Electronic portable appliance

Abstract: An electronic portable appliance is provided which can operate over a long time by enhancing the charging efficiency of the electronic portable appliance driven on generated power and reducing useless current consumed by those other than a drive circuit, or can operate over an equivalent drive time to the conventional appliance even where the feed power is reduced by reducing the size and weight of a power feed means configured by a power generating means, booster circuit, etc., in order to reduce the size and weight of the electronic portable appliance. The electronic portable appliance is configured by a power feed means (10) to supply power, a power storing means (40) to store the power of the power feed means, a drive circuit (50) to drive on power stored on the power of the power feed means or power stored on the power storing means, a switch means (20) provided on a charge path and a control circuit (30) for comparing voltages on the charging path at a forward and rear position of the switch means. The control circuit turns on the switch means to charge the power of the power feed means to the power storing means when detecting that the voltage at the forward stage of the switch means on the charging path is higher and to turn off the switch means to prevent the stored power from reversely flowing from the power storing means to the power feed means when detecting that the voltage at the forward stage of the switch means on the charging path is lower.

Description: The present invention relates to electronic portable appliances to be driven on power generated from a power generating means or the like. More particularly, the present invention relates to an electronic portable appliance provided with a power feed means having a power generating means or a generating means and booster circuit to increase the voltage of the power generating means; a power storing means to store power supplied by the power feed means; and a drive circuit driven on power supplied by the power feed means or on storage power of the power storing means. The present invention is particularly for use in a wrist watch driven on power supplied from a thermoelectric conversion device, solar battery or the like. There is shown in Fig. 6 a schematic block diagram of an electronic portable appliance according to related prior art. In Fig. 6, an electronic portable appliance 600 is configured by a power feed means 10 for supplying electric power; a power storing means 40 for storing power supplied by the power feed means 10 through a diode element 601; and a drive circuit 50 to be driven on power supplied by the power feed means 10 through the same diode 601 or on storage power built up on the power storing means 40. Furthermore, the power feed means 10 is formed by a power generating means, a booster circuit for increasing the voltage of the power generating means and so on. In such an electronic portable appliance, the power feed means 10 is also required to be reduced in size and weight due to the reductions of size and weight of the appliance. Due to this, there is a tendency toward decreasing the power supplied by the power feed means 10. On the other hand, there is a desire to improve the charge efficiency to the power storing means 40 and effectively utilize the power stored on the storage means 50, due to a desire for increasing the operating time of the electronic portable appliance. Accordingly, to realize the further reduction in size and weight or further increase the operation time for the electronic portable appliance, it is indispensable to further increase the charge efficiency to the power storing means and effectively utilize the storage power on the power storing means. In the prior art electronic portable appliance, rectification is made by the diode element 601 in order to prevent the stored power from reversely flowing in the event that the generation of power runs out. However, the major cause of lowering the charge efficiency lies in losses due to the forward drop of voltage across the diode element 601. Accordingly, the use of a diode element with a low forward drop voltage improves the charge efficiency. Meanwhile, the major cause of preventing effective utilization of the power stored on the power storing means 40 is current loss due to the reverse current through the diode element 601. That is, it is satisfactory to use such a diode element that is low in forward drop voltage but less in reverse current. However, for the diode element, any decrease in the forward drop voltage and any reduction in the reverse current are in a trade off relationship. That is, there has been a problem that it is impossible to realize an electronic portable appliance smaller in size and lighter in weight and operable over a longer time so long as a diode element is used in the above-stated position. US Patent No. 4291266 discloses a device for charging an accumulator from an electrical energy source such as a solar cell. The solar cell feeds a charging current to the accumulator via a p-channel MOSFET transistor. The conduction state of the transistor is monitored by a differential amplifier. When the voltage U S produced by the solar cell is less than the voltage U A produced by the accumulator, the transistor is switched off, thereby preventing discharge of the accumulator into the solar cell. However, when voltage U S is greater than voltage U A , the transistors is switched on to allow the solar cell to charge the accumulator. It is therefore an object of the present invention to provide an electronic portable appliance which is improved in charge efficiency but reduces lost power such as reverse current, in order to realize a reduction of the size and weight and enable a longer time for the operation of the apparatus. An electronic appliance of the present invention comprises a power feed means for supplying electric power; a power storing means for storing electric power of said power feed means; a drive circuit to be driven on electric power of said power feed means or on electric power stored on said power storing means; a switch means provided on a charging path between said power feed means to said power storing means; and a control circuit comprising a voltage comparator circuit provided to compare voltages on the charging path at forward and rear points of said switch means; wherein said control circuit in use turns on said switch means when detecting a higher voltage at said forward point, and turns off said switch means when detecting a lower voltage at said forward point compared to the rear point; and characterised in that said voltage comparator circuit operates intermittently and said control circuit includes a memory circuit to memorize a result of the comparison by said voltage comparator circuit and updated each time said voltage comparator circuit operates and outputs said memorized comparison result as a control signal for said switch means. An electronic appliance of the present invention comprises a resistance element provided in series with the switch means on the charging path. As discussed before, the resistance component possessed by the switch means produces a potential difference at respective ends of the switch means during charging or current reverse flow. It is therefore possible for the voltage comparator circuit in the control circuit to perform stable voltage comparison. Thus, realized is a control circuit capable of stably controlling the switch means. Accordingly, the switch means and control circuit can realize an equivalent function to the diode element used in the conventional electronic portable appliance. In the case of a large charge current, the switch means decreases the efficiency of charging to a degree corresponding to the resistance component due to a voltage drop through the resistance component. Where the charge current is low, there is almost no decrease of charge current due to the voltage drop through the resistance component. Moreover, reverse current is suppressed to an extremely low level. Accordingly, where only a certain degree of charge current occurs, it is possible to improve the charge efficiency and decrease the reverse current. Furthermore, the invention in the above configuration is structured that a diode element is provided in a forward charging direction on the charging path and the switch means is provided in series with said diode element . The diode has a lower forward drop voltage than that of the diode used in the conventional electronic portable appliance. Due to this, the diode element, in place of the resistor element, can produce a potential difference during charging or reverse current flow. Thus, realized is a control circuit to stably control the switch means, as discussed above. Moreover, because of the lower forward drop voltage of a diode element, than that of the diode element used in the conventional electronic portable appliance, then the charging efficiency is improved. Moreover, the switch element can cut off any reverse current, hence reducing the reverse current. Furthermore, for any large charge current the diode element is lower in drop voltage in a charging direction as compared to the resistor element. In such a case, the charging efficiency increases as compared to the structure using the resistor element. Furthermore, in the above structure, a diode element is provided in a forward charging direction on the charging path; and a resistor element is provided in parallel with said diode element on said charging path; and the switch means is provided in series with said diode element or said resistor element. This makes possible charging through the resistor element for low charge current and through the diode element for high charge current, thus enhancing the charging efficiency regardless of the amount of charge current. Furthermore, the switch means comprises a MOS transistor. The MOS transistor is less in turning on/off power and correspondingly reduces useless power consumption. Furthermore, the switch means can be minimised, resulting in reduction in size and weight for the electronic portable appliance. Furthermore, the control circuit is provided with a function to intermittently operate the incorporated voltage comparator circuit and a memory circuit to memorize a last-time voltage comparison result of the voltage comparator circuit until a next operation of the voltage comparator circuit so that the switch means is controlled by the voltage comparison result memorized in the memory circuit. This allows the control circuit to operate with reduced power consumption, correspondingly reducing useless power. Furthermore, the drive circuit includes an oscillation circuit or an oscillation circuit and frequency dividing circuit, whereby an intermittent pulse is created based on an output signal of one of said oscillation circuit and said frequency dividing circuit to cause said voltage comparator circuit to intermittently operate. This eliminates the necessity for the control circuit to have an intermittent pulse, correspondingly reducing power consumption in the control circuit and hence reducing useless power as stated above. Furthermore, the power feed means includes a booster circuit to increase an electromotive force voltage of a power generating means by utilizing output signals of said power generating means and said oscillation circuit, whereby an intermittent pulse is created based on an output signal of said oscillation circuit to cause said voltage comparator circuit of said control circuit to intermittently operate. Due to this, the control circuit does not require an oscillation circuit conventionally required to create an intermittent pulse, correspondingly reducing current consumption of the control circuit and hence useless power. Embodiments of the present invention will now be described by way of further example only and with reference to the accompanying drawings, in which: Fig. 1 is a schematic block diagram of an electronic portable appliance showing Embodiment 1 of the present invention; Fig. 2 is a schematic block diagram of an electronic portable appliance showing Embodiment 2 of the present invention; Fig. 3 is a schematic block diagram of an electronic portable appliance showing Embodiment 3 of the present invention; Fig. 4 is a schematic block diagram of an electronic portable appliance showing Embodiment 4 of the present invention; Fig. 5 is a block diagram of a control circuit for the electronic portable appliance of the present invention; and Fig. 6 is a schematic block diagram showing a conventional electronic portable appliance. Now an electronic portable appliance according to the present invention will be described as examples only and with reference to the drawings. Fig. 1 is a schematic block diagram of an electronic portable appliance according to Embodiment 1 of the invention. As shown in Fig. 1, an electronic portable appliance 100 driven on generated power comprises a power feed means 10 having a power generating means 11 and a booster circuit 12, a switch means 20, a control circuit 30, a power storing means 40 and a drive circuit 50. The power feed means 10 does not necessarily require the booster circuit 12 provided that the power generating means 11 can generate an electromotive force higher than an operation voltage of the drive circuit 50 during most part of the power generation. However, if not so the booster circuit 12 has to be provided. It is noted that the power generating means may be any of a scheme utilizing a coil self-induction, a solar battery cell, a thermoelectric conversion device and a piezoelectric effect, or a combination of these power generating schemes. Meanwhile, the booster circuit may be any of a switched capacitor scheme, a charge pump scheme, a scheme of rectifying and outputting alternating current amplified by a transformer and a scheme of rectifying and outputting alternating current amplified by piezoelectric element resonance, or a combination of these schemes. On the other hand, the switch means 20 is provided on a power charge path for charging the power of the power feed means 10 to the power storing means 40. The control circuit 30 incorporates therein a voltage comparator circuit to compare a terminal voltage of the switch means 20 on the side of a power feed means 10 output terminal and a terminal voltage thereof on the side of the power storing means 40. When this voltage comparator circuit detects that the terminal voltage of the switch means 20 on the power feed means is higher than the terminal voltage on the power storing means 40, the switch means 20 is turned on to supply the power of the power feed means 10 to the power storing means 40 or the drive circuit 50. In other cases, the switch means 20 are turned off to prevent the power stored on the power storing means 40 from reversely flowing to the power feed means 10. Due to this, it is possible to realize a rectification function by the use of the switch means 20 that has conventionally been realizable only by a diode element. The switch means 20 is lower in voltage drop caused due to passing charge current as compared to that of a diode element, thus eliminating almost all of the charge loss due to the voltage drop. That is, the use of the switch means 20 instead of a diode element drastically improves charge efficiency. Furthermore, the switch means 20 is extremely low in any reverse current which is when the switch means is off, i.e. corresponding to a reverse current through a diode element, as compared to a diode element. That is, there is almost no consumption of useless power in the form of reverse current. Consequently, it is possible to realize further a longer time operation for an electronic portable appliance operating on generated power. Because less generated power is required for a same operation time as the conventional, the power generating means can be reduced in size and weight. Due to this, the electronic portable appliance can be reduced in size and weight. It is noted that, although the switch means 20 may be formed from any of a number of switch elements, the invention recommends the use of a MOS transistor. The MOS transistor, among switch elements, requires less power to turn on and off, and has a feature of a categorically smallest size. Accordingly, the use of a MOS transistor for the switch element 20 enables longer operation and a size and weight reduction for the electronic portable appliance. Incidentally, Fig. 1 shows the case that the switch means 20 utilizes a P channel MOS transistor. As shown in Fig. 1, the P channel MOS transistor has a source and substrate connected to the power storing means 40; a drain connected to the power feed means 10; and a gate connected to receive a control signal from the control circuit 30. Furthermore, the switch means 20 has a resistance component to provide a drop voltage of approximately 20 mV, due to current caused when charging the power of the power feed means 10 to the power storing means 40 or when the storage power on the power storing means 40 reversely flows to the power feed means 10. Due to this, even where the voltage comparator circuit of the control circuit 30 has an offset voltage to be encountered as an unavoidable problem with the voltage comparator circuit, the 20 mV drop voltage by the resistance component can absorb such an offset voltage. Accordingly, it is possible to prevent an oscillation phenomenon, malfunction and so on to be caused due to the relationship between the switch means 20 and the control circuit 30. It is also possible to prevent malfunction in the control circuit 30 to be caused due to erroneous detection resulting from gain insufficiency, which is another unavoidable problem with a voltage comparator circuit of the control circuit 30. That is, because the control circuit 30 stably controls the switch means 20, the switch means 20 can realize an equivalent function to the conventional diode element. Also, the voltage to be compared by the voltage comparator circuit of the control circuit 30 may be taken at any location provided that it is on a charging path at forward and rear points of the switch element 20. Furthermore, the switch element 20 may be at any location on the charge path. Referring to Fig. 2, there is shown a schematic block diagram of an electronic portable appliance according to Embodiment 2 of the invention. This is almost the same structure as the schematic block diagram of the electronic portable appliance of Embodiment 1 shown in Fig. 1. In Fig. 2 an electronic portable appliance 200 to be operated on generated power is different in that a resistor element 201 with the same resistance value as the resistance component of the switch means 20 is provided, in place of the resistance component, in series with the switch means 20 on the charging path in order to reduce the resistance value of the resistance component. Furthermore, in Embodiment 2 of Fig. 2 the voltage points to be compared by the voltage comparator circuit of the control circuit 30 are taken from a terminal of a resistor element 201 on a power feed means 10 side and a terminal of the switch means 20 on a power storing means 40 side, although they are across the switch means 20 in Embodiment 1 of Fig. 1. Due to this, a best resistance value can be set for stably operating the control circuit 30 in accordance with the ability of the power feed means 10 by using the resistor element 201, in addition to the effect offered by the electronic portable appliance 100 of Embodiment 1 shown in Fig. 1. Thus, there is obtained the effect that time and labour can be omitted in designing a switch means 20 having a best resistance component for stably operating the control circuit 30 in accordance with the ability of the power feed means 10 or searching for a switch means 20 having a close resistance value to a best resistance value. Incidentally, in Fig. 2 the voltage points to be compared by the voltage comparator circuit of the control means 30 may be anywhere, provided that they are on a charging path at the forward and rear points of the resistor element 201 and switch means 20. Furthermore, the resistor element 201 may be anywhere on the charging path. Furthermore, the resistor element 201 and switch means 20 may be anywhere on the charging path. Referring to Fig. 3, there is shown a schematic block diagram of an electronic portable appliance according to Embodiment 3 of the invention. As shown in Fig. 3, the electronic portable appliance of Embodiment 3 is different from Embodiment 2 of Fig. 2 in that a diode element 301 is provided to replace the resistor element 201 of the electronic portable appliance 200 of Embodiment 2 in Fig. 2. That is, the electronic portable appliance of Embodiment 3 has the diode element 301 connected to provide forward charging from the power feed means 10 to the power storing means 30. Here, the diode element 301 adopts a diode element having a forward drop voltage which is far lower than that of a diode element used in the conventional electronic portable appliance driven on generated power. This can suppress to a low level any drop voltage on a charging path from the power feed means 10 to the power storing means 40 and hence improve charge efficiency, as compared to the conventional electronic portable appliance driven on generated power. Of course, the adoption of the diode element with such low forward drop voltage increases reverse current through the diode element. However, any such reverse current, when flowing, can be turned off by the switch means 20. Thus, reverse current can be suppressed to a very low level. Furthermore, the diode element 301 has the function of producing a drop voltage to be provided by the resistance component of the switch means 20 of the electronic portable appliance shown in Fig. 1 or by the resistor element 201 of the electronic portable appliance shown in Fig. 2, thereby providing an effect of stably operating the control circuit 30. Furthermore, for high charge currents, there is provided an effect of improving the charge efficiency. This is because the drop voltage, due to a resistance component caused upon passing the resistance component by a charge current, linearly increases with increases in the charge current. On the other hand, for low charging current the drop voltage due, to a diode element, is greater by an amount of a forward drop voltage than a drop voltage due to a resistance component. For high charging current, that drop voltage is lower than a drop voltage due to the resistance component. That is, in the case of high charging current, the utilization of a diode element provides higher charging efficiency than the use of a resistance component. Incidentally, in Fig. 3 the voltage points to be compared by the voltage comparator circuit of the control means 30 may be anywhere, provided that they are positioned on a charging path at forward and rear points of the diode element 301 and switch means 20. Furthermore, the diode element 301 and the switch means 20 may be provided anywhere on the charging path. Referring to Fig. 4, there is shown a schematic block diagram of an electronic portable appliance according to Embodiment 4 of the invention. The structure is almost the same as that of Embodiment 3 shown in Fig. 3. The different point is that a resistor element 201 is provided in parallel with the diode element 301 as shown in Fig. 4. This structure realizes an electronic portable appliance possessing both the effect given by the structure shown in Fig. 2 and the effect given by the structure of Fig. 3. That is, for low charge current nearly all the charge current is supplied through the resistor element 201. For high charge current almost all the charge current is supplied through the diode element 301. Due to this reason, in both the low and high charge current cases, it is possible to decrease the drop voltage upon charging thus offering efficient charging. Incidentally, in Fig. 4 the voltage points to be compared by the voltage comparator circuit of the control means 30 may be anywhere provided that they are located on a charging path at forward and rear points of the diode element 301 and resistor element 201 connected in parallel therewith. Furthermore, the diode element 301 and the resistor element 201 connected in parallel therewith or the switch means 20 may be anywhere on the charging path. Referring to Fig. 5, there is shown a schematic block diagram of a control circuit 30 to be used in the electronic portable appliance for Embodiments 1 to 4 shown in Fig. 1 to Fig. 4, or indeed in any other situation involving comparator control. As shown in Fig. 5, a first input terminal 502 is connected to a charging path at a front stage of the means for causing a drop voltage due to a charge current or to a charging path at a front stage of a switch means 20. A second input terminal 503 is connected to a charging path at a rear stage of the means for causing a drop voltage due to a charge current or to a charging path at a rear stage of the switch means 20. Furthermore, a GND connection terminal 504 is connected to a GND terminal. Also, a control circuit 30 is provided with an output terminal 501 to output a control signal to turn on and off the switch means. The input power voltage to the first input terminal 502 is divided by a first bleeder resistor formed by a resistor 507 and a resistor 508. The input power voltage to the second input terminal 503 is divided by a second bleeder resistor formed by a resistor 509 and a resistor 510. A voltage comparator circuit 506 compares a voltage divided by a first bleeder resistor with a voltage divided by a second bleeder resistor, and outputs a comparison result to a memory circuit 505. Furthermore, a switch means 511 is provided between the first bleeder resistor and the GND terminal. A switch means 513 is provided between the second bleeder resistor and the GND terminal. A switch means 512 is provided between the voltage comparator circuit 506 and the GND terminal. Each switch means 511, 512, 513 is intermittently turned on by an intermittent signal outputted by an intermittent pulse generating circuit 516. Also, the memory circuit 505 receives such an intermittent pulse to acknowledge the timing of turning on the switch means 511, 512, 513, and rememorize the result of the comparison by the voltage comparator circuit 506 each time the switch means 511, 512, 513 turns on. The comparison result memorized by the memory circuit 505 is outputted to the output terminal 501, as a signal to control the switch means 20 shown in Fig. 1 to Fig. 4. Furthermore, the intermittent pulse generating circuit 516 creates an intermittent pulse based on a frequency divided signal divided of a clock signal of an oscillation circuit 514 by the frequency dividing circuit 515. It is noted that here the ratio of the resistor 507 to the resistor 508 is taken to be the same as the ratio of the resistor 509 to the resistor 510, in order to enhance the highest accuracy of comparison by the voltage comparator circuit 506 but it need not necessarily be so. The control circuit 30 configured as above makes possible the intermittent operation of the voltage comparator circuit 506 with the first bleeder resistor and the second bleeder resistor, hence providing a current reduction for the control circuit 30. Furthermore, where the drive circuit 50 shown in Fig. 1 to Fig. 4 incorporates an oscillation circuit and frequency dividing circuit as in a timepiece IC or a booster circuit 12 is a booster circuit incorporating an oscillation circuit of a switched capacitor scheme or the like, the oscillation circuit 514 and the frequency dividing circuit 515 shown in Fig. 5 are not required. It is satisfactory that the intermittent pulse generating circuit 516 be inputted by a divided clock signal from a timepiece IC or the frequency dividing circuit 515 be inputted by a clock signal of the oscillation circuit provided in the booster circuit. Thus, it is possible to reduce the current to be consumed by the oscillation circuit 514 and frequency dividing circuit 515 or the oscillation circuit 514, hence further reducing current consumption for the control circuit 30. According to the invention, the electronic portable appliance to be driven on generated power can efficiently charge generated power or increase generated power to the power storing means. Furthermore, it is possible to decrease other consumption than by the drive circuit of power charged on the power storing means, making possible long-time operation of the electronic portable appliance. Also, for the same operating time of the electronic portable appliance, it is possible to operate over the same time with a reduced amount of generated power. Accordingly, the power generating means or booster circuit can be reduced in size and weight, correspondingly reducing the size and weight of the electronic portable appliance. Furthermore, according to the invention, where the drive circuit or booster circuit has an oscillation circuit or frequency dividing circuit, it is possible to reduce other consumption than by the drive circuit of power stored on the power storing means, further increasing the operating time of the electronic portable appliance or reducing the size and weight thereof. The aforegoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention.

Claims: An electronic device, comprising: a power feed means (10) for supplying electric power; a power storing means (40) for storing electric power of said power feed means (10); a drive circuit (50) to be driven on electric power of said power feed means (10) or on electric power stored on said power storing means (40); a switch means (20) provided on a charging path between said power feed means (10) to said power storing means (40); and a control circuit (30) comprising a voltage comparator circuit (506) provided to compare voltages on the charging path at forward and rear points of said switch means (20); wherein said control circuit (30) in use turns on said switch means (20) when detecting a higher voltage at said forward point, and turns off said switch means (20) when detecting a lower voltage at said forward point compared to the rear point; and characterised in that said voltage comparator circuit (506) operates intermittently and said control circuit (30) includes memory circuit (505) to memorize a result of the comparison by said voltage comparator circuit (506) and updated each time said voltage comparator circuit (506) operates and outputs said memorized comparison result as a control signal for said switch means (20). An electronic device as claimed in claim 1, further comprising: a resistance element (201) provided in series with the switch means (20) on the charging path. An electronic device as claimed in claim 1, further comprising: a diode element (301) provided in a forward charging direction on the charging path; and wherein the switch means (20) is provided in series with said diode element (301). An electronic device, as claimed in claim 1, further comprising: a diode element (301) provided in a forward charging direction on the charging path; and a resistor element (201) provided in parallel with said diode element (301) on said charging path; and wherein the switch means (20) is provided in series with said diode element (301) or said resistor element (201). An electronic device according to any of claims 1 to 4, wherein said switch means (20) comprises a MOS transistor. An electronic device according to any one of claims 1 to 5, wherein said drive circuit (30) includes an oscillation circuit (514) or an oscillation circuit (514) and frequency dividing circuit (515), whereby an intermittent pulse is created based on an output signal of one of said oscillation circuit (514) and said frequency dividing circuit (515) to cause said voltage comparator circuit (506) to intermittently operate. An electronic device according to any one of claims 1 to 5, wherein said power feed means (10) includes a booster circuit (12) to increase an electromotive force voltage of a power generating means (11) by utilizing output signals of said power generating means (11) and said oscillation circuit (514), whereby an intermittent pulse is created based on an output signal of said oscillation circuit (514) to cause said voltage comparator circuit (506) of said control circuit (30) to intermittently operate.

Inventors: UTSUNOMIYA FUMIYASU, UTSUNOMIYA, FUMIYASU, Utsunomiya, Fumiyasu, Seiko Instruments R&amp;D C.Inc.
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 1999
Main classification: H02J7
IPC codes: G05F1, H02J7, H02J1, G04C10