JP2004253762A - Piezoelectric transformer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric transformer that has high machine coupling coefficients k and Q, can output large power even in low-voltage input, has a small amount of self-heating and high efficiency even in an application for high power, and cannot be cracked easily by mechanical vibration even in the application for high power. <P>SOLUTION: The piezoelectric transformer has a piezoelectric vibrating plate 12 consisting of a lithium niobate single crystal plate having a spontaneous polarization axis as a Z axis. The piezoelectric vibrating plate 12 is formed by rectangularly cutting a rotation Y plate, where the coordinates axis of a crystal is rotated around an X axis so that the long side or the short one becomes in parallel with the X axis of the crystal or the short side or the long one becomes in parallel with the Y-axis projection line of the crystal. In the piezoelectric transformer, the divided electrodes of at least two places are connected in parallel for setting to be an input electrode and the divided electrode of at least one place is set to be an output electrode, thus utilizing a lateral effect vibration mode of a λ/2 mode propagating in the Y-axis projection direction of the crystal (for example, the short side direction of the piezoelectric vibrating plate). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

表１より、１２８回転Ｙ板の基板で長辺方向に伝搬するλモード振動を利用する場合、実施例１−１２８Ｙの機械結合係数ｋは０．２６と比較例１−１２８Ｙの０．２９に比べて悪いが、機械的品質係数Ｑは実施例１−１２８Ｙの１８３８６が比較例１−１２８Ｙの１２４０７に比べて良いことがわかる。
【００３７】
昇圧比は機械結合係数ｋと機械的品質係数Ｑとで決まるため、機械的品質係数Ｑと機械結合係数ｋが共に大きい方が望ましいが、１２８回転Ｙ板の基板で長辺方向に伝搬するλモード振動を利用する場合はｋ、Ｑ共に最高の値を得ることは出来ない。
【００３８】
圧電トランスの効率は機械結合係数ｋに依存し、高電力での効率は機械的品質係数Ｑに依存するため、１２８回転Ｙ板の圧電振動板で長辺方向に伝搬するλモードの振動を利用する場合は、実施例１、比較例１共に大差ないことが分かる。
【００３９】
実施例１−１２８Ｙおよび比較例１−１２８Ｙの短辺方向に伝搬するλ／２モード振動のＬＣＲ等価回路の測定結果を表２に示す。
【表２】

表２より、１２８回転Ｙ板の基板で短辺方向に発生するλ／２モードを圧電トランスに利用する場合、実施例１−１２８Ｙの機械結合係数ｋは０．２８と比較例１−１２８Ｙの０．１６に比べて良く、機械的品質係数Ｑは実施例１−１２８Ｙ、比較例１−１２８Ｙ共大差ないことが分かる。故に、１２８回転Ｙ板の基板で短辺方向に発生するλ／２モードを圧電トランスに利用する場合は、図１に示すように、結晶のＸ軸と平行に長辺を切り出すのが望ましいことがわかる。
【００４０】
また、短辺方向に伝搬するλ／２モードの振動を利用するため、機械的振動で発生する応力を基板の長辺方向に分散することが可能で、高電力用途でも割れにくいことがわかる。
【００４１】
これらの結果から、機械結合係数ｋおよび機械的品質係数Ｑが大きい１２８回転Ｙ板を使用し、図１に示すように結晶のＸ軸と平行に圧電振動板の長辺を切り出し圧電振動板の短辺方向に伝搬するλ／２モードの振動を利用することで、高電力用途でも圧電トランスの発熱が少なく高効率でかつ高電力を入力しても機械的振動で割れることが少ない圧電トランスを作成することが出来る。
【００４２】
【実施例２】
図３（ａ）に示すように、自発分極軸をＺ軸として有するニオブ酸リチウム単結晶をＸ軸のまわりに１２８°回転した回転Ｙ板をそれぞれ長辺方向と結晶のＸ軸が平行になるように長さ３３．０ｍｍ×幅１２．２ｍｍの短冊状に切り出し、両面に研磨加工による鏡面仕上げを行い、厚み０．５６ｍｍの圧電振動板１２を得た。この圧電振動板１２の片面２箇所に長さ１２ｍｍ×幅１０ｍｍの入力電極１３ａ、１３ｂ、と片面１箇所に長さ５ｍｍ×幅１０ｍｍの出力電極１４を、圧電振動板の裏面に長さ３２ｍｍ×幅１０ｍｍのグランド共通電極１５をそれぞれ銀蒸着にて形成し、圧電トランス（実施例１）を得た。なお、図中の矢印Ｐは分極方向を概念的に示している。
なお、図３（ａ）において、１６は入力用リード線、１７は出力用リード線、１８はグランド共通リード線を示している。図３（ｂ）において、２０は振動の節、２１は圧電振動の変位、２２は圧電振動により生じる応力を示している。
【００４３】
実施例２の圧電トランスの入力電極１３ａと入力電極１３ｂを並列接続して合成入力電極とした場合と入力電極１３ａのみを入力電極とした場合での入力電極とグランド共通電極間の共振周波数ｆｒ、反共振周波数ｆａ、共振周波数でのインピーダンスＺｒ、機械的品質係数Ｑと機械結合係数ｋをインピーダンスアナライザで測定した結果を表３に示す。
表３の入力電極１端子は、入力電極１３ａとグランド共通電極１５間の周波数特性の測定値であり、表３の入力電極並列接続は、入力電極１３ａと１３ｂを並列に接続した合成電極とグランド電極１５間の周波数特性を測定したものである。
【００４４】
なお、測定した共振周波数は圧電振動板のＹ軸投影方向にλ／２の定在波が生じる横効果振動モードの周波数特性である。
表３より分かるように入力電極を並列接続することで共振点が低周波側にシフトし共振点と反共振点の帯域幅を広げ、共振点のインピーダンスも低下することを確認した。また入力電極を並列接続することで機械結合係数ｋの向上と機械的品質係数Ｑの向上が可能であることを確認した。
【表３】

このように３個の分割電極のうち、少なくとも２個の分割電極を並列接続して合成入力電極とし、長方形板の短辺方向に伝搬するλ／２モードの振動を強制に駆動させることで、機械結合係数ｋおよび機械的品質係数Ｑの向上と入力インピーダンスの低減が可能であることが分かる。
【００４５】
【実施例３】
図３（ａ）に示すように、自発分極軸をＺ軸として有するニオブ酸リチウム単結晶をＸ軸のまわりに１２８°回転した回転Ｙ板をそれぞれ長辺方向と結晶のＸ軸が平行になるように長さ３３ｍｍ×幅１２．２ｍｍの短冊状に切り出し、両面に研磨加工による鏡面仕上げを行い、厚み０．５６ｍｍの圧電振動板１２を得た。この圧電振動板１２の片面２箇所に長さ１２ｍｍ×幅１０ｍｍの入力電極１３ａ、１３ｂ、と片面１箇所に長さ２ｍｍ×幅１０ｍｍの出力電極１４を、圧電振動板の裏面に長さ３２ｍｍ×幅１０ｍｍのグランド共通電極１５をそれぞれ銀蒸着にて形成し、圧電トランス（実施例３）を得た。なお、図中の矢印Ｐは分極方向を概念的に示している。
【００４６】
図３（ａ）に示すように、圧電トランスの入力側分割電極１３ａ、１３ｂを入力とし、出力側分割電極１４を出力として、この出力分割電極１４に５〜２００ｋΩの負荷抵抗をそれぞれ接続した。圧電トランスへの入力電圧は関数発生器を用い振幅１０Ｖの正弦波を入力側分割電極に印加し、入力電圧（Ｖ）、入力電流（ｍＡ）、入力電力力率を検出し、出力側分割電極からは出力電圧（Ｖ）を検出した。上記の測定結果より、入力インピーダンス、昇圧比、効率を求めた。また、比較のため、前述の比較例１−１２８Ｙを用いて同様にして試験した。それらの結果を表４に示す。
【表４】

表４より分かる様に、従来の技術である長辺方向に伝搬するλモードを利用した比較例の圧電トランスの場合、その構造のため入力インピーダンスが高く低電圧入力で大電力を出力することが困難であり実用的でない。これに対して、実施例３は５ｋΩ〜１００ｋΩの負荷において効率９１％以上を達成出来、負荷との整合が取れている状態であれば、効率９５％を達成出来ることを確認した。
【００４７】
このように、圧電振動板の片側主面に形成されたグランド電極と、他側主面に形成された３個以上の分割電極を該圧電振動板の結晶座標系のＸ軸方向に交互に配置し、３個の分割電極のうち両側の分割電極を並列接続して入力側分割電極とし、中央の分割電極を出力側分割電極とする構造にすれば、圧電振動板のほぼ全面に入力電極を形成することが可能で、入力インピーダンスを低減することが可能となる。
【００４８】
特に液晶バックライト用冷陰極管インバータの圧電トランスでは高昇圧比と低電圧入力が必要なため入力側電極面積を広くして出力電極面積を狭くすることで、高昇圧比と低電圧入力が実現出来、整合負荷もハイインピーダンス側にシフトし用途にあった圧電トランスを設計することが出来る。
また、各種照明用の熱陰極管点灯用インバータ等では整合負荷が数十Ωと低インピーダンスであるため、トランスの昇圧比は数倍で良い。このため出力電極を複数個並列に接続するか出力電極面積を広くすれば良い。
また、本発明では圧電振動板の幅方向に伝搬するλ／２モードの振動を利用するため、第一の入力電極および第２の入力電極は圧電振動板長辺の約半分まで形成して電極面積を広げることが出来、入力インピーダンスを低減することが可能である。
さらに、出力側分割電極の面積を変更することで容易に最大効率が得られる整合負荷を調整することが可能となる。
【００４９】
【実施例４】
上記実施例３の圧電トランスの入力側分割電極（１次側電極）を入力とし、出力側電極（２次側電極）を出力として、この出力電極に５０ｋΩの負荷を接続した。入力電圧は関数発生器を用い電力増幅器で所定の電圧に増幅した正弦波を入力側分割電極に印加し、入力電圧（Ｖ）、入力電流（ｍＡ）、入力電力力率を検出して入力電力を求め、出力側分割電極からは出力電圧（Ｖ）を検出して出力電力を求めた。
圧電トランスの駆動周波数は圧電トランスの昇圧比が最高となる周波数で測定した。上記の測定結果より、昇圧比、効率を求めた。その結果を表５を得た。
【表５】

表５より分かる様に、入力電力を１７．５Ｗ入力しても効率の低下が無いことが確認された。また、出力電力を１６．９Ｗ取り出すための入力電圧も３９．５Ｖｒｍｓと低くすることが可能であり、低電圧入力でも大電力を出力出来ることが分かる。
【００５０】
【実施例５】
また、圧電振動板を長方形に切り出す際の結晶のＣＵＴ軸と圧電振動の伝搬軸の影響を調査するために、図３（実施例３）と同じ形状の圧電トランスを用いて、自発分極軸をＺ軸として有するニオブ酸リチウム単結晶をＸ軸のまわりに１２８°回転した回転Ｙ板（０、３８、０）からなる圧電トランスを、図４（ｂ）に示すように圧電振動板の長辺と結晶のＸ軸のなす角度をψとして結晶のＺ’軸に対して０〜１８０°の範囲内で回転させ、λ／２モードの機械結合係数ｋの影響を調査した。図６に結晶の座標系（ｘ、ｙ’、ｚ’）のｚ’軸に対して０〜１８０°回転させたλ／２モードの機械結合係数ｋの関係を示す。
図６より、ψ＝０°の時すなわち結晶のＹ軸投影方向と圧電振動の伝搬方向が一致するＣＵＴ軸を選択すれば、結晶のＹ軸投影方向に伝搬するλ／２モードを強制に振動させることが可能で機械結合係数ｋが０．３８と最高になり、高昇圧比と変換効率の向上が可能となることが分かる。
【００５１】
また、自発分極軸をＺ軸として有するニオブ酸リチウム単結晶のＸ軸と該圧電振動板の長辺とが平行になるように切り出した図１（実施例２）と同じ形状の圧電トランスを用いて、図４（ａ）に示すように結晶のＸ軸のまわりに０°￣１８０°の範囲内で回転し、結晶のＹ軸投影方向に伝搬するλ／２モードの回転Ｙ板の回転角と機械結合係数ｋの関係を求めたものを図５に示す。
図５より、ニオブ酸リチウム単結晶板を結晶のＸ軸を中心にθ＝１０°〜６０°もしくはθ＝１０５°〜１７０°の範囲内で回転させた圧電振動板を用い、ることで機械結合係数ｋを０．１５以上にすることが可能であることが分かる。望ましくはθ＝１２５°〜１４５°の範囲内で回転させた圧電振動板を用いることで、機械結合係数を最高とすることが可能となり高昇圧比と変換効率の向上が可能となることがわかる。
【００５２】
【他の実施例】
図１（ａ）に示すように結晶のＸ軸と平行に圧電振動板の長辺を切り出すことで、機械結合係数ｋ、及び機械的品質係数Ｑの大きな短辺に依存するλ／２モードの波を利用することが出来、高電力用途でも圧電トランスの発熱が少なく高効率でかつ高電力を入力しても機械的振動で割れることが少ない圧電トランスを作成することが出来る。
【００５３】
更に、入力電極１３ａ、１３ｂと出力電極１１４ａの面積比を変えることで圧電トランスの昇圧比を簡単に調整することが出来、使用する用途にあった特性の圧電トランスを簡単に作成することが可能となる。
図１の実施例の場合は、裏面にグランド電極１５を設けることにより、グランド側のリード線を一箇所とすることが可能となり、リード線での振動の損失が軽減される。
【００５４】
また、図７は、圧電振動板１２の短辺長さと長辺長さを変化させて圧電振動板１２の外形比を変化させた例（すなわち短辺をＸ軸とした場合）を示している。その他は図３と同様である。この場合でも、上記と同様の電極構造でニオブ酸リチウム単結晶を短冊状に切り出す際に、結晶のＣＵＴ面および圧電振動の伝搬軸を圧電振動の振動モードに対して最適に選び、圧電振動の伝搬方向と結晶のＹ軸投影線を一致させる構造にすれば、同様の効果が得られる。
【００５５】
更に、図８に示すように圧電振動板１２の片側主面に形成されたグランド電極１５と、他側主面に形成された分割電極１３ａ，１３ｂ，１３ｃと分割電極１４ａ，１４ｂとを圧電振動板１２の長辺方向に交互に配置し、３個の分割電極１３ａ、１３ｂ、１３ｃを入力側分割電極又は出力側分割電極とし、他の２個の分割電極１４ａ、１４ｂを出力側分割電極又は入力側分割電極とした多重平面構造とすることで、実施例２と同様に機械結合係数ｋと機械的品質係数Ｑの向上および低入力インピーダンスを実現出来、使用する負荷との整合も分割電極の面積を調整することで容易に実現することが可能となる。
【００５６】
【発明の効果】
本発明によれば、自発分極軸をＺ軸として有するニオブ酸リチウム単結晶の回転Ｙ板を、圧電振動板の長辺もしくは短辺と結晶のＸ軸が平行になるように長方形に切り出した圧電振動板を使用し、該圧電振動板の片側主面に形成した２箇所以上の分割電極を並列接続して入力電極とし１箇所以上の分割電極を出力電極とすることでＹ軸投影方向（例えば圧電振動板の短辺方向）に伝搬するλ／２モードの機械結合係数ｋおよび機械的品質係数Ｑを向上させ、大画面液晶に使用される冷陰極管点灯用インバータや熱陰極管点灯用インバータ等の５Ｗ以上の高電力用途の昇圧用トランスとして使用することが可能であり、高効率な圧電トランスを提供することが出来る。このため消費電力の効率向上とインバータの低背化、小型を実現することが可能である。
また、圧電振動板にニオブ酸リチウム単結晶を利用するため環境に有害な物質が含まれておらず、管理が容易である。
その他にも、圧電トランスは正弦波を出力するためランプの寿命を向上することが可能でありランプ寿命の向上や不要な電磁ノイズの放射が削減できることが期待出来る。
【図面の簡単な説明】
【図１】（ａ）は実施例１にかかる圧電トランスの斜視図、（ｂ）はその横断面図である。
【図２】圧電振動子のＬＣＲ等価回路を示す回路図である。
【図３】（ａ）は実施例１、２にかかる圧電トランスの斜視図、（ｂ）はその横断面図である。
【図４】（ａ）は圧電振動板を結晶の座標軸Ｘ軸を中心に角度θ回転させた斜視図、（ｂ）は圧電振動板を結晶の座標軸Ｚ’軸を中心に角度ψ回転させた斜視図である。
【図５】図６（ａ）の圧電トランスを結晶の座標軸ｘ軸を中心に回転させた回転角θと機械結合係数ｋとの関係を示すグラフである。
【図６】図６（ｂ）の圧電トランスを結晶の座標軸ｚ’軸を中心に回転させた回転角ψと機械結合係数ｋとの関係を示すグラフである。。
【図７】（ａ）は他の実施例にかかる圧電トランスの斜視図、（ｂ）はその縦断面図である。
【図８】（ａ）は他の実施例にかかる圧電トランスの斜視図、（ｂ）はその縦断面図である。
【図９】（ａ）は従来の圧電トランスの斜視図、（ｂ）はその縦断面図である。
【符号の説明】
１２：圧電振動板、１３、１３ａ、１３ｂ、１３ｃ：入力電極、１４、１４ａ、１４ｂ：出力電極、１５、１５ａ、１５ｂ：グランド電極、１６：入力用リード線、１７：出力用リード線、１８、１８ａ、１８ｂ：グランド用リード線、２０：圧電振動の節、２１：圧電振動の変位曲線、２２：圧電振動によりに生じる応力曲線[0001]
[Industrial applications]
The present invention is a hot-cathode tube inverter used for fluorescent lamps and the like, a large-screen liquid crystal television, a notebook computer, a backlight cold-cathode tube inverter for a liquid crystal display used for portable terminals, etc., various high-voltage generators, The present invention relates to a piezoelectric transformer used for an AC adapter and a DC-DC converter used for a negative ion generator, an air purifier, and other various electronic devices.
[0002]
[Prior art]
There are many devices that require a high voltage of several kV or more, such as the voltage conversion transformer used for the AC adapter and the DC-DC converter as described above. At present, electromagnetic transformers are generally used. However, piezoelectric transformers have attracted attention as small, lightweight and solid-state devices, and some of them have been specifically proposed.
[0003]
As the piezoelectric transformer, a ceramic piezoelectric transformer using PZT porcelain is generally used. However, since the mechanical quality factor Q is as small as 3000 to 4000, the characteristic change and power loss due to heat generation of the piezoelectric transformer itself are large, and 5 W In the high-power applications described above, the efficiency has decreased due to heat generation.
For this reason, ceramic piezoelectric transformers using PZT porcelain are used only for applications of 5 W or less, and hot cathode tubes used for cold cathode tube lighting inverters used for applications of 5 W or more and fluorescent lamps of 5 W or more. Inverters, various high voltage generators, AC adapters, and voltage transformers used in DC-DC have employed winding transformers.
[0004]
In addition, a single-plate piezoelectric transformer using a PZT porcelain cannot realize a high step-up ratio due to a small mechanical quality factor Q. Therefore, a laminated piezoelectric transformer having a large difference in capacitance between the drive side and the pickup side. I needed to. However, in the multilayer piezoelectric transformer, the thickness of the piezoelectric transformer is increased due to the multilayer structure, and the height cannot be reduced. Therefore, the advantages of the piezoelectric transformer, such as small size, light weight, and low height, cannot be sufficiently satisfied. In addition, when PZT porcelain is used, Pb, which is a substance harmful to the environment, is contained, so that Pb must be managed.
[0005]
In the case of a winding transformer of 5 W or more, it is necessary to increase the winding ratio in order to obtain a high step-up ratio, it is difficult to reduce the height and size, and the efficiency is 75% to 85% due to heat generation and magnetic flux leakage. %. In addition, since the output voltage waveform is distorted, the luminous efficiency of the cold-cathode tube is reduced, which causes a reduction in the life of the cold-cathode tube.
[0006]
On the other hand, Patent Literatures 1 and 2 below disclose a piezoelectric transformer using a lithium niobate single crystal as a piezoelectric transformer using a Lame mode vibration cut out so that the long side and the short side of the piezoelectric vibrating plate are integral multiples. Has been described. Patent Literatures 3 and 4 below disclose a piezoelectric transformer using a lithium niobate single crystal using a λ / 2 mode or a λ mode that propagates in a long side direction.
[0007]
When a lithium niobate single crystal is used, the mechanical quality factor Q is as large as 10,000 or more as compared with a ceramic piezoelectric transformer such as PZT, and there is no characteristic deterioration or Q reduction due to heat generation when a high power is input. Although it is said that a boost ratio and high efficiency can be realized, there is no description of the efficiency as a piezoelectric transformer at the time of Hi Power input, and there is no measurement result of the efficiency when a load is connected to the output side of the piezoelectric transformer.
[0008]
FIG. 9A shows a configuration diagram of a conventional piezoelectric transformer. In the piezoelectric transformer shown in FIG. 9A, reference numeral 12 denotes a piezoelectric vibrating plate (substrate), which is, for example, 140 cut out of a single crystal of a lithium niobate single crystal plate uniformly polarized in the Z-axis direction. ° Rotating Y-cut plate. The rotating Y plate is cut into a rectangle such that the short side is parallel to the X axis and the long side is parallel to the Y axis projection line. In addition, the input electrode and the output electrode are formed so as to be at one place each.
[0009]
In FIG. 9A, reference numeral 13 denotes an input electrode, which is a vapor-deposited film formed of, for example, a two-layer film of Au / NiCr provided on both surfaces on the left half from the center of the piezoelectric vibrating plate 12. Reference numeral 14 denotes an output electrode, which is formed on both sides of the right half from the center of the piezoelectric vibrating plate 12 by a vapor deposition film of a two-layer Au / NiCr film. Arrow P in the figure conceptually shows the direction of polarization.
[0010]
Now, when an input voltage V1 having a resonance frequency determined by the length in the length direction is applied between the input electrode 13 and the ground electrode 15a from an AC oscillation electrode (not shown), mechanical vibration in the length direction (due to the electrostrictive effect of the piezoelectric material). Basic vibration) occurs (piezoelectric reverse effect). Next, the distortion caused by the vibration is converted into electric energy by the piezoelectric material on the secondary side (piezoelectric positive effect) to obtain an output voltage transformed according to the structure of the piezoelectric transformer. In FIG. 2, since a high voltage V0 is generated between the output electrode 14 and the ground electrode 15b via the piezoelectric transverse effect, if the high voltage V0 is measured by, for example, a high impedance AC voltmeter, the boost ratio (V0 / V1) can be obtained. it can.
[0011]
In this example, the input unit is driven by the piezoelectric lateral effect (that is, the case where the direction of the electric field is orthogonal to the propagation direction of the elastic wave), and the output unit also extracts the output using the lateral effect.
[0012]
Thus, a piezoelectric transformer is a device that converts electricity → machine → electricity and energy. During the operation of the piezoelectric transformer, a standing wave 21 corresponding to the frequency of the applied voltage and a stress 22 generated by the piezoelectric vibration are generated in the longitudinal direction as shown in FIG. 9B. In the figure, the point indicated by 20 is the minimum displacement point, and the point where the stress generated by the piezoelectric vibration is concentrated most is called a node of the vibration. Generally, by supporting this section, high efficiency and high reliability can be maintained.
[0013]
However, conventional piezoelectric transformers using lithium niobate single crystal have high impedance on the input side, so it is necessary to place a choke coil or winding transformer before the piezoelectric transformer and boost the voltage once. It was difficult to reduce the size, weight, and height. On the other hand, hot cathode tube inverters used for fluorescent lamps, etc., backlight cold cathode tube inverters for liquid crystal displays used for large-screen liquid crystal televisions, notebook computers, portable terminals, etc., various high voltage generators, negative ions In piezoelectric transformers used in generators, air purifiers, AC adapters used in various electronic devices, and DC-DC converters, it is necessary to reduce the size and height of the piezoelectric transformer in order to reduce the size of the devices.
[0014]
Further, even if a high power could be input by inserting a winding transformer in the preceding stage, the stress generated by mechanical vibration was concentrated at the node of the vibration, and the piezoelectric transformer sometimes cracked at the node of the vibration. Even in high-power applications, in order to make the piezoelectric transformer hard to crack, it is necessary to increase the thickness of the vibration node where the stress is concentrated or to increase the mechanical strength by widening the substrate.
However, when the thickness of the piezoelectric transformer is increased, the operating impedance is increased. Therefore, it is necessary to insert a winding transformer or the like in the previous stage of the piezoelectric transformer to increase the voltage, and it is not possible to reduce the size and height. In addition, when the width of the substrate is increased, spurious vibration occurs, which causes a reduction in efficiency.
[0015]
In order to reduce the characteristic deterioration due to heat generation with high efficiency even in high power applications, it is desirable to select an appropriate vibration mode having a large mechanical coupling coefficient k and a large mechanical quality coefficient Q. Here, the mechanical coupling coefficient k is the efficiency when a voltage is applied between the electrodes to convert the energy given to the piezoelectric body to ideal mechanical energy, and the mechanical energy given to the piezoelectric body is ideally calculated. This is the efficiency when converting to electrical energy. In addition, when the mechanical quality factor Q is high, deterioration in characteristics and deterioration in efficiency due to self-heating are reduced even when used at high power.
[0016]
[Patent Document 1] JP-A-8-191161
[Patent Document 2] JP-A-7-106660
[Patent Document 3] JP-A-2-249574
[Patent Document 4] Japanese Patent Application Laid-Open No. 4-124886
[0017]
[Problems to be solved by the invention]
The present invention realizes a high-efficiency piezoelectric transformer even at a high power output of 5 W or more in a cold cathode tube lighting inverter unit used for high power applications and various high power lamp lighting inverter units, and has a small size and a low profile. The main task is to provide a piezoelectric transformer.
[0018]
Further, the present invention provides a piezoelectric transformer capable of improving the mechanical coupling coefficient k and the mechanical quality coefficient Q and reducing the input impedance of the piezoelectric transformer so that large power can be output even at a low voltage input based on the above characteristics. Is another task.
[0019]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, when cutting a lithium niobate single crystal into a strip shape, the crystal CUT plane and the propagation axis of the piezoelectric vibration are set with respect to the vibration mode of the piezoelectric vibration. Transverse effect vibration that produces a standing wave of λ / 2 in the Y-axis projection direction of the crystal coordinate system of the piezoelectric diaphragm by connecting two or more input electrodes formed on one side of the piezoelectric diaphragm in parallel, optimally selected The mode is forced to improve the mechanical coupling coefficient k and the mechanical quality factor Q, and large power is output from one or more output electrodes attached to the center of the piezoelectric vibrating plate, so that the vicinity of the matching load of the piezoelectric transformer In this regard, the present inventors have obtained a new finding that a piezoelectric transformer having a high efficiency of 92% or more can be provided even when used at 5 W or more.
[0020]
That is, in the case of a piezoelectric transformer using a lithium niobate single crystal, the spontaneous polarization axis is determined to be the Z-axis, and the CUT plane of the crystal and the CUT of the crystal cut into strips due to the anisotropy of the crystal. The characteristics of the piezoelectric vibration change depending on the axis.
In addition, the efficiency of the piezoelectric transformer depends on the mechanical coupling coefficient k and the mechanical quality factor Q of the piezoelectric vibration, and the higher the mechanical coupling coefficient k and the mechanical quality factor Q, the more the piezoelectric transformer can be used even when used with large power. High efficiency.
[0021]
The piezoelectric transformer of the present invention includes a piezoelectric vibrating plate made of a lithium niobate single crystal plate having a spontaneous polarization axis as a Z axis, and the piezoelectric vibrating plate has a coordinate axis of the crystal of 10 ° to 60 ° around the X axis or The rotating Y plate rotated within the range of 105 ° to 170 ° is rotated so that the long side or the short side is within a range of −40 ° to 40 ° with respect to the X axis of the crystal, and the short side is relative to the long side. And cut out into a rectangular plate so that the angle の formed by the X axis of the crystal is within the range of ψ = 0 ° ± 10 °, and further to the Y axis projection line of the crystal. By utilizing the transverse effect vibration mode in which a standing wave of λ / 2 is generated, a high mechanical coupling coefficient k and a high mechanical quality coefficient Q can be realized, and mechanical vibration can be performed with high efficiency even at a high power input. It is possible to provide a piezoelectric transformer That. Alternatively, the short side may be rotated within 0 ° ± 40 ° with respect to the Y axis and cut into a rectangle.
[0022]
According to the present invention, a CUT capable of reducing the input impedance of a piezoelectric transformer by rotating a lithium niobate single crystal plate around the X-axis of a crystal in the range of θ = 10 ° to 60 ° or θ = 105 ° to 170 ° By cutting out the surface and processing the single crystal wafer to an arbitrary thickness, the input impedance can be controlled, and high power can be output even with a low voltage input.
[0023]
That is, the piezoelectric transformer of the present invention includes a piezoelectric vibrating plate made of a lithium niobate single crystal plate having a spontaneous polarization axis as the Z axis, and the piezoelectric vibrating plate has a rotation Y obtained by rotating the crystal coordinate axis around the X axis. The plate is cut into a rectangle so that the long side or short side is parallel to the X axis of the crystal and the short side or long side is parallel to the projection line of the Y axis of the crystal, and λ / 2 is propagated in the Y axis projection direction. It utilizes the lateral effect vibration mode of the mode. Here, the “Y-axis projection line” refers to a projection line drawn from the y-axis of the (x, y, z) coordinate system of the crystal. Specifically, it refers to a line drawn from the Y-axis for a crystal cut in an arbitrary direction.
[0024]
Here, the thickness of the piezoelectric vibration plate is 0.2 to 3.0 mm, preferably 0.2 to 0.6 mm. The piezoelectric vibrating plate is preferably made of a high dielectric constant lithium niobate single crystal plate rotated by 10 ° to 60 ° or 105 ° to 170 °, preferably 125 ° to 145 ° around the X axis.
[0025]
The piezoelectric vibrating plate has an input electrode and an output electrode on one surface and a ground electrode on the other surface.
That is, in the piezoelectric transformer, two divided electrodes formed on one main surface of the piezoelectric vibration plate are arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibration plate, and a ground electrode is formed on the other main surface. A piezoelectric transformer having a first split electrode of the two split electrodes as an input split electrode and a second split electrode as an output split electrode, wherein the other main surface is In all of the divided electrodes, at least a part of the electrodes is formed at a position on the center line of the short side or the long side of the piezoelectric vibrating plate.
[0026]
Alternatively, the piezoelectric vibrating plate is formed by projecting a ground electrode formed on one main surface of the piezoelectric vibrating plate and three or more divided electrodes formed on the other main surface of the piezoelectric vibrating plate in a Y-axis projection of a crystal coordinate system of the piezoelectric vibrating plate. It is better to arrange the electrodes in the direction and to use the split electrodes on both sides of the three split electrodes as input-side split electrodes or output-side split electrodes, and the central split electrode as the output-side split electrode or input-side split electrode. This makes it possible to arbitrarily adjust the boost ratio, the input impedance, and the output impedance by adjusting the input electrode area and the output electrode area.
[0027]
Also, a piezoelectric transformer in which three or more divided electrodes formed on one main surface of the piezoelectric vibrating plate are arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibrating plate and a ground electrode is formed on the other main surface. In the case of the above, the three or more divided electrodes are composed of input side divided electrodes and output side divided electrodes alternately arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibrating plate, or Two or more of the divided electrodes are connected in parallel to form an input-side divided electrode, or one or more of three or more divided electrodes of the piezoelectric vibrating plate are connected in parallel to output. It is preferable to use side split electrodes.
[0028]
All the divided electrodes formed on the other main surface of the piezoelectric vibrating plate are preferably formed such that at least a part of the electrode extends on a line connecting the centers of both short sides or long sides of the piezoelectric vibrating plate. As a result, a transverse effect vibration mode in which a standing wave of λ / 2 occurs in the Y-axis projection direction of the piezoelectric diaphragm can be efficiently extracted.
[0029]
It is preferable to connect two or more input electrodes provided on one side of the piezoelectric vibrating plate in parallel. Thereby, it is possible to improve the mechanical coupling coefficient k and the mechanical quality coefficient Q in the transverse effect vibration mode in which a standing wave of λ / 2 is generated in the Y-axis projection direction of the piezoelectric diaphragm, and to reduce the resonance impedance. As a result, high power can be output even with a low voltage input, and a piezoelectric transformer with high efficiency, a high step-up ratio, and low input impedance can be realized.
[0030]
The piezoelectric transformer of the present invention has a mechanical quality factor Q of 1000 or more, preferably 4000 or more, and a mechanical coupling coefficient k of 0.2 or more, preferably 0.25 or more. It is possible to achieve a low profile and a high step-up ratio, and even with a high power input of 5 W or more, power loss due to heat generation is small and the efficiency of the piezoelectric transformer can be 92% or more. Further, the piezoelectric transformer of the present invention preferably has an input impedance of 300Ω or less.
[0031]
Embodiment 1
As shown in FIG. 1A, a rotating Y plate obtained by rotating a lithium niobate single crystal having a spontaneous polarization axis as the Z axis by 128 ° around the X axis becomes parallel to the long side direction and the X axis of the crystal. Thus, a rectangular shape having a length of 33 mm and a width of 12.2 mm was cut out, and both surfaces were mirror-finished by polishing to obtain a piezoelectric vibrating plate 12 having a thickness of 0.597 mm. Input electrodes 13a, 13b and output electrodes 14a, 14b each having a length of 12 mm and a width of 10 mm were formed on both surfaces of the piezoelectric vibrating plate 12 by silver deposition, respectively, to obtain a piezoelectric transformer (Example 1-128Y). Note that the arrow P in the figure conceptually indicates the polarization direction.
[0032]
[Comparative Example 1]
As shown in FIG. 9 (a), a rotating Y plate obtained by rotating a lithium niobate single crystal having a spontaneous polarization axis as the Z axis by 128 ° around the X axis is set so that the short side direction is parallel to the X axis of the crystal. The piezoelectric vibrating plate 12 having a thickness of 0.612 mm was obtained by cutting it into a piece having a length of 33 mm and a width of 12.2 mm. Input electrodes 13 and 15a and output electrodes 14 and 15b each having a length of 12 mm and a width of 10 mm were formed on both surfaces of the piezoelectric vibrating plate 12 by silver evaporation to obtain a piezoelectric transformer (Comparative Example 1-128Y).
[0033]
When the frequency characteristics of the piezoelectric transformers of Example 1-128Y and Comparative Example 1-128Y were measured by ADVANTEST NETWORK ANALYZER, very sharp resonance was observed at around 185 kHz and around 235 kHz.
[0034]
The resonance point around 185 kHz of Example 1-128Y and Comparative Example 1-128Y is a λ-mode piezoelectric vibration in which a standing wave of one wavelength (λ) is generated in the long side direction of the piezoelectric vibrating plate. It was at a quarter of the long side of the piezoelectric diaphragm. The resonance point near 235 kHz is a λ / 2 mode piezoelectric vibration in which a standing wave of 波長 wavelength (λ / 2) is generated in the short side direction of the piezoelectric vibration plate. It was at half of the short side.
When supporting a piezoelectric transformer, the value of the mechanical quality factor Q greatly changes depending on the fixing method and the fixing position. Therefore, use a spring-type probe to avoid the influence of the measurement, and compare at the position where the resonance is sharpest. investigated.
[0035]
Table 1 shows the measurement results of LCR equivalent circuits of λ-mode vibration propagating in the long side direction of the piezoelectric vibrating plate of Example 1-128Y and Comparative Example 1-128Y. An LCR equivalent circuit of the piezoelectric vibrator is represented as shown in FIG. 2, and a mechanical quality coefficient Q and a mechanical coupling coefficient k are obtained from the parameters of the equivalent circuit. In FIG. 2, R1 represents a series resistance, C1 represents a series capacitance, C2 represents a parallel capacitance, and L1 represents a series inductance.
[0036]
[Table 1]

From Table 1, when using the λ-mode vibration propagating in the long side direction on the substrate of the 128 rotation Y plate, the mechanical coupling coefficient k of Example 1-128Y is 0.26 and 0.29 of Comparative Example 1-128Y. Although it is worse, the mechanical quality factor Q of 18386 of Example 1-128Y is better than 12407 of Comparative Example 1-128Y.
[0037]
Since the step-up ratio is determined by the mechanical coupling coefficient k and the mechanical quality coefficient Q, it is desirable that both the mechanical quality coefficient Q and the mechanical coupling coefficient k be large. When modal vibration is used, the highest values of k and Q cannot be obtained.
[0038]
Since the efficiency of the piezoelectric transformer depends on the mechanical coupling coefficient k, and the efficiency at high power depends on the mechanical quality factor Q, the λ-mode vibration propagated in the long side direction by the 128-rotation Y-plate piezoelectric diaphragm is used. In this case, it can be seen that there is not much difference between Example 1 and Comparative Example 1.
[0039]
Table 2 shows the measurement results of the LCR equivalent circuits of the λ / 2 mode vibration propagating in the short side direction in Example 1-128Y and Comparative Example 1-128Y.
[Table 2]

From Table 2, when the λ / 2 mode generated in the short side direction on the substrate of the 128 rotation Y plate is used for the piezoelectric transformer, the mechanical coupling coefficient k of Example 1-128Y is 0.28 and that of Comparative Example 1-128Y. This is better than 0.16, and it can be seen that the mechanical quality factor Q is not much different between Example 1-128Y and Comparative Example 1-128Y. Therefore, when using a λ / 2 mode generated in the short side direction on a 128-rotation Y-plate substrate in a piezoelectric transformer, it is desirable to cut out the long side in parallel with the X axis of the crystal as shown in FIG. I understand.
[0040]
Further, since the λ / 2 mode vibration propagating in the short side direction is used, the stress generated by the mechanical vibration can be dispersed in the long side direction of the substrate, and it can be seen that it is hard to crack even in high power applications.
[0041]
From these results, a 128-rotation Y plate having a large mechanical coupling coefficient k and a large mechanical quality factor Q was used, and the long side of the piezoelectric vibration plate was cut out in parallel with the X axis of the crystal as shown in FIG. By using the λ / 2 mode vibration that propagates in the short side direction, a piezoelectric transformer that generates less heat from the piezoelectric transformer even in high power applications and that is less likely to break due to mechanical vibration even when high power is input. Can be created.
[0042]
Embodiment 2
As shown in FIG. 3A, a rotating Y plate obtained by rotating a single crystal of lithium niobate having a spontaneous polarization axis as a Z axis by 128 ° around the X axis becomes parallel to the long side direction and the X axis of the crystal. Thus, a rectangular shape having a length of 33.0 mm and a width of 12.2 mm was cut out, and mirror polishing was performed on both sides to obtain a piezoelectric vibrating plate 12 having a thickness of 0.56 mm. Input electrodes 13a and 13b having a length of 12 mm and a width of 10 mm are provided at two places on one side of the piezoelectric vibrating plate 12, and an output electrode 14 having a length of 5 mm and a width of 10 mm is provided at one place on one side. Each of the ground common electrodes 15 having a width of 10 mm was formed by silver deposition to obtain a piezoelectric transformer (Example 1). Note that the arrow P in the figure conceptually indicates the polarization direction.
In FIG. 3A, 16 is an input lead, 17 is an output lead, and 18 is a common ground lead. In FIG. 3B, reference numeral 20 denotes a node of the vibration, reference numeral 21 denotes a displacement of the piezoelectric vibration, and reference numeral 22 denotes a stress generated by the piezoelectric vibration.
[0043]
The resonance frequency fr between the input electrode and the common ground electrode when the input electrode 13a and the input electrode 13b of the piezoelectric transformer of the second embodiment are connected in parallel to form a composite input electrode and when only the input electrode 13a is an input electrode, Table 3 shows the results of measuring the anti-resonance frequency fa, the impedance Zr at the resonance frequency, the mechanical quality factor Q, and the mechanical coupling factor k with an impedance analyzer.
The input electrode 1 terminal in Table 3 is a measured value of the frequency characteristic between the input electrode 13a and the ground common electrode 15, and the input electrode parallel connection in Table 3 indicates that the combined electrode and the ground in which the input electrodes 13a and 13b are connected in parallel are connected to the ground. The frequency characteristics between the electrodes 15 are measured.
[0044]
Note that the measured resonance frequency is a frequency characteristic of a transverse effect vibration mode in which a standing wave of λ / 2 is generated in the Y-axis projection direction of the piezoelectric diaphragm.
As can be seen from Table 3, it was confirmed that by connecting the input electrodes in parallel, the resonance point shifted to the low frequency side, the bandwidth between the resonance point and the anti-resonance point was widened, and the impedance at the resonance point was also reduced. Also, it was confirmed that the mechanical coupling coefficient k and the mechanical quality coefficient Q could be improved by connecting the input electrodes in parallel.
[Table 3]

As described above, by connecting at least two of the three divided electrodes in parallel to form a composite input electrode and forcibly driving the λ / 2 mode vibration propagating in the short side direction of the rectangular plate, It can be seen that the mechanical coupling coefficient k and the mechanical quality coefficient Q can be improved and the input impedance can be reduced.
[0045]
Embodiment 3
As shown in FIG. 3A, a rotating Y plate obtained by rotating a single crystal of lithium niobate having a spontaneous polarization axis as a Z axis by 128 ° around the X axis becomes parallel to the long side direction and the X axis of the crystal. Thus, a rectangular shape having a length of 33 mm × a width of 12.2 mm was cut out, and both surfaces were mirror-finished by polishing to obtain a piezoelectric vibrating plate 12 having a thickness of 0.56 mm. Input electrodes 13a and 13b having a length of 12 mm and a width of 10 mm are provided at two places on one side of the piezoelectric vibrating plate 12, and an output electrode 14 having a length of 2 mm and a width of 10 mm is provided on one side of the piezoelectric vibrating plate. Each of the ground common electrodes 15 having a width of 10 mm was formed by silver evaporation to obtain a piezoelectric transformer (Example 3). Note that the arrow P in the figure conceptually indicates the polarization direction.
[0046]
As shown in FIG. 3 (a), the input split electrodes 13a and 13b of the piezoelectric transformer were used as inputs, the output split electrode 14 was used as an output, and a load resistance of 5 to 200 kΩ was connected to the output split electrode 14. As for the input voltage to the piezoelectric transformer, a sine wave having an amplitude of 10 V is applied to the input-side split electrode using a function generator, and the input voltage (V), input current (mA), and input power power factor are detected, and the output-side split electrode is detected. , The output voltage (V) was detected. From the above measurement results, the input impedance, the boost ratio, and the efficiency were obtained. For comparison, a similar test was performed using Comparative Example 1-128Y described above. Table 4 shows the results.
[Table 4]

As can be seen from Table 4, in the case of the piezoelectric transformer of the comparative example using the λ mode propagating in the long side direction, which is a conventional technique, the input impedance is high due to its structure, so that large power can be output with low voltage input. Difficult and impractical. On the other hand, in Example 3, it was confirmed that an efficiency of 91% or more could be achieved with a load of 5 kΩ to 100 kΩ, and an efficiency of 95% could be achieved if the load was matched.
[0047]
As described above, the ground electrode formed on one main surface of the piezoelectric vibrating plate and the three or more divided electrodes formed on the other main surface are alternately arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibrating plate. If the split electrodes on both sides of the three split electrodes are connected in parallel to form an input-side split electrode, and the central split electrode is used as an output-side split electrode, the input electrodes can be formed on almost the entire surface of the piezoelectric vibrating plate. And the input impedance can be reduced.
[0048]
In particular, a high voltage step-up ratio and a low voltage input are necessary for the piezoelectric transformer of a cold cathode tube inverter for liquid crystal backlights, so by increasing the input electrode area and narrowing the output electrode area, a high voltage step-up ratio and a low voltage input are realized. As a result, the matching load is shifted to the high impedance side, and a piezoelectric transformer suitable for the application can be designed.
Further, in a hot-cathode tube lighting inverter or the like for various illuminations, since the matching load has a low impedance of several tens Ω, the step-up ratio of the transformer may be several times. Therefore, a plurality of output electrodes may be connected in parallel or the output electrode area may be increased.
Further, in the present invention, since the λ / 2 mode vibration propagating in the width direction of the piezoelectric vibrating plate is used, the first input electrode and the second input electrode are formed up to about half of the long side of the piezoelectric vibrating plate. The area can be increased, and the input impedance can be reduced.
Further, by changing the area of the output-side split electrode, it is possible to easily adjust the matching load at which the maximum efficiency is obtained.
[0049]
Embodiment 4
The input side split electrode (primary side electrode) of the piezoelectric transformer of the third embodiment was used as an input, the output side electrode (secondary side electrode) was used as an output, and a load of 50 kΩ was connected to this output electrode. As for the input voltage, a sine wave amplified to a predetermined voltage by a power amplifier using a function generator is applied to the input-side split electrode, and the input voltage (V), the input current (mA), and the input power power factor are detected, and the input power is detected. , And the output voltage (V) was detected from the output-side split electrode to determine the output power.
The driving frequency of the piezoelectric transformer was measured at a frequency at which the step-up ratio of the piezoelectric transformer was highest. From the above measurement results, the boost ratio and the efficiency were obtained. The results are shown in Table 5.
[Table 5]

As can be seen from Table 5, it was confirmed that the efficiency did not decrease even when the input power was input at 17.5 W. Also, the input voltage for extracting 16.9 W of output power can be reduced to 39.5 Vrms, and it can be seen that large power can be output even with a low voltage input.
[0050]
Embodiment 5
Further, in order to investigate the influence of the CUT axis of the crystal and the propagation axis of the piezoelectric vibration when the piezoelectric vibrating plate is cut into a rectangle, the spontaneous polarization axis is determined using a piezoelectric transformer having the same shape as that of FIG. 3 (Example 3). As shown in FIG. 4 (b), a piezoelectric transformer composed of a rotating Y plate (0, 38, 0) obtained by rotating a lithium niobate single crystal having a Z axis by 128 ° around the X axis is used. And the angle formed by the X axis of the crystal and ψ was rotated within the range of 0 to 180 ° with respect to the Z ′ axis of the crystal, and the effect of the mechanical coupling coefficient k in the λ / 2 mode was investigated. FIG. 6 shows the relationship of the mechanical coupling coefficient k in the λ / 2 mode rotated by 0 to 180 ° with respect to the z ′ axis of the crystal coordinate system (x, y ′, z ′).
From FIG. 6, when 時 = 0 °, that is, when the CUT axis in which the crystal Y-axis projection direction and the piezoelectric vibration propagation direction are selected is selected, the λ / 2 mode propagating in the crystal Y-axis projection direction is forcibly vibrated. It can be seen that the mechanical coupling coefficient k is 0.38, which is the highest, and that a high step-up ratio and an improvement in conversion efficiency can be achieved.
[0051]
Further, a piezoelectric transformer having the same shape as that of FIG. 1 (Example 2) cut out so that the X-axis of a lithium niobate single crystal having a spontaneous polarization axis as a Z-axis and the long side of the piezoelectric vibrating plate are parallel is used. As shown in FIG. 4 (a), the rotation angle of the λ / 2 mode rotating Y plate that rotates within the range of 0 ° ￣180 ° around the X axis of the crystal and propagates in the Y axis projection direction of the crystal. FIG. 5 shows the relationship between the relationship and the mechanical coupling coefficient k.
As shown in FIG. 5, a mechanical structure is obtained by using a piezoelectric vibrating plate in which a lithium niobate single crystal plate is rotated around the X axis of the crystal in the range of θ = 10 ° to 60 ° or θ = 105 ° to 170 °. It is understood that the coupling coefficient k can be set to 0.15 or more. Desirably, by using a piezoelectric vibrating plate rotated within the range of θ = 125 ° to 145 °, the mechanical coupling coefficient can be maximized, and the high step-up ratio and the conversion efficiency can be improved. .
[0052]
[Other embodiments]
By cutting out the long side of the piezoelectric vibrating plate in parallel with the X axis of the crystal as shown in FIG. 1A, the λ / 2 mode in which the mechanical coupling coefficient k and the mechanical quality coefficient Q depend on the large short side is determined. Waves can be used, and a piezoelectric transformer can be produced which has a small amount of heat generation of the piezoelectric transformer even in a high-power application, is highly efficient, and is less likely to be broken by mechanical vibration even when high power is input.
[0053]
Further, the step-up ratio of the piezoelectric transformer can be easily adjusted by changing the area ratio between the input electrodes 13a and 13b and the output electrode 114a, and a piezoelectric transformer having characteristics suitable for the intended use can be easily created. It becomes.
In the case of the embodiment shown in FIG. 1, the ground electrode 15 is provided on the back surface, so that the ground-side lead wire can be provided at one location, and vibration loss in the lead wire is reduced.
[0054]
FIG. 7 shows an example in which the outer shape ratio of the piezoelectric vibrating plate 12 is changed by changing the short side length and the long side length of the piezoelectric vibrating plate 12 (that is, when the short side is the X axis). . Others are the same as FIG. Even in this case, when the lithium niobate single crystal is cut into strips with the same electrode structure as described above, the CUT plane of the crystal and the propagation axis of the piezoelectric vibration are optimally selected for the vibration mode of the piezoelectric vibration, and A similar effect can be obtained by adopting a structure in which the propagation direction and the Y-axis projection line of the crystal coincide.
[0055]
Further, as shown in FIG. 8, the ground electrode 15 formed on one main surface of the piezoelectric vibration plate 12 and the divided electrodes 13a, 13b, 13c and the divided electrodes 14a, 14b formed on the other main surface are subjected to piezoelectric vibration. The three divided electrodes 13a, 13b, and 13c are alternately arranged in the long side direction of the plate 12, and the three divided electrodes 13a, 13b, and 13c are used as input-side divided electrodes or output-side divided electrodes, and the other two divided electrodes 14a and 14b are used as output-side divided electrodes or By adopting a multi-planar structure with the input-side split electrodes, the mechanical coupling coefficient k and the mechanical quality factor Q can be improved and a low input impedance can be realized as in the second embodiment. It can be easily realized by adjusting the area.
[0056]
【The invention's effect】
According to the present invention, a piezoelectric Y is obtained by cutting a rotating Y plate of lithium niobate single crystal having a spontaneous polarization axis as a Z axis into a rectangle such that the X axis of the crystal is parallel to the long or short side of the piezoelectric vibrating plate. Using a diaphragm, two or more divided electrodes formed on one main surface of one side of the piezoelectric diaphragm are connected in parallel, and an input electrode is used as one input electrode and one or more divided electrodes are used as an output electrode. Inverter for lighting a cold cathode tube or lighting a hot cathode tube used in a large-screen liquid crystal by improving the mechanical coupling coefficient k and the mechanical quality coefficient Q of the λ / 2 mode propagating in the short side direction of the piezoelectric vibrating plate). And the like, and can be used as a step-up transformer for high power applications of 5 W or more, and a highly efficient piezoelectric transformer can be provided. For this reason, it is possible to improve the efficiency of power consumption, to reduce the height of the inverter, and to reduce the size.
Further, since lithium niobate single crystal is used for the piezoelectric vibrating plate, it does not contain substances harmful to the environment, and is easy to manage.
In addition, since the piezoelectric transformer outputs a sine wave, the life of the lamp can be improved, and it is expected that the life of the lamp can be improved and unnecessary electromagnetic noise can be reduced.
[Brief description of the drawings]
FIG. 1A is a perspective view of a piezoelectric transformer according to a first embodiment, and FIG. 1B is a cross-sectional view thereof.
FIG. 2 is a circuit diagram showing an LCR equivalent circuit of the piezoelectric vibrator.
FIG. 3A is a perspective view of a piezoelectric transformer according to Examples 1 and 2, and FIG. 3B is a cross-sectional view thereof.
4A is a perspective view in which the piezoelectric vibrating plate is rotated by an angle θ about the crystal coordinate axis X axis, and FIG. 4B is a perspective view in which the piezoelectric vibrating plate is rotated by an angle に about the crystal coordinate axis Z ′ axis. It is a perspective view.
FIG. 5 is a graph showing a relationship between a mechanical coupling coefficient k and a rotation angle θ obtained by rotating the piezoelectric transformer of FIG. 6A around a coordinate axis x of a crystal.
FIG. 6 is a graph showing a relationship between a mechanical coupling coefficient k and a rotation angle た obtained by rotating the piezoelectric transformer of FIG. 6B around a crystal coordinate axis z ′ axis. .
FIG. 7A is a perspective view of a piezoelectric transformer according to another embodiment, and FIG. 7B is a longitudinal sectional view thereof.
FIG. 8A is a perspective view of a piezoelectric transformer according to another embodiment, and FIG. 8B is a longitudinal sectional view thereof.
9A is a perspective view of a conventional piezoelectric transformer, and FIG. 9B is a longitudinal sectional view thereof.
[Explanation of symbols]
12: piezoelectric vibration plate, 13, 13a, 13b, 13c: input electrode, 14, 14a, 14b: output electrode, 15, 15a, 15b: ground electrode, 16: input lead wire, 17: output lead wire, 18 , 18a, 18b: lead wire for ground, 20: node of piezoelectric vibration, 21: displacement curve of piezoelectric vibration, 22: stress curve generated by piezoelectric vibration

Claims (11)

A piezoelectric vibrating plate comprising a lithium niobate single crystal plate having a spontaneous polarization axis as a Z-axis; the piezoelectric vibrating plate comprising a rotating Y-plate obtained by rotating a coordinate axis of a crystal around an X-axis; The angle す between the long side or the short side and the X axis of the crystal when cutting into a rectangular plate is within the range of ψ = 0 ± 40 °, and the rectangular plate is cut out within this range and the Y axis projection direction of the rectangular plate Wherein a transverse effect vibration mode in which a standing wave of λ / 2 is generated is used. 2. The piezoelectric transformer according to claim 1, wherein an input electrode and an output electrode are provided on one surface of the piezoelectric vibration plate, and a ground electrode is provided on the other surface. 3. The piezoelectric transformer according to claim 1, wherein the thickness of the piezoelectric vibrating plate is 0.2 to 3.0 mm. The piezoelectric transformer according to claim 1, wherein the piezoelectric vibrating plate is a high dielectric constant lithium niobate single crystal plate rotated by 10 ° to 60 ° or 105 ° to 170 ° around the X axis. The piezoelectric transformer according to any one of claims 1 to 3, wherein a mechanical quality factor Q of the piezoelectric vibrating plate on the input electrode side is 1000 or more, and a mechanical coupling coefficient k is 0.2 or more. A piezoelectric transformer in which two divided electrodes formed on one main surface of the piezoelectric vibration plate are arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibration plate, and a ground electrode is formed on the other main surface. A piezoelectric transformer in which a first divided electrode of the two divided electrodes is used as an input-side divided electrode and a second divided electrode is used as an output-side divided electrode. The piezoelectric transformer according to claim 2, wherein at least a part of the electrode is formed at a position on a center line of a short side or a long side of the piezoelectric diaphragm. A piezoelectric transformer in which three divided electrodes formed on one main surface of the piezoelectric vibrating plate are arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibrating plate, and a ground electrode is formed on the other main surface. Of the three divided electrodes, the divided electrodes on both sides are defined as input-side divided electrodes or output-side divided electrodes, the central divided electrode is defined as the output-side divided electrode or the input-side divided electrode, and all divisions arranged on one main surface 3. The piezoelectric transformer according to claim 2, wherein at least a part of the electrode is formed at a position on a center line of a short side or a long side of the piezoelectric diaphragm. A piezoelectric transformer in which three or more divided electrodes formed on one main surface of the piezoelectric vibrating plate are arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibrating plate, and a ground electrode is formed on the other main surface. 3. The method according to claim 2, wherein the three or more divided electrodes are composed of input-side divided electrodes and output-side divided electrodes alternately arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibrating plate. 4. The piezoelectric transformer according to claim 1. A piezoelectric transformer in which three or more divided electrodes formed on one main surface of the piezoelectric vibrating plate are arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibrating plate, and a ground electrode is formed on the other main surface. The piezoelectric transformer according to claim 2, wherein two or more of the three or more divided electrodes are connected in parallel to form an input-side divided electrode. A piezoelectric transformer in which three or more divided electrodes formed on one main surface of the piezoelectric vibrating plate are arranged in the X-axis direction of the crystal coordinate system of the piezoelectric vibrating plate, and a ground electrode is formed on the other main surface. 3. The piezoelectric transformer according to claim 2, wherein two or more divided electrodes of the three or more divided electrodes of the piezoelectric diaphragm are connected in parallel to form an output-side divided electrode. The piezoelectric transformer according to any one of claims 1 to 10, wherein an input impedance is 300Ω or less.

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