JP2581394B2 - 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 ceramic transformer used in various power supply circuits for generating a high voltage, and in particular, a small, thin piezoelectric ceramic transformer which requires a small size and high reliability and generates a high voltage. And its driving method.

[0002]

2. Description of the Related Art In recent years, a winding type electromagnetic transformer has been used as a transformer for generating a high voltage 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. . This electromagnetic transformer has a structure in which a conductive wire is wound around a core of a magnetic material. In order to realize a high transformation ratio, it is necessary to increase the number of conductive wires to be wound. Therefore, it has been very difficult to realize a small and thin electromagnetic transformer.

On the other hand, a piezoelectric transformer using a piezoelectric effect has been proposed. FIG. 4 shows the structure of a Rosen type piezoelectric transformer which is a typical conventional piezoelectric transformer. Less than,
This will be described with reference to the drawings. When taking out a high voltage, the portion indicated by 41 in the piezoelectric plate having the electrodes provided on the surface thereof is:
The piezoelectric transformer is a low-impedance drive unit, and electrodes 43 and 44 are provided on upper and lower surfaces thereof, and this part is polarized in the thickness direction as indicated by an arrow in the figure.
Similarly, a portion indicated by reference numeral 42 is a high-impedance power generation unit, and an electrode 45 is provided on an end face of the power generation unit. The power generation unit 42 is polarized in the length direction of the piezoelectric plate as indicated by an arrow in the drawing. ing. The operation of this piezoelectric transformer is as follows. Driving electrodes 43, 44 from external terminals 46, 47
When a voltage is applied to the drive unit 41, an electric field is applied in the polarization direction in the driving unit 41, and the longitudinal vibration in the length direction is excited by the piezoelectric effect (hereinafter, abbreviated as piezoelectric transverse effect 31 mode) in which the polarization is displaced in the vertical direction. As a result, the entire transformer vibrates. Furthermore, power generation unit 4
In (2), a voltage having the same frequency as the input voltage is applied from the output electrode 45 to the external terminal 48 by a piezoelectric effect (hereinafter, abbreviated as a piezoelectric longitudinal effect 33 mode) in which mechanical distortion occurs in the polarization direction and a potential difference occurs in the polarization direction. Taken out. 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 a high voltage is input and a low voltage is output, the high impedance portion 42 of the vertical effect is used as the input side, and the low impedance portion 4 of the horizontal effect is used.
It is clear that 1 should be set to the output side.

This piezoelectric transformer is used in a resonance state,
Compared to general electromagnetic transformers, (1) the coil structure is unnecessary and the energy density is high, so that it can be made smaller and thinner, (2) it can be made nonflammable, (3) it can be free from electromagnetic induction noise, etc. Has many advantages.

[0005]

In the conventional Rosen type piezoelectric transformer, since the electrode of the power generation unit is located at the antinode of the vibration, the connection of the external terminals adversely affects the vibration and the reliability is greatly reduced. There were disadvantages. Also, if the load resistance is extremely large compared to the impedance of the piezoelectric transformer, a relatively high output voltage can be obtained, but if the value of the load resistance is not so large, a very high output voltage cannot be obtained. There were drawbacks.

An object of the present invention is to provide a piezoelectric ceramic transformer having high voltage and high reliability characteristics and a driving method thereof.

[0007]

To achieve the above object, a piezoelectric ceramic transformer according to the present invention comprises a piezoelectric ceramic plate,
A pair of external electrodes and a set of comb-shaped electrodes, each having two electrodes
A piezoelectric ceramic transformer having two pairs of external electrical terminals each including an air terminal , wherein the piezoelectric ceramic plate is a plate-shaped piezoelectric vibrator, having a drive unit and a power generation unit, and a drive unit and a power generation unit. Is arranged separately in the length direction of the piezoelectric ceramic plate, the pair of external electrodes is provided to face the end surface in the thickness direction of the piezoelectric ceramic plate of the drive unit, and the comb-shaped electrodes forming a pair are: Comb-type electrode fingers are alternately arranged on one or both end faces in the thickness direction of the piezoelectric ceramic plate of the power generation unit, and provided so as to face each other. And the piezoelectric ceramic plate of the power generating unit is alternately polarized in the length direction between adjacent comb-shaped electrode fingers, and one of two external electric terminal pairs
Is a pair of input terminals for applying voltage to the piezoelectric ceramic plate. Two terminals are connected to external electrodes facing each other on the drive unit.
They are connected, and the other electrical terminal pair and an output terminal piece pairs to pick up the voltage of the piezoelectric ceramic plate, two ends
Those which are respectively connected to the child on opposite comb-shaped electrode of the power generation unit.

A method of driving a piezoelectric ceramic transformer according to the present invention is a method of driving a piezoelectric ceramic transformer that applies a voltage to a piezoelectric ceramic plate and excites the piezoelectric ceramic plate to output a voltage. The plate is a plate-shaped piezoelectric vibrator, and includes a driving unit uniformly polarized in the thickness direction of the piezoelectric ceramic plate, and a power generation unit alternately polarized in the length direction of the piezoelectric ceramic plate. , M driving units and n power generating units are alternately arranged in the longitudinal direction of the piezoelectric ceramic plate, and the AC driving voltage having a frequency near the resonance frequency of the longitudinal vibration in the longitudinal direction is applied to the m driving units. Is applied, and the piezoelectric ceramic plate is moved to the total number of the drive units and the power generation units (m +
Excitation is performed in the longitudinal vibration (m + n) order mode corresponding to n), and a voltage is picked up from the power generation unit.

[0009]

FIG. 1 is a plan view of an electromagnetic transformer according to the present invention.
FIG. 1A shows a cross-sectional view of FIG. Drive unit 11
Is composed of a piezoelectric ceramic plate 17 polarized in the thickness direction as indicated by an arrow in the figure, and external electrodes 131 and 132 on the upper and lower main surfaces of the piezoelectric ceramic plate 17 one by one.
32 to the external electrical terminals 151, 15
2 are respectively taken out. On the other hand, the power generation section 12 has opposing comb-shaped electrodes 141 and 142 arranged on the main surface of the piezoelectric ceramic plate 18.
8 is a comb-shaped electrode finger 141 of the comb-shaped electrodes 141 and 142
a and 142a are alternately polarized in the length direction, and the external electric terminals 161 and 162 are respectively arranged from the center in the length direction of the electrode fingers 141a or 142a arranged at the center of the comb-shaped electrodes 141 and 142, respectively. It has a structure to be taken out.

When an AC voltage having a frequency near the resonance frequency of the longitudinal longitudinal vibration is applied between the external electric terminals 151 and 152 of the drive unit 11 having the structure shown in FIG.
Longitudinal vibration in the longitudinal direction in the piezoelectric transverse effect 31 mode generated by _31. Its longitudinal vibration is propagated to the power generation unit 12, the comb-shaped electrode 1 by the electromechanical coupling factor k ₃₃ in the piezoelectric longitudinal effect 33 mode
A voltage is generated between 41 and 142, and the voltage is taken out from the external electric terminals 161 and 162. At this time, if the frequency of the applied voltage is equal to the resonance frequency of the longitudinal vibration of the piezoelectric ceramic transformer, a considerably high output voltage can be obtained. Here, in FIG. 1 (b), the comb-shaped electrodes are arranged on both upper and lower main surfaces so as to be vertically aligned. However, even if arranged on only one main surface, the power generation efficiency is slightly lowered. ,
Operation is possible.

The position of the external terminal of the piezoelectric ceramic transformer and the driving frequency will be described. Figure 2 as an example
(A) shows a connection position of an external terminal of a piezoelectric transformer having two driving units 11 and two power generating units 12 according to the present invention. FIG. 2B shows the displacement of (2 + 2), that is, the fourth-order longitudinal vibration. As is apparent from the figure, the external electric terminals 151, 152, 153, 154, 161, 16
The take-out positions of 2,163,164 are the nodes A,
B, C, and D. As described above, in the p-th longitudinal vibration in the longitudinal direction, a vibration node is formed at the center of the portion where the piezoelectric ceramic transformer is divided into p in the longitudinal direction, so that m driving units and n power generating units are provided. In the piezoelectric ceramic transformer consisting of
+ N) If driven at the longitudinal vibration resonance frequency in the following length direction,
All the external electric terminals can be taken out from the nodes of the vibration, and good vibration characteristics and high reliability can be realized. Here, as an example, two drive units and two power generation units are connected alternately. However, if at least one drive unit and at least one power generation unit are present, the piezoelectric ceramic transformer operates, There is no need to connect them alternately. The electrical connection between the plurality of drive units and the power generation unit may be in series, in parallel, or in a mixture as long as the combination does not cancel out the electric charge.

The lumped constant approximation equivalent circuit near the resonance frequency of the piezoelectric ceramic transformer is similar to that of other piezoelectric transformers in FIG.
Indicated by In FIG. 3, Cd ₁ and Cd ₂ are the braking capacity on the input side and the output side, respectively, A ₁ and A ₂ are the input and output force coefficients,
m, c, r _m is the equivalent mass, equivalent compliance, 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 are
It varies depending on the width, thickness, distance between the electrode fingers of the drive unit, and the number of electrode fingers. As is apparent from the equivalent circuit of FIG. 3, generally, the output voltage V _out of the piezoelectric transformer changes depending on the resistance of the connected load, and the larger the load resistance, the larger the value of V _out . 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.
The piezoelectric ceramic transformer of the present invention has a degree of freedom in the number of electrode fingers, the length between electrode fingers, and the like in addition to the overall length of the transformer (the number of drive units and power generation units), width, and thickness. And the output impedance of the piezoelectric ceramic transformer is widened.

As is apparent from FIGS. 1 and 3, the piezoelectric ceramic transformer has a four-terminal structure in which the input and output electric terminals are each insulated in a DC manner, and the three-terminal type shown in FIG. The degree of freedom of the peripheral circuit can be increased as compared with the Rosen type piezoelectric transformer.

[0014]

The present invention will be described below with reference to examples.

(Example 1) As an example of a piezoelectric ceramic transformer according to the present invention, a piezoelectric ceramic transformer having the configuration shown in FIG. 1 was manufactured. The material of the piezoelectric ceramic plates 17 and 18 is P
ZT was used (PbZrO ₃ -PbTiO ₃₎ based piezoelectric ceramic plate. First, the calcined piezoelectric ceramic block is cut with a diamond cutter, and polished into parallel planes using # 3000 SiC polishing powder, so that the length is 24 mm and the width is 8 m.
A piezoelectric ceramic plate having a thickness of m and a thickness of 1.26 mm is prepared. The electrodes 131, 132, 141 and 142 were formed by screen printing and baking an Ag paste on the piezoelectric ceramic plate. The number of electrode fingers of the comb-shaped electrodes 141 and 142 is three and two, respectively. The distance between the adjacent electrode fingers 141a and 142a of the comb-shaped electrodes 141 and 142 is 2 mm, and the width of one electrode finger is 0.5 mm. And 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. Subsequently, the external terminals 151, 152, 161, and 162 were taken out by connecting the conductors using solder. At this time, the connection position of the solder was set to a position 6 mm from the center of the drive unit and the power generation unit, that is, from the end. After that, both the drive unit and the power generation unit were subjected to a polarization process of applying a voltage of 4 kV / mm in insulating oil at 100 ° C.

The resonance frequency of the secondary mode of longitudinal vibration of the piezoelectric ceramic transformer has a resonance frequency of 1 from the frequency characteristic of admittance.
It was measured at 45 kHz. This piezoelectric ceramic transformer has 10
When a load resistance of 0 kΩ was connected, an output voltage of 530 V was obtained for an input voltage of 10 V, and the output power at this time was 2.8 W.

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

Embodiment 2 As an example of a transformer having a plurality of drive units 11 and a plurality of power generation units 12, a piezoelectric ceramic transformer having two drive units 11 and two power generation units 12 shown in FIG. Was prepared. The manufacturing method is the same as in Example 1, and the overall length is 48 mm, the width is 8 mm, and the thickness is 1.2 mm. The external terminal was taken out from a node of the vibration, that is, the center in the length direction of each region. The external terminals of the drive unit 11 were connected to 151 and 153 and 152 and 154 so as to be electrically parallel, and a voltage was applied between them. On the other hand, in the power generation unit 12, the external terminals 162 and 163 were connected so as to be electrically connected in series, and a voltage was taken out between the external terminals 161 to 164. The resonance frequency of the fourth longitudinal mode in the longitudinal direction of the piezoelectric ceramic transformer actually manufactured is 147.
When a load resistance of 220 kHz was connected at kHz, an output voltage of 880 V, that is, an output power of 3.5 W was obtained at an input voltage of 10 V.

[0019]

As described above, the piezoelectric ceramic transformer of the present invention has high voltage, high power, high reliability characteristics, and is small and thin, and has advantages over conventional piezoelectric transformers. Yes, and the industrial value is great.

[Brief description of the drawings]

FIG. 1A is a plan view showing a piezoelectric ceramic transformer of the present invention, and FIG. 1B is a sectional view thereof.

FIG. 2A is a connection diagram of a piezoelectric ceramic transformer of the present invention,
(B) is a displacement distribution diagram.

FIG. 3 is a lumped constant equivalent circuit diagram of a piezoelectric ceramic transformer.

FIG. 4 is a perspective view showing a conventional Rosen-type piezoelectric transformer.

[Explanation of symbols]

11, 41 Drive unit 12, 42 Power generation unit 131, 132 External electrode 141, 142 Comb-shaped electrode 46, 47, 48, 151, 152, 153, 154,
161, 162, 163, 164 External electrical terminals 17, 18 Piezoelectric ceramic plate

Claims (2)

(57) [Claims] 1. A piezoelectric ceramic plate, a pair of external electrodes, a set of comb-shaped electrodes, and two sets of external terminals each comprising two electric terminals.
A piezoelectric ceramic transformer having a pair of electrical terminals , wherein the piezoelectric ceramic plate is a plate-shaped piezoelectric vibrator, and has a driving unit and a power generation unit. The external electrodes, which are arranged separately in the length direction, are provided so as to face the end face in the thickness direction of the piezoelectric ceramic plate of the drive unit, and the comb-shaped electrodes forming a pair are formed of the piezoelectric electrodes of the power generation unit. Comb-shaped electrode fingers are alternately arranged on one or both end faces in the thickness direction and provided so as to face each other. The piezoelectric ceramic plate of the drive unit is polarized in the thickness direction, and the power generation unit is polarized. Are alternately polarized in the length direction between adjacent comb-shaped electrode fingers, and one of the two external electrical terminal pairs has an input for applying a voltage to the piezoelectric ceramic plate. A pair of terminals, two ends
They are respectively connected to the child on opposite external electrodes of the driving unit and the other electrical terminal pair and an output terminal piece pairs to pick up the voltage of the piezoelectric ceramic plate, the two terminals on opposite comb-shaped electrode of the power generation unit A piezoelectric ceramic transformer characterized by being connected to each other . 2. A method of driving a piezoelectric ceramic transformer for applying a voltage to a piezoelectric ceramic plate and exciting the piezoelectric ceramic plate to output a voltage, wherein the piezoelectric ceramic plate is a plate-shaped piezoelectric vibrator. A drive unit uniformly polarized in the thickness direction of the piezoelectric ceramic plate, and a power generation unit alternately polarized in the length direction of the piezoelectric ceramic plate, m drive units and n power generation units Are alternately arranged in the longitudinal direction of the piezoelectric ceramic plate, and an AC voltage having a frequency near the resonance frequency of the longitudinal vibration in the longitudinal direction is applied to the m driving units, and the piezoelectric ceramic plate is Length longitudinal vibration (m + n) corresponding to the total number (m + n) of power generation units
n) A method of driving a piezoelectric ceramic transformer, wherein the piezoelectric ceramic transformer is excited in the next mode and a voltage is picked up from a power generation unit.