JP2531087B2 - Piezoelectric transformer and driving method thereof - 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 transformer capable of operating in a high frequency band, and more particularly to an onboard piezoelectric ceramic transformer required to be downsized and reduced in noise and a driving method thereof.

[0002]

2. Description of the Related Art In recent years, the switching frequency of a switching power supply has been increased to reduce the size of a power supply circuit of an electronic device. Conventionally, an electromagnetic transformer has been used for this switching power supply, and as is well known, it is desirable to increase the switching frequency to miniaturize the switching power supply. However, when the switching frequency is increased, the hysteresis loss of the magnetic material used in the electromagnetic transformer, the eddy current loss, and the loss due to the skin effect of the conductor wire are rapidly increased, and the efficiency of the transformer is extremely low. Therefore, the upper limit of the practical frequency band of the electromagnetic transformer is at most 500 kHz.

On the other hand, the piezoelectric transformer is used in a resonance state, and (1) has a higher energy density at the same frequency than a general electromagnetic transformer, so that it can be downsized, and (2) non-combustible. It has many advantages such as being able to achieve it and (3) being unable to generate noise due to electromagnetic induction.

FIG. 3 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. In the case of taking out a high voltage, in the piezoelectric plate provided with electrodes on the surface, a portion indicated by 31 is a low impedance driving portion of the piezoelectric transformer, and electrodes 33 and 34 are provided on the upper and lower surfaces thereof. Are polarized in the thickness direction as indicated by the arrow in the figure. Similarly, a portion indicated by 32 is a high-impedance power generation unit, and an electrode 35 is provided on an end surface of the power generation unit 32.
Are polarized in the length direction of the piezoelectric plate as indicated by the arrow in the figure. The operation of this piezoelectric transformer is performed by the drive electrodes 33, 3
When a voltage is applied to 4, the longitudinal vibration is excited by the electromechanical coupling coefficient k _{31 in the} transverse effect 31 mode, and the entire transformer vibrates. Further, in the power generation section 32, a high voltage is taken out from the output electrode 35 in the longitudinal effect longitudinal vibration mode (33 mode) due to the electromechanical coupling coefficient k ₃₃ . On the other hand, when a high voltage is input and a low voltage is output, it is clear that the vertical effect high impedance portion 32 may be the input side and the horizontal effect low impedance portion 31 may be the output side. The other types of piezoelectric transformers also use the same extension vibration of a flat plate and radial vibration of a circular plate as in the Rosen type, and the applicable frequency is up to about 200 kHz.

On the other hand, the piezoelectric ceramic transformer (Japanese Patent Application No. 01-139525) previously invented by the present inventors has a structure in which piezoelectric ceramic plates polarized in the thickness direction are stacked.
By driving at the resonant frequency of thickness longitudinal vibration, MHz
It is possible to operate in a band.

[0006]

DISCLOSURE OF THE INVENTION The piezoelectric ceramic transformer previously invented by the present inventors (Japanese Patent Application No. 01-139525).
2A and 2B are cross-sectional views and stress distributions. In the figure, 21 and 22 are a low impedance part and a high impedance part, respectively, 23 is an internal electrode, and 24 is an external electrode. As is clear from the stress distribution in the figure, in the thickness longitudinal vibration first-order mode, near the boundary between the low impedance part and the high impedance part, and in the thickness longitudinal vibration second mode, near the center of the low impedance part (and the high impedance part). Maximum stress. That is, the structure is such that a strong stress is applied to the internal electrode portion. As is well known, the tensile strength at the interface between the metal internal electrode and the oxide piezoelectric ceramic is considerably lower than the tensile strength of the piezoelectric ceramic alone. Therefore, peeling easily occurs at the time of driving with high power, and it is difficult to transmit power up to the limit performance of the piezoelectric ceramic.

An object of the present invention is to provide a piezoelectric ceramic transformer which can be used with high power in a high frequency band of 1 MHz or more, and a driving method thereof.

[0008]

In order to achieve the above object, a piezoelectric ceramic transformer according to the present invention is a piezoelectric ceramic transformer having a low impedance portion and a high impedance portion, and a low impedance portion and a high impedance portion. Are different in impedance and function as a transformer element, the low impedance part has a piezoelectric ceramic layer and a pair of electrodes, and the piezoelectric ceramic layer is a plate-like body polarized in the thickness direction. , The pair of electrodes are provided so as to face each other on the end face in the thickness direction of the piezoelectric ceramic layer, and the high impedance portion has the piezoelectric ceramic layer and a pair of electrodes, The porcelain layer is a plate-like body that is polarized in the thickness direction, and the pair of electrodes is arranged at a position facing the end face in the thickness direction of the piezoelectric ceramic layer and in the longitudinal direction of the piezoelectric ceramic layer. Separately installed Has been connected, wherein the low impedance section and the high impedance section, in which are stacked in the thickness direction.

Further, a method of driving a piezoelectric ceramic transformer according to the present invention is a method of driving a piezoelectric ceramic transformer which excites the piezoelectric ceramic transformer in a thickness longitudinal vibration mode to transmit a voltage, wherein the piezoelectric ceramic transformer has a thickness direction. Of the low-impedance portion formed with a pair of electrodes on the end face in the thickness direction of the piezoelectric porcelain layer polarized in the horizontal direction, and the pair of electrodes formed on the end face in the thickness direction of the piezoelectric porcelain layer polarized in the thickness direction. It has a high impedance part in which a set is connected in series, the low impedance part and the high impedance part are laminated in the thickness direction, and the piezoelectric ceramic transformer is excited in the thickness longitudinal vibration secondary mode.

[0010]

The present invention has been made in order to provide a piezoelectric transformer which has a low loss and a sufficient function at a high frequency of 1 MHz or more and which does not apply a large stress to the internal electrodes. As shown in FIG. 1, the piezoelectric ceramic transformer of the present invention includes a low impedance portion 11 and a high impedance portion 12.
Is laminated in the thickness direction. In the low impedance portion 11, the piezoelectric ceramic layer 17 polarized in the thickness direction
The internal electrodes 141 and 142 are arranged on the upper and lower sides of each layer one by one. On the other hand, in the high impedance section 12,
Internal electrodes are arranged above and below the piezoelectric ceramic layer 18 polarized in the thickness direction, but each is divided into a plurality in the same plane. In FIG. 1, since it is divided into four regions as an example, the four upper internal electrodes 131, 133, 135, 1
37 and the lower four inner electrodes 132, 134, 13
It consists of 6,138. External leads 151,15
2 and 153 are used to connect adjacent upper and lower internal electrodes in series (for example, electrodes 132 and 133 with a conductor 151), and the internal electrodes 13 located at both ends of the serially connected internal electrodes
External electrical terminals 163 and 164 are connected to 1 and 138, respectively. By making such a connection, the four regions of the piezoelectric ceramic layer 18 are mechanically connected in parallel and electrically connected in series. Therefore, the external electric terminal 16
The impedance between 3 and 164 is the external electric terminal 161.
Higher than the impedance between ~ 162.

In the piezoelectric ceramic transformer of the present invention, the internal electrodes of both the low impedance portion 11 and the high impedance portion 12 are located near the upper and lower ends of the entire piezoelectric ceramic transformer (141, 1).
32, 134, 136, 138) or near the center (142, 131, 133, 135, 137). Therefore, as is clear from the stress distribution in the thickness longitudinal vibration secondary mode of FIG. 1, when the piezoelectric ceramic transformer according to the present invention is driven in the thickness longitudinal vibration secondary mode, the internal electrodes and the interface between the electrode and the piezoelectric ceramic are not affected. , No large stress is applied. Therefore, it is possible to drive the piezoelectric ceramic material with high power up to the stress limit.

[0012]

The present invention will be described below with reference to examples. As an example of the piezoelectric ceramic transformer according to the present invention, the piezoelectric ceramic transformer having the configuration shown in FIG. 1 was manufactured by the green sheet method. The material of the piezoelectric ceramic is a PbTiO ₃ system piezoelectric ceramic. The overall size of the piezoelectric ceramic transformer is 20 mm ×
The thickness of the low impedance portion 11 and the high impedance portion 12 was 1.1 mm, and the thickness of the piezoelectric ceramic layers 17 and 18 was 0.88 mm. The Pt paste is screen-printed and integrally sintered together with the piezoelectric ceramic, so that the Pt internal electrodes 131 to 3
8, 141, 142 were formed. An Ag electrode electrode was formed on the side surface by applying and firing an Ag paste to form an internal electrode connection electrode. After that, # 3000
Parallel polishing was performed on the upper and lower surfaces using the above abrasive.
Temporarily connect the conductor to the Ag electrode on the side with solder and
The polarization treatment was performed by applying a DC high voltage of 5 kV / mm in insulating oil at 00 ° C. After the polarization process, the electrodes are connected as shown in FIG.
162, 163 and 164 were taken out.

The resonance frequency of the thickness longitudinal vibration secondary mode of this piezoelectric ceramic transformer was measured to be 2.030 MHz from the frequency characteristic of admittance. The external electric terminals 163, 164 of this piezoelectric ceramic transformer are input terminals, 161, 1
When 62 was used as an output terminal and a load resistance of 10Ω was connected, an output voltage of 18 V was obtained for an input voltage of 80 V, and the output power at this time was 32.4 W. Further, even after continuous driving for 1000 hours, no deterioration in performance such as peeling of internal electrodes was observed.

[0014]

As described above, according to the present invention, a structure in which a low impedance portion and a high impedance portion are laminated in the thickness direction is used, and driving is performed at the resonance frequency of the thickness longitudinal vibration secondary mode. Since no large stress is applied to the boundary between the parts, there is an effect that it can be used with high power in a high frequency band of 1 MHz or more, and that it is small and can transmit power with high efficiency.

[Brief description of drawings]

1A is a sectional view showing a piezoelectric ceramic transformer of the present invention, and FIG. 1B is a stress distribution diagram.

FIG. 2A is a sectional view showing a conventional piezoelectric ceramic transformer utilizing thickness longitudinal vibration, and FIG. 2B is a stress distribution diagram.

FIG. 3 is a perspective view showing a conventional Rosen type piezoelectric ceramic transformer.

[Explanation of symbols]

11,21,31 Low impedance part 12,22,32 High impedance part 29,131,
132, 133, 134, 135, 136, 137, 1
38, 141, 142 Internal electrode 24, 33, 34, 35 External electrode 151, 152, 153 Connection conductor wire 46, 47, 48, 161, 162, 163, 164
External electrical terminals 17, 18 Piezoelectric layer

Claims (2)

(57) [Claims] 1. A piezoelectric ceramic transformer having a low impedance part and a high impedance part, wherein the low impedance part and the high impedance part have different impedances and function as a transformer element. The piezoelectric ceramic layer has a pair of electrodes, and the piezoelectric ceramic layer is a plate body polarized in the thickness direction, and the paired electrodes face the end faces in the thickness direction of the piezoelectric ceramic layer. The high impedance portion has a piezoelectric ceramic layer and a pair of electrodes, and the piezoelectric ceramic layer is a plate-like body polarized in the thickness direction and forms a pair. The set of electrodes is on the end face in the thickness direction of the piezoelectric ceramic layer,
The piezoelectric ceramic layers are provided so as to be opposed to each other and are divided in the length direction of the piezoelectric ceramic layers, and are further connected in series, and the low impedance portion and the high impedance portion are laminated in the thickness direction. A piezoelectric ceramic transformer characterized in that 2. A method of driving a piezoelectric ceramic transformer, which excites the piezoelectric ceramic transformer in a thickness longitudinal vibration mode to transmit a voltage, wherein the piezoelectric ceramic transformer comprises a piezoelectric ceramic layer polarized in a thickness direction in a thickness direction. It has a low impedance part with a pair of electrodes formed on the end face and a high impedance part with a pair of electrodes formed on the end face in the thickness direction of the piezoelectric ceramic layer polarized in the thickness direction connected in series. A low-impedance part and a high-impedance part are laminated in the thickness direction, and the piezoelectric ceramic transformer is excited in a thickness longitudinal vibration secondary mode, and a method of driving the piezoelectric ceramic transformer.