JP3616930B2

JP3616930B2 - Piezoelectric transformer and adjusting method of braking capacity value thereof

Info

Publication number: JP3616930B2
Application number: JP00118795A
Authority: JP
Inventors: 克典熊坂; 太志塩谷; 僖良中村
Original assignee: NEC Tokin Corp
Current assignee: Tokin Corp
Priority date: 1995-01-09
Filing date: 1995-01-09
Publication date: 2005-02-02
Anticipated expiration: 2020-02-02
Also published as: JPH08191161A

Description

【０００１】
【産業上の利用分野】
本発明は、電子式複写機や静電式空気清浄器等に用いられる直流高電圧電源や、液晶ディスプレー用バックライト点灯用のインバータ電源に用いられる圧電トランスに関し、特に負荷インピーダンスの異なる用途にも容易に適用可能な圧電トランスに関する。
【０００２】
【従来の技術】
図６は従来の圧電トランスの構造の概略を示す斜視図である。図６において、圧電振動子矩形板１には長さ方向のおよそ半分の部分に厚さ方向で相対向する電極２及び電極３が形成され、電極２及び電極３が形成された部分から遠い方の圧電振動子矩形板の端面に電極４が形成されている。尚、図中白抜き矢印は分極方向を示す。
【０００３】
図７は従来の圧電トランスの動作原理の説明図であり、図７（ａ）は圧電振動子矩形板の断面図、図７（ｂ）は圧電振動子矩形板が長さ方向振動の１波長共振モードで振動している場合の変位分布であり、図７（ｃ）はその時の歪分布を示している。図７（ａ）において、電極３をアース端子とし、電極２に圧電振動子矩形板の長さ方向振動の１波長共振モードの共振周波数に等しい周波数の電圧を印加すると圧電振動子矩形板１は、図７（ｂ），（ｃ）に示すように振動する。この時、電極３と端面電極４との間には圧電効果により電圧を発生する。
【０００４】
圧電トランスの電気的な等価回路は図８のように表わされる。図８（ａ）は、それぞれの変成比φ１及びφ２の１次側及び２次側の電気−機械変換の変成器を含む場合であり、ｍ，ｓ，ｒは、それぞれ、機械振動系の等価質量、等価スティフネス及び等価抵抗である。また、Ｃｄ１及びＣｄ２は、それぞれ、１次側及び２次側の制動容量である。更に、ＲＬは負荷抵抗である。図８（ｂ）は図８（ａ）の回路を１次側から見た場合の等価回路である。図８（ｂ）において、等価回路の各定数は次式で与えられる。
【０００５】
Ｌ＝ｍ／φ１ ^２，Ｃ＝φ１ ^２／ｓ，Ｒ＝ｒ／φ１ ^２
Ｃｄ２ ′＝Ａ１ ^２／Ａ２ ^２・Ｃｄ２，ＲＬ ′＝Ａ２ ^２／Ａ１ ^２・ＲＬ
図８の（ｂ）の等価回路における等価直列インダクタンスＬ、等価直列キャパシタンスＣ、２次側の制動容量Ｃｄ２ ′の直列回路の共振周波数で励振すると、等価直列インダクタンスＬの端子電圧と等価直列キャパシタンスＣと２次側の制動容量Ｃｄ２ ′の直列接続した合計のキャパシタンスの端子には、（１）式で与えられる振幅の極性の逆の出力電圧が発生する。
【０００６】
ＶＬ＝−Ｖｃ＝Ｑｍ・Ｖ１ …（１）
ここで、Ｑｍは直列共振回路のＱであり、Ｖ１は入力電圧である。
【０００７】
したがって、圧電トランスの出力電圧は（１）式で表わされる入力電圧のＱｍ倍の電圧が、等価直列キャパシタンスＣと２次側の制動容量Ｃｄ２ ′とで分圧された電圧となる。したがって、高い出力電圧を得るためには、（２）式で表される２次側の容量比γ２の値が小さいことが要求される。
【０００８】
γ２＝Ｃｄ２ ′／Ｃ …（２）
一方、圧電トランスに負荷抵抗ＲＬを接続した場合、負荷抵抗ＲＬにより、実効的な入力電圧Ｑｍの値が低下し、負荷抵抗ＲＬが小さくなると出力電圧が急激に低下する。更に、圧電トランスの効率は、負荷抵抗ＲＬの値が２次側の制動容量Ｃｄ２の共振周波数でのインピーダンス１／（ωｒ・Ｃｄ２）に等しい時に最大になることが知られている。
【０００９】
したがって、圧電トランスが使用される負荷抵抗の条件により、必要な出力電圧と効率の両方を満足させる条件を求める必要がある。
【００１０】
しかし、図６及び図７に示した従来の圧電トランスにおいて、結合振動の無い長さ振動モードで励振しようとした場合、幅と長さの比を４倍以上にする必要があり、２次側の電極間距離が大きくなり、制動容量Ｃｄ２の値が小さくなる。したがって、図６のタイプの圧電トランスでは、負荷抵抗ＲＬが大きい時に、出力電圧が大きくなり、効率も高くなる。一方、この圧電トランスの負荷抵抗ＲＬが小さいときは、出力電圧と効率が大幅に低下する。
【００１１】
図６に示した従来の圧電トランスの構造において、２次側の制動容量Ｃｄ２の値を大きくしようとすると、２次側の電極間距離を短くするか、圧電振動子矩形板の厚さを厚くする必要がある。しかし、圧電振動子矩形板の厚さを厚くすることは、１次側の制動容量Ｃｄ１の値が小さくなり、出力電圧の低下を招くことになり、２次側の電極間距離を短くすることは、圧電振動子矩形板の幅を小さくしないと結合振動を生じさせることになり、幅を小さくするとまた２次側の制動容量Ｃｄ２が小さくなり、設計の自由度は極めて狭いものであった。
【００１２】
また、圧電トランスの実用化を考えた場合は、振動子をパッケージ等に支持して使うのが一般的だが、図６及び図７に示した従来の圧電トランスでは、支持により特性が大幅に低下し、仮に支持を行ったとしても振動子の振動により特性が劣化してしまい信頼性が悪いという欠点があった。
【００１３】
【発明が解決しようとする課題】
本発明の目的は以上に示した従来の圧電トランスの欠点を除去し、しかも、ニオブ酸リチウム単結晶圧電振動子矩形板の寸法、電極寸法を変化させることにより、広い範囲の負荷抵抗の変化に容易に対応可能にすること、更に支持による特性の劣化の低減し、信頼性にも優れた圧電トランスを提供することを目的としている。
【００１４】
【課題を解決するための手段】
請求項１記載の発明によれば、自発分極方向を座標系のＺ軸と平行にした場合において、前記座標系のＸ軸のまわりに１２０〜１７０°回転した座標系（Ｘ，Ｙ′，Ｚ′）を更にそのＺ′軸のまわりに−２０〜２０°回転した座標系（Ｘ′，Ｙ″，Ｚ′）のＸ′軸及びＺ′軸に対して、側面が平行になるように切り出されたニオブ酸リチウム圧電単結晶から成る圧電振動子矩形板を有し、該圧電振動子矩形板は、正方形板を１単位として少なくとも１単位の前記正方形板から構成されると共に前記正方形板の四隅が振動の節となるラーメモード振動を行うものであり、前記圧電振動子矩形板の長手方向の一端面からおよそ前記圧電振動子矩形板の長さの２分の１の領域に、前記圧電振動子矩形板の厚さ方向で相対向する第１側の対向電極を形成し、少なくとも前記圧電振動子矩形板の前記長手方向の他端面、或いは前記圧電振動子矩形板の上下面の内の少なくとも一方の面の前記他端面近傍に第２側の電極を形成し、前記第１側の対向電極を１次側電極、前記第２側の電極を２次側電極としたことを特徴とする圧電トランスが得られる。
【００１５】
請求項２記載の発明によれば、前記上下面内の少なくとも一方の面の前記他端面近傍に形成された第２側の電極１４は、前記他端面から前記圧電振動子矩形板の長さの４分の１以内の領域に形成されていることを特徴とする請求項１記載の圧電トランスが得られる。
【００１６】
請求項３記載の発明によれば、自発分極方向を座標系のＺ軸と平行にした場合において、前記座標系のＸ軸のまわりに１２０〜１７０°回転した座標系（Ｘ，Ｙ′，Ｚ′）を更にそのＺ′軸のまわりに−２０〜２０°回転した座標系（Ｘ′，Ｙ″，Ｚ′）のＸ′軸及びＺ′軸に対して、側面が平行になるように切り出されたニオブ酸リチウム圧電単結晶から成る圧電振動子矩形板を有し、該圧電振動子矩形板は、正方形板を３枚長さ方向に連ねた長方形板を１単位として少なくとも１単位の前記長方形板から構成されると共に前記長方形板の四隅が振動の節となるラーメモード振動を行うものであり、前記長方形板を構成する前記正方形板のそれぞれに電気的に独立した前記圧電振動子矩形板の厚さ方向で相対向する対向電極を形成し、該対向電極の内、前記長方形板の両側の対向電極を１次側電極とし、前記長方形板の中央の対向電極を２次側電極としたことを特徴とする圧電トランスが得られる。
【００１７】
請求項４記載の発明によれば、自発分極方向を座標系のＺ軸と平行にした場合において、前記座標系のＸ軸のまわりに１２０〜１７０°回転した座標系（Ｘ，Ｙ′，Ｚ′）を更にそのＺ′軸のまわりに−２０〜２０°回転した座標系（Ｘ′，Ｙ″，Ｚ′）のＸ′軸及びＺ′軸に対して、側面が平行になるように切り出されたニオブ酸リチウム圧電単結晶から成る圧電振動子矩形板を有し、該圧電振動子矩形板は、正方形板を３枚長さ方向に連ねた長方形板を１単位として少なくとも１単位の前記長方形板から構成されると共に前記長方形板の四隅が振動の節となるラーメモード振動を行うものであり、前記長方形板を構成する前記正方形板のそれぞれに電気的に独立した前記圧電振動子矩形板の厚さ方向で相対向する対向電極を形成し、該対向電極の内、前記長方形板の両側の対向電極を１次側電極とし、残りの中央の対向電極の少なくとも１つと前記両側の対向電極の内の一方の対向電極とを２次側電極としたことを特徴とする圧電トランスが得られる。
【００１８】
請求項５記載の発明によれば、前記１次側電極、前記２次側電極以外に帰還用の電極が前記圧電振動子矩形板に形成されていることを特徴とする請求項１乃至請求項４記載の圧電トランスが得られる。
【００１９】
請求項６記載の発明によれば、請求項１乃至請求項５記載の圧電トランスにおいて、前記圧電振動子矩形板の厚さと前記２次側電極の寸法の内、少なくとも一方を変化させることにより前記圧電振動子矩形板の１次側及び２次側の制動容量値を調整することを特徴とする圧電トランスの制動容量値の調整方法が得られる。
【００２０】
【実施例】
図１は請求項１記載の発明の圧電トランスの一実施例の構造の概略を示す斜視図であり、ニオブ酸リチウム単結晶から成る圧電振動子矩形板１１の長手方向の一端面からおよそ圧電振動子矩形板１１の長さの２分の１の領域のほぼ全面に、圧電振動子矩形板１１の厚さ方向で相対向する第１側の対向電極１２及び対向電極１３を形成し、また、圧電振動子矩形板１１の長手方向の他端面に第２側の電極１４が形成されている。この圧電振動子矩形板１１を構成するニオブ酸リチウム圧電単結晶は、自発分極方向を座標系のＺ軸と平行にした場合において、この座標系のＸ軸のまわりに１２０〜１７０°回転した座標系（Ｘ，Ｙ′，Ｚ′）を更にそのＺ′軸のまわりに−２０〜２０°回転した座標系（Ｘ′，Ｙ″，Ｚ′）のＸ′軸及びＺ′軸に対して、側面が平行になるように切り出されたものである。また、この圧電振動子矩形板１１は、上述のニオブ酸リチウム圧電単結晶の正方形板を１単位として少なくとも１単位（本実施例の場合１単位）を有しており、上述の正方形板の四隅が振動の節となるラーメモードを行うものである。図１で白抜き矢印はニオブ酸リチウム圧電単結晶の自発分極Ｚ軸である。また図１において、第１側の対向電極１２，１３を１次側電極として、圧電振動子矩形板１１の四隅が振動しないがラーメモードの共振周波数にほぼ等しい周波数の電圧を印加すると、逆圧電横効果により圧電振動子矩形板１１は四隅を振動の節としたラーメモードで共振する。このとき第２側の電極１４を２次側電極とすると、圧電縦効果により、電極１３−電極１４間に出力電圧を発生する。このようにして圧電トランスを構成することができる。
【００２１】
また、図１に示した圧電トランスでは、四隅が振動しないラーメモード振動のため、支持が容易であり、更に支持による特性の劣化がほとんどない。四隅が振動しないラーメモードの振動モードを図２に示す。図２（ａ）は、図１に示した圧電トランスの圧電振動子矩形板１１を構成する１単位の正方形板のラーメモードの振動モードを示し、図２（ｂ）は、図１に示した圧電トランスの圧電振動子矩形板１１（２単位）のラーメモードの振動モードを示す。
【００２２】
次に図１に示した圧電トランスの制動容量値の調整方法について説明する。
【００２３】
図１に示した圧電トランスでは、例えば
１）圧電振動子矩形板の厚さを薄く変化させると、１次側の制動容量Ｃｄ１の値が大きくなり、同時に２次側の制動容量Ｃｄ２の値が小さくなる。
【００２４】
逆に厚さを厚くした場合は、１次側の制動容量Ｃｄ１の値が小さくなり、同時に２次側の制動容量Ｃｄ２の値が大きくなる。
【００２５】
２）圧電振動子矩形板の寸法を変化させず、１次側の制動容量Ｃｄ１を固定した場合でも、図２に示すように２次側電極１４の面積を変化させることにより制動容量Ｃｄ２の値を調整することが可能である。２次側電極１４を端面のみに形成すれば、２次側の制動容量Ｃｄ２は小さくなり、逆に２次側電極１４を端面だけではなく圧電振動子矩形板１１の表面まで形成すれば、２次側の制動容量Ｃｄ２の値は大きくなる。
【００２６】
尚、図２に示した圧電トランスでは、第２側の電極１４が圧電振動子矩形板１１の長手方向他端面から上面に掛けて形成されているが、この上面に延在する第２側の電極１４は、圧電振動子矩形板１１の長手方向他端面から圧電振動子矩形板１１の長さの４分の１以内の領域に形成されている。また、図２に示した圧電トランスでは、第２側の電極１４が圧電振動子矩形板１１の長手方向他端面から上面に掛けて形成されているが、これに限らず、第２側の電極１４は、圧電振動子矩形板１１の長手方向他端面から下面に掛けて、若しくは長手方向他端面から上下面に掛けて、又は圧電振動子矩形板１１の上下面の少なくとも一方の面の長手方向他端面近傍に形成しても良い。
【００２７】
このように、用途に合わせて、最適の設計が可能となる。
【００２８】
表１に長さ２０ｍｍ、幅１０ｍｍ、高さ０．５ｍｍ、の圧電振動子矩形板を用いて場合の図１に示した本発明の圧電トランスと図６に示した従来の構成の圧電トランスの支持前後の特性の変化を表１に示す。
【００２９】
【表１】

【００３０】
表１から明らかなように本発明に係る図１に示した圧電トランスにおいては、支持前後で特性はほとんど変化していないが、図６に示した従来の圧電トランスにおいては、支持前後で特性がかなり低下していることがわかる。
【００３１】
尚、このリード取付部は振動の節となるのが好ましいので、圧電振動子矩形板１１の長さ方向において、第２の電極１４が設けられている方の端面から、矩形板１１の四隅あるいは長さの１／２の距離の側面、更に長さの１／４，３／４で幅の１／２の距離の点にすると良い。また、１次側電極と２次側電極以外に、帰還用の電極を圧電振動子矩形板１１の形成しても良い。
【００３２】
図４は請求項３記載の発明の圧電トランスの一実施例の構造の概略を示す斜視図であり、圧電振動子矩形板３１は、ニオブ酸リチウム圧電単結晶から成り、このニオブ酸リチウム圧電単結晶は、図１に示した圧電振動子矩形板１１を構成するニオブ酸リチウム圧電単結晶と同じものである。また、圧電振動子矩形板３１は、上述のニオブ酸リチウム圧電単結晶の正方形板を３枚長さ方向に連ねた長方形板を１単位として少なくとも１単位の長方形板（本実施例の場合、１単位）から成るように形成されると共にこの長方形板の四隅が振動の節となるラーメモード振動を行うように成っている。図５に圧電振動子矩形板３１のラーメモードの振動の振動モードを示す。このように３枚の正方形板を連ねた長方形板から成る圧電振動子矩形板３１のそれぞれの正方形板の領域に電気的に独立した厚さ方向で相対向する対向電極を形成し、この長方形板を構成する各正方形板上にそれぞれ形成した電極の内、長方形板の両側の対向電極１２（ａ），１２（ｂ）及び１３（ａ），１３（ｂ）を１次側電極とし、、残りの中央の対向電極１４（ａ），１４（ｂ）を２次側電極とした。また、圧電振動子矩形板３１には、１次側電極と２次側電極以外に帰還用電極１５が形成されている。
【００３３】
以上説明した図１、図３及び図４に示した圧電トランスの昇圧比と負荷抵抗の特性例を表２に示す。
【００３４】
【表２】

【００３５】
表２から明らかなように図１及び図４に示した圧電トランスは冷陰極管点灯用インバータ等の低インピーダンスに適し、図３に示した圧電トランスは普通紙コピートナー帯電等の高圧電源等の用途に適している。
【００３６】
尚、図４に示した圧電トランスは、図１及び図３に示した圧電トランスと同様に、圧電振動子矩形板の厚さと、２次側電極の寸法の内、少なくとも一方を変化させることにより、圧電振動子矩形板の１次側及び２次側の制動容量値を調整することができる。また、図４に示した圧電トランスの場合、上述のように長方形板の両側の対向電極１２（ａ），１２（ｂ）及び１３（ａ），１３（ｂ）を１次側電極とし、残りの中央の対向電極１４（ａ）を２次側としたが、長方形板の両側の対向電極１２（ａ），１２（ｂ）及び１３（ａ），１３（ｂ）を１次側電極とし、残りの中央の対向電極１４（ａ）或いは対向電極１４（ｂ）の少なくとも１つと対向電極１２（ａ），１２（ｂ）或いは１３（ａ），１３（ｂ）とを２次側電極とした構成としても良い。
【００３７】
【発明の効果】
以上示したように、本発明の圧電トランスの場合、ニオブ酸リチウム単結晶圧電振動子矩形板の厚さ、或いは電極の寸法を変化させることにより、１次側及び２次側の制動容量の値を幅広く変化させることが可能であり、広い負荷抵抗範囲の用途に対して、所望の出力電圧を効率良く発生させることが可能な圧電トランスを得ることが可能となり、実用的な効果は非常に大きい。
【００３８】
更に、圧電振動子矩形板の四隅が振動の節となるラーメモード振動を用いる事により、支持が容易で、かつ支持による特性の劣化がほとんど無い特性に優れた圧電トランスを得ることが可能となる。
【図面の簡単な説明】
【図１】請求項１記載の発明の圧電トランスの一実施例の構造概略図である。
【図２】図１に示した圧電トランスの振動モードを説明する説明図である。
【図３】請求項１記載の発明の圧電トランスの他の実施例の構造概略図である。
【図４】請求項３記載の発明の圧電トランスの一実施例の構造概略図である。
【図５】図４に示した圧電トランスの振動モードを説明する説明図である。
【図６】従来の圧電トランスの一例の構造概略図である。
【図７】図６に示した圧電トランスの動作説明図である。
【図８】圧電トランスの一般的な電気的等価回路図である。
【符号の説明】
１１圧電振動子矩形板
１２第１側の対向電極
１２（ａ）第１側の対向電極
１２（ｂ）第１側の対向電極
１３第１側の対向電極
１３（ａ）第１側の対向電極
１３（ｂ）第１側の対向電極
１４第２側の電極
１４（ａ）第２側の対向電極
１４（ｂ）第２側の対向電極
１５帰還用電極
３１圧電振動子矩形板[0001]
[Industrial application fields]
The present invention relates to a direct current high voltage power source used for an electronic copying machine, an electrostatic air cleaner, etc., and a piezoelectric transformer used for an inverter power source for lighting a backlight for a liquid crystal display. The present invention relates to a piezoelectric transformer that can be easily applied.
[0002]
[Prior art]
FIG. 6 is a perspective view schematically showing the structure of a conventional piezoelectric transformer. In FIG. 6, the piezoelectric vibrator rectangular plate 1 has

electrodes

2 and 3 opposed to each other in the thickness direction in approximately half of the length direction, and is far from the portion where the

electrodes

2 and 3 are formed. An electrode 4 is formed on the end face of the piezoelectric vibrator rectangular plate. In the figure, the white arrow indicates the polarization direction.
[0003]
7A and 7B are explanatory views of the operation principle of a conventional piezoelectric transformer. FIG. 7A is a cross-sectional view of the piezoelectric vibrator rectangular plate, and FIG. 7B is one wavelength of the longitudinal vibration of the piezoelectric vibrator rectangular plate. FIG. 7 (c) shows the strain distribution when the vibration is oscillating in the resonance mode. In FIG. 7A, when the electrode 3 is a ground terminal and a voltage having a frequency equal to the resonance frequency of the one-wave resonance mode of the longitudinal vibration of the piezoelectric vibrator rectangular plate is applied to the electrode 2, the piezoelectric vibrator rectangular plate 1 is Oscillates as shown in FIGS. 7B and 7C. At this time, a voltage is generated between the electrode 3 and the end face electrode 4 by the piezoelectric effect.
[0004]
An electrical equivalent circuit of the piezoelectric transformer is represented as shown in FIG. FIG. 8A shows a case in which primary and secondary electro-mechanical transformation transformers of the transformation ratios φ1 and φ2 are included, and m, s, and r are equivalents of the mechanical vibration system, respectively. Mass, equivalent stiffness and equivalent resistance. Further, Cd1 and Cd2 are braking capacities on the primary side and the secondary side, respectively. Furthermore, RL is a load resistance. FIG. 8B is an equivalent circuit when the circuit of FIG. 8A is viewed from the primary side. In FIG. 8B, each constant of the equivalent circuit is given by the following equation.
[0005]
L = m / φ1 ² , C = φ1 ² / s, R = r / φ1 ²
Cd2 ′ = A1 ² / A2 ² · Cd2, RL ′ = A2 ² / A1 ² · RL
When excited at the resonance frequency of the series circuit of the equivalent series inductance L, equivalent series capacitance C, and secondary braking capacitance Cd2 'in the equivalent circuit of FIG. 8B, the terminal voltage of the equivalent series inductance L and the equivalent series capacitance C And a secondary-side braking capacitance Cd2 'in series-connected total capacitance terminals generate an output voltage having the opposite polarity of the amplitude given by equation (1).
[0006]
VL = −Vc = Qm · V1 (1)
Here, Qm is Q of the series resonance circuit, and V1 is an input voltage.
[0007]
Therefore, the output voltage of the piezoelectric transformer is a voltage obtained by dividing the voltage Qm times the input voltage represented by the equation (1) by the equivalent series capacitance C and the secondary-side braking capacitance Cd2 '. Therefore, in order to obtain a high output voltage, it is required that the value of the secondary side capacitance ratio γ2 expressed by the equation (2) is small.
[0008]
γ2 = Cd2 ′ / C (2)
On the other hand, when the load resistance RL is connected to the piezoelectric transformer, the effective input voltage Qm decreases due to the load resistance RL, and when the load resistance RL decreases, the output voltage rapidly decreases. Furthermore, it is known that the efficiency of the piezoelectric transformer is maximized when the value of the load resistance RL is equal to the impedance 1 / (ωr · Cd2) at the resonance frequency of the secondary braking capacitance Cd2.
[0009]
Therefore, it is necessary to obtain a condition that satisfies both the required output voltage and efficiency depending on the load resistance condition in which the piezoelectric transformer is used.
[0010]
However, in the conventional piezoelectric transformer shown in FIGS. 6 and 7, when it is attempted to excite in the length vibration mode without coupling vibration, the ratio of width to length needs to be four times or more. The distance between the electrodes increases, and the value of the braking capacity Cd2 decreases. Therefore, in the piezoelectric transformer of the type shown in FIG. 6, when the load resistance RL is large, the output voltage increases and the efficiency also increases. On the other hand, when the load resistance RL of the piezoelectric transformer is small, the output voltage and the efficiency are greatly reduced.
[0011]
In the structure of the conventional piezoelectric transformer shown in FIG. 6, when the value of the secondary side braking capacity Cd2 is increased, the distance between the electrodes on the secondary side is shortened or the thickness of the piezoelectric vibrator rectangular plate is increased. There is a need to. However, increasing the thickness of the piezoelectric vibrator rectangular plate decreases the value of the braking capacity Cd1 on the primary side, leading to a decrease in output voltage and shortening the distance between the electrodes on the secondary side. If the width of the piezoelectric vibrator rectangular plate is not reduced, coupling vibration will occur. If the width is reduced, the secondary-side braking capacity Cd2 will be reduced, and the degree of freedom in design is extremely narrow.
[0012]
When considering the practical use of a piezoelectric transformer, it is common to use a vibrator supported on a package or the like, but the characteristics of the conventional piezoelectric transformer shown in FIGS. However, even if it is supported, there is a drawback that the characteristics are deteriorated due to vibration of the vibrator and the reliability is poor.
[0013]
[Problems to be solved by the invention]
The object of the present invention is to eliminate the above-mentioned disadvantages of the conventional piezoelectric transformer, and to change the load resistance in a wide range by changing the dimensions and electrode dimensions of the lithium niobate single crystal piezoelectric vibrator rectangular plate. An object of the present invention is to provide a piezoelectric transformer which can be easily handled, further reduces deterioration of characteristics due to support, and has excellent reliability.
[0014]
[Means for Solving the Problems]
According to the first aspect of the present invention, when the spontaneous polarization direction is parallel to the Z axis of the coordinate system, the coordinate system (X, Y ′, Z rotated by 120 to 170 ° around the X axis of the coordinate system). ′) Is further cut out so that the side faces are parallel to the X ′ axis and the Z ′ axis of the coordinate system (X ′, Y ″, Z ′) rotated −20 to 20 ° around the Z ′ axis. A piezoelectric vibrator rectangular plate made of a lithium niobate piezoelectric single crystal, the piezoelectric vibrator rectangular plate being composed of at least one unit of the square plate with a square plate as one unit, and four corners of the square plate Performs lame mode vibration that becomes a node of vibration, and the piezoelectric vibration is approximately half the length of the piezoelectric vibrator rectangular plate from one end surface in the longitudinal direction of the piezoelectric vibrator rectangular plate. Forms first-side counter electrodes facing each other in the thickness direction of the child rectangular plate A second side electrode is formed in the vicinity of the other end surface of at least the other end surface of the piezoelectric vibrator rectangular plate in the longitudinal direction or at least one of the upper and lower surfaces of the piezoelectric vibrator rectangular plate; A piezoelectric transformer is obtained in which the first-side counter electrode is a primary-side electrode, and the second-side electrode is a secondary-side electrode.
[0015]
According to the second aspect of the present invention, the second electrode 14 formed in the vicinity of the other end surface of at least one of the upper and lower surfaces has a length of the piezoelectric vibrator rectangular plate from the other end surface. 2. The piezoelectric transformer according to claim 1, wherein the piezoelectric transformer is formed in a region within a quarter.
[0016]
According to the third aspect of the present invention, when the spontaneous polarization direction is parallel to the Z axis of the coordinate system, the coordinate system (X, Y ′, Z rotated by 120 to 170 ° around the X axis of the coordinate system). ′) Is further cut out so that the side faces are parallel to the X ′ axis and the Z ′ axis of the coordinate system (X ′, Y ″, Z ′) rotated −20 to 20 ° around the Z ′ axis. A piezoelectric vibrator rectangular plate made of a lithium niobate piezoelectric single crystal, wherein the piezoelectric vibrator rectangular plate is composed of at least one unit of a rectangular plate obtained by connecting three square plates in the length direction. The rectangular plate is configured to perform a lame mode vibration in which the four corners of the rectangular plate serve as vibration nodes, and the piezoelectric vibrator rectangular plate electrically independent of each of the square plates constituting the rectangular plate. Form counter electrodes that face each other in the thickness direction, Among the electrodes, a piezoelectric transformer is obtained in which the counter electrode on both sides of the rectangular plate is a primary side electrode and the counter electrode at the center of the rectangular plate is a secondary side electrode.
[0017]
According to the fourth aspect of the present invention, when the spontaneous polarization direction is parallel to the Z axis of the coordinate system, the coordinate system (X, Y ′, Z rotated by 120 to 170 ° around the X axis of the coordinate system). ′) Is further cut out so that the side faces are parallel to the X ′ axis and the Z ′ axis of the coordinate system (X ′, Y ″, Z ′) rotated −20 to 20 ° around the Z ′ axis. A piezoelectric vibrator rectangular plate made of a lithium niobate piezoelectric single crystal, wherein the piezoelectric vibrator rectangular plate is composed of at least one unit of a rectangular plate obtained by connecting three square plates in the length direction. The rectangular plate is configured to perform a lame mode vibration in which the four corners of the rectangular plate serve as vibration nodes, and the piezoelectric vibrator rectangular plate electrically independent of each of the square plates constituting the rectangular plate. Form counter electrodes that face each other in the thickness direction, Of the electrodes, the counter electrode on both sides of the rectangular plate is a primary electrode, and at least one of the remaining central counter electrodes and one of the counter electrodes on both sides is a secondary electrode. Is obtained.
[0018]
According to a fifth aspect of the present invention, in addition to the primary side electrode and the secondary side electrode, a return electrode is formed on the piezoelectric vibrator rectangular plate. 4 is obtained.
[0019]
According to a sixth aspect of the present invention, in the piezoelectric transformer according to the first to fifth aspects, the at least one of a thickness of the piezoelectric vibrator rectangular plate and a dimension of the secondary electrode is changed. A method for adjusting the braking capacity value of the piezoelectric transformer, characterized in that the braking capacity values on the primary side and the secondary side of the piezoelectric vibrator rectangular plate are adjusted.
[0020]
【Example】
FIG. 1 is a perspective view showing an outline of the structure of an embodiment of a piezoelectric transformer according to the first aspect of the present invention. The piezoelectric vibration is approximately from one end surface in the longitudinal direction of a piezoelectric vibrator rectangular plate 11 made of lithium niobate single crystal. The counter electrode 12 and the counter electrode 13 on the first side opposed to each other in the thickness direction of the piezoelectric vibrator rectangular plate 11 are formed on almost the entire surface of a half of the length of the child rectangular plate 11, A second-side electrode 14 is formed on the other end surface in the longitudinal direction of the piezoelectric vibrator rectangular plate 11. The lithium niobate piezoelectric single crystal constituting the piezoelectric vibrator rectangular plate 11 has coordinates rotated by 120 to 170 ° around the X axis of the coordinate system when the spontaneous polarization direction is parallel to the Z axis of the coordinate system. With respect to the X ′ axis and Z ′ axis of the coordinate system (X ′, Y ″, Z ′) obtained by further rotating the system (X, Y ′, Z ′) about −20 to 20 ° around the Z ′ axis, In addition, the piezoelectric vibrator rectangular plate 11 is at least 1 unit (1 in the case of the present embodiment, 1) with the above-described lithium niobate piezoelectric single crystal square plate as one unit. 1 is used to perform a lame mode in which the four corners of the above-mentioned square plate are nodes of vibration, and the white arrow in Fig. 1 is the spontaneous polarization Z-axis of the lithium niobate piezoelectric single crystal. In FIG. 1, the first-

side counter electrodes

12 and 13 are connected to the primary-side power. As a pole, when a voltage having a frequency substantially equal to the resonance frequency of the Lame mode is applied while the four corners of the piezoelectric vibrator rectangular plate 11 do not vibrate, the piezoelectric vibrator rectangular plate 11 has a lame with the four corners as vibration nodes due to the inverse piezoelectric lateral effect. In this case, if the second electrode 14 is a secondary electrode, an output voltage is generated between the electrode 13 and the electrode 14 due to the piezoelectric longitudinal effect. it can.
[0021]
In addition, the piezoelectric transformer shown in FIG. 1 is easy to support because of the lame mode vibration in which the four corners do not vibrate, and there is almost no deterioration in characteristics due to the support. FIG. 2 shows a vibration mode of the lame mode in which the four corners do not vibrate. 2A shows a lame mode vibration mode of one unit square plate constituting the piezoelectric vibrator rectangular plate 11 of the piezoelectric transformer shown in FIG. 1, and FIG. 2B shows the vibration mode shown in FIG. The vibration mode of the lame mode of the piezoelectric vibrator rectangular plate 11 (2 units) of the piezoelectric transformer is shown.
[0022]
Next, a method for adjusting the braking capacity value of the piezoelectric transformer shown in FIG. 1 will be described.
[0023]
In the piezoelectric transformer shown in FIG. 1, for example, 1) When the thickness of the piezoelectric vibrator rectangular plate is changed thinly, the value of the primary side braking capacity Cd1 increases, and at the same time, the value of the secondary side braking capacity Cd2 increases. Get smaller.
[0024]
Conversely, when the thickness is increased, the value of the primary side braking capacity Cd1 decreases, and at the same time, the value of the secondary side braking capacity Cd2 increases.
[0025]
2) Even when the primary-side braking capacitance Cd1 is fixed without changing the dimensions of the piezoelectric vibrator rectangular plate, the value of the braking capacitance Cd2 is obtained by changing the area of the secondary-side electrode 14 as shown in FIG. Can be adjusted. If the secondary electrode 14 is formed only on the end surface, the secondary braking capacity Cd2 is reduced. Conversely, if the secondary electrode 14 is formed not only on the end surface but also on the surface of the piezoelectric vibrator rectangular plate 11, 2 The value of the next braking capacity Cd2 is increased.
[0026]
In the piezoelectric transformer shown in FIG. 2, the second-side electrode 14 is formed from the other end surface in the longitudinal direction of the piezoelectric vibrator rectangular plate 11 to the upper surface, but the second-side electrode 14 extends to the upper surface. The electrode 14 is formed in a region within a quarter of the length of the piezoelectric vibrator rectangular plate 11 from the other end surface in the longitudinal direction of the piezoelectric vibrator rectangular plate 11. In the piezoelectric transformer shown in FIG. 2, the second-side electrode 14 is formed so as to extend from the other end surface in the longitudinal direction of the piezoelectric vibrator rectangular plate 11 to the upper surface. 14 extends from the other longitudinal end surface of the piezoelectric vibrator rectangular plate 11 to the lower surface or from the other longitudinal end surface to the upper and lower surfaces, or the longitudinal direction of at least one surface of the upper and lower surfaces of the piezoelectric vibrator rectangular plate 11. You may form in the other end surface vicinity.
[0027]
In this way, an optimum design can be made according to the application.
[0028]
Table 1 shows the piezoelectric transformer of the present invention shown in FIG. 1 and the conventional piezoelectric transformer shown in FIG. 6 when using a piezoelectric vibrator rectangular plate having a length of 20 mm, a width of 10 mm, and a height of 0.5 mm. Table 1 shows changes in characteristics before and after the support.
[0029]
[Table 1]

[0030]
As is apparent from Table 1, the piezoelectric transformer shown in FIG. 1 according to the present invention has almost no change in characteristics before and after the support, but the conventional piezoelectric transformer shown in FIG. It turns out that it has fallen considerably.
[0031]
Since this lead attachment portion is preferably a vibration node, in the length direction of the piezoelectric vibrator rectangular plate 11, from the end surface on which the second electrode 14 is provided, the four corners of the rectangular plate 11 or It is preferable to set the side surface at a distance of ½ of the length, and further at a point at a distance of ¼, 3/4 of the length and ½ of the width. In addition to the primary side electrode and the secondary side electrode, a feedback electrode may be formed on the piezoelectric vibrator rectangular plate 11.
[0032]
FIG. 4 is a perspective view schematically showing the structure of an embodiment of the piezoelectric transformer according to the third aspect of the present invention. The piezoelectric vibrator rectangular plate 31 is made of a lithium niobate piezoelectric single crystal, and this lithium niobate piezoelectric single crystal. The crystal is the same as the lithium niobate piezoelectric single crystal constituting the piezoelectric vibrator rectangular plate 11 shown in FIG. In addition, the piezoelectric vibrator rectangular plate 31 has at least one rectangular plate (one in the case of the present embodiment, 1 unit), which is a rectangular plate obtained by connecting three square plates of the above-described lithium niobate piezoelectric single crystal in the length direction. Unit) and the four corners of the rectangular plate perform a lame mode vibration as a vibration node. FIG. 5 shows the vibration mode of the lame mode vibration of the piezoelectric vibrator rectangular plate 31. In this way, opposing electrodes opposing each other in the thickness direction are formed in the respective square plate regions of the piezoelectric vibrator rectangular plate 31 composed of a rectangular plate formed by connecting three square plates. Among the electrodes formed on each square plate constituting each, the opposing electrodes 12 (a), 12 (b) and 13 (a), 13 (b) on both sides of the rectangular plate are used as the primary side electrodes, and the rest The counter electrodes 14 (a) and 14 (b) at the center of these were used as secondary electrodes. In addition to the primary electrode and the secondary electrode, a feedback electrode 15 is formed on the piezoelectric vibrator rectangular plate 31.
[0033]
Table 2 shows characteristic examples of the step-up ratio and load resistance of the piezoelectric transformer shown in FIGS. 1, 3 and 4 described above.
[0034]
[Table 2]

[0035]
As apparent from Table 2, the piezoelectric transformer shown in FIGS. 1 and 4 is suitable for low impedance such as a cold cathode tube lighting inverter, and the piezoelectric transformer shown in FIG. Suitable for use.
[0036]
4 is changed by changing at least one of the thickness of the piezoelectric vibrator rectangular plate and the dimension of the secondary electrode, similarly to the piezoelectric transformer shown in FIGS. The braking capacity values on the primary side and the secondary side of the piezoelectric vibrator rectangular plate can be adjusted. In the case of the piezoelectric transformer shown in FIG. 4, the counter electrodes 12 (a), 12 (b) and 13 (a), 13 (b) on both sides of the rectangular plate are used as primary electrodes as described above, and the rest The counter electrode 14 (a) at the center of the rectangular plate is the secondary side, but the counter electrodes 12 (a), 12 (b) and 13 (a), 13 (b) on both sides of the rectangular plate are the primary side electrodes, At least one of the remaining central counter electrode 14 (a) or counter electrode 14 (b) and the counter electrodes 12 (a), 12 (b) or 13 (a), 13 (b) are used as secondary electrodes. It is good also as a structure.
[0037]
【The invention's effect】
As described above, in the case of the piezoelectric transformer of the present invention, the values of the primary and secondary braking capacities are obtained by changing the thickness of the lithium niobate single crystal piezoelectric vibrator rectangular plate or the dimensions of the electrodes. It is possible to obtain a piezoelectric transformer capable of efficiently generating a desired output voltage for applications in a wide load resistance range, and the practical effect is very large. .
[0038]
Furthermore, by using the lame mode vibration in which the four corners of the piezoelectric vibrator rectangular plate are vibration nodes, it becomes possible to obtain a piezoelectric transformer that is easy to support and has excellent characteristics with little deterioration of characteristics due to support. .
[Brief description of the drawings]
FIG. 1 is a schematic structural view of an embodiment of a piezoelectric transformer according to a first aspect of the present invention.
2 is an explanatory diagram for explaining a vibration mode of the piezoelectric transformer shown in FIG. 1; FIG.
FIG. 3 is a schematic structural view of another embodiment of the piezoelectric transformer according to the first aspect of the present invention;
FIG. 4 is a schematic structural view of an embodiment of a piezoelectric transformer according to a third aspect of the present invention.
FIG. 5 is an explanatory diagram for explaining a vibration mode of the piezoelectric transformer shown in FIG. 4;
FIG. 6 is a schematic structural diagram of an example of a conventional piezoelectric transformer.
7 is an operation explanatory diagram of the piezoelectric transformer shown in FIG. 6. FIG.
FIG. 8 is a general electrical equivalent circuit diagram of a piezoelectric transformer.
[Explanation of symbols]
11 Piezoelectric vibrator rectangular plate 12 First side counter electrode 12 (a) First side counter electrode 12 (b) First side counter electrode 13 First side counter electrode 13 (a) First side counter electrode 13 (b) First side counter electrode 14 Second side electrode 14 (a) Second side counter electrode 14 (b) Second side counter electrode 15 Return electrode 31 Piezoelectric vibrator rectangular plate

Claims

When the direction of spontaneous polarization is parallel to the Z-axis of the coordinate system, a coordinate system (X, Y ′, Z ′) rotated 120 to 170 ° around the X-axis of the coordinate system is further rotated around the Z′-axis. And a lithium niobate piezoelectric single crystal cut so that the side surface is parallel to the X ′ axis and the Z ′ axis of the coordinate system (X ′, Y ″, Z ′) rotated −20 to 20 ° The piezoelectric vibrator rectangular plate has a square plate as a unit and is composed of at least one unit of the square plate, and has a Lame mode vibration in which four corners of the square plate serve as vibration nodes. In the thickness direction of the piezoelectric vibrator rectangular plate, it is opposed to an area of about one half of the length of the piezoelectric vibrator rectangular plate from one end surface in the longitudinal direction of the piezoelectric vibrator rectangular plate. And forming at least the piezoelectric vibrator A second side electrode is formed in the vicinity of the other end surface of the other end surface of the rectangular plate in the longitudinal direction or at least one of upper and lower surfaces of the piezoelectric vibrator rectangular plate, and the counter electrode on the first side is formed A piezoelectric transformer comprising a primary side electrode and the second side electrode as a secondary side electrode.

The second electrode 14 formed in the vicinity of the other end surface of at least one of the upper and lower surfaces is formed in a region within a quarter of the length of the piezoelectric vibrator rectangular plate from the other end surface. The piezoelectric transformer according to claim 1 , wherein the piezoelectric transformer is provided.

When the direction of spontaneous polarization is parallel to the Z-axis of the coordinate system, a coordinate system (X, Y ′, Z ′) rotated 120 to 170 ° around the X-axis of the coordinate system is further rotated around the Z′-axis. And a lithium niobate piezoelectric single crystal cut so that the side surface is parallel to the X ′ axis and the Z ′ axis of the coordinate system (X ′, Y ″, Z ′) rotated −20 to 20 ° The piezoelectric vibrator rectangular plate is composed of at least one unit of the rectangular plate with a rectangular plate obtained by connecting three square plates in the length direction as one unit. The laminar mode vibration with the four corners serving as vibration nodes is performed, and the opposing electrodes facing each other in the thickness direction of the piezoelectric vibrator rectangular plate electrically independent of each of the square plates constituting the rectangular plate are provided. And forming both sides of the rectangular plate of the counter electrode The piezoelectric transformer is characterized in that the counter electrode is a primary electrode and the counter electrode at the center of the rectangular plate is a secondary electrode.

When the direction of spontaneous polarization is parallel to the Z axis of the coordinate system, a coordinate system (X, Y ′, Z ′) rotated by 120 to 170 ° around the X axis of the coordinate system is further rotated around the Z ′ axis. And a lithium niobate piezoelectric single crystal cut so that the side surface is parallel to the X ′ axis and the Z ′ axis of the coordinate system (X ′, Y ″, Z ′) rotated −20 to 20 ° A piezoelectric vibrator rectangular plate;
The piezoelectric vibrator rectangular plate is composed of at least one unit of the rectangular plate with a rectangular plate formed by connecting three square plates in the length direction as a unit, and a lame mode in which four corners of the rectangular plate are nodes of vibration. Which vibrates,
Forming opposing electrodes that oppose each other in the thickness direction of the piezoelectric vibrator rectangular plate electrically independent of each of the square plates constituting the rectangular plate;
Among the counter electrodes, one set of counter electrodes on both sides in the longitudinal direction formed on one plate surface of the piezoelectric vibrator rectangular plate and the other plate surface of the piezoelectric vibrator rectangular plate The other set of the opposing electrodes on both sides in the length direction formed as a primary side electrode,
A piezoelectric transformer characterized in that at least one of the remaining central counter electrodes and the one set of the counter electrodes on both sides in the longitudinal direction are used as secondary electrodes.

The primary electrode, a piezoelectric according to any one of claims 1 to 4 electrode for feedback in addition to the secondary electrode is characterized in that it is formed on the piezoelectric vibrator rectangular plate Trance.

6. The piezoelectric transformer according to claim 1, wherein at least one of a thickness of the piezoelectric vibrator rectangular plate and a dimension of the secondary electrode is changed to change the piezoelectric vibrator rectangular shape. A method for adjusting a braking capacity value of a piezoelectric transformer, comprising adjusting a braking capacity value on a primary side and a secondary side of a plate.