BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric transformer adapted as a high-voltage DC generating device, and more particularly to a piezoelectric transformer provided with node point recognition patterns for visually indicating respective node points, at which external electrical connection of input and output electrodes is made, thereby allowing the external electrical connection of the input and output electrodes to be easily achieved.
2. Description of the Related Art
Recently, piezoelectric transformers, which are adapted as high-voltage DC generating devices, have been used at an increased rate, as compared to coil transformers, because they have features of reduced size, high efficiency, high electrical insulation, and nonflammable, as compared to those coil transformers.
Piezoelectric transformers are mainly used in inverters for back light adapted to turn on and off color liquid crystal displays of notebooks, PDA (Personal Digital Assistant), DVC (Digital Video Camera), DSC (Digital Still Camera) and the like, and in high-voltage power supply devices equipped static brushes, air cleaners, and ozone generators.
Such a piezoelectric transformer basically consists of a piezoelectric member, an input electrode attached to the piezoelectric member and adapted to apply voltage of a certain level to the piezoelectric member, and an output electrode for outputting a voltage of a desired level from the piezoelectric member. When AC voltage having a frequency corresponding to the intrinsic vibration frequency of the piezoelectric member is applied to the piezoelectric member via the input electrode, the piezoelectric member vibrates mechanically. The mechanical vibration energy of the piezoelectric member is transformed into electrical energy, and then outputted via the output electrode. Thus, the piezoelectric transformer boosts the input voltage using piezoelectric vibrations.
FIG. 1 illustrates a general Rosen type piezoelectric transformer. As shown in FIG. 1, the Rosen type piezoelectric transformer, which is denoted by the reference numeral 10, includes a piezoelectric member 11 having two opposite rectangular major surfaces, that is, first and second surfaces, and four side surfaces, that is, third through sixth surfaces, connecting the first and second surfaces. The piezoelectric transformer 10 also includes an input electrode 12 formed on a first one of two equal surface portions longitudinally divided on the first surface of the piezoelectric member 11, an output electrode 13 formed on the third surface of the piezoelectric member 11 not contacting the input electrode 12, and a ground electrode 14 formed on a first one of two equal surface portions longitudinally divided on the second surface of the piezoelectric member 11 while being arranged opposite to the input electrode 12. That is, the piezoelectric member 11 is longitudinally divided into two portions, that is, a first portion provided with the input electrode 12 and ground electrode 13, and a second portion provided with the output electrode 13
When AC voltage of a certain level from an AC power source S is applied between the input electrode 12 and the ground electrode 14 in the above mentioned conventional Rosen type piezoelectric transformer, mechanical vibrations are generated in vertical directions at the first portion of the piezoelectric member 11 in accordance with the electrical energy of the applied voltage. By virtue of the vibrations, the second portion of the piezoelectric member 11 vibrates in longitudinal directions. The longitudinal vibrations are transformed into electrical energy which is, in turn, outputted via the output electrode 13. Such a piezoelectric effect provided in accordance with the application of AC voltage serves to generate a boosting effect.
The waveform diagram shown in the lower portion of FIG. 1 illustrates the waveform of vibrations generated at the Rosen type piezoelectric transformer 10. The first portion of the piezoelectric member 11 formed with the input electrode serves as a driving section (or an input section) for transforming electrical energy into mechanical vibration energy, whereas the second portion of the piezoelectric member 11 formed with the output electrode 13 serves as an electrical output generating section (or outputting section) for transforming vibration energy into electrical energy.
FIG. 2 illustrates an improved Rosen type piezoelectric transformer which has an output electrode structure improved over the above mentioned Rosen type piezoelectric transformer, in order to achieve easy external electrical connection of electrodes. As shown in FIG. 2, this piezoelectric transformer, which is denoted by the reference numeral 20, includes a rectangular piezoelectric member 21 having the same structure as the piezoelectric member 11 of the conventional Rosen type piezoelectric transformer 10. Similarly to the conventional Rosen type piezoelectric transformer 10, the piezoelectric transformer 20 also includes an input electrode 22 formed on the first portion of the first surface of the piezoelectric member 21, an output electrode 23 formed on the second surface portion of the first surface of the piezoelectric member 21 at the end of the second surface portion spaced away from the input electrode 22, and ground electrodes 24 and 25 respectively formed on the second surface of the piezoelectric member 21 while being vertically symmetrical with the input and output electrodes 22 and 23.
In order to implement an inverter or a high-voltage power supply device using the above mentioned piezoelectric transformer of FIG. 1 or 2, it is necessary to conduct a wire soldering process for the input, output, and ground electrodes of the piezoelectric transformer in order to achieve external electrical connection of those electrodes.
In the wire soldering process, a wire is soldered at a node point corresponding to the center of an associated electrode. Where wire is soldered at a portion of the electrode other than the node point, dispersion of characteristics may occur, thereby causing non-uniform vibration. As a result, the product exhibits a degraded reliability.
Furthermore, where the soldering positions on the upper and lower surfaces of the input section of the piezoelectric transformer are misaligned from each other, the piezoelectric transformer exhibits an increase in characteristic dispersion and a degradation in characteristics. In particular, where piezoelectric transformers are mass-produced, there is a problem involved with productivity. Where it is desired to conduct an automatic wire soldering process, it is necessary to install automatic equipment, in which the position of each node point is set for a particular size of piezoelectric transformers. For this reason, there is a problem in that it is necessary to modify the equipment to cope with a change of the size of piezoelectric transformers to be produced.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in view of the above mentioned problems involved with the related art, and an object of the invention is to provide a piezoelectric transformer provided with node point recognition patterns for visually indicating respective node points, at which external electrical connection of input and output electrodes is made, thereby allowing the external electrical connection of the input and output electrodes to be easily achieved in a manual wire soldering process, while allowing the wire soldering process to be automatically carried out irrespective of the size of the piezoelectric transformer.
In order to accomplish this object, the present invention provides A piezoelectric transformer comprising a piezoelectric member, an input electrode, an output electrode, and a ground electrode, the electrodes being printed on the piezoelectric member, further comprising: a plurality of node point recognition patterns extending radially about the center of each of the input, output, and ground electrodes while being spaced apart from the center of the electrode by a desired radial distance, each of the node point recognition patterns being formed by removing a portion of the electrode corresponding to the node point recognition pattern.
The node point recognition patterns may comprise two line patterns extending radially about the center of the electrode while being radially aligned with each other, respectively.
Alternatively, the node point recognition patterns may comprise four line patterns extending radially about the center of the electrode while forming a cross, respectively.
Each of the node point recognition patterns preferably has a line width of 100 to 150 μm, and/or a length 0.5 to 3 mm in order to prevent a degradation in piezoelectric characteristics.
The center of the electrode surrounded by the node point recognition patterns corresponds to a node point, at which a wire is soldered.