JP2940282B2 - Thickness vertical vibration piezoelectric transformer and method of driving the same - 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 operable in a high frequency band, and more particularly to a piezoelectric transformer for an on-board power supply which requires a reduction in size and noise, and a driving method thereof.

[0002]

2. Description of the Related Art In recent years, an electromagnetic transformer has been used as a switching power supply in order to reduce the size of a power supply circuit of an electronic device. To reduce the size of the switching power supply, it is desirable to increase the switching frequency. However, when the switching frequency is increased, the hysteresis loss, the eddy current loss, and the loss due to the skin effect of the conductive wire of the magnetic material used in the electromagnetic transformer increase sharply, and the efficiency of the transformer becomes extremely low. For this reason, the upper limit of the practical frequency band of the electromagnetic transformer is at most 500 kHz.

On the other hand, a laminated 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 the size can be reduced.

(2) Non-combustibility can be achieved.

(3) No noise due to electromagnetic induction. It has many advantages.

FIG. 5 shows the structure of a Rosen type piezoelectric transformer, which is a typical conventional laminated type piezoelectric transformer. Hereinafter, description will be given with reference to the drawings. In the case of extracting a high voltage, in the piezoelectric plate having electrodes provided on the surface, a portion indicated by 51 is a low impedance driving portion of the piezoelectric transformer, and electrodes 53 and 54 are provided on the upper and lower surfaces thereof. It is polarized in the thickness direction as indicated by 56 in the figure. Also,
Similarly, a portion indicated by 52 is a high-impedance power generation portion, and an electrode 55 is provided on an end face thereof. The power generation portion 52 is polarized in the length direction of the piezoelectric plate as indicated by 57 in the figure. The operation of the piezoelectric transformer is based on the driving electrodes 53,
54 longitudinal vibration is excited when a voltage is applied by the transverse effect 31 mode through electromechanical coupling factor k _{3 1,} the entire transformer vibrates. In addition power portion 52, longitudinal effect longitudinal vibration mode by electromechanical coupling coefficient k _{3 3} (33 mode)
As a result, a high voltage is extracted from the output electrode 55. On the other hand, when a high voltage is input and a low voltage is output, it is clear that the high impedance portion 52 of the vertical effect should be on the input side and the low impedance portion 51 of the horizontal effect should be on the output side. All other types of piezoelectric transformers use the same extensional vibration of a flat plate and the radial expansion of a circular plate as the Rosen type.
It is up to about kHz. On the other hand, JP-A-3-173484
Discloses a laminated piezoelectric ceramic transformer, but it is difficult to achieve high power, multiple outputs, and downsizing.

[0007]

As shown in the above conventional example, the applicable frequency range of the piezoelectric transformer is 200 kHz.
Only in the following low frequency regions. In addition, the Rosen-type piezoelectric transformer has an electromechanical coupling coefficient k in the transverse effect vibration mode that is significantly smaller than the electromechanical coupling coefficient in the longitudinal effect.
_Since there is no choice but to use ₃₁ , there is a disadvantage that the bandwidth is small. It was also difficult to realize high power and multiple outputs.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to overcome the above drawbacks. According to the present invention, a plurality of internal electrode layers and piezoelectric ceramic layers are alternately laminated,
Piezoelectric ceramic layers adjacent via the internal electrode layer are a laminated body polarized in opposite directions to each other, and are a thickness longitudinal vibration piezoelectric ceramic transformer having two low impedance parts and one high impedance part, The high impedance portion is a thickness vibration piezoelectric ceramic transformer, which is located between the two low impedance portions. In addition, as a method of driving the transformer, a half-wavelength piezoelectric
Lamic layer thickness and the two low impedance portions
This is a method of driving at the resonance frequency of the third mode of the thickness longitudinal vibration mode, which is the same as the thickness of each of the minutes .

[0009]

SUMMARY OF THE INVENTION The present invention has been made to provide a piezoelectric ceramic transformer having a sufficient function with a low loss at a high frequency of 1 MHz or more. 1, 2, and 3 show a perspective view, a sectional view, and a connection diagram of an example of the present invention. 1, 2 and 3, a piezoelectric ceramic transformer according to the present invention comprises two low-impedance portions 11 and 11 'in which a large number of piezoelectric ceramic layers 16 polarized in the thickness direction are laminated, and a piezoelectric ceramic layer 1 between the low impedance portions 11 and 11'.
And a high-impedance section 12 composed of a high-impedance section 7.
Further, electrodes are uniformly arranged on the ceramic layer 16 of each of the low impedance portions 11 and 11 '. As shown in FIG. 2, the electrodes 13 of the low impedance portions 11 and 11 ′ were alternately connected outside to form output terminals 20 and 21. Next, the input terminals 22 and 23 were taken out from the upper and lower electrodes 14 of the high impedance portion 12. Also, the thickness of the piezoelectric ceramic layer of the high impedance section 12 and the low impedance sections 11, 1
1 ′ was configured to have the same thickness. In FIG. 3, the output terminals of the two pairs of low impedance sections 11 and 11 'are completely separated. Here, the piezoelectric ceramic layers 16 and 17 are arranged such that the polarization directions of adjacent layers are opposite to each other. An internal electrode 1 is provided between each piezoelectric ceramic plate.
3, it is possible to apply an electric field to the piezoelectric ceramic plate 10 in the thickness direction. Piezoelectric ceramic transformers having such internal multilayer electrodes can be manufactured by the multilayer ceramic technology (doctor blade method) used in multilayer piezoelectric ceramic capacitors, multilayer piezoelectric actuators, and the like. In such a piezoelectric ceramic transformer, the layer spacing can be reduced to about 25 μm. Therefore, the 3/2 wavelength mode (3
When using the thickness longitudinal resonance vibration of the following mode), using a multilayer ceramic technique, it can also be realized piezoelectric transducer operating in the ultra high frequency range of 2~10MHz band.

FIG. 2 shows a connection diagram in which the present piezoelectric transformer is used in thickness longitudinal vibration. In such a connection, when a high voltage having a frequency equal to the resonance frequency of the thickness longitudinal vibration is applied between the electric terminals 22 and 23 of the high impedance section, the piezoelectric ceramic transformer as a whole is mechanically driven by the inverse piezoelectric effect of the high impedance section 12. 2 (a), a voltage having the same frequency as the input voltage is generated in the low impedance portions 11 and 11 ′ by the positive piezoelectric effect and output to the electric terminals 20 and 21. At this time, the voltage between the output terminals 20 and 21 is changed to the input terminal 2 by the difference in impedance between the input side and the output side.
It becomes lower than the voltage between 2 and 23. However, by connecting two low impedances (parallel connection), it is possible to take out the output voltage without canceling the charge as apparent from the charge distribution (charge distribution in FIG. 2B). As a result, the output voltage does not change and the current is doubled. Also,
As shown in FIG. 3, the output voltage 3
When 0, 31 and 32, 33 are extracted, two outputs are obtained for one input. Further, different voltages can be freely output by changing the interval between the low impedance electrodes. When converting low voltage to high voltage,
If a low voltage is applied between the electric terminals 20 and 21, a high voltage is output from between the electric terminals 22 and 23. Further, if the insulating plate 15 is arranged between the low impedance portion 11 and the high impedance portion 12 and the insulating plate 15 is arranged between the low impedance portion 11 'and the high impedance portion 12, the input terminals 22 and 23 and the output terminal are provided. Since the components 20, 21 can be electrically separated, the degree of freedom of the peripheral circuit can be increased.

The resonance frequency of the thickness longitudinal vibration can be expressed by the following equation if the decrease in the resonance frequency due to the piezoelectric longitudinal effect is ignored. f _r = n · v _t 2t (n = 1, 2, 3,...) where f _r : resonance frequency of thickness longitudinal vibration n: mode order v _t : sound speed of longitudinal wave in thickness direction t: thickness here v _t, t but is constant resonant frequency f _r of the thickness extensional vibration if fabricated piezoelectric transducer to be constant, the resonant frequency of the necessarily as designed by integrally firing time of shrinkage variations in It does not become. Therefore, a structure that can adjust the resonance frequency after firing is desirable. It is not easy to adjust the piezoelectric transformer with electrodes on the upper and lower main surfaces after firing, but it is not easy to adjust after firing with the piezoelectric transformer of the present invention, but it can be polished up and down with the piezoelectric transformer of the present invention Since a suitable frequency adjustment layer is provided, the desired resonance frequency can be obtained by polishing after firing, and can be accurately matched with the drive frequency of the external circuit.

Next, the efficiency will be described. Most of the loss of the piezoelectric ceramic transformer is a mechanical loss, and the mechanical loss increases as the mechanical quality factor Qm decreases. This mechanical quality factor Qm largely exists in the parallelism and flatness of the upper and lower main surfaces. The surface of the piezoelectric transformer that has just been fired has poor parallelism and flatness, and its mechanical quality factor Qm is at most several.
00. On the other hand, in the piezoelectric transformer of the present invention, by performing parallel plane polishing, it is possible to obtain parallelism and flatness within several μm, and a mechanical quality factor Qm of 1000 or more can be easily obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of a piezoelectric ceramic transformer according to the present invention, a piezoelectric ceramic transformer having the structure shown in FIGS. 1, 2 and 3 was produced by a green sheet method. FIG. 1, FIG. 2, FIG.
1 is a perspective view, a sectional view, and a connection diagram of an embodiment of a piezoelectric ceramic transformer according to the present invention, respectively. The 4-terminal and 6-terminal piezoelectric transformers shown in FIGS. 1, 2 and 3 are 2.4 MHz.
The third resonance third mode is used for the thickness of the belt, and a PbTiO ₃ piezoelectric material is used as the piezoelectric material. In FIG. 2, the thickness of one layer of the piezoelectric ceramic of the low impedance portions 11, 11 'was set to about 0.18 mm. The frequency adjustment layer 18
The same material was used, and the thickness was about 0.25 mm. The frequency adjustment layer may be made of another material as long as it can be fired integrally with the low impedance portion and the high impedance portion. Pt internal electrodes 13 and 14 were formed by printing a Pt paste by a screen printing method and integrally sintering the Pt paste together with a piezoelectric ceramic. After firing, the external electrodes are baked to connect the electrode terminals 20, 21, 22, 23, respectively. A direct current voltage of 7 kV / mm is applied between the electrode terminals 20, 21 and 22 and 23 to polarize. Finally, parallel plane polishing is performed to a thickness necessary for adjusting the resonance frequency. In this embodiment, since the piezoelectric transformer is driven at 2.4 MHz, the thickness of the piezoelectric transformer is 3.3.
mm was polished in parallel plane. Next, a high-frequency / high-voltage signal for exciting the longitudinal tertiary mode is input from the electric terminals 22 and 23 of the high-impedance section 12, and the electric terminals 20 and 21 of the low-impedance sections 11 and 11 'are terminated with an appropriate resistance load. The output was evaluated as a step-down type transformer. FIG. 4 shows measured values of the frequency-gain and efficiency characteristics. The resonance frequency was 2.4 MHz, the mechanical quality factor Qm was 850, and the maximum energy conversion efficiency was 97%. In particular, a power capacity of 10 W was realized, and a power capacity about twice that of a piezoelectric transformer having a low impedance portion was obtained. FIG. 3 shows a one-input, two-output piezoelectric transformer shown in FIG.
It was produced in the same manner as described above. Electrical terminal 2 of high impedance part
2, 23 as inputs and low impedance electrical terminals 30,
31, 32, and 33 were output. As a result of evaluation in the same manner as in FIG. 2, the maximum output energy conversion efficiency was 97% and the power capacity was 5 W at each of the two output terminals, and two completely independent output voltages were obtained. Further, it was confirmed that a desired voltage could be obtained by changing the layer spacing of each layer in the low impedance portion. The prototype piezoelectric transformer
It is clear that the transformer has a step-down function and high energy conversion efficiency, and in particular, realizes high power and multiple outputs. It goes without saying that the input terminal can be used as a step-up transformer by taking out the input terminal from the low impedance part and the output terminal from the high impedance part.

[0014]

As described above, the piezoelectric ceramic transformer according to the structure of the present invention can be used in a wide band in a high frequency band of 1 MHz or more, and is compact, highly efficient and
It is clear that high power and multiple outputs are realized,
It has advantages that the conventional piezoelectric transformer does not have, and has great industrial value.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a connection diagram and an electric charge and vibration distribution diagram showing an embodiment of the present invention.

FIG. 3 is a connection diagram showing an embodiment of the present invention.

FIG. 4 is a characteristic diagram of the piezoelectric ceramic transformer of the present invention.

FIG. 5 is a diagram showing a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Piezoelectric ceramic 11, 11 'Low impedance part of piezoelectric transformer 12 High impedance part of piezoelectric transformer 13, 14 Internal electrode 15, 16, 17, 18 Piezoelectric ceramic layer 20, 21, 22, 23, 30, 31, 32, 33 Electrical terminal 51 Low impedance part of conventional Rosen-type piezoelectric transformer 52 High impedance part of conventional Rosen-type piezoelectric transformer 53,54,55 Electrode 56,57 Polarization direction

Claims (5)

(57) [Claims] 1. A laminated body in which a plurality of internal electrode layers and piezoelectric ceramic layers are alternately laminated, and adjacent piezoelectric ceramic layers via the internal electrode layers are polarized in directions opposite to each other. And a high-impedance vibrating piezoelectric transformer comprising a high-impedance section and a high-impedance section located between two low-impedance sections. 2. Two low-impedance portions comprising a laminate in which a plurality of internal electrode layers and piezoelectric ceramic layers are alternately stacked, and adjacent piezoelectric ceramic layers are polarized in opposite directions via the internal electrode layers; And a high-impedance piezoelectric ceramic transformer comprising one high-impedance section comprising a piezoelectric ceramic layer provided between the two low-impedance sections. 3. The transformer according to claim 1, wherein the high impedance portion is polarized in a thickness direction. (4) The thickness of each of the two low impedance portions
And that the thickness of the high impedance portion is the same
A thickness longitudinal vibration according to any one of claims 1 to 3,
Piezoelectric transformer. 5. The piezoelectric ceramic transformer according to claim 4, wherein
A thickness-longitudinal-vibration piezoelectric transformer driven at a resonance frequency of a third-order thickness-longitudinal-vibration mode in which the wavelength is the same as the thickness of the piezoelectric ceramic layer in the high-impedance portion and the thickness of each of the two low-impedance portions. Drive method.