JP3734637B2 - Drive device for 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 driving device for a piezoelectric transformer used in a device or the like.
[0002]
[Prior art]
Conventionally, this type of piezoelectric transformer has a rectangular plate shape as shown in FIG. 5, for example. In the figure, 11 is a primary side (input side) and primary side electrodes 11a are provided on both sides, and 12 is a secondary side (output side), and a secondary side electrode 12a for output extraction is provided at an end thereof. Is provided.
[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 internal electrodes and peeling between layers.
[0007]
In order to increase the step-up ratio, there is a symmetrical third-order Rosen transformer configured as shown in FIG. 6, but there are two nodes as shown in FIG. 5 (nodes where no vibration occurs). Even if the length is the same as that of the conventional general secondary rosen type having the above, the frequency becomes high, and when the frequency becomes high, the leakage current from the cold cathode tube connected to and driven by the piezoelectric transformer Is not preferable from the viewpoint of the efficiency of the inverter.
[0008]
In addition, the conventional three-terminal type piezoelectric transformer has a problem that it is inconvenient in design and leakage current 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 drive device that is easy and can reduce leakage current as compared with the conventional type when used as a piezoelectric inverter.
[0010]
[Means for Solving the Problems]
The present invention comprises first and second piezoelectric transformers 1 and 2 each having a rectangular single plate type, and these first and second piezoelectric transformer bodies 1 and 2 are respectively in the same direction in the thickness direction of the body. Are polarized in opposite directions in the longitudinal direction of the primary side 3, 4 and the main body as the input side having primary electrodes 3a, 3a ', 4a, 4a' on both sides and on the longitudinal end faces of the main body secondary electrodes 5a, has a secondary side 5, 6 as an output side having a 6a, the ends first, primary electrodes 3a of the second piezoelectric transformer body 1,2, 3 a ', 4a, 4a a power supply V ₀ connected in parallel to 'the ends first, second piezoelectric transformer body and second secondary-side electrode 5a, a structure consisting of a cold cathode tube L connected between 6a, the object Have achieved.
Further, the polarization of the primary sides 3 and 3 is opposite to the thickness direction, and the secondary sides 5 and 5 are polarized in the same direction with respect to the length direction, respectively, and the primary electrodes 3a, 3a ′, 3a ′, 3a the power V ₀ connected in parallel, and formed by connecting the cold cathode tubes L configuration between the secondary-side electrode 5a, 5a, has achieved the above objects.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
A so-called Rosen-type piezoelectric transformer is obtained by providing primary and secondary electrodes on a piezoelectric ceramic such as PZT and polarizing each with a high electric field. When a voltage having a natural resonance frequency determined by the length direction on the primary side is applied, the element vibrates due to the inverse piezoelectric effect, and a voltage corresponding to the vibration can be extracted from the secondary side due to the piezoelectric effect.
[0012]
By the way, the piezoelectric body can be obtained by applying a high electric field in a certain direction of the ceramic and aligning the crystal axes. Then, when tension is applied to the piezoelectric body, positive charge is generated in the positive direction of the coordinate axis with respect to the force (piezoelectric sign is positive) and negative charge is generated (piezoelectric sign is negative). There is something. Therefore, when the polarization of the secondary side or the primary side of the piezoelectric transformer made of the same material is reversed, when the voltage of the resonance frequency is applied to the primary side, a potential of the same magnitude with a different sign is generated on the secondary side. .
[0013]
In view of the above, the present invention uses two single-plate piezoelectric transformers, with the primary polarization direction being the same direction and the secondary side being reversed, or the primary side polarization direction being reversed and the secondary direction being reversed. The sides are in the same direction, a load is connected between the secondary sides of each piezoelectric transformer, a positive potential is generated on one secondary side, and a negative potential is generated on the other secondary side. A large potential difference is generated so that a high step-up ratio can be expected.
[0014]
[Example 1]
FIG. 1 shows a first embodiment of the present invention. In this embodiment, a rectangular plate-shaped first piezoelectric transformer body 1 and a second piezoelectric transformer body 2 having the same shape are provided. In the state shown in the figure, the substantially left half of the first and second piezoelectric transformer bodies 1 and 2 is the primary side 3 and 4, respectively, and the opposite right half is the secondary side 5 and 6. ing.
[0015]
Characteristically, the primary sides 3 and 4 are polarized in the same direction as indicated by arrows, while the secondary sides 5 and 6 are indicated by arrows in the length direction, respectively. Conversely, it is polarized.
[0016]
As is well known, primary and secondary electrodes 3a, 3a ', 4a and 4a' are provided on the front and back surfaces of the primary sides 3 and 4, respectively, and the outer ends of the secondary sides 5 and 6 are used for output extraction. Secondary electrodes 5a and 6a are provided.
[0017]
One end of the power source V ₀ is connected to the primary electrode 3 a on the surface side of the first piezoelectric transformer body 1, and the primary electrode 3 a is connected to the primary electrode 4 a of the second piezoelectric transformer body 2. Yes. The first piezoelectric transformer body 1 on the back side of the primary-side electrode 3a 'and the second primary-side electrode 4a of the piezoelectric transformer body 2' with is connected to, is connected to the other end of the power supply V _0, and Grounded. Further, a cold cathode tube L is connected between the secondary side electrodes 5a and 6a of the first and second piezoelectric transformer bodies 5 and 6, and the piezoelectric transformer bodies 1 and 2 are driven, and the cold cathode tube is driven by the secondary side output. L is turned on.
[0018]
FIG. 2A shows a driving method of a conventional piezoelectric inverter. In the figure, C is a schematic representation of the stray capacitance C generated when the cold cathode tube L is driven, and Ia is a leakage current generated by the stray capacitance C. Leakage current also increases. FIG. 2B shows the above-described driving method of the present invention in comparison with the conventional example.
[0019]
Conventionally, as shown in FIG. 2 (a), connecting one end of the cold cathode fluorescent lamps L is the load to the piezoelectric transformer secondary side 12, down the other end to ground, and through the power supply V ₀ to the primary side 11 An input voltage was applied to light the cold cathode tube L.
[0020]
However, this method has a drawback that a leakage current Ia occurs due to the stray capacitance C parasitic on the cold cathode tube L, and this leakage current greatly affects the efficiency of the piezoelectric inverter and the luminance unevenness of the cold cathode tube L. there were. Here, the leakage current Ia is Ia = 2πfC · V (f is the driving frequency, and V is the lighting voltage).
[0021]
On the other hand, in the first embodiment of the present invention, as shown in FIGS. 1 and 2B, the polarizations of the primary sides 3 and 4 of the piezoelectric transformer bodies 1 and 2 are set in the same direction, and the secondary side 5 , 6 are reversed and a cold cathode tube L is connected between the secondary electrodes 5a, 6b.
[0022]
In this way, when the piezoelectric transformer bodies 1 and 2 with the polarizations of the secondary sides 5 and 6 reversed are used for lighting the cold cathode tube L, the secondary sides 5 and 6 of the piezoelectric transformer bodies 1 and 2 are used. Since the polarization directions are respectively reversed, if only the potential difference V of the cold-cathode tube L is generated, a positive voltage + V / 2 is applied to one secondary side portion, and a negative voltage is applied to the other secondary side portion. A voltage −V / 2 is generated, and a large potential difference is generated across the cold cathode tube L. That is, if the two piezoelectric transformer bodies 1 and 2 are driven in this way, a high step-up ratio can be expected.
[0023]
That is, as shown in FIG. 2A, if there is one piezoelectric transformer, for example, if a voltage V of +1000 V is generated on the secondary side, the potential difference is 1000 V if this voltage is dropped to ground (0 V). .
On the other hand, when the first and second piezoelectric transformers 1 and 2 are used as in the present invention of FIG. 2B, the secondary side becomes + 1000V − (− 1000V) and the potential difference becomes 2000V. eventually, the power supply voltage V ₀ by obtaining the brightness of the same extent as FIGS. 2 (a) to the cold cathode fluorescent lamps L would need 1/2.
[0024]
In the present invention, since the secondary sides of the piezoelectric transformer bodies 1 and 2 output different sign voltages + 1 / 2V and -1 / 2V having the same magnitude, the central portion of the cold cathode tube L becomes 0V. The stray capacitance becomes C / 2, and the leakage current is reduced.
[0025]
According to this method, since both pressures are high, luminance unevenness hardly occurs. Further, if attention is paid to only one of the outputs, the leakage current is expressed by the following equation.
[0026]
Ib1 = 2πf (C / 2) · (V / 2)
[0027]
The overall leakage current is:
[0028]
Ib ₁ + Ib ₂ = πfC · V = (1/2) Ia
[0029]
Therefore, the leakage current is also halved.
[0030]
[Example 2]
FIG. 3 is a perspective view of two piezoelectric transformer bodies 1 and 2 used in the second embodiment of the present invention. In this embodiment, the piezoelectric transformer bodies 1 and 1 are used, one of them is turned over, the polarizations in the thickness direction of the primary sides 3 and 3 are reversed to each other as indicated by arrows, and the secondary sides 5 and 5 are used. Is characterized by being used in the same direction as it is in the length direction. In this case, the polarizations of the primary sides 3 and 3 are reversed, and electric potentials of the same magnitude with different signs are generated on the respective secondary sides, resulting in a large electric potential difference.
[0031]
In the piezoelectric inverter using these two piezoelectric transformer bodies 1 and 1 and applied to the drive circuit shown in FIG. 2B, the same effects as the first embodiment can be obtained.
[0032]
In FIG. 4, auxiliary primary electrodes 3b and 3b 'are further added to these, and in this application example, auxiliary electrodes are added to increase the drive unit. Moreover, as shown by the arrows, it is possible to increase the step-up ratio by reversing the polarization. Further, if the sizes of the auxiliary primary electrodes 3b and 3b 'are changed, the drive unit can be adjusted, and the step-up ratio can be controlled without impairing the efficiency of the piezoelectric transformer.
[0033]
The above embodiment can also be applied to a symmetrical third-order rosen. Moreover, although the example which drives the cold cathode tube L was demonstrated, it can be used also for high voltage power supplies.
[0034]
【The invention's effect】
As described above, according to the present invention, two piezoelectric transformers are used to reverse the polarization of the secondary side or the primary side, and positive and negative potentials are generated at the output ends of the secondary sides, respectively. If a potential difference is generated, a substantially high step-up ratio can be expected, and the leakage current can be reduced with the four-terminal structure.
[Brief description of the drawings]
FIG. 1 shows a first embodiment of the present invention.
2A is a conventional piezoelectric inverter system, and FIG. 2B is a system according to the present invention.
FIG. 3 shows a second embodiment of the present invention.
FIG. 4 shows a third embodiment of the present invention.
FIG. 5 is a perspective view of a conventional secondary Rosen piezoelectric transformer.
FIG. 6 is a perspective view of a conventional symmetrical third-order Rosen piezoelectric transformer.
[Explanation of symbols]
1, 2 Piezoelectric transformer body 3, 4 Primary side 3a, 3a ', 4a, 4a' Primary electrode 3b, 3b 'Auxiliary primary electrode 5, 6 Secondary side

Claims (2)

Each of the first and second piezoelectric transformer bodies (1) and (2) is a rectangular single plate type, and each of the first and second piezoelectric transformer bodies (1) and (2) has a thickness of the body. Primary side (3), (4) as an input side that is polarized in the same direction and has primary side electrodes (3a, 3a '), (4a, 4a') on both sides and in the longitudinal direction of the body It has secondary sides (5) and (6) as output sides that are polarized in the opposite direction and have secondary side electrodes (5a) and (6a) on the longitudinal end faces of the main body. The power supply V connected in parallel to the primary electrodes (3a, 3a ′), (4a, 4a ′) of the piezoelectric transformer bodies (1), (2) of 2 ₀ And a cold cathode tube L having both ends connected between the secondary side electrodes (5a) and (6a) of the first and second piezoelectric transformer bodies (1) and (2). Drive device. Each of the first and second piezoelectric transformer bodies (1) and (1) is a rectangular single plate type, and each of the first and second piezoelectric transformer bodies (1) and (1) has a thickness of the body. Primary side (3), (3) as an input side polarized in opposite directions to each other and having primary side electrodes (3a, 3a '), (3a', 3a) on both sides and in the longitudinal direction of the body It has secondary sides (5) and (5) as output sides that are polarized in the same direction and have secondary side electrodes (5a) and (5a) on the longitudinal end faces of the main body. The power supply V connected in parallel to the primary electrodes (3a, 3a ′), (3a ′, 3a) of the piezoelectric transformer bodies (1), (1) of 2 ₀ And a cold cathode tube L having both ends connected between the first and second piezoelectric transformer bodies (1) and the secondary side electrodes (5a) and (5a) of (1). Drive device.

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