JP2015092545A - Piezoelectric transformer, and wireless power transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer that can set a ratio of capacitances occurring at a high voltage part and a low voltage part, and a wireless power transmission system including the same.SOLUTION: There is provided a piezoelectric transformer 21 using a longitudinal vibration mode of a degree n (n is an integer of 1 or more), and including a piezoelectric plate 30 having a length of nλ/2, a width of less than nλ/2, and a thickness of less than λ/2, where λ represents a wavelength at a resonance frequency. The piezoelectric plate 30 has, in order along the length direction, a first high-voltage area 31, a low-voltage area 33, and a second high-voltage area 32. The low-voltage area 33 has a polarization direction in the thickness direction, and has a first output electrode E33 and a second output electrode E34 arranged opposite to each other in the thickness direction. The first high-voltage area 31 has a polarization direction in the longitudinal direction, and has a first input electrode E31 provided at one end of the piezoelectric plate 30. The second high-voltage area 32 has a polarization direction in the length direction, and has a second input electrode E32 provided at the other end of the piezoelectric plate 30.

Description

  The present invention relates to a piezoelectric transformer and a wireless power transmission system that can be used when the drive frequency is increased.

  In recent years, when charging an electronic device such as a mobile phone or a mobile PC, wireless power transmission can be performed simply by installing the electronic device in the charging device in order to eliminate the trouble of connecting a charging cable to the electronic device. Has been proposed. As wireless power transmission, a method of transmitting electric power from a power transmission device (charging device) side to a power reception device (electronic device) side using electric field coupling is known (for example, see Patent Document 1).

  In the power transmission system described in Patent Literature 1, each of the power transmission device and the power receiving device includes an active electrode on the high potential side and a passive electrode on the low potential side, and the electrodes are connected between the active electrodes and between the passive electrodes. By facing each other through a gap, a strong electric field is formed between the electrodes, and the electrodes are electric field coupled. This electric field coupling enables wireless power transmission between devices.

Special table 2009-531009

  In this electric field coupling type wireless power transmission system, power is transmitted from the power transmitting apparatus to the power receiving apparatus by the electric field (voltage) between the electrodes. For this reason, the potential difference between the active electrode and the passive electrode is large. In order to determine the ground potential of the device, a capacitance formed between the ground of the device and the active electrode (high voltage portion) and a capacitance formed between the ground of the device and the passive electrode (low voltage portion). It is necessary to set the capacity ratio to an appropriate value. When the capacitance ratio fluctuates, the ground potential of the device fluctuates, and a malfunction may occur in the power receiving device.

  In recent years, mobile phones and the like corresponding to power receiving devices have been reduced in size and thickness. Even in such a power receiving device, it is necessary to provide a transformer in order to handle a high voltage. Although it is possible to use a high-voltage transformer using a winding as the transformer, it is effective to use a piezoelectric device for the transformer in accordance with demands for downsizing and the like. However, even when a piezoelectric device is used, as described above, it is necessary to maintain the capacitance ratio between the ground of the apparatus and the active electrode and the passive electrode at an appropriate value. If a capacitance (capacitor) is added separately in order to maintain the capacitance ratio, the added capacitance decreases the coupling degree of the electric field coupling unit, and as a result, the reactive power is increased, resulting in a reduction in efficiency. In addition, there is a problem that the number of parts increases, and as a result, downsizing is hindered.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric transformer capable of setting a capacity ratio generated between a high voltage part and a low voltage part, and a wireless power transmission system including the piezoelectric transformer.

  The piezoelectric transformer according to the present invention is a piezoelectric transformer using a longitudinal vibration mode of order n (n is an integer of 1 or more), and the wavelength at the resonance frequency is represented by λ, and the length is nλ / 2. , A width of less than λ / 2, and a thickness of less than λ / 2, and the piezoelectric plate has a first high voltage portion, a low voltage portion, and a second height along the length direction. The low voltage part has a first low voltage electrode and a second low voltage electrode opposite to each other in the thickness direction, and the low voltage part includes the first high voltage part. Includes a first high-voltage electrode provided at one end of the piezoelectric plate, the polarization direction of the second high-voltage portion is a length direction, A second high-voltage electrode provided on the other end of the piezoelectric plate, wherein the first high-voltage part and the second high-voltage part have different lengths; To.

  In this configuration, by setting the length of the second high voltage portion, the capacitance generated between the first high voltage electrode and the first low voltage electrode (or the second low voltage electrode), and the second high voltage portion are set. The capacitance ratio with the capacitance generated between the voltage electrode and the first low voltage electrode (or the second low voltage electrode) can be adjusted. That is, the capacity ratio generated in the high pressure part and the low pressure part can be determined.

  Further, for example, when a voltage is applied to the first high voltage electrode and the second high voltage electrode, a high-order longitudinal vibration mode in the longitudinal direction of the piezoelectric plate is excited, and the piezoelectric effect and the inverse piezoelectric effect are obtained. By the action, the stepped down voltage can be taken out from the first low voltage electrode and the second low voltage electrode in the low voltage portion. Since the first high voltage electrode and the second high voltage electrode are insulated from the first low voltage electrode and the second low voltage electrode, the piezoelectric transformer handles a high voltage. Can do. Further, by mounting this piezoelectric transformer on a circuit, the circuit can be reduced in size and height.

  The order n is 4 or more, the low voltage part is divided into a plurality of regions in the length direction, and the direction of the stress distribution at the time of stress generation is reversed at the boundary with the adjacent region, and the plurality of regions Is preferably opposite to the adjacent regions, and the first low voltage electrode and the second low voltage electrode are provided in each of the plurality of regions.

  In this configuration, by setting the length of the second high-voltage part, it is possible to determine the capacity ratio generated in the high-voltage part and the low-voltage part even when there is a stress distribution in a different direction in the low-voltage part. it can.

  The order n is 4 or more, and at least one of the first high voltage portion and the second high voltage portion is divided into a plurality of regions in the length direction and provided in the thickness direction at the boundary with the adjacent region. Preferably, each of the plurality of regions has a polarization direction opposite to the adjacent region.

  In this configuration, for example, the present invention can be applied even in a higher order mode such as a fourth order or a seventh order.

  The piezoelectric plate is preferably a laminated body in which a plurality of piezoelectric ceramic sheets are laminated.

  With this configuration, it is easy to manufacture the piezoelectric transformer.

  According to the present invention, by setting the length of the second high voltage portion, the capacitance generated between the first high voltage electrode and the first low voltage electrode (or the second low voltage electrode), (2) The capacitance ratio with the capacitance generated between the high voltage electrode and the first low voltage electrode (or the second low voltage electrode) can be adjusted. That is, the capacity ratio generated in the high pressure part and the low pressure part can be determined.

Circuit diagram of wireless power transmission system according to the present invention 1 is a perspective view of a piezoelectric transformer according to Embodiment 1. FIG. Sectional view taken along line III-III in FIG. Sectional view taken along line IV-IV in FIG. The figure for demonstrating the polarization direction of a 1st high voltage area | region, a 2nd high voltage area | region, and a low voltage area | region. The perspective view of the piezoelectric transformer which shows another example of Embodiment 1. FIG. Sectional view taken along line VII-VII in FIG. Sectional drawing of the piezoelectric transformer which concerns on Embodiment 2. FIG. Sectional drawing of the piezoelectric transformer which concerns on Embodiment 3. FIG. A perspective view of a piezoelectric transformer according to a fourth embodiment. Sectional view taken along line XI-XI in FIG. Sectional drawing of the piezoelectric transformer which concerns on Embodiment 5. FIG.

(Embodiment 1)
Hereinafter, the piezoelectric transformer according to the present invention will be described as being used in a wireless power transmission system that wirelessly transmits power from a power transmission device to a power reception device using electric field coupling. First, a wireless power transmission system will be described.

  FIG. 1 is a circuit diagram of a wireless power transmission system 100 according to the present invention. The wireless power transmission system 100 includes a power transmission device 101 and a power reception device 201.

  The power transmission apparatus 101 includes an input power supply circuit 11. The input power circuit 11 converts a DC voltage (for example, DC 19 V) converted from an AC voltage (AC 100 V to 230 V) by an AC adapter connected to a commercial power source into an AC voltage by a DC-AC inverter circuit, and boosts the voltage by a step-up transformer. To do. It is desirable to generate a sinusoidal AC voltage by resonating the inductance component of the step-up transformer and the capacitance of the capacitive coupling portion.

  An active electrode 12 and a passive electrode 13 are connected to the input power circuit 11. The active electrode 12 and the passive electrode 13 are both flat, and the active electrode 12 has a smaller area than the passive electrode 13. The active electrode 12 is on the high potential side, and the passive electrode 13 is on the low potential side. An alternating voltage output from the input power supply circuit 11 is applied to the active electrode 12 and the passive electrode 13.

  A capacitance component including a series circuit of capacitors C1a and C1p is connected in parallel to the input power supply circuit 11, more specifically, to the secondary coil of the step-up transformer provided in the input power supply circuit 11. The capacitive component including the capacitors C1a and C1p forms a parallel resonance circuit with the inductance of the step-up transformer. The capacitance component including the capacitors C1a and C1p forms a series resonance circuit together with the leakage inductance of the secondary coil of the step-up transformer or the inductor of the actual part.

  A capacitor C3 is connected to the active electrode 12 and the passive electrode 13. The capacitor C3 is a stray capacitance generated between the active electrode 12 and the passive electrode 13, or a stray capacitance generated between coils of the step-up transformer included in the input power supply circuit 11. C3, together with C1a and C1p, is a part of the capacity that resonates with the leakage inductance component on the power transmission side, and is an element that sets the resonance frequency of the power transmission side resonance circuit.

  The power receiving device 201 includes an active electrode 22 and a passive electrode 23. Each of the active electrode 22 and the passive electrode 23 has substantially the same area as each of the active electrode 12 and the passive electrode 13, and when the power receiving device 201 is placed on the power transmitting device 101, the active electrode 12 and the passive electrode of the power transmitting device 101. It faces 13 through a gap. When an AC voltage is applied to the active electrode 12 and the passive electrode 13, an electric field is generated in the active electrodes 12, 22 and the passive electrodes 13, 22 that are opposed to each other. Power is transmitted to 201.

  A capacitor C4 is connected to the active electrode 22 and the passive electrode 23. The capacitor C4 is a stray capacitance generated between the active electrode 22 and the passive electrode 23. It is desirable that the capacitor C4 be as small as possible in order to increase the degree of coupling between the power transmitting apparatus 101 and the power receiving apparatus 201 and reduce reactive power.

  In addition, the piezoelectric transformer 21 according to the first embodiment is connected to the active electrode 22 and the passive electrode 23 of the power receiving device 201. The piezoelectric transformer 21 includes a first input electrode E31 and a second input electrode E32, and a first output electrode E33 and a second output electrode E34. The active electrode 22 is connected to the input electrode E31, and the passive electrode 23 is connected to the second input electrode E32. The piezoelectric transformer 21 steps down the voltage applied to the first input electrode E31 and the second input electrode E32 and outputs the voltage from the first output electrode E33 and the second output electrode E34.

  The first output electrode E33 and the second output electrode E34 are connected to the secondary circuit (including the reference potential) of the power receiving apparatus 201. A resonance inductor L1, a rectification diode bridge DB, a smoothing inductor L2 and a capacitor C5 are connected to the first output electrode E33 and the second output electrode E34. The rectified and smoothed voltage is supplied to a load circuit RL including a secondary battery and a charging circuit.

  Although the specific configuration of the piezoelectric transformer 21 will be described later, the first input electrode E31 and the second input electrode E32, and the first output electrode E33 and the second output electrode E34 of the piezoelectric transformer 21 are kept insulative. . For this reason, in the step-down unit of the power receiving apparatus 201, the influence of noise due to the high-voltage unit (the coupling of the active electrodes 12 and 22) to the load circuit RL side can be suppressed by electrically insulating the input and output.

  1 is a capacitance component generated between the first input electrode E31 and the first output electrodes E33 and E34 of the piezoelectric transformer 21, and the capacitor C2p includes the second input electrode E32 and the second input electrode E32. 1 is a capacitance component generated between the output electrodes E33 and E34. The first output electrode E33 is connected to the reference potential of the power receiving device 201. In other words, the capacitor C2a is a capacitance generated between the active electrode 22 and the reference potential, and the capacitor C2p is a capacitance generated between the passive electrode 23 and the reference potential.

  Here, on the power transmission device 101 side, in order to maintain the connection point of the capacitors C1a and C1p at the reference potential (0 V) of the power transmission device 101, the capacitance ratio of the capacitors C1a and C1p is (according to the equilibrium condition of Wheatstone bridge). The capacitance ratio between the capacitance formed by the active electrodes 12 and 22 and the capacitance formed by the passive electrodes 13 and 23 is set to be the same.

  Similarly, also on the power receiving device 201 side, in order to maintain the connection point of the capacitors C2a and C2p, that is, the potential (reference potential) of the first output electrode E33 at a constant value (0 V), the capacitance ratio of the capacitors C2a and C2p. Is desired to be the same as the capacitance ratio between the capacitance formed by the active electrodes 12 and 22 and the capacitance formed by the passive electrodes 13 and 23. In this case, the reference potential of the power receiving apparatus 201 can be stabilized, and as a result, problems due to fluctuations in the reference potential can be suppressed. For this reason, the piezoelectric transformer 21 according to the present embodiment has a capacitance between the first input electrode E31 and the first output electrode E33 and a capacitance between the second input electrode E32 and the first output electrode E33. The ratio can be set.

  In addition, by connecting capacitors externally, it is possible to absorb variations due to individual differences of piezoelectric transformers or to have a slightly different capacitance ratio. In this case, the capacitance value of the external capacitor can be minimized, and a decrease in the coupling degree of the electric field coupling portion can be minimized.

  Below, the specific structure of the piezoelectric transformer 21 which concerns on this embodiment is demonstrated.

  FIG. 2 is a perspective view of the piezoelectric transformer according to the first embodiment. 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. 2 is a perspective view, the internal electrodes shown in FIGS. 3 and 4 are omitted.

  The piezoelectric transformer 1 according to this embodiment includes a rectangular plate-shaped piezoelectric body plate 30 having a length L, a thickness T, and a width W. The piezoelectric plate 30 is formed by stacking, for example, PZT ceramic sheets. In the following, the length direction is the X-axis direction, the width direction is the Y-axis direction, and the thickness direction is the Z-axis direction.

  The piezoelectric transformer 21 according to the present embodiment is assumed to vibrate in the length direction in the (λ / 2) resonance mode. Here, λ is one wavelength of vibration in the length direction. Therefore, the length L is (λ / 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 the vibration of the entire piezoelectric transformer 21 is not unstable.

  The piezoelectric plate 30 has a first high voltage region 31, a second high voltage region 32, and a low voltage region 33 formed along the X-axis direction. More specifically, the first high voltage region 31 and the second high voltage region 32 are provided on both ends of the piezoelectric plate 30 with the low voltage region 33 interposed therebetween. The length of the first high voltage region 31 is longer than that of the second high voltage region 32.

  The first high voltage region 31 is provided with a first input electrode E31, and the second high voltage region 32 is provided with a second input electrode E32. The first input electrode E31 and the second input electrode E32 are provided on both side surfaces of the piezoelectric plate 30 facing each other in the X-axis direction, and face each other. The first input electrode E31 is connected to the active electrode 22 shown in FIG. 1, and the second input electrode E32 is connected to the passive electrode 23. The first input electrode E31 corresponds to a first high voltage electrode according to the present invention, and the second input electrode E32 corresponds to a second high voltage electrode according to the present invention.

  A first output electrode E33 and a second output electrode E34 are provided on the side surface of the low voltage region 33 facing the Y-axis direction. The low voltage region 33 is provided with a plurality of internal electrodes E331 and E341 that are alternately provided along the Z-axis direction. The internal electrode E331 is connected to the first output electrode E33, and the internal electrode E341 is connected to the second output electrode E34. That is, the first output electrode E33 and the internal electrode E331 form an electrode having the same potential, and this electrode corresponds to the first low voltage electrode according to the present invention. The second output electrode E34 and the internal electrode E341 form an electrode having the same potential, and this electrode corresponds to the second low voltage electrode according to the present invention. The first output electrode E33 and the second output electrode E34 are connected to a rectifying / smoothing circuit including a diode bridge DB. The first output electrode E33 is connected to the reference potential of the power receiving device 201.

  FIG. 5 is a diagram for explaining the polarization directions of the first high voltage region 31, the second high voltage region 32, and the low voltage region 33. The arrows shown in FIG. 5 are the polarization directions in the regions 31 to 33, and the broken lines indicate the stress distribution of the piezoelectric plate 30. The waveform shown in the lower part of FIG. 5 shows the displacement distribution of the vibrating piezoelectric plate 30.

  The first high voltage region 31 has a length L / 2. The second high voltage region 32 has a length X (<L / 2). Each of the first high voltage region 31 and the second high voltage region 32 is polarized in the X-axis direction. The low voltage region 33 is polarized in the Z-axis direction. Examples of the polarization treatment method include a method of applying a voltage of 2 kV / mm to the piezoelectric plate 30 in an insulating oil at 170 ° C.

  When the piezoelectric transformer 21 is mounted, the piezoelectric transformer 21 is supported and wired at the position P where the vibration displacement is the smallest (broken arrow in the figure), so that the vibration of the piezoelectric transformer 21 is not hindered. It is possible to prevent the connection reliability from lowering due to the displacement of the piezoelectric plate 30 later. In the present embodiment, the length of the first high voltage region 31 is L / 2. However, as described above, the low voltage region 33 may be formed so as to straddle the position P where the vibration displacement is smallest. The length of one high voltage region 31 is not necessarily L / 2.

  In the piezoelectric transformer 1, when an AC voltage is applied to the first input electrode E31 and the second input electrode E32, longitudinal vibration in the length direction is excited by the inverse piezoelectric effect, and the entire piezoelectric plate 30 vibrates. Thereby, in the low voltage region 33, a voltage is generated between the internal electrodes E331 and E341 due to the piezoelectric effect. Then, it is possible to take out the transformed (step-down) voltage from the first output electrode E33 and the second output electrode E34.

  In the piezoelectric transformer 21 configured as described above, by determining the length X of the second high voltage region 32, each of the capacitors C2p between the second input electrode E32 and the second output electrode E33 described in FIG. Can be set. As a result, the capacitance ratio of the capacitors C2a and C2p can be set, and the capacitance ratio between the capacitance formed by the active electrodes 12 and 22 and the capacitance formed by the passive electrodes 13 and 23 can be made the same. Thereby, the reference potential of the power receiving apparatus 201 can be stabilized.

  In addition, since the first input electrode E31 and the second input electrode E32 are insulated from the first output electrode E33 and the second output electrode E34, an insulating transformer can be realized by the piezoelectric transformer 21, and a high voltage is generated. Can be handled. Furthermore, by using the piezoelectric transformer 21 for the transformer, the power receiving device 201 can be reduced in size and height.

  FIG. 6 is a perspective view of a piezoelectric transformer 21 showing another example of the first embodiment. 7 is a cross-sectional view taken along line VII-VII in FIG.

  In this example, the configuration of the input electrodes provided in the first high voltage region 31 and the second high voltage region 32 is different from the configuration shown in FIGS. Opposite first input electrodes E31A and E31B are provided on the side surfaces of the first high voltage region 31 that oppose each other in the Y-axis direction. A plurality of internal electrodes E311 provided along the Z-axis direction are provided in the first high voltage region 31. The laminated internal electrodes E311 are alternately connected to the first input electrodes E31A and E31B.

  Similarly, opposing second input electrodes E32A and E32B are provided on the side surfaces of the second high voltage region 32 that face each other in the Y-axis direction. A plurality of internal electrodes E321 provided along the Z-axis direction are provided inside the second high voltage region 32. The laminated internal electrodes E321 are alternately connected to the second input electrodes E32A and E32B.

  That is, the first input electrodes E31A, E31B and the internal electrode E311 form one electrode, and the second input electrodes E32A, E32B and the internal electrode E321 form one electrode.

  The piezoelectric transformer 21 of this example can be mounted on the same plane (both side surfaces in this example) of the piezoelectric plate 30 for both the input electrode and the output electrode, so that the piezoelectric transformer 21 can be easily mounted.

(Embodiment 2)
The piezoelectric transformer according to Embodiment 2 of the present invention will be described below. The piezoelectric transformer according to this embodiment vibrates in the λ resonance mode.

  FIG. 8 is a cross-sectional view of the piezoelectric transformer according to the second embodiment. The arrows shown in FIG. 8 are the polarization directions in the regions 31 to 33, and the broken lines indicate the stress distribution of the piezoelectric plate 30. The waveform shown in the lower part of FIG. 8 shows the displacement distribution of the vibrating piezoelectric plate 30. In FIG. 8, internal electrodes E331 and E341 (see FIG. 3) provided in the low voltage region 33 are the same as those in the first embodiment, and illustration thereof is omitted.

  In this example, like the first embodiment, the first high voltage region 31 has a length L / 2. The second high voltage region 32 has a length X (<L / 2). The polarization direction of the second high voltage region 32 is opposite to the polarization direction of the first high voltage region 31. In the case of the λ mode of the present embodiment, unlike the first embodiment, the direction of the stress is reverse with respect to the center of the piezoelectric plate 30 (the boundary between the first high voltage region 31 and the low voltage region 33). Therefore, the polarization directions of the first high voltage region 31 and the second high voltage region 32 need to be opposite to each other.

  In this example as well, the capacitance ratio of the capacitors C2a and C2p shown in FIG. 1 can be set by setting the length of the second high voltage region 32 in the X-axis direction as in the first embodiment. Further, when the piezoelectric transformer 21 is mounted, it is preferable to support and wire the piezoelectric transformer 21 at a position P having a smallest displacement distribution (broken arrow in the figure).

  In addition, since the first input electrode E31 and the second input electrode E32 are insulated from the first output electrode E33 and the second output electrode E34, an insulating transformer can be realized by the piezoelectric transformer 21, and a high voltage is generated. Can be handled. Furthermore, by using the piezoelectric transformer 21 for the transformer, the power receiving device 201 can be reduced in size and height.

(Embodiment 3)
The piezoelectric transformer according to Embodiment 3 of the present invention will be described below. The piezoelectric transformer according to this embodiment vibrates in the (4λ / 2) resonance mode.

  FIG. 9 is a cross-sectional view of the piezoelectric transformer according to the third embodiment. The arrows shown in FIG. 9 are the polarization directions in the regions 31 to 33, and the broken lines indicate the stress distribution of the piezoelectric plate 30. Further, the waveform shown in the lower part of FIG. 9 shows the displacement distribution of the vibrating piezoelectric plate 30. In FIG. 9, internal electrodes E331 and E341 (see FIG. 3) provided in the low voltage region 33 are the same as those in the first embodiment, and illustration thereof is omitted.

  In this example, the first high voltage region 31 has a length L / 2. The first high voltage region 31 includes a first region 311 and a second region 312 that are equally divided. Since the stress directions of the first region 311 and the second region 312 are reversed with respect to the boundary, the polarization directions of the first region 311 and the second region 312 are opposite to each other. In this case, a polarization internal electrode E35 having a laminated structure is provided between the first region 311 and the second region 312.

  Second high voltage region 32 has a length L / 4. That is, the length of the first high voltage region 31 in the X-axis direction is about twice that of the second high voltage region 32, and the capacitance of the capacitor C2p is twice that of the capacitor C2a. The second high voltage region 32 has the same stress direction and the same polarization direction as the second region 312 of the first high voltage region 31.

  In this example as well, the capacitance ratio of the capacitors C2a and C2p shown in FIG. 1 can be set by setting the length of the second high voltage region 32 in the X-axis direction as in the first embodiment. In this case, the capacitance ratio of the capacitors C2a and C2p is 1: 2. Further, when the piezoelectric transformer 21 is mounted, it is preferable to support and wire the piezoelectric transformer 21 at a position P having a smallest displacement distribution (broken arrow in the figure). Furthermore, the piezoelectric transformer 21 according to the present embodiment that vibrates in the (4λ / 2) resonance mode can be driven at a high frequency, and can achieve high power.

  In addition, since the first input electrode E31 and the second input electrode E32 are insulated from the first output electrode E33 and the second output electrode E34, an insulating transformer can be realized by the piezoelectric transformer 21, and a high voltage is generated. Can be handled. Furthermore, by using the piezoelectric transformer 21 for the transformer, the power receiving device 201 can be reduced in size and height.

(Embodiment 4)
The piezoelectric transformer according to Embodiment 4 of the present invention will be described below. The piezoelectric transformer according to the present embodiment vibrates in the (4λ / 2) resonance mode as in the third embodiment, but differs in that the length of the second high voltage region is shorter than that in the third embodiment.

  FIG. 10 is a perspective view of the piezoelectric transformer according to the fourth embodiment. 11 is a cross-sectional view taken along line XI-XI in FIG. The arrows shown in FIG. 11 are the polarization directions in the regions 31 to 33, and the broken lines indicate the stress distribution of the piezoelectric plate 30. Further, the waveform shown in the lower part of FIG. 11 shows the displacement distribution of the vibrating piezoelectric plate 30. In FIG. 11, internal electrodes E331 and E341 (see FIG. 3) provided in the low voltage region 33 are the same as those in the first embodiment, and illustration thereof is omitted.

  In this example, the first high voltage region 31 has a length L / 2 as in the third embodiment. The first high voltage region 31 includes a first region 311 and a second region 312 whose polarization directions are opposite directions. Between the first region 311 and the second region 312, a polarization-structured internal electrode E35 having a laminated structure is provided.

  The second high voltage region 32 has a length X (<L / 4). Since the length of the second high voltage region 32 in the X-axis direction is shortened, the length of the low voltage region 33 is longer than L / 4 (= λ / 2). As a result, in the low voltage region 33, there are two regions where the stress distributions are in opposite directions. For this reason, the low voltage region 33 includes a first region 331 and a second region 332 that are divided at a position where the stress distribution is in the opposite direction. The first region 331 and the second region 332 have opposite polarization directions. The output electrode provided in the low voltage region 33 is separated into a first region 331 and a second region 332. Specifically, a first output electrode E33A and a second output electrode E34A that are opposed to each other in the Y-axis direction are provided in the first region 331, and a second output electrode E33B and a second output electrode that are opposed to each other in the Y-axis direction are provided in the second region 332. An output electrode E34B is provided.

  Although not shown in FIG. 11, the plurality of internal electrodes described in FIG. In the present embodiment, the plurality of internal electrodes are provided separately in the first region 331 and the second region 332.

  In this example as well, the capacitance ratio of the capacitors C2a and C2p shown in FIG. 1 can be set by setting the length of the second high voltage region 32 in the X-axis direction as in the first embodiment. Further, when the piezoelectric transformer 21 is mounted, it is preferable to support and wire the piezoelectric transformer 21 at a position P having a smallest displacement distribution (broken arrow in the figure). Furthermore, the piezoelectric transformer 21 according to the present embodiment that vibrates in the (4λ / 2) resonance mode can be driven at a high frequency, and can achieve high power.

  In addition, since the first input electrode E31 and the second input electrode E32 are insulated from the first output electrode E33 and the second output electrode E34, an insulating transformer can be realized by the piezoelectric transformer 21, and a high voltage is generated. Can be handled. Furthermore, by using the piezoelectric transformer 21 for the transformer, the power receiving device 201 can be reduced in size and height.

(Embodiment 5)
The piezoelectric transformer according to Embodiment 5 of the present invention will be described below. The piezoelectric transformer according to this embodiment vibrates in the (7λ / 2) resonance mode.

  FIG. 12 is a cross-sectional view of the piezoelectric transformer according to the fifth embodiment. The arrows shown in FIG. 12 are the polarization directions in the respective regions 31 to 33, and the broken lines indicate the stress distribution of the piezoelectric plate 30. Further, the waveform shown in the lower part of FIG. 12 shows the displacement distribution of the vibrating piezoelectric plate 30.

  The first high voltage region 31 has a length of 3L / 7. The first high voltage region 31 includes a first region 311, a second region 312, and a third region 313 having the same length L / 7 (= λ / 2). The first region 311 and the third region 313 have the same direction of stress and the same polarization direction. The second region 312 has a direction of stress opposite to that of the first region 311 and the third region 313, and thus the polarization direction is also opposite. Further, polarization internal electrodes E351 and E352 having a laminated structure are provided between the first region 311 and the second region 312 and between the second region 312 and the third region 313, respectively.

  The second high voltage region 32 has a length L / 7 (= λ / 2). The second high voltage region 32 has the same stress direction as that of the first region 311 and the third region 313, and the polarization direction is also the same as that of the first region 311 and the third region 313.

  The low voltage region 33 has a length of 3L / 7. The low voltage region 33 includes a first region 331, a second region 332, and a third region 333 having the same length L / 7 (= λ / 2). The first region 331 and the third region 333 have the same stress direction and the same polarization direction. The second region 332 is opposite to the first region 331 and the third region 333 in the direction of stress, and the polarization direction is opposite to that of the first region 331 and the third region 333. Although not shown, the output electrode provided in the low voltage region 33 is separated into a first region 331, a second region 332, and a third region 333, as in the fourth embodiment. Further, although not shown in FIG. 12, the plurality of internal electrodes described in FIG. In the present embodiment, the plurality of internal electrodes are provided separately in the first region 331, the second region 332, and the third region 333, respectively.

  In this example as well, the capacitance ratio of the capacitors C2a and C2p shown in FIG. 1 can be set by setting the length of the second high voltage region 32 in the X-axis direction as in the first embodiment. In this case, the capacitance ratio of the capacitors C2a and C2p is 1: 3. Further, when the piezoelectric transformer 21 is mounted, it is preferable to support and wire the piezoelectric transformer 21 at a position P having a smallest displacement distribution (broken arrow in the figure). Furthermore, the piezoelectric transformer 21 according to the present embodiment that vibrates in the (7λ / 2) resonance mode can be driven at a high frequency, and can achieve high power.

  In addition, since the first input electrode E31 and the second input electrode E32 are insulated from the first output electrode E33 and the second output electrode E34, an insulating transformer can be realized by the piezoelectric transformer 21, and a high voltage is generated. Can be handled. Furthermore, by using the piezoelectric transformer 21 for the transformer, the power receiving device 201 can be reduced in size and height.

  As described above, the piezoelectric transformer according to the present invention has been described in the first to fifth embodiments. However, any of the piezoelectric transformers can set the capacitance ratio of the capacitors C2a and C2p. By using this piezoelectric transformer for the device 201, the reference potential of the power receiving device 201 can be stabilized. As a result, it is possible to prevent problems caused by fluctuations in the reference potential. Further, by using a piezoelectric transformer for the power receiving apparatus 201, the power receiving apparatus 201 can be reduced in size and height.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric transformer 11 ... Input power supply circuit 12 ... Active electrode (power transmission side active electrode)
13 ... Passive electrode (power transmission side passive electrode)
21 ... Piezoelectric transformer 22 ... Active electrode (power-receiving-side active electrode)
23 ... Passive electrode (power-receiving-side passive electrode)
30 ... piezoelectric plate 31 ... first high voltage region (first high voltage part)
32. Second high voltage region (second high voltage section)
33 ... Low voltage region (low voltage part)
DESCRIPTION OF SYMBOLS 100 ... Wireless power transmission system 101 ... Power transmission apparatus 201 ... Power receiving apparatus 311 ... 1st area | region 312 ... 2nd area | region 313 ... 3rd area | region 331 ... 1st area | region 332 ... 2nd area | region 333 ... 3rd area | region C1a, C1p ... Capacitor C2a , C2p, capacitor C2p, capacitors C3, C4, C5, capacitor DB, diode bridge E31, first input electrode E311, internal electrodes E31A, E31B, first input electrode E32, second input electrode E321, internal electrodes E32A, E32B,. 2nd input electrode E33 ... 1st output electrode E33 ... 2nd output electrode E331, E341 ... Internal electrode E33A ... 1st output electrode E33B ... 2nd output electrode E34 ... 2nd output electrode E341 ... Internal electrode E34A ... 2nd output electrode E34B: Second output electrode E35: Polarization internal electrodes E351, E352: Polarization Part electrodes L1, L2 ... inductor RL ... load circuit

Claims (5)

A piezoelectric transformer using a longitudinal vibration mode of order n (n is an integer of 1 or more),
When the 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,
The piezoelectric plate is
Along the length direction, the first high voltage part, the low voltage part, and the second high voltage part in order,
The low voltage part is
The polarization direction is the thickness direction, and the first low voltage electrode and the second low voltage electrode are opposed to the thickness direction,
The first high voltage unit includes:
The polarization direction is the length direction, and has a first high voltage electrode provided at one end of the piezoelectric plate,
The second high voltage unit includes:
The polarization direction is the length direction, and has a second high voltage electrode provided at the other end of the piezoelectric plate,
The first high voltage part and the second high voltage part have different lengths.
Piezoelectric transformer. The order n is 4 or more;
The low voltage part is
Divided into multiple regions in the length direction, the direction of the stress distribution at the time of stress generation is reversed at the boundary with the adjacent region,
The plurality of regions have opposite directions to the adjacent regions of the respective polarization directions;
The first low voltage electrode and the second low voltage electrode are provided in each of the plurality of regions.
The piezoelectric transformer according to claim 1. The order n is 4 or more;
At least one of the first high voltage part and the second high voltage part is:
The boundary electrode is divided into a plurality of regions in the length direction and provided in the thickness direction at the boundary with the adjacent region,
The plurality of regions are in directions opposite to the regions where the respective polarization directions are adjacent to each other.
The piezoelectric transformer according to claim 1 or 2.   The piezoelectric transformer according to claim 1, wherein the piezoelectric plate is a laminated body in which a plurality of piezoelectric ceramic sheets are laminated. A power transmission device for applying a voltage to the power transmission side active electrode and the power transmission side passive electrode;
A power receiving device that steps down a voltage generated between a power receiving side active electrode facing the power transmitting side active electrode and a power receiving side passive electrode facing the power transmitting side passive electrode by a step-down unit;
With
The step-down unit is
n (n is an integer of 1 or more) having a piezoelectric transformer using the following longitudinal vibration mode,
The piezoelectric transformer is
When the 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,
The piezoelectric plate is
Along the length direction, the first high voltage part, the low voltage part, and the second high voltage part in order,
The low voltage part is
The polarization direction is the thickness direction, and the first low voltage electrode and the second low voltage electrode are opposed in the width direction,
The first high voltage unit includes:
The polarization direction is the length direction, and has a first high voltage electrode provided at one end of the piezoelectric plate,
The second high voltage unit includes:
The polarization direction is the length direction, and has a second high voltage electrode provided at the other end of the piezoelectric plate,
The wireless power transmission system, wherein the first high voltage unit and the second high voltage unit have different lengths.

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