JPH1012943A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric transformer in which the transformer performance can be modified without requiring any modification in the shape of a piezoelectric when diversified requirements are imposed on the step-up ratio or the efficiency of the piezoelectric transformer or regulation is required for the output performance of an inverter circuit when it is mounted on a system employing the transformer. SOLUTION: The ratio of polarization at the driving section and the power generating section of a piezoelectric to the saturated polarization is differentiated between the driving section and the power generating section. The step-up ratio and the efficiency of a transformer exhibit different characteristics as compared with those of a piezoelectric where both the driving section and the power generating section are subjected to saturated pogarization. Since the characteristics vary differently depending on the extent of polarization at the driving section and the power generating section, performance of the transformer can be modified using a piezoelectric of identical shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer, and more particularly, to a piezoelectric transformer having a structure in which an electrode for applying an AC voltage and an electrode for extracting an output voltage are provided on the surface of a long plate-shaped piezoelectric body.

[0002]

2. Description of the Related Art In a piezoelectric transformer of this type, basically, an AC voltage is externally input to a pair of input electrodes provided on the surface of a long plate-shaped piezoelectric body, and the piezoelectric body mechanically resonates in the longitudinal direction by a piezoelectric effect. This is based on the operation principle that a voltage generated by the inverse piezoelectric effect based on the resonance is taken out from an output electrode provided separately from the input electrode.

FIG. 5 is a perspective view showing an example of a conventional piezoelectric transformer. Referring to FIG. 5, a long plate-shaped piezoelectric body 1 is bisected in the longitudinal direction. The left area is the drive unit 5
Called. Above and below, input electrodes 2 and 3 are formed which extend over almost the entire area. The area on the right side is called the power generation unit 6. On an end face perpendicular to the longitudinal axis, an output electrode 7 is formed which extends over the entire end face. Each of the drive unit 5 and the power generation unit 6 is polarized, and the drive unit 5 is polarized along the thickness axis of the piezoelectric body 1 as indicated by an upward arrow in the drawing. The power generation unit 6 is polarized in a direction along the longitudinal axis of the piezoelectric body as indicated by a right-pointing arrow. The above-described polarization is usually performed separately for each of the driving unit and the power generation unit by using the electrodes 2, 3, and 7 formed on the surface of the piezoelectric body during the manufacturing process.

In order to perform voltage boosting using this transformer, the input terminals 4A and 4A are connected between two electrodes 2 and 3 of the driving section.
During B, an external AC voltage e _in is applied. With this configuration, the piezoelectric body 1 generates longitudinal vibration in the longitudinal direction according to the frequency of the input AC voltage due to the piezoelectric transverse effect generated in the driving unit 5. At this time, the frequency of the input AC voltage e _in is set to, for example, the resonance frequency of the fundamental mode of the longitudinal vibration of the piezoelectric body (when the wavelength of the AC voltage e _in is λ and the length of the piezoelectric body is L, L = λ / 2), longitudinal resonance occurs in the entire piezoelectric body 1. Since a large voltage is generated between the end face electrode 7 and the input electrode 2 or the input electrode 3 by the inverse piezoelectric effect based on the resonance in the power generation unit 6, this voltage is taken out as a boosted voltage. That is, the end face electrode 7 and the input electrode 3 are commonly connected to the output terminal 8A, and the input electrode 2
Is connected to the output terminal 8B, and an output voltage e _out is taken _out between both terminals 8A and 8B.

FIG. 6 is a perspective view of another example of this type of piezoelectric transformer. The transformer shown in this figure is a transformer that operates in a third-order resonance mode (L = 3 · (λ / 2), where λ is the wavelength of the input AC voltage e _in and L is the length of the piezoelectric body 1). Referring to FIG. 6, long plate-shaped piezoelectric body 1 is largely divided along the longitudinal axis into three regions of the same length, that is, drive unit 5L, power generation unit 6, and drive unit 5R. Drive unit 5L
On both upper and lower surfaces, electrodes 2L and 3L are provided in regions 5L, respectively.
It is provided almost all over the area. Similarly, electrodes 2R and 3R are provided on the upper and lower surfaces of the other driving unit 5R. During the manufacturing process, the driving units 5L and 5R are polarized along the thickness axis of the piezoelectric body 1 as shown by vertical arrows in the figure.

On the other hand, the power generating section 6 is provided with thin electrodes 7 extending in the width direction of the piezoelectric body 1 above and below the center of the longitudinal axis of this area. As shown by an arrow along the longitudinal axis in the figure, the power generating unit 6 has a portion on the drive unit 5L side and a portion on the drive unit 5R side with the electrode 7 interposed therebetween, which are polarized in opposite directions along the longitudinal axis. Have been.

In this piezoelectric transformer, the boosting operation is performed as follows. First, the electrodes 2L and 2R on the upper surfaces of the two drive units are connected so as to have the same potential. Similarly, the lower electrodes 3L and 3R are connected. And
Between the upper and lower electrodes, that is, between the input terminals 4A and 4B,
Input the AC voltage e _in . When the frequency of the AC input voltage is selected as the resonance frequency of the third mode, the piezoelectric body 1 causes mechanical resonance of longitudinal vibration along the longitudinal axis. Due to the resonance vibration of the longitudinal axis, a vibration stress corresponding to the vibration displacement of the longitudinal axis is generated in the power generation unit 6. Then, an electric charge is generated by the vibration stress and an inverse piezoelectric effect based on the polarization of the longitudinal axis, and an electric charge is generated between the electrode 7 of the power generation unit and the electrodes 2L and 2R of the drive unit, that is, the output terminal 8
A boosted output voltage e _out is obtained between A and the output terminal 8B.

As described above, this type of transformer has been described using two examples. In this type of piezoelectric transformer, the piezoelectric body on the long plate has a mechanical resonance along the longitudinal axis along the longitudinal axis. Drive and a power generator for generating a voltage by mechanical resonance of the piezoelectric element. The drive and the power generator are arranged in the thickness direction and the length direction of the piezoelectric body. Structural characteristics that polarization is applied in different directions.

Here, during the manufacturing process, the polarization is maintained at a high temperature of, for example, about 150 ° C. or more in the manufacturing process, and the driving unit and the power generation unit are subjected to a coercive electric field of, for example, 2 kV / m or more.
This is performed by applying a DC high electric field of about m. In this case, the directions of polarization are different in the driving section in the thickness direction of the piezoelectric body 1 and in the power generation section in the longitudinal direction, so that each polarization is performed separately. The application of an electric field required for polarization is performed as follows. That is, first, FIG.
When the driving unit 5 is polarized by the transformer in the basic mode shown in FIG. 1, a voltage is applied between the two electrodes 2 and 3 above and below the driving unit to apply an electric field in the thickness direction. When the power generation unit is polarized, the two electrodes of the drive unit are short-circuited so that they have the same potential.
A voltage is applied between the electrodes 2 and 3 and the end face electrode 7 of the power generation unit to apply an electric field along the longitudinal axis to the piezoelectric body. Next, when the polarization of the driving units 5L and 5R is performed by the tertiary mode transformer shown in FIG. 6, the electrodes 2L and 2R on the upper surfaces of the driving units 5L and 5R are used.
Rs are short-circuited to have the same potential. Also, the electrodes 3L and 3R on the lower surface of each drive unit are short-circuited so as to have the same potential. Then, the upper electrodes 2L, 2R and the lower electrodes 3
A DC voltage is applied between L and 3R to apply an electric field to the piezoelectric body 1 along the thickness axis. On the other hand, regarding the polarization of the power generation unit 6,
The upper and lower four electrodes 2L, 3L, 2R, 3R of the drive unit are all connected so as to have the same potential. Then, a DC voltage is applied between the electrode 7 of the power generation unit and the electrodes 2L, 3L, 2R, 3R of the drive unit, and the voltage is applied to the piezoelectric body 1 in opposite directions along the longitudinal axis with the electrode 7 interposed therebetween. Apply an electric field.

By the way, the performance of the piezoelectric transformer can be said as follows assuming that the polarization in the thickness direction of the driving portion of the piezoelectric body and the polarization in the longitudinal direction of the power generation portion are both sufficiently saturated. That is, the most important step-up ratio as the transformer performance is shown by the following equation when the output terminal is open (in short, a consideration of a piezoelectric ceramic transformer, Journal of the Acoustical Society of Japan, No. 32
Vol. 1976, No. 8, pp. 470-479).

[0011]

According to the equation, it is desirable that the material of the piezoelectric transformer has a large electromechanical coupling coefficient k ₃₁ , k _{33 and a} large mechanical quality coefficient Q _m . Also, once the material is decided,
The step-up ratio γ is determined only by the geometric dimensions of the piezoelectric body. Further, from the equation, it is required that the polarization of the piezoelectric body is sufficiently saturated in order to maximize the boost ratio. That is, as is well known, the polarization amount P of the piezoelectric ceramic body and the electromechanical coupling coefficient k
Are related to each other, and k increases as P increases. Then, as P approaches a saturation state, k also converges to a certain constant value. From this, by saturating the amount of polarization, the coefficients k ₃₁ and k ₃₃ of the material can be used to the maximum, and as a result, the boost ratio can be increased.

However, for example, Japanese Patent Application Laid-Open No. 6-252467
As disclosed in the above publication, the following problem arises by increasing the efficiency of the transformer by saturating the amount of polarization P. In other words, considering the operating principle of a piezoelectric transformer, improving efficiency means that mechanical resonance with a larger amplitude is excited for the same input voltage, and a larger vibration stress acts on the piezoelectric body in proportion to this. , A larger charge is generated, and a larger output voltage is obtained. This means that the piezoelectric body is mechanically broken even with a smaller input voltage than the conventional one. In order to solve the problem of breakage of the piezoelectric body due to such a small input voltage, in the above-mentioned publication, the driving section and the power generation section are not discriminated and the polarization is suppressed to 30 to 90% of the saturation state, thereby suppressing the generation of large vibration stress. This guarantees the mechanical durability of the piezoelectric body. still,
In this durability improvement measure, the lower limit of the amount of polarization is determined as follows. That is, when the amount of polarization is reduced, the step-up ratio is reduced and the efficiency of the transformer is reduced, and the heat generated by the transformer during driving is increased. Since this heat also lowers the reliability of the transformer, the lower limit of the amount of polarization is set to 30% from the allowable limit of heat generation.

From the above description, when considering the reliability of the mechanical strength of the piezoelectric body, there is an optimum range of the polarization amount, and when the polarization amount is changed, the electromechanical coupling coefficient changes. It can be seen that the step-up ratio of the transformer also changes according to the equation.

Next, regarding the output characteristics of the piezoelectric transformer,
Load dependence is known. For example, according to the above-mentioned literature, the step-up ratio of a piezoelectric transformer increases as the electrical impedance of a load connected to the transformer increases.
In particular, when the load impedance becomes larger than the size matching the output impedance of the transformer, the boost ratio rapidly increases. In other words, even if the performance of the piezoelectric body alone (with no load) is the same, (when the load is connected)
The performance as a transformer greatly depends on the impedance of the connected load.

[0016]

This type of imaged piezoelectric transformer has room for improvement in the following points. That is, (1) Taking an inverter for a backlight for a liquid crystal display as an example, the size (tube diameter and length) of a cold cathode tube used naturally differs for each display screen size. This means that the inverter output voltage, electric power, and the like required for stable lighting of the cold-cathode tubes differ for each screen size. In other words, if the transformer is the same, the input voltage will be different. However, the input voltage of the inverter is often constant due to a limitation due to battery drive or a limitation on the IC used. This means that the output characteristics of the transformer must be variously changed in accordance with the screen size to meet various required output performances.

In general, not only the backlight inverter but also a power supply generally has a strong tendency to be customized for each circuit design. However, since the step-up and step-down transformers play a central role in such a power supply device, it is desired that the output characteristics such as the step-up ratio and the efficiency can be easily changed in design.

On the other hand, as one means for changing the performance of the piezoelectric transformer, there is a method of changing the shape of the piezoelectric body based on the above equation. However, changing the shape of the piezoelectric body causes the following problems. First, when the piezoelectric transformer is driven, since the circuit is a resonance circuit, the circuit constant of the resonance circuit must be redesigned due to a change in capacitance due to a change in dimensions of the piezoelectric body. That is, in addition to the design change of the transformer itself, the design of the drive circuit must also be changed. If you are using a dedicated IC, you will need to change that IC.
In terms of the man-hours for developing ICs and the lead time, it is extremely difficult to deal with them. Next, when the components are mounted on the inverter board, the above-described drive circuit is also changed, so the printed wiring board must be newly designed. In the case of a transformer having a structure incorporated in a package, it is necessary to change the design of the package. As described above, it is extremely difficult to change the shape of the piezoelectric body using a power supply device that supports customization.

(2) Considering the wiring between the inverter and the load, if the load has a high impedance, the effect of the stray capacitance between the inverter and the load is large. This is for the following reason. As described above, the load characteristics of the output characteristics of the piezoelectric transformer are extremely large. By the way, since the stray capacitance is applied in parallel to the high impedance load, the load of the piezoelectric transformer is effectively significantly reduced in impedance by the parallel stray capacitance. Therefore, the output voltage of the transformer decreases and its efficiency also decreases.
Such a decrease in transformer performance due to stray capacitance is a problem that occurs when the inverter is actually mounted on a system such as a backlight, and is difficult to predict in advance. Therefore, in some cases, it will be necessary to respond individually in a case-by-case manner,
As described above, since the performance of the piezoelectric transformer is determined by the size of the piezoelectric body, it is difficult to make a large adjustment there, and in some cases, the design of the inverter circuit may be changed. This means a significant extension of the development lead time, as in (1) above.

As described above, the change in the shape of the piezoelectric body in the piezoelectric transformer prolongs the development lead time of the inverter and increases the cost. On the other hand, if it is attempted to change the piezoelectric transformer without changing it, the series of the piezoelectric transformer must be advanced, and the degree of freedom in product performance and commerciality is impaired. Alternatively, a large number of man-hours are required for individual physical adjustment. Therefore, a method for changing or adjusting the transformer performance without changing the shape of the piezoelectric body is strongly desired.

[0021]

A piezoelectric transformer according to the present invention comprises a long plate-shaped piezoelectric ceramic body and electrodes formed on the surface thereof, and the piezoelectric ceramic body has a thickness in a longitudinal direction. In a piezoelectric transformer having a structure divided into a drive unit polarized along the axis and a power generation unit polarized along the longitudinal axis, the saturation of the amount of polarization in each of the drive unit and the power generation unit The ratio of the state to the amount of polarization is different between the driving unit and the power generation unit.

According to the present invention, it is possible to realize a performance of a piezoelectric transformer that is not expected from a known equation. For example, in a piezoelectric transformer in which only the polarization of the drive unit is in a saturated state and the polarization of the power generation unit is in a state before reaching saturation, the step-up ratio when driving the piezoelectric transformer increases with an increase in the amount of polarization, and the amount of saturation polarization increases. On the other hand, it becomes a local maximum once at around 50%, and decreases when the amount of polarization further increases. The boost ratio at that maximum is
Both the polarization of the drive unit and the polarization of the power generation unit are about 40% larger than the step-up ratio in the piezoelectric transformer in which the polarization is saturated.

On the other hand, when the power generation unit is set to the saturation polarization and the amount of polarization of the driving unit is changed, the step-up ratio becomes smaller as the amount of polarization decreases, but the efficiency tends to be improved.

Therefore, if the amount of polarization of the power generation unit and the amount of polarization of the drive unit are individually controlled, it is possible to obtain a piezoelectric transformer having the desired performance while using piezoelectric bodies of the same dimensions.

[0025]

Next, an embodiment of the present invention will be described with reference to the drawings. In the three examples described below, a long plate-shaped piezoelectric body made of a piezoelectric ceramic material was used, and a piezoelectric transformer whose perspective view was shown in FIG. 6 was manufactured. Then, the relationship between the amount of polarization of the drive unit or the power generation unit and the step-up ratio and efficiency of the transformer was investigated. That is, with reference to FIG. 6, the piezoelectric transformer of the embodiment described below is the same as the above-described conventional piezoelectric transformer, and utilizes a third-order longitudinal mechanical resonance. The electrodes 2L, 3L, 2R, 3R of the drive unit and the external input terminals 4A, 4B
9L, 10L, 9R, 10R and connection points 11, 12 between the electrode 7 of the power generation unit and the external output terminals 8A, 8B.
Are all located at the nodes of the third-order mode resonance. Hereinafter, embodiments of the present invention will be specifically described based on examples.

(Embodiment 1) First, the manufacturing process of this embodiment will be described. In manufacturing the transformer of this embodiment, first, a piezoelectric ceramic material having a large electromechanical coupling coefficient and a large mechanical quality coefficient (trade name: NEPEC)
8. (Tokin Co., Ltd.) was prepared. Then, the sintered body is 36.8 mm long, 5.3 mm wide, and 1.3 mm thick.
The piezoelectric body 1 was obtained by cutting into a long plate shape. Next, predetermined portions of the surface of the piezoelectric body 1 (electrodes 2L, 3L, 2R, 3R)
R, 7), an electrode pattern is formed by a normal thick film screen printing method using a silver paste,
Bake at 0 ° C. Lastly, the piezoelectric body 1 was subjected to a polarization treatment to give piezoelectric activity, thereby enabling operation as a transformer. In this case, since two kinds of polarizations, that is, polarization in the thickness direction and polarization in the longitudinal direction, exist in the piezoelectric body 1, polarization was performed in each direction, and a total of twice polarization processing was performed. The method of connecting the electrodes during each polarization process is the same as in the above-described conventional piezoelectric transformer. Here, in the present embodiment, the polarization of the driving unit is set to be a saturated polarization, and the amount of polarization of the power generation unit is set to be 100, 80, 60, 40, and 30% smaller than the saturated state, and 10% for each level. Transformers were manufactured individually. In each direction, a DC electric field of 1.5 kV / mm was applied in insulating oil heated to 170 ° C.
Obtained by holding for 5 minutes. On the other hand, the polarization was kept in a state before saturation by adjusting the magnitude of the applied DC voltage.

Next, a pure resistance of 600 kΩ was connected as a pseudo load between the output terminals 8A and 8B of the piezoelectric transformer manufactured as described above, while a sine wave from the synthesizer was once amplified through an amplifier and then input. Terminal 4A, 4
By applying a voltage between B and B, the device was operated as a transformer. The resonance frequency at this time varies depending on the level of the transformer, but both the drive section and the power generation section have saturation polarization and are 136 kHz. The resonance frequency tends to increase as the polarization of the power generation unit decreases, and is approximately 149 kHz for a 30% polarization.
Met.

FIG. 1 shows the relationship between the degree of polarization of the power generation unit, the boost ratio as a transformer, and the efficiency in this embodiment. Referring to FIG. 1, the step-up ratio increases as the degree of polarization of the driving section increases, and reaches a local maximum value near 60% with respect to the saturated state, but decreases when the degree of polarization further increases. I do. The step-up ratio at this maximum is such that the polarization of the power generation section is 10
It is about 40% larger than the step-up ratio at the level of 0% (both the driving section and the saturation section side have a saturation polarization transformer). On the other hand, the efficiency tends to decrease as the degree of polarization of the actuation portion decreases, and the efficiency of a 30% polarization decreases to about 20%.

As described above, by setting the polarization of the driving section to the saturation polarization and lowering the degree of the polarization only in the power generation section, it is possible to obtain transformers having different step-up ratios as transformers while using piezoelectric bodies of the same dimensions. .

The step-up ratio γ of this type of piezoelectric transformer is theoretically expressed by the following equation using equivalent circuit analysis.

[0031]

However, in the field of this type of piezoelectric transformer, discussions have been made based on the fact that both the drive section and the power generation section have saturation polarization. Generally, both the polarization of the drive unit and the polarization of the power generation unit are changed without discrimination, as in JP-A-252467. That is, the result of the present embodiment shown in FIG. 1 is not a matter predicted in advance through an equation or the like, but is obtained only by controlling the polarization of the driving unit and the power generation unit separately.

Example 2 In the same manner as in Example 1, a piezoelectric transformer having the same piezoelectric dimensions as in Example 1 was manufactured. However, the polarization of the piezoelectric body is different from that of the first embodiment.
0.45%. The control of the degree of polarization of the drive unit in the present embodiment also depends on the applied voltage during the polarization processing.
The number of transformers manufactured is 10 for each level.

The above-described transformer was driven under the same driving conditions as in Example 1, and the relationship between the degree of polarization of the driving section and the boosting ratio and efficiency of the transformer was investigated. In this case, the resonance frequency was 136 kHz without being changed depending on each level. The results of the above investigation are shown in FIG. Referring to FIG. 2, when the polarization of the driving unit is reduced, the step-up ratio monotonically decreases accordingly, and when the driving unit is 45% polarized, the boost ratio becomes 10%.
It is about 55% smaller than the level of 0% polarization (both the drive section and the power generation section are transformers with saturation polarization). On the other hand, the efficiency of the transformer is constant regardless of the degree of polarization of the driving unit.

As described above, the polarization of the drive unit is made lower than the saturation polarization while the power generation unit is made to have the saturation polarization.
A unique result was obtained which was different from the results of JP-A-252467, in which both the drive unit and the power generation unit were reduced in polarization, resulting in a decrease in boost ratio and efficiency.

The following can be said based on the results obtained in the first and second embodiments. That is, first, assuming that the efficiency is maintained at 80% or more, the polarization of the power generation unit may be set to 85% or more with respect to the saturated state. Furthermore, assuming that the step-up ratio is maintained at a value equal to or more than 1/2 of that in the case of the saturation polarization, the polarization of the driving unit may be set to 50% or more with respect to the saturation state. The reason why the efficiency is kept at 80% or more is as follows. A decrease in efficiency is a factor that increases heat generation and lowers reliability. Therefore, it is desirable that the efficiency be high. However, from an industrial point of view, the efficiency is comparable to that of a low-height electromagnetic transformer which is currently the mainstream. On the other hand, if the polarization of the driving portion is made too small, it causes a loss in the conversion efficiency of the electric input energy to the mechanical output energy to the piezoelectric body, and the efficiency equivalent to the electromagnetic transformer cannot be obtained.

(Embodiment 3) The size of the piezoelectric body is 42 m in length.
m, a width of 10 mm, and a thickness of 1 mm, which were different from the piezoelectric bodies in Examples 1 and 2. Thereafter, a single cold-cathode tube backlight for a 9.4-inch color liquid crystal display was used as a load, and a sine wave from the synthesizer was once amplified and applied to the piezoelectric body to drive the transformer. Then, the relationship between the degree of polarization of the drive unit or the power generation unit and the step-up ratio and efficiency of the transformer was investigated. In this example, the following two types of polarization states of the piezoelectric body were prepared. A transformer in which the polarization of the drive unit is fixed at the saturation polarization and the amount of polarization of the power generation unit is reduced to 100, 92, 81% of the saturation polarization. A transformer in which the polarization of the power generation unit is fixed at the saturation polarization and the amount of polarization of the driving unit is reduced to 100, 92, and 85% of the saturation polarization.

FIG. 3 shows the results of the investigation performed on the above transformer. Fig. 4
Shown in The results are as follows. The luminance of the backlight is 1800 cd / m ² required by a notebook personal computer, and the driving conditions are adjusted so that the output current of the piezoelectric transformer is constant at 6.5 mA. It is a result in.

Referring to FIG. 3, the step-up ratio slightly increases when the amount of polarization of the power generation unit is gradually reduced from the saturation polarization. When the power generation unit is 81% polarized, the boost ratio increases from 19.5 to 2 times.
It increases about 10% by 1.1 times. On the other hand, the transformer efficiency sharply decreases as the amount of polarization of the power generation unit decreases, and drops to 66% in the case of 81% polarization. Next, referring to FIG. 4, when the amount of polarization of the driving unit is reduced with respect to saturation, the efficiency is improved although the boost ratio is reduced.

From the results of FIGS. 3 and 4, it can be seen that if the amount of polarization of the power generation unit is made smaller than the saturation polarization and the polarization of the drive unit is also made small, the step-up ratio can be adjusted within the range where the transformer efficiency is not impaired. I understand. In other words, in response to the aforementioned performance degradation of the piezoelectric transformer due to the effect of stray capacitance that occurs when the inverter is installed in the system, the degree of polarization of the drive unit and the power generation unit is individually adjusted, and the performance of the transformer is adjusted. Can be finely adjusted.

[0041]

As described above, the present invention includes a long plate-shaped piezoelectric ceramic body and electrodes formed on the surface thereof, and the ceramic body extends along the thickness axis along the longitudinal direction. For a piezoelectric transformer having a structure that is divided into a driving part polarized in the vertical direction and a power generation part polarized along the longitudinal axis, the polarization amount in the saturated state of the polarization amount in each of the driving part and the power generation part. Are different between the drive unit and the power generation unit.

Thus, according to the present invention, the boosting ratio can be increased by setting the amount of polarization of the drive unit to the amount of saturation polarization and making the amount of polarization of the power generation unit smaller than the amount of saturation polarization.

Also, by making the amount of polarization of the driving unit smaller than the amount of saturation polarization and setting the amount of polarization of the power generation unit to the amount of saturation polarization,
The boost ratio can be reduced while keeping the transformer efficiency constant.

Further, by changing both the amount of polarization of the drive unit and the amount of polarization of the power generation unit, it is possible to finely adjust the piezoelectric transformer performance, that is, to increase the step-up ratio while keeping the transformer high ratio.

The present invention eliminates the need for a series of piezoelectric transformers and the change of the shape of the piezoelectric body for fine adjustment of performance, which has been conventionally required, thereby shortening the development lead time of the transformer itself and reducing the product cost. I do. Also, there is no need to change the design of the drive circuit due to the change in the shape of the piezoelectric body, or to change other components in the system that uses this transformer, such as packages and printed wiring boards. This also reduces the system development lead time and costs. To contribute.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a relationship between a boost ratio and efficiency of a piezoelectric transformer and a degree of polarization of a power generation unit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a boost ratio and efficiency of a piezoelectric transformer and a degree of polarization of a driving unit according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a relationship between a boost ratio and efficiency of a piezoelectric transformer and a degree of polarization of a power generation unit according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating a relationship between a boost ratio and efficiency of a piezoelectric transformer and a degree of polarization of a driving unit according to a third embodiment of the present invention.

FIG. 5 is a perspective view of an example of a conventional piezoelectric transformer.

FIG. 6 is a perspective view of another example of a conventional piezoelectric transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric body 2, 2L, 2R Input electrode 3, 3L, 3R Input electrode 4A, 4B Input terminal 5, 5L, 5R Drive part 6 Power generation part 7 Output electrode 8A, 8B Output electrode 9L, 9R, 10L, 10R , 11,12 Connection points

Claims (4)

[Claims] 1. A piezoelectric ceramic body comprising a long plate-shaped piezoelectric ceramic body and electrodes formed on the surface thereof, wherein the piezoelectric ceramic body is polarized along a thickness axis in a longitudinal direction. A piezoelectric transformer having a structure that is divided into a part and a power generation part polarized along a longitudinal axis, wherein the ratio of the amount of polarization to the amount of polarization in a saturated state in each of the drive part and the power generation part is determined by the drive part. And a power generating unit, wherein the piezoelectric transformer is different from the power generating unit. 2. The piezoelectric transformer according to claim 1, wherein the amount of polarization of the driving unit is a saturation polarization amount, and the amount of polarization of the power generation unit is smaller than the saturation polarization amount. 3. The piezoelectric transformer according to claim 1, wherein the amount of polarization of the drive unit is smaller than the amount of saturation polarization, and the amount of polarization of the power generation unit is the amount of saturation polarization. 4. The piezoelectric transformer according to claim 1, wherein the amount of polarization of the driving unit is 50% or more of the amount of polarization in a saturated state, and the amount of polarization of the power generating unit is 85% or more of the amount of polarization in a saturated state. A piezoelectric transformer, characterized in that: