Abstract:
A device for charging a headphones battery. The device includes a first module adapted to receive a first power source through a first power source connector, the first module having a connector adapted to fit the headphones battery; and a second module adapted to receive a second power source through a second power source connector, the second power source connector distinct from the first power source connector, the second module having a connector adapted to fit the headphones battery, wherein the headphones battery is removed from the headphones and charged from the first power source when the first module is connected to the headphones battery and the headphones battery is removed from the headphones and charged from the second power source when the second module is connected to the headphones battery.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates in general to headphones that reproduce sounds such as music, speech, or other acoustic information and more particularly concerns the electrical recharging of batteries included in headphones. 
       BACKGROUND 
       [0002]    Active noise reducing headphones generally require batteries to power electronics to which enable the headphones to generate enough energy to cancel sounds from the outside environment. Wireless headphones require batteries because there is no connection to an outside power source. It is known to use rechargeable batteries for these purposes and to recharge these batteries with a portable recharging unit that plugs into the AC mains electrical source. 
       SUMMARY 
       [0003]    In general in one aspect an apparatus for charging a headphones battery that powers a set of headphones. The apparatus includes a first module adapted to receive power from a first power source through a first power source connector, the first module having a first battery connector adapted to fit the headphones battery; and a second module adapted to receive power from a second power source through a second power source connector, the second power source connector distinct from the first power source connector, the second module having a second battery connector adapted to fit the headphones battery. The first module is constructed and arranged to recharge the headphones battery connected to the first battery connector when the first module is receiving power from the first power source, and the second module is constructed and arranged to recharge the headphones battery connected to the second battery connector when the second module is receiving power from the second power source. 
         [0004]    Implementations may include one or more of the following features. The first power source may be characterized by a first voltage; the second power source may be characterized by a second voltage; and the first voltage may be distinct from the second voltage. The first power source may include a primary battery power source. The first power source may include an AC mains power source. The first module may include a primary battery module and the primary battery powers the primary battery module. The second module may include an AC mains module that connects to an AC mains power source. The headphones may be active noise reduction headphones or wireless headphones. The headphones battery may weigh less than 20 grams or less than 11 grams. 
         [0005]    In another aspect, an apparatus for charging a headphones battery that powers a set of headphones includes an adaptor module. The adaptor module has a corresponding input connector and a battery connector adapted to fit the headphones battery. A first module is adapted to receive power from a first power source through a first power source connector and has a corresponding output connector adapted to fit the corresponding input connector of the adaptor module. A second module is adapted to receive power from a second power source through a second power source connector. The second power source connector is distinct from the first power source connector. The second module has a corresponding output connector adapted to fit the corresponding input connector of the adaptor module. The first module recharges the headphones battery through the adaptor module when the first module is receiving power from the first power source. The second module is recharges the headphones battery through the adaptor module when the second module is receiving power from the second power source. 
         [0006]    The first power source may be characterized by a first voltage; the second power source may be characterized by a second voltage; and the first voltage may be distinct from the second voltage. The first power source may include a primary battery power source. The first power source may include an AC mains power source. The first module may include a primary battery module. A primary battery powers the primary battery module. The second module may include an AC mains module that connects to an AC mains power source. The headphones may be active noise reduction headphones or wireless headphones. The headphones battery may weigh less than 20 grams or less than 11 grams. The corresponding input connector and corresponding output connector may be USB connectors. The first module and the second module may have a corresponding output voltage. The corresponding output voltage may be selected from a range of 4 to 6 volts DC. There may be no substantial current drawn from the primary battery when the primary battery module is not charging the headphones battery. At least one of the modules may further include a charge rate selector for selectively adjusting charge rate as a function of power source characteristics. The charge rate selector may select a charge rate depending on whether the adaptor module is connected to the primary battery module or the AC mains module. The charge rate may be lower when the adaptor module is connected to the primary battery module than when the adaptor module is connected to the AC mains module. 
         [0007]    In another aspect, an apparatus for charging a headphones battery includes a carrying case adapted for storage of a set of headphones, and a recharging module is integrated into the carrying case adapted for use with the headphones battery. The carrying case may include a compartment to accept primary batteries that power the recharging module. 
         [0008]    In another aspect, an apparatus for charging a headphones battery that powers a set of headphones includes a primary battery and a primary battery module adapted for charging the headphones battery. The primary battery module contains the primary battery. The primary battery module may be disposable. The primary battery module may include a charging circuit. The headphones battery may be removable from the headphones. 
         [0009]    In another aspect, a method of charging a headphones battery that powers a set of headphones includes selecting a first module from a plurality of available modules, each module of the plurality of modules connectable to at least one distinct power source type; connecting a first power source to the selected first module; and removing the headphones battery from the headphones and connecting it to the selected first module for recharging. The method may further include selecting a second module from the plurality of available modules, the first module distinct from the second module; connecting a second power source to the selected second module; and removing the headphones battery from the set of headphones and connecting it to the selected second module for recharging. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0010]      FIG. 1  is a drawing of a pair of headphones, a carrying case, and a battery charger; 
           [0011]      FIG. 2  is a drawing of a headphone cup and battery; 
           [0012]      FIG. 3  is a schematic drawing of a modular charging system; 
           [0013]      FIG. 4  is a schematic drawing of a USB connector set; 
           [0014]      FIG. 5  is an electrical schematic drawing of an AC charging module; 
           [0015]      FIG. 6  is an electrical schematic drawing of a primary battery module; and 
           [0016]      FIG. 7  is an electrical schematic drawing of a rechargeable-battery charging module. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The schematic drawings are not drawn to scale. The actual dimensions are as stated in the specification. 
         [0018]    Referring to  FIG. 1 , there is shown a drawing of a pair of active noise canceling headphones  100 , a carrying case  102 , and a removable battery charger  104 . The headphones  100  include earcup  106 , earcup with switch and battery  107 , on-off switch  108 , electrical cord  110 , and electrical connector  112 . Removable battery charger  104  includes electrical prongs  114 . The carrying case may include built-in recharging circuit  116 , recharging compartment  118 , recharging compartment door  120 , primary battery compartment  122 , and primary battery compartment door  124 . The earcups  106  and  107  fit on the user&#39;s ears. Alternatively the earcups or earpieces can be designed to fit over or in the user&#39;s ears. The electrical connector  112  is plugged into a source of audio content such as a portable music player. The electrical prongs  114  are plugged into an alternating current (AC) mains electrical source such as a 110 Volt AC electrical wall socket. The headphones  100  and the removable battery charger  104  fit into the carrying case for portability and storage. The earcups  106  and  107  in  FIG. 1  are shown rotated to fit into the carrying case. The optional recharging circuit  116  may substitute for the removable battery charger  104  or it may be provided in addition to the removable battery charger  104 . In some embodiments, the headphones  100  may consist of only a single earcup  106  or  107  or a single earpiece that fits in the user&#39;s ears. 
         [0019]    Referring to  FIG. 2 , there is shown a detailed drawing of the earcup  107 . The earcup  107  incorporates on-off switch  108 , port  200 , and cushion  202 . A rechargeable battery  204  plugs into the earcup  107  with a set of positioning prongs  206 . The battery incorporates a set of electrical battery contacts  208 . The port  200  provides improved acoustic performance according to known principles. The cushion  202  provides comfort and isolation from outside sounds in the environment. The rechargeable battery  204  provides power to headphones  100  for powering electrical circuitry such as active noise reduction circuitry, through electrical battery contacts  208 . Recharging of battery  204  may also take place through electrical battery contacts  208 . 
         [0020]    Referring again to  FIG. 1 , the rechargeable battery  204  is inserted through the recharging compartment door  120  and into die recharging compartment  118  of case  102 . Battery  204  can be charged with the recharging circuit  116 . A primary battery is inserted through the primary battery compartment door  124  into the primary battery compartment  122  of case  102 . In some embodiments, the primary battery provides power to recharging circuit  116 , for recharging rechargeable battery  204 . 
         [0021]    Referring to  FIG. 3 , there is shown a schematic drawing of a modular charging system  360 . In one embodiment, the modular charging system  360  can operate in various modes that allow charging of a headphones battery from a variety of power sources such as, for example: an AC mains power supply, a primary battery, or a USB device. The modular charging system  360  includes an AC mains module  300 , a primary battery module  310 , and an adaptor module  320 . 
         [0022]    In  FIG. 3 , AC mains module  300  includes a pair of AC electrical prongs  302  for connection to AC electrical mains, AC voltage conditioning circuit  304 , female (universal serial bus) USB connector  306 , and sensing contact  308 . Primary battery module  310  includes primary battery  312 , primary voltage conditioning circuit  314 , female USB connector  316 , and may incorporate sensing contact  318 . Rechargeable-battery charging module (also called an adaptor module)  320  includes male USB connector  322  (also called an input connector), rechargeable charging circuit  324 , rate selector  326 , positioning receptacles  328 , electrical contacts  332 , and may further incorporate sensing contact  330 . Rechargeable battery  301  incorporates electrical battery contacts  305 , positioning prongs  303 , and a temperature sensing element  344 . A computer  350  works together with the modular charging system  360  and includes a female USB connector  352  and may have an internal battery  354 . 
         [0023]    The operation of the components shown in  FIG. 3  are as follows. The modular charging system  360  allows a rechargeable battery to be recharged using a number of methods. For example, it may be recharged using power provided by AC mains, by a permanent or replaceable primary cell, or by a USB connected device. Specifically, the AC electrical prongs  302  of the AC mains module  300  plug into the AC mains electrical source. The AC voltage conditioning circuit  304  converts the AC power to direct current (DC) power at 5 Volts DC which is provided to female USB connector  306 . The primary battery  312  of the primary battery module  310  may be a replaceable 1.5 Volt AA-size alkaline battery or other battery commonly available. The primary battery  312  may be permanently contained in the primary battery module  310  in which ease the primary battery module  310  may be disposable. The primary voltage conditioning circuit  314  converts the primary battery voltage to a voltage which powers the female USB connector  316 . The voltage may be less than the standard 5 Volts DC that is conventionally used by the USB standard. In some implementations the efficiency of primary voltage conditioning circuit  314  is dependent on the input and/or output voltage. In one embodiment when the voltage is approximately 4.2 to 4.5 Volts DC, there is a more efficient power conversion from the primary battery  312  to the rechargeable battery  301 . In some implementations the primary voltage conditioning circuitry  314  is not included when the adaptor module  320  is designed to operate directly from the primary battery voltage. 
         [0024]    Source modules consist of electrical modules that connect to various types of power sources. Each type of power source may have its own type of source module. A connector type (using complimentary connectors such as male and female connectors) is incorporated into the adaptor module  320  and corresponding connector types are incorporated in the various source modules. A source module input connector is used to bring power into a source module and an output connector that corresponds to the adaptor module input connector is used to bring power out from a source module. One type of corresponding connector is USB. In some embodiments, other types of connectors may be used. The corresponding connector type may be any type of connector that includes structures that allow power to be supplied. The AC mains module  300  and the primary battery module  310  are two types of source modules that provide power to recharge the rechargeable battery  301  through the adaptor module  320 . The male USB connector  322  is a corresponding input connector on the adaptor module  320  which plugs into either the female USB connector  306  in the AC mains module  300 , the female USB connector  316  in the primary battery module  310 , or the female USB connector  352  in the computer  350 . These female USB connectors are corresponding output connectors. The input connector type of the adaptor module may be a corresponding connector type such as USB that matches the corresponding output connector type of the source modules. The input voltage of the adaptor module is the desired voltage that the adaptor is designed to accommodate and is the voltage that matches the corresponding output voltage of the source modules. The corresponding input voltage of the adaptor module may be a voltage that fluctuates slightly within standard limits. For example, the corresponding input voltage for the adaptor module may be 5 Volts DC plus or minus 0.25 Volts DC for a USB connector. The corresponding input voltage of the adaptor module may be selected from a larger range of voltages such as 4 to 6 Volts DC. In some embodiments, there is a desired current range associated with the corresponding input voltage. 
         [0025]    The computer  350  may be a laptop computer, or may be another computing device with a female USB connector, or may be any other portable electrical device with a female USB connector. The USB standard provides for transfer of power through pins on the connector. Instead of the computer  350 , another mains powered device, with or without a battery, which has a USB port may be used as a power source that connects to the adaptor module  320 . 
         [0026]    Using the USB port provides a convenient power source of known voltage and power capability, regardless of the mains power type. The charging circuit  324  converts the approximately 5 Volt DC power from the male USB connector  322  (which is the input voltage to the adaptor module) to a voltage that charges the rechargeable battery  301 . According to the USB standard, female USB connector  306 ,  316 , or  352  provides 5 Volts DC on pin  424  (shown in  FIG. 4 ). Female USB connector  306 ,  316 , or  352  mates to male USB connector  322  on adaptor module  320 . Pin  424  on female USB connector  306 ,  316 , or  352  connects to pin  410  on male USB connector  322  of adaptor module  320 . Pin  410  conducts the power present on pin  410  to the input of charging circuit  324 . Charging circuit  324  converts the 5 Volts DC present on pin  410  to a voltage suitable for charging rechargeable battery  301 . One embodiment of the electrical connections is described in more detail below and shown in the electrical schematics of  FIGS. 5 ,  6 , and  7 . 
         [0027]    The charging rate of charging circuit  324  can be adapted as a function of the characteristics of the source providing power. Rate selector  326  may use the sensing contacts  308 ,  318  and  330  to determine which source it is connected to and to adjust the charge rate based on whether adaptor module  320  is connected to AC mains module  300 , primary battery module  310 , or computer  350 . The rate selector  326  controls the charging rate of charging circuit  324  as described below. 
         [0028]    Rechargeable battery  301  is removable from headphones  100  and is both mechanically and electrically coupled to adaptor module  320  while charging. Electrical contacts  305  of the rechargeable battery  301  plug into electrical contacts  332  of adaptor module  320 . Electrical contacts  332  form one embodiment of a battery connector for adaptor module  320 . The positioning prongs  303  plug into the positioning receptacles  328 . The positioning prongs  303  are used to hold the rechargeable battery  301  into the proper position for recharging. Positioning prongs  303  are also used to align the parts when they are assembled together. In some embodiments, the battery connector may be formed into a shape that performs both the electrical connection function and the alignment function, eliminating the need for separate elements. 
         [0029]    The temperature sensing element  344  is electrically connected to rate selector  326  through electrical battery contacts  305  and electrical contacts  332 . In some embodiments, the temperature sensing element  344  is a thermistor used by the rate selector  326  to limit the charging rate of rechargeable battery  301  if rechargeable battery  301  becomes too hot. 
         [0030]    In some embodiments the charging circuit  324  and rate selector  326  are combined into a single circuit. In some embodiments, different charging rates for the rechargeable battery  301  may be used when connected to the AC mains module  300 , the primary battery module  310 , and the computer  350  because energy can typically be drawn faster from the AC mains than from the primary battery  312  or the computer  350 . In some embodiments, more efficient conversion of power from the primary battery  312  or computer  350  to the rechargeable battery  301  will occur when the charge rate is limited by the rate selector  326 . The modular charging system  360  allows the recharger to take advantage of source characteristics so that it charge at rates that can be supported by each type of power source that is used. 
         [0031]    The physical shape and dimensions of the electrical prongs  302  and the AC mains voltage may be different depending on the standards in each region or country. Different type&#39;s of AC mains modules  300  can be used with different AC mains standards. 
         [0032]    In some embodiments, it is desirable to achieve at least 20 hours of portable operation from a lightweight headphone battery for noise-reducing headphones. This operation time will cover most travel purposes including airplane flights over the Pacific Ocean. By using a Lithium-Ion rechargeable battery (or equivalent) as rechargeable battery  301 , primary battery module  310  and adaptor module  320 , flexible charging may be achieved in a variety of circumstances while minimizing the weight and size of electronic equipment that must be carried to achieve the hours of operation desired. Because there are many options to recharge, the rechargeable battery does not require as much energy storage. For example, if a laptop or other source of USB power is available, the rechargeable battery  301  may be charged from the source of USB power. If no other power is available, the rechargeable battery  301  may be charged from the primary battery module  310 . 
         [0033]    Use of modular charging system  360  allows size and weight of the rechargeable battery and recharging circuits to be reduced while providing the possibility of recharging under a variety of circumstances (such as from sources with varying output voltages or connector types, as might be encountered in different geographical regions in the world) and with a variety of power sources (i.e., AC main power, primary batteries, secondary batteries, solar cells, fuel cells, generators (powered or hand operated) or other devices which provide a power connection, for example a computer with a USB connector, a vehicle DC power connector, etc.). Only the necessary modules for each circumstance need be brought while traveling. Modular charging system  360  is sufficiently flexible to allow charging from future types of power sources that are not currently available. 
         [0034]    In some embodiments, the rechargeable batteries may be separable from the headphones so that multiple rechargeable batteries can be used. Enabling use of multiple rechargeable batteries allows one battery to be charged while another battery is attached to and provides power to the headphones. When the battery supplying power to the headphones is discharged, it can be exchanged for a charged battery so operation can continue. In some embodiments, the headphones do not contain recharging circuitry, which reduces the weight of the headphones. 
         [0035]    The electrical capacity, weight, and size of the primary battery  312  and the primary battery module  310  depend on the amount of recharging desired and the capacity of the rechargeable battery  301 . The total energy capacity of the rechargeable battery and primary battery determine how much energy is available to power the headphones (when the primary battery is the only source of secondary power available.) A smaller rechargeable battery may be used to minimize weight of the headphone, trading off how often the battery needs to be recharged. In some embodiments, the capacity of the rechargeable battery may be less than 400 mAh. In some embodiments, the rechargeable battery capacity may be less than 200 mAh. In some embodiments the weight of the rechargeable battery may be less than 20 g. In some embodiments the weight of the rechargeable battery may be less than 11 g. 
         [0036]    In some embodiments, a power source module may include adaptor module circuitry and electrical battery contacts for direct connection to the rechargeable battery. 
         [0037]    USB connectors are commonly used as data communications and electrical power connectors for electronic products such as computers, computer peripherals, user input devices, portable media devices, and portable memory storage devices. The adaptor module  320  may be plugged directly into computers or other devices with female USB connectors and the rechargeable battery  301  may be recharged from a desktop or laptop computer even when there is no AC mains power or primary battery available. In some embodiments, a cable may be used to connect between modules, between the modules and the power sources, or between the rechargeable battery  301  and the modules. In some embodiments, other connector types may be used to connect power sources to the adaptor module. For example, power source connector types may include USB connectors (both type A and B), or other equivalent connectors such as PCMCIA (Peripheral Component MicroChannel Interconnect Architecture) or IEEE (Institute of Electrical and Electronics Engineers) 1394 as well as any other connector which includes usable voltage connections. Instead of a direct electrical connection, inductive coupling may also be used. Inductive coupling uses an AC electrical voltage to transfer electrical power from one coil to another coil. The power source generates a magnetic field in a first coil which is coupled to a second coil. The second coil generates a voltage that powers the charging circuit. 
         [0038]    Referring to  FIG. 4 , there is shown a section view of the connecting ends of a USB Type A connector set. A male USB connector  400  has a non-conducting substrate  402 , a conducting shell  412 , and electrical contacts  404 ,  406 ,  408 , and  410 . A female USB connector  420  has a non-conducting substrate  422 , a conducting shell  432 , and electrical contacts  424 ,  426 ,  428 , and  430 . The exterior dimensions of the male USB connector shell  412  is approximately 5 mm by 12 mm. USB connector  400  electrical contacts  404 ,  406 ,  408 , and  410  are supported by substrate  402 . USB connector  420  electrical contacts  424 ,  426 ,  428 , and  430  are supported by the substrate  422 . When the male USB connector  400  is connected to the female USB connector  420 , shell  412  fits inside of and electrically connects to shell  432 , substrate  402  fits next to substrate  422 , contact  404  electrically connects to contact  430 , contact  406  electrically connects to contact  428 , contact  408  electrically connects to contact  426 , and contact  410  electrically connects to contact  424 . Contacts  404  and  430  are used for electrical ground, which is the return path for the USB power circuit. Contacts  406 ,  408 ,  426 , and  428  may be data transfer or sensing contacts, and contacts  410  and  424  are used for 5 Volts DC power transfer. Contacts  406 ,  408 ,  426 , and  428  may be used instead of or in addition to the sensing contacts  308 ,  318 , and  330 . If the USB contacts  406 ,  408 ,  426 , and  428  are used instead of the sensing contacts  308 ,  318 , and  330 , the USB contacts  406 ,  408 ,  426 , and  428  may use a signal to communicate between the source module  300 ,  310 , or  350  and the adaptor module  320 . The sensing contact signal or USB contact signal may be either a digital or analog signal. In some embodiments, the sensing contact signal or USB contact signal may be a simple logical high or low signal that senses the presence or absence of a specific module. The circuit diagrams described below in  FIGS. 5 ,  6 , and  7  show an example embodiment of the USB contact signal. 
         [0039]    Referring to  FIG. 5 , there is shown an electrical schematic drawing of an example AC mains module  300 . A 5-volt-regulator IC  500  converts the transformed, full-wave-rectified and filtered AC mains voltage to a regulated 5 Volts DC. The components of the AC mains module  300  includes AC electrical prongs  302 , electrical contacts  424 ,  426 ,  428 ,  430 , 5-Volt regulator integrated circuit (IC)  500 , and female USB connector  306 . The 5-volt-regulator IC  500  outputs 5 Volts DC to USB contact  424  of the female USB connector  306 . As described in  FIG. 7  below, a logical high voltage on USB contact  430  of female USB connector  306  increases the charge rate of adaptor module  320 , when adaptor module  320  is connected to the AC mains module  300 . In some embodiments, the signal levels present on electrical contacts of the USB connectors  306 ,  316 ,  352 , and  322  are designed so that when other USB devices (such as a computer mouse) are accidentally plugged into the modules or the modules are accidentally plugged into the other devices, there is no damage to the electrical circuits of the modules or the other USB devices. According to the USB standard, the signal levels should be less than 5.25 Volts to avoid damage. The 5-volt-regulator IC  500  in this example is commercially available from National Semiconductor (Santa Clara, Calif.) as part number LM309. 
         [0040]    Referring to  FIG. 6 , there is shown an electrical schematic drawing of an example primary battery module  310 . Primary battery module  310  incorporates primary battery  312 , electrical contacts  424 ,  426 ,  428 ,  430 , DC-to-DC converter IC  600 , power switch  610 , shutdown pin  620 , and female USB connector  316 . The DC-to-DC converter  600  converts the voltage from the primary battery  312  to output 5 Volts DC on contact  424  of the female USB connector  316 . As described in  FIG. 7  below, contact  430  of female USB connector  316  is electrically grounded to lower the charge rate of adaptor module  320 . Power switch  610  is used to start the charging cycle of primary battery module  310 . The power switch  610  may be a momentary switch, as shown in  FIG. 6 , or it may be a non-momentary switch. The DC-to-DC converter IC  600  in this example is commercially available from Linear Technology Corporation (Milpitas, Calif.) as part number LTC3422. The DC-to-DC converter IC  600  and associated circuitry draws a very low current when not being used so that it avoids discharging the primary battery  312  when the primary battery module  310  is not being used to charge the rechargeable battery  301 . The maximum current draw from primary battery  312  when the headphones are not being charged may be limited to avoid premature discharge of primary battery  312  during storage. In some embodiments, primary battery module  310  incorporates more than one primary battery  312  electrically connected in series in order to raise the voltage of the primary battery assembly. In some embodiments, higher primary battery  312  voltage increases the conversion efficiency of power from primary battery  312  to the rechargeable battery  301 . The size of the primary battery module  310  may be only slightly larger than the size of the primary battery  312 . Primary battery  312  may be a standard AAA-size or AA-size battery. The other circuitry associated with DC-to-DC converter IC  600  is used in the conventional manner to adjust the parameters of DC-to-DC converter IC  600 . 
         [0041]    Referring to  FIG. 7 , there is shown an electrical schematic drawing of an example adaptor module  320 . The adaptor module  320  incorporates male USB connector  322 , electrical contacts  404 ,  406 ,  408 ,  410 , Lithium-Ion battery charging IC  700 , program (PRG) pin  710 , NPN bipolar junction, transistor  720 , field effect transistor (FET)  730 , charge pin  740 , charging LED  750 , and thermistor  760 . The voltage from contact  410  of the male USB connector  322  powers the charging IC  700  which charges the rechargeable lithium-fan battery  301 . The charging rate is controlled by contact  404  of the male USB connector  322 . Contact  404  of the male USB connector  322  is connected to the FET  730  which controls the program pin of the charging IC  700 . When contact  404  of male USB connector  322  is grounded, the FET  730  turns off and the resistance on the program pin  710  is high. This high resistance reduces the charging rate of charging IC  700 . When contact  404  of the USB connector is pulled up in voltage, FET  730  turns on, the resistance on the program pin  710  is low, and the charging rate of charging IC  700  becomes high. 
         [0042]    When the charging of rechargeable battery  301  is finished, charging IC  700  pulls the charge pin  740  to a logical high voltage which is inverted by transistor  720  to become a logical low voltage and passes through contact  408  of the male USB connector  322  and contact  426  of the female USB connector  316  to the shutdown pin  620  of DC-to-DC converter IC  600 . This switches off the primary battery module  310  to avoid draining the primary battery  312  after the charging cycle is complete. Charging LED  750  lights when the charging of rechargeable battery  301  is occurring. In some embodiments, the thermistor  760  is used by the charging IC  700  to limit the charge if the rechargeable battery  301  becomes too hot. The charging IC  700  in this example is commercially available from Linear Technology Corporation (Milpitas, Calif.) as part number LTC4069. 
         [0043]    It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific apparatus and techniques herein disclosed without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of the appended claims.