JP2014175484A - Piezoelectric transformer, mounting structure of piezoelectric transformer, and wireless power transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact piezoelectric transformer ensuring high efficiency energy conversion even if the drive frequency is increased, and to provide its mounting structure, and a wireless power transmission system including the piezoelectric transformer.SOLUTION: A piezoelectric transformer 100 includes a piezoelectric plate 110. The piezoelectric plate 110 includes regions L1, L2, L3. The region L1 is provided at one end in the length direction, and is a non-polarization part having a length of λ/2. The region L2 is adjacent to the region L1 in the length direction, polarized in the length direction, and has a length mλ/2(m is an integer between 1 and (n-2)). The region L3 is adjacent to the region L2 in the length direction, polarized in the length direction or the thickness direction, and has a length (n-m-1)λ/2. External electrodes 120, 130 are provided in the region L1, and arranged to face each other. External electrodes 140, 150 are provided in the region L3, and arranged to face each other in the polarization direction of the region L3.

Description

  The present invention relates to a piezoelectric transformer in which various electrodes are formed on a piezoelectric plate and performs voltage conversion by electromechanical vibration, a mounting structure thereof, and a wireless power transmission system.

  2. Description of the Related Art In recent years, when charging an electronic device such as a mobile phone or a mobile PC, a wireless charging system that can be charged only by installing the electronic device in a charging device has been provided to eliminate the trouble of connecting a charging cable to the electronic device. Proposed. As such a wireless power transmission method, an electric field coupling method is known in which electric power is transmitted from a power transmission device (charging device) side to a power reception device (electronic device) side using a quasi-electrostatic field (for example, Patent Documents). 1).

  The power transmission system described in Patent Document 1 includes a power transmission device and a power reception device each including a passive electrode and an active electrode. And when the active electrode of a power transmission apparatus and the active electrode of a power receiving apparatus adjoin through a gap | interval, a strong electric field is formed between these two electrodes, and electrodes couple | bond together by an electric field.

  By the way, in general, it is effective to incorporate a low-loss resonance circuit in a technique for increasing the transmission efficiency of a power transmission system. This resonance circuit is composed of an electrostatic capacity and an inductor of a coupling portion between the power transmission device and the power reception device. In order to incorporate this resonance circuit into a device that has been reduced in size and thickness in recent years, it is necessary to realize a reduction in the size of the resonance circuit and a reduction in loss. As one method for solving the problem, it is effective to use a piezoelectric device for the inductor.

  FIG. 16 is a diagram illustrating the piezoelectric device described in Patent Document 2 and displacement of the piezoelectric device. Patent Document 2 discloses a Rosen tertiary type piezoelectric transformer having a symmetrical structure as one of piezoelectric devices as shown in FIG. The piezoelectric transformer described in Patent Document 2 includes a piezoelectric plate 200 having a rectangular plate shape. At both ends of the piezoelectric plate 200, planar input electrodes 201A and 201B and input electrodes 202A and 202B are provided on the upper and lower surfaces. In the piezoelectric plate 200, each of these electrodes serves as a drive unit and is polarized in the thickness direction. Further, the central portion of the piezoelectric plate 200 is provided with output electrodes 203A and 203B on the upper and lower surfaces to form a power generation unit, and is polarized in the length direction.

  As shown in the waveform diagram at the bottom of FIG. 16, the vibration of this piezoelectric transformer becomes a so-called node point where the vibration displacement becomes zero at a distance of λ / 2 from the center in the longitudinal direction and from the center to both ends. The vibration displacement becomes maximum at a point of λ / 2 inward. When a voltage is applied between the input electrodes 201A and 201B and between the input electrodes 202A and 202B, a high voltage boosted from the output electrode 203A is extracted by the action of the piezoelectric effect and the inverse piezoelectric effect.

Special table 2009-531009 Japanese Patent No. 3080052

  In wireless power transmission using the electric field coupling method, it is desirable to reduce the capacitive coupling impedance between the active electrodes in order to reduce the size of the power receiving device. In this case, the frequency of the voltage transmitted from the power transmitting device is increased. This can be achieved. However, if the element size of the piezoelectric transformer is reduced due to the demand for downsizing of the power receiving device, the vibration state of the piezoelectric transformer becomes more susceptible to the mounting part, the withstand voltage decreases, the heat capacity is small, and the temperature easily rises. There is a problem that efficiency is lowered.

  In view of the above problems, an object of the present invention is to provide a compact piezoelectric transformer capable of high-efficiency energy conversion even when the drive frequency is increased, a mounting structure thereof, and a wireless power transmission system including the piezoelectric transformer. It is to provide.

(1) The piezoelectric transformer according to the present invention uses an n-order (n is an integer of 3 or more) longitudinal vibration mode. The piezoelectric transformer includes a piezoelectric plate. The piezoelectric plate has a length of nλ / 2, a width of less than λ / 2, and a thickness of less than λ / 2 when one wavelength at the resonance frequency is represented by λ.

  The piezoelectric plate includes a high voltage part, an intermediate part, and a low voltage part. The high voltage portion is a non-polarized portion provided at one end in the length direction and having a length of λ / 2. The intermediate portion is adjacent to the high voltage portion along the length direction, is polarized in the length direction, and has a length of mλ / 2 (m is an integer of 1 to (n−2)). The low voltage portion is adjacent to the intermediate portion along the length direction, is polarized in the length direction or the thickness direction, and has a length of (n−m−1) λ / 2.

  The piezoelectric transformer according to the present invention includes a first electrode, a second electrode, a third electrode, and a fourth electrode. The first electrode and the second electrode are provided in the high voltage portion and are arranged to face each other. The third electrode and the fourth electrode are provided in the low voltage part, and are arranged to face each other along the polarization direction of the low voltage part.

  In this configuration, since the high voltage portion is arranged at the end of the piezoelectric plate, there is only one gap with the low voltage portion, so the capacity of the high voltage portion can be reduced. Therefore, the entire piezoelectric transformer can be reduced in size and the transformation ratio can be increased, and can be easily used in parallel. Further, since it is not necessary to perform wiring at the maximum vibration portion of the piezoelectric transformer, reliability at the time of mounting the piezoelectric transformer can be improved.

  Further, in this configuration, since it can be driven at a high frequency and a high voltage, the degree of freedom of use of the piezoelectric transformer can be improved. Moreover, since the wiring of the low voltage part can be simplified, the entire piezoelectric transformer can be reduced in size. Furthermore, since vibration inhibition can be reduced when a piezoelectric transformer is mounted, high-efficiency transmission is possible. In addition, since the electrode width of the high voltage portion can be relatively increased, the mountability is improved.

(2) The low voltage portion includes a plurality of regions that are divided into (nm-1) equal parts along the length direction, and each of these regions has a polarization direction of an adjacent region. Is polarized in the opposite direction, and the third electrode and the fourth electrode are preferably provided in each of the plurality of regions. With this configuration, even if the drive frequency is increased, the element size does not become too small, so that it is not easily affected by the mounting portion.

(3) In the above (2), a first connection electrode that connects the third electrodes provided in adjacent regions, and a second connection electrode that connects the fourth electrodes provided in adjacent regions; It is preferable to provide. Thereby, the number of connection places with the printed circuit board of the mounting destination does not increase.

(4) The low voltage portion is polarized in the thickness direction,
The third electrode and the fourth electrode include a first external electrode and a second external electrode provided on both side surfaces of the piezoelectric plate facing in the width direction, and the low voltage portion in the thickness direction. And a plurality of internal electrodes that are alternately connected to the first external electrode and the second external electrode. With this structure, the voltage conversion ratio can be increased, and the interelectrode impedance of the low voltage portion can be further reduced.

(5) The low voltage portion is polarized in the length direction,
The third electrode and the fourth electrode include a first external electrode and a second external electrode provided on both side surfaces of the piezoelectric plate facing in the width direction, and the low voltage along the length direction. It is preferable to have a plurality of internal electrodes stacked inside the portion and alternately connected to the first external electrode and the second external electrode. With this structure, the voltage conversion ratio can be increased, and the interelectrode impedance of the low voltage portion can be further reduced.

(6) Preferably, the piezoelectric plate is configured by laminating ceramic sheets. With this structure, the electrodes can be formed inside, the distance between the electrodes can be narrowed, the amount of displacement per voltage can be increased, and the efficiency can be increased.

(7) As a structure for mounting the piezoelectric transformer according to any one of (1) to (6) on a printed board, the first electrode, the second electrode, the third electrode, and the fourth electrode are mounted on the piezoelectric transformer. It is formed on the side surface when the surface is the bottom surface, and the middle point in the length direction of the high voltage part and the middle point in every length direction of the low voltage part are supported and mounted on the printed circuit board. It is preferable that With this mounting structure, mechanical interference between the piezoelectric transformer and the printed board is suppressed, and a decrease in efficiency of the piezoelectric transformer can be suppressed.

(8) The piezoelectric transformer according to (3) described above is mounted on a printed circuit board as a structure in which the middle point in the length direction of the region in contact with the intermediate portion among the regions of the low voltage portion, and the high voltage portion It is preferable that the middle point in the length direction is supported and mounted on the printed circuit board. With this mounting structure, mechanical interference between the piezoelectric transformer and the printed board is suppressed, and a decrease in efficiency of the piezoelectric transformer can be suppressed.

(9) The wireless power transmission system of the present invention
A power transmission device having a power generation side active electrode, a power transmission side passive electrode, and a voltage generation circuit for applying a voltage between the power transmission side active electrode and the power transmission side passive electrode;
A power receiving side active electrode facing the power transmitting side active electrode, a power receiving side passive electrode facing or contacting the power transmitting side passive electrode, the power receiving side active electrode, and the power receiving side when mounted on the power transmitting device A step-down circuit for stepping down a voltage generated between the passive electrodes, and a power receiving device having a load circuit for inputting the output voltage of the step-down circuit as a power supply voltage, the power transmission side active electrode and the power receiving side active electrode, In a wireless power transmission system in which power is transmitted from the power transmission device side to the power reception device side by facing through a gap and capacitively coupling,
The voltage generating circuit is boosted using the piezoelectric transformer described in (1) above. Alternatively, the voltage is stepped down using the piezoelectric transformer described in (1) above in the step-down circuit.

  According to the present invention, the capacity of the high voltage section can be reduced, the entire piezoelectric transformer can be reduced in size, and the transformation ratio can be increased. Moreover, it becomes easy to use in parallel. Further, since it is not necessary to wire at the maximum vibration portion of the piezoelectric transformer, the reliability at the time of mounting the piezoelectric transformer is improved. In addition, since it can be driven at a high frequency and a high voltage, the degree of freedom of use of the piezoelectric transformer can be improved. Moreover, since the wiring of the low voltage part can be simplified, the entire piezoelectric transformer can be reduced in size.

1 is a perspective view of a piezoelectric transformer according to a first embodiment of the present invention. It is sectional drawing of the II-II line of FIG. It is sectional drawing of the III-III line | wire of FIG. It is sectional drawing of the IV-IV line of FIG. It is a figure which shows the stress and displacement in the piezoelectric transformer which concerns on 1st Embodiment of this invention. It is a figure which shows the mounting format at the time of mounting a piezoelectric transformer on the board | substrate which concerns on 1st Embodiment of this invention. 1 is a plan view of a piezoelectric transformer according to a first embodiment of the present invention. It is a perspective view of the piezoelectric transformer which concerns on 2nd Embodiment of this invention. It is a figure which shows the stress and displacement in the piezoelectric transformer which concerns on 2nd Embodiment of this invention. It is a perspective view of the piezoelectric transformer which concerns on 3rd Embodiment of this invention. It is side surface sectional drawing which shows the structure of the power transmission apparatus and power receiving apparatus which concern on 3rd Embodiment of this invention. It is a perspective view of the piezoelectric transformer which concerns on 4th Embodiment of this invention. It is a figure which shows the stress and displacement in the piezoelectric transformer which concerns on 4th Embodiment of this invention. It is a figure which shows the state which incorporated the piezoelectric transformer which concerns on 5th Embodiment of this invention in the circuit. It is a figure which shows the state which incorporated the piezoelectric transformer which concerns on 5th Embodiment of this invention in the circuit. It is a figure which shows the state which incorporated the piezoelectric transformer which concerns on 5th Embodiment of this invention in the circuit. It is a figure which shows the state which incorporated the piezoelectric transformer which concerns on 5th Embodiment of this invention in the circuit. It is a figure which shows the displacement of the piezoelectric device described in patent document 2, and a piezoelectric device.

  Hereinafter, a piezoelectric transformer according to an embodiment of the present invention will be described in detail with reference to the drawings.

<< First Embodiment >>
FIG. 1 is a perspective view of the piezoelectric transformer according to the first embodiment. 2 is a cross-sectional view taken along line II-II in FIG. 3 is a cross-sectional view taken along line III-III in FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. Although FIG. 1 is a perspective view, the internal electrodes are not shown.

  The piezoelectric transformer 100 uses a third-order longitudinal vibration mode. The piezoelectric transformer 100 includes a rectangular plate-shaped piezoelectric body plate 110 having a length L, a thickness T, and a width W. The piezoelectric plate 110 is made of PZT ceramics or the like. The piezoelectric transformer 100 is assumed to vibrate in the 3λ / 2 resonance mode. Here, λ is one wavelength of vibration in the piezoelectric plate 110. Therefore, the length L is 3λ / 2. Here, the thickness T and the width W are preferably less than λ / 2. This is because the vibration in the thickness T and width W directions is not coupled to the vibration in the length direction, and spurious is suppressed.

  The piezoelectric plate 110 has regions L1, L2, and L3 that are divided into three equal parts in the longitudinal direction and have respective lengths of L / 3 (ie, λ / 2). The regions L1 and L3 are located at both ends in the longitudinal direction of the piezoelectric plate 110, and the region L2 is interposed between the regions L1 and L3. The region L1 is a non-polarized high voltage part. The region L2 is an intermediate portion that is polarized in the length direction. The region L3 is a low voltage portion that is polarized in the thickness direction.

  On the side surface of the region L1 of the piezoelectric plate 110, external electrodes 120 and 130 facing each other are formed. On the side surface of the region L3 of the piezoelectric plate 110, external electrodes 140 and 150 facing each other are formed. Since the region L2 is polarized as described above, when an AC voltage is applied between the external electrode (120, 130) and the external electrode (140 or 150), the longitudinal direction in the longitudinal direction is caused by the inverse piezoelectric effect. The vibration is excited, and the entire piezoelectric plate 110 vibrates in the length direction (vibrates in the longitudinal vibration mode). As a result, a voltage is generated between the external electrodes 140 and 150 in the low voltage portion L3 due to the piezoelectric effect.

  The external electrode 120 corresponds to the first electrode of the present invention, the external electrode 130 corresponds to the second electrode of the present invention, the external electrode 140 corresponds to the third electrode of the present invention, and the external electrode 150 corresponds to the present invention. Corresponds to the fourth electrode.

  2 is a cross-sectional view taken along line II-II in FIG. 3 is a cross-sectional view taken along line III-III in FIG. 4 is a cross-sectional view taken along line IV-IV in FIG.

  In the region L1, a plurality of internal electrodes 131 that are electrically connected to the external electrodes 120 and 130 and extend in the width W direction are formed.

  A plurality of internal electrodes 141 and 151 extending in the width W direction are formed between the external electrode 140 and the external electrode 150 in the region L3. The internal electrodes 141 and 151 are arranged so as to face each other in the layer direction.

  By using these structures, that is, a laminated structure, the transformation ratio can be increased.

  FIG. 5 is a diagram showing stress and displacement in the piezoelectric transformer. The sinusoidal curve superimposed on the piezoelectric plate 110 represents the stress applied to the piezoelectric plate 110, and the waveform in the lower part of FIG. 5 represents the vibration displacement of the piezoelectric plate 110.

  The vibration of the piezoelectric transformer 100 becomes a so-called node point where the vibration displacement becomes zero at the center in the longitudinal direction of each of the regions L1, L2, and L3, and the maximum displacement at both ends in the longitudinal direction of each of the regions L1, L2, and L3. . The piezoelectric transformer 100 is supported and wired at the node points of the region L1 and the region L3.

  FIG. 6 is a view showing a mounting structure of a piezoelectric transformer on a printed circuit board.

  The piezoelectric transformer 100 is connected to the flexible substrate 101 via solder. Further, the flexible substrate 101 is connected to the printed circuit board 200 through solder. That is, the piezoelectric transformer 100 is mounted on the printed board 200 via the flexible board 101 in a state of being separated from the printed board 200.

  With this configuration, the vibration of the piezoelectric transformer 100 does not leak to the mounting substrate 200 and the vibration of the piezoelectric transformer 100 can be confined, so that highly efficient power transmission can be realized. Moreover, the connection reliability of a solder part is securable.

  FIG. 7 is a plan view of the piezoelectric transformer. So far, the example in which the region L3 of the piezoelectric transformer 100 is polarized in the thickness direction has been described, but the present invention is not limited to this. FIG. 7 shows an example in which the region L3 of the piezoelectric transformer 100 is polarized in the length direction. In FIG. 7, a plurality of internal electrodes 141 and 151 extending in the thickness direction and extending in the width direction are formed between the external electrode 140 and the external electrode 150 in the region L3. The internal electrodes 141 and 151 are arranged so as to face each other in the length direction.

  When an AC voltage is applied between the external electrode (120, 130) and the external electrode (140 or 150), longitudinal vibration in the longitudinal direction is excited by the inverse piezoelectric effect, and the entire piezoelectric plate 110 is long. Vibrates in the vertical direction (vibrates in the longitudinal vibration mode). As a result, a voltage is generated between the external electrodes 140 and 150 in the low voltage portion L3 due to the piezoelectric effect.

  In the configuration of the present embodiment, since the high voltage portion is arranged at the end of the piezoelectric plate, there is only one gap with the low voltage portion, and the capacity of the high voltage portion can be reduced. Therefore, the entire piezoelectric transformer can be reduced in size and the transformation ratio can be increased, and can be easily used in parallel. Further, since it is not necessary to perform wiring at the maximum vibration portion of the piezoelectric transformer, reliability at the time of mounting the piezoelectric transformer can be improved.

  Further, in the configuration of the present embodiment, since it can be driven at a high frequency and a high voltage, the degree of freedom of use of the piezoelectric transformer can be improved. Moreover, since the wiring of the low voltage part can be simplified, the entire piezoelectric transformer can be reduced in size. Furthermore, since vibration inhibition can be reduced when a piezoelectric transformer is mounted, high-efficiency transmission is possible.

<< Second Embodiment >>
In each of the embodiments after the first embodiment, the description of matters similar to those of the first embodiment will be omitted as appropriate.

  FIG. 8 is a perspective view of the piezoelectric transformer according to the second embodiment.

  The piezoelectric transformer 100A uses a fifth-order longitudinal vibration mode. The piezoelectric transformer 100A is assumed to vibrate in the 5λ / 2 resonance mode. Here, λ is one wavelength of vibration in the piezoelectric plate 110.

  The piezoelectric transformer 100A has a region L4 and a region L5 in addition to the regions L1 to L3 shown in the first embodiment. The region L4 and the region L5 are low voltage portions that are polarized in the thickness direction. External electrodes 140 and 150 facing each other are formed on the side surfaces of the regions L4 and L5 of the piezoelectric plate 110A.

  FIG. 9 is a diagram showing stress and displacement in the piezoelectric transformer. The sinusoidal curve superimposed on the piezoelectric plate 110A represents the stress applied to the piezoelectric plate 110A, and the waveform at the bottom of FIG. 9 represents the vibration displacement of the piezoelectric plate 110A.

  The vibration of the piezoelectric transformer 100A becomes a so-called node point where the vibration displacement becomes zero at the center in the longitudinal direction of each of the regions L1 to L5, and is the maximum displacement at both ends in the longitudinal direction of each of the regions L1 to L5. The piezoelectric transformer 100A is supported and wired at each node point in the regions L1, L3, L4, and L5. Each of the regions L3 to L5 is polarized in a direction opposite to the polarization direction of the adjacent region.

  In the configuration of the present embodiment, since the interelectrode capacitance of the low voltage portion in the piezoelectric transformer 100A is large, the interelectrode impedance of the low voltage portion can be lowered, and a relatively large current capacity can be obtained.

<< Third Embodiment >>
FIG. 10 is a perspective view of the piezoelectric transformer according to the third embodiment.

  The piezoelectric transformer 100B includes a connection electrode 160 and a connection electrode 170 in addition to the configuration of the second embodiment. The connection electrode 160 is a first connection electrode that connects the external electrodes 140 provided in adjacent regions. The connection electrode 170 is a second connection electrode that connects the external electrodes 150 provided in adjacent regions. Connection electrode 160 and connection electrode 170 are connected after polarization of regions L3 to L5. That is, in the polarization process, the external electrodes 140 and 150 are polarized by applying a high voltage between the external electrodes 140 and 150 in an independent state. Thereafter, connection electrodes 160 and 170 are formed.

  FIG. 11 is a diagram illustrating stress and displacement in the piezoelectric transformer.

  The vibration of the piezoelectric transformer 100A becomes a so-called node point where the vibration displacement becomes zero at the center in the longitudinal direction of each of the regions L1 to L5, and is the maximum displacement at both ends in the longitudinal direction of each of the regions L1 to L5. The piezoelectric transformer 100A is supported and wired at the node points of the regions L1 and L3. Each of the regions L3 to L5 is polarized in a direction opposite to the polarization direction of the adjacent region.

  In the configuration of the present embodiment, the number of mounting support portions can be reduced.

<< Fourth Embodiment >>
FIG. 12 is a perspective view of the piezoelectric transformer of the fourth embodiment. The piezoelectric transformer 100C includes five regions L1 to L5 and vibrates in a 5λ / 2 resonance mode.

  FIG. 13 is a diagram illustrating stress and displacement in the piezoelectric transformer 100C. The sinusoidal curve superimposed on the piezoelectric plate 110C represents the stress applied to the piezoelectric plate 110C, and the waveform at the bottom of FIG. 13 represents the vibration displacement of the piezoelectric plate 110C.

  The vibration of the piezoelectric transformer 100C is a so-called node point where the vibration displacement becomes zero at the center in the longitudinal direction of each of the regions L1 to L5, and is the maximum displacement at both ends in the longitudinal direction of each of the regions L1 to L5. The piezoelectric transformer 100C is supported and wired at each node point in the regions L1 and L4. The regions L2 and L3 are polarized in the length direction and in opposite directions. The regions L4 and L5 are polarized in the thickness direction and in opposite directions.

  Thus, the intermediate portions L2 and L3 may be provided over a length of mλ / 2 (m = 2 in this example).

  By providing a plurality of intermediate portions, the input capacity can be reduced and the withstand voltage can be increased.

<< Fifth Embodiment >>
14 and 15 are views showing a state in which the piezoelectric transformer is incorporated in a circuit.

  FIG. 14 is a circuit diagram of a booster circuit including the piezoelectric transformer 100A. FIG. 15 is a circuit diagram of a step-down circuit including the piezoelectric transformer 100A. Here, the output voltage is smaller than the input voltage.

  In FIG. 14, the input voltage Vin is applied via the inductor L between the external electrodes 140-150 in the low voltage part. In this example, the external electrode 150 is a common electrode, and a high voltage Vout is generated between the external electrode 150 and the external electrodes (120, 130) of the high voltage portion, and is output to the load R. The inductor L is provided to resonate with the capacitance between the external electrodes 140-150 of the low voltage portion at a predetermined resonance frequency.

  In FIG. 15, the input voltage Vin is applied via the capacitor C between the external electrode (120, 130) of the high voltage section and the external electrode 140 which is a common electrode. As a result, a low voltage Vout is generated between the external electrodes 140-150 of the low voltage portion and is output to the load R. The inductor L is provided to resonate with the capacitance between the external electrodes 140-150 of the low voltage portion at a predetermined resonance frequency.

<< Sixth Embodiment >>
In the sixth embodiment, an example in which the piezoelectric transformer described above is applied to a wireless power transmission system will be described. The wireless power transmission system includes a power transmission device and a power reception device. The power receiving device is, for example, a portable electronic device including a secondary battery. Examples of the portable electronic device include a mobile phone, a PDA (Personal Digital Assistant), a portable music player, a notebook PC, and a digital camera. The power transmission device is a charging stand on which the power reception device is mounted and charges a secondary battery of the power reception device. The power transmission device and the power reception device each include an active electrode and a passive electrode. Power is transmitted from the power transmitting apparatus to the power receiving apparatus by capacitively coupling the active electrodes and the passive electrodes.

  FIG. 16 is a diagram illustrating a circuit configuration of the wireless power transmission system. In this embodiment, a piezoelectric transformer is used for the step-down circuit included in the power receiving device 300.

  The high frequency high voltage generation circuit 101 of the power transmission device 200 generates a high frequency voltage of, for example, 100 kHz to several tens of MHz. A voltage generated by the high-frequency high-voltage generation circuit 101 is applied between the active electrode 103 and the passive electrode 104 via the inductor La. The capacitor CG is a capacitance mainly composed of the active electrode 103 and the passive electrode 104, and constitutes a resonance circuit together with the inductor La.

  A step-down circuit including two piezoelectric transformers 100A and inductors Lb1 and Lb2 is connected between the active electrode 203 and the passive electrode 204 of the power receiving device 300. The capacitance element CL is a capacitance mainly composed of the active electrode 203 and the passive electrode 204.

  The coupling of the coupling electrode by the active electrode 103 and the passive electrode 104 of the power transmission device 200 and the coupling electrode by the active electrode 203 and the passive electrode 204 of the power reception device 300 can be expressed as being coupled via the mutual capacitance Cm. it can.

  As described in the fifth embodiment, the step-down circuit using the piezoelectric transformer 100A steps down the voltage applied between the external electrodes (120, 130) and the external electrode 140 and outputs the voltage from between the external electrodes 140-150. To do. This output voltage is rectified and smoothed by the diodes D1, D2, D3, D4, the inductor Lc, and the capacitor C1, and charges the DC load RL (secondary battery of the power receiving device 300).

  As described above, by using the low-loss piezoelectric transformer 100A in the step-down circuit, a small-sized step-down circuit with low loss can be realized, and as a result, the power receiving device 300 can be downsized.

  FIG. 17 is a diagram illustrating another circuit configuration of the wireless power transmission system. The power receiving device 300 is an example in which two piezoelectric transformers 100A are symmetrically connected. The external electrodes 140 of the two piezoelectric transformers 100A are commonly connected. A rectifying / smoothing circuit including diodes D1 and D2, an inductor Lc, and a capacitor C1 is connected between the external electrodes 140 and 150.

  By performing balanced output in this way, the matching with the balanced input type rectifier circuit is good and stable operation is possible.

  Here, a plurality of intermediate portions L2 may be provided. By providing a plurality of intermediate sections, the input capacity of the piezoelectric transformer can be reduced even when the coupling capacity of the electric field coupling section is small, so loss in the power transmission circuit can be reduced without excessively increasing the voltage on the power transmission side. Since it can reduce, highly efficient transmission can be carried out.

  In each of the above embodiments, the laminated piezoelectric transformer has been described. However, the piezoelectric plate may have a single plate structure.

  Finally, the description of the above-described embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

100-Piezoelectric transformer 100A-Piezoelectric transformer 100B-Piezoelectric transformer 110-Piezoelectric plate 110A-Piezoelectric plate 120-External electrode (first electrode)
130-External electrode (second electrode)
140 -External electrode (third electrode)
150-External electrode (fourth electrode)
160—Connection electrode (first connection electrode)
170—Connection electrode (second connection electrode)

Claims (9)

A piezoelectric transformer using an nth-order (n is an integer of 3 or more) longitudinal vibration mode,
When one wavelength at the resonance frequency is represented by λ, a piezoelectric plate having a length of nλ / 2, a width of less than λ / 2, and a thickness of less than λ / 2 is provided.
The piezoelectric plate is provided at one end portion in the length direction, is adjacent to the high voltage portion along the length direction, the non-polarized high voltage portion having a length of λ / 2, and the length An intermediate portion polarized in the direction and having a length of mλ / 2 (m is an integer of 1 to (n−2)), and adjacent to the intermediate portion along the length direction, the length direction or A low voltage portion that is polarized in the thickness direction and has a length of (n−m−1) λ / 2,
The first electrode and the second electrode which are provided in the high voltage part and are arranged opposite to each other, and the third electrode and the fourth electrode which are provided in the low voltage part and are arranged to face each other along the polarization direction of the low voltage part. And a piezoelectric transformer. The low voltage part has a plurality of regions configured to be equally divided (n−m−1) along the length direction,
Each of the plurality of regions is polarized in a direction opposite to the polarization direction of the adjacent region,
The third electrode and the fourth electrode are provided in each of the plurality of regions.
The piezoelectric transformer according to claim 1. A first connection electrode for connecting the third electrodes provided in adjacent regions;
A second connection electrode for connecting the fourth electrodes provided in adjacent regions;
The piezoelectric transformer according to claim 2, comprising: The low voltage portion is polarized in the thickness direction,
The third electrode and the fourth electrode include a first external electrode and a second external electrode provided on both side surfaces of the piezoelectric plate facing in the width direction, and the low voltage portion in the thickness direction. The piezoelectric transformer according to claim 1, further comprising: a plurality of internal electrodes that are stacked inside and alternately connected to the first external electrode and the second external electrode. The low voltage portion is polarized in the length direction,
The third electrode and the fourth electrode include a first external electrode and a second external electrode provided on both side surfaces of the piezoelectric plate facing in the width direction, and the low voltage along the length direction. 4. The piezoelectric transformer according to claim 1, further comprising: a plurality of internal electrodes that are stacked inside the unit and are alternately connected to the first external electrode and the second external electrode. 5.   The piezoelectric transformer according to claim 1, wherein the piezoelectric plate is configured by laminating ceramic sheets. A mounting structure of the piezoelectric transformer according to any one of claims 1 to 6 on a printed circuit board,
The first electrode, the second electrode, the third electrode, and the fourth electrode are respectively formed on side surfaces when the mounting surface of the piezoelectric transformer is a bottom surface,
A mounting structure of a piezoelectric transformer, in which a midpoint in the length direction of the high voltage portion and a midpoint for each λ / 2 in the length direction of the low voltage portion are supported and mounted on a printed board. A mounting structure of the piezoelectric transformer according to claim 3 on a printed circuit board,
Of each region of the low voltage portion, a midpoint in the length direction of the region in contact with the intermediate portion, and a midpoint in the length direction of the high voltage portion are supported and mounted on the printed circuit board. Mounting structure of piezoelectric transformer. A power transmission device having a power generation side active electrode, a power transmission side passive electrode, and a voltage generation circuit for applying a voltage between the power transmission side active electrode and the power transmission side passive electrode;
A power receiving side active electrode facing the power transmitting side active electrode, a power receiving side passive electrode facing or contacting the power transmitting side passive electrode, the power receiving side active electrode, and the power receiving side when mounted on the power transmitting device A step-down circuit for stepping down a voltage generated between the passive electrodes, and a power receiving device having a load circuit for inputting the output voltage of the step-down circuit as a power supply voltage, the power transmission side active electrode and the power receiving side active electrode, In a wireless power transmission system in which power is transmitted from the power transmission device side to the power reception device side by facing through a gap and capacitively coupling,
The voltage generation circuit or the step-down circuit includes a piezoelectric transformer using an n-order (n is an integer of 3 or more) longitudinal vibration mode,
The piezoelectric transformer is
When one wavelength at the resonance frequency is represented by λ, a piezoelectric plate having a length of nλ / 2, a width of less than λ / 2, and a thickness of less than λ / 2 is provided.
The piezoelectric plate is provided at one end portion in the length direction, is adjacent to the high voltage portion along the length direction, the non-polarized high voltage portion having a length of λ / 2, and the length An intermediate portion polarized in the direction and having a length of mλ / 2 (m is an integer of 1 to (n−2)), and adjacent to the intermediate portion along the length direction, the length direction or A low voltage portion that is polarized in the thickness direction and has a length of (n−m−1) λ / 2,
The first electrode and the second electrode which are provided in the high voltage part and are arranged opposite to each other, and the third electrode and the fourth electrode which are provided in the low voltage part and are arranged to face each other along the polarization direction of the low voltage part. A wireless power transmission system.

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