JP2005129475A - High power piezo-electric transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem; as to a lighting device used for a liquid crystal backlight, which uses a piezo-electric inverter having a piezo-electric transformer as a voltage boosting means, and mainly drives a large-sized cold cathode discharge tube, since conventional piezo-electric inverters are mostly ones with applied power of about 3 W, and if more than 5 W is applied, generation of high heat and thermal runaway are caused and the piezo-electric inverter is eventually broken, the limit of output wattage has not been exceeded. <P>SOLUTION: An oscillation mode in a twisting direction generated during high power drive, and an oscillation mode in a meandering direction are completely prevented from being generated by making a rigid part comprising a non-polarized part in the center part of this piezo-electric transformer. Thereby, this highly efficient, light, and thin high power piezo-electric transformer wherein rise of its temperature is saturated at low temperatures can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

Detailed Description of the Invention

  The present invention relates to a lighting device mainly used for driving a large-sized cold cathode discharge tube of a piezoelectric inverter using a piezoelectric transformer as a boosting means, which is used for a liquid crystal backlight or the like.

  In a conventional piezoelectric inverter, a piezoelectric inverter having an output of about 3 W and a maximum wattage of about 15 inches to 17 inches in a liquid crystal backlight size has been developed and put into practical use.

Problems to be solved by the invention

  In the conventional piezoelectric inverter, a cold cathode discharge tube having a diameter of about 2 mm and a length of about 250 mm has been developed and practically used for notebook computers of about 15 to 17 inches with an output specification of about 3 W. However, in addition to this, recently, the large liquid crystal display market such as the liquid crystal television market has more than doubled compared to the previous year, and the market for 30-inch and 40-inch large-sized liquid crystal televisions has expanded dramatically. .

  For this reason, it is required to increase the output of the piezoelectric inverter, but the high voltage output or the large current output is 4 to 5 times the current 12W to about 15W or more, or about 6 to 10 times or more the current 18W. Therefore, an output increase of about 30 W is required. However, current piezoelectric inverters generate high heat with high power, resulting in reduced output and reduced efficiency. If the power exceeds 3W to 5W, the piezoelectric transformer will eventually break down and eventually break down. There was a big problem that the limit could not be exceeded.

  The present invention pays attention to the secondary mode (λ mode) and higher frequency modes of the piezoelectric transformer, and can generate high power of about 4 to 5 times, and drive frequency can be increased. By realizing a low drive frequency of about 40-50 KHz, which is a half value of a relatively high drive frequency, from 80 KHz to 120 KHz, the leakage current is suppressed and the output wattage is, for example, 6 W to 10 times 18 W or more An object of the present invention is to provide a novel piezoelectric inverter that is capable of outputting a high wattage of around 30 W and that exceeds the limit of conventional piezoelectric inverter performance.

Means to solve the problem

  In order to achieve the above object, a piezoelectric inverter using the piezoelectric transformer of the present invention is a small, high output and low drive frequency piezoelectric device using the primary mode (1/2 wavelength) disclosed in Japanese Patent Application Laid-Open No. 2000-332315. It focuses on the transformer.

  In the piezoelectric transformer, the piezoelectric transformer is composed of three regions, that is, an output unit serving as a first region, an input unit serving as a second region, and a rigid body serving as a third region. As a conventional piezoelectric ceramic transformer, the polarization point in the length direction, the stress maximum point at the time of polarization of the thickness direction polarization part, and the stress maximum point generated next to the drive, which are the weak points of power-up, By the invention configured in a different position without superimposing, it is possible to increase the practical power up to about several watts by the primary mode (1/2 wavelength) drive, in which output with power was impossible due to destruction of the piezoelectric transformer. It is a success.

  Japanese Patent Application Laid-Open No. 2000-332315 discloses a piezoelectric transformer using a primary mode (1/2 wavelength) and a piezoelectric transformer polarized by changing the polarization direction of the output portion of the piezoelectric transformer by 180 °. High voltages with different phases of 180 ° are generated at a plurality of output portions of the piezoelectric transformer used as a set.

Cold cathode discharge tubes used for large displays of about 40 inches have a diameter of 3 to 4 mm and a length of about 580 mm to 1.2 m, for example, a stable discharge voltage of 3500 Vp-p and a tube current of With an output specification ranging from 17 mAp-p to several times, practical power is about 12-15 W to 18-30 W. When driving by connecting the output part of the pair of piezoelectric transformers to both ends of the discharge tube, a positive high voltage and a negative high voltage are applied simultaneously and synchronously to both ends of the discharge tube of the long tube. Therefore, for example, a target of 28000 cd / m ² can be output at a high voltage of about ½ of the conventional value.

  However, when multiple piezoelectric transformers are used, the resonance frequency and resonance impedance are slightly different, so sidebands caused by the difference frequency are generated, resulting in beats and electrical noise, resulting in oscillation, which makes the drive unstable. It was.

  For the reasons described above, in a piezoelectric transformer configuration using a plurality of primary modes (1/2 wavelength), it is necessary to select and combine piezoelectric transformers having the same characteristics from among a large number of piezoelectric transformers. Caused the disadvantage of large. Therefore, it is necessary to realize a high voltage output, a large current output, and a large power drive with a single piezoelectric transformer configuration.

  Embodiments of the invention will be described based on examples with reference to the drawings. Piezoelectric transformers that have been used in conventional piezoelectric inverters have driven the piezoelectric transformer with a power of about 3W to 5W. When driving with more power, at the boundary between thickness direction polarization and length direction polarization, or at the minimum vibration amplitude, at the node where the stress is maximum, or near the output electrode where the vibration speed is maximum, Along with the increase of the electric power, the electric power of about 10 W, which is nearly twice as much as before, suddenly generated heat and led to destruction. The cause of this destruction is that the piezoelectric transformer is softened due to the high heat generated by the application of the above-mentioned high power, so that the vibration mode in the torsional direction and the meandering direction do not contribute to the characteristics of the piezoelectric transformer due to the soft vibration of the λ mode. It is clear from the analysis of the latest high-frequency vibration measuring instruments such as laser Doppler that the cause is that the vibration modes of the above occur.

  Furthermore, the frequency-impedance characteristics of a piezoelectric transformer made of piezoelectric ceramics are, for example, a characteristic with a primary mode of about 50 KHz-10Ω in a piezoelectric transformer having a length of 63 mm, a width of 15 mm, and a thickness of 1.2 mm. With the characteristic of 120 KHz-5Ω, the characteristic in which the third mode is about 180 KHz-30Ω was obtained. In a higher order, there are resonance points of width direction vibration and thickness direction vibration. When the piezoelectric transformer is driven with a 50 KHz fundamental component, the low-impedance secondary mode is at about double frequency as described above, and the impedance is about 5 Ω, as described above, depending on the drive waveform of the FET in the previous stage. Due to the low impedance, the higher order modes, mainly the second order mode, cannot be ignored. The piezoelectric transformer shows a complicated vibration state and the temperature rise of the piezoelectric transformer is It rose to 70-80 ° C instantly.

  If the unnecessary and invalid vibration components generated during driving are removed, the loss during driving is reduced, the conversion efficiency of the piezoelectric transformer is increased to a high level, and the temperature rise is also reduced to a low level. In order to suppress the high-order component of the piezoelectric transformer and realize the driving of the ultrasonic region with the fundamental component, the impedance of the primary mode as the drive frequency is lower than the impedance of the secondary mode. Need to be

  As this new configuration, a piezoelectric transformer made of piezoelectric ceramics is composed of a plurality of input parts, a plurality of output parts, and a rigid part consisting of an unpolarized part at the center, and the dimension in the length direction of the transformer, In a piezoelectric transformer having a dimensional ratio of about 0.2 or less in the width direction, such as a length of 63 mm, a width of 8 mm, and a thickness of about 1.2 mm, the primary mode has a characteristic of about 50 KHz-10Ω, The secondary mode has a characteristic of about 115 KHz-180Ω, and the third mode has a characteristic of about 210 KHz-10Ω. Furthermore, resonance points of width direction vibration and thickness direction vibration exist at higher order frequencies. When the piezoelectric transformer having a dimensional ratio of about 0.2 or less in the length direction and width direction of the piezoelectric transformer is driven, the temperature rise during power driving of about 15 W and about 30 W increases to room temperature plus Saturated at a temperature around 10 ° C to 20 ° C. Furthermore, the piezoelectric inverter efficiency using this piezoelectric transformer is the first to realize a high efficiency of 90% to 95%.

  The direction of spontaneous polarization of piezoelectric ceramics used for piezoelectric transformers immediately after firing is considered to be an isotropic body because they are arranged at random, and when a DC electric field is applied for polarization, the direction of the applied electric field is Although slightly extended and contracted in a direction perpendicular to the polarization, it becomes almost tetragonal, and when an alternating electric field near the resonance frequency is applied to the porcelain after polarization treatment, the original dimensions and residual strain are added. By going back and forth between these dimensions, mechanical resonance occurs in the piezoelectric ceramic porcelain, and it can be applied as a piezoelectric transformer.

  As shown in FIG. 1, for example, the piezoelectric transformer in which the E-plane electrode 1 and the G-plane electrode 2 are provided on both end faces of a piezoelectric ceramic having a length of 63 mm, a width of 10 mm, and a thickness of about 1.2 mm is substantially in the length direction. The region of the piezoelectric transformer is divided so as to have a ratio of 2: 2: 1: 2: 2. The first area and the fifth area are output units. As indicated by the arrows, the left and right sides are polarized in a phase relationship that is 180 degrees different in polarization direction. The second region and the fourth region are input portions, and are polarized in a phase relationship in which the directions of polarization differ by 180 degrees as indicated by arrows. The third region is a rigid part that is an unpolarized part. In order to drive the piezoelectric transformer, the input terminals 3 and 4 are connected together, and the other input terminals 5 and 6 are connected together as another group. When applied, the E plane electrode 1 and the G plane electrode 2 simultaneously output high voltage signals having a phase difference of 180 degrees.

  The piezoelectric transformer made of piezoelectric ceramics having the above-described configuration is a torsional direction vibration mode generated at the time of high power drive, because the central part of the ultrasonic vibration excitation functions as a rigid part that is not polarized and does not vibrate, Both the meandering direction vibration mode is suppressed and the configuration works in the direction of reducing the loss system. Due to the effect of this vibration mode, the piezoelectric inverter efficiency is as high as about 18 W to 30 W even when driving at about 15 W. For the first time, high efficiency of 90% to 95% was achieved in both cases. Also, the temperature rise of the piezoelectric transformer reached saturation with a temperature rise of room temperature plus 10 to 20 degrees.

  A piezoelectric inverter using a high-power piezoelectric transformer having a high-efficiency configuration configured as described above is connected to the input-output terminal of a large-sized cold cathode discharge lamp used inside a flat panel display of a liquid crystal television. The high-voltage in the positive direction and the high voltage in the negative direction are respectively connected to the G-plane electrode of the output portion and the output portions of the H-plane electrode having a 180-degree output phase different from that of the G-plane electrode through high-voltage lines. Due to the effect that the voltage is output simultaneously in synchronism, the display unit can be driven with a normal voltage value of 1/2, and the heat generated in the flat panel display unit is saturated at a low temperature. There was an effect that the influence of the fever on the image was completely eliminated.

  Similarly, the input and output portions of a plurality of large-sized cold cathode discharge lamps connected in series used in a flat panel display or the like have a G-phase electrode of the output of the piezoelectric transformer and the G-pole surface and a 180-degree output phase. Since the output parts of different H-plane electrodes are connected via high-voltage lines, etc., the heat generated in the flat panel display part is saturated at a low temperature. The effect was that there was nothing.

The invention's effect

  Since the present invention is configured as described above, the following effects can be obtained. Conventional piezoelectric inverters do not generate electromagnetic waves, and are small, lightweight, inexpensive, and have good space-saving features, so they are small, portable equipment, health equipment such as cooling / heating equipment and ionizers, or 15 inches or more. It has been widely used as an inverter for personal computers with a maximum of about 17 inches. Although the present invention has the same effect, the conventional product has been mainly used as an output inverter of 3 W to 5 W at most. The above-mentioned current piezoelectric inverter generates high heat instantaneously when power is applied at about 10 W, with a decrease in output and efficiency, etc., and thermal runaway with an increase in power. There was a problem that the conventional limit value of the output wattage of about 5 W could not be exceeded.

In the present invention, the cause is high heat generated during high-power driving, and the piezoelectric transformer is softened to soften the λ-mode bending vibration, which does not contribute to the characteristics of the piezoelectric transformer. It has been clarified by vibration analysis using a laser Doppler that the modes are caused by superposition.

As a countermeasure against the above phenomenon, when a rigid body portion made of an unpolarized portion is provided at the center of a piezoelectric transformer driven in the λ mode, generation of a vibration mode in a torsional direction or generation of a vibration mode in a meandering direction is eliminated. . Further, the piezoelectric transformer is composed of a plurality of input sections and a plurality of output sections, and is composed of a dimensional ratio in which the dimensional ratio in the length direction and the dimensional ratio in the width direction of the piezoelectric transformer is about 0.2 or less. In the characteristic piezoelectric transformer, the temperature rise during high-power driving at around 15 W and 30 W was both saturated at room temperature plus 10 to 20 degrees. Furthermore, the piezoelectric inverter efficiency using this piezoelectric transformer is the first to achieve a high efficiency of 90% to 95% even during high power drive. The piezoelectric transformer is highly efficient and has a low temperature rise, so that there is no effect on the image due to the heat generated in the liquid crystal display unit. Furthermore, one piezoelectric transformer has the feature that it can drive two or several cold cathode discharge tubes, and there are many such as immeasurable economic effects at the time of mass production of large liquid crystal televisions, etc. There is an effect.

Explanation of symbols

1 E surface electrode 2 G surface electrode 3, 4, 5, 6 Input terminal 7, 8 Output terminal

Claims (7)

A piezoelectric transformer made of piezoelectric ceramic is composed of a plurality of input sections and a plurality of output sections, and a plurality of cold cathode discharge tubes are connected to an output section in which the electrical phases of the plurality of output sections differ by 180 degrees. A high-power piezoelectric transformer characterized by being configured as described above. A piezoelectric transformer made of piezoelectric ceramics is composed of a plurality of input parts and a plurality of output parts, and the dimension ratio in which the dimension in the length direction and the dimension in the width direction of the piezoelectric transformer is about 0.2 or less. A high-power piezoelectric transformer characterized by comprising In the piezoelectric transformer made of piezoelectric ceramics, the piezoelectric transformer that resonates in the longitudinal direction of the piezoelectric transformer with a second mode (λ wavelength) and a frequency higher than the second is a second region and a fourth region; The region is composed of the above-mentioned five regions, that is, an output portion serving as the first region and the fifth region, and a rigid portion composed of the unpolarized portion serving as the third region. Each region is approximately 2: 2 in the longitudinal direction. A high power piezoelectric transformer characterized in that it is divided and configured at a ratio of 1: 2: 2. In a piezoelectric transformer made of piezoelectric ceramics, a torsional direction vibration mode induced during high-power drive can be suppressed and a loss system can be reduced by forming a rigid body portion consisting of an unpolarized portion at the center of the piezoelectric transformer. A high-power piezoelectric transformer characterized by having a high-efficiency piezoelectric transformer configuration. In a piezoelectric transformer made of piezoelectric ceramics, by forming a rigid body portion made of an unpolarized portion at the center of the piezoelectric transformer, the meandering direction vibration mode induced at the time of high power drive is suppressed and the loss system is reduced. A high-power piezoelectric transformer characterized by having a high-efficiency piezoelectric transformer configuration. The G-plane electrode of the piezoelectric transformer and the H-plane electrode having an electrical phase different from that of the G-plane electrode by 180 degrees are connected to both ends of a large-sized cold cathode discharge lamp built in a flat panel display or the like via high-voltage lines. High-power piezoelectric transformer characterized by The G-plane electrode of the piezoelectric transformer and the H-plane electrode having an electrical phase of 180 degrees different from that of the G-plane electrode at the input and output portions of a plurality of large-scale cold cathode discharge lamps built in a flat panel display or the like are respectively high pressure. A high-power piezoelectric transformer characterized by being connected via a wire or the like.

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