Electrical power unit

A fuel cell 1 and an electric double-layer capacitor 2 are parallelly arranged for a power supply. A DC/DC converter 3 steps up voltage of the fuel cell 1 and the electric double-layer capacitor 2, to thereby output power. An output switch 5 is disposed on an output pathway of the DC/DC converter 3. By controlling the output switch 5 with a control IC 4, output power can be switched on and off. When there is a fuel shortage or abnormality in the fuel cell 1, the control IC 4 controls the output switch 5, to thereby intermittently alter the output power. With this configuration, when the power supply is used for a mobile telephone as a portable electronic device connected thereto, a user can confirm whether there is a fuel shortage or a fuel cell abnormality by checking of blinking state of a charge pilot lamp of the mobile telephone.

TECHNICAL FIELD

The present invention relates to an electrical power unit to be connected to an electronic device having an electric storage means, such as a secondary cell, for supplying power to the electronic device.

BACKGROUND ART

Due to recent developments in electronics, use of portable electronic devices, such as mobile telephone, portable personal computer, audio-visual device and mobile terminal equipment, has been rapidly spreading. A secondary cell used in such a portable electronic device has been developed from a conventional sealed lead battery, to a nickel-cadmium cell and a nickel-metal-hydride cell, further to a lithium-ion cell. As for any of these cells, attempts have been made to achieve a high energy density by developing cell active materials and cell structures with high-capacity, so as to realize a power source with a longer operating time. On the other hand, in the portable electronic devices, efforts have been made to reduce power consumption, and the power consumption per function has been reduced. However, it is expected that the total power consumption will further increase, since new functions will be added for upgrading the device, in order to satisfy user demands.

In the portable electronic devices, a capacity of the secondary cell mounted therein is limited, due to spacial limitation of a casing. In order to ensure a long operating time, it is necessary to introduce an external electrical power unit for supplying power, which is to be connected to the electronic device. When the electrical power unit, also called sub-battery, is used, it becomes especially important to check a remaining battery level. Conventionally, the electrical power unit has a light emitting diode or a liquid crystal display to display the remaining battery level.

However, adding a display function device, such as the light emitting diode and the liquid crystal display, to the electrical power unit increases a production cost. In addition, energy is consumed for displaying the remaining battery level, which reduces an energy density of the electrical power unit.

Therefore, it would be desirable to provide an electrical power unit that can reduce expenses, with which a user can still check internal states, including a remaining battery level, of the electrical power unit without reducing the energy density.

DISCLOSURE OF THE INVENTION

The present invention provides an electrical power unit for being connected to an electronic device including an electric storage means and displaying a charge state when the electric storage means is charged, which electrical power unit includes an electric power source for supplying power to the electronic device, and a transmission means for intermittently altering output power of the electric power source and transmitting specific information, and allows the electronic device to display the specific information by altering a displaying mode of the electronic device when the electronic device is supplied with power.

With this configuration, when the electronic device is supplied with power, the transmitted specific information can be displayed utilizing a display function of the electronic device, by altering the output power. For example, when remaining battery level information of the electrical power unit is transmitted, a user can confirm a remaining battery level indicated on a display means of the electronic device, by checking the change in the display in accordance with an intermittence of the output power.

According to the present invention, by simply altering the power output to the electronic device, the specific information, such as the remaining battery level, becomes checkable. Therefore, it becomes possible to omit a display means in the electrical power unit, leading to a reduced cost and an improved energy density. As a result, an electrical power unit which ensures a longer operating time is obtained.

The various aspects, other advantages and further features of the present invention will become more apparent by describing in detail illustrative, non-limiting embodiments thereof with reference to the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1shows a circuit diagram of an electrical power unit according to a first embodiment.

As shown inFIG. 1, an electrical power unit10according to the first embodiment includes: a cell1and an electric storage means2as electric power sources; a circuit part3; a control IC4; and an output switch5. The cell1and the electric storage means2are parallelly arranged, with both ends thereof being connected to an input terminal Vin and a ground (GND) terminal of the circuit part3. To the Vin terminal of the circuit part3, positive terminals of the cell1and the electric storage means2are connected, and to the ground (GND) terminal, negative terminals are connected. The circuit part3is for transforming output voltage into output power, with an output terminal Vout thereof being connected to an output terminal V+, and the ground terminal connected to an output terminal V− through the output switch5formed of an N-channel power MOSFET. A control terminal of the output switch5is connected to an output switch driving terminal of the control IC4. The positive terminal of the electric storage means2is connected to an EDLC voltage input terminal of the control IC4. To the control IC4, values detected at a remaining fuel level detector6and a temperature sensor7are output. Based on the voltages of the cell1and the electric storage means2, and the detected values from the remaining fuel level detector6and the temperature sensor7, the control IC4determines a remaining battery level and a cell state of the cell1and electric storage means2, and transmits the determined results as information by switching the output switch5on and off. Herein, the control IC4and the output switch5correspond to a transmission means in the appended claims.

In the first embodiment, a fuel cell is used for the cell1. Since the electrical power unit10is used for a portable electronic device connected thereto, for the fuel cell, a direct methanol fuel cell (DMFC) utilizing a methanol-water solution as a fuel is used. However, a modified version thereof or a fuel cell using a direct hydrogen fuel may also be used.

For the electric storage means2, an electric double-layer capacitor (EDLC) is used. The electric storage means2is charged by the cell1, and outputs power when a power supply from the cell1alone is not sufficient. Accordingly for the electric storage means2, for example, a lithium-based secondary cell can be used instead of the electric double-layer capacitor. In this case, it is desirable that a high-output type cell used for a hybrid electric vehicle (HEV) or the like be used.

For a combination of the cell1and the electric storage means2that supplies power, any combination may be used as long as the cell1is characterized as a power source with a high energy density and the electric storage means2is characterized as a power source with a high power density. For example, a combination of a lithium-ion cell as the cell1and the electric double-layer capacitor as the electric storage means2can be used.

For transforming voltage, a DC/DC converter is used in the circuit part3, so as to make the output voltage therefrom correspond to the voltage of the portable electronic device. In the first embodiment, a step-up converter is used in order to reduce the number of serial connection in the cell1and the electric storage means2. However, depending on the voltage of the portable electronic device, a step-up/step-down converter or a step-down converter may be used.

Hereinafter, an explanation is made in a case where the direct methanol fuel cell is used as the cell1, and the electric double-layer capacitor is used as the electric storage means2. It should be noted that, in the following descriptions including other embodiments, the cell1, the electric storage means2and the circuit part3are referred to as fuel cell1, electric double-layer capacitor2and DC/DC converter3, respectively. The remaining fuel level detector6and the temperature sensor7detect a remaining fuel level and a temperature, respectively, of the fuel cell1.

In the first embodiment, a portable electronic device is an object to be supplied with power by the electrical power unit10. An output power of the fuel cell1is set so as to corresponds to an average value of the power required in the portable electronic device (not shown), and thus set smaller than the maximum power required. A shortfall in the required power is compensated from the electric double-layer capacitor2. With this setting, the electrical power unit10can be made compact as compared with an electrical power unit in which the output power is set to correspond to the maximum power required in the portable electronic device. Since the output power of the fuel cell1is set corresponding to the average value, the electrical power unit10outputs the power to an external system when the power is stored in the electric double-layer capacitor2; while the electrical power unit10stops the power output to the external system, when the electric double-layer capacitor2is charged. This control can be realized by the control IC4that obtains the voltage of the electric double-layer capacitor2and switches the output switch5on and off in accordance with the voltage of the electric double-layer capacitor2.

Specifically, the control IC4checks the voltage of the electric double-layer capacitor2input through the EDLC voltage input terminal, and when the voltage exceeds an upper limit voltage set as a threshold value, the control IC4outputs a control signal to the output switch5, and switches the output switch5on. As a result, the fuel cell1and the electric double-layer capacitor2output the power in parallel, to the portable electronic device connected to the output terminals V+, V−. As the power is output, the voltage of the electric double-layer capacitor2decreases, as does the output voltage of the fuel cell1. When the voltage of the electric double-layer capacitor2reaches a lower limit voltage value set as a threshold value, the control IC4stops the output of the control signal and switches the output switch5off.

When the output switch5is switched off and the power output to the external system is stopped, a load is reduced which in turn increases the output voltage of the fuel cell1, which then charges the electric double-layer capacitor2. When the voltage of the electric double-layer capacitor2reaches the upper limit voltage set as a threshold value as a result of the charging, the control IC4outputs a control signal and switches the output switch5on. Consequently, the fuel cell1and the electric double-layer capacitor2again supply the power to the portable electronic device. In this manner, the portable electronic device is supplied with power by repeated output of a power supply pulse P at a specific interval, as shown in (a) ofFIG. 2.

The fuel cell1is provided with the remaining fuel level detector6and the temperature sensor7, and based on the detection signals therefrom, the control IC4determines a fuel supply state of the fuel cell1or determines whether or not there is an abnormality in the fuel cell1. When it is determined that there is a fuel shortage or an abnormality in the fuel cell1, the control IC4divides timewise the power supply pulse P shown in (a) ofFIG. 2into, for example, a pulse group P1shown in (b) or a pulse group P2in (c), and outputs the divided pulses. Specifically, the control IC4stores various control patterns corresponding to a fuel shortage and abnormalities in the fuel cell1, and when it is determined that there is a fuel shortage or an abnormality in the fuel cell1, the control IC4applies a corresponding control pattern to divide timewise the power supply pulse P, by switching the output switch5on and off.

Accordingly, when the fuel runs out, as shown in (b) ofFIG. 2, the pulse group P1obtained by dividing the normal power supply pulse P is output to the portable electronic device. In the case of an abnormality in the fuel cell1, as shown in (c), the pulse group P2obtained by dividing the normal power supply pulse P is output to the portable electronic device. Since a width of the pulse output for a fuel shortage is set smaller than a width of the pulse output when the fuel cell1is in an abnormal state, and a quiescent time in each pulse group is set equal, it can be confirmed whether or not there is a fuel shortage or an abnormality in the fuel cell1, by reading the difference in the pulse group appearing on the portable electronic device. Since the portable electronic device typically has a charge pilot lamp that lights when power is supplied, a user can confirm whether or not there is an abnormal state of the electrical power unit10, by checking a blinking state of the charge pilot lamp, and can further confirm whether the state is a fuel shortage or an abnormality in the fuel cell1. In this case, by utilizing a standard function of displaying a charge state provided in the typical portable electronic device, a cell state in the electrical power unit10can be confirmed. Of course, the checked result can be displayed by other means, such as voice, by providing the portable electronic device with a function of checking the pulse number and the pulse width.

As shown inFIG. 2, the division of the power supply pulse with a control pattern can be applied to all power supply pulses P. Alternatively, the division can be applied solely to the first power supply pulse P after detecting an abnormality or the like. With respect to the control pattern, the division number of the pulse can be altered in accordance with a fuel state or an abnormal state in the fuel cell1. With respect to the division number of the power supply pulse, the number may be altered in accordance with a number of power supply pulse P, for example, two divided pulses for the first power supply pulse, three divided pulses for the second power supply pulse, and so forth.

FIG. 3is a diagram showing output power in a case where a pulse number is altered in accordance with a remaining fuel level, as an example of time division.

When the remaining fuel level is high, the normal power supply pulse P shown in (a) ofFIG. 3is divided into three pulses, such as a pulse group P1shown in (b), and output. When the remaining fuel level is medium, the normal power supply pulse P is divided into two pulses, such as a pulse group P2shown in (c), and output. When the remaining fuel level is low, the normal power supply pulse P is converted into one pulse with a smaller pulse width, such as a pulse P3shown in (d), and output. It should be noted that, inFIG. 3, the pulse group P1and the pulse group P2differ only in the pulse number, and are the same in the pulse width and the quiescent time.

Even in this case, the fuel state in the fuel cell can be confirmed in the portable electronic device, by counting the pulse number. When the portable electronic device is provided with a charge pilot lamp, the fuel state can be confirmed by a short blinking of the charge pilot lamp.

FIG. 4is an explanatory diagram in which an electrical power unit is used with a mobile telephone connected thereto.

Herein, a mobile telephone20is used as the portable electronic device. The electrical power unit10is connected to the mobile telephone20through a cord12. The electrical power unit10has a circuit shown inFIG. 1built therein, and the cord12is connected to the output terminals V+, V− of the circuit. Therefore, power can be supplied to the mobile telephone20, by a control on a side of the electrical power unit10.

On the mobile telephone20, a charge pilot lamp21is mounted as a standard function, which lights when charging is performed on a secondary cell built in the mobile telephone20. When the electrical power unit10supplies power to the mobile telephone20as a portable electronic device, the charge pilot lamp21blinks in accordance with the power pulses shown inFIG. 2orFIG. 3. With this feature, a user can confirm whether or not there is a fuel shortage or an abnormality in the fuel cell1, or confirm a fuel state in the fuel cell1, by checking a blinking state of the charge pilot lamp21, without modifying the portable electronic device. It should be noted that, in a case of the mobile telephone in which a charge icon is displayed on a liquid crystal display when charging, the information described above can be confirmed by checking the blinking of the charge icon.

As described above, the states of the fuel cell1are classified mainly into the remaining fuel level (fuel shortage) and the fuel cell abnormality. With respect to the fuel (a methanol-water solution is used), when the fuel is reduced nearly to zero, the power from the fuel cell1decreases, and thus a duty ratio of the power supply to the mobile telephone becomes notably small. That is, a period of lighting of the charge pilot lamp21becomes short. With respect to the abnormality in the cell1, representative examples include: an output limit set by a control initiated when the temperature exceeds a specific threshold value (e.g., 45° C.) (the temperature of the fuel cell rises with the progress of the reaction); hindrance to an oxygen supply due to water clogging in an air electrode, caused in accordance with the fuel cell power generation; and a decline of power output due to hindrance to a methanol-water solution supply due to carbon dioxide clogging in an fuel electrode.

As a common characteristic between the fuel shortage and the fuel cell abnormality, there can be mentioned a decline of power output. Since a user can check whether or not there is a decline of power output by blinking state of the charge pilot lamp21in the mobile telephone20, the problem can be easily solved by replacing the fuel cartridge, in the case of the fuel shortage. In the case of the abnormality in the fuel cell1, as shown inFIG. 2, a power pulse with a width different from that in the case of the fuel shortage is output, and thus the abnormality is distinguishable from the fuel shortage by the blinking state of the charge pilot lamp21, against which a measure can be taken, such as turning off the power source.

Next, detection of the remaining fuel level and the abnormality in the fuel cell will be described.

FIG. 5is a cross sectional view showing a fuel cartridge used in the fuel cell.

Electrodes1A,1B are opposingly provided on an inner circumference of a fuel cartridge1C. A fuel FR3is composed of a methanol-water solution that receives a pressure from a compressed gas GR3through a partition member20A. When the fuel FR3is consumed, the partition member20A moves upward, and thus a space above the partition member20A is always filled with the fuel FR3. Depending on the remaining level of the fuel FR3in the fuel cartridge1C, surface areas of the electrodes1A,1B with which the fuel FR3comes into contact differ, and thus by measuring a resistor between the electrodes1A and1B, the remaining fuel level can be detected.

In the fuel cell1, when water clogging or carbon dioxide clogging, for example, occurs, the output voltage rapidly decreases. By detecting the rapid decrease of the voltage, water clogging or carbon dioxide clogging can be detected.

In addition, when the methanol concentration becomes abnormally high, there occurs a phenomenon in which a temperature rises in the fuel cell1even though the output voltage does not increase. Therefore, when a high temperature is detected while the output voltage is low, it is determined that the concentration of methanol is high.

Further, when the output current requested by the portable electronic device is increased but the requested power generation is not performed and the temperature remains low, it is determined that the concentration of methanol in the fuel cell1is low.

When these abnormalities are detected, the control IC4applies a corresponding pattern as described above, to divide timewise the power supply pulse P as shown inFIG. 2, and output the divided pulses. As a result, a user can confirm whether or not there is an abnormality by, for example, checking a blinking state of the charge pilot lamp21of the mobile telephone20.

As described above, according to the electrical power unit10of the first embodiment, the remaining fuel level or the fuel cell abnormality can be determined even though the function of displaying a cell state is not provided in the electrical power unit10, leading to a cost reduction. In addition, since no energy is used for displaying, an energy density can be improved.

In the first embodiment, the description is made while illustrating that a user confirms a fuel shortage or an abnormality in the fuel cell1by checking a blinking state of the charge pilot lamp21. However, the width and number of the power pulse may be detected by a circuit in the portable electronic device, and displayed with another mode, or used for control, such as switching of the portable electronic device to a low-power consumption mode.

In the first embodiment, a fuel cell is used for the cell1. Therefore, the operating time can be elongated by supplying a fuel, with replacing the fuel cartridge1C. Likewise, for the purpose of a continuous usage, a replaceable primary cell is used instead of the fuel cell1, and power can be supplied by a combination of the primary cell and the electric double-layer capacitor2.

For the control IC4, a specialized IC is desirable in order to achieve the functions thereof. However, the IC can be replaced with a comparator, a microprocessor or the like.

Finally, the output switch5uses the N-channel power MOSFET on the ground side as shown inFIG. 1, but may use a P-channel power MOSFET on the V+ side, or may be replaced with other switching elements.

In the first embodiment, the supplied power supply pulse P is divided timewise to transmit information, such as a fuel state and an abnormality in the fuel cell1, to the mobile telephone20, and the information is displayed on the mobile telephone20utilizing the charge display function of the mobile telephone20equipped as a standard function. When the power of the fuel cell1is available, the electric double-layer capacitor2does not output power, and thus the continuous power is supplied to the portable electronic device. Even in this case, by switching the output switch5on and off as described above at a predetermined interval, information such as a fuel state and an abnormality in the fuel cell1can be transmitted and displayed. It should be noted that, for information transmitted to the portable electronic device, a variety of information can be used, such as voltage information and abnormal current information of the fuel cell1.

Next, a second embodiment will be described.

FIG. 6is a circuit diagram of an electrical power unit according to a second embodiment. This electrical power unit is different from one shown inFIG. 1, in that a changeover switch8ais added to the control IC4a, which is operable by a user. The fuel cell1, the electric double-layer capacitor2, the output switch5and the like are the same as those in the first embodiment.

For the changeover switch8a, a common direct current (DC) switch, such as a tactile switch and a push switch, can be used.

In the first embodiment, when it is determined that there is a fuel shortage or an abnormality in the fuel cell1, the power supply pulse P shown in (a) ofFIG. 2is divided timewise into, for example, a pulse group P1of (b) or a pulse group P2of (c) and output. Therefore, when there is an abnormality, the power pulse obtained by dividing the power supply pulse P is always output. In the second embodiment, the division of the power supply pulse P, i.e., a display of a cell state, is performed depending on the arbitrary operation of a user.

Specifically, when the changeover switch8ais opened, the control IC4aperforms a normal control. In this case, the control IC4achecks the voltage of the electric double-layer capacitor2input through the EDLC voltage input terminal, and when the voltage exceeds the set upper limit voltage, the control IC4aoutputs a control signal to the output switch5, and switches the output switch5on, to thereby output power from the fuel cell1and the electric double-layer capacitor2. As an electrical discharge proceeds, the voltage of the electric double-layer capacitor2decreases, as does the output voltage of the fuel cell1. When the voltage of the electric double-layer capacitor2reaches the set lower limit voltage value, the control IC4stops the output of the control signal to thereby stop the power supply.

In this case, as shown in (a) ofFIG. 2or (a) ofFIG. 3, the normal power supply pulse P is output. This control continues while the changeover switch8ais opened. When the changeover switch8ais closed, as shown in (e) ofFIG. 7, an input signal is input to the control IC4a, and then values detected at the remaining fuel level detector6and the temperature sensor7are input. When it is determined that there is a fuel shortage or an abnormality in the fuel cell1, the control IC4applies a corresponding control pattern to divide timewise the power supply pulse P, by switching the output switch5on and off.

FIG. 7is a diagram showing output power in a case where a pulse number is altered in accordance with a remaining fuel level, as an example of time division.

In this case, like inFIG. 3, when the remaining fuel level is high, the normal power supply pulse P is divided into three pulses as shown in (b), and output. When the remaining fuel level is medium, the normal power supply pulse P is divided into two pulses as shown in (c), and output. When the remaining fuel level is low, the normal power supply pulse P is converted into one pulse with a smaller pulse width as shown in (d), and output.

According to the second embodiment, the control IC4adetects a state change of the input switch8acaused by the operation of a user, and information of the electrical power unit, such as remaining fuel level information, is displayed on the portable electronic device, by utilizing the timewise divided power supply pulse P. In this embodiment, the normal power supply pulse P is divided timewise and transmitted as shown inFIG. 7. However, information is transmitted by utilizing the number of power supply pulse having the same interval therebetween or an interval with a specific value or more. The control with the control IC4afor the purpose of controlling the power supply pulse may be realized by equally dividing an interval between the upper limit voltage and the lower limit voltage (or between the upper limit current and the lower limit current) into a several equivalents, or by a timer function. InFIG. 7, the altered power supply pulse is transmitted over one cycle after the operation by a user. However, the pulse may be continuously transmitted over several cycles. Alternatively, the information may be displayed to a user by utilizing a number of normal pulses, for example, one pulse for the first time, two pulses for the second time, and three pulses for the third time.

Next, a third embodiment will be described.

FIG. 8is a circuit diagram of an electrical power unit according to a third embodiment. This electrical power unit10shown inFIG. 8is different from one shown inFIG. 1, in that a changeover switch (pulse alteration switch)8bis added. The other components and arrangements are the same. For the changeover switch8b, a slide switch or the like can be used. Of course, instead of the slide switch, a plurality of switches, such as push switch, may be used.

By operating the changeover switch8b, in the control IC4b, an upper limit voltage and a lower limit voltage for determining a voltage at the electric double-layer capacitor2are changed.

As shown inFIG. 9, the fuel cell has output characteristics in which the output voltage decreases as the output current increases. Therefore, for example, when the lower limit voltage and the upper limit voltage for controlling the voltage of the electric double-layer capacitor2are set at those of a use range1shown inFIG. 9, and the upper limit voltage is switched to a lower one, such as that of a use range2or use range3, a cycle of the power supply pulse P shown in (a) ofFIG. 2becomes short, and therefore, a cycle of the pulse groups P1, P2shown in (b), (c) ofFIG. 2become short as well. Accordingly, the display cycle can be altered according to the preference of a user. Of course, threshold values of both the upper limit voltage and the lower limit voltage may be altered. Moreover, a power supply pulse corresponding to selected characteristics of the portable electronic device may be supplied, by assigning states of the input switch8bto respective characteristics of the portable electronic device, with an operation by a user.

Next, a fourth embodiment will be described.

FIG. 10is a circuit diagram of an electrical power unit according to a fourth embodiment.

In the case where a portable personal computer20′ is used as the portable electronic device as shown inFIG. 11, an output terminal of an interrupt signal is typically provided at a connecting terminal31. Corresponding to this output terminal, the electrical power unit10is provided with an INT12as an input terminal for an interrupt signal, in addition to the power output terminal, in order to enable an input of the interrupt signal. The interrupt signal is output when the electrical power unit10is properly connected to the connecting terminal31and the power is supplied. Therefore, in a case where the electrical power unit is used for the portable personal computer20′ from which such an interrupt signal is output, in addition to two terminals, i.e., the output terminals V+ and V− for power supply, an INT terminal for inputting the interrupt signal is also provided as shown inFIG. 10, through which the interrupt signal is input to the control IC4c. The electrical power unit10checks a cell condition only when the interrupt signal is input, and divides timewise the power supply pulse P and transmits the divided pulse. Processings after the input of the interrupt signal from the portable personal computer20′ are the same as those of the second embodiment.

In the second embodiment, as shown inFIG. 6, the changeover switch8ais connected to the control IC4aand a user operates the changeover switch8ato display a remaining fuel level or an abnormality in the fuel cell1on the portable electronic device; while in the fourth embodiment, instead of the input switch8aoperable by a user, an interrupt signal (input signal) from the portable electronic device is used for dividing timewise the power supply pulse P to display a state of the fuel cell1, as shown inFIG. 7.

Herein, as the portable electronic device, the portable personal computer20′ is used. In this portable personal computer20′, by an input of a power supply pulse, the electrical power unit10is recognized as a sub-battery, and at the same time, an image is displayed on a screen of the portable personal computer20′ that shows that the main battery and the sub-battery are connected, as shown inFIG. 11, for example. After the input of the power supply pulse P, the portable personal computer20′ outputs an interrupt signal to the INT terminal connected to the interrupt input terminal, to thereby allow the electrical power unit10to transmit the power supply pulse P. The portable personal computer20′ counts, for example, the pulse number, and displays the remaining fuel level of the electrical power unit10on the screen. Since there may be a case where the interrupt on the INT terminal by the portable personal computer20′ coincides with the normal power supply period, it is desired that the pulse number be counted at rising. It should be noted that, when there is no response for a specific period of time or abnormality information of the fuel cell1is transmitted after the interrupt signal is output to the INT terminal, the display of the sub-battery is deleted from the screen, as it is determined by the portable personal computer20′ that the power is not supplied from the electrical power unit10. With this configuration, a user can recognize when the electrical power unit10does not supply power. In this case, the information may be displayed to a user by a popup view.

Next, as a modified embodiment, a description is made in a case where a primary cell or a secondary cell, instead of the fuel cell1, is used for the cell1.

For example, in the circuit shown inFIG. 1, when a primary cell or a secondary cell is used for the cell1instead of the fuel cell1, the voltage of the primary cell or the secondary cell decreases as an electrical discharge proceeds. The remaining battery level can be determined by monitoring the voltage. In order to display the remaining battery level, the lower limit voltage is set at, for example, an extinction voltage of the cell (in the case of lithium cell, 2.7 V or 3.0 V). The upper limit voltage may be set at the voltage near the above-mentioned lower limit voltage (e.g., the lower limit voltage plus 0.1 V). Alternatively, the upper limit voltage may not be particularly set at a specific value, and a time period in which the voltage is above the lower limit voltage may be measured by a timer function.

By setting the upper limit voltage and the lower limit voltage as described above, the remaining level can be detected by the portable electronic device. First, the control IC4detects that the voltage of the primary cell or the secondary cell1reaches the lower limit voltage, and controls the output switch5to switch off to thereby stop the electrical discharge. The termination of the discharge raises the voltage of the primary cell or the secondary cell1. When the voltage of the primary cell or the secondary cell1reaches the upper limit voltage, the electrical discharge is resumed, and when the voltage does not recover to the upper limit voltage, the electrical discharge is terminated. In this situation, a period of lighting of the charge pilot lamp on the portable electronic device becomes gradually short, and a user can check whether or not there is a fuel shortage in the cell1.

Next, a protection circuit of the electric double-layer capacitor will be described.

In the embodiments above, the direct methanol fuel cell is used for the fuel cell1, and therefore as shown in the characteristics diagram ofFIG. 9, there is a notable difference especially between the lower limit voltage used and the open-circuit voltage (OCV) as the maximum voltage. Therefore, especially inFIG. 9, when a control range is set at the use range1or2having a high upper limit voltage, the electric double-layer capacitor2may be used at a value around the limit of the withstand voltage. In this case, in order to protect the electric double-layer capacitor2, it is desirable that the circuit be provided with a protection circuit for limiting the voltage.

FIG. 12is a circuit diagram of an electrical power unit with a protection circuit. The protection circuit9ais connected to the DC/DC converter3on an input terminal Vin side, and when the voltage of the fuel cell1exceeds a set cut-off voltage, they become electrically continuous, to thereby limit the maximum output voltage of the fuel cell1to the cut-off voltage or less.

In this case, when the DC/DC converter3is a step-up converter, the current value cut off by the protection circuit9abecomes high, and therefore each device used in the protection circuit9ashould have a large allowable dissipation.

In order to avoid this, as shown inFIG. 13, the protection circuit9bmay be connected to the DC/DC converter3on an output terminal Vout side. In this case, the voltage of the output terminal Vout is higher than the input terminal Vin of the DC/DC converter3, and therefore, the current to be cut can be made small. As a result, a device with a small allowable dissipation can be used, providing advantage of down-sizing.

When an output of the DC/DC converter3to the control IC4cis used as a power source as shown inFIG. 14, for example, by connecting the output terminal to the ground (GND) through the resistor9cand allowing the control IC4cto switch the output terminal on, voltage can be cut, which serves as a protection circuit.

Next, other modified embodiments will be described.

FIG. 15is a circuit diagram of an electrical power unit in which an output switch is omitted, as compared with the electrical power unit ofFIG. 1.

The output switch driving terminal of the control IC4is directly connected to the control terminal of the DC/DC converter3a. Switching on and off of the output power of the DC/DC converter3acan be performed by controlling the output voltage of the DC/DC converter3awith the control IC4.

FIG. 16is a circuit diagram of an electrical power unit in which an electric storage means is omitted, as compared with the electrical power unit ofFIG. 1.

Since this circuit has no electric storage means, it is necessary to set the output of the fuel cell1higher than the maximum power of the portable electronic device. In this case, unlike the embodiments above, the power supply pulse is not required for supplying power, and thus a continuous power supply can be performed. The remaining fuel level and the abnormality in the fuel cell1can be displayed by, as described above, controlling the output switch5or the DC/DC converter3and forming a specific number of power supply pulses with a specific duty ratio, in the output power.

In the embodiments above, by controlling the voltage of the fuel cell1, the output power of the fuel cell is controlled. The above-mentioned control can be realized based on either one of voltage value and current value. Especially when the control is based on the current value, a change in the output becomes large due to environmental conditions, including temperature and humidity. Therefore, it is desirable that the upper limit value and the lower limit value be modified using sensed environmental information.

FIG. 17is a circuit diagram of an electrical power unit in which a control is performed based on an output current of a fuel cell.

In the above-mentioned embodiments and modified embodiments, the output power is switched on and off by controlling the output switch5with the control IC4based on the output voltage of the fuel cell1. On the other hand in this embodiment, a resistor R is disposed between the fuel cell1and the electric double-layer capacitor2, the output current of the fuel cell1is converted into voltage at the resistor R, and input to the current input terminal of the control IC4. In the control IC4, the output switch5is switched on and off based on the output current value of the fuel cell1; at the lower limit current value, the output switch5is switched on to thereby output the power, while at the upper limit current value, the output switch5is switched off to thereby block output power. With this configuration, a similar effect can be obtained to those described with respect to the above-mentioned embodiments in which the control is performed based on voltage.