JPH10135529A - Driving circuit piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to conduct both voltage boosting and voltage dropping on a single unit by a method in which driving frequency only is controlled in a laminated type piezoelectric transformer suitable to be used for purposes relating to power. SOLUTION: An input-side circuit 11 converts the applied DC voltage into sine wave AC voltage and outputs it. A laminated type piezoelectric transformer 13, on which the ratio of transformation becomes maximum when a driving frequency is changed to a resonance frequency and the ratio of transformation decreases when it is shifted from the resonance frequency, is used and it is by connecting load resistance on which the power transmission efficiency becomes maximum. The rate of transformation is determined by the input part of a transformer 13 and the sheet ratio of piezoelectric ceramic boards. An output-side circuit 15 outputs DC voltage which is formed by rectifying and smoothing the sine wave AC voltage sent from the transformer 13. A voltage detection circuit 17 detects the DC voltage sent from the output-side circuit 15 and outputs the voltage. A frequency modulation circuit 19 forms a control signal and output it to change the frequency of the sine wave AC voltage formed by the input-side circuit 11 in the region between the resonant point to the antiresonant point of the transformer based on the driving frequency-transformation ratio/impedance characteristics and the output from the voltage detection circuit 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a multilayer piezoelectric transformer, and more particularly to a power application (low voltage output,
The present invention relates to a drive circuit for a multi-layer piezoelectric transformer capable of stepping up / down by itself, which is suitable for large current output.

[0002]

2. Description of the Related Art As a piezoelectric transformer, a single-layer piezoelectric transformer having a single piezoelectric ceramic plate, represented by a Rosen type, and a plurality of piezoelectric transformers disclosed in, for example, JP-A-4-18776. There is a laminated piezoelectric transformer that includes laminated piezoelectric ceramic plates and utilizes piezoelectric longitudinal vibration. Rosen-type piezoelectric transformers are mainly used as step-up transformers having a transformation ratio (= output voltage / input voltage) of several tens of times or more. However, since the transformation ratio is high, the output voltage is high and the application is limited. Had been. On the other hand, the multilayer piezoelectric transformer is used as a step-down transformer, but due to its configuration, it has been used only for the step-down region where the step-down ratio is 1 or less.

[0003]

In an electric circuit using a battery as a driving power source, the input voltage decreases as the battery is discharged. Therefore, stabilization for keeping the input voltage to the electric circuit constant is required. Power supply is required.
For example, in a device using a Li-ion battery as a driving power source, the initial output voltage of the Li-ion battery is 4.2.
V, the output voltage at the end is 2.5 V, and the output voltage range is wide. Therefore, when a single Li-ion battery is used to supply a voltage of +3.3 V for driving an IC or the like, it is necessary to step down the voltage in the beginning and to step up the voltage in the middle.

[0004] When transforming a voltage in a region having a low transformation ratio, a DC-DC converter provided with a semiconductor switching element and a choke coil, which has been downsized in recent years, is frequently used in addition to an electromagnetic transformer of an old age. ing. However, such a DC-DC converter that does not use an electromagnetic transformer can perform only one of the step-up and step-down control in principle.

In view of the above, instead of the above-described DC-DC converter, a control IC having a configuration capable of performing step-up and step-down by itself has been developed. However, in the control method using the control IC, the operation method must be changed between the time of boosting and the time of stepping down. Therefore, the power transmission efficiency is significantly different between the time of stepping up and the time of stepping down. Transformation ratio = 1)
There is a disadvantage that the operation becomes unstable in a nearby area.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to make it possible to perform both step-up and step-down operations by controlling only the driving frequency of a laminated piezoelectric transformer suitable for power use.

[0007]

A drive circuit for a laminated piezoelectric transformer according to the present invention comprises frequency variable means for varying the frequency of the piezoelectric transformer in a range from step-up to step-down.

According to this configuration, since the frequency varying means varies the frequency in the range from step-up to step-down of the piezoelectric transformer, only the drive frequency of the piezoelectric transformer is controlled, so that either the step-up or step-down can be performed by itself. Can also be realized.

In a preferred embodiment of the drive circuit for a laminated piezoelectric transformer according to the present invention, a load resistance that maximizes the power transmission efficiency is connected to the piezoelectric transformer. It is desirable to use a piezoelectric transformer having a step-up / step-down characteristic such that the transformation ratio becomes maximum when the driving frequency is set to the resonance frequency, and the transformation ratio decreases as the frequency is shifted from the resonance frequency. This is based on new findings obtained as a result of experiments performed by the present inventors.

The frequency varying means varies the driving frequency of the piezoelectric transformer so that it becomes a resonance frequency when the voltage is increased.
When stepping down, it is varied so as to deviate from the resonance frequency. If the driving frequency of the piezoelectric transformer is varied in the frequency range from the resonance frequency to the anti-resonance frequency at the time of step-down, the power transmission efficiency of the piezoelectric transformer can be increased.

Further, by providing voltage detecting means for detecting a voltage applied to a voltage monitoring piezoelectric layer provided at an input portion of the piezoelectric transformer and outputting the voltage to frequency varying means, the input and output portions of the piezoelectric transformer can be connected to each other. It is possible to omit the connection of a photocoupler, a transformer, and the like, which are required for insulating between them.

[0012]

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

FIG. 1, FIG. 2 and FIG. 3 respectively show typical embodiments of a laminated piezoelectric transformer which can be driven in the piezoelectric lateral vibration mode of the present invention.

In the piezoelectric transformer shown in FIG. 1, two piezoelectric ceramic plates 1A and 1B having a circular planar shape are laminated in the thickness direction. Each piezoelectric ceramic plate 1A,
1B has electrodes 3A to 3C on its front and back surfaces. One piezoelectric ceramic plate 1A is an input unit, and the other piezoelectric ceramic plate 1B is an output unit. Also, in the piezoelectric transformer shown in FIG. 2, two piezoelectric ceramic plates 2A and 2B having a circular planar shape are laminated in the thickness direction, and each of the piezoelectric ceramic plates 2A and 2B has an electrode 4A on its front and back surfaces. 4C, one of the piezoelectric ceramic plates 2A is an input unit, and the other piezoelectric ceramic plate 2B is an output unit.

On the other hand, in the piezoelectric transformer shown in FIG. 3, a plurality of (for example, 10) piezoelectric plates 5A to 5J each having a rectangular planar shape are laminated in the thickness direction, and are manufactured by firing and polarization. Electrodes 7A to 7K on each front and back
have. Each of the piezoelectric plates 5A to 5J is polarized in the thickness direction and has, for example, a polarization axis in a direction indicated by an arrow. Of the ten stacked piezoelectric plates 5A to 5J, for example, nine are the input unit and the other is the output unit.

In FIGS. 1 to 3, the directions of the polarization axes indicated by arrows are merely examples, and the electric charges generated at each electrode are connected to each other so that the vibrations of the piezoelectric elements on both sides of the electrode do not cancel each other. The direction of the polarization axis may be opposite to that shown in the drawings as long as it is performed. Further, the number of stacked piezoelectric elements constituting the input section and the output section, whether or not to provide an insulating layer between the input section and the output section, and the respective piezoelectric materials constituting the input section and the output section. The composition and the like can be appropriately selected and adjusted according to the required transformer characteristics and the structure of the transformer.

It should be noted that the configuration of the piezoelectric transformer shown in FIGS. 1 to 3 is that the dimensions and directions of all the piezoelectric ceramic plates coincide in a specific lateral direction perpendicular to the polarization axis. is there. Therefore, the driving method for exciting the piezoelectric vibration in the specific lateral direction can be applied. For example, FIG.
In the piezoelectric transformer shown in FIG. 2 (or FIG. 2), each piezoelectric ceramic plate 1A (or 2A), 1B (or 2
The dimension and the direction of B) match in the radial direction of the planar shape. Therefore, power having a frequency corresponding to the resonance frequency of the transformer determined by the length of the radius is input to the transformer of FIG. 1 (or FIG. 2) so as to excite the piezoelectric transverse vibration (radial spreading vibration) in the radial direction. Drive method is applied. Further, for example, in the piezoelectric transformer shown in FIG. 3, the dimensions and directions of all the piezoelectric plates 5A to 5J match in the long side direction of the planar shape. Therefore, the driving method of inputting power having a frequency equal to the resonance frequency determined by the length of the long side so as to excite the piezoelectric transverse vibration (length vibration) in the long side direction is applied to the piezoelectric transformer of FIG. Is done.

By applying such a driving method, the input section converts electric energy into vibration energy by exciting the piezoelectric transverse vibration, and the vibration energy is transmitted from the input section to the output section. In the output unit, conversion from vibration energy to electric energy using piezoelectric lateral vibration is performed.

Another point to note regarding the configuration of the laminated piezoelectric transformer of the present invention is that the input is not performed in a direction other than the specific piezoelectric lateral vibration to be excited, that is, in another lateral direction or vertical direction (thickness direction). The directions of the unit and the output unit may be different from each other, and the size does not need to be a whole number such as 1/2 or 1/3 of the entire transformer.
Therefore, there is a high degree of freedom in the design of the transformer, particularly in the selection of the dimensions and arrangement of the piezoelectric ceramic plate. For example, FIG.
In each of the piezoelectric transformers shown in FIG. 3, it is also possible to use piezoelectric ceramic plates having different thicknesses.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some specific embodiments of the multilayer piezoelectric transformer according to the present invention and experimental results for each embodiment will be described below.

[First Embodiment] Two stacked disks In this embodiment, a piezoelectric transformer having the structure shown in FIG. 1 is driven. The material of the piezoelectric ceramic plates 1A and 1B is PZ
T-based piezoelectric ceramics. Each piezoelectric ceramic plate 1
A and 1B are disks having a diameter of 18 mm and a thickness of 1 mm. The method of manufacturing the transformer is as follows. First, each of the piezoelectric ceramic plates 1A and 1B is fired, and silver electrodes are fired on the front and back surfaces of each. Next, each of the piezoelectric ceramic plates 1A, 1B
A high DC voltage is applied between the electrodes to polarize the piezoelectric ceramic plates 1A and 1B in the thickness direction. Next, two piezoelectric ceramic plates 1A and 1B are placed between the two piezoelectric ceramic plates 1A and 1B.
Are laminated and bonded with a copper foil having a thickness of 10 μm therebetween. The dimensions of the completed piezoelectric transformer have a diameter of 18
mm and a thickness of 2 mm.

In this embodiment, a three-terminal structure is adopted in which one of the two piezoelectric ceramic plates 1A and 1B is used as an input portion, the other is used as an output portion, and the internal electrode 3B sandwiched therebetween is used as a common ground line. I do. By inputting high-frequency power for exciting radial expansion vibration, which is a form of piezoelectric transverse vibration, from the external electrode 3A (input terminal) of the input unit and extracting output power from the external electrode 3C (output terminal) of the output unit. The characteristics of the transformer were evaluated.

FIG. 4 shows the dependency of the transformation ratio (output voltage / input voltage) and the power transmission efficiency of the multilayer piezoelectric transformer of this embodiment on the load resistance, obtained by experiments.

As in the case of a general piezoelectric transformer, the transformer ratio and the power transmission efficiency ratio greatly depend on the load resistance. In this embodiment, the power transmission efficiency is 98% or more when the load resistance is in the range of 220Ω to 560Ω. It was very high. Since the shape, material, and number of piezoelectric ceramics of the input portion and the output portion are the same, the transformation ratios at load resistance values of 220Ω and 560Ω at which the power transmission efficiency is maximum are 1.2 and 2.
It was about 1.

FIG. 5 shows the dependence of the transformation ratio and the power transmission efficiency of the laminated piezoelectric transformer on the driving frequency obtained in the present embodiment, obtained by experiments. The data shown in FIG.
This is obtained by measuring the drive frequency dependence of the transformation ratio and the power transmission efficiency while fixing the voltage to 0Ω and 560Ω, respectively.

The transformer ratio deviates from the resonance point and becomes smaller with the peak when driven at the resonance frequency. When the load resistance is 220Ω, the transformation ratio is 0.3 to 1.2.
When the load resistance is 560Ω, the transformation ratio is 0.4 ~
Although it changes to about 2.1, the power transmission efficiency at this time keeps substantially the same value.

[Second Embodiment] An integrated firing type (input / output) of 10 laminated long plates = (9/1) = 9 In this embodiment, a piezoelectric transformer having the configuration shown in FIG. 3 is driven. I do. Piezoelectric plates 5A to 5J constituting this piezoelectric transformer
Is a PZT-based piezoelectric ceramic. Each of the piezoelectric plates 5A to 5J has a long side of 37 mm, a short side of 7 mm, and a thickness of 0.1 mm.
It is an 8 mm rectangular plate. The method of manufacturing the transformer is as follows. First, platinum electrodes 7A to 7I are formed on one side of each of the piezoelectric plates 5A to 5I by screen printing. Regarding the remaining one piezoelectric plate 5J, platinum electrodes 7J and 7K are formed on both surfaces thereof by screen printing. Next, the respective piezoelectric plates 5A to 5J and the respective platinum electrodes 7A to 7K are laminated so as to be alternately interposed therebetween, thermocompression-bonded, and sintered integrally,
A high DC voltage is applied between the electrodes of each of the piezoelectric plates 5A to 5J,
The piezoelectric plates 5A to 5J are polarized in the thickness direction. The dimensions of the piezoelectric transformer completed in this way are long side 37 mm, short side 7 m
m, thickness 2 mm.

In this embodiment, nine out of ten piezoelectric plates 5
A to 5I are input portions, the remaining one piezoelectric plate 5J is an output portion, electrodes 7A, 7C, 7E, 7G and 7I are connected to input terminals, electrode 7K is connected to an output terminal, and electrodes 7B, 7D, 7
A three-terminal configuration using F, 7H and 7J as a common ground line is adopted. As a result, the ratio of the number of stacked layers between the input unit and the output unit becomes 9. High-frequency power for exciting longitudinal vibration, which is a form of piezoelectric transverse vibration, is input from an electrode 7A (input terminal) of the input unit, and output power is extracted from an electrode 7K (output terminal) of the output unit. The properties were evaluated.

FIG. 6 shows the dependency of the transformation ratio (output voltage / input voltage) and the power transmission efficiency on the load resistance of the multilayer piezoelectric transformer in this embodiment, obtained by experiments.

Like a general piezoelectric transformer, the transformer ratio and the power transmission efficiency greatly depend on the load resistance. In this embodiment, when the load resistance is 220Ω, the power transmission efficiency is about 70%.
%Became. The transformation ratio at a load resistance value of 220Ω was about 8.5.

FIG. 7 shows the dependence of the transformation ratio and the power transmission efficiency of the laminated piezoelectric transformer on the driving frequency obtained in the present embodiment, obtained by experiments. The data shown in FIG.
This is obtained by measuring the drive frequency dependence of the transformation ratio and the power transmission efficiency while fixing to 0Ω.

The transformer ratio deviates from the resonance point and becomes smaller with the peak at the time of driving at the resonance frequency. When the load resistance is 220Ω, the transformation ratio changes to about 0.4 to 8.0, but at this time, if driven at a frequency higher than the resonance point, the power transmission efficiency keeps almost the same value.

[Third Embodiment] Two discs laminated Dielectric constant (input / output) = 2 In this embodiment, the piezoelectric transformer shown in FIG. 2 is driven.
The material of the piezoelectric ceramic plates 2A and 2B is a PZT-based piezoelectric ceramic, and an input portion (piezoelectric ceramic plate 2) is used.
PZT-based piezoelectric ceramics having different dielectric constants between the piezoelectric ceramic plates 2A and 2B are used so that the ratio of the capacitance between A) and the output portion (piezoelectric ceramic plate 2B) becomes 2. Each piezoelectric ceramic plate 2A, 2B has a diameter of 18m
m, a 1 mm thick disk. The method of manufacturing the transformer is as follows. First, each of the piezoelectric ceramic plates 2A, 2B
And baking silver electrodes on each of the front and back surfaces. next,
A high DC voltage is applied between the electrodes of the piezoelectric ceramic plates 2A, 2B to polarize the piezoelectric ceramic plates 2A, 2B in the thickness direction. Next, two piezoelectric ceramic plates 2
A, 2B, 10 μm in thickness between them as an internal electrode 4B
m and sandwiched between the copper foils. The dimensions of the completed piezoelectric transformer are 18 mm in diameter and 2 mm in thickness.

In this embodiment, a three-terminal structure is adopted in which one of the two piezoelectric ceramic plates 2A and 2B is used as an input portion, the other is used as an output portion, and the internal electrode 4B sandwiched between them is used as a common ground line. I do. By inputting high-frequency power for exciting radial expansion vibration, which is a form of piezoelectric lateral vibration, from the external electrode 4A (input terminal) of the input unit and extracting output power from the external electrode 4C (output terminal) of the output unit. The characteristics of the transformer were evaluated.

FIG. 8 shows the dependency of the transformation ratio (output voltage / input voltage) and the power transmission efficiency of the multilayer piezoelectric transformer of the present embodiment on the load resistance, obtained by experiments.

As with a general piezoelectric transformer, the transformation ratio and transmission efficiency greatly depend on the load resistance. In this embodiment, the power transmission efficiency is 7 when the load resistance is in the range of 220Ω to 560Ω.
0% or more. The transformation ratio at a load resistance value of 220Ω and 560Ω was about 1.5 and 2.0, respectively.

FIG. 9 shows the dependence of the transformation ratio and the power transmission efficiency of the multilayer piezoelectric transformer in the present embodiment on the driving frequency, obtained by experiments. The data shown in FIG.
It is obtained as a result of measuring the drive frequency dependence of the transformation ratio and the power transmission efficiency while fixing to 0Ω and 560Ω.

The transformer ratio deviates from the resonance point and decreases with the peak at the time of driving at the resonance frequency. When the load resistance is 220Ω, the transformation ratio is about 0.3 to 1.5, and when the load resistance is 560Ω, the transformation ratio is 0.4 to 2.1.
The power transmission efficiency at this time remains almost the same.

FIG. 10 is a block diagram showing a driving circuit for a laminated piezoelectric transformer according to one embodiment of the present invention.

The drive circuit includes an input circuit 11, a piezoelectric transformer 13, an output circuit 15, a voltage detection circuit 17, and a frequency modulation circuit 19, as shown in the figure.

The input side circuit 11 has a frequency modulation terminal, and converts a DC voltage applied from the DC power supply 21 into, for example, a sine wave AC voltage and outputs it to the piezoelectric transformer 13.

The piezoelectric transformer 13 converts the sine wave AC voltage output from the input side circuit 11 into a voltage, and outputs the converted voltage to the output side circuit 15. When the driving frequency is set to the resonance frequency, the transformer ratio is maximized. Therefore, it is desirable to employ a capacitor having a step-up / step-down characteristic in which the transformation ratio decreases as the frequency shifts from the resonance frequency. Further, it is desirable to connect and use a load resistor (not shown) that maximizes power transmission efficiency to the piezoelectric transformer 13 having such step-up / step-down characteristics. The transformation ratio (boost ratio) of the piezoelectric transformer 13 is
The ratio is determined by the ratio of the number of piezoelectric ceramic plates forming the input section to the number of piezoelectric ceramic plates forming the output section, and the ratio of the capacitance of the piezoelectric ceramic plate forming the input section to the piezoelectric ceramic plate forming the output section. The reason why the transformation ratio is determined by the capacitance ratio is that the structure of the piezoelectric transformer 13 is equivalent to a capacitor.

The output side circuit 15 has an output terminal 23, and inputs a sine wave AC voltage output from the piezoelectric transformer 13, rectifies and smoothes the DC voltage, and outputs the DC voltage through the output terminal 23. Output.

The voltage detection circuit 17 detects a DC voltage applied from the output side circuit 15 to the output terminal 23, and outputs the detection result to the frequency modulation circuit 19.

The frequency modulation circuit 19 holds, for example, a driving frequency-transformation ratio / impedance characteristic of a piezoelectric transformer as data as shown in FIG. The frequency modulation circuit 19 changes the frequency of the sine wave AC voltage generated by the input side circuit 11 based on the data and the output from the voltage detection circuit 17 into the frequency between the resonance point a and the anti-resonance point b in FIG. A control signal is generated and applied to the frequency modulation terminal of the input side circuit 11 so as to be variable in the area c.

That is, when boosting, the piezoelectric transformer 13
And the driving frequency of the piezoelectric transformer 13 is shifted from the resonance point a to the anti-resonance point b side (the area on the right side of the resonance point a in FIG. 11) at the time of step-down. , And outputs a control signal to the input side circuit 11. The reason for shifting the driving frequency to the region on the right side of the resonance point a during the step-down is that the piezoelectric transformer 1
This is because the power transmission efficiency is increased because the impedance characteristic of No. 3 is indicated by the curve Z as shown in FIG.
The above-mentioned transformation ratio of the piezoelectric transformer 13 is, for example, when the above-described piezoelectric transformer of FIG.
By varying the frequency of the sine wave AC voltage generated in step 1, it can be controlled to about 0.10 to about 10.00 times, and no problem occurred when actually used in this range.

According to the above configuration, the power transmission of both the step-up and the step-down at a relatively low transformation ratio by one piezoelectric transformer 13 is performed only by controlling the driving frequency of the piezoelectric transformer 13 by the frequency modulation circuit 19. The operation can be performed in a state where problems such as deterioration of efficiency and instability of operation in a region where the transformation ratio is 1 do not occur.

FIG. 12 is a block diagram showing a driving circuit for a laminated piezoelectric transformer according to a modification of the embodiment of the present invention.

In this modification, the voltage detection circuit 25 detects the voltage applied to one voltage monitoring piezoelectric layer (monitor layer) 14 a provided on the input side of the piezoelectric transformer 14 and sends the voltage to the frequency modulation circuit 19. The output is different from the drive circuit shown in FIG. Other configurations are the same as those shown in FIG.

The piezoelectric transformer 14 is a piezoelectric transformer 1
As in the case of 3, since the piezoelectric actuator is driven in the piezoelectric lateral vibration mode,
Since the transformer characteristics are not affected by the thickness of the laminate, there is no problem even if the monitor layer 14a is inserted into the input section.
In addition, unlike the drive circuit shown in FIG. 10, the voltage detection circuit 25 is not configured to directly detect the output of the output side circuit 15, so that the output of the output side circuit 15 is output through the voltage detection circuit 25 and the frequency modulation circuit 19. A loop that is fed back to the input side circuit 13 is not formed. Therefore,
This modification also has an advantage that the drive circuit shown in FIG. 10 does not require connection of a photocoupler, a transformer, or the like, which is required to insulate between an input unit and an output unit of the piezoelectric transformer. is there.

It should be noted that the above-mentioned contents relate only to one embodiment of the present invention and modifications thereof, and do not mean that the present invention is limited to only the above-described contents.

[0052]

As described above, according to the present invention,
In a laminated piezoelectric transformer suitable for power use, by controlling only the drive frequency, it is possible to raise or lower the voltage by itself.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a laminated piezoelectric transformer which can be driven in a piezoelectric lateral vibration mode of the present invention.

FIG. 2 is a perspective view showing another embodiment of the laminated piezoelectric transformer drivable in the piezoelectric lateral vibration mode of the present invention.

FIG. 3 is a perspective view showing still another embodiment of the laminated piezoelectric transformer drivable in the piezoelectric lateral vibration mode of the present invention.

FIG. 4 is a diagram showing the load resistance dependence of the transformation ratio and power transmission efficiency of the multilayer piezoelectric transformer in the first embodiment.

FIG. 5 is a diagram illustrating a driving frequency dependency of a voltage change ratio and power transmission efficiency of the multilayer piezoelectric transformer in the first embodiment.

FIG. 6 is a diagram showing the load resistance dependence of the transformation ratio and power transmission efficiency of the multilayer piezoelectric transformer in the second embodiment.

FIG. 7 is a diagram illustrating a drive frequency dependency of a voltage change ratio and power transmission efficiency of the multilayer piezoelectric transformer in the second embodiment.

FIG. 8 is a view showing the load resistance dependence of the transformation ratio and power transmission efficiency of the multilayer piezoelectric transformer in the third embodiment.

FIG. 9 is a diagram illustrating a drive frequency dependency of a voltage change ratio and power transmission efficiency of the multilayer piezoelectric transformer in the third embodiment.

FIG. 10 is a block diagram of a driving circuit of the multilayer piezoelectric transformer according to one embodiment of the present invention.

FIG. 11 is a diagram showing a driving frequency-transformation ratio / impedance characteristic of the piezoelectric transformer according to one embodiment.

FIG. 12 is a block diagram of a driving circuit for a multilayer piezoelectric transformer according to a modification of the embodiment.

[Explanation of symbols]

 1A, 1B, 2A, 2B Piezoelectric ceramic plate 3A-3C, 4A-4C, 7A-7K Electrode 5A-5J Piezoelectric plate 11 Input side circuit 13, 14 Piezoelectric transformer 14a Monitor layer of piezoelectric transformer 15 Output side circuit 17, 25 Voltage Detection circuit 19 Frequency modulation circuit 21 DC power supply 23 Output terminal

Continued on the front page (72) Inventor Kenichi Kato 2-1-1, Nakajima, Kokurakita-ku, Kitakyushu-shi, Fukuoka Tochiki Kiki Co., Ltd. (72) Ichiro Kikuchi 2-1-1, Nakajima, Kokurakita-ku, Kitakyushu-shi, Fukuoka No. 1 Toto Kiki Co., Ltd.

Claims (6)

[Claims] 1. A driving circuit for a laminated piezoelectric transformer, comprising: a frequency varying means for varying a frequency of the piezoelectric transformer in a range from step-up to step-down. 2. The driving circuit for a piezoelectric transformer according to claim 1, wherein a load resistance that maximizes power transmission efficiency is connected to the piezoelectric transformer. 3. The driving circuit for a piezoelectric transformer according to claim 1, wherein the piezoelectric transformer has a maximum transformation ratio when the driving frequency is set to a resonance frequency, and the transformation ratio decreases as the resonance frequency is shifted from the resonance frequency. A driving circuit for a piezoelectric transformer having a step-up / step-down characteristic. 4. The piezoelectric transformer drive circuit according to claim 1, wherein the frequency varying means varies the drive frequency of the piezoelectric transformer so as to approach the resonance frequency when boosting the voltage, and varies the drive frequency away from the resonance frequency when the voltage decreases. A driving circuit for a piezoelectric transformer, comprising: 5. The driving circuit for a piezoelectric transformer according to claim 4, wherein the frequency variable means changes a driving frequency of the piezoelectric transformer in a frequency range from the resonance frequency to an anti-resonance frequency at the time of step-down. Drive circuit for the piezoelectric transformer. 6. The driving circuit for a piezoelectric transformer according to claim 1, further comprising: a voltage detecting unit that detects a voltage applied to a voltage monitoring piezoelectric layer provided at an input unit of the piezoelectric transformer and outputs the voltage to the frequency variable unit. And a driving circuit for a piezoelectric transformer.