Booster device and booster system

Abstract

To provide a booster device and a booster system that can efficiently obtain necessary power from a thermionic element.SOLUTION: A booster device includes a positive electrode terminal to which a positive electrode of a thermionic element is connected, a negative electrode terminal to which a negative electrode is connected, an induction element that has first and second terminals, the first terminal being connected to the positive electrode terminal, a first switch element that has a first control terminal, a first input terminal, and a first output terminal, the first input terminal being connected to the second terminal of the induction element, the first output terminal being connected to the negative electrode terminal, a second switch element that has a second control terminal, a second input terminal, and a second output terminal, the second input terminal being connected to the second terminal of the induction element, and a control unit that boosts DC power outputted from the thermionic element. An internal resistance of the thermionic element, a DC resistance of the induction element, an ON resistance of the first switch element, a wiring resistance, an input voltage, and an output voltage satisfy a prescribed condition expression.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a boosting device and a boosting system.

Background Art

[0002] Conventionally, technologies related to so-called DC-DC converters that boost the voltage of input DC power and output it have been disclosed (for example, refer to Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, IoT (Internet of Things) devices have been developing. In such IoT devices, thermoelectric power generation that generates electricity from the heat flow in the environment is expected to secure an operating power supply. However, the current thermoelectric elements have an extremely low power generation voltage of 1 mV or less per thermoelectric element. On the other hand, it is necessary to secure a voltage (for example, about 1 V) at which a general electronic circuit that provides a sensor function or a communication function provided in an IoT device operates. There has been a problem in efficiently obtaining power at a required voltage from the low voltage generated by the thermoelectric elements as described above.

[0005] This invention has been made in view of the above circumstances, and aims to provide a voltage booster and a voltage booster system that can efficiently obtain the required voltage from a thermoelectric element. [Means for solving the problem]

[0006] One embodiment of the present invention includes a thermoelectric material that converts a temperature difference into DC power, a thermoelectric element comprising a positive electrode terminal to which the positive electrode of a thermoelectric element is connected, a negative electrode terminal to which the negative electrode is connected, an inductive element comprising a first terminal and a second terminal, with the first terminal connected to the positive electrode terminal, a first control terminal, a first input terminal, and a first output terminal, with the first input terminal connected to the second terminal of the inductive element and the first output terminal connected to the negative electrode terminal, a second switch element comprising a second control terminal, a second input terminal, and a second output terminal, with the second input terminal connected to the second terminal of the inductive element, and a first control signal being transmitted to the first control terminal of the first switch element. The boost converter comprises a control unit that outputs a second control signal to the second control terminal of the second switch element with a predetermined duty cycle, thereby boosting the DC power output by the thermoelectric element by alternately turning the first switch element and the second switch element on and off, wherein the internal resistance of the thermoelectric element is RIN, the DC resistance of the inductive element is RL, the on-resistance of the first switch element is RON, the wiring resistance from the positive terminal to the negative terminal via the inductive element and the first switch element is RCAB, the output voltage of the thermoelectric element when the positive terminal and the negative terminal are open is VOC, and the boosted power output to a load connected between both ends of the output terminal is output power POUT, and the boost converter satisfies the conditional equation described below.

[0007] One embodiment of the present invention is a single-layer thermoelectric element in which, in the above-described booster device, the thermoelectric element is provided with only one set of the thermoelectric material, the positive electrode and the negative electrode on the current path of the DC power.

[0008] In one embodiment of the present invention, in the boost converter described above, the first time, which is the time during which the first control signal keeps the first switch element in the ON state, and the second time, which is the time during which the second control signal keeps the second switch element in the ON state, are such that the first time is 100 times or more the second time.

[0009] One embodiment of the present invention is a boost converter described above, wherein the inductance of the inductive element is 0.1 millihenry or more, and the control unit controls the on / off state of the first and second switch elements by setting a first switching frequency, in which the on time during which the first control signal keeps the first switch element in the ON state and the off time during which the first switch element keeps the first switch element in the OFF state constitutes one cycle, and a second switching frequency, in which the on time during which the second control signal keeps the second switch element in the ON state and the off time during which the second switch element keeps the second switch element in the OFF state constitutes one cycle, both between 100 Hz and 5 kHz.

[0010] In one embodiment of the present invention, in the boost converter described above, the control unit controls the on / off state of the first switch element and the second switch element such that the time for which the first control signal maintains the first switch element in the ON state and the time for which the second control signal maintains the second switch element in the ON state do not overlap.

[0011] One embodiment of the present invention is a boost converter described above, in which the gate capacitance of the first switch element is C1, the gate capacitance of the second switch element is C2, the gate voltage applied to the first control terminal and the second control terminal is VCONT, the period of the waveform of the coil current flowing through the inductor element is τ, the internal resistance of the thermoelectric element is RIN, the DC resistance of the inductor element is RL, the on-resistance of the first switch element is RON, the combined resistance of the wiring from the positive terminal to the negative terminal via the inductor element and the first switch element is RCAB is RS, and the output voltage of the thermoelectric element when the positive terminal and the negative terminal are open is VOC, and the following conditional equation is satisfied.

[0012] One embodiment of the present invention is a boost converter described above, in which the internal resistance RIN of the thermoelectric element, the DC resistance RL of the inductive element, the on-resistance RON of the first switch element, and the wiring resistance RCAB from the positive terminal through the inductive element and the first switch element to the negative terminal are all less than 10 milliohms.

[0013] In one embodiment of the present invention, a boost circuit comprising the positive terminal, the negative terminal, the inductive element, the first switch element, and the second switch element is connected in cascaded order in the boost device described above.

[0014] One embodiment of the present invention is a boost system comprising a thermoelectric material that converts a temperature difference into DC power, a thermoelectric element consisting of a positive electrode and a negative electrode connected to the thermoelectric material and extracting the DC power from the thermoelectric material, and a boost device according to any one of claims 1 to 7.

[0015] One embodiment of the present invention is a boost system described above, in which the load resistor R connected to the output side of the boost device satisfies the following condition when T1 is the time during which the first switch element is kept in the ON state and T2 is the time during which the first switch element is kept in the OFF state.

[0016] One embodiment of the present invention is a boost system described above in which, when a load resistor is connected to the output side of the boost device, the voltage at the output terminal is half the voltage when the output terminal is open. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a voltage booster and a voltage booster system that can efficiently obtain the required voltage power from a thermoelectric element. [Brief explanation of the drawing]

[0018] [Figure 1] This figure shows an example of the configuration of the single-layer thermoelectric element in this embodiment. [Figure 2] This figure shows an example of the configuration of the boost converter according to this embodiment. [Figure 3] It is a diagram showing the equivalent resistance of the boost circuit of the present embodiment. [Figure 4] It is a diagram showing an example of the waveform of the control signal output by the control device of the present embodiment. [Figure 5] It is a diagram showing an example of the relationship between the combined resistance value and the output voltage. [Figure 6] It is a diagram showing an example of the relationship between the switching frequency, the control power, and the output power for each inductance of the inductive element of the boost circuit of the present embodiment. [Figure 7] It is a diagram showing an example of the operating characteristics of the boost circuit of the present embodiment. [Figure 8] It is a diagram showing another example of the operating characteristics of the boost circuit of the present embodiment. [Figure 9] It is a diagram showing an example of a multi-stage thermoelectric element with a bi-leg structure. [Figure 10] It is a diagram showing an example of a multi-stage thermoelectric element with a uni-leg structure.

Mode for Carrying Out the Invention

[0019] Hereinafter, the boost system of the present embodiment will be described with reference to the drawings. The boost system includes a boost circuit 10, a single-layer thermoelectric element 20, and a control device 30, and boosts the power generated by the single-layer thermoelectric element 20 to a required voltage and supplies it to a load 40. First, the single-layer thermoelectric element 20 will be described.

[0020] FIG. 1 is a diagram showing an example of the configuration of the single-layer thermoelectric element 20 of the present embodiment. The single-layer thermoelectric element 20 includes a positive electrode 21, a negative electrode 22, and a thermoelectric material 23. The thermoelectric material 23 converts a temperature difference into direct-current power. The positive electrode 21 and the negative electrode 22 are connected to the thermoelectric material 23 and extract direct-current power from the thermoelectric material 23. In an example of the present embodiment, the thermoelectric material 23 contains a compound of bismuth (Bi) and tellurium (Te) (also referred to as bismuth telluride or bismuth telluride). The positive electrode 21 and the negative electrode 22 are, for example, copper alloys (or pure copper). When a temperature difference (i.e., ΔT) is given between the temperature on the negative electrode 22 side (e.g., temperature T0, also called the reference temperature) and the temperature on the positive electrode 21 side (e.g., temperature T0 + ΔT), the thermoelectric material 23 generates a potential difference between the positive electrode 21 and the negative electrode 22, for example, by the Seebeck effect. In the following explanation, the direction between the positive electrode 21 and the negative electrode 22 shown in the figure, that is, the direction of the temperature difference, will also be referred to as the heat flow direction.

[0021] In one example of this embodiment, the temperature difference ΔT is 5[K]. Furthermore, the thermoelectric material 23 of this embodiment has a cross-sectional area of ​​10 × 0.1 [cm], a dimension in the heat flow direction of 5 [cm], a Seebeck coefficient of -240 [μV / K], a thermal conductivity of 2 W / (m·K), and an electrical conductivity of 500 [S / cm]. The positive electrode 21 and negative electrode 22 of this embodiment have a thermal conductivity of 400 W / (m·K) and an electrical conductivity of 6.4E5 [S / cm] (E5 is 10 to the power of 5). In the example described above, the open-circuit voltage of the single-layer thermoelectric element 20 is 1.2 [mV]. These figures are just examples and are not exhaustive.

[0022] Here, a single-layer thermoelectric element 20 refers to a thermoelectric element comprising only one set of a positive electrode 21, a negative electrode 22, and a thermoelectric material 23 on a DC current path. In other words, the single-layer thermoelectric element 20 comprises only one set of thermoelectric elements on the current path of the DC power, each consisting of a thermoelectric material 23 that converts a temperature difference into DC power, and a positive electrode 21 and a negative electrode 22 connected to the thermoelectric material 23 that extract DC power from the thermoelectric material 23. In this embodiment, the single-layer thermoelectric elements 20 may be connected in series to increase the generated voltage. However, if series-connected single-layer thermoelectric elements 20 are used, the cost becomes relatively high due to assembly costs for stacking the single-layer thermoelectric elements 20, and cost issues may need to be resolved in order to mount them in IoT devices. Therefore, it is preferable to use a single (single-layer) thermoelectric element (i.e., a single-layer thermoelectric element 20) without connecting thermoelectric elements in series as a power source mounted in IoT devices.

[0023] For comparison with the single-layer thermoelectric element 20 of this embodiment, examples of conventional thermoelectric elements that do not have a single-layer structure are shown in Figures 9 and 10. Figure 9 shows an example of a multi-stage thermoelectric element with a bileg structure. The bileg multi-stage thermoelectric element 820 has a configuration in which multiple thermoelectric materials 823 of p-type and n-type thermoelectric materials are alternately connected, with a positive electrode 821 connected to the p-type thermoelectric material at the end and a negative electrode 822 connected to the n-type thermoelectric material at the end.

[0024] Figure 10 shows an example of a multi-stage thermoelectric element with a Unireg structure. The Unireg multi-stage thermoelectric element 920 has a configuration in which multiple n-type thermoelectric materials are connected in sequence, and a positive electrode 921 or a negative electrode 922 is connected to the n-type thermoelectric materials at both ends.

[0025] Both the bi-leg multi-stage thermoelectric element 820 and the uni-leg multi-stage thermoelectric element 920 have a structure in which multiple thermoelectric materials are connected in series in multiple stages on a DC current path. By connecting thermoelectric materials in series in multiple stages, the electromotive force can be increased, for example, like a stacked battery compared to a unit battery. According to conventional technology, thermoelectric elements have been proposed that can obtain an electromotive force of several volts by connecting, for example, several hundred thermoelectric materials in series in multiple stages. However, connecting thermoelectric elements in multiple stages incurs costs for microfabrication and assembly. The boost converter 1 of this embodiment aims to provide an inexpensive and simplified power supply device by utilizing a single-layer thermoelectric element 20, which has significantly lower microfabrication and assembly costs compared to the multi-stage thermoelectric elements described above.

[0026] In this embodiment, the boost converter 1 is described as utilizing a single-layer thermoelectric element 20, but it is not limited to this. When there is little need for an inexpensive and simplified power supply, the boost converter 1 of this embodiment may use a thermoelectric element in which several thermoelectric materials are connected in series or in multiple stages on the DC current path. In this case, the description of "single-layer thermoelectric element 20" should be appropriately replaced with "thermoelectric element".

[0027] The specific configuration of the boost converter 1 of this embodiment will be described with reference to Figure 2.

[0028] Figure 2 shows an example of the configuration of the boost converter 1 of this embodiment. The boost converter 1 comprises a boost circuit 10 and a control device 30.

[0029] The boost circuit 10 includes a positive power supply terminal T11 and a negative power supply terminal T12 as terminals connected to the single-layer thermoelectric element 20. The positive electrode 21 of the single-layer thermoelectric element 20 is connected to the positive power terminal T11 (positive terminal). The negative electrode 22 of the single-layer thermoelectric element 20 is connected to the negative power terminal T12 (negative terminal).

[0030] The boost circuit 10 includes, as its internal elements, an inductive element 11, a first switching element 12, a second switching element 13, and a capacitive element 14.

[0031] The inductive element 11 is, for example, a coil and has inductive electrical properties (inductive reactance). The inductive element 11 has a first terminal 111 and a second terminal 112, and the first terminal 111 is connected to the positive power supply terminal T11. The inductive element 11 in this embodiment has a DC resistance of less than 10 [mΩ]. That is, the inductive element 11 in this embodiment is selected to have a DC resistance of less than 10 [mΩ].

[0032] The first switching element 12 and the second switching element 13 are both, for example, field-effect transistors (FETs). The first switch element 12 includes a first control terminal 121 (e.g., gate terminal), a first input terminal 122 (e.g., drain terminal), and a first output terminal 123 (e.g., source terminal). The first input terminal 122 of the first switch element 12 is connected to the second terminal 112 of the inductive element 11, and the first output terminal 123 is connected to the negative power supply terminal T12 (negative terminal).

[0033] The second switch element 13 includes a second control terminal 131 (e.g., a gate terminal), a second input terminal 132 (e.g., a drain terminal), and a second output terminal 133 (e.g., a source terminal). The second input terminal 132 of the second switch element 13 is connected to the second terminal 112 of the inductive element 11.

[0034] The capacitive element 14 is, for example, a capacitor and has capacitive electrical characteristics (capacitive reactance). One end (first capacitance terminal 141) of the capacitive element 14 is connected to the second output terminal 133 of the second switch element 13, and the other end (second capacitance terminal 142) is connected to the negative power supply terminal T12 (negative terminal).

[0035] The boost circuit 10 includes a positive load terminal T13 and a negative load terminal T14 as terminals connected to the load 40. The positive load terminal T13 is connected to one end (first capacitance terminal 141) of the capacitive element 14. The negative load terminal T14 is connected to the other end (second capacitance terminal 142) of the capacitive element 14.

[0036] The boost circuit 10 includes a first control input terminal T15 and a second control input terminal T16 as terminals connected to the control device 30. The first control input terminal T15 is connected to the first control terminal 121 (e.g., gate terminal) of the first switch element 12. The second control input terminal T16 is connected to the second control terminal 131 (e.g., gate terminal) of the second switch element 13.

[0037] With the circuit configuration described above, the boost circuit 10 functions as a so-called boost DC-DC converter (boost chopper).

[0038] The control device 30 includes a control unit 31. This control unit 31 is composed of analog elements such as operational amplifiers (OP amps), resistors, and capacitors, and controls the operating timing of the first switch element 12 and the second switch element 13. Alternatively, the control unit 31 may be configured as a discrete circuit combining multiple transistors without using an operational amplifier (OP amp). In other words, the control unit 31 is an analog circuit that controls the switching timing. The control device 30 configured in this way can operate with extremely low power consumption. The control device 30 may be configured as an embedded microcomputer if the power balance is met. In this case, for example, it comprises a control unit 31 and a memory unit 32. The memory unit 32 is equipped with semiconductor memory or the like, and programs and data that define the operation of the control unit 31 are stored in it in advance. The control device 30 operates using the power stored in the capacitive element 14 of the boost circuit 10. Note that the power supply path from the boost circuit 10 to the control device 30 is not shown in the figure. The control unit 31, for example, includes an embedded microcomputer and provides various functions by operating based on a program stored in the memory unit 32. In the following description, when the control unit 31 is mentioned, it may refer to the analog circuit described above or to an embedded microcomputer.

[0039] The control unit 31 outputs a first control signal S1 to the first control terminal 121 of the first switch element 12, and a second control signal S2 to the second control terminal 131 of the second switch element 13.

[0040] The first control signal S1 controls the first switch element 12 to an ON state or an OFF state by driving the first control terminal 121 (for example, the gate terminal) of the first switch element 12. The ON state of the first switch element 12 means that the resistance between the first input terminal 122 (e.g., drain terminal) and the first output terminal 123 (e.g., source terminal) of the first switch element 12 is sufficiently low, and there is conductivity between the first input terminal 122 (e.g., drain terminal) and the first output terminal 123 (e.g., source terminal). The first switch element 12 in this embodiment has a DC resistance value (on-resistance) of less than 10 mΩ when it is in the ON state. In other words, the first switch element 12 in this embodiment is selected to have an on-resistance of less than 10 mΩ. The off state of the first switch element 12 means that the resistance between the first input terminal 122 (e.g., the drain terminal) and the first output terminal 123 (e.g., the source terminal) is sufficiently high, resulting in a non-conductive state between the first input terminal 122 (e.g., the drain terminal) and the first output terminal 123 (e.g., the source terminal).

[0041] The second control signal S2 controls the second switch element 13 to an ON state or an OFF state by driving the second control terminal 131 (for example, the gate terminal) of the second switch element 13. The ON state of the second switch element 13 means that the resistance between the second input terminal 132 (e.g., drain terminal) and the second output terminal 133 (e.g., source terminal) of the second switch element 13 is sufficiently low, and there is conductivity between the second input terminal 132 (e.g., drain terminal) and the second output terminal 133 (e.g., source terminal). The off state of the second switching element 13 means that the resistance between the second input terminal 132 (e.g., the drain terminal) and the second output terminal 133 (e.g., the source terminal) is sufficiently high, resulting in a non-conductive state between the second input terminal 132 (e.g., the drain terminal) and the second output terminal 133 (e.g., the source terminal).

[0042] Furthermore, it is desirable that the second switch element 13 in this embodiment has a DC resistance value (on-resistance) of less than 10 mΩ when it is in the ON state. In other words, it is desirable that the second switch element 13 in this embodiment is selected to have an on-resistance of less than 10 mΩ.

[0043] In the above explanation, it was stated that it is preferable for the DC resistance of the inductive element 11 and the on-resistance of the first switching element 12 to be less than 10 [mΩ]. Furthermore, it is more preferable if the internal resistance RIN of the single-layer thermoelectric element 20, the DC resistance RL of the inductive element 11, the on-resistance RON of the first switch element 12, and the wiring resistance RCAB of the circuit connecting the single-layer thermoelectric element 20, the inductive element 11, and the first switch element 12 are all less than 10 [mΩ].

[0044] Specifically, if we consider the voltage VOC as the open-circuit voltage of the single-layer thermoelectric element 20, the resistance RIN as the internal resistance of the single-layer thermoelectric element 20, the resistance RL as the DC resistance of the inductive element 11, the resistance RON as the on-resistance of the first switch element 12, and the resistance RCAB as the wiring resistance, the maximum output power POUT when the input impedance (i.e., load resistance) of the load 40, calculated from the positive load terminal T13 and the negative load terminal T14, is optimized is expressed by equation (1). Considering the impedance matching between the thermoelectric element (for example, the single-layer thermoelectric element 20; the same applies in the following explanation) and the boost circuit 10, the maximum power that can be extracted from the thermoelectric element is VOC^2 / 4RIN (the ^ (hat) in the equation represents exponentiation. VOC means voltage VOC, and RIN means internal resistance RIN; the same applies in the following explanation). However, the maximum power POUT that can be extracted from the combination of the thermoelectric element and the boost circuit 10 cannot be given by VOC^2 / 4RIN. The RIN part must be replaced with RIN + RL + RON + RCAB, which includes the parasitic resistance inside the power supply circuit (in the formula, RL represents the DC resistance RL, RON represents the on-resistance RON, and RCAB represents the wiring resistance RCAB. The same applies in the following explanation). In other words, the correct design value cannot be obtained by considering the RIN of the thermoelectric element and the parasitic resistance component of the boost circuit 10 (RL + RON + RCAB) separately. They must be designed in a coordinated manner as a combined (RIN + RL + RON + RCAB). This is an important point in this embodiment. When the open-circuit voltage VOC of the thermoelectric element is sufficiently greater than 1 [mV], RIN becomes relatively large, so RL + RON + RCAB can be ignored, and therefore RL + RON + RCAB has not directly affected POUT (POUT in the equation means output power POUT; the same applies in the following explanation). However, when the open-circuit voltage VOC of the thermoelectric element is only about 1 mV, RIN becomes extremely small, and RL + RON + RCAB strongly affects POUT. As a result, in a boost circuit starting from 1 [mV], it is necessary to design the circuit to be small enough to adequately consider RL + RON + RCAB, and its value is given by equation (1) when the required POUT and the VOC of the generating element are given.

[0045]

number

[0046] Here, when the output power POUT is several tens [μW], and the input voltage VOC from the single-layer thermoelectric element 20 is 1 [mV], it is preferable that the internal resistance RIN of the single-layer thermoelectric element 20, the DC resistance RL of the inductive element 11, the on-resistance RON of the first switch element 12, and the wiring resistance RCAB of the circuit connecting the single-layer thermoelectric element 20, the inductive element 11, and the first switch element 12 are all less than 10 [mΩ]. The combined resistance of resistances RIN, RL, RON, and RCAB is also called the combined resistance Rs.

[0047] Figure 3 shows the equivalent resistance of the boost circuit of this embodiment. The boost circuit 10 is configured as a circuit that goes from the single-layer thermoelectric element 20 through the positive power terminal T11, the inductive element 11, the first switch element 12, the negative power terminal T12, and back to the single-layer thermoelectric element 20. The figure shows the equivalent resistance of each part of this circuit. Specifically, resistor 24 is the equivalent resistance (resistance RIN) of the single-layer thermoelectric element 20. Note that since the resistance value of resistance RIN is extremely small, it may be omitted in the following explanation. Resistor 114 is the equivalent resistance of the inductive element 11. Resistor 125 is the equivalent resistance of the on-resistance of the first switch element 12. In this figure, the first switch element 12 is shown separately as an equivalent switch element 124 that does not consider the on-resistance, and resistor 125 which is the equivalent resistance of the on-resistance. Resistor 151 is the equivalent resistance of the wiring from the single-layer thermoelectric element 20 to the inductive element 11. Resistor 152 is the equivalent resistance of the wiring from the inductive element 11 to the first switch element 12. Resistor 153 is the equivalent resistance of the wiring from the first switch element 12 to the single-layer thermoelectric element 20.

[0048] Note that while resistor 151 is defined as the equivalent resistance of the wiring from the single-layer thermoelectric element 20 to the inductive element 11, it is not limited to this. For example, if the resistance of the wiring from the single-layer thermoelectric element 20 to the positive power supply terminal T11 is sufficiently small, resistor 151 may be defined as the equivalent resistance of the wiring from the positive power supply terminal T11 to the inductive element 11. Similarly, while resistor 153 is defined as the equivalent resistance of the wiring from the first switch element 12 to the single-layer thermoelectric element 20, it is not limited to this. For example, if the resistance of the wiring from the negative power supply terminal T12 to the single-layer thermoelectric element 20 is sufficiently small, resistor 153 may be defined as the equivalent resistance of the wiring from the first switch element 12 to the negative power supply terminal T12.

[0049] The control unit 31 outputs the first control signal S1 and the second control signal S2 with predetermined duty cycles, and by alternately turning the first switch element 12 and the second switch element 13 on and off, it boosts the DC power output by the single-layer thermoelectric element 20.

[0050] Figure 4 shows an example of the waveform of the control signal output by the control device 30 of this embodiment. Figure (A) shows an example of the waveform of the first control signal S1 output by the control device 30. In this figure, the horizontal axis represents time t, and the vertical axis represents the voltage V1 applied to the first control terminal 121. Regarding the applied voltage V1, voltage V1L represents the voltage that turns the first switch element 12 to the off state, and voltage V1H represents the voltage that turns the first switch element 12 to the on state. The first control signal S1 is a signal that controls the on / off state of the first switch element 12 according to a predetermined duty cycle. The first on time T1on (first time T1) shown in the figure is the time during which the first switch element 12 is kept in the on state. The first off time T1off (second time T2) is the time during which the first switch element 12 is kept in the off state. The sum of the first on time T1on and the first off time T1off, that is, the sum of the first time T1 and the second time T2, is also called the switching period τ.

[0051] Figure (B) shows an example of the waveform of the second control signal S2 output by the control device 30. In this figure, the horizontal axis represents time t, and the vertical axis represents the voltage V2 applied to the second control terminal 131. Regarding the applied voltage V2, voltage V2L represents the voltage that turns the second switch element 13 off, and voltage V2H represents the voltage that turns the second switch element 13 on. The second control signal S2 is a signal that controls the on / off state of the second switch element 13 according to a predetermined duty cycle. The second on time T2on shown in the figure is the time during which the second switch element 13 is kept in the on state and corresponds to the second time T2 described above. The second off time T2off is the time during which the second switch element 13 is kept in the off state and corresponds to the first time T1 described above. The sum of the second on time T2on and the second off time T2off corresponds to the switching period τ described above.

[0052] Figure (C) shows an example of the waveform of the coil current IL flowing through the inductor element 11 as a result of control by the first control signal S1 and the second control signal S2. In this figure, the horizontal axis represents time t, and the vertical axis represents the current value of the coil current IL. The current value ILH shows an example of the maximum value of the coil current IL. The current value ILL shows an example of the minimum value of the coil current IL.

[0053] Furthermore, if the first switch element 12 and the second switch element 13 are turned on simultaneously, leakage current may occur from the capacitive element 14 to the negative load terminal T14 side via the second switch element 13 and the first switch element 12. In this case, the capacitive element 14 may not be able to store sufficient charge, which could cause a decrease in the output voltage.

[0054] In this embodiment, the control unit 31 has the parameters of each analog element in the circuit set so as not to turn on the first switch element 12 and the second switch element 13 at the same time (or the program stored in the memory unit 32 is set to do so). That is, the control unit 31 turns on and off the first switch element 12 and the second switch element 13 such that the time for which the first control signal S1 keeps the first switch element 12 in the ON state and the time for which the second control signal S2 keeps the second switch element 13 in the ON state do not overlap.

[0055] With the boost converter 1 configured in this way, it is possible to suppress the generation of leakage current from the capacitive element 14 to the negative load terminal T14 side via the second switch element 13 and the first switch element 12.

[0056] Here, the voltage between the positive power supply terminal T11 and the negative power supply terminal T12 (i.e., the output voltage of the single-layer thermoelectric element 20) is defined as the input voltage VOC, and the voltage between the positive load terminal T13 and the negative load terminal T14 (i.e., the voltage output to the load 40) is defined as the output voltage Vout. In this case, the input voltage VOC, the output voltage Vout, the first on-time T1on (also referred to as the first time T1), and the second on-time T2on (also referred to as the second time T2) have the relationship shown in equation (2) as an approximation neglecting the resistive component.

[0057]

number

[0058] In this embodiment, the control unit 31 outputs a first control signal S1 and a second control signal S2 by setting the ratio of the first ON time T1on (first time T1) to the second ON time T2on (second time T2) to 100 times or more. In other words, the first on-time T1on (first time T1), which is the time that the first control signal S1 keeps the first switch element 12 in the ON state, and the second on-time T2on (second time T2), which is the time that the second control signal S2 keeps the second switch element 13 in the ON state, are such that the first on-time T1on (first time T1) is 100 times or more the time that the second on-time T2on (second time T2) is 100 times longer.

[0059] With the boost converter 1 configured in this way, even if the input voltage VOC (i.e., the output voltage of the single-layer thermoelectric element 20) is around 1.0 to 1.5 [mV], if the ratio of the first on-time T1on (first time T1) to the second on-time T2on (second time T2) is increased by several hundred times (e.g., 700 times) to about 1000 times (e.g., 1000 times), the output voltage Vout can be boosted to about 1.0 [V]. Therefore, with the boost converter 1, even if a simple single-layer thermoelectric element 20 is used, it is possible to supply power of about 1.0 [V], which is sufficient to operate a typical electronic circuit (e.g., a sensor circuit or a communication circuit).

[0060] The period of the waveform of the coil current IL shown in Figure 4(C) is defined as the switching period τ. The combined resistance Rs is defined as the combined value of the internal resistance RIN of the single-layer thermoelectric element 20, the DC resistance RL of the inductor element 11, the on-resistance RON of the first switch element 12, and the wiring resistance RCAB of the circuit connecting the single-layer thermoelectric element 20, the inductor element 11, and the first switch element 12. The inductance L of the inductor element 11 is defined as the inductance. In this case, the condition under which Joule losses due to resistance can be ignored, expressed in terms of period τ, equivalent resistance Rs, and inductance L, is given by equation (3). The time constant of a series connection circuit of equivalent resistance Rs and inductance L is (L / Rs). In other words, equation (3) means that if the switching period τ (i.e., the right-hand side of equation (3)) is sufficiently shorter than this time constant (i.e., the left-hand side of equation (3)), then Joule losses in the equivalent resistance Rs can be ignored.

[0061]

number

[0062] If the gate capacitance of the first switch element 12 is capacitance C1, the gate capacitance of the second switch element 13 is capacitance C2, and the control voltage is control voltage VCONT, then the control power PCONT required for control in the boost circuit 10 can be expressed by equation (4). Here, the control voltage VCONT is the so-called gate drive voltage applied to the first control terminal 121 of the first switch element 12 and the second control terminal 131 of the second switch element 13. Also, the control power PCONT is the power consumed on the control side required for the switching operation of the first switch element 12 and the second switch element 13. Note that in equation (4), the energy required per charge of capacitances C1 and C2 (charging energy) is calculated as [(C1+C2)VCONT], taking into account the Joule loss due to the charging current. 2 This means that the charge energy is (i.e., the numerator on the right side of equation (4)), and dividing this charge energy by the switching period τ (i.e., the denominator on the right side of equation (4)) gives the control power PCONT.

[0063]

number

[0064] Based on the power supplied from the single-layer thermoelectric element 20 to the boost circuit 10, the power output from the boost circuit 10 (i.e., the power after boosting) is denoted as the output power POUT, and assuming that the losses in the boost circuit 10 are approximately zero, then the above equation (1) holds true. Furthermore, by setting D = T1 / (T2+T2), assuming that the increase and decrease in current across inductance L during one period of the switching period τ are equal, and letting the average current across inductance L be current IL, equation (5A) holds. Also, under the condition (steady-state condition) that the output current output from the boost circuit 10 to the load 40 is equal to the current consumed by the load 40 (RLOAD), equation (5B) holds. By solving equations (5A) and (5B) simultaneously, the boost ratio g is expressed by equation (5C), and the power consumed by the load 40 (RLOAD) (i.e., the output power POUT) is expressed by equation (5D). The condition under which the output power POUT, represented by equation (5D), takes its maximum value is the condition under which the denominator on the right side of equation (5D) takes its minimum value, with load 40 (RLOAD) as a variable. By finding the maximum value that the output power POUT can take, equation (1) described above can be derived.

[0065]

number

[0066] Here, the condition under which the control power PCONT can be ignored with respect to the output power POUT is as shown in equation (6).

[0067]

number

[0068] By substituting equations (1) and (4) into equation (6) above, equation (7) is derived.

[0069]

number

[0070] As typical parameters for readily available inductive element 11 and capacitive element 14, let's assume the inductance L is 0.1 [mH] and the capacitance C is 1 [μF]. In this case, equation (7) shows that the switching period τ should be sufficiently larger than 10 to the power of -4 [s]. That is, this result shows that the boost circuit 10 can be practically implemented if the switching frequency, which is the reciprocal of the period τ, is at most 5 [kHz] or less (for example, from 100 [Hz] to 5 [kHz]).

[0071] Here, the first switching frequency is defined as the reciprocal of the switching period (i.e., the switching period τ), which is defined as the on-time during which the first control signal S1 maintains the first switch element 12 in the ON state and the off-time during which the first switch element 12 maintains the first switch element 12 in the OFF state, with one period being defined as the ON period. The second switching frequency is defined as the reciprocal of the switching period (i.e., the switching period τ), which is defined as the on-time during which the second control signal S2 keeps the second switch element 13 in the ON state and the off-time during which the second switch element 13 is kept in the OFF state. Assume that the inductance L of the inductor element 11 is 0.1 [mH] or greater.

[0072] In this case, the control unit 31 controls the first switch element 12 and the second switch element 13 by setting both the first switching frequency and the second switching frequency from 500 Hz to 5 kHz.

[0073] With the boost converter 1 configured in this way, by combining the inductive element 11, the first switching element 12, the second switching element 13, and the capacitive element 14, which are practically available, it is possible to supply power of about 1.0[V], which is sufficient to operate a typical electronic circuit (e.g., a sensor circuit or a communication circuit), even if the input voltage VOC is about 1[mV] (for example, about 1.0~1.5[mV]). In other words, the boost converter 1 can be realized by combining components that are realistically available.

[0074] Figure 5 shows an example of the relationship between the combined resistance Rs and the output voltage Vout. As described above, the combined resistance Rs is the combined value of the internal resistance RIN of the single-layer thermoelectric element 20, the DC resistance RL of the inductive element 11, the on-resistance RON of the first switch element 12, and the wiring resistance RCAB of the circuit connecting the single-layer thermoelectric element 20, the inductive element 11, and the first switch element 12. The figure shows the output voltage Vout for the case where the combined resistance Rs is hypothetically 1000 [mΩ] (V1 in the figure), 100 [mΩ] (V2 in the figure), and 10 [mΩ] (V3 in the figure), which is an example of the combined resistance Rs in this embodiment, assuming that the parameters of the boost converter 1 are as described above, with the inductance L of the inductor element 11 being 0.1 [mH], the capacitance C of the capacitive element 14 being 1 [μF], and the switching frequency being 0.5 to 5 [kHz]. As shown in the figure, when the combined resistance Rs is 10 [mΩ], which is an example of the embodiment (V3 in the figure), a sufficiently high output voltage Vout can be obtained compared to when the combined resistance Rs is larger.

[0075] A specific example of the above-described embodiment will be explained in more detail. In the following description, the control voltage VCONT is 1.5[V]. The resistance RL of the inductive element 11 is 4[mΩ]. The wiring resistances are 7[mΩ] for resistor 151, 7[mΩ] for resistor 152, and 6[mΩ] for resistor 153, and their sum, resistance RCAB, is 20[mΩ]. The capacitance C of the capacitive element 14 is 10[μF]. Also, the capacitance C of the input capacitor (not shown) connected between the positive power supply terminal T11 and the negative power supply terminal T12 is 1[mF]. The on time (first on time T1on) of the first switch element 12 is 1000 [μs], and the off time (first off time T1off) is 1 [μs]. The on time (second on time T2on) of the second switch element 13 is 0.8 [μs], and the off time (second off time T2off) is 1000.2 [μs]. The time from the turn-off of the first switch element 12 to the turn-on of the second switch element 13, and the time from the turn-off of the second switch element 13 to the turn-on of the first switch element 12 (so-called dead time) are both 0.1 [μs].

[0076] Figure 6 shows an example of the relationship between switching frequency, control power, and output power for each inductance of the inductor element in the boost circuit of this embodiment. Here, as the switching frequency f increases, the output power POUT increases nonlinearly, and the control power PCONT increases linearly. At this time, there is a range of switching frequencies f in which the output power POUT exceeds the control power PCONT (i.e., the boost circuit 10 functions as a power supply). Furthermore, the switching frequency f characteristic of the output power POUT depends on the magnitude of the inductance L of the inductor element 11. In the case of the circuit constants described above, as shown in the figure, it is preferable to set the inductance L of the inductor element 11 to a sufficiently large value (for example, 1 [mH]) in order for the output power POUT to sufficiently exceed the control power PCONT. Also, when the inductance L of the inductor element 11 is 1 [mH], it is preferable to set the switching frequency f to a predetermined range (for example, from 500 [Hz] to 5 [kHz]).

[0077] Furthermore, the current ripple must be sufficiently small (as shown in equation (8)). The resistance ROUT in equation (8) is the input impedance (i.e., load resistance) of the load 40, calculated from the positive load terminal T13 and the negative load terminal T14.

[0078]

number

[0079] In other words, in this embodiment, the boost circuit 10 satisfies equation (9) with respect to the switching frequency f, the internal resistance of the single-layer thermoelectric element 20 being resistance RIN, the inductance of the inductor element 11 being inductance L, the DC resistance of the inductor element 11 being resistance RL, the on-resistance of the first switch element 12 (resistance 125) being resistance RON, the wiring resistance (sum of resistances 151, 152, and 153) being resistance RCAB, and the load resistances of the positive load terminal T13 and the negative load terminal T14 being resistance ROUT.

[0080]

number

[0081] Furthermore, in this embodiment, the boost circuit 10 satisfies equation (7) described above, with the gate capacitance of the first switch element 12 being capacitance C1, the gate capacitance of the second switch element 13 being capacitance C2, the control voltage (gate voltage) applied to the first control terminal 121 and the second control terminal 131 being the control voltage VCONT, the period of the waveform of the coil current flowing through the inductor being the switching period τ, the combined resistance Rs being the combined value of the internal resistance RIN of the thermoelectric element (for example, the single-layer thermoelectric element 20), the DC resistance value RL of the inductor element 11, the on-resistance RON of the first switch element 12, and the wiring resistance RCAB of the circuit connecting the single-layer thermoelectric element 20, the inductor element 11, and the first switch element 12, and the input voltage between the positive power supply terminal T11 and the negative power supply terminal T12 (i.e., the output voltage of the thermoelectric element) being voltage VOC.

[0082] Furthermore, the boost circuit 10 of this embodiment satisfies equation (10) with respect to the voltage generated by the single-layer thermoelectric element 20 (that is, the input voltage VOC of the boost circuit 10 (in other words, the input voltage between the positive power terminal T11 and the negative power terminal T12 is VOC) and the required output power POUT).

[0083]

number

[0084] Furthermore, at this time, the load resistor R connected to the output side satisfies equation (11) below, or the voltage at the output terminal when the load resistor R is connected to the output side is half the voltage when the output terminal is open.

[0085]

number

[0086] Figure 7 shows an example of the operating characteristics of the boost circuit of this embodiment. Figure 7(A) shows an example of the time-varying waveform of the output voltage Vout due to a change in the on-resistance (resistor 125) of the first switch element 12. In this figure, the vertical axis represents the output voltage Vout and the horizontal axis represents time. This figure shows that if the on-resistance (resistor 125) of the first switch element 12 is sufficiently low (for example, less than 10 [mΩ]; for example, 1 [mΩ]), a sufficiently high output voltage Vout (for example, 0.9 [V] or higher) can be obtained. Figure 7(B) shows an example of the relationship between the output voltage Vout and the output power POUT. In this figure, the vertical axis represents the output power POUT and the horizontal axis represents the output voltage Vout. Figure 7(C) shows an example of the relationship between the on-resistance (resistor 125) of the first switch element 12 and the output power POUT. The figure also shows that if the on-resistance (resistor 125) of the first switch element 12 is sufficiently low (for example, less than 10 [mΩ]; one example is 1 [mΩ]), a sufficiently high output power POUT (for example, 60 [μW] or more) can be obtained. In Figure 7(C), the graph labeled "Calculation" shows the results calculated using the aforementioned formula, that is, the values ​​obtained by substituting numerical values ​​into the formula. The graph labeled "Simulation" shows the results obtained using commercially available simulation software that uses a circuit model, that is, the values ​​of voltage, current, power, etc., obtained by creating a circuit diagram and running a commercially available simulator. Furthermore, the graphs in Figures 7(A) and 7(B) both show the results of the "Simulation" when the resistance RL = 1 [mΩ], the resistance RCAB = internal resistance RIN = 0, and the switching frequency f = 1 [kHz]. The same applies to Figure 8(B) below. In other words, in this embodiment, it can be seen that the result derived from the formula described above is almost correct.

[0087] Figure 8 shows another example of the operating characteristics of the boost circuit of this embodiment. Figure 8(A) shows an example of the time-varying waveform of the output voltage Vout due to the change in the sum of the resistance RL (resistor 114) of the inductive element 11 and the wiring resistance (sum of resistors 151, 152, and 153), which is resistor RCAB (resistor RL + resistor RCAB). This figure shows that if resistor RL + resistor RCAB is sufficiently low (for example, less than 10 [mΩ]), a sufficiently high output voltage Vout (for example, 0.9 [V] or more) can be obtained. Figure 8(B) shows an example of the relationship between resistor RL + resistor RCAB and output power POUT. This figure also shows that if resistor RL + resistor RCAB is sufficiently low (for example, less than 10 [mΩ]), a sufficiently high output power POUT (for example, 60 [μW] or more) can be obtained.

[0088] In this embodiment, the boost converter 1 may be configured by cascading a second boost converter (with the same configuration as the boost converter 10) after the boost converter 10 described above. That is, the boost converter 1 may comprise a preceding boost converter 10-1 and a subsequent boost converter 10-2, both having the same configuration as the boost converter 10 described above, with the positive load terminal T13 of the preceding boost converter 10-1 connected to the positive power supply terminal T11 of the subsequent boost converter 10-2, and the negative load terminal T14 of the preceding boost converter 10-1 connected to the negative power supply terminal T12 of the subsequent boost converter 10-2. In this case, a load 40 is connected between the positive load terminal T13 and the negative load terminal T14 of the subsequent boost converter 10-2.

[0089] Although embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments, and modifications can be made as appropriate without departing from the spirit of the present invention. For example, while we used a material made from bismuth telluride as the thermoelectric material, other materials are also acceptable as long as their parameters, such as resistance, are suitable. Furthermore, the single-layer thermoelectric element is not limited to the shape of the thermoelectric material 23 described above; other shapes are also acceptable, such as those with different cross-sectional area or heat flow direction dimensions than the thermoelectric material 23 described above. The element parameters of each element constituting the boost circuit, i.e., the resistance value and inductor value, may also be changed to suit the shape. Similarly, when using several single-layer thermoelectric elements connected in series or in multiple stages, the parameters of each element may be changed to suit the configuration.

[0090] Furthermore, as described above, the control device 30 may have an internal computer. In this case, the processes of each operation of the control device 30 are stored in the form of a program on a computer-readable recording medium, and the above operations are performed by the computer reading and executing this program. Here, a computer-readable recording medium refers to a magnetic disk, magneto-optical disk, CD-ROM, DVD-ROM, semiconductor memory, etc. Alternatively, this computer program may be distributed to a computer via a communication line, and the computer that receives this distribution may execute the program.

[0091] Furthermore, the above program may be intended to implement some of the functions described above. Furthermore, the aforementioned functions may be implemented in combination with programs already recorded in the computer system, such as so-called differential files (differential programs). [Explanation of Symbols]

[0092] 1... Boost converter, 10... Boost circuit, 11... Inductive element, 12... First switch element, 13... Second switch element, 14... Capacitive element, 20... Single-layer thermoelectric element, 30... Control device, 40... Load

Claims

1. A thermoelectric element comprising a thermoelectric material that converts a temperature difference into DC power, and a positive electrode terminal to which the positive electrode of a thermoelectric element, which consists of a positive electrode and a negative electrode that extract the DC power from the thermoelectric material, The negative electrode terminal to which the negative electrode is connected, An inductive element comprising a first terminal and a second terminal, wherein the first terminal is connected to the positive terminal, A first switch element comprising a first control terminal, a first input terminal, and a first output terminal, wherein the first input terminal is connected to the second terminal of the inductive element and the first output terminal is connected to the negative terminal, A second switch element comprising a second control terminal, a second input terminal, and a second output terminal, wherein the second input terminal is connected to the second terminal of the inductive element, A control unit that outputs a first control signal to the first control terminal of the first switch element and a second control signal to the second control terminal of the second switch element, each with a predetermined duty cycle, and alternately controls the first and second switch elements to be on and off, thereby boosting the DC power output by the thermoelectric element. Equipped with, When the internal resistance of the thermoelectric element is RIN, the DC resistance of the inductive element is RL, the on-resistance of the first switch element is RON, the wiring resistance from the positive terminal through the inductive element and the first switch element to the negative terminal is RCAB, the output voltage of the thermoelectric element when the positive terminal and the negative terminal are open is VOC, and the boosted power output to a load connected across both ends of the output terminal is output power POUT, then equation (A) [Math 1] Satisfying the conditions, Let C1 be the gate capacitance of the first switch element, C2 be the gate capacitance of the second switch element, VCONT be the gate voltage applied to the first and second control terminals, τ be the period of the waveform of the coil current flowing through the inductor element, RIN be the internal resistance of the thermoelectric element, RL be the DC resistance of the inductor element, RON be the on-resistance of the first switch element, RS be the combined resistance of RCAB be the wiring resistance from the positive terminal through the inductor element and the first switch element to the negative terminal, and VOC be the output voltage of the thermoelectric element when the positive and negative terminals are open. Then equation (B) [Math 2] A boost converter that satisfies the requirements.

2. The thermoelectric element uses the thermoelectric material and the set of the positive electrode and the negative electrode to generate the DC power It is a single-layer thermoelectric element that is provided in only one set on the current path. The booster device according to claim 1.

3. The first time is 100 times or more the time during which the first control signal keeps the first switch element in the ON state, and the second time is 100 times or more the time during which the second control signal keeps the second switch element in the ON state. The booster device according to claim 1.

4. The inductance of the aforementioned inductive element is 0.1 millihenry or more. The control unit, A first switching frequency having an on-time during which the first control signal maintains the first switch element in an ON state and an off-time during which the first switch element maintains an OFF state as one cycle, A second switching frequency having an on-time during which the second control signal keeps the second switch element in the ON state and an off-time during which the second switch element is kept in the OFF state as one cycle, Both are set to 100 Hz to 5 kHz, and the first switch element and the front The second switch element is controlled to be on / off. The booster device according to claim 1.

5. The control unit, The first and second switch elements are controlled to be turned on / off such that the time during which the first control signal keeps the first switch element in the ON state does not overlap with the time during which the second control signal keeps the second switch element in the ON state. The booster device according to claim 1.

6. The internal resistance RIN of the thermoelectric element, the DC resistance RL of the inductive element, the on-resistance RON of the first switch element, and the wiring resistance RCAB from the positive terminal through the inductive element and the first switch element to the negative terminal are all less than 10 milliohms. The booster device according to claim 1.

7. A boost circuit comprising the positive terminal, the negative terminal, the inductive element, the first switch element, and the second switch element is connected in cascaded order. The booster device according to claim 1.

8. A thermoelectric element comprising a thermoelectric material that converts a temperature difference into DC power, and a positive electrode terminal to which the positive electrode of a thermoelectric element comprising a positive electrode and a negative electrode that extract the DC power from the thermoelectric material is connected, The negative electrode terminal to which the negative electrode is connected, An inductive element comprising a first terminal and a second terminal, wherein the first terminal is connected to the positive terminal, A first switch element comprising a first control terminal, a first input terminal, and a first output terminal, wherein the first input terminal is connected to the second terminal of the inductive element and the first output terminal is connected to the negative terminal, A second switch element comprising a second control terminal, a second input terminal, and a second output terminal, wherein the second input terminal is connected to the second terminal of the inductive element, A control unit that outputs a first control signal to the first control terminal of the first switch element and a second control signal to the second control terminal of the second switch element, each with a predetermined duty cycle, and alternately controls the first and second switch elements to be on and off, thereby boosting the DC power output by the thermoelectric element. Equipped with, When the internal resistance of the thermoelectric element is RIN, the DC resistance of the inductive element is RL, the on-resistance of the first switch element is RON, the wiring resistance from the positive terminal through the inductive element and the first switch element to the negative terminal is RCAB, the output voltage of the thermoelectric element when the positive terminal and the negative terminal are open is VOC, and the boosted power output to a load connected across both ends of the output terminal is output power POUT, then equation (A) [Math 3] A boost converter that satisfies the following conditions, A thermoelectric element comprising a thermoelectric material that converts a temperature difference into DC power, and a positive electrode and a negative electrode connected to the thermoelectric material that extract the DC power from the thermoelectric material, Equipped with, When the load resistor R connected to the output side of the boost converter keeps the first switch element in the ON state for T1 and the first switch element in the OFF state for T2, then equation (C) [Math 4] A boost system that satisfies the requirements.

9. When a load resistor is connected to the output side of the boost converter, the voltage at the output terminal is half the voltage when the output terminal is open. The boost system according to claim 8.

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