JP2002329900A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer of high porcelain strength capable of stably outputting a high electric power even if a temperature changes. SOLUTION: A voltage input A1 and a voltage output B1 are alternately formed in the lengthwise direction of a piezoelectric substrate 11 in which both main surfaces are rectangles of a length L and a width W. The voltage input A1 and the voltage output B1 are provided with input side electrodes 12, 13, 15, and 16, and output side electrodes 14 and 17, respectively. The ratio (L/W), where L is the length of the main surface and W is the width of it, of the piezoelectric substrate is 1.1-1.4. The piezoelectric substrate 11 comprises Pb(ZrTi)O3 composite oxide. An A site comprises at least one kind selected from among Ba, Sa, and Ca. A B site comprises Nb, Yb, and Mn. The absolute value of the temperature coefficient of the elastic constant in the widthwise direction of the piezoelectric substrate 11 is 60 ppm/ deg.C or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer used for an AC adapter or a DC-DC converter used for various electronic devices, and a backlight cold-cathode tube inverter for a liquid crystal display used for a notebook computer or a portable terminal. It is about.

[0002]

2. Description of the Related Art In recent years, piezoelectric materials capable of converting electric energy into mechanical energy have been applied to actuators and transformers. In particular, a piezoelectric transformer has the following features as compared with a conventionally used electromagnetic transformer, and has been noticed in recent years for miniaturization and integration of a power supply, and has been partially commercialized.
The piezoelectric transformer (1) does not use any windings, so there is little possibility of smoke or ignition. (2) Since power is transmitted by the reverse piezoelectric effect via the mechanical vibration to the electromagnetic transformer that transmits power by transferring the generated magnetic field, there is no generation of electromagnetic noise. (3) Conversion efficiency can be improved by selecting a material having a small elastic loss.
(4) In terms of energy density, elastic energy is at least one order of magnitude higher than magnetic energy. Utilizing such features, it is spreading as an indispensable electronic component for an inverter circuit for a backlight of a liquid crystal display.

FIG. 10 shows the output power-drive frequency dependence of a piezoelectric transformer. Since the piezoelectric transformer is driven by resonance, it has frequency dependency such that electric power is generated near a vibration point due to the shape and elastic constant of the piezoelectric substrate.

[0004] The control of the output power includes a method of controlling by an external resistance and a method of controlling by a driving frequency. FIG. 11 shows the output power characteristics when the external resistance is changed. As can be understood from FIG. 11, the output control using the external resistance is performed with the frequency dependence curve of the output power greatly fluctuating. Since it is difficult, a method of controlling output power by a driving frequency is generally used. For example, the output power is controlled by fixing the external resistance RL to 500Ω and changing the driving frequency.

FIG. 6 shows a block diagram of a DC-DC converter. In a converter using a piezoelectric transformer, an input voltage having a drive frequency in a certain frequency range is applied to the piezoelectric transformer, the voltage and current converted to DC by a rectifier circuit are detected, and the drive frequency at which desired power is obtained is determined. The detection and the determination of the drive frequency by the feedback circuit are performed at any time, so that stable power supply is performed. In this feedback circuit, for example, an output of 20 W at a driving frequency of 120 kHz,
In the case of 23 W at 121 kHz and 20 W at 122 kHz,
When it is desired to obtain an output of 23 W, a drive frequency of 121 kHz is selected. However, when an output of 20 W is to be obtained, it is not possible to determine which of 120 kHz and 122 kHz is to be selected, resulting in an infinite loop.

Therefore, there must be no plurality of frequencies having the same output power value within the frequency range for detecting the drive frequency, and the usable frequency range is lower than the frequency at which the output power has the maximum value. This means that the frequency range is on either the high frequency side or the high frequency side.

As a material for a piezoelectric transformer, since it can be driven even under a high vibration speed or a large amplitude, the 28th
PbTiO ₃ -Pb disclosed in Japanese Patent No. 36572
ZrO ₃ —Pb (Mn _1/3 Sb _2/3 ) O ₃ based material
PbTiO ₃ -P disclosed in 1-310457
bZrO ₃ -Pb (Mn _1/3 Nb _2/3 ) O ₃ -based material, or Pb (Z) disclosed in JP-A-2000-294849.
(r, Ti) O ₃ has been proposed which contains Fe and Ag.

[0008]

The outer peripheral temperature of the piezoelectric transformer changes every moment due to the self-heating of the piezoelectric transformer and the heat generated by peripheral devices. Initially, the drive frequency was set to a frequency range from the frequency at which the output power shows the maximum value to the low frequency side or the high frequency side.However, the frequency dependence curve of the output power drifted due to a change in the outer peripheral temperature. The maximum value of the output power exists within the range, and there are a plurality of drive frequencies having the same output power value, which makes it difficult to perform output power control using a feedback circuit. was there.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a piezoelectric transformer which can stably output high power even when a temperature change occurs and has high porcelain strength.

[0010]

According to the piezoelectric transformer of the present invention, voltage input portions and voltage output portions are formed alternately in the length direction of a piezoelectric substrate having both main surfaces having a rectangular shape having a length L and a width W. In a piezoelectric transformer in which an input electrode and an output electrode are provided in the voltage input section and the voltage output section, respectively, the ratio (L / W) of the length L to the width W of the main surface of the piezoelectric substrate is 1.1. ~ 1.
4, and the piezoelectric substrate is made of a Pb (ZrTi) O ₃ type composite oxide, the A site contains at least one selected from Ba, Sr and Ca, and the B site contains Nb,
Yb and Mn are contained, and the absolute value of the temperature coefficient of the elastic constant in the width direction of the piezoelectric substrate is 60 ppm /
C. or lower.

In the present invention, since the ratio (L / W) of the length L to the width W of the main surface of the piezoelectric substrate is 1.1 to 1.4, it has high output power, high efficiency, and high energy. It can have conversion efficiency. And the length L of the main surface of the piezoelectric substrate
(F × L) of the driving frequency F and the driving frequency F is 4700 to 6000.
By setting the frequency to kHz · mm, it is possible to obtain a piezoelectric transformer exhibiting high output power and high efficiency characteristics at a low load resistance and having almost no fluctuation in efficiency due to frequency fluctuation.

The product (F × L) of the length L of the main surface of the piezoelectric substrate and the driving frequency F is 4700 to 6000 kHz · m.
By changing the drive frequency F so as to satisfy m, the output power from the voltage output unit of the piezoelectric transformer can be changed.

Further, the piezoelectric substrate is made of Pb (ZrTi) O ₃
Type composite oxide, and A, Ba, Sr and Ca
Containing at least one selected from the group consisting of N
b, Yb and Mn, and the absolute value of the temperature coefficient of the elastic constant in the width direction of the piezoelectric substrate is 60 pp.
Since the temperature is not more than m / ° C., even if the peripheral temperature of the piezoelectric transformer changes, the change in the driving frequency for obtaining the maximum output power is small, and the output power control using the feedback circuit can be easily performed.

Therefore, the piezoelectric transformer of the present invention can excite the vibration mode that causes the largest vibration in the voltage output section, and can generate high output power and high efficiency. Even if the outer peripheral temperature changes, the drift amount of the driving frequency for obtaining high output power is small, and output power control using a feedback circuit can be easily performed.

Further, according to the present invention, the piezoelectric substrate has a molar ratio of
The composition formula according to_1-xA_x[(Nb _eYb_fCo_gMn_h)
_a(Ti_bZr_1-b)_1-a] O_ThreeWhen expressed as above, a,
b and x are 0.05 ≦ a ≦ 0.20 0.5 ≦ b ≦ 0.6 0.02 ≦ x ≦ 0.10 A is at least one selected from Ba, Sr and Ca
It is desirable to satisfy

By having such a composition, higher output power can be obtained, and the absolute value of the temperature coefficient of the elastic constant in the width direction of the piezoelectric substrate can be further reduced. , The change in the driving frequency can be further reduced.

In the present invention, the piezoelectric substrate is made of Pb (Z
The main crystal particles are perovskite type oxide particles composed of rTi) O ₃ type composite oxide, and Zr is formed at the grain boundary of the main crystal particles.
Desirably, O ₂ particles are present. Thereby, the strength of the piezoelectric substrate can be improved without complicating the process, and the variation in the elastic constant in the width direction can be further reduced.

In the present invention, it is particularly preferable that a first voltage input portion, a voltage output portion, and a second voltage input portion are sequentially formed in the length direction of the piezoelectric substrate. Further, the piezoelectric transformer of the present invention can obtain high power and high efficiency by exciting the input voltages to the first voltage input unit and the second voltage input unit with AC signals having the same amplitude and the same phase. .

Further, according to the present invention, a plurality of input side electrodes and a plurality of output side electrodes are formed at predetermined intervals in the thickness direction inside the piezoelectric substrate in the voltage input section and the voltage output section, respectively. , And the output side electrodes are desirably electrically connected alternately. in this way,
By forming the internal electrodes inside the piezoelectric substrate in the voltage input section and the voltage output section, the capacitance can be arbitrarily changed and the step-up / step-down ratio can be controlled.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The single-plate type piezoelectric transformer of the present invention
As shown in FIG. 1, in the length direction of the rectangular piezoelectric substrate 11 which is polarized in the thickness direction and whose main surface is length L and width W,
A first voltage input section A1, a voltage output section B1, and a second voltage input section C1 are sequentially formed.

An input electrode 12, an output electrode 14, and an input electrode 13 are provided on the upper main surface of the piezoelectric substrate 11 in the first voltage input section A1, the voltage output section B1, and the second voltage input section C1. Each of these electrodes 1
2, 13, and 14 are formed at predetermined intervals in the length direction of the piezoelectric substrate 11. On the lower main surface of the piezoelectric substrate 11, an input-side electrode 15, an output-side electrode 17, and an input-side electrode 16 are formed at predetermined intervals in the length direction of the piezoelectric substrate 11.

That is, input electrodes 12 and 15 are formed on both main surfaces of the piezoelectric substrate 11 in the first voltage input unit A1, and output electrodes are formed on both main surfaces of the piezoelectric substrate 11 in the voltage output unit B1. 14 and 17 are formed, and the input side electrodes 1 are provided on both main surfaces of the piezoelectric substrate 11 in the second voltage input portion C1.
The electrodes 12 to 17 are formed such that one side has the same length as the width W of the main surface of the piezoelectric substrate 11, and the other side has an arbitrary length in the length direction of the main surface, for example, L1, L2. , L3
It has been.

The input electrode 12 and the input electrode 15 have the same size, the output electrode 14 and the output electrode 17 have the same size, and the input electrode 13 and the input electrode 16 have the same size. I have.

In the piezoelectric transformer of the present invention, the ratio (L / W) of the length L to the width W of the main surface of the piezoelectric substrate 11 is 1.1.
It is important that it is ~ 1.4. By setting the ratio (L / W) of the length L and the width W of the main surface of the piezoelectric substrate 11 to 1.1 to 1.4, high energy conversion efficiency can be achieved. On the other hand, when the ratio (L / W) of the length L to the width W of the main surface of the piezoelectric substrate 11 is smaller than 1.1 or larger than 1.4, the output power is reduced or the efficiency is reduced. descend.

In the piezoelectric transformer of the present invention, the product of the length L of the main surface of the piezoelectric substrate 11 and the driving frequency F (F × L)
Is set to 4700 to 6000 kHz · mm.

In the present invention, the length L of the main surface of the piezoelectric substrate 11
By setting the ratio (L / W) of the width and the width W to 1.1 to 1.4 and selecting a predetermined driving frequency, the fundamental wave that oscillates in the length direction of the piezoelectric substrate 11 is mainly used. The combined mode vibration including vibration is generated in the piezoelectric substrate 11, and the largest vibration can be generated in the voltage output portion formed in the center portion. For example, compared to the case where the most exciting vibration is used in the width direction, Also, the amount of charge induced in the voltage output unit increases, and high output power can be obtained.

The product (F × L) of the length L of the main surface of the piezoelectric substrate 11 and the driving frequency F needs to be 4700 to 6000 kHz · mm from the viewpoint that high output power can be obtained. Therefore, in order to obtain high output power and high efficiency, L / W is set to 1.1 to 1.4 and F × L is set to 4700 to
It is necessary to be 6000 kHz · mm.

According to the present invention, by setting the product (F × L) of the driving frequency F and the length L of the main surface in the above-mentioned structure in a predetermined range, high energy conversion efficiency and high input power can be obtained. A piezoelectric transformer with high output power and high efficiency that can be used at a voltage can be realized.

In the piezoelectric transformer of the present invention, for example, after forming electrodes 12 to 17 on a piezoelectric substrate 11 made of ceramics, the three electrodes 12, 13, and 13 on the upper surface of the piezoelectric substrate 11 are placed in silicone oil at 200 ° C. 14 and the piezoelectric substrate 11
Is obtained by applying a DC voltage between the three electrodes 15, 16 and 17 on the lower surface of the substrate and performing a polarization process for about 30 minutes.

The piezoelectric substrate 11 is made of Pb (ZrT
i) It is composed of O ₃ type composite oxide, and Ba, Sr
And at least one selected from Ca and Ca, Nb, Yb and Mn are contained in the B site, and the absolute value of the temperature coefficient of the elastic constant in the width direction of the piezoelectric substrate is 60 p.
It is important that the temperature be less than pm / ° C.

The absolute value of the temperature coefficient of the elastic constant is 60 ppm
The reason why the driving frequency for outputting high power is largely changed by the change of the outer peripheral temperature is higher than 60 ppm / ° C. In particular, from the viewpoint of outputting a high power, it is desirable to be 0 to 30 ppm / ° C.

The piezoelectric substrate is specifically a composition formula by molar _{ratio, Pb 1-x A x [} (Nb e Yb f Co g Mn h) a (T
i _b Zr _1-b) when expressed as _{1-a] O 3, a} , b, e, f,
g, h, and x are 0.05 ≦ a ≦ 0.20, 0.5 ≦ b ≦
0.6, 0.60 ≦ e ≦ 0.65, 0.10 ≦ f ≦ 0.
15, 0.06 ≦ g ≦ 0.10, 0.13 ≦ h ≦ 0.2
0, 0.02 ≦ x ≦ 0.10, A is Ba, Sr and C
It is desirable to satisfy at least one selected from a.

Here, the reason why a, b, e, f, g, h, and x are limited to the above ranges will be described. First, T
i, substituting the Zr site _{(Nb e Yb f Co g Mn} h)
Is effective in improving the output power. In particular, the inclusion of Mn can increase the output power to reduce the elastic loss of the piezoelectric substrate. When the third component amount a is less than 0.05, the output power improving effect tends to be small, and when the third component amount a is more than 0.20, the sinterability is insufficient and the elastic loss increases, so that the output power decreases. There is a tendency.

[0034] Nb, Yb, Co, each of the atomic ratio of Mn _{is, (Nb e Yb f Co g} Mn h) and when expressed, high output power, in terms of high efficiency, 0.60 ≦ e ≦ 0. 65,
0.10 ≦ f ≦ 0.15, 0.06 ≦ g ≦ 0.10,
It is desirable to satisfy 0.13 ≦ h ≦ 0.20.

Next, the Ti ratio b has the effect of reducing the absolute value of the temperature coefficient of the elastic constant. If the ratio b is outside the above range, the absolute value of the temperature coefficient of the elastic constant at −20 ° C. to 80 ° C. tends to increase, and the fluctuation of the output power tends to increase.

The substitution of Pb with any one of Ba, Ca and Sr has the effect of reducing the absolute value of the temperature coefficient of the elastic constant, but the substitution of x larger than 0.10 deteriorates the piezoelectricity. And substitutions less than 0.02 have less effect.

It is preferable that the piezoelectric substrate has perovskite oxide particles composed of Pb (ZrTi) O ₃ type composite oxide as main crystal particles, and ZrO ₂ particles exist at the grain boundaries of the main crystal particles. Thereby, the strength of the piezoelectric substrate can be improved without complicating the process, and the variation in the elastic constant in the width direction can be further reduced.

The present inventor performed a vibration analysis of the piezoelectric transformer of the present invention by computer simulation using the finite element method. As the analysis conditions, the above-described piezoelectric material was used, and in the piezoelectric transformer shape of FIG. 1, the length L of the piezoelectric substrate 11 was 32.80 mm, the width W was 25.5 mm,
The thickness t was set to 3.0 mm. The distance between the voltage input section and the voltage output section was 1.2 mm. Voltages having the same amplitude and the same phase were applied to the first and second voltage input sections, and the distribution of the displacement of the piezoelectric substrate was obtained.

FIG. 2 shows a driving frequency F of 69 kHz.
(F × L = 2263.2 kHz · mm) in the case of using the most exciting vibration in the width direction, and FIG.
Is 159 kHz (F × L = 5215.2 kHz · mm)
In this case, the displacement distribution of the piezoelectric transformer is shown.

In the case of a piezoelectric transformer using a driving frequency F of 69 kHz, vibrations in the width direction are generated as can be understood from FIG. 2, and almost no displacement occurs in the center of the piezoelectric substrate on which the voltage output portion is formed. It turns out that it has not occurred. On the other hand, in the piezoelectric transformer using the drive frequency F of 159 kHz, as can be seen from FIG. 3 showing the displacement distribution, a large displacement is obtained in the voltage output portion, and it is understood that high output power and high efficiency are obtained.

That is, the energy transfer of the piezoelectric transformer is as follows.
Since the vibration is performed by the vibration of the piezoelectric substrate 11, in the piezoelectric substrate 11 having the same shape, the larger the amount of displacement at the input voltage of the same amplitude, the larger the amount of electric charge induced in the voltage output unit B1. In the case of FIG. 3 in which the displacement of the central portion of the piezoelectric substrate 11 is larger than in FIG. 2, it can be seen that large output power is obtained and high efficiency is obtained. Thereby, L /
It can be seen that by setting W to 1.1 to 1.4 and controlling the drive frequency, the vibration shown in FIG. 3 can be generated.

Further, since the piezoelectric transformer of the present invention has a single polarization direction, there is no need to perform a polarization process in the length direction of the substrate, as compared with the Rosen type piezoelectric transformer. As a result, the polarization voltage can be reduced because the polarization is performed in the thickness direction, and the safety in the manufacturing process can be improved.

FIG. 4 shows a multi-layer piezoelectric transformer according to the present invention.
A first voltage input portion A2, a voltage output portion B2, and a second voltage input portion C are provided on a rectangular piezoelectric substrate 21 having a width W in the longitudinal direction.
2 are sequentially formed.

An input side electrode 22a, an output side electrode 24a, and an input side electrode 23a are provided on the upper main surface of the piezoelectric substrate 21 in the first voltage input section A2, the voltage output section B2, and the second voltage input section C2. The electrodes 22a, 23a, and 24a are formed at predetermined intervals in the length direction of the piezoelectric substrate 21. Also, the piezoelectric substrate 2
1, the input side electrode 22d, the output side electrode 2
4j and input-side electrodes 23d are formed at predetermined intervals in the length direction of the piezoelectric substrate 21.

The piezoelectric substrate 21 in the first voltage input section A2
, Input-side electrodes 22b and 22c are formed inside the piezoelectric substrate 21 in the voltage output unit B2, and output-side electrodes 24b to 24i are formed inside the piezoelectric substrate 21 in the voltage output unit B2. Have input electrodes 23b, 2
3c is formed.

The input electrodes 22a to 22d have the same dimensions, the output electrodes 24a to 24j have the same dimensions, and the input electrodes 23a to 23d have the same dimensions. The input side electrodes 22a and 23a and the output side electrode 24a
The input side electrodes 22 b and 23 b and the output side electrode 24 d are provided on the same plane inside the piezoelectric substrate 21, and the input side electrodes 22 b
c, 23c and an output-side electrode 24g are provided on the same plane inside the piezoelectric substrate 21.
d, 23 d and an output-side electrode 24 j are provided on the same plane on the lower main surface of the piezoelectric substrate 21. Note that the output side electrodes in FIG.

The input side electrodes 22a to 22d are
1 pair of external electrodes 25a1, 25 formed on both side surfaces
a2, the output side electrodes 24a to 24j
Are alternately connected by a pair of external electrodes 25b1 and 25b2, and the input-side electrodes 23a to 23d are
They are connected alternately by c1 and 25c2.

Also in this piezoelectric transformer, as in the piezoelectric transformer shown in FIG. 1, the ratio (L / W) of the length L to the width W of the main surface of the piezoelectric substrate 21 is 1.1 to 1.4. Yes,
It is important that the product (F × L) of the length L of the main surface of the piezoelectric substrate 21 and the driving frequency F is 4700 to 6000 kHz · mm. The ratio (L / W) of the length L to the width W of the main surface of the piezoelectric substrate 21 and the ratio (L / W) of the length L to the width W of the main surface of the piezoelectric substrate 21
/ W) is set in the predetermined range, and particularly the preferable range is the same as above. The same applies to the material of the piezoelectric substrate 21.

In such a laminated piezoelectric transformer, FIG.
Although the same effect as the piezoelectric transformer shown in FIG. 4 can be obtained, the multilayer piezoelectric transformer shown in FIG. 4 can further increase the area of the output-side electrode, and thus can be compared with a single-plate piezoelectric transformer having the same length and width. A large output current can be obtained.

The voltage step-up / step-down ratio (= V2 / V1) of the piezoelectric transformer is given by V2 / V1∝ (Cd1 / Cd1 / Cd1) where Cd1 is the input-side capacitance and Cd2 is the output-side capacitance.
Since Cd2) ^1/2 , Cd1 and Cd2 can be controlled by stacking piezoelectric transformers, and the step-up / step-down ratio can be set arbitrarily. That is, the piezoelectric transformer of the present invention
By arbitrarily determining the buck-boost ratio, the buck-boost converter can be suitably used for a buck-boost converter or a buck-boost inverter.
Note that, as shown in FIG. 9, the internal electrode may not be formed in the voltage input section.

A method for manufacturing such a piezoelectric transformer will be described. The piezoelectric substrate of the present invention can be manufactured, for example, as follows. First, as a starting material, P
_{bO, TiO 2, ZrO 2,} Nb 2 O 5, Co 3 O 4, Yb 2
O ₃ , MnO ₂ , BaCO ₃ , SrCO ₃ , CaCO
Each powder ₃ were wet-mixed in a predetermined ratio, discharge, and dried after sizing, it was placed in made of Al ₂ O ₃ crucible or the like, 850-105
Calcination at a temperature of 0 ° C. for 3 to 5 hours to obtain a calcined powder.

An organic binder is mixed with the powder and molded into a desired shape by a die press, a hydrostatic press or the like.
Porcelain can be obtained by firing at 1350 ° C. for 2 to 5 hours. The first voltage input section, the second voltage input section, and the voltage output section are formed on both main surfaces of the obtained porcelain by a technique such as baking or vapor deposition to obtain a single plate.

In the case of forming a laminate in which the voltage input section and the voltage output section are provided on the internal electrode, first, the calcined powder obtained is used to obtain a desired thickness by a doctor blade method, a calendaring method or the like. A ceramic green sheet having the same is produced.

Next, a high heat-resistant conductive paste such as an Ag-Pd paste is screen-printed on one surface of the ceramic green sheet. In this case, FIG.
As shown in FIG. 5, the green sheet 3 on which the pattern 36 serving as an input electrode and the pattern 37 serving as an output electrode are formed.
5 and a green sheet 32 on which only a pattern 37 to be an output-side electrode is formed, and these are laminated as shown in FIG. After degreasing by heating in
By firing at a temperature of 00 to 1300 ° C. for 2 to 4 hours, a laminated ceramic can be obtained. FIG. 5 shows only a part of the green sheets.

Next, a conductive paste is applied to both sides of the sintered body as external electrodes. The input electrodes 22a to 22d are alternately connected to each other by a pair of external electrodes 25a1 and 25a2. The output electrodes 24a to 24j are alternately connected to each other by a pair of external electrodes 25b1 and 25b2. Further, the input-side electrodes 23a to 23d are alternately connected by a pair of external electrodes 25c1 and 25c2. That is, the input-side electrode and the output-side electrode have a structure like a multilayer capacitor or a multilayer piezoelectric actuator, and the internal electrodes are connected alternately by the external electrodes.

Next, input-side electrodes 22a to 22d and 23a to 23d formed on both main surfaces of the obtained single plate and laminate are obtained.
And 80 to 20 on the output side electrodes 24a to 24j, respectively.
A piezoelectric field is obtained by applying a DC electric field of 1.0 to 5.0 kV / mm in an insulating oil at 0 ° C. for 10 to 60 minutes to perform a polarization process.

[0057] Further, the piezoelectric substrate particles mainly composed of ZrO ₂ was deposited in the grain boundary part, the part of the ZrO ₂ in the starting material _{Y 2 O 3, Nd 2 O} 3 or the like rare earth metals and MgO or CaO With ZrO ₂ stabilized or partially stabilized with
It can be produced by using a composition in which the amount of Pb is slightly reduced, or by applying the stabilized or partially stabilized ZrO ₂ to the calcined powder.

The raw material powder to be used is not limited to carbonates and oxides, but may be compounds such as acetates or organic metals as long as they become oxides by a heat treatment process such as firing. Absent.

In the piezoelectric ceramic according to the present invention, Rb, Hf, Si, Al, S
b, Fe, A diffused from the internal electrode of the laminate into the porcelain
Although unavoidable impurities such as g may be mixed in, there is no problem as long as the characteristics are not affected.

Further, the upper and lower surfaces of the laminated piezoelectric transformer may be covered with piezoelectric ceramics having the same composition in order to provide insulation from the outside. Further, the input side electrode and the output side electrode may not be formed on the main surface of the piezoelectric substrate 21 and may be formed only inside.

[0061]

EXAMPLE 1 PbO, TiO ₂ , ZrO ₂ , Nb
Using each powder of ₂ O ₅ , Co ₃ O ₄ , Yb ₂ O ₃ , MnO ₂ ,
Weighed and mixed, this mixed powder was wet-mixed using a 5 mmφ ZrO ₂ ball for 20 hours, discharged, dried, sized, poured into an Al ₂ O ₃ crucible, and calcined at 950 ° C. for 3 hours. Then, the calcined product was pulverized again by a ball mill.

Thereafter, an organic binder was mixed with the pulverized product and granulated. The obtained powder was press-formed at a pressure of 150 MPa into a square plate having a length of 37 mm, a width of 25 mm, and a thickness of 4 mm. Furthermore, these compacts are
sealed in a container made of gO or the like, and calcined for 2 hours at a temperature of 1200 ° C. in _{air, Pb 0.96 Sr 0.04 [(Nb} 0.62 5
Yb _0.125 Co _0.083 Mn _0.167 ) _0.1 (Ti _0.506 Zr
_0.494 ) _0.9 ] O ₃ was obtained.

The obtained sintered body is polished to produce a piezoelectric substrate, and an electrode paste containing silver and glass as main components is applied to both surfaces of the piezoelectric substrate, baked, and further baked in silicon oil at 200 ° C. A polarization treatment was performed by applying a DC electric field of 1.1 kV / mm for 10 minutes to produce a single-plate type piezoelectric transformer having an input electrode and an output electrode shown in FIG.

The shape of the piezoelectric transformer has a length L of 25.47 m.
m, the width W was 19.8 mm, and the thickness was 3.3 mm, and the relationship between the vibration mode, output power, output voltage, and efficiency was investigated. As shown in FIG. 7, the measuring circuit receives the input electrode (primary electrode) of the piezoelectric transformer as an input, outputs the output electrode (secondary electrode), and outputs a load resistance RL to the output electrode.
Connected. Here, RL = 500Ω. The input voltage is a sine wave of 141 Vpp, and 88.2 k of the frequency of the vibration most excited in the width direction of 84 kHz to 94 kHz.
Hz, frequency 198 k of the piezoelectric transformer in the present invention
From 20 Hz to 210 kHz, 203.5 kHz was applied from the input power source to the input electrode, and the power was determined by measuring the input current (App) and the phase difference between the voltage and the current. The output power (W) was obtained by measuring the output voltage (Vpp), output current (App), and phase difference from the output side electrode. The efficiency (%) was obtained from the maximum output power and the maximum input power. The results are shown in Table 1.

The elastic constant in the width direction of the piezoelectric substrate
Temperature coefficient δs₁₁ ^ETo the Electronic Materials Industries Association of Japan
Based on the elastic constant obtained according to MAS-6100, δs₁₁ ^E= [S₁₁ ^E _(temp.)-S₁₁ ^E _{(+25 ° C )}] ÷ s₁₁ ^E _{(+25
° C )}/(Temp.-25)×10⁶ [Unit: ppm
/ ° C] calculated from the equation
Temperature coefficient of sex constant δs₁₁ ^EIs 50 ppm / ° C.
Was.

[0066]

[Table 1]

From Table 1, it can be seen that a piezoelectric transformer using a driving frequency of 203.5 kHz can obtain higher output power and higher efficiency than a piezoelectric transformer using a driving frequency of 88.2 kHz. FIG. 8 shows the 203.5k
FIG. 5 is a diagram illustrating frequency characteristics of output power and efficiency of a piezoelectric transformer using a driving frequency of Hz. From FIG. 8, it can be seen that in this piezoelectric transformer, the output power can be easily controlled by the frequency because the efficiency is almost constant at about 96% with respect to the fluctuation of the frequency.

Example 2 The present inventors investigated the relationship between the shape of the piezoelectric transformer and the driving frequency. Using the same material and manufacturing method as in Example 1, a piezoelectric transformer was prepared in which the width W was 19.8 mm, the thickness was all 3.3 mm, and the length L was changed from 20.79 to 28.71 mm. Next, a DC voltage of 1.1 kV / mm was applied to the piezoelectric transformer in silicone oil at 200 ° C., and polarization was performed for 10 minutes, thereby polarizing the piezoelectric substrate in the thickness direction.

As shown in FIG. 7, the measuring circuit receives the input electrode (primary electrode) of the piezoelectric transformer as an input, outputs the output electrode (secondary electrode) as an output, and applies a load resistance to the output electrode. RL was connected. Here, RL = 500Ω.
A sine wave having an input voltage of 141 Vpp and a frequency shown in Table 2 is applied from the input power source to the input side electrode, and the input current (Ap
Power was determined by measuring p) and phase.

On the other hand, the output voltage (Vp
p), output current (App) and phase were measured to determine output power (W). The efficiency (%) was obtained from the maximum output power and the maximum input power, and the results are shown in Table 2.

[0071]

[Table 2]

From Table 2, in the piezoelectric transformer of the present invention, in the piezoelectric transformer of the present invention, the relationship between the length L and the width W is 1.1 ≦ L / W ≦ 1.4 and the length L And the driving frequency F of the piezoelectric transformer is 4700 kHz · mm ≦ F ×
When L ≦ 6000 kHz · mm, the output power 16
It is higher than W and the efficiency is 92.6% or higher, indicating that high output power and high efficiency can be obtained.

Example 3 PbO, TiO ₂ , ZrO ₂ , Nb
Using each powder of ₂ O ₅ , Co ₃ O ₄ , Yb ₂ O ₃ , MnO ₂ ,
_{Pb 1-x A x [(} Nb e Yb f Co g Mn h) a (Ti b Zr
_1-b ) _1-a ] O ₃ , a, b, e, f, g,
The powders were weighed so that h and x became the values shown in Table 3, and the mixed powder was wet-mixed using a 5 mmφ ZrO ₂ ball for 20 hours, discharged, dried, sized, and placed in an Al ₂ O ₃ crucible. It was thrown in and calcined at a temperature of 950 ° C. for 3 hours.

Thereafter, an organic binder was mixed with the pulverized product and granulated. The obtained powder was pressed into a square plate at a pressure of 150 MPa. Furthermore, these compacts are
The container was sealed in a container made of gO or the like, and fired in the air at a temperature of 1200 ° C. for 2 hours.

The obtained sintered body is polished to produce a piezoelectric substrate, and an electrode paste containing silver and glass as main components is applied to both surfaces of the piezoelectric substrate, baked, and further baked in silicon oil at 200 ° C. A polarization treatment was performed by applying a DC electric field of 1.1 kV / mm for 10 minutes to produce a single-plate type piezoelectric transformer having an input electrode and an output electrode shown in FIG.

The shape of the piezoelectric transformer has a length L of 25.47 m.
m, a width W of 19.8 mm, and a thickness of 3.3 mm. As shown in FIG.
The output electrode (secondary electrode) was used as an output, and a load resistor RL was connected to the output electrode.
Here, RL = 500Ω.

The temperature characteristics of the output power are determined by fixing the driving frequency, evaluating the output power at −20 ° C., + 25 ° C., and + 80 ° C., and calculating the variation rate δP _out of the output power by δP _out = [P _{out (max. )} -P _{out (min.)} ] ÷ P _{out (+25 ℃
)} × 100 [unit:%]

Here, P _{out (max.)} Is the maximum output power at three measured temperatures, P _{out (min.)} Is the minimum output power, and P _{out (max.)
out (+ 25 ° C. )} represents the output power at 25 ° C.

The temperature coefficient δs ₁₁ ^E of the elastic constant in the width direction of the piezoelectric substrate was determined in the same manner as described above. Table 3 shows the results.

[0080]

[Table 3]

In the sample of the present invention, the output power P. _out is 2
It can be seen that the output power fluctuation rate is 0 W or more and the fluctuation rate of the output power is 15% or less, the output power is high, and the fluctuation of the output power characteristic with respect to the temperature is small.

The sample No. having a temperature coefficient of elastic constant in the width direction of 48 ppm / ° C. 4 is driving frequency 2
Sample No. having an output power of 26 W at 70 kHz, a fluctuation rate of the output power of 13.3%, and a temperature coefficient of elastic constant in the width direction of 23 ppm / ° C. In No. 15, the output power at a drive frequency of 272 kHz was 23.8 W, and the fluctuation rate of the output power was 7.9%.

On the other hand, Sample No. which does not contain Nb, Yb and Mn and is out of the scope of the present invention. In Example 1, the temperature coefficient of the elastic constant in the width direction was 10 ppm / ° C., and the driving frequency was 265.
The output power at 10 kHz was 10 W, the fluctuation rate of the output power was 3.0%, and the output power was low. The sample No. having a temperature coefficient of 70 ppm / ° C. In 2, the driving frequency 27
The output power at 8 kHz was 20 W, the fluctuation rate of the output power was 30.0%, and the sample No. containing no Ba, Sr, and Ca. In No. 16, the temperature coefficient was 80 ppm / ° C., the output power at a drive frequency of 282 kHz was 18.8 W, and the fluctuation rate of the output power was 50.0%. The efficiency of the sample of the present invention in Table 3 was 90% or more.

Example 4 As starting materials, PbO, TiO ₂ , ZrO ₂ , Nb
Using each powder of ₂ O ₅ , Co ₃ O ₄ , Yb ₂ O ₃ , MnO ₂ ,
The composition is Pb _0.96 Sr _0.04 [(Nb _0.625 Yb _0.125 Co
_0.083 Mn _0.167 ) _0.1 (Ti _0.506 Zr _0.494 ) _0.9 ] O ₃
Is weighed, and wet-mixed using a 5 mmφ ZrO ₂ ball for 20 hours, discharged, dried and sized, put into an Al ₂ O ₃ crucible, and heated at a temperature of 950 ° C. for 3 hours After calcining, the calcined product is pulverized again by a ball mill.

A binder and a plasticizer are added to the obtained pulverized product and dispersed in an organic solvent to prepare a slurry. Using the obtained slurry, a thickness of 1
An 80 μm ceramic green sheet was produced. An Ag-Pd paste is screen-printed on one surface of the green sheet so as to have a shape shown in FIG. The printed green sheets are laminated, pressed and integrated by a hot press, degreased by heating at 400 to 500 ° C., and then fired at a temperature of 1120 ° C. for 3 hours to obtain a laminated body porcelain. Was.

An electrode paste mainly composed of silver and glass is applied to both main surfaces of the obtained laminated ceramic to form a first voltage input portion, a voltage output portion, and a second voltage input portion, and the electrodes are baked. After that, external electrodes were formed on the side surfaces of the laminated portion by connection with electrodes inside the porcelain using a conductive paste.

Then, a DC electric field of 1.1 kV / mm was applied to the voltage input electrode and the voltage output electrode formed on both main surfaces of the laminate in silicon oil at 200 ° C. for 30 minutes, respectively, to perform a polarization treatment. Thus, a laminated piezoelectric transformer was obtained.

The evaluation of the porcelain was performed according to the first embodiment. As a result, characteristics were obtained in which the output power at a drive frequency of 272 kHz was 28.4 W and the fluctuation rate of the output power was 11.3%. The effectiveness was confirmed also as a laminated body.

Example 5 Raw materials were weighed so as to have the composition shown below. Pb _0.96 Sr _0.04 [(Nb _0.625 Yb _0.125 Co _0.083 M
_{n 0.167) 0.1 (Ti 0.507 Zr} 0.493) 0.9] O 3 Here, among the Zr ratio 0.493, 0.420mol% normal ZrO _2, the ZrO ₂ stabilized with Y ₂ O ₃ 0.073 mol %. Thereafter, a single-plate type piezoelectric transformer was manufactured in the same manner as described above.

The driving frequency of this piezoelectric transformer is 275 kHz.
The characteristic that the output power at z was 20.3 W and the fluctuation rate of the output power was 5.4% was obtained. The temperature coefficient of the elastic constant of the piezoelectric substrate was 18 ppm / ° C. The inside of the porcelain was mirror-polished, and the porcelain was observed by SEM.
Precipitation of ２2 μm particles mainly composed of ZrO ₂ was confirmed. Also, the bending strength was evaluated according to JISR1601. As a result, a flexural strength of 140 MPa was obtained.

Similarly, the sample No. When the transverse rupture strength of No. 4 was evaluated, it was 120 MPa.
It can be seen that by depositing an appropriate amount of ZrO ₂ at the porcelain grain boundary portion, the transverse rupture strength of the porcelain can be improved.

[0092]

According to the piezoelectric transformer of the present invention, the absolute value of the temperature coefficient of the elastic constant in the width direction is 0 to 60 ppm / ° C.
By suppressing the fluctuation of the output power-frequency characteristic curve of the piezoelectric transformer that outputs power by resonance driving, the fluctuation of the output power can be reduced. At the same time, Pb, Zr, Ti, Nb, Yb, Mn
By containing at least one selected from Ba, Sr, and Ca, the elastic loss of the piezoelectric substrate can be reduced, and the output power can be increased. In addition, when the piezoelectric substrate has a predetermined composition, an excellent piezoelectric transformer having an output power of 16 W or more and a fluctuation rate of the output power of 15% or less can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a single-plate type piezoelectric transformer of the present invention.

FIG. 2 is a diagram illustrating a displacement distribution of a piezoelectric transformer when a product (F × L) of a length L of a main surface of a piezoelectric substrate and a driving frequency F is 2263.2 kHz · mm.

FIG. 3 is a diagram showing a displacement distribution of a piezoelectric transformer when a product (F × L) of a length L of a main surface of a piezoelectric substrate and a driving frequency F is 5215.2 kHz · mm.

FIG. 4 is a perspective view showing a multilayer piezoelectric transformer of the present invention.

FIG. 5 is an explanatory diagram for explaining a method of manufacturing the multilayer piezoelectric transformer of FIG.

FIG. 6 is an explanatory diagram showing a DC-DC converter of the present invention.

FIG. 7 is a perspective view showing a measurement circuit of the piezoelectric transformer of the present invention.

FIG. 8 is a diagram illustrating frequency characteristics of output power and efficiency of the piezoelectric transformer according to the first embodiment.

FIG. 9 is a perspective view showing a multilayer piezoelectric transformer of the present invention.

FIG. 10 is a diagram showing a relationship between a driving frequency and output power.

FIG. 11 is a diagram illustrating a relationship between a driving frequency and output power when a load resistance is changed in a single-plate type piezoelectric transformer.

[Explanation of symbols]

11, 21,... Piezoelectric substrate 12, 13, 15, 16, 22a-d, 23a-d,.
-Input side electrodes 14, 17, 24a-j ... Output side electrodes L ... Length of main surface W ... Width of main surface F ... Drive frequency of piezoelectric transformer A1, A2 ... 1 voltage input section B1, B2 ... voltage output section C1, C2 ... second voltage input section

Claims (4)

[Claims] 1. A voltage input portion and a voltage output portion are alternately formed in the length direction of a piezoelectric substrate having both main surfaces of a rectangular shape having a length L and a width W. In a piezoelectric transformer provided with an input side electrode and an output side electrode, the ratio (L / W) of the length L to the width W of the main surface of the piezoelectric substrate is 1.
1 to 1.4, and the piezoelectric substrate is made of Pb (ZrT
i) It is composed of O ₃ type composite oxide, and Ba, Sr
And Ca at least one selected from the group consisting of Nb, Yb and Mn at the B site, and the absolute value of the temperature coefficient of the elastic constant in the width direction of the piezoelectric substrate is 6%.
A piezoelectric transformer characterized by being at most 0 ppm / ° C. 2. The piezoelectric substrate according to claim 1, wherein the composition formula based on the molar ratio is represented by Pb
_{1-x A x [(Nb} e Yb f Co g Mn h) a (Ti b Zr 1-b)
_1-a ] O _{3 where} a, b, and x are 0.05 ≦ a ≦ 0.20 0.5 ≦ b ≦ 0.6 0.02 ≦ x ≦ 0.10 A is Ba 2. The piezoelectric transformer according to claim 1, wherein at least one selected from the group consisting of Sr, Ca and Sr is satisfied. 3. The piezoelectric substrate according to claim 1, wherein perovskite-type oxide particles composed of Pb (ZrTi) O ₃ type composite oxide are used as main crystal particles, and ZrO ₂ particles are present at the grain boundaries of the main crystal particles. The piezoelectric transformer according to claim 1, wherein: 4. The method according to claim 1, wherein a product (F × L) of a length L of the main surface of the piezoelectric substrate and a driving frequency F is 4700 to 6000 kHz · mm. Piezoelectric transformer.