JP4278750B2 - Piezoelectric transformer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drive circuit for a cold-cathode tube used as a light source for a backlight that illuminates a liquid crystal used in a personal computer with light from the back side, and other DC high voltage generation such as a television receiver and an electronic copying machine. The present invention relates to a piezoelectric transformer used in a device or the like.
[0002]
[Prior art]
Conventionally, this type of piezoelectric transformer is formed in a rectangular plate shape, for example, as shown in FIG. In the figure, 11 is a primary side (input side), and a primary side electrode 11a is provided on each side, and 12 is a secondary side (output side), and an electrode 12a for output extraction is provided at an end thereof. Yes.
[0003]
Each arrow indicates a polarization direction. The primary side 11 is polarized with a high electric field in the thickness direction, the secondary side 12 is polarized in the length direction, and the primary resonance is determined by the length dimension on the primary side 11. When a voltage having a frequency is input, mechanical vibration is generated by the inverse piezoelectric effect, and a high voltage corresponding to the vibration is output from the secondary side 12 by the piezoelectric effect.
[0004]
Conventionally, the above-mentioned shape (rectangular plate shape) has a low step-up ratio, so that when a cold-cathode tube is turned on, a means for increasing voltage such as a winding transformer is required in the previous stage.
[0005]
In order to solve this problem, multilayer piezoelectric transformers have been actively studied in recent years.
[0006]
[Problems to be solved by the invention]
However, although this multilayer piezoelectric transformer has a high step-up ratio, there are problems in reliability such as high material cost used for the internal electrodes and peeling between layers.
[0007]
Further, in order to increase the step-up ratio, a symmetrical third-order Rosen transformer as shown in FIG. 9 has two nodes as shown in FIG. 8 (node points where vibration does not occur). Even if the length is the same as that of the conventional general secondary Rosen type, the frequency is increased, and when the frequency is increased, the leakage current from the cold cathode tube connected to the piezoelectric transformer and lighting is increased. Therefore, it is not preferable from the viewpoint of the efficiency of the inverter. In FIG. 9, the arrow indicates the secondary polarization direction.
[0008]
In addition, the conventional three-terminal type piezoelectric transformer has problems that it is inconvenient in design and that leakage current caused by stray capacitance in the cold cathode tube portion must be taken into consideration.
[0009]
The present invention has been proposed in view of the above, and the object of the present invention is to obtain a high step-up ratio even if it is a single plate type instead of a laminated type, and because it is a four-terminal, the design is It is an object of the present invention to provide a piezoelectric transformer that is easy and can reduce the leakage current as compared with the conventional type.
[0010]
[Means for Solving the Problems]
The present invention provides a piezoelectric transformer having a rectangular plate shape and having one side as a primary side 1 and the other side as a secondary side 2.
A notch 3 is formed in the substantially central portion of the secondary side 2, the secondary side 2 is divided into first and second secondary portions, and the capacity of the secondary side 2 is made smaller than the primary side 1 by the notch 3. In addition, the above-described object is achieved by a configuration in which the polarization directions of the first and second secondary side portions are opposite to each other.
[0011]
In addition, the inner end 3 a of the notch 3 is configured to bite into the primary and secondary polarization boundary portions or the primary side 1.
[0012]
Furthermore, the insulator 4 is provided between the first and second secondary portions.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The step-up ratio of the piezoelectric transformer is determined by the ratio of the equivalent capacitance on the primary side and the equivalent capacitance on the secondary side. With conventional piezoelectric transformers, it was possible to adjust the step-up ratio by changing this ratio depending on the dimensions such as thickness and length, but it was difficult to obtain a step-up ratio sufficient to light the cold cathode tube. A winding transformer was provided.
[0014]
In the present invention, the capacity of the secondary side 2 is reduced by the notch 3, the capacity of the primary side 1 is relatively increased, and the polarization of each secondary side part is reversed, so that a high step-up ratio is obtained, and The leakage current is reduced.
[0015]
[Example 1]
FIG. 1 shows a first embodiment of the present invention. In the figure, 1 is a primary side of the piezoelectric transformer, 2 is a secondary side, and a central portion of the secondary side 2 has, for example, a substantially rectangular cutout 3 extending from the secondary side outer end toward the primary side 1. And the notch 3 is formed, the capacity is reduced compared to the primary side 1 and the capacity of the primary side 1 is relatively increased. The notch 3 is not necessarily rectangular. Further, the secondary side 2 is divided into two by the notch 3, and the two first and second secondary side parts are polarized in different directions as indicated by arrows, and each secondary side part is Electric potentials having different phases are generated so that a higher step-up ratio can be obtained compared to those having the same polarization direction.
[0016]
The piezoelectric transformer, the front and back surfaces of the primary side 1, the primary-side electrodes 1a are respectively provided, and as shown in FIG. 2 (a), the power source voltage V ₀ power source is connected is applied It has become. Further, secondary electrodes 2a and 2b for output extraction are provided on the outer ends of the first and second secondary portions, respectively, and have a four-terminal structure, and the first and second secondary sides are provided. A cold cathode tube L is connected between the electrodes 2a and 2b.
[0017]
Then, as described above, the polarization direction of each secondary side portion is reversed, and when a potential difference V is generated at both ends of the cold cathode tube L, a positive voltage + V / 2 is applied to one secondary side portion. Since a negative voltage -V / 2 is generated on the other side, a large potential difference is generated across the cold cathode tube L connected between the secondary electrodes 2a and 2b. In the figure, C indicates the stray capacitance generated in the cold cathode tube L.
[0018]
FIG. 2B is a drive circuit of the conventional piezoelectric inverter using the piezoelectric transformer 11 shown in FIG. 8, and the leakage current I due to the stray capacitance C parasitic on the cold cathode tube L is large conventionally. The current I has a drawback that it greatly affects the efficiency of the piezoelectric inverter and the luminance unevenness of the cold cathode tube L.
[0019]
In the present embodiment shown in FIG. 2 (a), the voltage at one end of the secondary side of the piezoelectric transformer is + V / 2, and the voltage at the other end is -V / 2. Therefore, the central portion of the cold cathode tube L is OV, and the leakage current is reduced.
[0020]
Further, in this embodiment, assuming that the cold cathode tube L has a luminance comparable to that shown in FIG. 2B, a large potential difference is generated between the secondary electrodes 2a and 2b in this embodiment. The power supply voltage V ₀ may be small.
[0021]
Further, this piezoelectric transformer is not driven at high frequency as in the symmetrical third-order Rosen type shown in FIG. 9, and the natural resonance frequency determined by the length dimension is low. Therefore, low frequency driving is sufficient, and leakage current from the cold cathode tube L is sufficient. Can be reduced. That is, the leakage current I is generally expressed as I = 2πfCV (f: drive frequency, C: stray capacitance, V: output voltage). Therefore, if f is small, the leakage current can be reduced.
[0022]
[Example 2]
FIG. 3 shows a second embodiment of the present invention.
[0023]
In general, a piezoelectric transformer is polarized by applying a voltage in different directions on the primary side and the secondary side, as described in the conventional example of FIG. It is known to break from the polarization boundary.
[0024]
Therefore, in the first embodiment shown in FIG. 1, the inner end 3a of the notch 3 formed on the secondary side 2 is substantially on the primary and secondary boundary lines, which is not preferable from the viewpoint of reliability. .
[0025]
Therefore, this embodiment is characterized in that the inner end 3a of the notch 3 is bitten to the primary side 1 and is shifted from the polarization boundary line to prevent the possibility of destruction.
[0026]
[Example 3]
FIGS. 4A and 4B show a third embodiment of the present invention, FIG. 4A is a plan view, FIG. 4B is a perspective view, and an arrow in FIG. 4B indicates a polarization direction. In these drawings, 1 is a primary side, 1a is a primary side electrode, 1a 'is a folded electrode, 2 is a secondary side, 2a and 2b are secondary side electrodes, and 3 is a notch. In this embodiment, the notch 3 extends to the node on the primary side 1 and the back surface has a folded electrode 1a 'structure, so that the height can be reduced (when mounted on the substrate, the height dimension can be suppressed). It was.
[0027]
Other configurations and operations are the same as those in the above-described embodiment.
[0028]
[Example 4]
FIG. 5 shows a fourth embodiment of the present invention. This embodiment is characterized in that an insulator 4 is provided between the first and second secondary side portions 2a and 2b to prevent discharge between the secondary output terminals 2a and 2b. ing.
[0029]
FIG. 6 shows an application example of the present invention. In the figure, 1 is the primary side, 1a is the primary side electrode, and 2 is the secondary side. In this application example, the auxiliary primary electrode 1b is added to increase the drive unit. Further, it is possible to increase the step-up ratio by inverting the polarization of the first and second secondary side portions. Further, by changing the size of the auxiliary primary electrode 1b, the drive unit can be adjusted, and the boost ratio can be controlled without impairing the efficiency of the piezoelectric transformer.
[0030]
FIG. 7 also shows a schematic plan view of an application example of the present invention. This embodiment is characterized in that the piezoelectric transformer shown in FIG. 1 is used to form a symmetrical third-order Rosen type. In the figure, the arrow indicates the polarization direction, and the reference numeral 3 indicates a notch.
[0031]
【The invention's effect】
As described above, according to the present invention, the notch 3 is formed on the secondary side 2, the secondary side 2 is divided into two, the capacity of the primary side 1 is relatively increased, and the capacity of the secondary side 2 is increased. The two secondary side polarizations are reversed so that potentials of different phases appear from each other. Therefore, it is necessary to drive at a high frequency as in the conventional example shown in FIG. However, there is an advantage that a high step-up ratio can be obtained and a leakage current can be reduced in an inexpensive piezoelectric transformer with a single plate and a simple configuration.
[Brief description of the drawings]
FIG. 1 shows a plan view of a first embodiment of the present invention.
FIGS. 2A and 2B show a comparison between an example in which a cold cathode tube is connected to the same example and a conventional example, FIG. 2A shows this example, and FIG. 2B shows a conventional example.
FIG. 3 shows a plan view of a second embodiment of the present invention.
4A is a plan view and FIG. 4B is a perspective view of an application example of the third embodiment of the present invention.
FIG. 5 shows a plan view of a fourth embodiment of the present invention.
FIG. 6 shows a plan view of an application example of the present invention.
FIG. 7 is a plan view of a schematic configuration of another application example of the present invention.
FIG. 8 is a perspective view of a conventional secondary Rosen piezoelectric transformer.
FIG. 9 is a schematic plan view of a conventional symmetrical third-order Rosen piezoelectric transformer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Primary side 1a Electrode 2 Secondary side 2a Secondary side electrode 2b Secondary side electrode 3 Notch 3a Notch inner end part 4 Insulator

Claims (3)

In a piezoelectric transformer having a rectangular plate shape, one side being a primary side (1) and the other side being a secondary side (2),
A notch (3) is formed in the substantially central portion of the secondary side (2), the secondary side (2) is divided into first and second secondary side portions, and the secondary side ( 2. A piezoelectric transformer characterized in that the capacitance of 2) is smaller than that of the primary side (1), and the polarization directions of the first and second secondary side portions are opposite to each other. 2. The piezoelectric transformer according to claim 1, wherein the inner end (3a) of the notch (3) is cut into the primary and secondary polarization boundary portions or the primary side (1). The piezoelectric transformer according to claim 1, wherein an insulator (4) is provided between the first and second secondary portions.

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