Abstract:
An electronic system which includes a power delivery surface that delivers electrical power to an electrical or electronic device. The power delivery surface may be powered by any electrical power source, including, but not limited to: wall electrical outlet, solar power system, battery, vehicle cigarette lighter system, direct connection to electrical generator device, and any other electrical power source. The power delivery surface delivers power to the electronic device wirelessly. The power delivery surface may deliver power via a plurality of contacts on the electrical device conducting electricity from the power delivery surface. The electrical device may be mobile device. Each contact may be shaped to improve power delivery reliability. The power delivery surface may further include circuitry to protect against accidental electrocutions.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 11/800,427, filed on May 3, 2007, which claims the benefit of U.S. Provisional Application No. 60/797,140, filed May 3, 2006, all of which is incorporated herein by reference 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to electronic systems and methods for providing electrical power to one or more electronic devices with a power delivery surface. 
         [0004]    2. Description of the Related Art 
         [0005]    A variety of electronic devices, such as toys, game devices, cell phones, laptop computers, cameras and personal digital assistants, have been developed along with ways for powering them. Mobile electronic devices typically include a battery which is rechargeable by connecting it through a power cord unit to a power source, such as an electrical outlet. A non-mobile electronic device is generally one that is powered through a power cord unit and is not intended to be moved during use. 
         [0006]    In a typical set-up for a mobile device, the power cord unit includes an outlet connector for connecting it to the power source and a battery connector for connecting it to a corresponding battery power receptacle of the battery. The outlet and battery connectors are in communication with each other so electrical signals flow between them. In this way, the power source charges the battery through the power cord unit. 
         [0007]    In some setups, the power cord unit also includes a power adapter connected to the outlet and battery connectors through AC input and DC output cords, respectively. The power adapter adapts an AC input signal received from the power source through the outlet connector and AC input cord and outputs a DC output signal to the DC output cord. The DC output signal flows through the battery power receptacle and is used to charge the battery. 
         [0008]    Manufacturers, however, generally make their own model of electronic device and do not make their power cord unit compatible with the electronic devices of other manufacturers, or with other types of electronic devices. As a result, a battery connector made by one manufacturer will typically not fit into the battery power receptacle made by another manufacturer. Further, a battery connector made for one type of device typically will not fit into the battery power receptacle made for another type of device. Manufacturers do this for several reasons, such as cost, liability concerns, different power requirements, and to acquire a larger market share. 
         [0009]    This may be troublesome for the consumer because he or she has to buy a compatible power cord unit for their particular electronic device. Since people tend to switch devices often, it is inconvenient and expensive for them to also have to switch power cord units. Further, power cord units that are no longer useful are often discarded which leads to waste. Also, people generally own a number of different types of electronic devices and owning a power cord unit for each one is inconvenient because the consumer must deal with a large quantity of power cord units and the tangle of power cords the situation creates. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    An embodiment of the present invention may comprise an electrical apparatus, comprising: a power delivery surface that comprises at least a part of a support surface, the power delivery surface being connected to an electrical power source, the power delivery surface being capable of supplying electrical power, and the power delivery surface having a plurality of pads, wherein some of the pads are at a first voltage level and others of the pads are at a second voltage level; an electrical device, which is supplied electricity and is positionable in any location on a support surface, the electrical device obtaining electrical power from the power delivery surface that is at least part of the support surface; a plurality of contacts that are part of the electrical device, the plurality of contacts are spaced apart in relation to each other in positions to make power delivery capable contact with the power delivery surface; and a contact face for each contact of the plurality of contacts that has a plurality of raised regions that act as independent contact regions for power delivery capable contact with the power delivery surface. 
         [0011]    An embodiment of the present invention may further comprise an electrical apparatus, comprising: a power delivery surface that comprises at least a part of a support surface, the power delivery surface being connected to an electrical power source, the power delivery surface being capable of supplying electrical power; an electrical device, which is supplied electricity and is positionable in any location on a support surface, the electrical device obtaining electrical power from the power delivery surface that is at least part of the support surface; a capacitive load detection circuit that detects a capacitive load on the power delivery surface; and a shut down circuit that turns off the power delivery surface when a capacitive load exceeds a preset capacitive load limit. 
         [0012]    An embodiment of the present invention may further comprise an electrical apparatus, comprising: a power delivery surface that comprises at least a part of a support surface, the power delivery surface being connected to an electrical power source, the power delivery surface being capable of supplying electrical power, and the power delivery surface having a plurality of pads, wherein some of the pads are at a first voltage level and others of the pads are at a second voltage level; and an electrical device, which is supplied electricity and is positionable in any location on a support surface, the electrical device obtaining electrical power from the power delivery surface that is at least part of the support surface; a power receiver device that is attached and electrically connected to the electrical device in order to provide a plurality of contacts to the electrical device, the plurality of contacts are spaced apart in relation to each other in positions to make power delivery capable contact with the power delivery surface. 
         [0013]    These and other features, aspects, and advantages of the invention will become better understood with reference to the following drawings, description, and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1   a  is a perspective view of a power delivery system, in accordance with the invention, which includes a power delivery support structure operatively coupled with an electronic device. 
           [0015]      FIG. 1   b  is a top view of another embodiment of an electronic system with a power delivery surface for providing power to an electronic device. 
           [0016]      FIG. 1   c  is a perspective view of the bottom of an electronic device with contacts designed to obtain power from a power delivery surface. 
           [0017]      FIG. 1   d  is a side view of an electronic device with contacts designed to obtain power from a power delivery surface. 
           [0018]      FIG. 2   a  is a schematic perspective view of a contact shaped to improve power delivery capable contact with a power delivery surface. 
           [0019]      FIG. 2   b  is a schematic top view of the face of a contact shaped to improve power delivery capable contact with a power delivery surface. 
           [0020]      FIG. 2   c  is a side view of the physical shape of a contact shaped to improve power delivery capable contact with a power delivery surface. 
           [0021]      FIG. 2   d  is a topographical top view of the face of a contact shaped to improve power delivery capable contact with a power delivery surface. 
           [0022]      FIG. 3   a  is a schematic illustration of a hand on a power delivery surface. 
           [0023]      FIG. 3   b  is an electrical schematic of an equivalent circuit of a power delivery surface with a combined resistive (R) and capacitive (C) load. 
           [0024]      FIG. 3   c  is a graphical representation of a voltage waveform for a power delivery surface without a load. 
           [0025]      FIG. 3   d  is a graphical representation of a voltage waveform for a power deliver surface when a hand or other body part of a person or animal is resting on the power delivery surface. 
           [0026]      FIG. 4   a  is schematic diagram of a typical mobile device where a battery is accessible behind a removable back cover. 
           [0027]      FIG. 4   b  is schematic diagram of a typical battery of a typical mobile device. 
           [0028]      FIG. 4   c  is schematic diagram of the top side of a flexible printed circuit that adds contacts for use with a power delivery surface to an existing battery. 
           [0029]      FIG. 4   d  is schematic diagram of the bottom side of a flexible printed circuit that adds contacts for use with a power delivery surface to an existing battery. 
           [0030]      FIG. 4   e  is schematic diagram of a flexible printed circuit that adds contacts for use with a power delivery surface being attached to an existing battery. 
           [0031]      FIG. 4   f  is schematic diagram of a flexible printed circuit that adds contacts for use with a power delivery surface attached to an existing battery. 
           [0032]      FIG. 5   a  is a schematic diagram of a removable power receiver that adds contacts for use with a power delivery surface attached to a larger host mobile device. 
           [0033]      FIG. 5   b  is a schematic diagram of a side view of a removable power receiver that adds contacts for use with a power delivery surface to a larger host mobile device. 
           [0034]      FIG. 5   c  is a schematic diagram of a front view of a removable power receiver that adds contacts for use with a power delivery surface to a larger host mobile device. 
           [0035]      FIG. 5   d  is a schematic diagram of a bottom view of a removable power receiver that adds contacts for use with a power delivery surface to a larger host mobile device. 
           [0036]      FIG. 5   e  is a schematic diagram of a three dimensional view of a removable power receiver that adds contacts for use with a power delivery surface to a larger host mobile device. 
           [0037]      FIG. 5   f  is a schematic diagram of a removable power receiver with a spring loaded shelf that adds contacts for use with a power delivery surface attached to a larger host mobile device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]      FIG. 1   a  is a perspective view of a power delivery system  100 , in accordance with the invention, for providing power to an electrical or electronic device  112  with a power delivery surface  111   a . System  100  has many different embodiments that provide the features discussed herein and as well as other features. Several embodiments are discussed in co-pending U.S. patent application Ser. No. 11/670,842 filed on Feb. 2, 2007, co-pending U.S. patent application Ser. No. 11/672,010 filed Feb. 6, 2007, and co-pending U.S. patent application Ser. No. 11/682,309 filed Mar. 5, 2007. Power delivery system  100  can power more than one electronic device made by the same or different manufacturers. It can also power different types of electronic devices. This reduces the need for the consumer to have a power cord unit for each electronic device they use. Electronic device  112  can be of many different types, such as a toys, game devices, cell phone, laptop computer, camera, personal digital assistant, etc. Most of these devices are mobile and powered by a rechargeable battery. However, the invention is also applicable to electronic devices, such as a desktop computer, that are not generally considered to be mobile. 
         [0039]    System  100  includes a power delivery support structure  111  connected to a power source (not shown) through a power cord unit  113 . The power source can be of many different types, such as an electrical outlet or battery, and provides a potential difference through unit  113  to separate conductive regions in structure  111 . The potential difference is provided to electronic device  112  in response to device  112  being carried by structure  111  on surface  111   a . In this way, surface  111   a  operates to deliver power to electronic device  112 . 
         [0040]    Electronic device  112  can be powered in many different ways by the power delivery surface. For example, surface  111   a  can provide charge to a battery included in device  112 , which is often the case for mobile devices. Device  112  can also be powered directly by surface  111   a . This is useful in situations where device  112  is not battery operated or it is desirable to operate device  112  with its battery removed. An example of this is when using a laptop computer, which can operate if power is provided to it by surface  111   a  after its battery has been removed. 
         [0041]    Power delivery support structure  111  can include many different materials, but it preferably includes an insulative material with separate conductive regions which define at least a portion of surface  111   a . As discussed in more detail below, the conductive regions are separate so they provide the potential difference to electronic device  112 . 
         [0042]    In this embodiment, electronic device  112  includes and carries contacts and an electronic circuit which are in communication with each other. In operation, the circuit receives the potential difference from the power delivery surface through the contacts when they engage surface  111   a . The potential difference is rectified by the electronic circuit to provide a desired voltage potential which is used to power electronic device  112 . It is advantageous that the circuit be carried by device  112  so it can be designed to receive the potential difference from the power delivery surface and provide device  112  with the desired voltage potential. 
         [0043]    This feature is useful because sometimes it is desirable to power multiple electronic devices with the power delivery surface. These devices may operate in response to different ranges of voltage potentials. In some situations, the electronic devices are the same type of device (i.e. two cell phones). The electronic devices can be the same models and have the same voltage requirements or they can be different models and have different voltage requirements. The different models can be made by the same or different manufacturers. In other situations the electronic devices are different types of devices (i.e. a cell phone and laptop computer). Different types of devices generally require different ranges of voltage potentials, although they can be the same in some examples. The different types of devices can be made by the same or different manufacturers. Hence, the electronic circuit for each device is designed so the power delivery surface can provide power to multiple electronic devices having many different voltage requirements. 
         [0044]    In accordance with the invention, the contacts are arranged so the potential difference is provided to the electronic circuit independently of the orientation of device  112  on power delivery surface  111   a . In other words, the potential difference is provided to the electronic circuit for all angles φ. This feature is advantageous for several reasons. For example, the contacts can engage surface  111   a  without the need to align them with it, so at least two contacts are at different potentials. In this example, angle φ corresponds to the angle between a side of structure  111  and a reference line  142  extending through device  112  and parallel to surface  112   a . It should be noted, however, that another reference can be used. Here, angle φ has values between about 0° and 360°. 
         [0045]    This feature is also advantageous when powering multiple electronic devices because they can be arranged in many more different ways on surface  111   a . This allows surface  111   a  to be used more efficiently so more devices can be carried on and charged by the power delivery surface. This is useful in situations where there are not enough electrical outlets available to charge the multiple electronic devices individually. In general, structure  111  can carry more electronic devices when length L and/or width W are increased and fewer when length L and/or width W are decreased. The number of devices that structure  111  can carry also depends on their size. For example, cell phones are typically smaller than laptop computers. 
         [0046]    Power delivery support structure  111  can have many different shapes, but here it is shown with surface  111   a  being rectangular so structure  111  defines a cubic volume. Surface  111   a  is shown as being substantially flat and the separate conductive regions define continuous surfaces separated from each other by an insulative material region. The distance between the conductive regions is referred to as the gap G. Surface  111   a  extends between opposed sides  115   a  and  115   b , as well as opposed sides  115   c  and  115   d . Opposed sides  115   c  and  115   d  extend from opposite ends of sides  115   a  and  115   b  and between them. Sides  115   a  and  115   b  are oriented at non-zero angles relative to sides  115   c  and  115   d . In this particular example, the non-zero angle is about 90° since surface  111   a  is rectangular. In other examples, surface  111   a  can be curved, triangular, etc. When surface  111   a  is circular, structure  111  defines a cylindrical volume. 
         [0047]      FIG. 1   b  is a top view of an electronic system, embodied as a power delivery system  101 , for providing power with a power delivery surface to electronic device  112 . System  101  is similar to system  100  and includes power delivery support structure  111  and power cord unit  113 . In this embodiment, the power delivery surface, denoted as surface  111   a ′, includes two separate conductive regions, denoted as regions  116  and  117 . Regions  116  and  117  are separated from each other by an insulative region  119  and define separate continuous surfaces. In this document, the distance of the separation between conductive regions achieved by the insulative region  119  is generally referred as the gap G. 
         [0048]    Region  119  provides electrical isolation between conductive regions  116  and  117  so a potential difference can be provided between them. If a current flows between conductive regions  116  and  117 , it also flows through the electronic circuit carried by electronic device  112  when the contacts engage surface  111   a ′. In this way, power is provided to device  112  when it is carried by power delivery support structure  111 . If a current flows between regions  116  and  117  without flowing through the electronic circuit, then it is typically an undesirable leakage current. In general, as the separation between regions  116  and  117  increases, the leakage current decreases. Similarly, as the separation between regions  116  and  117  decreases, the leakage current increases. The leakage current also depends on the material included in insulative region  119 . 
         [0049]    In this embodiment, conductive region  116  includes a base contact  114  which extends along side  115   a  and between sides  115   c  and  115   d . Region  116  also includes a first plurality of contact pads, some of which are denoted as contact pads  114   a ,  114   b  and  114   c . These contact pads are connected to base contact  114  and extend outwardly from it and towards side  115   b . Conductive region  117  includes a base contact  118  which extends along side  115   b  and between sides  115   c  and  115   d . Region  117  also includes a second plurality of contact pads, some of which are denoted as contact pads  118   a ,  118   b  and  118   c . These contact pads are connected to base contact  118  and extend outwardly from it and towards side  115   a . It should be noted that contacts  114  and  118  extend all the way between sides  115   c  and  115   d . However, in other embodiments, they can extend partially between sides  115   c  and  115   d . It should also be noted that base contacts  114  and  118  are shown as being rectangular in this example, but they can have other shapes, such as curved or triangular, in others. 
         [0050]    In this example, contact pads  114   a - 114   c  and  118   a - 118   c  extend parallel to each other and are interleaved so contact pad  114   a  is positioned between contact pad  118   a  and  118   b , and contact pad  114   b  is positioned between contact pads  118   b  and  118   c . As shown in  FIG. 1   b , the other contact pads in regions  116  and  117  are interleaved in the same manner. It should be noted that in some examples, the different contact pads in regions  117  and  118  can be connected together with vias. 
         [0051]    Power cord unit  113  includes conductive lines  113   a  and  113   b  which are connected to conductive regions  116  and  117 , respectively. In one mode of operation, the power supply provides conductive regions  116  and  117  with different voltage potentials through corresponding conductive lines  113   a  and  113   b . In this mode, there is a potential difference between regions  116  and  117 , and device  112  is provided with power in response to it, when device  112  is carried on surface  111   a ′ and the contacts engage surface  111   a ′. In this way, surface  111   a ′ is arranged so a potential difference is provided between at least two of the contacts carried by device  112 . 
         [0052]    It should be noted that more than two potentials can be provided to surface  111   a ′ by power cord unit  113  and the use of two here is for illustrative purposes. For example, power cord unit  113  can include three conductive lines which provide positive, negative, and zero potentials to a corresponding number of conductive regions the same or similar to regions  116  and  117 . 
         [0053]      FIG. 1   c  is a perspective view of the bottom of an electronic device  112  with contacts  120  designed to obtain power from a power delivery surface  111   a . The contacts  120  on the electronic device  112  appear on the surface of the electronic device  112  which is intended to be placed on the power delivery surface  111   a . The contacts  120  on the electronic device may be configured such that at least one contact is in electrical contact with a first conductive zone  116  of the power delivery surface  111   a  and a second contact is in electrical contact with a second conductive zone  117  of the power delivery surface  111   a.    
         [0054]      FIG. 1   d  is a side view of an electronic device  112  with contacts  120  designed to obtain power from a power delivery surface  111   a . The contacts  120  may extend below the electronic device  112  to facilitate electrical contact with the power delivery surface  111   a .  FIG. 1   c  and  1   d  show the relative structure of an electronic device  112  with contacts  120  in order to assist the reader in understanding the overall structure of the system prior to a more detailed discussion of specific portions of an embodiment. A more detailed disclosure regarding the structure, geometry and additional features of the power support structure  111  and the structure, geometry and additional features of the electronic device  112  is given in co-pending U.S. patent application Ser. No. 11/670,842 filed on Feb. 2, 2007, co-pending U.S. patent application Ser. No. 11/672,010 filed Feb. 6, 2007, and co-pending U.S. patent application Ser. No. 11/682,309 filed Mar. 5, 2007. 
         [0055]      FIG. 2   a  is a schematic perspective view of a contact  120  shaped to improve power delivery capable contact with a power delivery surface  111   a . The three-dimensional aspect of the drawing in  FIG. 2   a  is indicated by the x-y-z axis shown at  299 . The shaped contact  120  of the electronic device  112  is used for power delivery capable contact between the electronic device  112  and the power delivery surface  111   a . The shaped contact uses a special geometry to attain multiple, independent, contact redundancy, thereby improving power delivery reliability. For a shaped contact, the contact point for is not a point at all, instead, the contact point may be further subdivided into distinct contact regions. The shaped contact shown  120  appears as a circular disk. Other embodiments may use other shapes. The circular face  201  visible depicts the face of the shaped contact  120  that will come in contact with the substantially planar power delivery surface  111   a . Shown on the face  201  are three “x” marks  204  corresponding to desired independent contact regions of the shaped contact  120 . While three contact regions permits three-fold, independent contact redundancy, other embodiments may have a different number of contact regions. For at least one embodiment it is assumed that a means is provided by which the contact button can pivot within a solid angle θ 203  as shown in  FIG. 2   a . The vertical vector  202  represents the normal to the shaped contact face surface  201 . The three regions of contact  204  are marked by “x′s”. However, for clarity,  FIG. 2   a  does not show the contact regions  204  raised above the shaped contact&#39;s planar face surface  201 . 
         [0056]      FIG. 2   b  is a schematic top view of the face  201  of a contact  120  shaped to improve power delivery capable contact with a power delivery surface. The three desired contact locations  204  are shown forming an equilateral triangle, with each point located and equal distance R form the center  205  of the shaped contact. Other embodiments may choose to locate the contact regions at other points and may use other geometric shapes and a different number of contact regions. Each shaped contact  120  may be pivotably mounted to the electronic device  112  to allow the contact regions  204  to align and rest on the power deliver surface  111   a.    
         [0057]    Generally, the outer diameter of the shaped contact  120  is chosen to be as large as possible without allowing the shaped contact  120  to short two adjacent electrodes  116 ,  117  of the power delivery surface  111   a . The gap between electrodes  116  and  117  of the power delivery surface  111   a  is designated G. The parameter W max  defines the greatest distance spanned by the shaped contact  118 . W max  must be less than the electrode gap G. For the equilateral triangle placement of the contact regions  204 , W max  is 1.732 times the radius R, and W min  is 1.5 times R. Therefore, the radius R must be less than the gap G divided by 1.732 (i.e. 1.732*G, which equals 0.577*G). 
         [0058]      FIG. 2   c  is a side view of the physical shape of a contact  120  shaped to improve power delivery capable contact with a power delivery surface. In accordance with  FIGS. 2   a  and  2   b , there are three raised regions  204 . The highest point of each contact region  204  is located at the projection of the “x” marks in  FIGS. 2   a  and  2   b.    
         [0059]      FIG. 2   d  is a topographical top view  210  of the face of a contact  120  shaped to improve power delivery capable contact with a power delivery surface  111   a . As shown, the contour lines of the contact regions  204  show an increasing height from the center of the shaped contact  205  to the most elevated point of the contact regions  204 . The contour lines indicate a constant change in height in the Z-dimension. 
         [0060]      FIG. 3   a  is a schematic illustration of a hand  301  on a power delivery surface  111   a . For a conductive based power delivery surface  111   a , if a person or animal makes electrical contact with both conductive zones  116 ,  117  the person or animal may be electrocuted. When human or animal flesh comes in contact with the power delivery surface the output load typically has an unusually high capacitive component. To reduce the potential damage from electrocution, a capacitive load detection circuit may be employed by the power delivery surface to detect unusually high capacitive loads. If an unusually high capacitive load is detected a shut down circuit may shut down the power delivery surface to either avoid electrocution or minimize the damage from an electrocution. The shutdown circuit may use a preset capacitive load limit as the threshold for shutting down the system. The preset capacitive load limit may be set to a capacitive load threshold that is indicative of a person or animal being in contact with the power delivery system. There are many potential embodiments for a capacitive load detection and shutdown system. One embodiment is described in the disclosure with respect to  FIG. 3   b  through  3   d.    
         [0061]      FIG. 3   b  is an electrical schematic of an equivalent circuit of a power delivery surface  111   a  with a combined resistive (R EQ ) and capacitive (C EQ ) load. A human hand  301 , or flesh in general, may be represent by an equivalent capacitive and resistive component connected in parallel. Thus, a human hand  301  resting on a set of electrodes such as those contained in a power delivery surface  111   a  may be represented by the equivalent circuit depicted in  FIG. 3   b , where R EQ  and C EQ  represent the load of the hand  301 . A control unit (not shown) may contain the capacitive load detection circuit and the shut down circuit for a power delivery surface  111   a . The control unit would measure the voltage (V OP ) across the output terminals  303 , which, here, consists of R EQ  and C EQ . If the control unit detects an unusually high capacitive load, the control unit would operate the switch  302  to shut down the power delivery surface  111   a.    
         [0062]      FIG. 3   c  is a graphical representation of a voltage waveform for a power delivery surface  111   a  without a load. The control unit closes the switch  302  which applies V OP , to the output terminals  303 . Periodically, the control unit opens the switch  301  and, after a time, measures the voltage (V OP ) at the output terminals  303 . This voltage (V OP ) must be within the preset limits of the applied test voltage V TEST . Specifically, the switch  301  is opened at a time t OFF . After a time interval elapses, the output voltage (V OP ) is measured at time t TEST . At time t TEST , the control unit determines if it is appropriate to close the switch  301  again to start the process over again. The switch is not actually turned on until time t ON  accounting for the time it takes the control unit to decide to open the switch and to actually open the switch. With no load, the output voltage (V OP ) drops immediately to V TEST  when the switch  301  is opened. Practically, the amount of time it takes to go to V TEST  depends on the value of the resistor  304  connecting the test voltage (V TEST ) to the output terminals  303 . To some degree the amount of time it takes to go to V TEST  also depends on the stray capacitance present in the system. 
         [0063]      FIG. 3   d  is a graphical representation of a voltage waveform for a power deliver surface when a hand  301  or other body part of a person or animal is resting on the power delivery surface  111   a . The capacitance of a hand  301  or arm with typical electrode patterns suitable for a conductive based power delivery surface  111   a  is considerably greater than the stray capacitance intrinsically present in the power delivery surface  111   a  apparatus. In the presence of a significant capacitive load, as would be the case with a hand  301  or arm resting on the power delivery surface  111   a , the voltage follows an exponential curve  305  characteristic of a Resistive-Capacitive (RC) discharge. Provided that a predetermined time delay exists between t OFF  and t TEST , and provided that there exists a voltage threshold below which the output must fall during the delay, a capacitance threshold may be implemented. If the capacitance present on the output terminals  303  is greater than a predetermined value, then the voltage at time t TEST  will be greater than the predetermined threshold voltage value (V TEST ). Since the voltage did not fall below the V TEST  threshold value at time t TEST,  the control unit did not close the switch  301  and the system is shut down. Thus, in  FIG. 3   d , the control unit did not turn the system back on since the voltage at time t TEST  was greater than V TEST.  Once the capacitive load is removed, the system may automatically turn back on. 
         [0064]    Generally, an electrical device may be retrofitted for use with a power delivery surface by attaching a power receiver to the electrical device that electrically connects the electrical device to a plurality of contacts that are part of the power receiver. The plurality of contacts are capable of receiving power from the power delivery surface, thus, enabling the electrical device to receive power from the electrical delivery surface. 
         [0065]      FIG. 4   a  is schematic diagram of a typical mobile device  112  where a battery  401  is accessible behind a removable back cover  403 . In general, it is considered usual that the mobile device  112  rests on the mobile device&#39;s back cover  403  and back surface when set on a support surface. For a mobile device  112  that rests on the back cover  403 , it is practical and convenient to deliver wire free power according to the system shown in  FIG. 4   a . A wire-free power receiver and electronics  404  may be integrated into the back cover such that when the mobile device  112  is at rest on a power deliver surface  111   a , power can be sufficiently received by the mobile device  112 . The power receiver consists of a plurality of contacts designed for power delivery between a power delivery surface  111   a  and an electrical device  112 . The plurality of contacts would be on the outside of the back cover  403  so that the contacts rest on the power delivery surface  111   a . Contact fingers  405  on the inside of the back cover  403  make contact with contact assembly  406  attached to the mobile device battery  401 . The contact assembly  406  is electrically connected to the mobile device battery  401 . The contact assembly  406  has exposed contacts  407  that permit the contact assembly to make electrical contact with the contact fingers  405  on the back cover, that in turn, make electrical contact with the plurality of contacts that are part of the power receiver and electronics  404 . A temperature sensor  402  may also be included in the power receiver and electronics  404  to monitor the heat of the mobile device battery  401  to ensure the mobile device battery  401  does not overheat while charging. The temperature sensor  402 , or other sensors, may be included to increase safety and/or charging efficiency. 
         [0066]      FIG. 4   b  is schematic diagram of a typical battery  401  of a typical mobile device  112 . The battery shown  401  has connections on the side  409  intended to connect the host mobile device  112  to the battery for power transfer and battery management. The battery connections  409  to the mobile device  112  may appear in other locations for other embodiments. The exposed battery contacts  408  on top of the battery allow charging current to flow into the battery  401  from the power receiver  404  integrated into the back cover  403 . In one embodiment, the battery  401  is a smart battery and implements a data bus between itself and the host mobile device  112 . In one variation of the embodiment, the power receiver  404  does not have access to data available from the battery  401  on the smart data bus. When the power receiver  404  does not have access smart data bus, the power receiver  404  does not have complete information on the system status, including information that the battery  401  may be receiving about charging current from the host mobile device  112 . The power receiver  404  may not have access to the smart data bus if the host mobile device  112  is plugged into a USB cable (for example) and is being charged via the USB power source. If the mobile device  112  is simultaneously resting on a power delivery surface  111   a , the power receiver may also be supplying charging current to the battery resulting in a potentially unsafe situation in which the battery could be damaged or destroyed. A temperature sensor  402  in the power receiver  404  arranged to monitor the battery temperature may be used to maintain safety. The temperature sensor  402  shuts down the charging current from the power receiver  404  if the battery temperature exceeds a predetermined threshold. 
         [0067]      FIG. 4   c  is schematic diagram of the top side of a flexible printed circuit  413  that adds contacts for use with a power delivery surface  111   a  to an existing battery  401 . The contacts on the battery  401  may be built into the battery from the manufacturer using techniques known to those skilled in the art. Alternatively, contacts may be added to an existing battery using a flexible circuit  413 . The “top” side of the flexible circuit board  413  provides the bare contacts  411  on the battery  401  for connection to the power receiver  404  while simultaneously allowing connection of the battery  401  to the host mobile device  112 . This is enabled by the cutout  412 , and by traces on both sides of the printed circuit  413  that are connected together to form a pass-through connection by vias  410  between the top and bottom sides of the flexible printed circuit  413 .  FIG. 4   d  is schematic diagram of the bottom side of a flexible printed circuit  413  that adds contacts for use with a power delivery surface  111   a  to an existing battery  401 . 
         [0068]      FIG. 4   e  is schematic diagram of a flexible printed circuit  413  that adds contacts for use with a power delivery surface  111   a  being attached to an existing battery  401 . Adhesive on the “bottom” of the flexible printed circuit  414  keep the flexible printed circuit  413  affixed to the battery  401 . There is no adhesive on the exposed traces  415  since that would interfere with the electrical connection to the battery  404 . 
         [0069]      FIG. 4   f  is schematic diagram of a flexible printed circuit that adds contacts for use with a power delivery surface attached to an existing battery. The traces and cutout  412  of the flexible printed circuit  413  are arranged to align with the battery contacts  409 . The cutout  412  allows certain of the battery contacts  409  to remain exposed for connection to the host mobile device  112 . Where the flexible circuit board  413  covers selected battery contacts  409 , a circuit trace on the bottom side of the flexible circuit board  413  is aligned over the battery contact  409  and makes an electrical connection to with the battery contact  409 . A top-side trace is also aligned over the selected battery contact  409  duplicating the battery connection to the host mobile device  112 . In one embodiment, the top-side trace and the bottom-side trace over a given battery contact  409  are connected through a via  410  in the flexible printed circuit  413 . The via  410  provides a tap into the selected battery contact  409  without affecting operation with the host mobile device  112 . In other embodiments, circuitry may be provided between the top and bottom-side traces to provide alternative functionality. The connection of the bottom-side traces to the corresponding battery contact  409  is realized through the contact pressure supplied by the spring-loaded contact fingers (not the contact fingers  405  on the back cover  403 ) present in the host mobile device  112 . The flexible printed circuit  413  is compliant sufficiently to not significantly react against the pressure of the host mobile device&#39;s contact fingers. In addition, gold plating may be used on the traces to insure good electrical connections. 
         [0070]      FIG. 5   a  is a schematic diagram of a removable power receiver  501  that adds contacts for use with a power delivery surface  111   a  attached to a larger host mobile device  112 . The removable power receiver  501  may be designed to support the weight of the larger mobile device  112  when the system is resting on the power delivery surface  111   a . The removable power receiver  501  plugs into the host mobile device&#39;s existing power input port. 
         [0071]      FIGS. 5   b ,  5   c ,  5   d , and  5   e  are schematic diagrams of a side view, a front view, a bottom view, and a three-dimensional view, respectively, of a removable power receiver  501  that adds contacts for use with a power delivery surface  111   a  to a larger host mobile device  112 . The plug  502  on the power receiver  501  plugs into the power receptacle on the larger mobile device  112 . The plug  502  on the power receiver  501  is able to slide up and down such that the height H may vary as needed. Varying the height of the plug  502  allows the host mobile device  112  to rest on the portion of the power receiver that lies below the host mobile device  502  without applying significant pressure to the electrical plug  501 . 
         [0072]      FIG. 5   f  is a schematic diagram of a removable power receiver  501  with a spring loaded shelf  504  that adds contacts for use with a power delivery surface  111   a  attached to a larger host mobile device  112 . The electrical plug  502  may be spring loaded slightly in such a way as to minimize H when at rest. The slight pressure of the spring would keep the power receiver  501  attached to the host mobile device  112 . Alternatively a spring loaded shelf  504  may be used to clamp onto the host mobile device  112 . For the spring loaded shelf  504 , the plug  502  on the power receiver  501  would be free-floating and would not need to be spring loaded as discussed above. An embodiment may be designed such that the power receiver  501  would be compatible with many types of host mobile devices  112 . The plug  502  of the power receiver  501  that connects to the power input of the host mobile device  112  would be interchangeable such that many types of plugs would fit on the power receiver  501 . 
         [0073]    Since these and numerous other modifications and combinations of the above-described method and embodiments will readily occur to those skilled in the art, it is not desired to limit the invention to any of the exact construction and process shown and described above. While a number of example aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions, and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, and sub-combinations as are within their true spirit and scope. The words “comprise,” “comprises,” “comprising,” “has,” “have,” “having,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features or steps, but they do not preclude the presence or addition of one or more other features, steps, or groups thereof.