JPH11186627A - Piezoelectric transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized piezoelectric transducer which can be used without hindrance even when the oscillating speed of the transducer approaches its limit oscillating speed and, at the same time, which utilizes an oscillation mode in which stress hardly exists on the surface of a piezoelectric body. SOLUTION: A piezoelectric transducer is composed of a piezoelectric body 11 (rectangular piezoelectric ceramic thin plate) which is formed by laminating a plurality of piezoelectric thin plates (rectangular piezoelectric ceramic thin plates) upon another in one direction in which the thickness of the body 11 is decided and in which a plurality of pairs of electrodes 12, 13, and 14 are arranged in one direction in such a state that the electrodes 12, 13, and 14 are faced oppositely to each other and part 12 and 13 of the electrode pairs are used for exciting the energy trapping oscillation mode of a thickness mode. The other electrode pairs 13 and 14 are used for taking out the output associated with the excitation of the energy confining oscillation mode. Since the polarization among the electrodes 12, 13, and 14 which are faced oppositely to each other in one direction is made in the direction shown by the arrow and an oscillation mode in which stress hardly exists on the surface of the piezoelectric body 11 is used, the transduce can be used without hindrance even when the oscillating speed of the transducer approaches its limit speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly used for DC / DC converters and DC / AC inverters provided in small-sized portable electronic equipment and OA equipment, and has a vibration mode in which there is almost no stress on the piezoelectric body surface. The present invention relates to a small-sized piezoelectric transformer used.

[0002]

2. Description of the Related Art Conventionally, this type of piezoelectric transformer utilizes an inverse piezoelectric effect and a piezoelectric effect of a piezoelectric vibrating element, first converts electric input into mechanical energy to mechanically excite a piezoelectric vibrator, and It is known as an electronic device that obtains voltage boosting and step-down functions by converting this mechanical vibration into electrical output again, and has the feature of having no windings as compared with general-purpose electromagnetic transformers. doing.

FIG. 4 is a perspective view showing a basic structure of a conventional piezoelectric transformer. In this piezoelectric transformer, opposing electrodes 42a and 42b are formed on upper and lower surfaces of a region approximately half in the length direction of a piezoelectric body (piezoelectric ceramic rectangular plate) 41, and this region is subjected to a polarization process in a thickness direction. And the piezoelectric body 41
An electrode 43 is formed on the longitudinal end face of the other half of the region, and this region is polarized in the longitudinal direction. The electrodes 42a, between 42b are hardwired to the input voltage V _in is applied, so that the output voltage V _out between a predetermined position and the electrodes 43 of the electrode 42b side of the wiring is obtained Are connected by wire.

FIG. 5 shows an electric equivalent circuit including a mechanical vibration system of the piezoelectric transformer. The equivalent circuit, the step-up ratio 1: A1 braking between the input terminal T _in the primary side defined by the (constant) capacity Cd1 is formed, the step-up ratio A2
(Constant) A braking capacitance Cd2 is formed between the secondary-side output terminals T _out defined by 1, and a series inductance m, a series capacitance s, and a series resistance r are connected in series between the braking capacitance Cd1 and the braking capacitance Cd2. Made of connected.

FIG. 6 is a rewritten version of this equivalent circuit as viewed from the input side. In this equivalent circuit, the form in place of the step-up ratio, the input terminal T _in between the primary side of the damping capacity Cd1 is connected to an AC power supply including a resistance while being formed, the braking of the secondary side between the output terminal T _out Capacity Cd2
, A load resistance RL is connected, and a series inductance L, a series capacitance C, and a series resistance R are connected in series between the braking capacitance Cd1 and the braking capacitance Cd2.

In these equivalent circuits, the input terminal T _in is connected to the electrodes 42a and 42b, respectively, and the output terminal T _out is connected.
Are connected to the electrodes 43 and 42b, respectively. In these equivalent circuits, applying an AC voltage of a frequency approximately equal to the resonant frequency of the resonant modes of the piezoelectric element 41 to the input terminal T _in, the piezoelectric body 41 resonates in the corresponding vibration mode. As a resonance mode, a primary (half wavelength) or secondary (one wavelength) mode is generally used.

At this time, in the equivalent circuit shown in FIG. 6, the series inductance L and the combined capacitance C 'obtained by combining the series capacitance C and the capacitance Cd2' resonate, the current flowing through the circuit becomes maximum, and the combined capacitance C ' terminal voltage input voltage _{V in} = V _o
Qm times of Here, Qm is a quality coefficient representing the sharpness of resonance, and given by ωr = 2πfr (fr is the resonance frequency), Qm = ωrL / R. Therefore, the output voltage _Vout is obtained by dividing the voltage generated at the terminal voltage of the combined capacitor C 'by the capacitor Cd2'.

In an actual piezoelectric transformer, Qm is effectively changed by a load resistance. In order to improve the power efficiency, the braking capacity Cd1 on the input side and the braking capacity Cd1 on the output side are improved.
An inductor that resonates at the resonance frequency is connected in series or parallel with the inductor 2. Further, on the output side, a load resistor RL may be connected to the braking capacitor Cd2 instead of connecting an inductor, but this load resistor RL is RL = 1 /
(ΩrCd2).

When an attempt is made to construct a small piezoelectric transformer, one criterion is how large the amplitude of the piezoelectric material can be excited. In general, not only the piezoelectric material but also the excitation of a large-amplitude elastic body generates or destroys heat due to an increase in internal loss. it can.

Such an amplitude limit greatly differs depending on the piezoelectric material. In the case of ordinary piezoelectric ceramics, the vibration speed is about 0.3 m / s, whereas LiN
In the case of a piezoelectric single crystal such as bO _3, it is about one digit larger. Since the energy of the mechanical oscillator is proportional to the square of the oscillation speed and the volume, it is expected that the size can be significantly reduced by forming a piezoelectric transformer using such a piezoelectric single crystal.

[0011]

In the case of the above-described piezoelectric transformer shown in FIG. 4, if a piezoelectric single crystal is used as the piezoelectric material of the piezoelectric body, the volume should be reduced to several tenths in principle. In practice, the stress applied to the piezoelectric body increases in proportion to the increase in the vibration speed, so a serious drawback is that the piezoelectric body breaks at a vibration speed lower than the expected vibration speed due to minute cracks generated during machining. There is.

The present invention has been made in order to solve such a problem, and the technical problem thereof is that a vibration mode in which almost no stress is applied to the surface of a piezoelectric body can be used without any problem even in a state near a vibration limit speed. An object of the present invention is to provide a small-sized piezoelectric transformer utilizing the above.

[0013]

According to the present invention, a plurality of piezoelectric thin plates are stacked in one direction to determine the thickness so that a plurality of electrodes are arranged in a plurality of pairs in the one direction so as to face each other. A plurality of electrodes, some of which form a plurality of pairs are used for exciting the energy confinement vibration mode in the thickness vibration mode, and the others are used for exciting the energy confinement vibration mode. As a result, a piezoelectric transformer used for taking out an output voltage accompanying the excitation of the vibration mode is obtained.

Further, according to the present invention, in the above-mentioned piezoelectric transformer, a piezoelectric transformer in which the piezoelectric thin plate is made of a piezoelectric single crystal and the piezoelectric body is laminated by coupling the piezoelectric single crystal is obtained.

Further, according to the present invention, in any one of the above-mentioned piezoelectric transformers, the electrode buried inside the plural pairs of electrodes is disposed in a portion other than the nodal surface of the thickness vibration in the piezoelectric body. A piezoelectric transformer is obtained.

In addition, according to the present invention, in any one of the above piezoelectric transformers, the electrodes forming a plurality of pairs include extraction electrodes for extracting to the outside, and the extraction electrodes have different potentials in one direction from each other. A piezoelectric transformer is obtained which is displaced so as not to overlap with another one.

[0017]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows the basic structure of a piezoelectric transformer according to an embodiment of the present invention. FIG. 1 (a) relates to an external perspective view, and FIG. 1 (b) shows the same. A-
It relates to a sectional side view in the direction of the line A '.

In this piezoelectric transformer, a plurality of piezoelectric thin plates (piezoelectric ceramic rectangular thin plates) are stacked in one direction to determine the thickness, so that a plurality of electrodes 12, 13, 1 in one direction.
Reference numeral 4 denotes a plurality of pairs of piezoelectric bodies (piezoelectric ceramic rectangular plates) 11 which are arranged to face each other.
Reference numerals 3 and 14 denote a plurality of pairs (electrodes 12 and 1).
3) is used for exciting the energy confinement vibration mode of the thickness vibration mode, and the other parts (electrodes 13,
14) is used for extracting an output voltage accompanying the excitation of the energy trapping vibration mode. Here, it is assumed that the space between the electrodes 12, 13, and 14 facing each other in one direction is polarized in the direction of the arrow in the figure. Further, the piezoelectric thin plate is made of a piezoelectric single crystal, and the piezoelectric body 11 has a small structure in which the piezoelectric single crystals of the piezoelectric thin plate are laminated (or may be bonded) by bonding. Polarized in one direction.

In this piezoelectric transformer, when an AC voltage substantially equal to the resonance frequency of the energy trapping vibration in the thickness longitudinal vibration mode of the piezoelectric plate 11 is applied between the electrodes 12 and 13,
Energy trapped vibration in the thickness longitudinal vibration mode is excited near the opposed electrodes 12 and 13. At this time, an output voltage is generated between the electrodes 13 and 14 by a piezoelectric effect. Here, since the vibration mode in which there is almost no stress on the surface of the piezoelectric body 11 is used, it can be used without any trouble even in a state near the vibration limit speed.

Incidentally, the equivalent circuit of this piezoelectric transformer is:
It can be expressed as exactly the same as the equivalent circuit shown in FIG. 5 or FIG.

In the piezoelectric transformer of this embodiment, the case where the thickness longitudinal vibration mode is applied as the energy trapping vibration mode of the thickness vibration mode has been described. However, the thickness slip vibration mode is applied as another mode. Is also possible.

FIG. 2 is a sectional side view showing a basic configuration and functions of a piezoelectric transformer according to another embodiment of the present invention.

Also in this piezoelectric transformer, a plurality of piezoelectric thin plates (piezoelectric ceramic rectangular thin plates) are stacked in one direction to determine the thickness, so that a plurality of electrodes 22 and 23 are formed in one direction. , 24 in which a plurality of pairs of piezoelectric bodies (piezoelectric ceramic rectangular plates) are arranged facing each other.
A plurality of pairs of electrodes 22, 23, and 24 (electrodes 22, 23) are used for excitation in the energy trapping vibration mode in the thickness vibration mode, and in other parts. The (electrodes 23 and 24) are used for extracting an output voltage accompanying the excitation of the energy trapping vibration mode. Here, a plurality of pairs of electrodes 2
Buried inside (electrode 2
3, 24) are disposed at other portions avoiding the nodal plane of thickness vibration (indicating a plane of maximum stress or zero displacement) in the piezoelectric body 21. Also in this case, it is assumed that the electrodes 22, 23, and 24 facing each other in one direction are polarized as in the case of the embodiment, and the piezoelectric body 21 is bonded by bonding a piezoelectric single crystal of a piezoelectric thin plate (adhesion may be used). ) It is a laminated small structure, whereby the outside of the electrodes 22, 23, 24 is similarly polarized in one direction.

That is, when this piezoelectric transformer is driven by one-wavelength resonance in one direction (thickness direction), referring to FIG.
The stress distribution in the thickness direction is as shown by a curve, and assuming that the thickness of the piezoelectric body 21 is t, a plane with the maximum stress appears at a position of t / 4 from the surface of the piezoelectric body 21. Therefore, since the internal electrodes 23 and 24 are vulnerable to tension, by arranging the internal electrodes 23 and 24 in other portions while avoiding such a surface having a maximum stress or a surface having zero displacement, excellent strength is obtained. It can be a piezoelectric transformer having a structure.

Incidentally, the equivalent circuit of this piezoelectric transformer is
It can be expressed as exactly the same as the equivalent circuit shown in FIG. 5 or FIG.

FIG. 3 is an external perspective view showing a basic configuration of a piezoelectric transformer according to another embodiment of the present invention, with a main part seen through.

In this piezoelectric transformer, as in the case of the embodiment, a plurality of piezoelectric thin plates (piezoelectric ceramic rectangular thin plates) are stacked in one direction to determine the thickness, so that a plurality of electrodes 32 and 33 are formed in one direction. , 34 (piezoelectric ceramic rectangular plate) 3 in which a plurality of pairs are opposed to each other.
A plurality of pairs of electrodes (electrodes 32, 33) are used for exciting the energy confined vibration mode of the thickness vibration mode, and the other parts are used. The (electrodes 33, 34) are used for extracting an output voltage accompanying the excitation of the energy trapping vibration mode. However, a plurality of pairs of electrodes 3
2, 33, and 34 include extraction electrodes 32a, 33a, and 34a, respectively, for taking out to the outside. These extraction electrodes 32a, 33a, and 34a are arranged in one direction (thickness direction; vertical direction in the drawing). ) Are displaced so as not to overlap with other components having different potentials. The electrode 3 buried inside here
The extraction electrodes 33 a and 34 a of the piezoelectric body 31
Are connected by electrodes 35 and 36 formed on the adjacent end faces of. Also in this case, the electrodes 32 facing each other in one direction,
The portions between 33 and 34 are polarized in the same manner as in the embodiment, and the piezoelectric body 31 is a small-sized structure that is laminated (or may be bonded) by bonding a piezoelectric single crystal of a piezoelectric thin plate. , 33, and 34 are similarly polarized in one direction.

That is, a general piezoelectric transformer requires electrodes having at least three different potentials of input, output, and ground. Since the gaps are polarized, undesired propagation and reflection may occur when confining the elastic wave. However, the piezoelectric transformer here takes such points into consideration.

In each of the piezoelectric transformers utilizing the energy confinement vibration mode of the thickness vibration mode described in each of the above embodiments, the upper and lower surfaces of the piezoelectric plates 11, 21 and 31 have the maximum vibration amplitude and no stress. Since the vibration in the energy trapping vibration mode occurs only at the opposed input and output electrodes formed at the center of the piezoelectric plates 11, 21, 31, the piezoelectric plates 11, 21, 31 as the vibrators are maximally formed. When excited within the vibration amplitude limit, if the piezoelectric plate 1
Even if minute cracks are generated on the surfaces and end faces of the first, second, and 31 by machining, the piezoelectric plates 11, 21, and 31 themselves can be used without cracking.

In the piezoelectric transformers of the above embodiments, the case where the thickness longitudinal vibration mode is applied as the energy trapping vibration mode of the thickness vibration mode has been described. It is possible.

[0032]

As described above, according to the piezoelectric transformer of the present invention, since the energy trapping vibration mode of the thickness vibration mode in which the vibration stress on the surface of the piezoelectric material is almost zero is used, Even when excitation is performed with a vibration amplitude close to the maximum vibration velocity limit, a small-sized and efficient piezoelectric transformer can be obtained without fear of destruction of the vibrator (piezoelectric body) due to minute cracks on the surface.

[Brief description of the drawings]

1A and 1B show a basic configuration of a piezoelectric transformer according to one embodiment of the present invention, in which FIG. 1A is related to an external perspective view, and FIG. 1B is a cross section taken along line AA ′ of FIG. It relates to a side view.

FIG. 2 is a cross-sectional side view showing a basic configuration and functions of a piezoelectric transformer according to another embodiment of the present invention.

FIG. 3 is an external perspective view showing a basic configuration of a piezoelectric transformer according to another embodiment of the present invention, with a main part seen through.

FIG. 4 is a perspective view showing a basic configuration of a conventional piezoelectric transformer.

5 shows an electric equivalent circuit including a mechanical vibration system of the piezoelectric transformer shown in FIG.

FIG. 6 is a diagram in which the equivalent circuit shown in FIG. 5 is rewritten as viewed from the input side.

[Explanation of symbols]

11, 21, 31, 41 Piezoelectric body (piezoelectric ceramic rectangular plate) 12 to 14, 22 to 24, 32 to 36, 42a, 42
b, 43 electrode 32a, 33a, 34a extraction electrode

Claims (4)

[Claims] 1. A piezoelectric transformer comprising a piezoelectric body in which a plurality of piezoelectric thin plates are stacked in one direction to determine a thickness, and a plurality of electrodes are arranged in a plurality of pairs so as to face each other in the one direction. In the plurality of electrodes, a part of the plurality of electrodes is used for exciting the energy trapping vibration mode in the thickness vibration mode, and the other part is an output voltage accompanying excitation in the energy trapping vibration mode. A piezoelectric transformer characterized in that it is used for taking out an object. 2. The piezoelectric transformer according to claim 1, wherein
The piezoelectric transformer according to claim 1, wherein the piezoelectric thin plate is made of a piezoelectric single crystal, and the piezoelectric body is stacked by combining the piezoelectric single crystals. 3. The piezoelectric transformer according to claim 1, wherein one of the plurality of pairs of electrodes buried inside is disposed at a portion other than a nodal surface of the thickness vibration in the piezoelectric body. A piezoelectric transformer characterized by the following. 4. The piezoelectric transformer according to claim 1, wherein the plurality of pairs of electrodes include extraction electrodes for extracting to the outside, and the extraction electrodes are mutually separated in the one direction. A piezoelectric transformer, wherein the piezoelectric transformer is displaced so as not to overlap with another one having a different potential.