Power supply circuits, power generation devices, and electronic devices

Abstract

The power supply circuit comprises an input capacitor, a voltage conversion circuit, and a startup circuit. The input capacitor stores the power generated by the power generation element. The voltage conversion circuit converts the input voltage across the input capacitor into a voltage and outputs the converted output voltage to a load. The startup circuit applies an enable voltage to the enable terminal of the voltage conversion circuit to start the voltage conversion circuit. In an operating state after startup, the voltage conversion circuit outputs an output voltage when the input voltage is equal to or greater than a first threshold. The startup circuit applies an enable voltage to the enable terminal when the input voltage is equal to or greater than a second threshold that is greater than the first threshold. This power supply circuit can stabilize the power supplied to the load.

Description

[Technical field]

[0001] The present disclosure generally relates to a power supply circuit , issue The present invention relates to an electrical device and an electronic device, and more particularly to a power supply circuit for supplying power to a load. , issue The present invention relates to an electrical device and an electronic device. [Background technology]

[0002] Patent Document 1 discloses a conventional power generating device equipped with a vibration power generating element (power generating element).

[0003] The power generation device disclosed in Patent Document 1 includes a power storage unit, a rectifier circuit, and a DC-DC converter as a power supply circuit. The power storage unit stores the electric energy generated by the vibration power generation element. The rectifier circuit rectifies the AC voltage generated by the vibration power generation element. The DC-DC converter converts the output voltage of the power storage unit and outputs it to a control circuit, which is a load.

[0004] In such a power generating device, it is desirable to stabilize the power supplied to the load. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-86599 A Summary of the Invention

[0006] The power supply circuit supplies power to a load based on the power generated by the power generation element. The power supply circuit includes an input capacitor that stores the power generated by the power generation element, a voltage conversion circuit having an enable terminal configured to convert the input voltage between both ends of the input capacitor and output an output voltage obtained by converting the voltage to the load, and a start-up circuit that applies a voltage to the enable terminal of the voltage conversion circuit. The start-up circuit starts the voltage conversion circuit by applying an enable voltage to the enable terminal of the voltage conversion circuit. In an operating state after the start-up, the voltage conversion circuit outputs an output voltage when the input voltage is equal to or higher than a first threshold. The start-up circuit applies an enable voltage to the enable terminal when the input voltage becomes equal to or higher than a second threshold that is higher than the first threshold. The start-up circuit includes a series circuit of a Zener diode and a resistor electrically connected between both ends of the input capacitor, and a capacitor connected in parallel with the resistor. The input capacitor has a first end and a second end having a lower potential than the first end. The cathode of the Zener diode is connected to the first end of the input capacitor. The anode of the Zener diode is connected to the enable terminal. The resistor and capacitor of the start-up circuit constitute a time constant circuit that determines a voltage maintenance period, and the capacitor of the time constant circuit is connected in series with the enable terminal and the second end of the input capacitor. The start-up circuit continues to apply the enable voltage to the enable terminal for the voltage maintenance period from the time when the input voltage falls below the second threshold from a value equal to or greater than the second threshold. The power supply circuit is The power supply circuit supplies power to a load based on the power generated by a power generation element. The power supply circuit includes an input capacitor that stores the power generated by the power generation element, a voltage conversion circuit having an enable terminal configured to convert the input voltage between both ends of the input capacitor and output an output voltage obtained by converting the voltage to the load, and a startup circuit that applies a voltage to the enable terminal of the voltage conversion circuit. The startup circuit starts the voltage conversion circuit by applying an enable voltage to the enable terminal of the voltage conversion circuit. In an operating state after startup, the voltage conversion circuit outputs an output voltage when the input voltage is equal to or greater than a first threshold. When the input voltage becomes equal to or greater than a second threshold that is greater than the first threshold, the startup circuit applies the enable voltage to the enable terminal. When the enable voltage is applied to the enable terminal, the voltage conversion circuit continues to operate for a holding period.

[0007] This power supply circuit can stabilize the power supplied to the load. [Brief description of the drawings]

[0008] [Figure 1A] FIG. 1A is a circuit diagram of a power supply circuit according to an embodiment of the present disclosure. [Figure 1B] FIG. 1B is a schematic side view of a power generating element included in the power generating device according to the embodiment. [Diagram 2] FIG. 2 is a waveform diagram of an output voltage of a power generating element included in the power generating device according to the embodiment. [Figure 3A]FIG. 3A is a diagram illustrating the operation of the power supply circuit according to the embodiment. [Figure 3B] FIG. 3B is another operation explanatory diagram of the power supply circuit according to the embodiment. [Figure 4] FIG. 4 is a circuit diagram of a power supply circuit of the comparative example. [Diagram 5] FIG. 5 is a circuit diagram of a power supply circuit according to a first modified example of the embodiment. [Figure 6] FIG. 6 is a circuit diagram of a power supply circuit according to a second modified example of the embodiment. [Figure 7] FIG. 7 is a circuit diagram of a power supply circuit according to a reference example. [Figure 8] FIG. 8 is a circuit diagram of a power supply circuit according to a first modified example of the reference example. [Figure 9] FIG. 9 is a circuit diagram of a power supply circuit according to a second modified example of the reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The embodiment and modified examples described below are merely examples of the present disclosure, and the present disclosure is not limited to the embodiment and modified examples. Various modifications other than the embodiment and modified examples are possible according to the design, etc., as long as they do not deviate from the technical idea of ​​the present disclosure.

[0010] FIG. 1A shows a circuit diagram of a power supply circuit 1 according to this embodiment.

[0011] The power supply circuit 1 of this embodiment is configured to supply power to a load 90 based on the power generated by the power generating element 70. The power generating device 100 of this embodiment includes the power supply circuit 1 and the power generating element 70. The electronic device 200 of this embodiment includes the power generating device 100 and a load 90. The power generating device 100 is a vibration type power generating device that generates power by converting vibration energy applied to the power generating element 70 into electrical energy. The load 90 is a device that operates using power supplied from the power generating device 100.

[0012] Power generation element 1B is a schematic side view of the power generating element 70. The power generating element 70 includes a piezoelectric element 71 and a vibrating body 72.

[0013] The vibrating body 72 is made of an elastic plate, for example, a metal plate such as stainless steel. 72B is the fixed end, and the end 72B The other end of the 72A The vibrating body 72 has a cantilever structure with a fixed end. 72B The vibrating body 72 is held by the housing 500 by being fixed to the housing 500. The vibrating body 72 has an end portion which is a free end in the thickness direction of the vibrating body 72. 72A is variable relative to the housing 500, and the vibrating body 72 is vibrable.

[0014] The piezoelectric element 71 is attached to both sides 72C and 72D of the vibrating body 72 in the thickness direction. When the vibrating body 72 vibrates, a distortion is applied to the piezoelectric element 71, and the piezoelectric element 71 generates power. That is, the vibration energy accompanying the vibration of the vibrating body 72 is converted into electrical energy in the piezoelectric element 71. FIG. 2 shows the output voltage (generated voltage) of the piezoelectric element 71 when the end 72A, which is the free end of the vibrating body 72, is bounced in the vibration direction Dv and the vibrating body 72 vibrates. As shown in FIG. 2, the piezoelectric element 71 outputs an AC voltage accompanying the vibration of the vibrating body 72. The amplitude of the output voltage of the piezoelectric element 71 attenuates over time, that is, the voltage value of the output voltage of the piezoelectric element 71 decreases. In addition, the piezoelectric element 71 has an internal impedance Z11 (see FIG. 1A). The power generating element 70 has output terminals 70A and 70B, and outputs the output voltage of the piezoelectric element 71 from between the output terminals 70A and 70B.

[0015] The power generating device 100 further includes an operation unit 80. The operation unit 80 is, for example, a push button, and is configured to be movable relative to the housing. When the operation unit 80 is operated, it bends and vibrates the vibration body 72.

[0016] Therefore, in the power generating device 100, when the operation unit 80 is operated, the vibration body 72 bends and vibrates with the movement of the operation unit 80, and electric power is generated in the piezoelectric element 71. That is, in the power generating device 100, the power generating element 70 generates electric power every time the operation unit 80 is operated.

[0017] ·Power circuit The power supply circuit 1 includes a rectifier circuit 2, a voltage conversion circuit 3, a start-up circuit 4, an input capacitor C11, an output capacitor C12, and an inductor L11.

[0018] The rectifier circuit 2 is electrically connected between the output terminals of the power generating element 70, and receives the AC voltage output by the power generating element 70. The rectifier circuit 2 is a full-wave rectifier circuit having four bridge-connected diodes D11 to D14. The rectifier circuit 2 full-wave rectifies the output voltage (AC voltage) of the power generating element 70 and outputs the full-wave rectified voltage to the input capacitor C11.

[0019] Specifically, the rectifier circuit 2 has a pair of input terminals P11, P12 and a pair of output terminals P21, P22. However, the "terminals" referred to here do not have to be components for connecting electric wires or the like, and may be, for example, leads of an electronic component or parts of conductors included in a circuit board.

[0020] The input terminal P11 is electrically connected to one output end 70A of the power generating element 70, and the input terminal P12 is electrically connected to the other output end 70B of the power generating element 70. The output terminal P21 is electrically connected to one end C11A of the input capacitor C11, and the output terminal P22 is electrically connected to the other end C11B of the input capacitor C11. In addition, the output terminal P22 is electrically connected to the circuit ground PGND.

[0021] The diode D11 has an anode electrically connected to the input terminal P11 and a cathode electrically connected to the output terminal P21. The diode D12 has an anode electrically connected to the output terminal P22 and a cathode electrically connected to the input terminal P12. The diode D13 has an anode electrically connected to the input terminal P12 and a cathode electrically connected to the output terminal P21. The diode D14 has an anode electrically connected to the output terminal P22 and a cathode electrically connected to the input terminal P11. The diodes D11 to D14 are bridge-connected to form a full-wave rectifier circuit.

[0022] The rectifier circuit 2 is not limited to a full-wave rectifier circuit, and may be a half-wave rectifier circuit.

[0023] The input capacitor C11 is electrically connected between the output terminals P21, P22 of the rectifier circuit 2, and the output voltage of the rectifier circuit 2 is applied to it. In other words, a pulsating voltage obtained by full-wave rectifying the output voltage of the power generating element 70 by the rectifier circuit 2 is applied to the input capacitor C11. The input capacitor C11 stores the power generated by the power generating element 70 that is input via the rectifier circuit 2. As a result, a DC input voltage Vi is generated between both ends C11A, C11B of the input capacitor C11. Fig. 3A shows the change over time of the input voltage Vi of the input capacitor C11.

[0024] The voltage conversion circuit 3 is electrically connected to the input capacitor C11, and receives the input voltage Vi. The voltage conversion circuit 3 is a DC / DC converter circuit, which converts the input voltage Vi to a predetermined output voltage Vo and outputs it to the load 90. That is, the voltage conversion circuit 3 converts the voltage value of the input voltage Vi to obtain the predetermined output voltage Vo and outputs it to the load 90.

[0025] Specifically, the voltage conversion circuit 3 includes a switching circuit 31, a switch control unit 32, a start-up control unit 33, and a diode D21. In this embodiment, the voltage conversion circuit 3 is configured as an integrated circuit (IC). That is, the switching circuit 31, the switch control unit 32, the start-up control unit 33, and the diode D21 are integrated into one IC. The voltage conversion circuit 3 includes an input terminal P31, a ground terminal P32, an output terminal P33, an enable terminal P34, and a feedback terminal P35.

[0026] The input terminal P31 is electrically connected to one end C11A, which is the positive electrode side of the input capacitor C11. The ground terminal P32 is electrically connected to the other end C11B, which is the negative electrode side of the input capacitor C11, and the circuit ground PGND. That is, the input capacitor C11 is electrically connected between the input terminal P31 and the ground terminal P32, and the input voltage Vi is applied between both ends C11A and C11B of the input capacitor C11, that is, between the input terminal P31 and the ground terminal P32. The output terminal P33 is electrically connected to one end C12A of the output capacitor C12 via the inductor L11. The other end C12B of the output capacitor C12 is electrically connected to the circuit ground PGND. The enable terminal P34 is electrically connected to the start-up circuit 4. The start-up circuit 4 will be described later. The feedback terminal P35 is electrically connected to one end C12A of the output capacitor C12.

[0027] The switching circuit 31 is a chopper circuit having a switching element constituted by, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The switching circuit 31 is electrically connected to one end C11A and the other end C11B of the input capacitor C11 via an input terminal P31 and a ground terminal P32, respectively, and an input voltage Vi is inputted via the input terminal P31. The switching circuit 31 is also electrically connected to an output capacitor C12 via an output terminal P33 and an inductor L11. The switching circuit 31 performs a voltage conversion operation to convert the voltage value of the input voltage Vi to a predetermined value by driving the switching element on / off, and outputs the voltage to the output capacitor C12. That is, the output capacitor C12 stores the output power of the voltage conversion circuit 3 (switching circuit 31). As a result, a DC output voltage Vo is generated between both ends C12A and C12B of the output capacitor C12. The switching element of the switching circuit 31 is controlled by a switch control unit 32.

[0028] A diode D21 is electrically connected between the output terminal P33 and the ground terminal P32. The diode D21 is a regenerative diode, and has an anode electrically connected to the ground terminal P32 and a cathode electrically connected to the output terminal P33.

[0029] A load 90 is electrically connected between the two ends C12A and C12B of the output capacitor C12. Therefore, the load 90 is applied with the output voltage Vo between the two ends C12A and C12B of the output capacitor C12.

[0030] The load 90 of this embodiment is housed in a housing together with the power generating device 100. That is, in the electronic device 200 of this embodiment, the load 90 and the power generating device 100 are integrally provided. The load 90 is configured to operate using the power generating device 100 as a driving power source. The load 90 includes a communication unit 91. The communication unit 91 is configured to transmit a signal using power supplied from the power supply circuit 1. In this embodiment, the communication unit 91 is configured to transmit a wireless signal using radio waves as a medium to an external device. The power generating device 100 may also include a plurality of operation units 80. In this case, it is preferable that the communication unit 91 is configured to output a wireless signal that identifies the operation unit 80 that has been operated among the plurality of operation units 80.

[0031] The load 90 may be provided in a housing separate from the power generation device 100. The communication unit 91 may be configured to output a signal by wired communication. The load 90 is not limited to a configuration including the communication unit 91. For example, the load 90 may be configured to generate sound, light, or the like by using the power supplied from the power generation device 100.

[0032] The switch control unit 32 performs switch control to control the switching elements of the switching circuit 31. In the switch control, the switch control unit 32 controls the switching elements of the switching circuit 31 so that the voltage value of the output voltage of the switching circuit 31 becomes a predetermined value (e.g., 1.8 V). In other words, the switch control unit 32 performs constant voltage control on the switching circuit 31.

[0033] The switch control unit 32 is also electrically connected to the feedback terminal P35. The switch control unit 32 monitors the output voltage Vo between both ends C12A and C12B of the output capacitor C12 via the feedback terminal P35. That is, the switch control unit 32 monitors the voltage applied to the load 90 by monitoring the output voltage Vo of the output capacitor C12. The switch control unit 32 stops the switch control when the voltage V90 applied to the load 90 exceeds the output upper limit value Vomax. As a result, the switching circuit 31 stops the voltage conversion operation, and the output of the output voltage from the switching circuit 31 stops. The switch control unit 32 starts (resumes) the switch control when the voltage applied to the load 90 falls below the output lower limit value Vomin. As a result, the switching circuit 31 starts the voltage conversion operation, and the output of the output voltage Vo from the switching circuit 31 starts. That is, the switch control unit 32 repeatedly executes and stops the switch control so that the voltage applied to the load 90 changes between the output lower limit value Vomin and the output upper limit value Vomax.

[0034] The start and stop of the switch control unit 32 is controlled by the start control unit 33. When the switch control unit 32 is in an operating state after start-up, it is possible to execute switch control. When the switch control unit 32 is in a stopped state, the output terminal P33 is short-circuited to the ground terminal P32. At this time, the input terminal P31 and the output terminal P33 are electrically disconnected from each other.

[0035] The start-up control unit 33 controls the start and stop of the switch control unit 32 based on the voltage V34 applied to the enable terminal P34. FIG. 3A shows the voltage V34 together with the input voltage Vi. Specifically, the start-up control unit 33 monitors the voltage V34 applied to the enable terminal P34, more specifically, the voltage V34 between the enable terminal P34 and the ground terminal P32. When the voltage value of the voltage V34 applied to the enable terminal P34 exceeds a threshold Vth3 (see FIG. 3A), the start-up control unit 33 starts the switch control unit 32. The threshold Vth3 is, for example, 0.8V. Moreover, when the voltage value of the voltage V34 applied to the enable terminal P34 falls below a predetermined operating lower limit Vmin1 that is smaller than the threshold Vth3, the start-up control unit 33 stops the switch control unit 32. The operating lower limit Vmin1 is, for example, 0.4V. The lower operating limit value Vmin1 is not limited to a value smaller than the threshold value Vth3, and may be the same value as the threshold value Vth3, or may be a value larger than the threshold value Vth3.

[0036] Moreover, the switch control unit 32 monitors the input voltage Vi when the switch control unit 32 is in an operating state. When the switch control unit 32 is in an operating state, the switch control unit 32 executes switch control when the voltage value of the input voltage Vi exceeds a threshold value Vth1 (see FIG. 3A). The threshold value Vth1 is a value larger than the threshold value Vth3. The threshold value Vth1 is, for example, 2.5V. Moreover, the switch control unit 32 stops switch control when the voltage value of the input voltage Vi falls below a predetermined operating lower limit value Vmin2 that is smaller than the threshold value Vth1. The operating lower limit value Vmin2 is, for example, 1.8V. The operating lower limit value Vmin2 is not limited to a value smaller than the threshold value Vth1, and may be the same value as the threshold value Vth1 or may be a value larger than the threshold value Vth1. That is, the voltage conversion circuit 3 outputs the output voltage Vo when the input voltage Vi is equal to or larger than the threshold value Vth1 in the operating state after starting up. Furthermore, the voltage conversion circuit 3 stops outputting the output voltage Vo when the input voltage Vi falls below the operating lower limit value Vmin2 while outputting the output voltage Vo.

[0037] That is, in the voltage conversion circuit 3, when the voltage V34 applied to the enable terminal P34 exceeds the threshold Vth3, the start-up control unit 33 starts the switch control unit 32. When the input voltage Vi applied to the input terminal P31 is equal to or greater than the threshold Vth1 in an operating state after start-up, the switch control unit 32 executes switch control. By the switch control, the switching circuit 31 performs a voltage conversion operation and outputs an output voltage Vo obtained by voltage-converting the input voltage Vi. As a result, power is supplied to the load 90, and the load 90 starts operating. A detailed explanation of the operation of the voltage conversion circuit 3 will be given in the "Operation Example" section described later.

[0038] The start-up circuit 4 is configured to apply a voltage V34 to the enable terminal P34 of the voltage conversion circuit 3. The voltage V34 can be an enable voltage Ven. The start-up circuit 4 is electrically connected to the input capacitor C11 and the voltage conversion circuit 3. When the input voltage Vi between both ends C11A and C11B of the input capacitor C11 becomes equal to or greater than a threshold Vth2 (see FIG. 3A), the start-up circuit 4 applies the enable voltage Ven to the enable terminal P34. The enable voltage Ven in this embodiment is the voltage V34 that is equal to or greater than a threshold Vth3 and is applied to the enable terminal P34 of the voltage conversion circuit 3.

[0039] Specifically, the start-up circuit 4 includes a Zener diode ZD21 and a time constant circuit 40. The time constant circuit 40 includes a resistor R21 and a capacitor C21.

[0040] A series circuit of a Zener diode ZD21 and a resistor R21 is electrically connected between both ends of the input capacitor C11. The Zener diode ZD21 has a cathode electrically connected to the positive terminal C11A of the input capacitor C11 and the input terminal P31 of the voltage conversion circuit 3, and an anode electrically connected to the negative terminal C11B of the input capacitor C11, i.e., the circuit ground PGND, via the resistor R21. The capacitor C21 is electrically connected in parallel with the resistor R21. One end C21A of the capacitor C21 is electrically connected to the enable terminal P34 of the voltage conversion circuit 3, and the other end C21B is electrically connected to the ground terminal P32 of the voltage conversion circuit 3. The voltage between both ends C21A and C21B of the capacitor C21 is applied to the enable terminal P34 as a voltage V34 that can become the enable voltage Ven.

[0041] The terminal C11B of the input capacitor C11 has a lower potential than the terminal C11A. The cathode of the Zener diode ZD21 is connected to the terminal C11A of the input capacitor C11. The anode of the Zener diode ZD21 is connected to the enable terminal P34.

[0042] The capacitor C21 of the time constant circuit 40 is connected in series to the enable terminal P34 and the end C11B of the input capacitor C11. The resistor R21 of the time constant circuit 40 is connected in parallel to the capacitor C21.

[0043] The voltage value of the breakdown voltage of the Zener diode ZD21 is set to a threshold value Vth2. Therefore, when the input voltage Vi of the input capacitor C11 is equal to or higher than the threshold value Vth2, the Zener diode ZD21 is turned on (in a breakdown state). When the Zener diode ZD21 is turned on, a current is supplied from the input capacitor C11 to the capacitor C21 via the Zener diode ZD21, and the capacitor C21 is charged. As the capacitor C21 is charged, the voltage value of the enable voltage Ven, which is the voltage V34 between both ends C21A and C21B of the capacitor C21, becomes equal to or higher than the threshold value Vth3, and the start-up control unit 33 starts up the switch control unit 32.

[0044] Furthermore, when the input voltage Vi of the input capacitor C11 is less than the threshold Vth2, the Zener diode ZD21 is turned off. When the Zener diode ZD21 is turned off, the Zener diode ZD21 cuts off the current from the input capacitor C11 to the capacitor C21, and the capacitor C21 is not charged. At this time, if a charge is accumulated in the capacitor C21, the capacitor C21 is discharged through the resistor R21. That is, the resistor R21 functions as a discharge path 41 that discharges the capacitor C21. In other words, the start-up circuit 4 includes a discharge path 41 that discharges the capacitor C21.

[0045] Here, immediately after the input voltage Vi of the input capacitor C11 falls below the threshold Vth2 and the Zener diode ZD21 is turned off, electric charge is stored in the capacitor C21. As shown in FIG. 3A, this maintains a state in which the voltage value of the enable voltage Ven, which is the voltage V34 between both ends C21A and C21B of the capacitor C21, is equal to or higher than the threshold Vth3. Therefore, during the voltage maintenance period PT1 from time t3 when the input voltage Vi falls below the threshold Vth2 to time t4 when the capacitor C21 is discharged and the enable voltage Ven falls below the lower operating limit Vmin1, the switch control unit 32 is in an operating state. The voltage maintenance period PT1 is determined by the time constant circuit 40. Specifically, the time length of the voltage maintenance period PT1 is determined by a time constant based on the capacitance of the capacitor C21 and the resistance value of the resistor R21. In this embodiment, the capacitance of the capacitor C21 and the resistance value of the resistor R21 are set so that the time length of the voltage maintenance period PT1 is, for example, about 20 ms.

[0046] The voltage maintenance period PT1 is determined by the time constant, regardless of the state of charge stored in the input capacitor C11 or the power consumption in the load 90. Therefore, the input voltage Vi may excessively drop before the voltage maintenance period PT1 ends due to the state of charge stored in the input capacitor C11 or the power consumption in the load 90. In this case, if the voltage conversion circuit 3 continues to operate, the output voltage Vo may become unstable and may adversely affect the load 90. In the power supply circuit 1 according to the embodiment, the operation of the switching circuit 31 is stopped by the above-mentioned lower limit Vmin2. This operation is shown in FIG. 3B. When the switch control unit 32 is in an operating state, the switch control unit 32 monitors the input voltage Vi. If the input voltage Vi falls below the predetermined lower limit Vmin2 at time t5 even during the voltage maintenance period PT1, the switch control unit 32 stops switch control, stops the switching circuit 31, and stops the output of the output voltage Vo. In this way, in the power supply circuit 1, in an operating state in which the voltage conversion circuit 3 is started up and running, when at least one of the events occurring are that the voltage V34 falls below the lower operating limit Vmin1 and the input voltage Vi falls below the lower operating limit Vmin2, the operation of the switching circuit 31 is stopped and the output of the output voltage Vo is stopped.

[0047] Example of operation Next, an example of the operation of the power supply circuit 1 of this embodiment will be described with reference to Figure 2 and Figure 3A. Figure 3A shows the change over time of the input voltage Vi of the input capacitor C11.

[0048] At time t0, the operation unit 80 is operated. This causes the vibration body 72 to vibrate, and the piezoelectric element 71 to generate power. That is, the power generating element 70 starts generating power. When the power generating element 70 starts generating power, the input capacitor C11 is charged, and the input voltage Vi increases.

[0049] At time t1, the input voltage Vi reaches the threshold Vth3. The threshold Vth3 is smaller than the threshold Vth2, which is the voltage value of the breakdown voltage of the Zener diode ZD21. Therefore, at time t1, the Zener diode ZD21 is in the off state, and the capacitor C21 is not charged. Therefore, the voltage value of the voltage V34 applied to the enable terminal P34 of the voltage conversion circuit 3 is equal to or smaller than the threshold Vth3, and the voltage conversion circuit 3 (switch control unit 32) is in the stopped state.

[0050] At time t2, the input voltage Vi reaches the threshold Vth1. The threshold Vth1 is smaller than the threshold Vth2, which is the voltage value of the breakdown voltage of the Zener diode ZD21. Therefore, at time t2, the Zener diode ZD21 is in the off state, and the capacitor C21 is not charged. Therefore, the voltage value of the voltage V34 applied to the enable terminal P34 of the voltage conversion circuit 3 is equal to or smaller than the threshold Vth3, and the voltage conversion circuit 3 (switch control unit 32) is still in the stopped state.

[0051] That is, at time t2, the voltage value of the input voltage Vi input to the voltage conversion circuit 3 reaches the threshold value Vth1 at which the switch control section 32 can execute switch control, but the start-up control section 33 stops the switch control section 32. Therefore, the switching circuit 31 of the voltage conversion circuit 3 does not execute the voltage conversion operation, and no output voltage is output from the voltage conversion circuit 3. Therefore, the load 90 is in a stopped state.

[0052] At time t3, the input voltage Vi reaches the threshold Vth2. Therefore, the Zener diode ZD21 is turned on and the capacitor C21 is charged, so that the voltage V34 between both ends C21A and C21B of the capacitor C21 rises and exceeds the threshold Vth3. When the voltage value of the voltage V34 applied to the enable terminal P34 exceeds the threshold Vth3, the voltage V34 starts the start-up control unit 33 as the enable voltage Ven, and the start-up control unit 33 starts the switch control unit 32. When the switch control unit 32 starts, it determines whether the input voltage Vi applied to the input terminal P31 is equal to or greater than the threshold Vth1. At the time when the switch control unit 32 starts, the input voltage Vi is equal to or greater than the threshold Vth1, so the switch control unit 32 starts to execute switch control. As a result, the switching circuit 31 starts a voltage conversion operation, so that an output voltage is output from the voltage conversion circuit 3, that is, power supply to the load 90 is started. The load 90 operates by the power supplied from the voltage conversion circuit 3. In this embodiment, a wireless signal is output from the communication unit 91.

[0053] Here, after time t3, the voltage conversion circuit 3 and the load 90 start operating, and the input voltage Vi is reduced due to power consumption in the voltage conversion circuit 3 and the load 90. As a result, the input voltage Vi falls below the threshold Vth2 and the Zener diode ZD21 is turned off. During the voltage maintenance period PT1 after the Zener diode ZD21 is turned off, the charge stored in the capacitor C21 maintains the voltage value V34 between both ends C21A and C21B of the capacitor C21 as the enable voltage Ven at or above the threshold Vth3. Therefore, the voltage conversion circuit 3 and the load 90 can continue to operate.

[0054] In this manner, in the electronic device 200 of the present embodiment, the power generating element 70 starts generating power and the input capacitor C11 is charged by operating the operation unit 80. Then, after the input capacitor C11 is sufficiently charged by the start-up circuit 4, that is, the input voltage Vi is equal to or higher than the threshold value Vth2, the voltage conversion circuit 3 starts up and power supply to the load 90 starts.

[0055] That is, during the period up to time t3 when the output voltage of the power generating element 70 at the beginning of power generation (see FIG. 2) is high, the voltage conversion circuit 3 is not operated and power is not supplied to the load 90. This increases the load impedance of the power generating element 70, making it possible to achieve impedance matching that reduces the difference between the internal impedance Z11 of the power generating element 70 and the load impedance. As a result, it is possible to improve the efficiency of charging the input capacitor C11 with power. Furthermore, since the voltage conversion circuit 3 is started and power is supplied to the load 90 after the input capacitor C11 is sufficiently charged, it is possible to stabilize the power supplied to the load 90 and stabilize the operation of the load 90.

[0056] After the voltage conversion circuit 3 is started, the load impedance of the power generating element 70 becomes relatively smaller than that before the voltage conversion circuit 3 is started, in order to supply power to the load 90. As a result, the difference between the internal impedance Z11 of the power generating element 70 and the load impedance becomes large, and the efficiency of charging the input capacitor C11 with power decreases. However, as shown in FIG. 2, the output voltage in the later period of power generation becomes smaller (attenuates) than in the early period of power generation. Therefore, the proportion of the power generation amount in the later period to the total power generation amount is small, and the effect of the impedance difference on the extraction efficiency of the total generated power can be suppressed.

[0057] Furthermore, the switch control unit 32 of the voltage conversion circuit 3 stops the switch control when the voltage V90 supplied to the load 90, i.e., the output voltage Vo between both ends C12A and C12B of the output capacitor C12, exceeds the output upper limit value Vomax. Therefore, when the power consumption in the load 90 is small, the voltage value of the output voltage Vo of the output capacitor C12 reaches the output upper limit value Vomax, and the switch control unit 32 can stop the operation of the voltage conversion circuit 3. Even during the period when the voltage conversion operation of the voltage conversion circuit 3 is stopped, the input capacitor C11 is charged by the power generation of the power generation element 70. The load impedance of the power generation element 70 increases as the voltage conversion operation of the voltage conversion circuit 3 is stopped. As a result, the difference between the internal impedance Z11 of the power generation element 70 and the load impedance becomes smaller, and the efficiency of extracting the generated power in the power generation element 70 can be improved.

[0058] In the electronic device 200 of this embodiment, the power generating element 70 generates power every time the operation unit 80 is operated. Therefore, when the operation of the operation unit 80 is performed repeatedly, the power generating element 70 generates power intermittently, and the input capacitor C11 is charged intermittently. As described above, in order to start the voltage conversion circuit 3 with the input capacitor C11 sufficiently charged, it is necessary to stop the voltage conversion circuit 3 between operations on the operation unit 80.

[0059] 4 shows a circuit diagram of a power supply circuit 1X of the comparative example. In the power supply circuit 1X of the comparative example, the configuration of a start-up circuit 4X is different from that of the power supply circuit 1 of the present embodiment. Other configurations are similar to those of the power supply circuit 1 of the present embodiment, so the same reference numerals are used and the description is omitted.

[0060] The start-up circuit 4X of the comparative example includes a delay circuit 40X. The delay circuit 40X has a resistor R31 and a capacitor C31. A series circuit of the resistor R31 and the capacitor C31 is electrically connected between both ends of the input capacitor C11. The voltage across the capacitor C31 is applied to the enable terminal P34 of the voltage conversion circuit 3.

[0061] In the power supply circuit 1X of the comparative example, the delay circuit 40X can delay the rise in the voltage applied to the enable terminal P34 of the voltage conversion circuit 3 relative to the rise in the input voltage Vi of the input capacitor C11. This can delay the start of the voltage conversion operation of the voltage conversion circuit 3, stabilize the power supplied to the load 90, and stabilize the operation of the load 90.

[0062] However, the power supply circuit 1X of the comparative example does not have a discharge path for discharging the input capacitor C11 and the capacitor C31. Therefore, when the operation unit 80 is operated repeatedly, the input capacitor C11 and the capacitor C31 may not be discharged between operations on the operation unit 80, and the operating state of the voltage conversion circuit 3 may continue. Therefore, when the voltage conversion circuit 3 performs a voltage conversion operation when the input capacitor C11 is not sufficiently charged, the voltage conversion operation may become unstable, and the power supplied to the load 90 may become unstable.

[0063] In the power supply circuit 1 of this embodiment, the start-up circuit 4 includes a resistor R21 as a discharge path 41. When the Zener diode ZD21 is in an off state, the capacitor C21 is discharged through the resistor R21. Therefore, the capacitor C21 can be discharged faster than when the capacitor C21 is naturally discharged. Therefore, between operations on the operation unit 80, the capacitor C21 is discharged, the voltage across the capacitor C21 becomes equal to or lower than the lower limit Vmin1 of operation, and the voltage conversion circuit 3 can be stopped. That is, the application of the enable voltage Ven from the start-up circuit 4 to the enable terminal P34 of the voltage conversion circuit 3 is stopped, and the voltage conversion circuit 3 is stopped. Then, when the operation unit 80 is operated and the input voltage Vi exceeds the threshold Vth2, the enable voltage Ven is applied from the start-up circuit 4 to the enable terminal P34, and the voltage conversion circuit 3 is started. As a result, even when the operation of the operation unit 80 is repeatedly performed, the power supplied to the load 90 can be stabilized, and the operation of the load 90 can be stabilized. Therefore, in this embodiment, when the operation of the operation unit 80 is repeatedly performed, it is possible to cause the communication unit 91 of the load 90 to transmit a wireless signal every time the operation unit 80 is operated.

[0064] Modifications First modified example FIG. 5 is a circuit diagram of a power supply circuit 1A according to a first modified example of the embodiment.

[0065] A power supply circuit 1A of this modification differs from the power supply circuit 1 of the above embodiment (see FIG. 1A) in the configuration of a start-up circuit 4A. Other configurations are similar to those of the power supply circuit 1 of the above embodiment, so the same reference numerals are used and descriptions are omitted.

[0066] The start-up circuit 4A of this modification includes a voltage detector 42 instead of the Zener diode ZD21. A series circuit including the voltage detector 42 and a resistor R21 connected in series with each other is electrically connected between both ends C11A and C11B of the input capacitor C11.

[0067] The voltage detector 42 has an input terminal 42A electrically connected to the terminal C11A of the input capacitor C11, and an output terminal 42B electrically connected to the resistor R21 and the capacitor C21 of the time constant circuit 40. The voltage detector 42 compares the input voltage Vi, which is the voltage between both ends C11A and C11B of the input capacitor C11, with a predetermined threshold Vth2. The voltage detector 42 changes the level of the output signal output from the output terminal 42B according to the comparison result between the input voltage Vi and the threshold Vth2. When the input voltage Vi is equal to or greater than the threshold Vth2, the voltage detector 42 sets the level of the output signal to a Hi level. Therefore, when the input voltage Vi is equal to or greater than the threshold Vth2, the capacitor C21 is charged by the output signal of the voltage detector 42. When the input voltage Vi is less than the threshold Vth2, the voltage detector 42 sets the level of the output signal to a Low level, which is the ground potential lower than the Hi level. Therefore, when the input voltage Vi is less than the threshold Vth2, the capacitor C21 is not charged.

[0068] In the power supply circuit 1A of this modified example, when the input voltage Vi of the input capacitor C11 exceeds the threshold Vth2, the signal level of the output signal of the voltage detector 42 becomes Hi level and the capacitor C21 is charged. Then, when the voltage V34 between both ends C21A, C21B of the capacitor C21 exceeds the threshold Vth3, the voltage V34 is applied to the enable terminal P34 as the enable voltage Ven, and the start-up control unit 33 starts the switch control unit 32. This causes the voltage conversion circuit 3 to start a voltage conversion operation, starts supplying power to the load 90, and the communication unit 91 of the load 90 operates to transmit a wireless signal.

[0069] In the power supply circuit 1A of this modification, the voltage conversion circuit 3 starts up and starts supplying power to the load 90 after the input capacitor C11 is sufficiently charged, that is, after the input voltage Vi is equal to or higher than the threshold value Vth2. This makes it possible to stabilize the power supplied to the load 90, and thus to stabilize the operation of the load 90.

[0070] Second variant FIG. 6 is a circuit diagram of a power supply circuit 1B according to a second modified example of the embodiment.

[0071] The power supply circuit 1B of this modification differs from the power supply circuit 1 of the above embodiment (see FIG. 1A) in the configurations of a start-up circuit 4B and a voltage conversion circuit 3B. The other configurations are similar to those of the power supply circuit 1 of the above embodiment, so the same reference numerals are used and the description will be omitted.

[0072] The start-up circuit 4B of this modification includes a Zener diode ZD21 and a resistor R21, and does not include the capacitor C21. A series circuit including the Zener diode ZD21 and the resistor R21 connected in series to each other at a connection point N21 is electrically connected between both ends C11A and C11B of the input capacitor C11. The connection point N21 between the Zener diode ZD21 and the resistor R21 is electrically connected to the enable terminal P34 of the voltage conversion circuit 3. When the input voltage Vi of the input capacitor C11 exceeds the threshold Vth2 and the Zener diode ZD21 is turned on, the voltage V34 across the resistor R21 is applied to the enable terminal P34 of the voltage conversion circuit 3 as the enable voltage Ven. The resistance value of the resistor R21 is set so that the voltage value of the voltage V34 across the resistor R21 (enable voltage Ven) at this time is greater than the threshold Vth3.

[0073] The voltage conversion circuit 3B of this modified example includes a switching circuit 31, a switch control section 32, a start-up control section 33, and further includes a timer .

[0074] The timer 34 is configured to start measuring time when the enable voltage Ven is applied to the enable terminal P34. Specifically, when the voltage value of the voltage V34 (enable voltage Ven) applied to the enable terminal P34 exceeds the threshold Vth3, the timer 34 starts measuring the holding period PT2. The holding period PT2 is, for example, 20 ms. That is, when the voltage value of the voltage V34 (enable voltage Ven) applied to the enable terminal P34 exceeds the threshold Vth3, the timer 34 starts measuring time, and ends measuring time when the measured time reaches the holding period PT2.

[0075] When the voltage value of the voltage V34 (enable voltage Ven) applied to the enable terminal P34 exceeds the threshold value Vth3, the start-up control unit 33 starts the switch control unit 32, and the timer 34 starts timing the holding period PT2. Then, the start-up control unit 33 keeps the switch control unit 32 in operation while the timer 34 is timing the holding period PT2. At this time, even if the voltage value of the voltage applied to the enable terminal P34 falls below the operating lower limit value Vmin1, the start-up control unit 33 sets the switch control unit 32 in operation if the timer 34 is timing the holding period PT2. In other words, even if the application of the enable voltage Ven from the start-up circuit 4 is stopped, the start-up control unit 33 sets the switch control unit 32 in operation if the timer 34 is timing the holding period PT2. The start-up control unit 33 stops the switch control unit 32 when the holding period PT2 has elapsed, that is, when the timer 34 has finished timing the holding period PT2. That is, the start-up control unit 33 keeps the switch control unit 32 in the operating state until the holding period PT2 elapses after the voltage value of the voltage V34 (enable voltage Ven) applied to the enable terminal P34 exceeds the threshold Vth3.

[0076] In the power supply circuit 1B of this modified example, the time constant circuit 40 is omitted, and therefore when the input voltage Vi falls below the threshold Vth2, the Zener diode ZD21 is turned off, and the voltage applied to the enable terminal P34 is reduced to less than the threshold Vth3. However, the timer 34 keeps the switch control unit 32 in operation for a holding period PT2 after the voltage applied to the enable terminal P34 exceeds the threshold Vth3. This allows the voltage conversion circuit 3 and the load 90 to continue operating until the holding period PT2 has elapsed after the input voltage Vi falls below the threshold Vth2.

[0077] The length of the holding period PT2 measured by the timer 34 may be configured to be changeable. For example, the length of the holding period PT2 may be configured to be changeable by changing a program executed by a processor included in the timer 34. This makes it possible to adjust the time during which the voltage conversion circuit 3 and the load 90 continue to operate. Also, the interval at which repeated operations on the operation unit 80 are possible can be adjusted.

[0078] In the above example, the timer 34 is integral with the voltage conversion circuit 3B, but may be provided separately from the voltage conversion circuit 3B.

[0079] (summary) The power supply circuit (1) according to the first embodiment supplies power to a load (90) based on power generated by a power generating element (70). The power supply circuit (1) includes an input capacitor (C11), a voltage conversion circuit (3, 3B), and a start-up circuit (4, 4A, 4B). The input capacitor (C11) stores the power generated by the power generating element (70). The voltage conversion circuit (3, 3B) outputs an output voltage (Vo) obtained by converting an input voltage (Vi) between both ends of the input capacitor (C11) to the load (90). The start-up circuit (4, 4A, 4B) applies an enable voltage (Ven) to an enable terminal (P34) of the voltage conversion circuit (3, 3B) to start up the voltage conversion circuit (3, 3B). In an operating state after start-up, the voltage conversion circuit (3, 3B) outputs an output voltage (Vo) when the input voltage (Vi) is equal to or higher than a first threshold (Vth1). When the input voltage (Vi) becomes equal to or higher than a second threshold (Vth2) that is higher than the first threshold (Vth1), the start-up circuit (4, 4A, 4B) applies an enable voltage (Ven) to the enable terminal (P34).

[0080] According to this embodiment, the voltage conversion circuit (3, 3B) is activated and starts a voltage conversion operation when the input voltage (Vi) is higher, thereby stabilizing the operation of the voltage conversion circuit (3, 3B) and stabilizing the power supplied to the load (90).

[0081] In the power supply circuit (1) according to the second aspect, in the first aspect, the voltage conversion circuit (3, 3B) is activated when the voltage (V34) applied to the enable terminal (P34) becomes equal to or higher than a third threshold (Vth3) which is lower than the first threshold (Vth1).

[0082] According to this embodiment, the voltage conversion circuit (3, 3B) can be started up with the enable voltage (Ven) having a smaller voltage value.

[0083] In the power supply circuit (1) according to the third aspect, in the first or second aspect, the start-up circuit (4, 4B) includes a Zener diode (ZD21) electrically connected across the input capacitor (C11).

[0084] According to this embodiment, the start-up circuit (4, 4B) can be configured with a simple structure, and further, the power consumption of the start-up circuit (4, 4B) can be reduced.

[0085] In the power supply circuit (1) according to the fourth aspect, in the first or second aspect, the start-up circuit (4A) includes a voltage detector (42) electrically connected between both ends (C11A, C11B) of the input capacitor (C11).

[0086] According to this embodiment, the start-up circuit (4A) can be configured with a simple structure, and further, the power consumption of the start-up circuit (4A) can be reduced.

[0087] In the power supply circuit (1) according to the fifth aspect, in any one of the first to fourth aspects, the start-up circuit (4, 4A) has a time constant circuit (40) that determines a voltage maintenance period (PT1). The start-up circuit (4, 4A) maintains application of the enable voltage (Ven) to the enable terminal (P34) during the voltage maintenance period (PT1) after the input voltage (Vi) falls below the second threshold (Vth2).

[0088] According to this embodiment, the operating state of the voltage conversion circuit (3, 3B) can be continued even after the input voltage (Vi) falls below the second threshold (Vth2).

[0089] In the power supply circuit (1) according to a sixth aspect, in the fifth aspect, the time constant circuit (40) includes a resistor (R21) and a capacitor (C21).

[0090] According to this embodiment, the time constant circuit (40) can be realized with a simple configuration.

[0091] In the power supply circuit (1) according to the seventh aspect, in the sixth aspect, the start-up circuit (4, 4A) includes a discharge path (41) that discharges the capacitor (C21).

[0092] According to this embodiment, it is possible to reduce the time required to stop the voltage conversion circuit (3, 3B) after the voltage conversion circuit (3, 3B) has supplied power to the load (90).

[0093] In the power supply circuit (1) according to the eighth aspect, in the first to fourth aspects, the voltage conversion circuit (3B) continues the operating state for the hold period (PT2) when the enable voltage (Ven) is applied to the enable terminal (P34).

[0094] According to this embodiment, the operating state of the voltage conversion circuit (3B) can be continued even after the input voltage (Vi) falls below the second threshold (Vth2).

[0095] In the power supply circuit (1) according to the ninth aspect, in the eighth aspect, the time length of the hold period (PT2) is changeable.

[0096] According to this embodiment, it is possible to adjust the time from when the voltage conversion circuit (3B) starts supplying power to the load (90) until when the voltage conversion circuit (3B) is stopped.

[0097] In the power supply circuit (1) according to the tenth aspect, in any of the first to ninth aspects, the voltage conversion circuit (3, 3B) stops outputting the output voltage (Vo) when the voltage applied to the load (90) reaches an output upper limit value (Vomax).

[0098] According to this embodiment, when the power consumption of the load (90) is relatively small, the voltage conversion operation of the voltage conversion circuit (3, 3B) is stopped, thereby improving the power generation efficiency of the power generating element (70).

[0099] A start-up circuit (4, 4A, 4B) according to the eleventh aspect is used in the power supply circuit (1) according to any one of the first to tenth aspects.

[0100] According to this embodiment, the operation of the voltage conversion circuits (3, 3B) in the power supply circuit (1) can be stabilized, and the power supplied to the load (90) can be stabilized.

[0101] A power generating device (100) according to a twelfth aspect includes a power supply circuit (1) according to any one of the first to tenth aspects, and a power generating element (70).

[0102] According to this embodiment, in the power supply circuit (1), the operation of the voltage conversion circuits (3, 3B) is stabilized, and the power supplied to the load (90) can be stabilized.

[0103] An electronic device (200) according to a thirteenth aspect includes the power generation device (100) according to the twelfth aspect and a load (90).

[0104] According to this embodiment, in the power supply circuit (1) of the power generation device (100), the operation of the voltage conversion circuits (3, 3B) is stabilized, and the power supplied to the load (90) can be stabilized.

[0105] In the electronic device (200) according to the fourteenth aspect, in the thirteenth aspect, the load (90) transmits a signal using power supplied from the power supply circuit (1).

[0106] According to this embodiment, the power supplied from the power supply circuit (1) to the load (90) is stable, so that the load (90) can transmit a signal stably.

[0107] ·Reference example FIG. 7 is a circuit diagram of a power supply circuit 1S of a reference example.

[0108] A conventional power generating device including a vibration power generating element (power generating element) is disclosed in Patent Document 1 (JP 2016-86599 A).

[0109] The power generation device of Patent Document 1 includes a power storage unit, a rectifier circuit, and a DC-DC converter as a power supply circuit. The power storage unit stores the electric energy generated by the vibration power generation element. The rectifier circuit rectifies the AC voltage generated by the vibration power generation element. The DC-DC converter stabilizes the output voltage of the power storage unit and outputs it to a control circuit (load).

[0110] 2. Description of the Related Art In a power supply circuit that supplies power to a load based on power generated by a power generating element, it is desirable to stabilize the power supplied to the load.

[0111] The power supply circuit 1S of the reference example is configured to supply power to a load 90 based on the power generated by the power generating element 70. The power generating device 100 includes the power supply circuit 1S and the power generating element 70. The electronic device 200 includes the power generating device 100 and a load 90. The power generating device 100 is a vibration type power generating device that generates power by converting vibration energy applied to the power generating element 70 into electrical energy. The load 90 is a device that operates using power supplied from the power generating device 100.

[0112] The power supply circuit 1S of the reference example further includes an input capacitor C11, a voltage conversion circuit 3, and a start-up circuit 5. In the power supply circuit 1S of the reference example, the configuration of the start-up circuit 5 differs from that of the power supply circuit 1 of the above embodiment (see FIG. 1A). Since the other configurations are similar to those of the power supply circuit 1 of the above embodiment, the same reference numerals are used and the description will be omitted.

[0113] The start-up circuit 5 of the reference example includes a delay circuit 50 and a resistor R42 (discharge resistor). The delay circuit 50 has a resistor R41 (delay resistor) and a capacitor C41 (delay capacitor). A series circuit including the resistor R41 and the capacitor C41 connected in series to each other is electrically connected between both ends of the input capacitor C11. The voltage across the capacitor C41 is applied to the enable terminal P34 of the voltage conversion circuit 3 as the enable voltage Ven.

[0114] In the power supply circuit 1S of the reference example, the delay circuit 50 can delay the rise in the enable voltage Ven applied to the enable terminal P34 of the voltage conversion circuit 3 relative to the rise in the input voltage Vi of the input capacitor C11. Therefore, the start of the voltage conversion operation of the voltage conversion circuit 3 can be delayed. This stabilizes the voltage conversion operation of the voltage conversion circuit 3, stabilizes the power supplied to the load 90, and stabilizes the operation of the load 90.

[0115] The resistor R42 is electrically connected across the input capacitor C11. The resistor R42 functions as a discharge path 51 that discharges the input capacitor C11 and the capacitor C41. When the power generating element 70 is not generating power, the input capacitor C11 discharges via the resistor R42 (discharge path 51). When the power generating element 70 is not generating power, the capacitor C41 discharges via the resistor R41 and the resistor R42 (discharge path 51).

[0116] Therefore, when the operation unit 80 is operated repeatedly, the input capacitor C11 and the capacitor C41 are discharged between operations on the operation unit 80. This causes the voltage across the capacitor C41 (enable voltage Ven) to become equal to or lower than the lower limit Vmin1 of operation, and the voltage conversion circuit 3 can be stopped. Then, when the operation unit 80 is operated, the voltage conversion circuit 3 is started.

[0117] In this way, in the power supply circuit 1S of the reference example, even when the operation of the operation unit 80 is performed repeatedly, it is possible to stabilize the power supplied to the load 90 and stabilize the operation of the load 90. Therefore, when the operation of the operation unit 80 is performed repeatedly, the communication unit 91 of the load 90 operates to transmit a wireless signal every time the operation unit 80 is operated.

[0118] 8 is a circuit diagram of a power supply circuit 1T of a first modified example of the power supply circuit 1S according to the reference example. In the power supply circuit 1T of this modified example, the configuration of the start-up circuit 5A is different from that of the power supply circuit 1S of the reference example (see FIG. 7). Since the other configurations are similar to those of the power supply circuit 1S of the reference example, the same reference symbols are used and the description is omitted.

[0119] The start-up circuit 5A includes a delay circuit 50 and a resistor R43 (delay resistor). The resistor R43 is electrically connected across the capacitor C41 of the delay circuit 50. The resistor R43 functions as a discharge path 51 that discharges the input capacitor C11 and the capacitor C41. When the power generating element 70 is not generating power, the input capacitor C11 discharges through the resistors R41 and R43 (discharge path 51). When the power generating element 70 is not generating power, the capacitor C41 discharges through the resistor R43 (discharge path 51).

[0120] In this modification, a voltage obtained by dividing the input voltage Vi by resistors R41 and R43 is applied to the enable terminal P34 of the voltage conversion circuit 3. Therefore, it is possible to reduce the voltage applied to the enable terminal P34 of the voltage conversion circuit 3. In addition, since the voltage across the capacitor C41 is reduced, the time required for discharging the capacitor C41 is shortened.

[0121] Fig. 9 is a circuit diagram of a power supply circuit 1U of a second modified example of the power supply circuit 1S according to the reference example. In the power supply circuit 1U of this modified example, a start-up circuit 5A includes both a resistor R42 electrically connected between both ends of the input capacitor C11 and a resistor R43 electrically connected between both ends of the capacitor C41 as a discharge path 51. The power supply circuit 1U shown in Fig. 9 has the same effects as the power supply circuits 1S and 1T shown in Figs. 7 and 8.

[0122] As described above, the power supply circuit (1S) according to the fifteenth aspect supplies power to the load (90) based on the power generated by the power generating element (70). The power supply circuit (1S) includes an input capacitor (C11), a voltage conversion circuit (3), and a start-up circuit (5, 5A). The input capacitor (C11) stores the power generated by the power generating element (70). The voltage conversion circuit (3) outputs an output voltage (Vo) obtained by converting an input voltage (Vi) between both ends of the input capacitor (C11) to the load (90). The start-up circuit (5) applies an enable voltage (Ven) to an enable terminal (P34) of the voltage conversion circuit (3) to start the voltage conversion circuit (3). The start-up circuit (5, 5A) includes a delay circuit (50) and a discharge path (51). The delay circuit 50 includes a series circuit of a delay resistor R41 and a delay capacitor C41 electrically connected across the input capacitor C11, and delays the rise of the enable voltage Ven relative to the rise of the input voltage Vi. The discharge path 51 discharges the input capacitor C11 and the delay capacitor C41.

[0123] According to this embodiment, the voltage conversion circuit (3) is started and starts a voltage conversion operation when the input voltage (Vi) is higher, which stabilizes the operation of the voltage conversion circuit (3) and makes it possible to stabilize the power supplied to the load (90).

[0124] In a power supply circuit (1S) according to a sixteenth aspect, in the fifteenth aspect, the discharge path (51) includes a discharge resistor (R42) electrically connected across the input capacitor (C11).

[0125] According to this embodiment, the time for discharging the input capacitor (C11) and the delay capacitor (C41) can be adjusted according to the resistance value of the discharge resistor (R42).

[0126] In a power supply circuit (1S) according to a seventeenth aspect, in the fifteenth aspect, the discharge path (51) includes a discharge resistor (R43) electrically connected across the delay capacitor (C41).

[0127] According to this embodiment, the time for discharging the input capacitor (C11) and the delay capacitor (C41) can be adjusted according to the resistance value of the discharge resistor (R42). Also, the voltage value of the enable voltage (Ven) can be made smaller with respect to the input voltage (Vi). [Explanation of symbols]

[0128] 1 Power circuit 3,3B Voltage conversion circuit 4,4A,4B starting circuit 42 Voltage detector 40 Time constant circuit 41 Discharge Path ZD21 Zener diode C11 Input capacitor C21 Capacitor R21 resistor Vi input voltage Vo output voltage Ven Enable voltage Vth1 threshold (first threshold) Vth2 threshold (second threshold) Vth3 threshold (third threshold) P34 Enable terminal 70 Power generating element 90 Load 100 Power generation equipment 200 Electronic equipment

Claims

1. A power supply circuit that supplies power to a load based on power generated by a power generation element, an input capacitor that stores the power generated by the power generation element; a voltage conversion circuit configured to convert an input voltage between both ends of the input capacitor and output an output voltage to the load, the voltage conversion circuit having an enable terminal; a start-up circuit that applies a voltage to the enable terminal of the voltage conversion circuit; Equipped with the startup circuit starts up the voltage conversion circuit by applying an enable voltage to the enable terminal of the voltage conversion circuit; the voltage conversion circuit outputs the output voltage when the input voltage is equal to or higher than a first threshold in an operating state after startup; the startup circuit applies the enable voltage to the enable terminal when the input voltage becomes equal to or greater than a second threshold value that is greater than the first threshold value; the start-up circuit includes a series circuit of a Zener diode and a resistor electrically connected across the input capacitor, and a capacitor connected in parallel with the resistor; the two ends of the input capacitor include a first end and a second end at a lower potential than the first end; a cathode of the Zener diode connected to the first end of the input capacitor; the anode of the Zener diode is connected to the enable terminal; the resistor and the capacitor of the start-up circuit form a time constant circuit that determines a voltage maintenance period; the capacitor of the time constant circuit is connected in series with the enable terminal and the second end of the input capacitor; the startup circuit continues to apply the enable voltage to the enable terminal during the voltage maintenance period from a point in time when the input voltage falls below the second threshold from a value equal to or greater than the second threshold; power circuit.

2. A power supply circuit that supplies power to a load based on power generated by a power generation element, an input capacitor that stores the power generated by the power generation element; a voltage conversion circuit configured to convert an input voltage between both ends of the input capacitor and output an output voltage to the load, the voltage conversion circuit having an enable terminal; a start-up circuit that applies a voltage to the enable terminal of the voltage conversion circuit; Equipped with the startup circuit starts up the voltage conversion circuit by applying an enable voltage to the enable terminal of the voltage conversion circuit; the voltage conversion circuit outputs the output voltage when the input voltage is equal to or higher than a first threshold in an operating state after startup; the startup circuit applies the enable voltage to the enable terminal when the input voltage becomes equal to or greater than a second threshold value that is greater than the first threshold value; When the enable voltage is applied to the enable terminal, the voltage conversion circuit continues the operating state for a holding period. power circuit.

3. The power supply circuit according to claim 2 , wherein the length of said hold period is variable.

4. The power supply circuit according to any one of claims 1 to 3, wherein the voltage conversion circuit is configured to be activated when a value of the voltage applied to the enable terminal becomes equal to or greater than a third threshold value that is smaller than the first threshold value.

5. A power supply circuit according to any one of claims 1 to 4, The power generating element; A power generating device equipped with the above.

6. A power generation device according to claim 5, The load; Electronic equipment equipped with

7. The electronic device described in Claim 6, wherein the load transmits a signal using power supplied from the power supply circuit.

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