Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1997-10-03
2000-04-18
Dougherty, Thomas M.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310366, H01L 41107
Patent
active
060519150
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a piezoelectric transformer which utilizes a piezoelectric vibrator of a one-wavelength resonance type using a rectangular plate of piezoelectric ceramics.
BACKGROUND ART
As a transformer (voltage transformer), there is well known an electromagnetic transformer comprising windings wound around an iron core. The electromagnetic transformer is unsuitable for use in a power supply for a small-sized electric apparatus because it is bulky in size, is large in power consumption, and generates electromagnetic noise and heat. For example, for use in a high-voltage power supply in an electrostatic generating device or a back-lighting lamp of a liquid-crystal display, the transformer does not require a large output current but requires an output voltage between 1 kV and about several watts. In addition, it is required to reduce the electromagnetic noise, the power consumption, and the size.
On the other hand, since a piezoelectric transformer utilizing a piezoelectric phenomenon generates little electromagnetic noise and can be reduced in size, practical use is considered as a power supply transformer for a small-sized apparatus.
Referring to FIGS. 1(a) and (b), a conventional piezoelectric transformer 11 comprises a piezoelectric-ceramics rectangular plate 13, two surface electrodes 15 and 15 formed on the piezoelectric-ceramics rectangular plate 13 opposite to each other in a thickness direction at a part (hereinafter referred to as a first part) extending from one end to an approximate half in a longitudinal direction, and a plurality of internal electrodes 16 and 17 formed in the interior of the above-mentioned first part between the both surface electrodes with a space kept from one another in the thickness direction. Side electrodes 18 and 19 formed on confronting side surfaces of the above-mentioned first part, respectively, are connected to the surface electrodes 15 and 15, respectively, and to the alternate internal electrodes 16 and the remaining internal electrodes 17, respectively. Moreover, an end electrode 20 for output extraction is formed on the piezoelectric-ceramics rectangular plate 13 over an end surface of a half part (hereinafter referred to as a second part) opposite to the above-mentioned first part.
The above-mentioned first part of the piezo-electric-ceramics rectangular plate 13 is polarized by applying a DC voltage between the side electrodes 18 and 19. Specifically, the piezoelectric-ceramics rectangular plate 13 is polarized between adjacent electrodes of the surface electrodes 15 and 15 and the internal electrodes 16 and 17. The polarization directions are opposite to each other at both sides of each of the internal electrodes 16 and 17, as depicted by small arrows in FIG. 2(b). Furthermore, by applying a DC voltage between the both surface electrodes 15 and the end electrode 20, the second part of the piezoelectric-ceramics rectangular plate 13 is polarized in the longitudinal direction, as depicted by a large arrow in FIG. 1(b).
The piezoelectric transformer of the one-wavelength resonance type having the above-mentioned electrode structure is referred to as a Lozen type piezoelectric transformer.
The above-mentioned type including the plurality of internal electrodes as input electrodes will be referred to as a stacked type because it is actually formed by alternately stacking the internal electrodes and piezoelectric members during manufacture. On the other hand, another type is also known in which the polarization in the thickness direction is only one direction between the confronting surface electrodes 15 and 15 without any internal electrodes formed. This type will be referred to as a single plate type because no stacking is required during manufacture and it is implemented by a single piezoelectric member with electrodes formed on its surface.
Description will now be made as regards an operation of the Lozen type piezoelectric transformer illustrated in FIGS. 1(a) and (b).
Now, one of the side electrodes 18 and 19 is used as a grou
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Fuda Yoshiaki
Katsuno Masafumi
Dougherty Thomas M.
Tokin Corporation
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