Power-Generation Detection Circuit for Use in an Electronic Device and Power-Generation Detection Method and Power Consumption Control Method for Use in Connection Therewith

The present invention relates to a power-generation detection circuit and, in particular, to power-generation detection for use in an electronic device which is driven by an AC power generated by motion of a rotating weight or motion of a spring. The invention further relates to a semiconductor device in which the power-generation detection circuit is formed. And more in particular an electronic device, having the power-generation detection circuit, which is a timepiece and a power-generation detection method and a power consumption control method for operating the electronic device.

In a compact portable electronic device, such as a wrist watch, it is known to incorporate a power-generation device therein to obtain power for driving the electronic device without a battery. Referring now to FIG. 15, there is shown a simplified configuration of an electronic device which incorporates a power-generation device 6. This portable electronic device includes an electromagnetic power-generation device as the power-generation device 6. Power-generation device 6 includes a rotating weight 7 that moves in a swinging motion when the electronic device is moved or shaken, a train wheel mechanism 8 for transmitting the rotating motion of rotating weight 7, a stator 9 and a rotor 10. When rotor 10 rotates, an electromotive force is generated by an output coil 11 of stator 9, so that an AC power is output. In addition, the AC power output from electromagnetic generator 6 is full-wave rectified by a rectification diode bridge 12 to supply the power to a large-capacity capacitor 13 and a circuit unit 14 of the electronic device. When no power generation is performed by electromagnetic generator 6, circuit unit 14 is driven by power stored in large-capacity capacitor 13. For this reason, the portable electronic device can continuously operate circuit unit 14 without a battery.

Because the electronic device described above has no means for detecting the state of power generation supplied from power-generation device 6, the current consumption of circuit unit 14 is constant regardless of the state of power generation of power-generation device 6. As a result, power is consumed by circuit unit 14 even while no power is being generated by power-generation device 6. This may result in large-capacity capacitor 13 being discharged within a short period of time with the possibility of circuit unit 14 stopping completely.

The present invention is for a power-generation detection circuit for detecting the state of power generation in an electronic device. In accordance with the present invention, a power-generation detection circuit is provided which includes a switching element for performing a switching operation in response to the cycle of an externally generated AC power signal. A capacitor element is coupled to the switch for storing charges depending on the state of the switch, the capacitor element having a discharge path. A discharging element is inserted in the discharging path of the capacitor element for discharging the charges stored in the capacitor element. A voltage detector is coupled to the capacitor element for detecting whether voltage of the capacitor element exceeds a predetermined value.

In an exemplary embodiment, the discharging element of the power-generation detection circuit of the present invention is a resistor element.

In an exemplary embodiment, the discharging element of the power-generation detection circuit of the present invention is a constant-current circuit. The constant-current circuit of the power-generation detection circuit of the present invention includes a constant-current source and a current mirror circuit.

In an exemplary embodiment, the power-generation detection circuit of the present invention includes a current-limiter connected in series with the capacitor element for limiting the charge current of the capacitor element.

In an exemplary embodiment, the voltage detector of the power-generation detection circuit of the present invention is an inverter circuit.

In an exemplary embodiment, the voltage detector of the power-generation detection circuit of the present invention is a Schmidt trigger inverter circuit.

In an exemplary embodiment, the voltage detector of the power-generation detection circuit of the present invention is a comparator circuit.

In an exemplary embodiment, the switching element of the power-generation detection circuit of the present invention is a transistor. The transistor may be a MOS transistor or a bipolar transistor.

In accordance with the present invention, a semiconductor device is provided which includes a switching element for performing a switching operation in response to the cycle of an externally generated AC power signal. A capacitor element is coupled to the switch for storing charges depending on the state of the switch, the capacitor element having a discharge path. A discharging element is inserted in the discharging path of the capacit element for discharging the charges stored in the capacitor element. A voltage detector is coupled to the capacitor element for detecting whether a voltage of the capacitor element exceeds a predetermined value.

In an exemplary embodiment, the discharging element of the semiconductor device of the present invention is a constant-current source and a current mirror circuit. The current mirror circuit of the semiconductor device of the present invention is a pair of transistors.

In an exemplary embodiment, the switching element of the semiconductor device of the present invention is a transistor. The transistor may be a MOS transistor or a bipolar transistor.

In accordance with the present invention, an electronic device is provided which includes a power-generation device for generating AC power. A power-generation detection circuit, coupled to the power generation device, includes a switching element for performing a switching operation in response to the cycle of AC power generated by the power-generation device; a capacitor element is coupled to the switch for storing charges depending on the switching operation performed by the switching element, the capacitor element having a discharge path; a discharging element is inserted in the discharging path of the capacitor element for discharging the charges stored in the capacitor element, and a voltage detector is coupled to the capacitor element for detecting whether a voltage of the capacitor element exceeds a predetermined value.

In an exemplary embodiment, the power-generation device of the electronic device has a rotating weight for performing swinging motion and a power-generation element for generating electromotive force from the rotating motion of the rotating weight.

In an exemplary embodiment, the power-generation device includes an elastic member on which deformation forces act. A rotating member rotates as a result of a recovery force generated by the elastic member returning to its original shape. A power-generation element generates electromotive force from the rotating motion of the rotating member.

In an exemplary embodiment, the power-generation includes a piezoelectric element which generates electromotive force by a piezoelectric effect when displacement acts on the piezoelectric element.

In accordance with the present invention, an electronic device is provided which includes a power-generation device for generating AC power. A power-generation detection circuit, coupled to the power generation device, includes a switching element for performing a switching operation in response to the cycle of the AC power generated by the power-generation device; a capacitor element, coupled to the switch, stores charges in response to the switching operation performed by the switching element. A discharging element, inserted in the discharging path of the capacitor element, discharges the charges stored in the capacitor element; a voltage detector, coupled to the capacitor element, detects whether a voltage across the capacitor element exceeds a predetermined value; and a control circuit is coupled to the voltage detector for controlling power consumption of the device in response to the detection of the voltage detector.

In an exemplary embodiment, the control circuit of the electronic device of the present invention determines that the power-generation device is not performing power generation when a voltage across the capacitor element is not more than the predetermined value, and, as a result, reduces power consumption of the device. The control circuit of the electronic device of the present invention determines that the power-generation device is performing power generation when a voltage across the capacitor element exceeds the predetermined value, and, as a result, cancels the reduction in power consumption.

In an exemplary embodiment, the control circuit of the electronic device of the present invention controls the power consumption of the device based on the length of time in which a voltage across the capacitor element exceeds the predetermined value.

In accordance with the present invention, a timepiece includes a power-generation device for generating AC power. A power-generation detection circuit, coupled to the power-generation device includes a switching element, coupled to the power-generation device, for performing a switching operation in response to a cycle of AC power generated by the power-generation device; a capacitor element, coupled to the switching element, stores charges in response to the switching operation performed by the switching element; a discharging element is inserted in a discharging path of the capacitor element for discharging the charges stored in the capacitor element; and a voltage detector is coupled to the discharge element for detecting that a voltage across the capacitor element exceeds a predetermined value; and a timer circuit for counting time.

In an exemplary embodiment of the timepiece of the present invention, the power-generation detection device, power-generation circuit, and timer circuit are included in a housing of a wrist watch.

In an exemplary embodiment of the timepiece of the present invention, the power-generation device, power-generation detection circuit, and timer circuit are included in a housing of a pocket watch.

In an exemplary embodiment of the timepiece of the present invention, the power-generation device, power-generation detection circuit, and timer circuit are included in a housing of a table timepiece.

In accordance with the present invention, a power-generation detection method is provided that includes the steps of charging a capacitor element by a switching operation in response to a cycle of AC power which is externally generated; discharging the capacitor element when charging of the capacitor element is not performed; determining whether the voltage across the capacitor element is a predetermined voltage; and determining that power generation is being performed when the voltage across the capacitor element exceeds the predetermined voltage.

In accordance with the present invention, a power consumption control method is provided that includes the steps of charging a capacitor element by a switching operation in response to a cycle of AC power 8 which is externally generated; discharging the capacitor element when charging of the capacitor element is not performed, determining whether the voltage of the capacitor element is a predetermined voltage; determining that no power generation is performed when the voltage across the capacitor element does not exceed the predetermined voltage; and reducing power consumption of a circuit unit when no power generation is performed.

In an exemplary embodiment, a power consumption control method of the present invention also includes the steps of determining whether the voltage exceeds the predetermined voltage for a predetermined period of time, and canceling a reduction in power consumption of the circuit unit when the voltage exceeds the predetermined voltage for the predetermined period of time.

Accordingly, it is an object of the present invention to provide a power-generation detection circuit which can detect the state of generation power (i.e., the presence/absence of power generation and the strength of power generation) supplied from a power-generation device of an electronic device by a simple method so that power consumption of a circuit unit can be controlled depending on the detected state of power generation.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a circuit block diagram of an electronic device including a power-generation circuit constructed in accordance with the present invention;

FIG. 2 is a circuit block diagram of a power-generation detection circuit according to the present invention;

FIG. 3 is a timing chart of the operation of the power-generation detection circuit in accordance with the present invention;

FIG. 4 is a circuit block diagram of a power-generation detection circuit constructed in accordance with a second embodiment of the present invention;

FIG. 5 is a circuit block diagram of a power-generation detection circuit constructed in accordance with a third embodiment of the present invention;

FIG. 6 is a circuit block diagram of a power-generation detection circuit constructed in accordance with a fourth embodiment of the present invention;

FIG. 7 is a circuit block diagram of a power-generation detection circuit constructed in accordance with a fifth embodiment of the present invention;

FIG. 8 is a circuit block diagram of a power-generation detection circuit in accordance with a sixth embodiment of the present invention;

FIGS. 9(a) and 9(b) are charts showing a comparison between a power-generation device output and a power-generation detection signal over time in accordance with a seventh embodiment of the present invention;

FIGS. 10(a) and 10(b) are charts showing a comparison between a power-generation device output and a power-generation detection signal over time in accordance with an eight embodiment of the present invention;

FIG. 11 is a circuit diagram showing a power supply block in accordance with a ninth embodiment of the present invention;

FIG. 12 is a chart showing V1 and V2 outputs from the power-generation device in accordance with the ninth embodiment of the present invention;

FIG. 13 is a circuit diagram showing a power-generation detection circuit in accordance with the ninth embodiment of the present invention;

FIG. 14 is a timing chart of the power-generation detection circuit of the present invention;

FIG. 15 is a schematic view of a prior art power supply block of an electronic device having a power-generation device constructed in accordance with the prior art;

FIG. 16 is a schematic view of a power-generation device that operates in conjunction with the power-generation detection circuit of the present invention;

FIG. 17 is a circuit diagram showing the power-generation device of FIG. 16;

FIG. 18 is a schematic view of a power-generation device of an alternative embodiment that operates in conjunction with the power-generation detection device of the present invention; and

FIG. 19 is a circuit diagram of a power-generation device in which the charge amount may be detected in real-time.

Embodiments of a power-generation detection circuit constructed according to the present invention will be described below with reference to the accompanying drawings.

Referring now to FIGS. 1-2, there is shown a circuit block diagram of an electronic device generally indicated as 50 including a power-generation detection circuit 1 constructed in accordance with the present invention. Elements in FIG. 1 that are similar to elements in FIG. 15 will be denoted with the same reference numerals and a description thereof will be omitted. Referring to FIG. 1, electronic device 50 includes power-generation detection circuit 1. A power save control circuit 30 is coupled between power-generation detection circuit 1 and circuit unit 14. A power-generation device 6 is coupled between power generation-detection circuit 1 and a rectification diode bridge 12. A large-capacity capacitor 13 is connected in parallel with rectification bridge diode and circuit unit 14.

Power-generation detection circuit 1, which is connected to power-generation device 6, further includes a MOS transistor 2 of the n-channel type which receives a V1 output of power-generation device 6 as its gate input. A capacitor 3 is coupled between a voltage Vdd and transistor 2. A pull-up resistor 4 is coupled across capacitor 3. An inverter circuit 5 coupled between pull up resistor 4 and power save control circuit 30 provides an output Vout to power save control 30.

Because power-generation device 6 is connected to the gate of MOS transistor 2, MOS transistor 2 undergoes repeated ON/OFF cycles in response to an AC voltage V1 generated by power-generation device 6. When MOS transistor 2 is used as a switching element, power-generation detection circuit 1 and inverter circuit 5 can be formed using an inexpensive CMOSIC while the switching element and the voltage detection circuit may be formed using bipolar transistors.

Pull-up resistor 4 functions to fix a voltage value V3 of capacitor 3 to a Vdd potential and generate a leakage current in a no-power-generation state, i.e. when power generation device 6 produces no or minimal power. In a exemplary embodiment, pull-up resistor 4 has a high resistance on the order of several tens to several hundreds M.OMEGA., and may also be formed using a MOS transistor having a high ON resistance. Voltage value V3 of capacitor 3 is sensed by inverter circuit 5 connected to capacitor 3. If power is being generated, inverter circuit 5 outputs a power-generation detection signal Vout that is "HI".

Although a low-voltage Vss is shown as a reference voltage in this embodiment, as is used in many wrist watch circuits, alternatively a high-voltage Vdd may be also be used as a reference without any difficulty. In addition, AC voltage V1 of power-generation device 6 may be connected to Vss through a high-resistance resistor to stabilize the circuit in the no-power-generation state. In addition, in order to turn off MOS transistor 2 in the no-power-generation state, output voltage V1 of power-generation device 6 must be made stable at Vss. Accordingly, power-generation device 6 is preferably connected to Vss through a resistor element.

Power save control circuit 30 sends a control signal S1 to circuit unit 14 based on power-generation detection signal Vout from inverter circuit 5 of power-generation detection circuit 1 to switch circuit unit 14 into a power save mode. When circuit unit 14 receives control signal S1, circuit unit 14 determines that the power save mode is set and, as a result, cuts power to a mechanical driver or some other functions of circuit unit 14 to reduce power consumption. For example, if circuit unit 14 is a timepiece (especially, a wrist watch), power may be conserved in power save mode by stopping the movement of the second hand or by turning off some other function of the circuit, for e.g., a sensor function, a chronograph function, or a liquid-crystal display function.

The operation of the power-generation detection circuit 1 according to this embodiment will now be described with reference to the timing chart shown in FIG. 3. When generation of AC power by the power-generation device 6 begins, AC signal V1 having an amplitude of Vdd+VF to Vss-VF' (where VF is the forward voltage of a rectification diode) appears at one terminal of power-generation device 6. A signal V2 having the same amplitude but opposite phase as that of V1 appears at the terminal V2 of power-generation device 6. When power generation begins and voltage V1 rises from Vss to Vdd, MOS transistor 2 is turned ON and capacitor 3 begins to charge. Before power generation occurs, the voltage at V3 is fixed to Vdd by pull-up resistor 4 in the no-power-generation state. However, when power generation occurs and capacitor 3 begins charging, the voltage at V3 begins to fall to Vss. When voltage V1 decreases to Vss, and MOS transistor 2 is turned off, charging of capacitor 3 stops. However, potential V3 is kept constant by capacitor 3. The above operation is repeated while power generation continues until the voltage at V3 stabilizes to Vss. When the voltage at V3 is lower than the threshold value of inverter circuit 5, power-generation detection signal Vout switches from "LOW" to "HI" thereby indicating that power generation is occurring. The response time for power generation to be detected in this manner may be arbitrarily set by either connecting a current-limiting resistor in series with capacitor 3, by changing the characteristics of MOS transistor 2 thereby adjusting the value of the charge current for capacitor 3, or changing the capacitance of capacitor 3.

When power generation stops, V1 is at Vss and MOS transistor 2 is kept in the OFF state. The voltage level at V3 is maintained for a period of time by capacitor 3. However, because capacitor 3 is discharged by a small leakage current generated by pull-up resistor 4, V3 begins to gradually increase from Vss to Vdd. When V3 exceeds the threshold value of inverter circuit 5, power-generation detection signal Vout switches from "HI" to "LOW" so that a no-power-generation state can be detected. The time required to detect a no-power generation state can be arbitrarily set by changing the resistance of pull-up resistor 4 and adjusting the leakage current of capacitor 3. When power-generation detection signal Vout is monitored as described above, the state of power generation can be detected.

Furthermore, if the state of power generation can be detected, setting/canceling of the power save mode can be set/canceled accordingly by power save control circuit 30, and the operation time of circuit unit 14 in no-power-generation state can be lengthened by reducing power consumption.

Embodiment 2

Referring now to FIG. 4, a second embodiment of the power-generation detection circuit, generally indicated as 100, constructed in accordance with the second embodiment of the invention is shown. The difference between power-generation detection circuit 1 and power-generation detection circuit 100 being a current-limiting resistor 15 connected in series with capacitor 3. Because this embodiment is similar to power-generation detection circuit 1, the same reference numerals used in the first embodiment are used in this embodiment and a detailed description thereof will be omitted. When MOS transistor 2 is turned on and capacitor 3 is being charged, the time until power-generation detection signal Vout is output can be adjusted by changing the value of current-limiting resistor 15. Because current-limiting resistor 15 reduces the charge current to capacitor 3, a longer time is required to bring voltage V3 to a level lower than the threshold voltage of inverter 5. Thus, it takes a longer time for power-generation detection signal Vout to be output.

Embodiment 3

Referring now to FIG. 5, a third embodiment of the power-generation detection circuit, generally indicated as 110, constructed in accordance with the third embodiment of the invention is shown. The difference between power-generation detection circuit 1 and power-generation detection circuit 110 being that a switching MOS transistor 16 of the p-channel type is used. Because this embodiment is similar to power-generation detection circuit 1, the same reference numerals used in the first embodiment are used in this embodiment and a detailed description thereof will be omitted.

In this embodiment, the positions of capacitor 3 and MOS transistor 16 relative to power generation device 6 are reversed as compared to the arrangement of a n-channel MOS transistor 2 and capacitor 3 shown in FIG. 2. In this embodiment, V1 is preferably connected to Vdd through a resistor. Alternatively, a MOS transistor having a high ON resistance may be used. In a no-power-generation state, p-channel MOS transistor 16, is turned off when output voltage V1 of power-generation device 6 is stabilized at Vdd.

Embodiment 4

Referring now to FIG. 6, a fourth embodiment of the power-generation detection circuit, generally indicated as 120, constructed in accordance with the fourth embodiment of the invention is shown. The difference between power-generation detection circuit 1 and power-generation detection circuit 120 being that a pull-up resistor is formed using a constant-current circuit 61. Because this embodiment is similar to power-generation detection circuit 1, the same reference numerals used in the first embodiment are used in this embodiment and a detailed description thereof will be omitted.

Constant-current circuit 61 is a current mirror circuit that includes a constant-current source 17 and a pair of MOS transistors 18 and 19 connected at the gates which allows a slight constant current to flow from Vdd to V3. To delay the output of power-generation detection signal Vout for a long period of time, the leakage current of capacitor 3 must be reduced so that the resistance of constant current circuit 61 is increased considerably. In this case, the variation in resistance is enlarged, and the output holding time of power-generation detection signal Vout also has a large variation. When power generation detection circuit 120 is constructed using constant-current circuit 61 according to this embodiment, a small leakage current value in the range of several nano-amperes can be set, and the variation in leakage current can be advantageously made considerably smaller than in the previous embodiments in which power-generation detector circuit 1 uses a resistor instead.

Embodiment 5

Referring now to FIG. 7, a fifth embodiment of the power-generation detection circuit, generally indicated as 130, constructed in accordance with the fifth embodiment of the invention is shown. The difference between power-generation detection circuit 1 and power-generation detection circuit 130 being that a voltage detector 20 is formed using a Schmidt trigger inverter circuit. Because this embodiment is similar to power-generation detection circuit 1, the same reference numerals used in the first embodiment are used in this embodiment and a detailed description thereof will be omitted. When the voltage detector 20 is formed using a Schmidt trigger inverter circuit having hysteresis characteristics, stable power-generation detection can be advantageously performed without being affected by an instantaneous variation in voltage V3 of capacitor 3.

Embodiment 6

Referring now to FIG. 8, a sixth embodiment of the power-generation detection circuit, generally indicated as 140, constructed in accordance with the sixth embodiment of the invention is shown. The difference between power-generation detection circuit 1 and power-generation circuit 140 being that a voltage detector 21 is formed using a comparator circuit 21. Because this embodiment is similar to power-generation detection circuit 1, the same reference numerals used in the first embodiment are used in this embodiment and a detailed description thereof will be omitted. Comparator circuit 21 compares an output voltage V4 from a reference voltage generation circuit 22 with capacitor voltage V3. If V3 is lower than V4, comparator circuit 20 outputs power-generation detection signal Vout set to "HI".

In power-generation detection circuit 1, the voltage changes of power-generation device 6 varies with the charging state of large-capacity capacitor 13 and the voltages at both the ends of large-capacity capacitor 13. Thus, when voltage detection is performed by inverter 5, the threshold voltage of inverter 5 changes with a variation in power supply voltage Vdd. For this reason, power-generation detection time also varies. When voltage detection is performed by comparator circuit 21, as in the present embodiment, the threshold value of power-generation detection is kept constant and is not affected by a variation in power supply voltage. Thus, stable detection with a high precision can be realized.

Embodiment 7

Referring now to FIGS. 9(a)-9(b), there is shown a chart showing V1 output from power-generation device 6 as a function of time, with the level of V1 varying with the changes in rotating speed of rotor 10, (see FIG. 15) and a comparison between V1 and power-generation detection signal Vout over time. In FIG. 9(a) rotor 10 rotates at a low rotating speed, while in FIG. 9(b) rotor 10 rotates at a high rotating speed. The voltage level and frequency of V1 output from power-generation device 6 changes as a function of the rotating speed of rotor 10. More specifically, at higher rotating speeds, the voltage level of V1 is higher, and the frequency of V1 is higher. Because of this, the length of output holding time (ON time) of power-generation detection signal Vout varies depending on the power output level of power-generation device 6. More specifically, when output V1 varies slightly, as in FIG. 9(a), the output holding time is represented by t1; when the variation of output V1 is greater, as in FIG. 9(b), the output holding time is represented by t2, with t1 and t2 having the relationship t1<t2. As described above, the power output level of power-generation device 6 can be determined based on the length of the output holding time of power-generation detection signal Vout. Embodiment 7 described above can also be applied to any one of Embodiment 1 to Embodiment 6 described above.

Embodiment 8

Referring now to FIGS. 10(a), 10(b), there is shown a chart showing V1 output from power-generation device 6 as a function of time, with the level of V1 changing as a function of the shaking of a wrist watch which causes the power-generation device 6 to generate power, and a comparison between V1 and power-generation detection signal Vout. For example, when power-generation detection circuit 1 is applied to a wrist watch, the rotating speed of rotor 10 changes depending on the motion of the user. More specifically, when the wrist watch is strongly shaken by the user, the output holding time of power-generation detection signal Vout is longer. In contrast, when the user does not strongly shake the watch, the output holding time of power-generation detection signal Vout is shorter. Therefore, when power-generation detection signal Vout for a predetermined period of time is detected, this indicates that the watch was strongly shaken by the user. Accordingly, if circuit unit 14 is previously set to power save mode and output holding time of the power-generation detection signal Vout continues for the predetermined period of time, it indicates that the user desires that power save mode be canceled.

However, power save mode may not always be canceled under these circumstances. For example, when the user strongly shakes the watch, as shown in FIG. 10(a), rotating weight 7 is irregularly rotated, causing output V1 from power-generation device 6 to have two amplitude peaks. If the capacitance of capacitor 3 is small, or if the resistance of pull-up resistor 4 inserted in the discharging path of capacitor 3 is low, which causes the discharge current to be large, power-generation detection signal Vout is temporarily discontinued at the trough between the two peaks. This results in the output holding time of power-generation detection signal Vout not corresponding to the strength of the power generation caused by the user strongly shaking the watch. Therefore, because power-generation detection signal Vout is not detected for the predetermined time, power save mode is not canceled as the user desires.

However, as described above, if the capacitance of capacitor 3 is increased, the discharge current from capacitor 3 is reduced thereby preventing power-generation detection signal Vout from being discontinued. Referring now to FIG. 10(b), there is shown a chart showing V1 obtained when a user strongly shakes a wrist watch in which the capacitance of capacitor 3 is increased, and also power-generation detection signal Vout as a function of V1. As shown in FIG. 10(b), when the capacitance of capacitor 3 is increased, current discharge is reduced and, as a result, power-generation detection signal Vout is continuously output. Therefore, the output holding time of power-generation detection signal Vout corresponds to the strength of power generation, and the power save mode is properly canceled.

In this manner, an increase in the capacitance of capacitor 3 described above is effective especially when, in canceling the power save mode, the wrist watch is strongly shaken by a user.

Although Embodiment 8 described above is applied to the arrangement of Embodiment 1, Embodiment 8 may be applied to not only the arrangement of Embodiment 1, but also to any of the arrangements of Embodiment 2 to Embodiment 7, as a matter of course.

Embodiment 9

Referring now to FIGS. 11-13, a ninth embodiment of the power-generation detection circuit, generally indicated as 160, constructed in accordance with the sixth embodiment of the invention is shown. The difference between power-generation detection circuit 1 and power-generation detection circuit 160 being that a second MOS transistor 2a is also used to charge capacitor 3. Because this embodiment is similar to power-generation detection circuit 1, the same reference numerals used in the first embodiment are used in this embodiment and a description thereof will be omitted.

In this embodiment, power-generation detection circuit 160, as shown in FIG. 13, is switched by using V1 and V2 to charge capacitor 3. V1 and V2 are output from power-generation device 6 and have AC waveforms that are out of phase with each other before being rectified by rectification diode bridge 12. V1 is supplied to the gate of MOS transistor 2, and V2 is supplied to the gate of MOS transistor 2a. As MOS transistor 2 and MOS transistor 2a are alternately turned on/off, the number of switching times is twice the number as that in power-generation detection circuit 1. As a result, the charging time of capacitor 3 becomes shorter, and the voltage at V3 can more rapidly reach Vss if power generation continues. Therefore, the rise time of the power-generation detection signal Vout is shortened.

Although power-generation detection circuit 160 is formed by adding MOS transistor 2a to the basic circuit arrangement of power-generation detection circuit 1, MOS transistor 2a may also be added to the circuit arrangements of power-generation detection circuit 100, 110, 120, 130 or 140 as a matter of course and provide the benefits of this embodiment.

In each of Embodiments 1 to 9, power-generation device 6 can be an electromagnetic power-generation device which transmits the rotating motion of rotating weight 7 to rotor 10 causing output coil 11 to generate electromotive force. However, power-generation device 6 is not limited to the above embodiment. For example, as shown in FIGS. 16-17, power-generation device 6 may be a device in which a rotating motion is generated by recovery force of a coiled spring 177 to generate electromotive force by the rotating motion. Alternatively, power-generation device 6' may be constructed as in FIG. 18 comprising a vibration arm 131, in the shape of a cantilevered beam, fixed to a case (base plate) 151. Piezoelectric layers 132 are provided on both sides of vibration arm 131, so that electric power generated in these piezoelectric layers 132 can be supplied to diode bridge 12 via an electrode 135 and wiring 159 on the surface thereof. A weight 138 is attached at the tip 133 of the vibration arm 131 so that when this weight 138 is moved by a drive system 171 which operates as a displacement application apparatus, a displacement is applied to vibration arm 131. Also, since vibration arm 131 is a cantilevered beam, after it is vibrated by drive system 171, the tip 133 of vibration arm 131 becomes a free end and freely vibrates with, while the opposite end thereof is fixed to the base plate 151 by a screw 137 serving as a support end 134, and the electric power generated thereby in the piezoelectric layer 132 is supplied to diode bridge 12.

Drive system 160 has a rotation weight 153 which is rotationally moved inside case 151. A rotation weight wheel 161 is coupled to weight 153 to rotate therewith. Rotation weight wheel 161 is provided with gear teeth and meshes with an intermediate wheel 162 rotably mounted on base plate 151. A cam drive wheel 163, rotatably mounted on base plate 151, is rotated by intermediate wheel 162. A cam 164 is pivotably mounted on base plate 151 and includes a hitting section disposed within weight 138. Cam driving wheel 163 pivots cam 164 between a first position and a second position.

When rotation weight 153 is attached to a wrist watch or the like, rotation weight 153 rotates in conjunction with the motion of the user's arm or body or the like, and electric power can be generated using the force thereof. The motion of rotation weight 153 is transmitted to an intermediate wheel 162 through a rotation weight wheel 161 and is accelerated. The motion of the intermediate wheel 162 through a rotation weight wheel 161 and is accelerated. The motion of the intermediate wheel 162 is transmitted to a cam drive wheel 163. A cam 164 is driven from side to side by this cam drive wheel 163, and a hitting section 165 which moves in linkage with the cam 164 housed inside weight 138 of the vibration arm is moved. Therefore, when the user moves his/her arm or body, rotation weight 153 rotates and cam 164 reciprocates parallel to the plane of the device as a result of that force. Hitting section 165 of cam 164 hits weight 138 of vibration arm 131, causing weight 138 to be hit repeatedly at appropriate intervals. The respective hittings by hitting section 165 cause a predetermined initial displacement to be applied to vibration arm 131. When cam 164 is released from vibration arm 131, subsequent free vibrations are excited in vibration arm 131. Since these free vibrations cause an electromotive force to be generated in piezoelectric layer 132, this electromotive force can be supplied to diode bridge 12 through electrode 135 and the wiring 159.

In power-generation device 6' constructed in accordance with this embodiment, the initial displacement applied from hitting section 165 to vibration arm 131 varies due to the pivot speed and pivot range of rotation weight 153. Since the acceleration of hitting section 165 increases if the rotation speed of rotation weight 153 increases, the initial displacement of vibration arm 131 increases similarly and, as a result, the initial value (the initial electromotive voltage) of the voltage generated due to the initial displacement becomes higher. Also, since the number of times that the hitting section 165 hits vibration arm 131 increases, if the pivot range (angle) of rotation weight 153 is increased, the period in which generation of electric power is possible while the rotation weight 153 rotates once is also increased.

The electronic device to which power-generation detection circuit 1 can be applied, in accordance with the present invention, is not limited to a wrist watch but may be included in any electronic device including a pocket watch, table timepiece, a pocket calculator, a portable telephone, a portable personal computer, an electronic organizer, or a portable radio. Power-generation detection circuit 1 of the present invention may also be used to recognize a charge amount of a large-capacity capacitor and to prevent an overvoltage from being applied in a power-generation state.

An application of power-generation detection circuit 160 described above is shown in FIGS. 14 and 19, in which the output holding time (time in a HI state) of power-generation detection signal Vout is counted, and the difference between the count value CNT and a time reference timepiece TCLK is counted by an up-down counter 191 or the like, so that a charge amount is detected in real time. When the charge amount is detected, the user can be notified.

When a circuit such as a constant-current generation circuit which is driven by sampling to perform a low-power operation is used, such a circuit is disadvantageously weak in a variation of power supply voltage (Vss). In a period in which power-generation detection signal Vout is set in a HI state (i.e. a power-generation detection state), a sampling duty of a constant-current generation circuit which is driven by sampling is increased, or the constant-current generation circuit is always driven, so that an erroneous operation or characteristic degradation caused by the variation in power supply voltage of the circuit can be prevented.

Large-capacity capacitor 13 shown in FIG. 1 has a drawback in that because of the internal resistance of large-capacity capacitor 13, voltages at both ends of large-capacity capacitor 13 are higher in a power-generation state than in a stationary state and overcharging occurs. To prevent overcharging in a state wherein the voltage of large-capacity capacitor 13 is equal to or higher than a predetermined voltage, if power generation is detected by power-generation detection circuit 1 (power-generation detection signal Vout is set in a HI state), a limiter circuit is operated, so that large-capacity capacitor 13 is not overcharged.

Because the present invention is arranged as described above, the present invention has the following advantages. When charging/discharging of a capacitor is controlled by a simple arrangement which includes a MOS transistor, a capacitor, and an inverter circuit to detect the voltage of the capacitor, the power-generation state of a power-generation device can be detected. By using the leakage current of a pull-up resistor, a state wherein power generation is stopped can also be detected. The detection time of a power-generation detection signal Vout can be arbitrarily adjusted by connecting a current-limiting resistor in series with the capacitor or changing the capacitance of the capacitor.

When a constant-current circuit is used in place of a resistor, a small leakage current of the capacitor can be set without variation, and power-generation detection at a high precision can be performed.

When the voltage detector includes a Schmidt trigger inverter circuit, its hysteresis characteristics make it possible to perform stable power-generation detection without being influenced by a variation in the voltage across the capacitor.

In addition, when the voltage detector includes a comparator circuit, an arbitrary threshold value can be set, and stable power-generation detection can be performed without being influenced by a variation in power supply voltage.

Furthermore, when the output holding time of power-generation detection signal Vout is considered, the strength of power generation can be known according to the output holding time of the power-generation detection signal Vout.

It will thus be seen that the objects set forth above, those made apparent from the preceding description, are efficiently attained and, because certain changes may be made in the above construction without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description are shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.