Abstract:
A power supply provides a low touch-temperature surface by utilizing a plurality of spaced apart pegs which extend from a surface of a case away from heat generating components enclosed within the case. The top and side surfaces of the pegs and the surface of the case not occupied by the pegs are entirely directly exposed to ambient air. The tops of the pegs provide a touch surface having a temperature which is cooler than that at the base of the pegs. The pegs are preferably arranged to minimize heat transfer between adjacent pegs.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to power supplies, also known as power adapters and power converters. In particular, the invention concerns a power supply which utilizes a case with a low touch-temperature surface. 
       BACKGROUND OF THE INVENTION 
       [0002]    Referring to  FIG. 1 , there is shown in block diagram form a conventional power supply used to provide DC power to portable electronic devices, such as notebook computers, cellular telephones, PDAs, MP3 players and the like. The power supply  2  is capable of receiving an input voltage from a DC power source, such as an automobile or airplane power port, as well as from an AC power source, such as a household wall outlet. Conversion circuitry  4  converts the input voltage to a DC output voltage which may be provided to an electronic device, such as a notebook PC. The DC voltage provided to the electronic device may be fixed in the case, for example, that the power supply  2  is dedicated for use with one model of notebook PC. Alternatively, a signal  6  may be used to program the conversion circuitry  4  to provide a particular voltage selectable from a range of output voltages. In this way, the power supply may be used with a variety of electronic devices having differing input voltage requirements. Conversion circuitry and various connector adapters, cables and switches used to program the conversion circuitry are disclosed in U.S. Pat. No. 7,450,390, the disclosure of which is incorporated herein by reference; particular reference is made to FIGS. 7A-7C; 24-40; and 51 of U.S. Pat. No. 7,450,390. 
         [0003]    The conversion circuitry is typically housed in a case which surrounds a printed circuit board(s). Components (e.g., transformers, transistors, resistors, capacitors, etc.) making up the conversion circuitry are fixed to the circuit board(s) and are interconnected by wiring traces on or within the circuit board. For ease of portability and user convenience, it is desirable to provide a power supply which is physically small in thickness, as well as in length and width. However, since the conversion circuitry components generate heat in operation, a problem is encountered with small dimensioned power supplies in that their surface temperature may reach undesirable levels. This in turn causes risk of injury to the power supply user. 
         [0004]    Efforts to lower the surface temperature of power supplies have included use of louvers and openings in the case to provide air gaps to promote air circulation (see, e.g., U.S. Pat. No. 7,450,390). While configurations of this type lower the surface temperature of the case, they require use of a precisely fitted layer(s) to resist entry of liquids into the case. In addition, the presence of openings or air gaps weaken the structural integrity of the case. It would be beneficial for a power supply to have a low touch-temperature, with good structural integrity and low risk of liquid penetration. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is a power supply having a low touch-temperature surface. The power supply includes conversion circuitry to convert an input voltage to an output voltage. The conversion circuitry is housed in a case having a surface and a plurality of spaced apart pegs which extend from the surface away from the conversion circuitry. At their tops, the pegs provide a touch surface having a temperature cooler than that at the base of the pegs. 
         [0006]    The pegs have a unitary construction with the case surface such that there is no joint between the case surface and a peg in the location where the case surface transitions into a peg. The case surface and the top and side surfaces of the pegs are preferably entirely directly exposed to ambient air. In an embodiment, the case is assembled from top and bottom plastic housings which matingly engage to enclose a circuit board on which conversion circuitry components are disposed. Injection molding is the preferred method for forming the housings. The pegs may be arranged in a particular row and column configuration to minimize heat transfer between adjacent pegs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a block diagram of a conventional power supply; 
           [0008]      FIG. 2  is a perspective view of a power supply according to an embodiment of the invention; 
           [0009]      FIG. 3  is an expanded perspective view of the power supply; 
           [0010]      FIG. 4  is an perspective view of a case of the power supply; 
           [0011]      FIG. 5  is a cross sectional perspective view of the case taken along the line V-V of  FIG. 4 ; 
           [0012]      FIG. 6  is a top view of the case of the power supply; 
           [0013]      FIG. 7  is a cross sectional view of the case taken along the line VII-VII of  FIG. 6 ; 
           [0014]      FIG. 8  is an enlarged cross-sectional view of a cross section of the case taken within the circular line VIII-VIII of  FIG. 7 ; and 
           [0015]      FIG. 9  is an enlarged view of the top of the case taken within the circular line IX-IX of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]      FIG. 2  is a perspective view of a power supply according to an embodiment of the invention. The power supply  8  has, in the illustrated embodiment, the shape of a right parallelepiped with rounded edges and corners. The unit has a length L, a width W and a thickness T. The dimensions may vary as a function of factors, such as the power output capacity of the power supply. In general, the area of the top and bottom surface areas, defined by “L” and “W”, should be much greater than the thickness “T”. In a preferred embodiment, the length L is about 119.14 mm, the width W is about 64.58 mm and the thickness T is about 11.00 mm. A pair of input terminals  10  are disposed along one width of the power supply to receive, via a cable, AC or DC input power. 
         [0017]      FIG. 3  is an expanded perspective view of the power supply  8 . A top housing  22  matingly engages with a bottom housing  24  to enclose a circuit board  26 . The circuit board has affixed to it electrical components, such as transformers, transistors, resistors, capacitors, etc. (only some of which are shown in  FIG. 3 ) constituting conversion circuitry for converting the AC or DC voltage applied to input terminals  10  to a regulated DC output voltage. The DC output voltage is provided at a pair of the terminals  12 . The third terminal of terminals  12  may be used for receiving a signal which programs the conversion circuitry to provide a particular voltage selectable from a range of output voltages. 
         [0018]    To ensure electrical isolation, the circuit board and components are preferably sandwiched between a pair of insulator layers  28 ,  30 . In a preferred embodiment, the insulator layers are each made of double-layer polyethylene naphthalate (PEN). Between the insulator layer  28  and the top housing  22 , there is disposed a heat spreading layer  32 . Likewise, between the insulator layer  30  and the bottom housing  24 , there is disposed a heat spreading layer  34 . The heat spreading layers  32 ,  34  are preferably made of aluminum, but other suitable heat conducting materials may be used. To further enhance heat distribution within the power supply, thermally conductive potting material, such as silicone or epoxy, may be pumped into the unit to fill air spaces therein with the thermally conductive potting. Preferably, the layers  32 ,  34  are made of a material which shields electromagnetic radiation generated by the power supply. Each of the layers  28 ,  30 ,  32 ,  34  may include cut-outs in selected regions to provide more clearance room between the top and bottom housing  22 ,  24  for some of the conversion circuitry components, such as a transformer  36 . 
         [0019]    The top and bottom housings are made from high impact plastic, such as acrylonitrile butadiene styrene (ABS), polyphenylene oxide (PPO), thermoplastic polycarbonate resin or nylon. Injection molding is the preferred method for forming the housings. The top and bottom housings may matingly engage by a snap lock or force fit or an ultrasonic weld. 
         [0020]      FIG. 4  is a perspective view of the top housing  22  and bottom housing  24  fitted together to form the case without the circuit board disposed therein. The top housing  22  has an upper surface  40  around the periphery of the housing. The surface  40  may have a smooth texture. Inset from the periphery of the top housing is a generally rectangular region which defines a floor  42 . The floor is preferably disposed above the heat generating components of an assembled power supply. The floor  42  may be defined by the area above the perimeter of the heat spreading layer  32 . 
         [0021]    Although not necessary, in the illustrated embodiment, the floor  42  is at a level which is lower than, i.e., below, the upper surface  40 . In such an embodiment, a wall  44  extends from the floor  42  to the upper surface  40  of the top housing  22 . The wall  44  is disposed around the perimeter of the floor  42 . Rising from the floor are a plurality of pegs  46 . The pegs are spaced apart from one another and may be arranged in offset rows and columns. The pegs may have a cylindrical form, but other geometric shapes may be utilized. In the illustrated embodiment, the pegs are shaped as square posts. Preferably, the pegs have a unitary construction with the floor. That is, there is no joint between the floor and a peg in the location where the floor transitions into the peg. It is also preferable that nothing overlies the floor or the pegs so that the top surfaces of the floor and the pegs and the side surfaces of the pegs are entirely directly exposed to the ambient air. This lessens the opportunity for moisture or debris being retained on the case and enhances the cooling effect of the pegs. 
         [0022]      FIG. 5  is a cross sectional perspective view of the case taken along the line V-V of  FIG. 4 . The figure illustrates a chamber  50  in which the circuit board and components are disposed in an assembled power supply. A pair of spaced apart downwardly extending upper legs  52  may be used to engage an upwardly extending lower leg  54  to assist in aligning the top housing  22  with the bottom housing  24 . In the preferred embodiment, the bottom housing  24  includes an upper surface, a floor, a wall and pegs corresponding to those illustrated in  FIG. 4 . The pegs  56  of the bottom housing extend downwardly from the floor when the power supply is “upright.” Owing to its construction, the power supply is operable whether it is “right side up” or “upside down.” While the following description primarily concerns the top housing  22 , it is likewise applicable to the bottom housing  24 . 
         [0023]      FIG. 6  is a top view of the case of the power supply. The pegs  46  are preferably arranged in rows and columns with an aisle  62  between the pegs in a first column and the pegs of an adjacent column. The rows and columns are arranged such that a peg in an odd-numbered column is spaced apart from the peg in the same row of the next odd-numbered column by unoccupied floor extending a distance equal to the length of a peg plus the width of two aisles  62 . The same is true for a peg in an even-numbered column relative to a peg of the same row in the next even-numbered column. The pegs in adjacent rows of the same column are separated by unoccupied floor extending a distance equal to the width of a peg, but there is not an aisle, as there is for the columns. In the illustrated embodiment, all of the aisles  62  have substantially the same width. 
         [0024]    It is preferable that the floor area occupied by the pegs be equal to or less than one fourth of the total floor area. Stated another way, the floor area not occupied by the pegs should be at least three times the floor area which is occupied by the pegs. Such an arrangement is beneficial in ensuring that each peg is sufficiently isolated from neighboring pegs so as not to transfer heat therebetween. The overall effect of the pegs is to significantly lower the touch-temperature of the case of an operating power supply. That is, the temperature at the top of the pegs is significantly lower than the temperature at the top surface of the floor, which would be the touch-temperature of a case without pegs. 
         [0025]    Referring to  FIG. 9 , which is an enlarged view of the top of the case taken within the circular line IX-IX of  FIG. 6 , a peg  46  has a length L p  and a width W p . The aisles  62  have a width W a . In the illustrated embodiment, each of L p , W p  and W a  is 1.00 mm. Thus, one peg occupies one square millimeter of floor area. 
         [0026]    The 1.0 mm dimensions for L p , W p  and W a  are illustrative. It is not necessary for L p , W p  and W a  to be equal. Some types of pegs are better described by dimensions other than length and width, such as a radius for a cylindrical peg. In general, the peg size and spacing should be such that heat transfer between the pegs is minimal, the pegs are not easily broken off from the floor and user fingertips are prevented from touching the top surface of the floor by the pegs. Pegs having a length and a width and a spacing in the range of about 0.5 mm-5.0 mm are preferable. 
         [0027]    Referring again to the illustrated embodiment of  FIG. 6 , there are 51 rows of pegs with 23 pegs in each row and two (outer) rows of pegs with 22 pegs in each row for a total of 1,217 pegs. In this embodiment, the length L f  of the floor is about 93 mm and the width W f  of the floor is about 55 mm. Thus, the total area of the floor is approximately 5,115 mm 2 . Since each of the 1,217 pegs occupies 1 mm 2 , the total floor area occupied by the pegs is 1,217 mm 2 . This leaves 3,898 mm 2  of floor area not occupied by the pegs, which is more than three times the amount of the floor area which is occupied by the pegs. 
         [0028]      FIG. 7  is a cross-sectional view of the case taken along the line VII-VII of  FIG. 6 . The figure illustrates the top housing  22  and the bottom housing  24  fitted together to form the case.  FIG. 8  is an enlarged cross-sectional view of the case taken within the circular line VIII-VIII of  FIG. 7 .  FIG. 8  illustrates that the floor  42  has a thickness T f  in regions of the floor on which the pegs are not disposed. Such regions include an aisle  62  and the area between adjacent pegs of the same column. A peg has a height H p  relative to the top surface of the floor  42 . The height of the pegs may range from about 0.5 mm to about 2.0 mm. In the preferred embodiment, the height of the pegs is about 0.75 mm. It is desirable that the floor thickness T f  be at least equal to the peg height H p , and preferably slightly (e.g., about 1.25 to 1.5 times) greater. 
         [0029]    From the pegs labeled by reference numeral  46  in  FIG. 8 , it can be seen that the pegs have a unitary construction with the floor such that there is no joint between the floor and a peg in the location where the floor transitions into the peg. The pegs adjacent to those labeled  46  in  FIG. 8  have the same construction. However, since they are located “behind” the cross-section line VII-VII of  FIG. 6 , such pegs are not shown in cross-section and a line representing the top surface of the floor  42  is shown under those pegs. In the cross sectional view of  FIG. 8 , the wall  44  can be seen at the end of an aisle  62 . The height of the pegs on the interior of the floor is preferably somewhat (about 25-50%) higher than the top surface of the wall  44 . The pegs in the rows and columns near the wall may be contoured so as to be substantially flush with the top of the wall  44 , i.e., the upper surface  40 . 
         [0030]    While the description above refers to particular embodiments of the present invention, it will be understood that modification may be made without departing from the spirit thereof. For example, a case having pegs as described above may be utilized to enclose heat generating components which function to perform work other than power conversion. The following claims are intended to cover all modifications which fall within the scope and spirit of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.