Abstract:
An electronic apparatus has a first fuel cell capable of generating first electric power, a second fuel cell capable of generating second electric power less than the first electric power, a switching circuit coupled to the first fuel cell and the second fuel cell, and an electronic device coupled to the switching circuit. The electronic device is operable with one of the first electric power and the second electric power, depending on the electric power demand of the electric device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2002-287890, filed Sep. 30, 2002, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to a fuel cell for generating electric power, and also an electronic apparatus, such as a portable computer, which incorporates the fuel cell.  
           [0004]    2. Description of the Related Art  
           [0005]    In these years, various kinds of electronic devices that can be driven by batteries, such as a mobile information terminal called a Personal Digital Assistant (hereinafter PDA), a personal (mobile) computer, and a digital camera, have been developed and widely used.  
           [0006]    On the other hand, in recent years, special attention has been focused upon environmental problems, and eco-friendly batteries have been actively developed. A direct methanol fuel cell (hereinafter DMFC) is well known as a battery of this kind.  
           [0007]    In the DMFC, methanol and oxygen, which are supplied as fuel components, are subjected to a chemical reaction, and electric energy is obtained by the chemical reaction. An electrolyte is interposed between two electrodes formed of porous metal or carbon. See, “NENRYO DENCHI NO SUBETE” (“ALL ABOUT FUEL CELLS”), Hironosuke IKEDA, Kabushiki-Kaisha Nihon Jitsugyo Shuppansha, Aug. 20, 2001, pp. 216-217 incorporated herein by reference. There is a strong demand for practical use of the DMFC, since it produces no harmful waste.  
           [0008]    In order to increase an output power per volume of the DMFC, an auxiliary mechanism (hereinafter auxiliary) such as a pump is required. In this specification, a DMFC using an auxiliary is referred to as “auxiliary-type DMFC”, and a DMFC using no auxiliary is referred to as “vaporization-type DMFC.” 
           [0009]    In the meantime, most of mobile information terminals (e.g. laptop computer) have a suspend function or mode for retaining operating state parameters effective immediately before switch-off. The operating state parameter retained typically in a non-volatile memory (e.g. hard disk for a personal computer) and may be used to quickly resume the operating state when power is turned on. This enables quick resumption of the previous work when power is turned on.  
           [0010]    Assume that an auxiliary-type DMFC is applied to a mobile information terminal having the suspend function, and that the suspend function is activated. In an ordinary mobile information terminal, about 200 to 300 mW power is consumed in the suspend mode in order to retain the state at the time of switch-off. On the other hand, the auxiliary-type DMFC consumes, in general, about 1 W power for operations of the auxiliary. In short, it is not desirable in terms of fuel consumption efficiency to activate the auxiliary that consumes about 1 W power in order to supply power is of about 200 to 300 mW.  
           [0011]    Besides, in some kinds of devices, even when power is off, a power of about 60 to 70 mW needs to be supplied to internal circuits such as a microcomputer. In this case, the fuel consumption efficiency further deteriorates. Moreover, the auxiliary such as a pump produces some noise, and it is preferable to not operate the auxiliary in the suspend mode or when power is off.  
         BRIEF SUMMARY OF THE INVENTION  
         [0012]    Embodiments of the present invention provide an electronic apparatus accompanying a fuel cell unit which supplies with electric power.  
           [0013]    According to an embodiment of the present invention, an electronic apparatus includes a first fuel cell for generating first electric power, a second fuel cell for generating second electric power less than the first electric power, a switching circuit coupled to the first fuel cell and the second fuel cell for selecting one of the first and second fuel cells, an electronic device coupled to the switching circuit, and a control circuit which is responsive to signals from the electronic device indicative of the power demand for controlling the switching circuit. The electronic device is operable with one of the first electric power and the second electric power, in responsive to electric power demand of the electric device.  
           [0014]    According to other embodiments of the present invention, an electronic apparatus includes a first fuel cell for generating electric power using an auxiliary mechanism for fuel supply, a second fuel cell for generating electric power without the auxiliary mechanism, a switching circuit coupled to the first fuel cell and the second fuel cell for selecting one of the first and second fuel cells, and an electronic device coupled to the switching circuit. The electronic device is operable with the electric power provided from one of the first fuel cell and the second fuel cell.  
           [0015]    According to further embodiments of the present invention, a method is provided for providing an electronic apparatus with electric power from fuel cells. In one embodiment, the method includes providing the electronic apparatus with electric power from a first fuel cell when the electronic apparatus is in first state requiring first electric power, the first fuel cell having an auxiliary mechanism for fuel supply, and providing the electronic apparatus with electric power from a second fuel cell capable of generating less electric power than that of the first fuel cell when the electronic apparatus is in second state requiring second electric power being lower than the first electric power.  
           [0016]    Additional features and advantages of embodiments of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.  
           [0017]    The features and advantages of embodiments of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0018]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0019]    [0019]FIG. 1 is a perspective view showing a portable personal computer according to a first embodiment of the present invention;  
         [0020]    [0020]FIG. 2 is a block diagram showing a hardware configuration of a fuel cell unit in the portable personal computer according to the first embodiment;  
         [0021]    [0021]FIG. 3 is a flowchart showing an operation control procedure for the fuel cell unit according to the first embodiment; and  
         [0022]    [0022]FIG. 4 is a block diagram showing a hardware configuration of a fuel cell unit according to a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0023]    Preferred embodiments according to the present invention will be described hereinafter with reference to the accompanying drawings.  
         [0024]    [0024]FIG. 1 shows an external appearance of an electronic apparatus according to a first embodiment of the present invention.  
         [0025]    As is shown in FIG. 1, an electronic apparatus  1  of this embodiment is a portable personal computer. A fuel cell unit  2  is accommodated within a main body of the electronic apparatus  1 . The fuel cell unit  2  supplies the electronic apparatus  1  with electric power, and the electronic apparatus  1  operates with the electric power. The fuel cell unit  2  is designed to be easily detachable and replaceable with a new fuel cell or the same fuel cell after refilling the fuel.  
         [0026]    The electronic apparatus  1  has a suspend function for retaining parameters of an operating state which occurs immediately before turn-off of a power switch. Thereby, when the power switch is turned on, the previous work that has been suspended is displayed and may be quickly resumed. Accordingly, even in the suspend mode, the fuel cell unit  2  supplies the electronic apparatus  1  with electric power. In addition, in order to keep operations of internal circuits of a microcomputer, etc., the fuel cell unit  2  provides the electronic apparatus  1  with electric power even when the power switch is turned off. The power consumption of the electronic apparatus  1  in this embodiment is about 3 to 20 W in the power-on state, about 200 to 300 mW in the suspend state, and about 60 to 70 mW in the power-off state.  
         [0027]    [0027]FIG. 2 shows a schematic structure of the fuel cell unit  2 .  
         [0028]    As shown in FIG. 2, the fuel cell unit  2  includes a fuel tank  21 , a vaporization-type DMFC  22 , an auxiliary-type DMFC  23 , a switching circuit  24  and a microcomputer  25 .  
         [0029]    The fuel tank  21  is a cartridge type container that contains methanol to be used as fuel by the vaporization-type DMFC  22  and auxiliary-type DMFC  23 . The fuel tank  21  is detachably disposed within the fuel cell unit  2  to permit replacement and/or refueling of it.  
         [0030]    The vaporization-type DMFC  22  is a DMFC of the type wherein methanol supplied from the fuel tank  21  is vaporized therein and caused to react with oxygen in the air. Although the output power per volume is small in the vaporization-type DMFC  22 , there is no power consumption by an auxiliary such as one or more pumps. On the other hand, the auxiliary-type DMFC  23  is a DMFC of the type wherein methanol in the fuel tank  21  and air are positively taken in by an auxiliary such as one or more pumps. Although the output power per volume is large in the auxiliary-type DMFC  23 , power consumption due to the auxiliary is incurred. In this embodiment, the output power of the vaporization-type DMFC  22  is about 300 mW, the output power of the auxiliary-type DMFC  23  is about 20 W, and the power consumption of the auxiliary used in the auxiliary-type DMFC  23  is about 1 W.  
         [0031]    The auxiliary-type DMFC  23  has a fuel pump  231 , a mixing tank  232 , a fluid-feed pump  233 , a DMFC cell stack  234  and an air-feed pump  235 . The auxiliary (or auxiliary mechanism) includes one or more of pumps  231 ,  233 , and  235 .  
         [0032]    Methanol in the fuel tank  21  is fed into the mixing tank  232  by the fuel pump  231  and vaporized therein. The vaporized methanol is fed to the DMFC cell stack  234  by the fluid-feed pump  233 . Air is fed to the DMFC cell stack  234  by the air-feed pump  235 . The oxygen in the air and the vaporized methanol react with each other to generate electric power. Specifically, the above-mentioned power consumption of about 1 W by the auxiliary is the power consumption by the fuel pump  231 , the fluid-feed pump  233 , and the air-feed pump  235 .  
         [0033]    The switching circuit  24  is a selector for selectively supplying either an output power from the vaporization-type DMFC  22  or an output power from the auxiliary-type DMFC  23  to the electronic apparatus  1 . The microcomputer  25  controls all operations of the fuel cell unit  2 , including the operation of the switching circuit  24 . The microcomputer  25  executes transmission/reception of various signals with the electronic apparatus  1 .  
         [0034]    Referring to FIG. 3, the principle of the operational control of the fuel cell unit  2  will now be described.  
         [0035]    The microcomputer  25  always monitors reception of a signal sent from the electronic apparatus  1  (step A 1 ). If the microcomputer  25  has received a signal (YES in step A 1 ), it determines whether the received signal is a signal indicative of the shift to the suspend mode or a signal indicative of the shift to power-off (step A 2 ). If the signal is indicative of the shift to the suspend mode or power-off (YES in step A 2 ), the microcomputer  25  turns off the respective pumps of the auxiliary-type DMFC  23  so as to stop fuel supply from the fuel tank  21  (step A 3 ). Then, the microcomputer  25  operates the switching circuit  24  so as to feed an output power from the vaporization-type DMFC  22  to the electronic apparatus  1  (step A 4 ).  
         [0036]    On the other hand, if the received signal from the electronic apparatus  1  does not indicate a suspend mode or power off mode (i.e. power on mode) (NO in step A 2 ), the microcomputer  25  detects that the electronic apparatus is in power-on state, and turns on the respective pumps of the auxiliary-type DMFC  23  (step A 5 ). Thus, the electronic apparatus  1  sends signals to the microcomputer  25  indicative of the power demands of the electronic apparatus  1 . The microcomputer  25  stands by until the auxiliary-type DMFC  23  has become ready to supply a predetermined amount of power (step A 6 ). If the auxiliary-type DMFC  23  has become ready to supply the power (YES in step A 6 ), the microcomputer  25  operates the switching circuit  24  so as to feed an output power from the auxiliary-type DMFC  23  to the electronic apparatus  1  (step A 7 ) and informs the electronic device  1  of the completion of preparation for power-on (step A 8 ).  
         [0037]    As described above, in the fuel cell unit  2 , the auxiliary-type DMFC  23  with the output power of about 20 W is used in the power-on state in which power of about 3 to 20 W is consumed. On the other hand, in the power-off state in which power of about 60 to 70 mW is consumed or in the suspend mode in which power of about 200 to 300 mW is consumed, the vaporization-type DMFC  22  with the output power of about 300 mW is used. This operational control realizes an improvement in fuel consumption efficiency and prevents noise from occurring due to the auxiliary in the suspend mode or in the power-off state.  
         [0038]    When the auxiliary-type DMFC  23  is activated, the microcomputer  25  first operates the fuel pump  231 , fluid-feed pump  233  and air-feed pump  235  using an output power of about 300 mW from the vaporization-type DMFC  22 . After the auxiliary-type DMFC  23  has begun to generate a power of, e.g. 1 W or more, the microcomputer  25  then operates the fuel pump  231 , fluid-feed pump  233  and air-feed pump  235  using an output power from the auxiliary-type DMFC  23 . In the power-off state or in the suspend mode, the microcomputer  25  is supplied with power from the vaporization-type DMFC  22 .  
         [0039]    [0039]FIG. 4 shows the second embodiment of the present invention. The fuel cell unit  2  of the second embodiment differs from that of the first embodiment in that a secondary cell  26  (e.g. a battery, capacitor) and a charging circuit  27  for charging the secondary cell are added to the fuel cell unit  2 . The switching circuit  24  carries out switching among the vaporization-type DMFC  22 , the auxiliary-type DMFC  23 , and the secondary cell  26 .  
         [0040]    In the second embodiment, the switching circuit  24  does not exclusively select only one of these three power supplies. Where necessary, power of the secondary cell  26  is added to the auxiliary-type DMFC  23  (e.g. the switching circuit  24  selects both the secondary cell  26  and the auxiliary-type DMFC  23 ).  
         [0041]    The fuel cell unit  2  of the second embodiment is advantageously used in an electronic apparatus  1  wherein power consumption may suddenly be increased. The secondary cell  26  can supply a power, which is needed in the electronic apparatus but may not completely be supplied from the auxiliary-type DMFC  23  or which is instantaneously required in the electronic apparatus.  
         [0042]    Besides, the charging circuit  27  charges the secondary cell  26  with an excess power of the vaporization-type DMFC  22  in the power-off state. Therefore, the fuel consumption efficiency is improved.  
         [0043]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.