JP2643810B2 - Piezoelectric transformer and its driving method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic transformer used in various power supply circuits for generating high voltage and a method of driving the same. And a method of driving the same.

[0002]

2. Description of the Related Art Conventionally, in a power supply circuit in a device requiring a high voltage such as a deflection device of a television or a charging device of a copying machine, a winding type electromagnetic transformer has been used as a transformer for generating a high voltage. . This electromagnetic transformer has a structure in which a conductor is wound around a core of a magnetic material, and it is necessary to increase the number of conductors to be wound in order to realize a high transformation ratio. That is, it is essential to wind the conductor at least several hundred to several thousand times. Therefore, in order to realize a small and thin electromagnetic transformer, it must first be a very thin wire,
Inevitably, copper loss increases, and miniaturization and high efficiency of the electromagnetic transformer conflict with each other.

On the other hand, a piezoelectric ceramic transformer using a piezoelectric effect (hereinafter referred to as a piezoelectric transformer) has been proposed. FIG. 6 shows the structure of a Rosen-type piezoelectric transformer which is a typical conventional piezoelectric transformer. Hereinafter, description will be given with reference to the drawings. A low-impedance drive section 61 of a piezoelectric transformer formed of a piezoelectric plate having electrodes provided on its surface is provided with opposing electrodes 63 and 64 on its upper and lower surfaces.
It is polarized in the thickness direction as shown by the thick arrow in the figure.
An electrode 65 is provided on the end face of the high-impedance power generation unit 62, and the power generation unit 62 is polarized in the length direction of the piezoelectric plate as indicated by a thick arrow in the drawing.

The operation of this piezoelectric transformer is as follows. When a voltage is applied to the drive electrodes 63 and 64 from the external terminals 66 and 67, an electric field is applied in the polarization direction in the drive unit 61, and the length is generated by a piezoelectric effect (piezoelectric lateral effect 31 mode) in which the electric field is displaced in a direction perpendicular to the polarization direction. Longitudinal vibration in the direction is excited,
The whole transformer vibrates. Further, in the power generating section 62, a mechanical strain is generated in the polarization direction, and a potential difference is generated in the polarization direction.
, A voltage having the same frequency as the input voltage is taken out to the external terminal 68. At this time, if the drive frequency is made equal to the resonance frequency of the piezoelectric transformer, a very high output voltage can be obtained. When inputting high voltage and outputting low voltage,
What is necessary is just to make the high impedance part 62 of a vertical effect into an input side, and make the low impedance part 61 of a horizontal effect into an output side.

This piezoelectric transformer is used in a resonance state,
Compared to general electromagnetic transformers, (1) The winding structure is unnecessary and the energy density is high, so that it can be made smaller and thinner, (2) It can be made non-combustible, (3) It has no electromagnetic induction noise, It has many advantages.

[0006]

In the above-mentioned conventional Rosen type piezoelectric transformer, since the electrode 65 of the power generation unit 62 is located at the antinode of vibration, the connection of the external terminal 68 increases the loss of vibration. During high-power driving, there was an accident that the lead wire connected to the power generation electrode 65 and the external terminal 68 was cut, and there was a problem in reliability.

Further, a load resistance (for example, 10 to 100 M) which is extremely large compared to the output impedance of the piezoelectric transformer
Ω), a high output voltage can be obtained, but if the value of the load resistance is not so large, there is a disadvantage that a very high output voltage cannot be obtained.

Further, in the conventional Rosen type transformer,
In order to perform large-amplitude driving at a low voltage, the plate thickness must be extremely thin. In this case, first of all, the output impedance of the transformer becomes too large, which may cause an impedance mismatch with the load impedance.
It is difficult to obtain a high output voltage at a substantially low voltage. Second, the volume of the transformer is too small, and it is not possible to obtain sufficient output power.

Accordingly, it is an object of the present invention to realize a piezoelectric transformer capable of extracting a sufficient output power even at a low input voltage, and to provide a highly reliable piezoelectric transformer.

[0010]

According to the piezoelectric ceramic transformer of the present invention, an internal electrode and a piezoelectric ceramic are provided on each of up to one-third of the length of the total pressure ceramic transformer from each of the two end faces in the longitudinal direction. And two low impedance portions having a structure in which a plurality of layers are alternately laminated in the plate thickness direction, and each of the piezoelectric ceramic layers facing each other across each internal electrode is polarized in a direction opposite to each other with respect to the lamination direction axis. And a central portion in the length direction has a pair of opposing electrodes on two opposing surfaces perpendicular to the plate thickness direction axis, and the piezoelectric ceramic layer between the pair of electrodes has the plate thickness. A high-impedance portion having a structure that is polarized in a direction is provided, and operates in a third mode in a longitudinal vertical direction.

In the piezoelectric ceramic transformer according to the present invention, an internal electrode and a piezoelectric ceramic layer are formed on each of the two end faces in the length direction at a maximum of one third or less of the total pressure ceramic transformer length. A plurality of low-impedance portions having a structure in which a plurality of piezoelectric ceramic layers facing each other across each internal electrode are polarized in opposite directions with respect to the stacking direction axis are formed by alternately laminating a plurality of layers in the thickness direction. The central portion in the vertical direction has a pair of opposing electrodes on two opposing surfaces perpendicular to the plate width direction axis, and a piezoelectric ceramic layer between the pair of electrodes is polarized in the plate width direction. And a high-impedance portion having the same structure as that described above, and operates in the third mode in the longitudinal vertical direction.

A piezoelectric ceramic transformer according to the present invention is a method for driving a piezoelectric ceramic transformer according to claim 1 or 2, wherein the two low impedance parts are used as input parts and the high impedance parts are used as output parts. In the driving method, an AC input voltage is applied to each of the low-impedance sections so that each of the internal electrodes constituting each of the low-impedance sections has the same potential, and the two low-impedance sections are driven in the same phase. By extracting the output voltage from the high impedance section, a high output voltage can be efficiently obtained with a low input voltage.

[0013]

As shown in FIG. 1, the piezoelectric transformer according to the present invention has one third of the total length of the piezoelectric transformer from the left end face in the longitudinal direction.
A plurality of internal electrodes 5L and piezoelectric ceramic layers 6
L are alternately stacked in the thickness direction. In addition, a low impedance portion 8R having a structure in which a plurality of internal electrodes 5R and piezoelectric ceramic layers 6R are alternately stacked in the thickness direction is provided at a portion of one third or less of the entire length from the right end face on the opposite side. . The piezoelectric ceramic layers 6L adjacent via the internal electrodes 5L and 5R
The Rs are polarized in opposite directions as indicated by thin arrows in the figure. The internal electrodes 5L and 5R are connected to external terminals 1L and 2L and 1R and 2R, respectively.

Electrodes 7A and 7B are formed on the lower surface and the upper surface in the thickness direction at the central portion where there is no internal electrode.
The inner piezoelectric ceramic layer 6C sandwiched between the electrodes 7B is polarized in a direction perpendicular to the electrodes 7A and 7B as indicated by thick arrows in the figure. This central portion is a high impedance portion 9.

The length of each of the internal electrodes 5L and 5R and the electrodes 7A and 7B is within one third of the length of the piezoelectric transformer in the longitudinal direction (the left-right direction on the paper). The external terminals 1L, 2L and 1R, 2R are connected to the low impedance section 8
Each of the internal electrodes 5L, 5R of L, 8R is connected to every other layer. Electrodes 7A, 7 of high impedance section 9
B is connected to the external terminals 3 and 4.

The piezoelectric ceramic transformer according to the present invention has a structure in which piezoelectric ceramic plates polarized in the thickness direction are stacked, and is a novel piezoelectric ceramic transformer that operates in the longitudinal longitudinal vibration third-order mode. As is clear from the vibration velocity distribution and the stress distribution shown in FIG. 1, the piezoelectric transformer according to the present invention operates most efficiently when operated in the tertiary longitudinal mode. As is well known, the vibration stress of the present piezoelectric transformer operating in the transverse effect length longitudinal vibration mode generates a tension or a compressive force in the length direction, and is perpendicular to the laminating direction of the internal electrodes 5L and 5R. In other words, since the structure is such that vibration stress is not applied in the laminating direction of the weakest internal electrodes, there is an advantage that sufficient strength can be maintained even during high power operation.

Next, how to take out the external terminal from the electrode will be described. The piezoelectric transformer operating in the tertiary mode has three vibration nodes (nodes). The vibration nodes are located at the center of the low impedance section 8L, the center of the high impedance section 9 and the center of the low impedance section 8R in order from the left side in FIG. Therefore, the external terminals 3 and 4 from the high impedance section 9 are connected to the electrodes 7A and 7A.
Since B is exposed to the outside, it can be taken out by a method such as ordinary soldering. On the other hand, the external terminals 1L, 2L (1R, 2R) from the low impedance section 8L (8R)
Is a structure in which the exposed portions of the internal electrodes 5L (5R) exposed on the side surfaces of the piezoelectric transformer are covered with an insulating layer every other layer and the remaining exposed portions are connected every other layer by, for example, electrophoresis. Extraction from the internal electrode is possible. Such a method of extracting the external terminals is a method usually used in a so-called full-electrode type multilayer ceramic piezoelectric actuator in which the planar shape of the internal electrode and the planar shape of the ceramic layer (piezoelectric ceramic layer) are the same, for example. And can be applied to the present invention. Alternatively, when the internal electrodes 5L and 5R of the low impedance portions 8L and 8R of the piezoelectric transformer according to the present invention have a so-called multilayer ceramic capacitor type structure in which the internal electrodes 5L and 5R are retracted from the ceramic layer except for a part of the side exposed portions, The external terminal take-out structure usually used in this multilayer ceramic capacitor is applicable to the present invention.

Next, a driving method of the present piezoelectric transformer will be described. First, a driving method of driving the low impedance portions 8L and 8R at the left and right ends and outputting a high voltage from the high impedance portion 9 will be described. When an AC voltage is applied to the low impedance portions 8L and 8R in the right and left ends of FIG. 1, via the transverse effect electromechanical coupling coefficient k _31, electrical energy is converted into mechanical vibration energy. At this time, it is important to drive the low-impedance sections 8L and 8R at the left and right ends in the same phase in order to efficiently excite the longitudinal third mode. In addition, when the electrical connection of the low impedance portions at both left and right ends is parallel, a large current can be supplied at a low voltage. Moreover, if techniques such as a multilayer ceramic capacitor and a piezoelectric actuator are applied, the internal electrodes can be formed thin and the distance between the electrodes can be reduced, so that so-called low-voltage high-power driving can be performed. That is, when a technique such as a multilayer ceramic capacitor is applied to the low impedance portions 8L and 8R of the present multilayer structure, the distance between the electrodes can be easily reduced to 50 μm or less, which is more remarkable than the drive voltage of the well-known Rosen type piezoelectric transformer. That is, it can be driven with a very small voltage.

Further, in the output-side high impedance section 9 of the piezoelectric transformer driven in the tertiary mode,
The low impedance driver 8L and 8R of the right and left ends vibration of opposite phase are excited, a high voltage through the coupling factor k ₃₁ in the transverse effect longitudinal vibration is outputted from the external terminals 3 and 4.

It is needless to say that a large current can be output from the piezoelectric transformer at a low voltage by following the reverse of the above-described driving. That is, the high impedance section 9 located at the center of the piezoelectric transformer is driven,
By using the low impedance sections 8L and 8R located at both ends as output sections, a low voltage and a large current can be output.

The lumped constant approximation equivalent circuit near the resonance frequency of the present piezoelectric ceramic transformer is similar to that of other piezoelectric transformers in FIG.
Is shown in In FIG. 2, Cd ₁ and Cd ₂ are input side and output side braking capacities, respectively. A ₁ and A ₂
Is the input / output force coefficient. m, respectively, c and r _m, which is equivalent mass, equivalent compliance and equivalent mechanical resistance on the length longitudinal vibration tertiary mode. The input and output force coefficients A ₁ and A ₂ of the piezoelectric ceramic transformer of the present invention vary depending on the width and thickness, the distance between the electrodes of the drive unit, and the number of electrode layers. When the driving unit has a laminated structure of n layers as in the piezoelectric transformer according to the present invention, the force coefficient A ₁ is n times that of a single plate, and the same level of vibration can be obtained at a low voltage of 1 / n. Excitable. As is clear from the equivalent circuit of FIG.
In general, the output power _Vout of the piezoelectric transformer changes depending on the resistance value of the connected load, and the larger the value of the load resistance, the larger the value of _Vout . Further, the energy transmission efficiency also depends on the load resistance, and the transmission efficiency is not so high except for a load having a value matched with the output impedance of the piezoelectric ceramic transformer. In the piezoelectric ceramic transformer of the present invention, there is a degree of freedom in the area of the output electrode or the area of the input electrode other than the length, width and thickness of the entire transformer, and the range in which the load and the output impedance of the piezoelectric ceramic transformer can be matched. The feature is that it is wide.

As is apparent from FIG. 1, the piezoelectric ceramic transformer has a four-terminal structure in which input and output external terminals are DC-insulated. Therefore, it is possible to increase the degree of freedom of the peripheral circuit as compared with the three-terminal Rosen type piezoelectric transformer shown in FIG.

As described above, the piezoelectric ceramic transformer according to the present invention shown in FIG. 1 can obtain a high output with low input power and can take out terminals from the electrodes of the vibrating part by soldering or the like. There are a number of features, including the ability to

Further, for an application in which an output voltage is required to be higher than that of the piezoelectric transformer shown in FIG. 1, as shown in FIG. 3, output electrodes 37A and 37B are provided on the side surface of the center of the piezoelectric transformer, and This can be dealt with by making the configuration polarized.

According to this structure, similarly to the piezoelectric transformer shown in FIG. 1, although the output voltage via a transverse effect coupling factor k ₃₁ is taken out, it is possible to set a high output impedance of the piezoelectric transformer, An output voltage higher than that of the piezoelectric transformer shown in FIG. 1 can be obtained.

In the piezoelectric transformer shown in FIG. 1, when it is desired to increase the output impedance, the thickness or the width of the piezoelectric transformer may be increased.
Conversely, in the piezoelectric transformer shown in FIG. 2, when increasing the output impedance, the plate thickness is reduced and the plate width is increased.

Further, in the piezoelectric transformer according to the present invention, the input-side low-impedance portion has three or five layers,
If it is an odd layer such as a layer, as shown in FIG. 4 or FIG.
The input side also has the same external electrode structure as the output side, and the external electrode can cover most of the main surface on the input side.
The electrodes 41A, 41B, 42A and 42B in FIG. 4 and the electrodes 51A, 51B, 52A and 52B in FIG. 5 are input electrodes of the external electrode structure. In this case, extraction of the external terminals 1L, 2L and 1R, 2R from the electrodes is as follows.
If this external electrode is used, it becomes easier than the piezoelectric transformer having the configuration shown in FIGS.

[0028]

EXAMPLE As a piezoelectric ceramic transformer according to a first embodiment of the present invention, a piezoelectric ceramic transformer having the structure shown in FIG. 1 was manufactured by a green sheet method. The material of the piezoelectric ceramic is P
ZT was used (PbZrO ₃ -PbTiO ₃₎ based piezoelectric ceramic. The internal electrodes were formed by screen-printing a Pt paste on a green sheet of a piezoelectric material and firing the same together with the piezoelectric material. Here, the PZT-based piezoelectric ceramic and Pt are used as the material of the piezoelectric ceramic and the internal electrode, but it goes without saying that other combinations may be used as long as the piezoelectric ceramic material having piezoelectricity and the electrode material that can be integrally fired therewith. No.

Each of the low impedance portions 8L and 8R has four active piezoelectric ceramic layers 6L and 6R,
L and 5R are alternately laminated in a five-layer structure, and the laminated structure further includes one inactive piezoelectric ceramic layer above and below. The thickness of each piezoelectric ceramic layer 6L, 6R was 0.2 mm, and the total thickness was 1.2 mm. After firing, overall length 30mm, width 7
It was cut to the size of mm.

On the low impedance portions 8L and 8R, glass as an insulator is alternately and alternately adhered to the exposed side surfaces of the internal electrodes 5L and 5R every other layer by electrophoresis, and then an Ag paste is applied. Then, for the high impedance portion 9, after applying Ag paste on the upper and lower main surfaces,
After firing, an external electrode was formed. These external electrodes may be formed by forming a thin film of a conductive material other than Ag using a method other than coating and firing, for example, a vapor deposition method or a sputtering method.

Thereafter, a voltage of 4 kV / mm was applied to the low-impedance portions 8L and 8R and the high-impedance portion 9 in an insulating oil at 100 ° C. to perform a polarization process. Further, a lead wire was soldered to each of the external electrodes. At this time, the low impedance portions 8L and 8R are soldered 5 mm inward from both ends of the piezoelectric ceramic transformer so that the connection point with the external electrode becomes a node of vibration. Soldered to the part. Here, in order to increase the boost ratio, 2
Terminals 1L and 2L taken out from two low impedance parts
And 1R and 2R are connected in parallel, but needless to say, they function as a transformer even if they are connected in series.

The resonance frequency of the third mode of the longitudinal vibration of the piezoelectric ceramic transformer has a resonance frequency of 1 from the frequency characteristic of admittance.
It was measured at 48 kHz. When a load resistance of 100 kΩ which is a relatively low resistance for high voltage use is connected to this piezoelectric ceramic transformer, 420 V is applied to an input voltage of 10 V.
Was obtained, and the output power at this time was 1.8 W.

When 100 piezoelectric ceramic transformers according to this embodiment were driven continuously for 2000 hours, none of the samples showed peeling of the external electrodes or abnormal characteristics.

In this piezoelectric ceramic transformer, as shown in FIG. 4, the upper and lower piezoelectric inactive layers are eliminated from the low impedance portion, and the odd-numbered piezoelectric active layers 5L and 5R, the internal electrodes, and the upper and lower portions of the low impedance portion are removed. External electrodes 41A provided on the main surface,
41B, 42A, and 42B, and electrical connection from the upper and lower main surfaces to the external terminals 1L, 2L, 1R, and 2R can be obtained. In this case, as in the case of the multilayer ceramic capacitor, the internal electrodes 6L and 6R are arranged so as to alternately reach different side surfaces, and the external electrodes 41A, 41B, 42A and 42B are formed by applying and baking Ag paste on the side surfaces. it can. Therefore, since the external terminals 1L, 2L, 1R, and 2R can be taken out from the upper and lower main surfaces, the degree of freedom in mounting increases.
In a piezoelectric transformer with three active layers actually manufactured,
When a load resistance of 100 kΩ is connected, input voltage 10
An output voltage of 370 V with respect to V was obtained, and the output power at this time was 1.4 W.

Subsequently, as shown in FIG. 3, a piezoelectric transformer of a second embodiment having a structure in which a high impedance portion was polarized in the width direction was manufactured. The method of integrally firing the piezoelectric ceramic layer and the internal electrode is the same as in the first embodiment. Here, the overall dimensions were 30 mm in length, 4 mm in width, and 1.2 mm in thickness.
Ag electrodes were formed on the side surfaces of the low impedance portions 8L and 8R by electrophoresis as in Example 1. External electrodes 37A and 37B were formed on the high impedance portion 9 by applying an Ag paste to the side surfaces and firing the paste. At this time, the internal electrodes 5L,
5R and external electrodes 37A and 37B of the high impedance section 9
Is 2 mm so that dielectric breakdown does not occur during polarization.
And These external electrodes 37A and 37B are formed by a method other than coating and firing, for example, by using an evaporation method or a sputtering method.
A thin film of a conductive material other than the above may be formed.

Thereafter, a voltage of 4 kV / mm was applied to the low-impedance portions 8L, 8R and the high-impedance portion 9 in an insulating oil at 100 ° C. to perform a polarization treatment. Further, a lead wire was soldered to each of the external electrodes. At this time, the low-impedance portions 8L and 8R are soldered 5 mm inside from both ends of the piezoelectric ceramic transformer so that the connection point with the external electrode becomes a node of vibration. Soldered. In this case, terminals 1L, 2L, and 1L taken out from two low impedance portions in order to increase the boost ratio.
Although R and 2R are connected in parallel, it goes without saying that they function as a transformer even if they are connected in series.

The resonance frequency of the third longitudinal mode in the longitudinal vibration of the piezoelectric ceramic transformer is 1 from the frequency characteristic of admittance.
It was measured at 7 kHz. When a load resistance of 100 kΩ, which is relatively low for high voltage use, is connected to this piezoelectric ceramic transformer, an output voltage of 530 V is obtained for an input voltage of 10 V, and the output power at this time is 2.8 W. Was.

Further, 100 piezoelectric ceramic transformers according to this embodiment were driven continuously for 2000 hours. However, none of the samples showed peeling of the external electrodes or abnormality in characteristics.

In this piezoelectric ceramic transformer, as shown in FIG. 5, the upper and lower piezoelectric inactive layers are eliminated from the low impedance portion, and the odd-numbered piezoelectric active layers, the internal electrodes, and the upper and lower main surfaces of each low impedance portion are removed. External electrodes 51A, 51B,
With the configuration including 52A and 52B, electrical connection to the external terminals 1L, 2L, 1R, and 2R can be obtained from the upper and lower main surfaces. In this case, as in the case of the multilayer ceramic condensate, the internal electrodes 6 are arranged so as to alternately reach different side surfaces, and the external electrodes 51A, 51B, 52A, 52B can be formed by applying and baking Ag paste on the side surfaces. Therefore, since the external terminals 1L, 2L, 1R, and 2R can be taken out from the upper and lower main surfaces, the degree of freedom in mounting increases. In a piezoelectric transformer having actually three layers of active layers, 10
When a load resistance of 0 kΩ was connected, an output voltage of 480 V was obtained for an input voltage of 10 V, and the output power at this time was 2.3 W.

[0040]

As described above, the piezoelectric ceramic transformer according to the present invention can be driven at a high power with a low input voltage and can easily extract a high voltage. In addition, because it has good matching with the load impedance, it has excellent characteristics,
In addition, the piezoelectric transformer has advantages such as high reliability, which are not found in conventional piezoelectric transformers, and has a great industrial value.

[Brief description of the drawings]

FIG. 1 is a diagram showing the structure, vibration velocity distribution and stress distribution during operation of a piezoelectric ceramic transformer according to a first embodiment of the present invention.

FIG. 2 is a lumped constant equivalent circuit diagram of the piezoelectric ceramic transformer of the present invention.

FIG. 3 is a view showing the structure, vibration velocity distribution and stress distribution during operation of a piezoelectric ceramic transformer according to a second embodiment of the present invention.

FIG. 4 is a perspective view showing a structure of a modification of the first embodiment of the present invention.

FIG. 5 is a perspective view showing the structure of a modification of the second embodiment of the present invention.

FIG. 6 is a perspective view showing the structure of a Rosen-type piezoelectric transformer as an example of a conventional piezoelectric ceramic transformer.

[Explanation of symbols]

1L, 1R, 2L, 2R, 3, 4 External terminal 5L, 5R Internal electrode 6L, 6R Piezoelectric ceramic layer 7A, 7B, 37A, 37B Electrode 41A, 41B, 42A, 42B, 51A, 51B, 5
2A, 52B Electrode 8L, 8R Low impedance section 9 High impedance section 61 Drive section 62 Power generation section 63, 64, 65 Electrode 66, 67, 68 External terminal

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takeshi Inoue 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation (56) References JP-A-4-167504 (JP, A) JP-A Sho56 −83984 (JP, A)

Claims (3)

(57) [Claims] 1. A plurality of internal electrodes and piezoelectric ceramic layers are alternately stacked in a thickness direction on each of two end faces in the longitudinal direction at a portion of not more than one third of the total piezoelectric ceramic transformer length at a maximum. Each of the piezoelectric ceramic layers facing each other with each internal electrode interposed therebetween is provided with two low-impedance portions having a structure in which polarization layers are polarized in directions opposite to each other with respect to the stacking direction axis. A high impedance portion having a structure in which a pair of electrodes facing each other is provided on two opposite surfaces perpendicular to the thickness direction axis, and a piezoelectric ceramic layer between the pair of electrodes is polarized in the thickness direction. With a length of 3
A piezoelectric ceramic transformer operating in the next mode. 2. A plurality of internal electrodes and piezoelectric ceramic layers are alternately stacked in the thickness direction from each of the two end faces in the longitudinal direction to a portion not more than one third of the total piezoelectric ceramic transformer length at the maximum. Each of the piezoelectric ceramic layers facing each other with each internal electrode interposed therebetween is provided with two low-impedance portions having a structure in which polarization layers are polarized in directions opposite to each other with respect to the stacking direction axis. A high impedance portion having a structure in which a pair of electrodes facing each other is provided on two opposite surfaces perpendicular to the plate width direction axis and a piezoelectric ceramic layer between the pair of electrodes is polarized in the plate width direction. A piezoelectric ceramic transformer comprising: a piezoelectric vertical transformer operating in a tertiary mode. 3. The method of driving a piezoelectric ceramic transformer according to claim 1, wherein the two low-impedance sections are used as input sections, and the high-impedance section is used as output sections. To each of the low impedance sections, an AC input voltage is applied so that each internal electrode constituting each layer has the same potential every other layer, and the two low impedance sections are driven in the same phase and output from the high impedance section. A method for driving a piezoelectric ceramic transformer, comprising extracting voltage.