces in an accommodated state or in a drawn-out state. Thus, the AC adapter  57  has drawbacks in that the number of components thereof is large, and that the structure thereof is complex.  
           [0010]    Moreover, in the AC adapter  57 , a supporting portion for the plug pieces  52   a ,  52   b  is unstable. Moreover, the AC adapter  57  has another drawback in that the size thereof becomes larger when a supporting mechanism having large mechanical strength is constructed to thereby securely support the plug pieces  52   a ,  52   b . Furthermore, the AC adapter  57  is constructed so that the casing  51  has a width sufficient to accommodate the plug pieces  52   a ,  52   b . Thus, the AC adapter  57  has another drawback in that there is a restriction on reduction in the entire size of the AC adapter  57 .  
         SUMMARY OF THE INVENTION  
         [0011]    It is therefore an object of the invention to provide a power conversion adapter that has a simple structure and that is enabled to significantly enhance the portability thereof by reduction in the weight and size thereof.  
           [0012]    In order to achieve the above object, according to the present invention, there is provided A power conversion adapter which is connected to an AC power supply receptacle to convert AC power supplied therefrom to DC power, comprising:  
           [0013]    a casing body having a first principal face and a second principal face which extend in parallel with each other, the casing body formed with at least one pair of connection passages extending from the first principal face to the second principal face;  
           [0014]    an AC/DC converter, deposed within the casing body;  
           [0015]    conductive members, disposed within the casing body so as to elastically protrude into the respective connection passages while being electrically connected to the AC/DC converter; and  
           [0016]    at least one plug member, each including:  
           [0017]    a base portion; and  
           [0018]    a pair of plug pieces extended from the base portion so as to have a length which is longer than a length of the connection passages, wherein:  
           [0019]    the plug member is detachably combined with one of the first principal face and the second principal face of the casing body such that the plug pieces are inserted into the connection passages while being electrically connected with the conductive members; and  
           [0020]    a portion of each plug piece protruded from the other one of the first principal face and the second principal face is inserted into each plug fitting hole of the AC power supply receptacle.  
           [0021]    In this configuration, the casing body and the plug member are provided as individual members so that the plug pieces of the plug member are fitted into the connection passages of the casing body only when the adapter is connected to the power supply receptacle. Consequently, the plug pieces do not protrude from the casing body when the adapter is not used. Thus, the adapter can be treated by reducing the entire size and thickness of the adapter. Moreover, since the plug pieces are not hindrances to carrying the adapter, the portability thereof is significantly enhanced. Furthermore, since there is no necessity for a mechanism for rotating and supporting the plug pieces or for sliding and supporting the plug pieces, the structure thereof can be simplified. Therefore, the size, weight, thickness and cost thereof can be totally reduced.  
           [0022]    Preferably, the casing body has side end faces defining a distance between the first principal face and the second principal face as a thickness of the casing body. The thickness is substantially identical with a distance between the pair of plug pieces.  
           [0023]    Here, it is preferable that the plug member is attached on one of the side end faces of the casing body so that one side end portion of the casing body enters into a space defined by the pair of plug pieces, when the plug member is not connected to the AC power supply receptacle.  
           [0024]    Preferably, the power conversion adapter further comprises a chain member which connects the casing body and the plug member.  
           [0025]    Preferably, the base portion is provided as an elastic flat plate member from which the plug pieces are extended in opposite directions. The base portion is flexed such that the plug pieces extend in parallel with each other when the plug pieces are inserted into the connection passages.  
           [0026]    Here, it is preferable that a holder is formed on the casing body to hold the plug member thereon when the plug member is not connected to the AC power supply receptacle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0028]    [0028]FIG. 1 is an exploded perspective view illustrating an AC adapter according to a first embodiment of the invention;  
         [0029]    [0029]FIG. 2 is an enlarged vertical section view illustrating a state in which the AC adapter is connected to a power supply receptacle;  
         [0030]    [0030]FIG. 3 is an enlarged horizontal section view illustrating a state in which the AC adapter is connected to the power supply receptacle;  
         [0031]    [0031]FIG. 4 is an exploded perspective view illustrating an AC adapter according to a second embodiment of the invention;  
         [0032]    [0032]FIG. 5 is a perspective view illustrating a plug member used in the AC adapter of the second embodiment;  
         [0033]    [0033]FIG. 6 is a perspective view illustrating a state in which the plug member is combined with an adapter body of the AC adapter of the second embodiment;  
         [0034]    [0034]FIG. 7 is a perspective view illustrating a first related AC adapter;  
         [0035]    [0035]FIG. 8 is a perspective view illustrating a second related AC adapter; and  
         [0036]    [0036]FIG. 9 is a perspective view illustrating a third related AC adapter. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]    Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.  
         [0038]    As illustrated in FIGS.  1  to  3 , an AC adapter  1  according to a first embodiment comprises an adapter body  2  and a plug member  3 , which are provided as individual members. The plug member  3  is connected to the adapter body  2  by a connection chain  4  so that the plug member  3  is prevented from being lost. As shown in FIG. 1, in the AC adapter  1 , a connection code  5  is drawn out of the adapter body  2 . DC power is obtained by performing power conversion on commercial power and supplied by connecting a plug  6  provided at an end of this connection code  5  to a charger for charging a rechargeable battery or to electronic equipment that requires a DC power supply.  
         [0039]    The adapter body  2  has a casing  7  that is obtained by assembling a pair of halves formed like rectangular shallow pans from an insulating synthetic resin material and that is presented like a thin housing as a whole. A circuit board  8  provided with an AC-DC conversion circuit, the description of details of which is omitted, is provided, is built in this casing  7 . In the adapter body  2 , appropriate electronic components of an AC-DC conversion circuit are mounted on the circuit board  8 . Moreover, coil elements and various thin film devices of a power transformer are formed on the circuit board  8  by utilizing thin film formation techniques. A pair of plug fitting holes  9   a  and  9   b  are formed in the adapter body  2  in such a way as to penetrate through the front and rear principal faces  7   a  and  7   b  of the casing  7 . A connection convex  10  for connecting an end portion of a connection chain  4  to one side face (top face)  7   c  in the longitudinal direction of the casing  7  is provided on the adapter body  2  in such a manner as to be integral therewith and to protrude therefrom.  
         [0040]    Incidentally, a drawing hole is formed in the other side face (bottom face) in the longitudinal direction of the casing  7  of the adapter body  2 . The aforementioned connection code  5  is drawn therefrom by inserting a bush into this drawing hole so as to prevent the slip-off thereof and as to protect the cord  5 . The connection code  5  is connected to an output terminal portion, which is formed on the circuit board  8 , at an end portion thereof drawn in to the casing  7 . The connection code  5  may be connected to the adapter body  2  by, for example, connecting a coaxial plug to an end thereof and inserting the coaxial plug into a jack attached to the casing  7 .  
         [0041]    The plug fitting holes  9   a  and  9   b  are formed in the casing  7  so that the distance therebetween and the opening size thereof are equal to the distance between the plug holes  61   a  and  61   b  and to the opening size of each of the holes  61   a  and  61   b , respectively. As illustrated in FIGS. 2 and 3, guide holes  11   a  and  11   b , which are formed in the circuit board  8  built in the casing  7  in such a way as to penetrate therethrough, communicate with each other. Each of the guide holes  11   a  and  11   b  is formed in the casing  8  so that the distance therebetween and the opening size thereof are equal to the distance between the plug fitting holes  9   a  and  9   b  and to the opening size of each of the holes  9   a  and  9   b , respectively.  
         [0042]    A pair of electrode pieces  12   a  and  12   b  are attached to the circuit board  8  in such a way as to be placed across the guide hole  11   a , while a pair of electrode pieces  13   a  and  13   b  are attached to the circuit board  8  in such a way as to be placed across the guide hole  11   b . Each of the pairs of the electrode pieces  12   a  and  12   b  and the electrode pieces  13   a  and  13   b  is integrally formed from a resilient metal plate member. Although the description of the details of the structure of the electrode piece is omitted, each of the electrode pieces has a base portion, which is fixed onto the primary face of the circuit board  8  along an opening edge of a corresponding one of the guide holes  11   a  and  11   b , and a contact piece portion that is formed in parallel with the guide holes  11   a  and  11   b  in such a way as to rise from this base portion.  
         [0043]    The contact piece portions of the electrode pieces  12   a ,  12   b  or  13   a ,  13   b  of each of the pairs face each other across a corresponding one of the guide holes  11   a  and  11   b . Moreover, as shown in FIG. 3, the contact piece portions of the electrode pieces of each of the pairs are bent so that the central parts thereof abut against each other. Therefore, the contact piece portions of the electrode pieces  12   a ,  12   b  or  13   a ,  13   b  of each of the pairs are made to extend along both sides of the corresponding one of the guide holes  11   a ,  11   b , in other words, the plug fitting holes  9   a  and  9   b , and to protrude therefrom.  
         [0044]    Incidentally, each of the electrode pieces may be constituted by, for instance, a metal ball and a spring for urging this metal ball so as to protrude into the plug fitting hole  9 . Further, the adapter body  2  may be constructed so that each of the electrode pieces  12  and  13  is attached to a predetermined portion, which is suitably formed in such a way as to be integral with the casing  7 , and connected to the terminal portion of the circuit board  8  by a lead wire.  
         [0045]    The plug member  3  comprises a plate-shaped base portion  14 , the entirety of which is formed from an insulating synthetic resin, and a pair of plug pieces  15   a  and  15   b  insert-molded into this base portion  14 . The plug member  3  has a connection convex  16  formed on the top part of the base portion  14  in such a manner as to be integral therewith, and the other end of the aforementioned connection chain  4  is connected to the connection convex  16 . It is sufficient for the base portion  14  to maintain the distance between the opposed plug pieces  15   a  and  15   b  and to support base end portions thereof. Thus, the base portion  14  does not require high mechanical strength. Consequently, the base portion  14  is formed in such a way as to be relatively thin.  
         [0046]    The plug pieces  15   a  and  15   b  are orthogonal to the primary face of this base portion  14  and placed in such a way as to be parallel to and to face each other. The distance between the plug pieces  15   a  and  15   b  is set to be equal to that between the plug holes  61   a  and  61   b  of the power supply receptacle  60 . The size of a section of each of the plug pieces  15   a  and  15   b  is nearly equal to the opening size of each of the plug holes  61   a  and  61   b . In other words, the distance between the plug pieces  15   a  and  15   b  and the size of the section of each of the plug pieces  15   a  and  15   b  are nearly equal to the distance between the plug fitting pieces  9   a  and  9   b  and the size of the section of each of the plug pieces  15   a  and  15   b . Moreover, each of the plug pieces  15   a  and  15   b  has a length that is sufficiently longer than the thickness of the casing  7  of the adapter body  2 .  
         [0047]    In the plug member  3  constructed as described above, the plug pieces  15   a  and  15   b  are fitted into the plug fitting holes  9   a  and  9   b  of the adapter body  2 , respectively. In the plug member  3 , the plug pieces  15   a  and  15   b  are respectively fitted into the plug fitting holes  9   a  and  9   b  from either of the front and rear primary faces  7   a  and  7   b  of the casing  7 . The plug member  3  is adapted so that, for example, when the plug pieces  15   a  and  15   b  are respectively fitted into the plug fitting holes  9   a  and  9   b  from one of the primary faces  7   a , the end portions of the plug pieces  15   a  and  15   b  protrude from the other primary face  7   b  of the casing  7 .  
         [0048]    The plug member  3  is constructed so that the plug pieces  15   a  and  15   b  fitted into the plug fitting holes  9   a  and  9   b  penetrate through the adapter body  2  during push-opening the pair of electrode pieces  12   a  and  12   b  and the pair of the electrode pieces  13   a  and  13   b , as illustrated in FIG. 3. Thus, in the plug member  3 , the plug piece  15   a  is electrically conducted to the electrode pieces  12   a  and  12   b , while the plug piece  15   b  is electrically conducted to the electrode pieces  13   a  and  13   b . Consequently, the plug member  3  is connected to the AC-DC conversion circuit provided on the circuit board  8  that is built in the adapter body  2 .  
         [0049]    As described the above, the base portion  14  is formed in such a way as to be thin, has a certain degree of elasticity so as to be deformable. Therefore, when the AC adapter  1  is unused, the plug pieces  15   a  and  15   b  are pulled out of the plug fitting holes  9   a  and  9   b , and the plug member  3  is placed on one side portion of the casing  7  such that the side portion is entered into a space between the plug pieces  15   a  and  15   b . This makes the AC adapter  1  portable. Since the adapter body  2  and the plug member  3  are provided as individual members, appropriate position at which the plug member  3  is placed can be selected.  
         [0050]    After combining the adapter body  2  and the plug member  3  such that the end portions of the plug pieces  15   a  and  15   b  are protruded and exposed from the primary face  7   b  of the casing  7  as described the above, the AC adapter  1  is fitted into the plug holes  61   a  and  61   b  of the power supply receptacle  60 . The plug pieces  15   a  and  15   b  are sandwiched by the electrode spring members  62   a  and  62   b  of the power supply receptacle  60  so that AC power is supplied from the power supply receptacle  60  through the electrode spring members  62   a  and  62   b  to the AC adapter  1 .  
         [0051]    In the AC adapter  1 , the AC power is supplied to the AC-DC conversion circuit through the plug pieces  15   a  and  15   b  so that an AC voltage is converted into a predetermined DC voltage. The AC adapter  1  outputs a DC current, which is obtained by the conversion, from the connection code  5 , and supplied the outputted DC current to equipment connected thereto.  
         [0052]    An AC adapter  20  according to a second embodiment of the invention is illustrated in FIGS. 4 and 5. In this embodiment, there is provided a configuration having a plug member  21  that enables further reduction in the size of the AC adapter. The AC adapter  20  employs the adapter body  2  of the aforementioned AC adapter  1 . Thus, the detail description of the adapter body of the AC adapter  20  is omitted herein. A plug member  21  of the AC adapter  20  has a basic configuration, which has a connecting base portion  22  formed from an insulating synthetic resin material and a pair of plug pieces  23   a  and  23   b  insert-molded into this connection base portion  22 , and which is similar to that of the plug member  3 .  
         [0053]    In the plug member  21 , the connection base portion  22  is shaped like a thin rectangle having a length that is slightly longer than the distance between the plug fitting holes  9   a  and  9   b  of the adapter body  2 . The connection base portion  22  has flexibility in the direction of thickness thereof. Plug pieces  23   a  and  23   b  are integrally insert-molded into the connection base portion  22  at both sides in the longitudinal direction thereof. As indicated by solid lines in FIG. 5, when unused, in the plug member  21 , the plug pieces  23   a  and  23   b  are aligned in a line through the connection base portion  22 , so that the entire plug member  21  is presented like a single plate.  
         [0054]    The plug pieces  23   a  and  23   b  are formed so that the size of a section of each of the plug pieces  23   a  and  23   b  is nearly equal to the opening size of each of the plug holes  61   a  and  61   b . In other words, each of the plug pieces  23   a  and  23   b  is formed so that the distance therebetween and the size of the section thereof are nearly equal to the distance between and the opening size of the plug fitting holes  9   a  and  9   b  of the adapter body  2 , respectively. Each of the pieces  23   a  and  23   b  has a length that is sufficiently longer than the thickness of the casing  7  of the adapter body  2 . The insulation between the plug pieces  23   a  and  23   b  is held by the connection base portion  22 . Therefore, in the AC adapter  20 , the plug pieces  23   a  and  23   b  of the plug member  21  do not project therefrom, so that these plug pieces do not hinder the AC adapter  20  from being carried. Consequently, not only the downsizing of the AC adapter  20  is achieved, but also the portability thereof is enhanced.  
         [0055]    The plug member  21  is adapted so that when the AC adapter  20  is used, the connection base portion  22  is bent so as to be U-shaped, as indicated by chain lines in FIG. 5. When the plug member  21  is in such a condition that the plug pieces  23   a  and  23   b  are caused to face each other, the plug pieces  23   a ,  23   a  are fitted into the plug fitting holes  9   a ,  9   a  of the adapter body  2 , as indicated by an arrow in FIG. 4. When the plug pieces  23   a ,  23   a  of the plug member  21  are respectively fitted into the plug fitting holes  9   a ,  9   b  from the one of the primary faces  7   a  of the casing  7  of the adapter body  2 , the end portions thereof project from the other primary face  7   b  of the casing  7 .  
         [0056]    In the plug member  21 , each of the plug pieces  23   a ,  23   b  fitted into the plug fitting holes  9   a ,  9   b  is electrically conducted to a corresponding one of pairs of electrode pieces  12   a ,  12   b  and electrode pieces  13   a ,  13   b , which are projected into the guide holes  11   a  and  11   b  of the circuit board  8 . Thus, the plug member  21  is connected to the AC-DC conversion circuit provided on the circuit board  8  built in the adapter body  2 .  
         [0057]    After the plug member  21  is combined with the adapter body  2  as described above, the end portions of the plug pieces  23   a ,  23   a  of the plug member  21 , which are projected and exposed from the other primary face  7   b  of the casing  7  of the adapter body  2 , are fitted into the plug holes  61   a ,  61   b  of the power supply receptacle  60 . In the AC adapter  20 , the plug pieces  23   a ,  23   b  are sandwiched by the electrode spring members  62   a ,  62   a  of the power supply receptacle  60  so that AC power is supplied from the power supply receptacle  60  to the AC-DC conversion circuit of the adapter body  2  of the AC adapter  20  through the electrode spring members  62   a ,  62   b  and the plug pieces  23   a ,  23   b.    
         [0058]    In the AC-DC conversion circuit of the AC adapter  20 , the AC power is converted so that an AC voltage is converted into a predetermined DC voltage. The AC adapter  20  outputs a DC current, which is obtained by the conversion, from the connection code  5 , and supplied the outputted DC current to equipment connected thereto.  
         [0059]    Since the plug member  21  becomes a single plate member in a normal condition, as described above, when the AC adapter  20  is carried or unused, the plug member  21  can be handled by being attached on the thin adapter body  22 .  
         [0060]    Namely, the aforementioned AC adapter  20  does not employ such a structure in which the plug member is connected to the adapter body by a connection chain, which prevents the plug member from being lost. Therefore, a structure for holding the unused plug member  21  may be formed in the casing  7  of the AC adapter  20 , similarly as the adapter body  2  illustrated in, for instance, FIG. 6.  
         [0061]    That is, in the adapter body  2 , a plug member holder  25  is formed over the entirety of one of the side faces  7   e  in the longitudinal direction of the casing  7 . The plug member holder  25  comprises a base portion holding part  25   a  of the central portion thereof, and plug piece holding parts  25   b ,  25   c  formed at both sides of this base portion holding part  25   a  in such a way as to communicate with each other. The base portion holding part  25   a  is shaped like a groove having a size, which is sufficient for fitting the connection base portion  22  of the plug member  21  thereinto. Each of the plug piece holding parts  25   b ,  25   c  is formed such that one end thereof is opened to this base portion holding part  25   a , and that the other end of each of the plug piece holding parts  25   b ,  25   c  is opened to a corresponding one of the top face  7   c  and the bottom face  7   c  of the casing  7 . Each of the plug piece holding parts  25   b ,  25   c  is shaped like a groove having a size, which is sufficient for fitting a corresponding one of the plug pieces  23   a ,  23   b  of the plug member  21  thereinto.  
         [0062]    As illustrated in FIG. 6, the plug member  21  is assembled to the adapter body  2  by fitting, when the AC adapter  20  is unused, the connection base portion  22  into the base portion holding part  25   a  and moreover, fitting the plug pieces  23   a ,  23   b  into the plug piece holding parts  25   b  and  25   c , respectively. The plug member  21  is formed in such a way as to be integral with the adapter body  2  by causing the groove walls of the plug member holder  25  to hold the connection base portion  22  or the plug pieces  23   a ,  23   b . Therefore, according to the AC adapter  20 , the plug member  21  is held by the adapter body  2 , so that this plug member  21  is restrained by from being lost, and that the handling of this adapter is facilitated still more.  
         [0063]    Incidentally, regarding the adapter body  2 , the configuration of the plug member holder  25  is not limited to the aforementioned configuration. An appropriate locking convex adapted to project into the groove so as to more reliably hold the plug member  21  may be formed in such a way as to be integral therewith. Further, regarding the adapter body  2 , when the length of the plug member  21  is longer than that of the side face  7   e  of the casing  7 , the plug member holder  25  may be formed in such a way as to extend over other side faces orthogonal to the side face  7   e.    
         [0064]    Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.