JP2006158171A - High power piezoelectric transformer inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a large-sized LCD back-light high-powered and to increase its power in a highly effective manner. <P>SOLUTION: The total length of a piezoelectric transformer is made to be approximately 75 mm to 85 mm, and the resonance frequency of a lambda mode (secondary mode) is decreased to 30 kHz - 40 kHz to reduce the number of repetition of a bending mode to approximately 1/2-1/3. A piezoelectric inverter driven with large electric power is realized using the high power piezoelectric transformer with the high efficiency thus obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high power piezoelectric inverter used for a backlight of a liquid crystal television or the like.

  In the conventional piezoelectric inverter, the output is about 3 W, and the liquid crystal backlight size has a maximum of about 15 inches to 17 inches, mainly a small wattage piezoelectric transformer for computers, and the piezoelectric transformer described above. Piezoelectric inverters have been developed and put into practical use. (For example, see Non-Patent Document 1)

"NIKKEI ELECTRONICS 1994.11.7 (No. 621)"

  In the conventional piezoelectric inverter, a cold cathode discharge tube having a diameter of about 2 mm and a length of about 250 mm is used mainly for notebook computers of about 15 to 17 inches with an output specification of about 3 W as described above. Although it has been developed and put into practical use, in addition to this, the market for large-sized liquid crystal televisions such as the liquid crystal television market has more than doubled compared to the previous year, and the market for large-sized liquid crystal televisions such as 30-inch and 40-inch has grown dramatically. Has expanded to.

  Recently, a 65-inch large-sized LCD TV with an aspect ratio of about 1: 1.4 has been commercialized for the first time with the aim of gaining the realism and power of a movie theater. These liquid crystal televisions are equipped with about 35 long-length cold cathode discharge tubes each having a length of about 1300 mm to 1500 mm.

  The present invention is intended to achieve high power and high power consumption of a liquid crystal backlight that increases in size in this manner with high efficiency. In a piezoelectric inverter using a conventional piezoelectric transformer as a boosting means, the piezoelectric transformer Even if it is a type that can drive one cold cathode discharge tube with one unit or output relatively large power, for example, a cold cathode discharge tube having a diameter of about 3 mm and a length of about 680 mm can be driven by a single piezoelectric transformer. The driving of was maximized. Moreover, what drives about 30W in total also with the both-ends drive system had the largest drive wattage. (Patent Document 1 Japanese Patent Application No. 2003-403797)

Japanese Patent Application No. 2003-403797

The light source of the liquid crystal display device has been devised in order to obtain a flat light source. In a liquid crystal television having a size of 30 to 40 inches, 30 to 40 cold cathode discharge tubes are used as the light source. It is used as
As described above, for example, the discharge tube having a diameter of 3 mm and a length of about 680 mm is used, and the gap between the discharge tube and the light guide plate is close to about 0.5 mm to 1.0 mm. The equivalent circuit when the discharge tube is lit shows an equivalent circuit in which a large number of innumerable coupling capacitors are arranged from the high voltage portion to the low voltage portion of the discharge tube. Thus, the reactive current is supplied to the infinite number of non-existing coupling capacitors at the time of lighting, resulting in a hot bed with high heat generation and low efficiency.

  The magnitude of the leakage current flowing through this coupling capacitor has become a magnitude that cannot be ignored in the current piezoelectric inverter driven at the current high frequency (80 kHz to 115 kHz), and has become an inverter with poor mounting efficiency. .

In order to achieve the above object, the present invention focuses on the resonance frequency and drive frequency of the piezoelectric transformer and the piezoelectric inverter as described below.
The total length of the piezoelectric ceramic transformer using the lambda mode (secondary mode) according to the present invention is about 82 mm, the width is about 15 mm, and the thickness is about 1 to 3 mm. The resonance frequency of the piezoelectric transformer is about 30 kHz. became. The piezoelectric transformer has a length of about 75 mm, a width of about 15 mm, and a thickness of about 1 to 3 mm. The resonance frequency in the lambda mode (secondary mode) of the piezoelectric transformer is about 40 kHz. Compared to the conventional drive frequency of piezoelectric transformers, it was possible to realize a drive frequency of approximately half or less.

  As described above, the number of repetitions of the bending mode of the piezoelectric transformer with the drive frequency of 80 to 90 kHz that has been used so far is approximately 80,000 times per second, but the resonance frequency is 40 kHz. This half value was reduced to 40,000 times, and the number of repetitions of the 30 kHz piezoelectric transformer was reduced to 30,000 times per second, from 1 / 2.7 to 1/3 compared to 80 kHz. Due to this effect, as described above, the equivalent circuit when the cold cathode discharge tube is mounted is in the form of an infinite number of non-existing coupling capacitors arranged in a row from the high voltage portion to the low pressure portion. The reactive current flowing through the capacitor can be reduced to half when driving at 40 kHz, and can be reduced to about 1/3 when driving at 30 kHz.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 1, for example, the above-mentioned piezoelectric transformer in which an E-plane electrode 1 and a G-plane electrode 2 are provided on both end faces of a single piezoelectric ceramic having a length of 75 to 82 mm, a width of 15 mm, and a thickness of 1 to 3 mm. The region of the piezoelectric transformer is divided so as to have a ratio of 2: 2: 1: 2: 2 in the length direction. 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 polarization directions 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.

  Piezoelectric transformers composed of piezoelectric ceramics with the above configuration are generated by softening due to repeated vibration during high-power driving because the central part of the ultrasonic vibration excitation functions as a rigid part that is not polarized and does not vibrate. The effect of suppressing both the torsional direction vibration mode and the meandering direction vibration mode, and the above-described configuration works in the direction of reducing the loss system. Due to this vibration mode, the piezoelectric inverter efficiency is about 50 W drive. Sometimes, for the first time, a high efficiency of 90% to 95% was achieved both when driving at 80W to 100W or more. The temperature rise of the piezoelectric transformer also reached saturation with a temperature rise of room temperature plus about 10 to 20 degrees.

1 is a perspective view of a piezoelectric transformer showing a basic embodiment of the present invention.

Explanation of symbols

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

Claims (6)

  A piezoelectric inverter, wherein a piezoelectric transformer made of piezoelectric ceramic is driven by using a lambda mode (secondary mode) resonance frequency of a relatively low frequency of about 30 kHz to about 40 kHz.   A piezoelectric inverter, wherein a piezoelectric transformer made of piezoelectric ceramics drives several or more cold cathode discharge tubes using a lambda mode (secondary mode) resonance frequency of a relatively low frequency of about 30 kHz to 40 kHz.   A piezoelectric inverter, wherein a piezoelectric transformer made of piezoelectric ceramic is driven with a power of several pick-up watts or more using a resonance frequency of a relatively low frequency lambda mode (secondary mode) of about 30 kHz to 40 kHz.   A piezoelectric inverter comprising a piezoelectric transformer made of piezoelectric ceramics having a total length of about 75 to 85 mm and driven by using a relatively low frequency lambda mode (secondary mode) resonance frequency .   A piezoelectric transformer made of piezoelectric ceramics is composed of a plurality of input sections and a plurality of output sections and is driven using a lambda mode (secondary mode) resonance frequency of a relatively low frequency of 30 kHz to around 40 kHz. A characteristic piezoelectric inverter.   In a piezoelectric transformer made of piezoelectric ceramics, a piezoelectric transformer that resonates in a lambda mode (secondary mode) at a relatively low frequency of about 30 kHz to about 40 kHz includes an input section serving as a second region and a fourth region, A piezoelectric inverter using a high-power piezoelectric transformer, characterized in that it is composed of the above-mentioned five regions of a rigid portion comprising an output portion serving as a region and a fifth region and an unpolarized portion serving as a third region.

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