Initial charging circuit, power supply device, and energy harvesting device

Abstract

It quickly supplies voltage to the system without generating voltage ripple by repeatedly switching the switch on and off, and charges energy storage devices with the excess power. [Solution] An initial charging circuit is provided that controls the current flowing between a first energy storage element, which stores energy from an energy harvesting power source, and a second energy storage element, which has a larger capacity than the first energy storage element and stores energy from the first energy storage element, wherein the initial charging circuit comprises a resistor with one end connected to the first energy storage element, a first transistor with one end connected to the other end of the resistor and the other end connected to the second energy storage element, and an operational amplifier that changes the amount of current flowing between the first energy storage element and the second energy storage element when the first transistor is ON, based on the difference between the voltage at one end of the first transistor and a reference voltage.

Description

Technical Field

[0001] The present invention relates to an initial charging circuit, a power supply device, and an energy harvesting device.

Background Art

[0002] Patent Document 1 describes an environmental monitoring system 1 "comprising a power storage system 100 that stores the generated power of a power generation element that performs environmental power generation in a storage battery, and an external load device 200 that is supplied with power from the power storage system 100" (paragraph 0021), and "in the power storage system according to the present embodiment, in order to solve the above problems, two types of storage batteries A121 and B122 having different capacities and a switch unit 140 (first switch unit) as a switching mechanism are used." (paragraph 0024). Patent Document 1: WO2015 / 099158

Summary of the Invention

Problems to be Solved by the Invention

[0003] Supply voltage to the system quickly without generating voltage ripple caused by repeatedly turning on and off the switch, and charge the power storage device with the surplus power.

Means for Solving the Problems

[0004] To solve the above problems, a first embodiment of the present invention provides an initial charging circuit that controls the current flowing between a first energy storage element, which stores energy from an energy harvesting power source, and a second energy storage element, which has a larger capacity than the first energy storage element and stores energy from the first energy storage element. The initial charging circuit may have a resistor, one end of which is connected to the first energy storage element. Any of the above initial charging circuits may have a first transistor, one end of which is connected to the other end of the resistor, and the other end of which is connected to the second energy storage element. Any of the above initial charging circuits may have an operational amplifier that changes the amount of current flowing between the first energy storage element and the second energy storage element when the first transistor is in the ON state, based on the difference between the voltage at one end of the first transistor and a reference voltage.

[0005] In any of the above initial charging circuits, the first transistor may be a MOSFET of a first conductivity type. In any of the above initial charging circuits, the resistor may include a second transistor which is a MOSFET of the first conductivity type. In any of the above initial charging circuits, the operational amplifier may change the on-resistance of the second transistor when it is on based on the difference between the voltage at one end of the first transistor and the reference voltage.

[0006] In any of the above initial charging circuits, the absolute value of the threshold voltage of the second transistor may be greater than the absolute value of the threshold voltage of the first transistor.

[0007] Any of the above initial charging circuits may have a third transistor, which is a MOSFET of the first conductivity type, with one end connected to the first energy storage element and the other end connected to the second energy storage element, and connected in parallel with the first transistor and the resistor. In any of the above initial charging circuits, the operational amplifier may change the on-resistance of the third transistor when a current flows between the first energy storage element and the second energy storage element, based on the difference between the voltage at one end of the first transistor and the reference voltage.

[0008] In any of the above initial charging circuits, the resistor may have a first resistor connected in series with the second transistor.

[0009] In any of the above initial charging circuits, the resistor may have a second resistor connected in parallel with the second transistor.

[0010] To solve the above problems, a second embodiment of the present invention provides a power supply device comprising any of the above initial charging circuits, the first energy storage element, and the second energy storage element. In the power supply device, at least one of the first energy storage element or the second energy storage element may supply power to an external system.

[0011] Any of the above power supply devices may include a voltage monitoring unit that monitors the output voltage of the second energy storage element and outputs an output signal corresponding to the output voltage. Any of the above power supply devices may output a switching signal that switches the system to an operating mode with different power consumption according to the output signal.

[0012] Any of the above power supply devices may include a voltage monitoring unit that monitors the output voltage of the operational amplifier and outputs an output signal corresponding to the output voltage. Any of the above power supply devices may output a switching signal that switches the system to an operating mode with different power consumption according to the output voltage.

[0013] To solve the above problems, a third embodiment of the present invention provides a power supply device comprising an initial charging circuit having the third transistor, the first energy storage element, and the second energy storage element. The power supply device may include a voltage monitoring unit for monitoring the output voltage of the second energy storage element and a control unit for controlling the initial charging circuit. In any of the above power supply devices, at least one of the first energy storage element or the second energy storage element may supply power to an external system. In any of the above power supply devices, the control unit may control the third transistor of the initial charging circuit to an ON state when the output voltage exceeds a predetermined value. In any of the above power supply devices, the initial charging circuit may include a fourth transistor, one end of which is connected to the output of the operational amplifier and the other end of which is connected to ground. In any of the above power supply devices, the control unit may control the third transistor to an ON state by controlling the fourth transistor to an ON state when the output voltage exceeds a predetermined value. To solve the above problems, a fourth embodiment of the present invention provides a power supply device comprising: an initial charging circuit having the third transistor; the first energy storage element; the second energy storage element; a voltage monitoring unit for monitoring the output voltage of the operational amplifier; and a control unit for controlling the initial charging circuit. In the power supply device, at least one of the first energy storage element or the second energy storage element may supply power to an external system. In the power supply device, the control unit may control the third transistor of the initial charging circuit to an ON state when the output voltage falls below a predetermined value. In the power supply device, the initial charging circuit may include a fourth transistor, one end of which is connected to the output of the operational amplifier and the other end of which is connected to ground. In the power supply device, the control unit may control the third transistor to an ON state by controlling the fourth transistor to an ON state when the output voltage falls below a predetermined value.

[0014] Any of the above power supply devices may include a voltage monitoring unit that monitors the output voltage of the second energy storage element, a control unit that controls the initial charging circuit, and a switch connected in parallel with the initial charging circuit between the first energy storage element and the second energy storage element. In any of the above power supply devices, the control unit may control the switch to the ON state when the output voltage becomes greater than a predetermined value. Any of the above power supply devices may include a voltage monitoring unit that monitors the output voltage of the operational amplifier, a control unit that controls the initial charging circuit, and a switch connected in parallel with the initial charging circuit between the first energy storage element and the second energy storage element. In any of the above power supply devices, the control unit may control the switch to the ON state when the output voltage becomes less than a predetermined value.

[0015] To solve the above problems, a fifth embodiment of the present invention provides an energy harvesting device comprising any of the above-mentioned power supply devices, the system, and the energy harvesting power supply.

[0016] The above summary of the invention does not enumerate all the necessary features of the present invention. Furthermore, subcombinations of these features may also constitute an invention. [Brief explanation of the drawing]

[0017] [Figure 1] This figure shows an example of an energy harvesting device 100 including an initial charging circuit 30 in an embodiment of the present invention. [Figure 2] This figure shows an example of an initial charging circuit 30 in an embodiment of the present invention. [Figure 3] This figure shows a modified example of the initial charging circuit 30 in the embodiment. [Figure 4] This figure shows another modified example of the initial charging circuit 30 in the embodiment. [Figure 5] This figure shows an example configuration of the voltage divider circuit 34. [Figure 6]FIG. 1 is a diagram showing an example of the time change of each voltage of the energy harvesting device 100. [Figure 7] FIG. 3 is a diagram showing another example of the energy harvesting device 100. [Figure 8] FIG. 7 is a flowchart for explaining the operation of the energy harvesting device 100. [Figure 9] FIG. 9 is a graph showing the time change of the voltage of each node and the operation of each part. [Figure 10] FIG. 12 is a diagram showing a modified example of the energy harvesting device 100 shown in FIG. 7. [Figure 11] FIG. 15 is a diagram showing another modified example of the initial charging circuit 30. MODE FOR CARRYING OUT THE INVENTION

[0018] Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution means of the invention.

[0019] In this specification, when referred to as "identical" or "equal", it may include cases having errors due to manufacturing variations or the like. The error is, for example, within 10%. Also, in this specification, expressions such as "connected between... and...", "provided between... and...", or "arranged between... and..." do not limit the physical arrangement, but mean "electrically connected between... and...".

[0020] FIG. 1 is a diagram showing an example of an energy harvesting device 100 including an initial charging circuit 30 in an embodiment of the present invention. The energy harvesting device 100 includes an energy harvesting power source 10, a power supply device 20, and a system 80.

[0021] The energy harvesting power supply 10 may be a power source composed of one or more elements, such as solar power generation, vibration power generation, or electromagnetic wave power supply. If the voltage output by these power sources is too low or too high, the energy harvesting power supply 10 may include a boost converter or a buck converter.

[0022] System 80 is powered by electricity generated by the energy harvesting power supply 10. System 80 is an IoT device consisting of sensors that convert physical quantities such as temperature, illuminance, carbon dioxide concentration, alcohol concentration, and odor into electrical signals, a microcomputer that processes the obtained electrical signals, and equipment that communicates with the outside world (e.g., a Bluetooth® communication device).

[0023] The power supply device 20 is installed between the energy harvesting power supply 10 and the system 80. The power obtained from the energy harvesting power supply 10 is usually small or unstable over time. Therefore, in order to operate the system 80 stably, the power is first stored in an energy storage element such as a capacitor or battery in the power supply device 20, and then supplied to the system 80 from the energy storage element.

[0024] However, in the case of secondary batteries such as lithium-ion batteries, once they are completely discharged, their large capacity means that it takes an enormous amount of time for the system 80 to recover to a voltage that allows it to operate, during which time the system 80 becomes inoperable. Therefore, the power supply device 20 in this example has a first energy storage element 61 and a second energy storage element 62 which has a larger capacity than the first energy storage element 61. The first energy storage element 61 is, for example, an element with a relatively small electrical capacity, such as a ceramic capacitor or a supercapacitor. The second energy storage element 62 is, for example, an element with a relatively large electrical capacity, such as a secondary battery like a nickel-metal hydride battery or a lithium-ion battery.

[0025] Capacitance comparisons can be made by comparing the capacitance [F] for capacitors or capacitors, or by comparing the battery capacity [Ah] for batteries. Alternatively, the electrical capacity of a battery may be considered larger than that of a capacitor or capacitor, and the comparison can be made by comparing the charge [C] obtained by multiplying the capacitance of a capacitor or capacitor by its rated voltage with the battery capacity [Ah=C].

[0026] The first energy storage element 61 is charged by power from the energy harvesting power supply 10. The second energy storage element 62 is also charged by power from the first energy storage element 61. At least one of the first energy storage element 61 or the second energy storage element 62 supplies power to the external system 80. This allows the power supply device 20 to quickly raise the voltage V1 supplied to the system 80 by charging the first energy storage element 61 to a voltage that allows the system 80 to operate, thereby driving the system 80. Voltage V1 is the output voltage of the first energy storage element 61, and voltage V2 is the output voltage of the second energy storage element 62.

[0027] The power supply device 20 has an initial charging circuit 30. The initial charging circuit 30 is provided between the first energy storage element 61 and the second energy storage element 62 and controls the current flowing between the first energy storage element 61 and the second energy storage element 62. The initial charging circuit 30 may charge the second energy storage element 62 by flowing current from the first energy storage element 61 to the second energy storage element 62. For example, current flows to the second energy storage element 62 only when the voltage V1 of the first energy storage element 61 is higher than the minimum voltage at which the system 80 can operate. This allows power from the energy harvesting power supply 10 to be stored, and power can be supplied to the system 80 for a long time by supplying power from the second energy storage element 62 when the output of the energy harvesting power supply 10 is unstable or when more power is needed.

[0028] When the initial charging circuit 30 is off, the first energy storage element 61 may supply power only to the system 80. The connection point between the system 80 and the power supply device 20 may be between the energy harvesting power supply 10 and the first energy storage element 61 and the initial charging circuit 30. In other words, the power supplied from the energy harvesting power supply 10 and the first energy storage element 61 may be supplied to the system 80 without going through the initial charging circuit 30. In this specification, the power supplied from the energy storage element to the system 80, or the power supplied from the first energy storage element 61 to the second energy storage element 62, may also include the power generated by the energy harvesting power supply 10.

[0029] Figure 2 shows an example of an initial charging circuit 30 in an embodiment of the present invention. The initial charging circuit 30 may have an output unit 40 and an operational amplifier 32. The initial charging circuit 30 may further have a voltage divider circuit 34.

[0030] The output unit 40 is provided between the first energy storage element 61 and the second energy storage element 62, and controls the current flowing between the first energy storage element 61 and the second energy storage element according to the output of the operational amplifier 32. In this example, the output unit 40 has a first transistor 41 and a resistor 50. One end of the first transistor 41 is connected to the first energy storage element 61, and the other end is connected to the second energy storage element 62. In this specification, when two elements are referred to as "connected," it may refer to a state in which the two elements are directly connected by wiring, or it may refer to a state in which the two elements are indirectly connected with a resistor in between. "Connected" may also include a state in which the two elements are indirectly connected with an element other than a resistor in between. In this example, the first transistor 41 is a P-type MOSFET, with its source connected to the resistor 50 and its drain connected to the second energy storage element 62. The gate of the first transistor 41 is connected to the output of the operational amplifier 32.

[0031] The resistor 50 is provided between the first transistor 41 and the first energy storage element 61. In this example, one end of the resistor 50 is connected to the first energy storage element 61, and the other end is connected to the source (one end) of the first transistor 41. The resistor 50 in this example has a resistor 46.

[0032] The operational amplifier 32 changes the amount of current flowing between the first energy storage element 61 and the second energy storage element 62 when the first transistor 41 is ON, based on the difference between the voltage VFB1 at one end (source) of the first transistor 41 and the reference voltage Vref. In other words, the amount of current flowing through the first transistor 41 changes in accordance with the change in the output voltage VGATE of the operational amplifier 32. The amount of current flowing through the first transistor 41 can take on multiple values ​​depending on the value of the output voltage VGATE. If the voltage value of the output voltage VGATE changes continuously, the amount of current flowing through the first transistor 41 may also change continuously. If the voltage value of the output voltage VGATE changes discretely, the amount of current flowing through the first transistor 41 may also change discretely. The operational amplifier 32 may output an output voltage VGATE whose voltage value changes continuously, or it may output an output voltage VGATE whose voltage value changes discretely. The operational amplifier 32 in this example is an operational amplifier in which the reference voltage Vref is input to the positive input terminal and the feedback voltage VFB2 is input to the negative input terminal. The reference voltage Vref is, for example, the output voltage of a bandgap reference voltage generation circuit. The operational amplifier 32 does not need to include a comparator. The output voltage VGATE of the operational amplifier 32 is output to the gate of the first transistor 41. The operational amplifier 32 may control the amount of current flowing through the first transistor 41 by changing the output voltage VGATE based on the difference between the voltage VFB2 and the reference voltage Vref in the saturation region of the first transistor 41.

[0033] In this example, the voltage divider circuit 34 is provided between one end of the first transistor 41 (the source terminal in this example) and the negative input terminal of the operational amplifier 32. The source voltage VFB1 of the first transistor 41 is multiplied by 1 / α in the voltage divider circuit 34 and input to the negative input terminal of the operational amplifier 32 as a feedback voltage VFB2. The operational amplifier 32 operates based on the difference between the feedback voltage VFB2 and the reference voltage Vref, thereby operating based on the difference between the voltage VFB1 at one end (source) of the first transistor 41 and the reference voltage Vref. In this specification, the fact that it is based on the difference between the voltage VFB1 at one end of the first transistor 41 and the reference voltage Vref may be expressed as being based on the difference between the voltage VFB1 at one end of the first transistor 41 and α × Vref.

[0034] The initial charging circuit 30 in Figure 2 uses a feedback loop consisting of an operational amplifier 32, an output unit 40, and a voltage divider circuit 34 to allow current to flow from the first energy storage element 61 to the second energy storage element 62, thereby charging the second energy storage element 62, without lowering the voltage V1 of the first energy storage element 61 to below α × Vref. Specifically, when the voltage V1 of the first energy storage element 61 is less than α × Vref, the output VGATE of the operational amplifier 32 in this example rises to near the voltage V1, and the first transistor 41 does not allow current to flow from the first energy storage element 61 to the second energy storage element 62. When sufficient power is supplied from the energy harvesting power supply 10 and the charging of the first energy storage element 61 progresses, and the voltage V1 of the first energy storage element 61 becomes α × Vref or higher, the operational amplifier 32 in this example lowers the output voltage VGATE and turns on the first transistor 41. The decrease in the output voltage VGATE increases as the difference between the voltage V1 and α × Vref increases. Consequently, the current flowing from the first energy storage element 61 to the second energy storage element 62 increases, and the voltage V1 of the first energy storage element 61 decreases. When the voltage V1 of the first energy storage element 61 decreases, the decrease in the output voltage VGATE becomes smaller. Consequently, the current flowing from the first energy storage element 61 to the second energy storage element 62 decreases, and the decrease in the voltage V1 of the first energy storage element 61 is mitigated.

[0035] For example, as described in Patent Document 1, if the first transistor 41 repeatedly switches on and off, ripple-like power supply noise is generated in the output voltage to the system 80. As in this example, by changing the current flowing through the first transistor 41 using the operational amplifier 32, current can be supplied from the first energy storage element 61 to the second energy storage element 62, thereby charging the second energy storage element 62, without generating ripple-like power supply noise.

[0036] Here, the stability of the feedback loop is affected by the poles and zeros of the loop transfer function that forms the loop, but it tends to be unstable due to the phase delay caused by pole P1 generated in the operational amplifier 32 and pole P2 generated in the output section 40. Here, pole P1 is generated, for example, by the output resistance Rop of the operational amplifier 32 and the parasitic capacitance Cop (not shown) driven by the output voltage VGATE of the operational amplifier 32, and is calculated as P1 = 1 / (2π × Rop × Cop) [Hz]. Pole P2 is generated by the transconductance Gm1 of the first transistor 41 and the capacitance C1 of the first energy storage element 61, and is calculated as P2 = Gm1 / (2π × C1) [Hz].

[0037] On the other hand, the resistance value R1 of the resistor 50 (the resistance value of resistor 46 in the case of Figure 2) and the capacitance C1 of the first energy storage element 61 form a zero point Z1 that causes a phase lead, thereby mitigating the influence of pole P2. The zero point Z1 is calculated as Z1 = 1 / (2π × R1 × C1) [Hz]. The stability of the feedback loop is ensured by selecting the resistance value R1 such that the pole P2 and the zero point Z1 are close in value or P2 > Z1.

[0038] Here, the transconductance Gm1 of the first transistor 41 constituting pole P2 increases when the current flowing from the first energy storage element 61 to the second energy storage element 62 increases, and decreases when the current decreases. Therefore, from the above equation, the frequency of pole P2 also increases with increasing current and decreases with decreasing current. As described above, the stability of the feedback loop is ensured if pole P2 and the zero point Z1 are close in value or if P2 > Z1, so when pole P2 rises due to increased current, there is room for the zero point Z1 to rise as well. From the above equation, the zero point Z1 includes the resistance value R1 of the resistor 50 in its denominator, so when the resistance value R1 decreases, the zero point Z1 rises. That is, when the current increases, there is room for the resistance value R1 to decrease. However, in order to satisfy the above relationship between pole P2 and the zero point Z1, it is desirable for the resistance value R1 to increase when the current decreases.

[0039] On the other hand, the voltage drop caused by current flowing through the resistor 50 increases with increasing current if the resistance value R1 of the resistor 46 shown in Figure 2 is fixed, resulting in heat loss and reducing charging efficiency. Therefore, from the viewpoint of charging efficiency, it is desirable that the resistance value R1 of the resistor 50 decreases as the current increases. In summary, by having the resistance value R1 decrease with increasing current and increase with decreasing current, it is possible to prevent a decrease in charging efficiency while ensuring the stability of the feedback loop.

[0040] Figure 3 shows a modified example of the initial charging circuit 30 in the embodiment. The initial charging circuit 30 in this example differs from the initial charging circuit 30 shown in Figure 2 in that the resistor 50 has a second transistor 42. The second transistor 42 in this example is a P-type MOSFET. The drain of the second transistor 42 is connected to the source of the first transistor 41, and the source of the second transistor 42 is connected to the first energy storage element 61.

[0041] The gate of the second transistor 42 is connected to the output of the operational amplifier 32 along with the gate of the first transistor 41, and both are input to the output voltage VGATE. That is, the operational amplifier 32 changes the on-resistance of the second transistor 42 when it is on, based on the difference between the voltage at one end of the first transistor 41 and α × Vref. The second transistor 42 may operate in the linear region.

[0042] The absolute value of the threshold voltage of the second transistor 42 may be greater than the absolute value of the threshold voltage of the first transistor 41. For example, the threshold voltage VTP2 of the second transistor 42 is -0.6V, and the threshold voltage VTP1 of the first transistor 41 is -0.4V.

[0043] When the voltage V1 of the first energy storage element increases or decreases, the feedback loop of the initial charging circuit 30 controls the output voltage VGATE so that the feedback voltage VFB2 approaches the reference voltage Vref, and controls the current flowing from the first energy storage element 61 to the second energy storage element 62 through the first transistor 41 and the second transistor 42 so that the source voltage VFB1 of the first transistor 41 is equal to α × Vref.

[0044] In the initial charging circuit 30 of this example, the resistance value R1 of the resistor 50 that determines the zero point Z1 is the on-resistance of the second transistor 42. This on-resistance is controlled by the output voltage VGATE of the operational amplifier 32. When the current flowing from the first energy storage element 61 to the second energy storage element 62 decreases (or becomes small), the output voltage VGATE increases and the on-resistance increases, and when the incoming current increases (or becomes large), the output voltage VGATE decreases and the on-resistance decreases. In other words, the zero point Z1 decreases as the current decreases and the zero point Z1 increases as the current increases.

[0045] On the other hand, the transconductance Gm1 of the first transistor 41 that determines pole P2 also decreases when the current flowing from the first energy storage element 61 to the second energy storage element 62 decreases (or becomes small), as the output voltage VGATE increases and transconductance Gm1 decreases, causing pole P2 to also decrease. Conversely, when the incoming current increases (or becomes large), the output voltage VGATE decreases and transconductance Gm1 increases, causing pole P2 to also increase. As a result, pole P2 and the zero point Z1 change in the same direction of increase or decrease according to the current flowing from the first energy storage element to the second energy storage element, ensuring stability. Furthermore, when the current is large, the on-resistance of the second transistor 42 decreases, preventing a decrease in charging efficiency due to voltage drop.

[0046] In this example, the second transistor 42 is a P-type MOSFET, but the second transistor 42 may also be an N-type MOSFET. The conductivity type of the first transistor 41 and the conductivity type of the second transistor 42 may be the same.

[0047] Figure 4 shows another modified example of the initial charging circuit 30 in the embodiment. The initial charging circuit 30 in Figure 4 has a third transistor 43 in the output section 40, in addition to the configuration of the modified example in Figure 3. Furthermore, the resistor section 50 in this example has a first resistor 51 and a second resistor 52, in addition to the configuration of the modified example in Figure 3.

[0048] The third transistor 43 has one end connected to the first energy storage element 61 and the other end connected to the second energy storage element 62. It is also connected in parallel with the first transistor 41 and the resistor 50. In this example, the third transistor 43 is a P-type MOSFET. In this example, the drain of the third transistor 43 is connected to the second energy storage element 62 and the source is connected to the first energy storage element 61.

[0049] The gate of the third transistor 43 is connected to the output of the operational amplifier 32, along with the gates of the first transistor 41 and the second transistor 42, and the output voltage VGATE is input to all of them. That is, the operational amplifier 32 changes the amount of current when the third transistor 43 is ON, based on the difference between the voltage at one end of the first transistor 41 and α × Vref. The above amount of current is the amount of current flowing between the first energy storage element 61 and the second energy storage element 62. The above amount of current may be the amount of current flowing from the drain to the source of the third transistor 43.

[0050] Since the first transistor 41 and the second transistor 42 are connected in series, the area of ​​the first transistor 41 and the second transistor 42 must be increased when the current flowing through the output section 40 is large. In contrast, the third transistor 43 added in this example is provided in parallel with the first transistor 41 and the second transistor 42, so it can carry the same current in an area of ​​about half to one-quarter of the area occupied by the first transistor 41 and the second transistor 42. Therefore, by selecting the size of each transistor so that the current flowing through the third transistor 43 is 10 to 100 times the current flowing through the first transistor 41, the area occupied by the initial charging circuit 30 within the integrated circuit can be reduced.

[0051] The absolute value of the threshold voltage of the third transistor 43 may be greater than or less than the threshold voltages of the first transistor 41 and the second transistor 42, and the absolute values ​​of the threshold voltages of each transistor may be equal. In this example, the third transistor 43 is a P-type MOSFET, but the third transistor 43 may be an N-type MOSFET. The conductivity types of the first transistor 41, the second transistor 42, and the third transistor 43 may all be the same.

[0052] The first resistor 51 may be connected in series with the second transistor 42. In this example, the first resistor 51 is provided between the source of the second transistor 42 and the first energy storage element 61. By providing the first resistor 51, the lower limit of the resistance value R1 of the resistor section 50 can be limited. Therefore, when a large current flows through the output section 40, the on-resistance of the second transistor 42 becomes too small, preventing the frequency of the zero point Z1 from becoming too high and ensuring stability at high currents.

[0053] The second resistor 52 may be connected in parallel with the second transistor 42. Connecting in parallel with the second transistor 42 includes cases where it is connected in parallel only with the second transistor 42, and cases where it is connected in parallel with other elements connected in series with the second transistor 42 (except for the first transistor 41). Connecting in parallel only with the second transistor 42 means that one end of the second resistor 52 is connected to the source of the second transistor 42 and the other end is connected to the drain of the second transistor 42. In this example, the second resistor 52 is connected in parallel with the second transistor 42 and the first resistor 51 (another element) connected in series with the second transistor 42. In this example, one end of the second resistor 52 is connected to the first energy storage element 61 and the other end is connected to the source of the first transistor 41. When the voltage V1 of the first energy storage element 61 drops, the current flowing through the first transistor 41 and the second transistor 42 approaches zero, and the second transistor 42 turns off, the source voltage VFB1 of the first transistor 41 may become unstable. In that case, the input voltage of the operational amplifier 32 becomes unstable, which may cause the feedback loop to run out of control or oscillate. By providing the second resistor 52, even when the second transistor 42 turns off, VFB1 = V1, and the input voltage of the operational amplifier 32 stabilizes, thus preventing the feedback loop from running out of control or oscillating.

[0054] In summary, in the modified configuration shown in Figure 4, the second energy storage element 62 can be efficiently charged over a wide current range in response to a wide range of input power without lowering the voltage V1 of the first energy storage element 61 below α × Vref.

[0055] The resistance value of the second resistor 52 may be greater than the resistance value of the first resistor 51. Also, although the third transistor 43, the first resistor 51, and the second resistor 52 are all provided in Figure 4, any one of these may be provided, or any two of them may be provided.

[0056] Figure 5 shows an example configuration of a voltage divider circuit 34. In this example, the voltage divider circuit 34 has a voltage tap 36 and a selection switch 38. The voltage tap 36 has multiple taps divided by multiple resistors, as shown in Figure 5. The selection switch 38 has multiple switches corresponding to the multiple taps. Each of the multiple taps is configured to be selected by a switch, and based on the selected tap, 1 / α of the source voltage VFB1 is output as the feedback voltage VFB2. When the tap selection is feedback controlled, it is desirable that the voltage of the source voltage VFB1 be set to be the same as or higher than the minimum operating voltage of the system 80. The value of α is a positive real number other than 0.

[0057] Figure 6 shows an example of the time variation of each voltage in the energy harvesting device 100 shown in Figure 1. When power is supplied from the energy harvesting power supply 10, the voltage V1 of the first energy storage element 61 rises rapidly. Until the voltage V1 reaches α × Vref at time T1, the feedback voltage VFB2 < reference voltage Vref, so no current is supplied to the second energy storage element 62, and the voltage V2 of the second energy storage element does not rise.

[0058] When voltage V1 reaches α × Vref at time T1, the feedback loop works so that the feedback voltage VFB2 ≈ reference voltage Vref. As a result, the output voltage VGATE of the operational amplifier 32 decreases, and voltage V1 is maintained at the same value as or slightly higher than α × Vref. If α × Vref is set to a value above the minimum voltage at which system 80 can operate, system 80 becomes operational after time T1. Then, the excess power flows into the second energy storage element 62, and voltage V2 begins to slowly rise.

[0059] As voltage V2 increases and the potential difference between voltages V1 and V2 decreases, the absolute value of the drain-source voltage of the first transistor 41 decreases, and it transitions from the saturation region to the linear region. In the linear region, current flows less easily, so the feedback loop lowers the output voltage VGATE, reducing the on-resistance between the first energy storage element 61 and the second energy storage element 62, so that at time T2, voltage V1 ≈ V2 ≈ α × Vref. After time T2, V1 ≈ V2 > α × Vref, and the operational amplifier 32 further lowers the output voltage VGATE, simultaneously charging both the first energy storage element 61 and the second energy storage element 62, and supplying power to the system 80 from both the first and second energy storage elements 61 and 62.

[0060] In this embodiment, the initial charging circuit 30 allows for rapid charging of only the first energy storage element 61, enabling the system 80 to be started without generating ripple due to switching. Furthermore, in the region where V1 ≈ V2 > α × Vref after time T2, the second energy storage element 62 can be charged and discharged with high efficiency, supplying stable power to the system 80.

[0061] Figure 7 shows another example of the energy harvesting device 100. In this example, the energy harvesting device 100 has a power supply unit 20 which has a second voltage monitoring unit 92. The power supply unit 20 may further include a control unit 90. The power supply unit 20 may further include a first voltage monitoring unit 91, a switch S1, and a switch S2.

[0062] The second voltage monitoring unit 92 monitors the voltage V2 of the second energy storage element 62. The second voltage monitoring unit 92 may directly monitor the output voltage V2 of the second energy storage element 62, or it may indirectly monitor the output voltage V2 as described later. The second voltage monitoring unit 92 may output an output signal corresponding to the voltage V2. In this example, the second voltage monitoring unit 92 outputs a logic signal output Vdet2 to the control unit 90 according to the state of the voltage V2 of the second energy storage element 62. As an example, the second voltage monitoring unit 92 outputs Vdet2="1" when V2 > Vth2, and outputs Vdet2="0" otherwise.

[0063] System 80 may have multiple operating modes with different power consumption. Examples of operating modes include a mode that performs minimal operations, such as using a communication function to inform the host computer that there is insufficient power (low-power mode), and a mode that performs operations such as acquiring environmental data using sensors that consume more power or performing complex signal processing (power-consuming mode).

[0064] The power supply device 20 may output a switching signal PGOOD to switch the operating mode of the system 80 in response to the output signal of the second voltage monitoring unit 92. In the power supply device 20 of this example, the control unit 90, upon receiving the output signal of the second voltage monitoring unit 92, outputs a switching signal PGOOD to notify the system 80 that the second energy storage element 62 is enabled. The second energy storage element 62 being enabled may mean that sufficient power is available, and may mean that V2 > Vth2. That is, the control unit 90 may determine whether the second energy storage element 62 is enabled or not based on whether the second voltage monitoring unit 92 outputs Vdet2="1". However, the second voltage monitoring unit 92 may also directly output a logic signal Vdet2 to the system 80.

[0065] The microcomputer of system 80 can determine whether the second energy storage element 62 is active based on the switching signal PGOOD, and decide whether to switch to an operating mode that requires more power and performs more complex processing. For example, when the switching signal PGOOD is "0" and the second energy storage element 62 is not active, system 80 is in low-power mode, minimizing the power used by system 80 and using the surplus power to charge the second energy storage element 62. When the switching signal PGOOD is "1" and the second energy storage element 62 is active, system 80 determines that sufficient power is supplied and implements a power consumption mode.

[0066] Switch S1 is provided between the first power storage element 61 and the system 80. A voltage VSYS controlled by the switch S1 is supplied to the system 80. The switch S2 is provided in parallel with the initial charging circuit 30 between the first power storage element 61 and the second power storage element 62. The switch S2 and the initial charging circuit 30 in this example are provided between the connection point of the first power storage element 61 and the system 80 and the second power storage element 62.

[0067] The first voltage monitoring unit 91 monitors the voltage V1 of the first power storage element 61 and outputs a logic signal output Vdet1 according to the state of the voltage V1. The first voltage monitoring unit 91 may be a hysteresis comparator that outputs Vdet1 = "1" when V1 > Vth1_H, outputs Vdet1 = "0" when V1 < Vth1_L, and holds the previous value otherwise.

[0068] The control unit 90 controls the operation of the initial charging circuit 30. The control unit 90 may output a control signal CT1 for controlling the on / off of the switch S1, a control signal CT2 for controlling the on / off of the switch S2, and a control signal CT3 for controlling the on / off of the initial charging circuit 30 based on the logic value of Vdet1 or Vdet2. For example, the control signal CT1 is output based on Vdet1, and when Vdet1 = "1", the switch S1 is turned on to start power supply from the first power storage element 61 to the system 80. The control unit 90 may control the switch S2 to be in the on state when the output voltage of the second power storage element 62 becomes greater than a predetermined value. The control unit 90 may control the switch S2 to be in the on state according to the output signal of the second voltage monitoring unit 92. For example, the control signal CT2 is output based on Vdet2, and when Vdet2 = "1", the switch S2 is turned on to start power supply from the second power storage element 62 to the system 80. The switch S1 and the switch S2 may be transistors.

[0069] Turning the initial charging circuit 30 ON indicates that the initial charging circuit 30 is in an operating state corresponding to the voltage V1 as described above. On the other hand, turning the initial charging circuit 30 OFF means that the current path from the first energy storage element 61 to the second energy storage element 62, passing through the output section 40 of the initial charging circuit 30, is interrupted. The state in which the current path from the first energy storage element 61 to the second energy storage element 62 is interrupted can be achieved, for example, in Figure 4 by connecting the output signal VGATE to the voltage V1 of the first energy storage element 61 or the higher voltage between voltage V1 and the voltage V2 of the second energy storage element 62. Alternatively, as another method of interrupting the current path from the first energy storage element 61 to the second energy storage element 62, a switch that disconnects the first energy storage element 61 and the output section 40, or a switch that disconnects the output section 40 and the second energy storage element 62, or multiple switches that disconnect both may be added. The above switches may be controlled by the control signal CT3.

[0070] Vth1_L may be set to a voltage at which the system can operate and above the battery discharge stop voltage. For example, when using a 3.7V lithium-ion battery, Vth1_L may be set to 2.9V, and Vth1_H may be set to be higher than Vth1_L and above the battery discharge start voltage. For example, when using a 3.7V lithium-ion battery, Vth1_H may be set to 3.3V. In that case, α of the initial charging circuit 30 is set so that, for example, α × Vref = Vth1_H = 3.3V, and Vth2 is set to, for example, 3.4V.

[0071] Figure 8 is a flowchart illustrating the operation of the energy harvesting device 100 shown in Figure 7. Figure 9 is a graph showing the time evolution of the voltage at each node and the operation of each part. Figure 9 shows, from top to bottom, graphs of the time evolution of voltages V1 and V2, voltage VSYS, and the switching signal PGOOD. Below that, the on / off states of switch S1, switch S2, the initial charging circuit 30, and the system 80 are shown. The operation of the energy harvesting device 100 shown in Figure 7 will be described below in accordance with Figures 8 and 9.

[0072] At the start of operation, the voltage V1 of the first energy storage element 61 and the voltage V2 of the second energy storage element 62 are low. This state corresponds to mode 0 in Step 1 of the flowchart, where switches S1 and S2 and the initial charging circuit 30 are all in the off state, no voltage is supplied to the system 80, and the second energy storage element 62 is in the off state.

[0073] When power is supplied from the energy harvesting power supply 10, the voltage V1 begins to rise. If the voltage V1 exceeds Vth1_H = 3.3V at time T1, the system transitions to mode 1 in Step 3, according to the judgment in Step 2 of the flowchart. In mode 1, switch S1 is turned on, and the initial charging circuit 30 is turned on, but switch S2 is off, and the switching signal PGOOD also outputs 0V.

[0074] When switch S1 is turned on, the voltage VSYS increases and is supplied to system 80. At this time, system 80 starts low-power operation OP1 (e.g., low-power mode) according to PGOOD=0V. In this example, since the power from the energy harvesting power supply 10 is less than the power consumed by system 80, voltages V1 and VSYS gradually decrease. Also, when V1 < α × Vref = 3.3V, the initial charging circuit 30 does not supply current to the second energy storage element 62, so the voltage V2 of the second energy storage element 62 does not change.

[0075] If the voltage V1 falls below Vth1_L = 2.9V at time T2, according to the determination in Step 4, the system returns to mode 0 of Step 1, and switches S1, S2, and the initial charging circuit 30 all return to the off state, no longer supplying voltage to the system 80, so the voltage V1 starts rising again. After that, the operation from time T3 to time T5 is the same as from time T1 to time T3.

[0076] At time T5, the system enters Mode 1 of Step 3. If the power from the energy harvesting power supply 10 is greater than the power consumption of the system 80 at this time, the initial charging circuit 30 maintains the voltage V1 at α × Vref = 3.3V and supplies the remaining power to the second energy storage element 62, causing the voltage V2 of the second energy storage element 62 to rise.

[0077] If the voltage V2 of the second energy storage element 62 exceeds Vth2 = 3.4V at time T6, the system transitions to mode 2 in Step 6 according to the judgment in Step 5. In mode 2, switch S2 is turned on, the initial charging circuit 30 is turned off, and the switching signal PGOOD outputs a voltage V1 with a logic output of "1".

[0078] With switch S2 turned on, charging and discharging of the first energy storage element 61 from the second energy storage element 62 becomes possible, and the combined power of the first energy storage element 61 and the second energy storage element 62 is supplied to the system 80. The system 80 can perform high-power operation OP2 (for example, power consumption mode) according to PGOOD=V1 (=VSYS).

[0079] In Mode 2, the system 80 operates stably by charging both the first and second energy storage elements 61 and 62 when the power supplied from the energy harvesting power supply 10 is large, and by discharging from both the first and second energy storage elements 61 and 62 when the supplied power is small. In Figure 9, the slope of the voltage change from time T6 to time T7 is depicted as steep, but in reality, because the capacity of the second energy storage element 62 is large, the voltage change is very slow and also lasts for a long time.

[0080] In Mode 2, the system continues stable operation, but at time T7, when the power of the first energy storage element 61 and the second energy storage element 62 is depleted and the voltage V1 falls below Vth1_L=2.9V, the system transitions to Mode 3 in Step 8 according to the judgment in Step 7 of the flowchart. In Mode 3, switches S1 and S2 remain on, and the switching signal PGOOD outputs 0V, which corresponds to the logical output "0". The system 80 senses from the change in the switching signal PGOOD that the remaining charge of the second energy storage element 62 is decreasing and performs necessary processing, such as appropriately terminating the ongoing operation or saving data to non-volatile memory.

[0081] After transitioning to Step 8, and after a predetermined delay time has elapsed, the system transitions to Mode 0 in Step 9, returning to the initial state. In this example, the delay time is 1 second. The delay time from Step 8 to Step 9 may be longer or shorter than 1 second, taking into account the time required for the system 80 to execute the processing. Since the duration of Mode 3 is short, it is not shown in Figure 9.

[0082] From time T7 onwards in Figure 9, the flowchart returns to its initial Step 1, and times T8 and T9 are the same as times T1 and T2, respectively. Thus, the energy harvesting device 100 in Figure 7 does not require an external power source or a coin cell battery or AA battery that needs to be replaced, and can achieve stable operation with only the energy harvesting power supply 10.

[0083] Figure 10 shows a modified example of the energy harvesting device 100 shown in Figure 7. In this example, the energy harvesting device 100 is equipped with a third voltage monitoring unit 93 in place of the second voltage monitoring unit 92 in the power supply device 20. The third voltage monitoring unit 93 monitors the output voltage VGATE of the operational amplifier 32 of the initial charging circuit 30.

[0084] In the example shown in Figure 7, the operating mode of the system 80 is switched by monitoring the voltage V2 of the second energy storage element 62. However, as shown in Figure 6, when both the voltage V1 of the first energy storage element 61 and the voltage V2 of the second energy storage element 62 reach α × Vref, the output voltage VGATE of the operational amplifier 32 of the initial charging circuit 30 drops sharply. Therefore, as shown in Figure 10, a third voltage monitoring unit 93 may be provided to monitor when the output voltage VGATE has dropped below a predetermined voltage instead of the voltage V2. The third voltage monitoring unit 93 may output an output signal corresponding to the output voltage VGATE. In this example, the third voltage monitoring unit 93 outputs a logic signal output Vdet2 corresponding to the output voltage VGATE to the control unit 90.

[0085] The power supply device 20 may output a switching signal to switch the operating mode of the system 80 according to the output voltage VGATE of the operational amplifier 32. In the power supply device 20 of this example, the control unit 90 outputs a switching signal PGOOD to notify the system 80 that the second energy storage element 62 is enabled. In this example, whether or not the second energy storage element 62 is enabled may be determined by whether or not the output voltage VGATE has dropped below a predetermined voltage. However, the third voltage monitoring unit 93 may also output a logic signal output Vdet2 directly to the system 80.

[0086] In the example in Figure 7, the timing of the transition to mode 2 in the flowchart is determined by monitoring the voltage V2 of the second energy storage element 62, but in this example, the timing of the transition to mode 2 may be determined by monitoring the output voltage VGATE. For example, the transition to mode 2 may occur when the output voltage VGATE becomes smaller than a predetermined value. The control unit 90 may control switch S2 to the ON state when the output voltage VGATE of the operational amplifier 32 becomes smaller than a predetermined value. The control unit 90 may control switch S2 to the ON state in accordance with the output signal of the third voltage monitoring unit 93. This also allows for a low-resistance connection between the first energy storage element 61 and the second energy storage element 62.

[0087] Figure 11 shows a modified example of the initial charging circuit 30. In this example, the initial charging circuit 30 has a fourth transistor 44 in addition to the configuration of the initial charging circuit 30 shown in Figure 4. The fourth transistor 44 in this example is an N-type MOSFET. One end (drain) of the fourth transistor 44 is connected to the output of the operational amplifier 32, and the other end (source) of the fourth transistor 44 is connected to ground (0V). In other words, the drain of the fourth transistor 44 is connected to the gates of the first transistor 41, the second transistor 42, and the third transistor 43.

[0088] The gate of the fourth transistor 44 is connected to the control unit 90 in Figure 7, and the control signal CT2 is input to it. The control unit 90 may control the third transistor 43 of the initial charging circuit 30 to the ON state when the voltage V2 of the second energy storage element 62 becomes greater than a predetermined value. The control unit 90 may control the third transistor 43 to the ON state according to the output signal of the second voltage monitoring unit 92. In this example, when the control unit 90 receives Vdet2="1" from the second voltage monitoring unit 92, it adjusts the control signal CT2 to turn on the fourth transistor 44. As a result, the third transistor 43 is turned on. This connects the first energy storage element 61 and the second energy storage element 62 with low resistance. At this time, the first transistor 41 may be controlled to the OFF state or to the ON state. Similarly, the second transistor 42 may be controlled to the OFF state or to the ON state. At this time, it is desirable that the operational amplifier 32 is turned off. In other words, in the example of Figure 7, the switch S2 is provided in parallel with the initial charging circuit 30, but in this example, the output section 40 of the initial charging circuit 30 is used as the switch S2. The control unit 90 may control the first transistor 41 of the initial charging circuit 30 to the ON state, or the second transistor 42 to the ON state, when the voltage V2 of the second energy storage element 62 becomes greater than a predetermined value. At this time, the third transistor 43 may be controlled to the OFF state or to the ON state.

[0089] As shown in Figure 10, the power supply device 20 may include a third voltage monitoring unit 93 instead of a second voltage monitoring unit 92. In that case, the control unit 90 may control the third transistor to be turned on based on the output voltage VGATE of the operational amplifier 32 shown in Figure 10, instead of the voltage V2 of the second energy storage element 62. The control unit 90 may control the third transistor to be turned on when the output voltage VGATE of the operational amplifier 32 becomes smaller than a predetermined value. The control unit 90 may control the third transistor 43 to be turned on in accordance with the output signal of the third voltage monitoring unit 93. The control unit 90 may control the third transistor 43 to be turned on by adjusting the control signal CT2 to control the fourth transistor 44 to be turned on. This also allows for a low-resistance connection between the first energy storage element 61 and the second energy storage element 62.

[0090] The fourth transistor 44 may be provided in any of the initial charging circuits 30 shown in Figures 2 to 4. The fourth transistor 44 may be a P-type MOSFET. The conductivity type of the fourth transistor 44 may be the same as or different from that of the other transistors. In addition, the initial charging circuit 30 in this example may be provided in the energy harvesting device 100 shown in Figure 10. In that case, the control unit 90 obtains the state of the voltage V2 of the second energy storage element 62 from the third voltage monitoring unit 93.

[0091] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications or improvements can be made to the above embodiments. It will be clear from the claims that such modified or improved forms may also be included in the technical scope of the present invention.

[0092] It should be noted that the execution order of operations, procedures, steps, and stages in the apparatus, systems, programs, and methods shown in the claims, specifications, and drawings is not explicitly stated as "before," "prior to," etc., and that these can be implemented in any order unless the output of a previous process is used in a later process. Even if the operation flow in the claims, specifications, and drawings is described using phrases such as "first," "next," etc. for convenience, it does not mean that it is essential to perform the operations in that order. [Explanation of symbols]

[0093] 10...Energy harvesting power supply, 20...Power supply device, 30...Initial charging circuit, 32...Operational amplifier, 34...Voltage divider circuit, 36...Voltage tap, 38...Selection switch, 40...Output section, 41...First transistor, 42...Second transistor, 43...Third transistor, 44...Fourth transistor, 46...Resistor, 50...Resistor section, 51...First resistor, 52...Second resistor, 61...First energy storage element, 62...Second energy storage element, 80...System, 90...Control section, 91...First voltage monitoring section, 92...Second voltage monitoring section, 93...Third voltage monitoring section, 100...Energy harvesting device

Claims

1. An initial charging circuit that controls the current flowing between a first energy storage element, which stores energy from an energy harvesting power source, and a second energy storage element, which has a larger capacity than the first energy storage element and stores energy from the first energy storage element, The initial charging circuit described above is A resistor with one end connected to the first energy storage element, A first transistor having one end connected to the other end of the resistor and the other end connected to the second energy storage element, An operational amplifier that changes the amount of current flowing between the first energy storage element and the second energy storage element when the first transistor is in the ON state, based on the difference between the voltage at one end of the first transistor and a reference voltage. An initial charging circuit having the following features.

2. The first transistor is a first-conductivity type MOSFET, The resistive portion includes a second transistor which is a first-conductivity type MOSFET. The operational amplifier changes the on-resistance of the second transistor when it is in the ON state based on the difference between the voltage at one end of the first transistor and the reference voltage. The initial charging circuit according to claim 1.

3. The absolute value of the threshold voltage of the second transistor is greater than the absolute value of the threshold voltage of the first transistor. The initial charging circuit according to claim 2.

4. The initial charging circuit has a third transistor, which is a first-conductivity type MOSFET, with one end connected to the first energy storage element and the other end connected to the second energy storage element, and connected in parallel with the first transistor and the resistor. The operational amplifier changes the amount of current flowing between the first and second energy storage elements when the third transistor is in the ON state, based on the difference between the voltage at one end of the first transistor and the reference voltage. The initial charging circuit according to claim 2.

5. The resistor has a first resistor connected in series with the second transistor. The initial charging circuit according to claim 2.

6. The resistor has a second resistor connected in parallel with the second transistor. The initial charging circuit according to claim 2.

7. An initial charging circuit according to any one of claims 1 to 6, The first energy storage element and, The second energy storage element and Equipped with, At least one of the first energy storage element or the second energy storage element supplies power to an external system. Power supply device.

8. The system includes a voltage monitoring unit that monitors the output voltage of the second energy storage element and outputs an output signal corresponding to the output voltage, Depending on the output signal, the system outputs a switching signal to switch to an operating mode with different power consumption. The power supply device according to claim 7.

9. The operational amplifier is equipped with a voltage monitoring unit that monitors the output voltage and outputs an output signal corresponding to the output voltage, Depending on the output voltage, the system outputs a switching signal to switch to an operating mode with different power consumption. The power supply device according to claim 7.

10. The initial charging circuit according to claim 4, The first energy storage element and, The second energy storage element and, A voltage monitoring unit that monitors the output voltage of the second energy storage element, A control unit that controls the initial charging circuit and Equipped with, At least one of the first energy storage element or the second energy storage element supplies power to an external system. The control unit controls the third transistor of the initial charging circuit to turn on when the output voltage becomes greater than a predetermined value. Power supply device.

11. The initial charging circuit comprises a fourth transistor, one end of which is connected to the output of the operational amplifier and the other end of which is connected to ground. When the output voltage exceeds a predetermined value, the control unit controls the fourth transistor to be turned on, thereby controlling the third transistor to be turned on. The power supply device according to claim 10.

12. The initial charging circuit according to claim 4, The first energy storage element and, The second energy storage element and, A voltage monitoring unit that monitors the output voltage of the operational amplifier, A control unit that controls the initial charging circuit and Equipped with, At least one of the first energy storage element or the second energy storage element supplies power to an external system. The control unit controls the third transistor of the initial charging circuit to turn on when the output voltage falls below a predetermined value. Power supply device.

13. The initial charging circuit comprises a fourth transistor, one end of which is connected to the output of the operational amplifier and the other end of which is connected to ground. When the output voltage falls below a predetermined value, the control unit controls the fourth transistor to be turned on, thereby controlling the third transistor to be turned on. The power supply device according to claim 12.

14. A voltage monitoring unit that monitors the output voltage of the second energy storage element, A control unit that controls the initial charging circuit, A switch connected in parallel with the initial charging circuit is placed between the first energy storage element and the second energy storage element. Equipped with, The control unit controls the switch to the ON state when the output voltage becomes greater than a predetermined value. The power supply device according to claim 7.

15. A voltage monitoring unit that monitors the output voltage of the operational amplifier, A control unit that controls the initial charging circuit, A switch connected in parallel with the initial charging circuit is placed between the first energy storage element and the second energy storage element. Equipped with, The control unit controls the switch to the ON state when the output voltage falls below a predetermined value. The power supply device according to claim 7.

16. The power supply device according to claim 7, The aforementioned system, The aforementioned energy harvesting power supply and An energy harvesting device equipped with the following features.

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