Power supply circuit and power supply module

Abstract

The present disclosure provides: a power supply circuit capable of changing the resonant frequency of an oscillator included in a power generation element; and a power supply module. A power supply circuit (120) extracts power from an electromagnetic induction-type power generation element including an oscillator. The power supply circuit (120) comprises a capacitor (Cx) which is connected in series with the power generation element (110), a switching circuit (switching transistor (M1,M2)) which is connected between the capacitor (Cx) and a load circuit (Rout), and a controller (130) which switches the switching circuit. The controller (130) changes the switching frequency of the switching circuit, thereby causing the input impedance (RLoad) of the power supply circuit (120) to change and modulating the resonant frequency (f) of the oscillator.

Description

Power supply circuit and power supply module

[0001] The present disclosure relates to a power supply circuit and a power supply module that extracts power from an electromagnetic induction power generating element including a vibrator.

[0002] There is a demand for standalone sensor modules for monitoring infrastructure facilities such as bridges. To enable standalone operation of a sensor module, a power generation element is required that converts renewable energy (also known as environmental energy) such as light, heat, vibration, and wind into electricity.

[0003] JP 2011-517277 A (Patent Document 1) discloses a power generating element that converts mechanical vibration energy into electrical energy. The power generating element includes an electrically conductive coil and a magnet, and two parts of the magnetic core are mounted with a bias element that can vibrate relatively at a resonant frequency with respect to a central position along an axis. As a result, in the power generating element, vibrating the bias element at the resonant frequency causes a change in the magnetic flux of the coil, generating electric power in the coil.

[0004] Special table 2011-517277 publication

[0005] In the case of a power generation element that converts mechanical vibration energy into electrical energy, as in JP2011-517277A (Patent Document 1), the maximum amount of power can be generated by vibrating a bias element (vibrator) at a resonant frequency. Therefore, the power generation element is set so that the resonant frequency of the bias element (vibrator) matches the frequency of the environmental vibrations in which it is placed.

[0006] However, the frequency of environmental vibrations is not always constant, and can change due to environmental changes. When the frequency of environmental vibrations changes due to environmental changes, the amount of power generated by a power generating element whose resonant frequency is set to match the frequency of the environmental vibration before the change will decrease significantly. For power generating elements used in sensor modules installed on bridges and other structures, it was virtually impossible to change the resonant frequency set after installation.

[0007] Therefore, an object of the present disclosure is to provide a power supply circuit and a power supply module that are capable of changing the resonance frequency of an oscillator included in a power generating element.

[0008] A power supply circuit according to one embodiment of the present disclosure is a power supply circuit that extracts power from an electromagnetic induction power generating element including a vibrator. The power supply circuit includes a capacitor connected in series with the electromagnetic induction power generating element, a switching circuit connected between the capacitor and a load, and a controller that switches the switching circuit. The controller changes the switching frequency of the switching circuit to change the input impedance of the power supply circuit and modulate the resonant frequency of the vibrator.

[0009] A power supply module according to an embodiment of the present disclosure includes an electromagnetic induction power generating element and the power supply circuit described above.

[0010] According to the present disclosure, by connecting a capacitor in series to the electromagnetic induction type power generation element and changing the switching frequency of the switching circuit using a controller, the input impedance of the power supply circuit can be changed to modulate the resonant frequency of the vibrator, making it possible to easily change the resonant frequency of the vibrator in accordance with changes in the frequency of environmental vibrations.

[0011] 1 is a circuit diagram of a power supply module according to an embodiment; FIG. 2 is a schematic diagram of a power generating element according to an embodiment; FIG. 3 is an equivalent circuit of a power generating element according to an embodiment; FIG. 4 is an equivalent circuit of a power generating element after unification into mechanical impedance; FIG. 5 is a diagram for explaining mechanical impedance in a complex plane; FIG. 6 is a diagram for explaining changes in mechanical impedance when the capacitance value of a capacitor and the input impedance of a power supply circuit are changed; FIG. 7 is a diagram for explaining the relationship between power output to a load circuit and the input impedance of a power supply circuit; FIG. 8 is a diagram for explaining modulation of a resonant frequency when the electromechanical coupling constant is changed;

[0012] A power supply circuit according to an embodiment and a power supply module including the power supply circuit will be described in detail below with reference to the drawings. Note that the same reference numerals in the drawings indicate the same or corresponding parts. The power supply circuit described below is applied to, for example, a magnetostrictive vibration power generation element, and can extract power from the power generation element. The power supply circuit is not limited to applications to magnetostrictive vibration power generation elements, and can be similarly applied to any electromagnetic induction power generation element that includes a vibrator.

[0013] 1 is a circuit diagram of a power supply module 100 according to an embodiment. The power supply module 100 includes a power generating element 110 and a power supply circuit 120. The power supply module 100 extracts power generated by the power generating element 110 through the power supply circuit 120 and supplies it to a load circuit R ｏｕｔ (e.g., a sensor, etc.)

[0014] A boost converter circuit (voltage step-up converter) is formed by combining the internal inductance L1 included in the power generating element 110 with the power supply circuit 120. The boost converter circuit can achieve voltage step-up operation by controlling the switching transistors M1 and M2 of the switching circuit with the controller 130. Furthermore, by controlling the switching transistors M1 and M2 with the controller 130, which will be described below, it is possible to determine the direction of current and achieve rectification at the same time as voltage step-up.

[0015] Specifically, the controller 130 simultaneously turns the switching transistors M1 and M2 OFF at regular intervals, thereby determining the direction of current from changes in the drain voltages of the switching transistors M1 and M2 detected at that time. The controller 130 then keeps the switching transistor M1 or M2 whose drain voltage has increased in the OFF state, while immediately controls the switching transistor M1 or M2 whose drain voltage has changed to 0 (zero) V or a negative voltage to the ON state. As a result, the boost converter circuit simultaneously achieves a rectifying function and a boosting function by connecting the charging capacitor C1 via rectifying elements D1 and D2 (diodes) to the wiring through which current flows from the power generation element 110 to the power supply circuit 120 and grounding the wiring that outputs the current.

[0016] The power generating element 110 is an electromagnetic induction power generating element including a vibrator. That is, the power generating element 110 is a power generating element that can generate electric power by vibrating the vibrator using environmental vibrations to change the magnetic flux. Specifically, a magnetostrictive vibration power generating element, which is an example of an electromagnetic induction power generating element including a vibrator, will be described. Fig. 2 is a schematic diagram of the power generating element 110 according to the embodiment. The power generating element 110 includes a spring plate 1, a weight 2, a coil 3, a magnetostrictive element 4, and magnets 5 and 6.

[0017] The spring plate 1 is U-shaped, with a weight 2 attached to one end. Furthermore, the spring plate 1 is provided with a coil 3 and a magnetostrictor 4 midway along the U-shape, and magnets 5 and 6 are attached to both ends. The magnetic flux generated in the power generating element 110 flows along the spring plate 1 via the magnets 5 and 6. Therefore, the power generating element 110 can change the magnetic flux flowing along the spring plate 1 by vibrating the spring plate 1 and the weight 2 as an oscillator using environmental vibrations, and the change in magnetic flux generates electricity in the coil 3.

[0018] 1, the power generating element 110 is shown as an equivalent circuit in which a power source 112, an internal inductance L1 (internal coil), and an internal resistance R1 are connected in series. The power generating element 110 is an ideal power source that generates an electromotive force V in the power source 112 by vibrating the vibrator at a resonance frequency f (resonance angular frequency ω = 2πf). In other words, the power generating element 110 can obtain the maximum amount of power generation by vibrating the vibrator at the resonance frequency f. Therefore, the power generating element 110 is set so that the resonance frequency of the vibrator matches the frequency of the environmental vibrations in which it is placed.

[0019] However, the frequency of the environmental vibration is not always constant, and the frequency of the environmental vibration may change due to environmental changes. If the frequency of the environmental vibration changes due to environmental changes, the power generating element 110 will no longer be able to vibrate the vibrator at the resonant frequency f, resulting in a significant drop in the amount of power generated. In the power supply module 100 according to this embodiment, even if the frequency of the environmental vibration changes due to environmental changes, the power supply circuit 120 can modulate the resonant frequency f of the vibrator accordingly. Therefore, in the power supply module 100, even if the frequency of the environmental vibration changes due to environmental changes, the load circuit R ｏｕｔ It is possible to maintain the amount of power generation required for the power supply (for example, sensors, etc.).

[0020] The power supply circuit 120 extracts power from the power generating element 110 and can modulate the resonant frequency f of the vibrator. The power supply circuit 120 includes a capacitor Cx, switching transistors M1 and M2, a rectifying element D1, a rectifying element D2, and a charging capacitor C1. The capacitor Cx is connected in series to the power generating element 110. If the capacitor Cx is connected in parallel to the power generating element 110, the voltage from the power generating element 110 is fixed by the capacitor Cx, and therefore the power supply circuit 120 cannot coexist with a switching circuit including the switching transistors M1 and M2. However, if the capacitor Cx is connected in series to the power generating element 110, the power supply circuit 120 can coexist with a switching circuit including the switching transistors M1 and M2.

[0021] The switching circuit including the switching transistors M1 and M2, the rectifying elements D1 and D2, and the charging capacitor C1, together with the internal inductance L1, forms a diode rectifying boost converter. Note that the power supply circuit 120 is not limited to the case where the switching transistors M1 and M2 etc. form a boost converter, and the capacitor Cx and the load circuit R ｏｕｔ It is only necessary to have a switching circuit including switching transistors M1 and M2 connected between the

[0022] The controller 130 drives the switching transistors M1 and M2 at a switching frequency. The switching transistors M1 and M2 are alternately turned on in one cycle, with a duty ratio of 50%. This switching frequency and the input impedance R of the power supply circuit 120 are Ｌｏａｄ is proportional to the input impedance R Ｌｏａｄ The input impedance R of the power supply circuit 120 becomes large. Ｌｏａｄ is the load circuit R as seen from the power generating element 110 as shown in FIG. ｏｕｔ In the power supply module 100 according to the present embodiment, the input impedance R of the power supply circuit 120 is changed by changing the switching frequency of the switching transistors M1 and M2. Ｌｏａｄ is changed to modulate the resonant frequency f of the vibrator.

[0023] Next, the input impedance R ＬｏａｄThe principle by which the resonant frequency f of the oscillator can be modulated by changing the σ is now described in detail. FIG. 3 shows an equivalent circuit of a power generating element 110 according to an embodiment. As shown in FIG. 3, the power generating element 110 applies a force F (excitation force) to the oscillator, vibrating the oscillator at a velocity v (vibration velocity), where m is an equivalent mass including the mass of the weight 2, 1 / k is the spring constant of the spring plate 1, and c is a viscous damping coefficient (damping constant). The power generating element 110 generates an electromotive force αv by generating an electromotive force αv, which generates a braking force αi as a reaction to the electromotive force αv. Therefore, the equation of motion of the power generating element 110 can be expressed as Equation 1. The equation of motion of the power generating element 110 is a combination of mass motion, damping motion, and spring motion, each of which has one degree of freedom. Here, α is the electromechanical coupling coefficient. The equivalent circuit of the power generating element 110 is expressed as the equation of motion and circuit equation shown below, which is described in detail in the literature "Shota Kita et al., "Improvement of force factor of magnetostrictive vibration power generator for high efficiency," Journal of Applied Physics 117, 17B508 (2015)."

[0024]

[0025] On the other hand, as shown in FIG. 3, the power generating element 110 can also be expressed as a circuit equation such as Equation 2, in which an internal resistance R1, an internal inductance L1, and a capacitor Cx of the power supply circuit 120 are connected in series, and a current i flows due to the generation of an electromotive force αv.

[0026]

[0027] As shown in Fig. 3, the equivalent circuit of the power generating element 110 has a mechanical system and an electrical system that are related to each other via the braking force αi and the electromotive force αv. Therefore, the power generating element 110 can be coupled with the equation of motion of Equation 1 and the circuit equation of Equation 2. By eliminating the current i from these two equations, the power generating element 110 can be expressed as a single unified equation of motion based on mechanical impedance, as shown in Equation 3. Note that the force F (excitation force) applied to the vibrator is assumed to be a sine wave with a resonant frequency f of the vibrator, and the resonant angular frequency is set to ω = 2πf.

[0028]

[0029] 4 shows an equivalent circuit of the power generating element 110 after unification into mechanical impedance. As shown in FIG. 4, even in the equivalent circuit after unification into mechanical impedance, the power generating element 110 includes electrical system parameters such as internal resistance R1, internal inductance L1, and capacitor Cx of the power supply circuit 120. Therefore, the resonant frequency f of the vibration depends on the internal resistance R1, internal inductance L1, and capacitor Cx of the power supply circuit 120. In other words, it can be seen that the resonant frequency f of the vibrator can be modulated by the capacitor Cx of the power supply circuit 120. Furthermore, since the power generating element 110 is electrically connected to the power supply circuit 120, the input impedance R Ｌｏａｄ The input impedance R of the power supply circuit 120 is Ｌｏａｄ It is also possible to modulate the resonant frequency f of the vibrator by

[0030] The mechanical impedance of the power generating element 110 expressed by Equation 3 will be explained by plotting it on a complex plane. FIG. 5 is a diagram for explaining the mechanical impedance on a complex plane. In FIG. 5, the vertical axis represents the imaginary part and the horizontal axis represents the real part. The first to third terms in Equation 3 are mechanical system terms, with the real part determined by the viscous damping coefficient c of the first term and the imaginary part determined by jωm of the second term, which includes the equivalent mass m, and k / (jω), which includes the spring constant 1 / k. In other words, it can be seen that the direction of the real part of the mechanical system parameters depends on the viscous damping coefficient c, and the direction of the imaginary part depends on the equivalent mass m and the spring constant 1 / k of the spring plate 1. Note that the frequency at which the imaginary part of the mechanical impedance becomes 0 (zero) is the resonance point, and therefore the resonance frequency f can be changed by changing the parameters related to the imaginary part.

[0031] Furthermore, the four items shown in Equation 3 are electrical system terms. In FIG. 5, points based on electrical system parameters are plotted in addition to the points plotted based on mechanical system parameters. As can be seen from FIG. 5, the plot can be changed in the direction of the imaginary part by changing the electrical system parameters. Therefore, the capacitor Cx of the power supply circuit 120 and the input impedance R Ｌｏａｄ The resonant frequency f of the vibrator can be modulated by

[0032] Next, the capacitor Cx of the power supply circuit 120 and the input impedance R of the power supply circuit 120 Ｌｏａｄ 6 shows the change in the mechanical impedance of the power generating element 110 when the capacitance value of the capacitor Cx and the input impedance R of the power supply circuit 120 are changed. Ｌｏａｄ 6 is a diagram illustrating the change in mechanical impedance when the parameter σ is changed. In FIG. 6, the vertical axis represents the imaginary part (unit: Ns / m), and the horizontal axis represents the real part (unit: Ns / m). In FIG. 6, the origin is set to the point plotted by the parameter of the mechanical system in order to show the change in impedance due to the parameter of the electrical system. The graph shown in FIG. 6 is the result of a simulation.

[0033] As shown in Figure 6, the impedance of the power generating element 110 changes in a semicircular shape when the capacitance value of the capacitor Cx is changed. By increasing the capacitance value of the capacitor Cx, the real part of the impedance increases, but the imaginary part of the impedance increases once and then returns to 0 (zero). The capacitance value of the capacitor Cx at the point (point P) where the imaginary part of the impedance is the largest is 0.4 μF, and the input impedance R Ｌｏａｄ The impedance was 1168 Ω. The resonant frequency f of the vibrator at this time was 349.6 Hz.

[0034] Furthermore, the capacitance value of the capacitor Cx is fixed to 0.4 μF, and the input impedance R Ｌｏａｄ The change in impedance when the input impedance R is changed is shown in FIG. Ｌｏａｄ By increasing the value of the real part and the imaginary part of the impedance, the values ​​of the real part and the imaginary part of the impedance decrease toward 0 (zero).

[0035] In the power supply circuit 120, changing the capacitance value of the capacitor Cx requires preparing multiple capacitor elements and switching between these elements, or using a variable capacitance capacitor, which makes the circuit configuration complicated. Therefore, the power supply circuit 120 sets the capacitance value of the capacitor Cx to a fixed value and changes the switching frequency of the switching transistors M1 and M2 to change the input impedance R Ｌｏａｄ Of course, if there are no constraints such as a complicated circuit configuration, the power supply circuit 120 may modulate the resonant frequency f of the resonator by changing the capacitance value of the capacitor Cx.

[0036] Input impedance R Ｌｏａｄ The optimal capacitance value of the capacitor Cx for modulating the resonant frequency f of the vibrator by changing ω can be calculated based on the resonant frequency f of the vibrator before modulation (resonant angular frequency ω = 2πf) and the internal resistance R1 of the power generating element 110, as shown in Equation 4.

[0037]

[0038] Next, the input impedance R of the power supply circuit 120Ｌｏａｄ and the power generating element 110 to the load circuit R ｏｕｔ Power P output to ｏｕｔ The relationship between the load circuit R ｏｕｔ Power P output to ｏｕｔ and the input impedance R of the power supply circuit 120. Ｌｏａｄ 7 is a diagram for explaining the relationship between the power P ｏｕｔ (unit: W), horizontal axis is R Ｌｏａｄ (unit: Ω).

[0039] Input impedance R Ｌｏａｄ When the resistance is 1168Ω, as shown in FIG. ｏｕｔ is approximately 0.0015 W. The input impedance R Ｌｏａｄ Even if the resistance is about 10 times as large as 10,000 Ω, the power P ｏｕｔ is approximately 0.001 W. If the input impedance R Ｌｏａｄ Power P ｏｕｔ Assuming that the change in is linear, the input impedance R Ｌｏａｄ Even if the input impedance R Ｌｏａｄ The power P is about 0.0008W, which is about half of the power P when the impedance is 1168Ω. ｏｕｔ can be secured.

[0040] Internal resistance R1<<α ２ In the case of / c, the influence of the internal resistance R1 is small, so the matching condition between the mechanical impedance and the electrical impedance is Ｌｏａｄ = α ２ / c, where α is the electromechanical coupling coefficient (unit: Ns / m) and c is the viscous damping coefficient (damping constant) (unit: Ns / m). Ｌｏａｄ = α ２ When / c is used as the reference value, the input impedance R Ｌｏａｄ As shown in Equation 5, it is possible to change the value within the range from the reference value to the internal resistance R1.

[0041]

[0042] When the input impedance RLoad becomes smaller than the internal resistance R1, the power loss due to the internal resistance R1 becomes dominant, and charging does not proceed. ２ / c, R satisfies Equation 5 Ｌｏａｄ The range no longer exists and no significant frequency modulation can be performed.

[0043] Next, the maximum frequency modulation amount that the power supply circuit 120 can modulate the resonant frequency f of the vibrator can be expressed as in Equation 6. Therefore, it can be seen that the maximum frequency modulation amount depends on the electromechanical coupling coefficient α, and the modulation amount increases as the electromechanical coupling coefficient α increases.

[0044]

[0045] Simulations show that the amount of modulation of the resonance frequency f depends on the electromechanical coupling coefficient α. Fig. 8 is a diagram for explaining the modulation of the resonance frequency. Fig. 9 is a diagram for explaining the modulation of the resonance frequency when the electromechanical coupling coefficient is changed. In Figs. 8 and 9, the vertical axis represents the power P ｏｕｔ The horizontal axis is the vibration frequency (unit: Hz), and the horizontal axis is the vibration frequency (unit: Hz). The graphs shown in Figures 8 and 9 are the results of simulations.

[0046] In FIG. 8, the electromechanical coupling coefficient α is set to 12.49, and the input impedance R Ｌｏａｄ Power P at each frequency when ｏｕｔ The change in power P ｏｕｔ In addition, in FIG. 8, the input impedance R Ｌｏａｄ Power P at each frequency when ｏｕｔ The change in power P ｏｕｔ That is, when the electromechanical coupling coefficient α is set to 12.49, the power supply circuit 120 has an input impedance R Ｌｏａｄ By changing the impedance from 1168 Ω to 5840 Ω by a factor of five, the resonance frequency f can be modulated by about 2 Hz.

[0047] On the other hand, in FIG. 9, the electromechanical coupling coefficient α is set to 30, and the input impedance RＬｏａｄ Power P at each frequency when ｏｕｔ The change in power P ｏｕｔ In addition, in FIG. 9, the input impedance R Ｌｏａｄ Power P at each frequency when ｏｕｔ The change in power P ｏｕｔ That is, when the electromechanical coupling coefficient α is set to 30, the power supply circuit 120 has an input impedance R Ｌｏａｄ By changing the input impedance R from 1168 Ω to 11680 Ω by a factor of 10, the resonant frequency f can be modulated by about 13 Hz. Ｌｏａｄ By changing the impedance in the range from 1168 Ω to 11680 Ω, the resonance frequency f can be modulated in the range of about 13 Hz enclosed by the dashed lines shown in FIG.

[0048] In this way, the power supply circuit 120 has an input impedance R Ｌｏａｄ Furthermore, the power supply circuit 120 can modulate the resonant frequency f by increasing the electromechanical coupling coefficient α from 12.49 to 30, thereby reducing the input impedance R Ｌｏａｄ By changing the frequency f, the range in which the resonance frequency f can be modulated can be dramatically improved.

[0049] (Aspects) (1) A power supply circuit according to the present disclosure is a power supply circuit that extracts power from an electromagnetic induction power generating element including a vibrator, and includes: a capacitor connected in series to the electromagnetic induction power generating element; a switching circuit connected between the capacitor and a load; and a controller that switches the switching circuit, wherein the controller changes the switching frequency of the switching circuit to change the input impedance of the power supply circuit and modulate the resonant frequency of the vibrator.

[0050] (2) In the power supply circuit described in (1), the switching circuit includes a switching transistor, a rectifying element, and a charging capacitor, and forms a boost converter together with the internal coil of the electromagnetic induction type power generating element.

[0051] (3) In the power supply circuit according to (1) or (2), the capacitance value of the capacitor is determined based on the resonant frequency of the vibrator and the internal resistance of the electromagnetic induction power generating element.

[0052] (4) In the power supply circuit described in (3), the value obtained by dividing the square of the electromechanical coupling constant by the damping constant is set as a reference value, and when the internal resistance is smaller than the reference value, the input impedance of the power supply circuit becomes the reference value, and when the internal resistance is equal to or greater than the reference value, the lower limit value of the input impedance of the power supply circuit becomes the reference value.

[0053] (5) In the power supply circuit described in (4), the input impedance of the power supply circuit can be changed within a range from a reference value to an internal resistance.

[0054] (6) In the power supply circuit according to any one of (1) to (5), the electromagnetic induction power generating element is a magnetostrictive vibration power generating element.

[0055] (7) A power supply module according to the present disclosure includes an electromagnetic induction power generating element and the power supply circuit according to any one of (1) to (6).

[0056] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0057] REFERENCE SIGNS LIST 1 spring plate, 2 weight, 3 coil, 4 magnetostrictive element, 5, 6 magnet, 100 power supply module, 110 power generating element, 112 power supply, 120 power supply circuit, 130 controller, C1 charging capacitor, Cx capacitor, D1, D2 rectifying element, L1 internal inductance, R1 internal resistance, R Ｌｏａｄ Input impedance, R ｏｕｔ load circuit

Claims

1. A power supply circuit that extracts power from an electromagnetic induction power generating element including a vibrator, comprising: a capacitor connected in series to the electromagnetic induction power generating element; a switching circuit connected between the capacitor and a load; and a controller that switches the switching circuit, wherein the controller changes the switching frequency of the switching circuit to change the input impedance of the power supply circuit and modulate the resonant frequency of the vibrator.

2. The power supply circuit according to claim 1, wherein the switching circuit includes a switching transistor, a rectifying element, and a charging capacitor, and forms a boost converter together with the internal coil of the electromagnetic induction type power generating element.

3. The power supply circuit according to claim 1 or 2, wherein the capacitance value of the capacitor is determined based on the resonant frequency of the vibrator and the internal resistance of the electromagnetic induction power generating element.

4. The power supply circuit according to claim 3, wherein a reference value is the square of the electromechanical coupling constant divided by a damping constant, and when the internal resistance is smaller than the reference value, the input impedance of the power supply circuit becomes the reference value, and when the internal resistance is equal to or greater than the reference value, the lower limit of the input impedance of the power supply circuit becomes the reference value.

5. The power supply circuit according to claim 4, wherein the input impedance of said power supply circuit can be changed within a range from said reference value to said internal resistance.

6. The power supply circuit according to claim 1 or 2, wherein the electromagnetic induction power generating element is a magnetostrictive vibration power generating element.

7. A power supply module comprising: the electromagnetic induction type power generating element; and the power supply circuit according to claim 1 or 2.

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