JP3627553B2

JP3627553B2 - Discharge device

Info

Publication number: JP3627553B2
Application number: JP01017399A
Authority: JP
Inventors: 眞一品田; 茂生御子柴; 智一志賀; 桂子平山; 清五十嵐
Original assignee: 日立ライティング株式会社
Priority date: 1999-01-19
Filing date: 1999-01-19
Publication date: 2005-03-09
Anticipated expiration: 2019-01-19
Also published as: JP2000208096A

Description

【０００１】
【発明の属する技術分野】
本発明は放電装置、液晶表示装置および情報機器に関し、特に可視光、紫外光等を放射する放電装置、液晶表示装置および情報機器に関する。より詳細には屋内外の照明用、表示用、機器用、あるいは液晶表示装置用のバックライト等に用いられる放電装置、液晶表示装置および情報機器に関するものである。ここで情報機器とは、例えば、液晶表示装置を有するか又は内蔵したコンピュータ、パーソナルコンピュータ、ビデオカメラ、デジタルカメラ、液晶テレビ等をいう。
【０００２】
【従来の技術】
放電を用いた光源、例えば照明用や表示用の蛍光ランプや平板型の放電装置等を駆動するには種々の方法がある。例えば、液晶表示装置のバックライト用インバータや高周波点灯の蛍光ランプ等、一般的な放電装置の駆動は、数１０ｋＨｚの高周波を用いている。これらの駆動方法の効率改善例として、例えば特開平９ー１１５４８３号公報に記載されている放電装置の駆動方法がある。
【０００３】
図１１は前記従来の放電装置の駆動方法による駆動電圧波形を示す図で、少なくとも一対の電極を有する放電装置において、一方の電極に―Ｖｈの電圧パルスを有する電圧Ｖ１が印可され、他の一方の電極にはＶ１と同じ電圧パルスで、半周期位相のずれた電圧パルス―Ｖｈを有する電圧Ｖ２が印可されて交流放電を行う。
【０００４】
【発明が解決しようとする課題】
上記した従来の駆動方法は、放電ガスに水銀を用いた場合に有効で、安定性が良く、高輝度、高効率な放電装置が得られる特徴がある。しかし、放電ガスとして水銀をなくし、キセノンあるいはキセノンと他の希ガスの混合ガスを用いた場合、従来の駆動方法では放電プラズマが不安定となり放電空間全体に均一に広がらず、一部分に集中したり、輝度が不均一になったりして放電空間全体が均一に発光しない問題があった。特に、平板状の放電装置において、電極間が長く陽光柱を発生させて発光させる構成の放電装置では従来の駆動方法では放電プラズマが広がらず陽光柱が収縮して平面発光にならない問題があった。また、輝度、効率も低下する問題もあった。
【０００５】
本発明の目的は、上述した課題を改善することにある。本発明の実施例によれば、放電用ガスとして水銀を有さず、かつ、キセノンを放電ガスに用いても放電プラズマが放電空間全体に広がって安定で均一性の良い放電が得られると共に高輝度、高発光効率の放電装置を提供することができる。
【０００６】
【課題を解決するための手段】
上記目的を達成するために本発明の実施例による放電装置は、一対の電極を有し、放電空間にキセノンを含む希ガスの混合ガスからなる放電用ガス（水銀を含まない。）が封入され、前記電極間で放電を行う放電装置において、前記電極間の発光面に放電プラズマが広がるよう電圧を印加した後、放電プラズマが収縮する前に放電を停止させることを繰り返す手段を有する。また、一対の電極を有し、放電空間にキセノンを含む希ガスの混合ガスからなる放電用ガスが封入され、前記電極間で放電を行う放電装置において、電圧を印加して放電プラズマを発生させ、前記電圧印加開始から放電電流が最大になる時間をｔとする時、電圧印加開始から１．１ｔの間に電圧を消去あるいは低減して放電を停止させることを繰り返す手段を有する。また、前記電圧印加開始から放電電流が最大になる時間をｔとする時、０．９ｔ以上から１．１ｔ以下の間に電圧を消去あるいは低減して放電を停止させることを繰り返す手段を有する。この場合、前記放電装置において、前記電極の少なくとも一方にアース電位に対して０Ｖ又は正又は負の直流電圧Ｖ_Ｌ１に、一定の周波数を有しピーク電圧がＶ_Ｈ１の正又は負の電圧が重畳された電圧を印加し、前記他の一方の電極に前記電圧Ｖ_Ｈ１とほぼ同じ電圧Ｖ_Ｈ２が重畳された直流電圧Ｖ_Ｌ２を印加し、前記電圧の関係を｜Ｖ_Ｌ１｜および｜Ｖ_Ｌ２｜が｜Ｖ_Ｈ１｜および｜Ｖ_Ｈ２｜より小さくなるようにする。また、前記電極に印加する電圧として、前記電極の少なくとも一方にアース電位に対して０Ｖ又は正又は負の直流電圧Ｖ_Ｌ３に、一定の周波数を有しピーク電圧がＶ_Ｈ３の正又は負の電圧が重畳された電圧を印加し、前記他の一方の電極に０Ｖ又は正又は負の直流電圧Ｖ_Ｌ４を印加し、前記電圧の関係を｜Ｖ_Ｌ３｜および｜Ｖ_Ｌ４｜が｜Ｖ_Ｈ３｜より小さくなるようにする。さらに、前記電圧として矩形若しくは略矩形の電圧パルスとする。また、前記電極に印加する電圧パルスとして、互いに略半周期位相のずれた電圧パルスとする。また、前記電極間に発生する放電プラズマが陽光柱を有している。また、前記放電ガスとしてキセノンと一種類以上の他の希ガスを混合したガスを用い、キセノンの混合比を７％以上３８％以下にする。また、前記放電ガスの封入圧力を１，７００Ｐａ以上１２，６００Ｐａ以下にする。さらに、前記放電装置として、透光性を有する前面板と背面板とを略平行に位置させて扁平状の放電空間を有する密閉容器を構成し、前記密閉容器の内面に蛍光体を塗布し、前記放電空間の互いに離間した辺に所定の長さに渡って第一及び第二の電極を設けた平板型の放電装置とする。また、前記電極を前面板に形成する。また、前記電極の表面を覆って誘電体層を設ける。
【０００７】
本発明の実施例に係る放電装置は液晶表示装置のバックライトとして有効であるが、直接照明装置の光源としても使用できる。
【０００８】
【発明の実施の形態】
つぎに本発明の実施例を図面と共に説明する。図１は本発明による平板型放電装置の一実施例を示す断面斜視図である。図に示すように、ソーダガラス等からなる透光性の前面板２と、ソーダガラスやセラミック等からなる浅皿形の背面板３とが、例えば低融点ガラス（図示せず）で略平行に位置するよう一体に気密封着され、扁平状の放電空間８を有する密閉容器１が構成されている。発光面となる前面板２の内面には互いに略平行な第一および第二の放電電極４、５が放電空間８の互いに離間した第一および第二の辺に沿って長さ方向全体に渡って設けられており、さらに放電電極４、５の表面には誘電体層６が形成されている。前面板２と背面板３の内面には蛍光体７が塗布され、放電空間８には、例えばキセノンとアルゴンの混合ガスやキセノンとアルゴンとネオンの混合ガス等が封入されている。発光面の大きさは、例えば２．５インチ液晶用のバックライトに用いる場合５２ｍｍ×４０ｍｍで、この時、電極間距離は約５４ｍｍ、放電空間８の高さは１．８ｍｍで、例えば５インチの場合、発光面の大きさは１０５ｍｍ×７４ｍｍで、この時、電極間距離は約７６ｍｍ、放電空間８の高さは２．４ｍｍである。
【０００９】
本構造による平板型光源は、両放電電極４、５間に電圧を印加することにより放電空間８内にキセノンの希ガス放電が発生し、キセノンの陽光柱から放射される紫外線により蛍光体７が励起されて発光し、前面板を通して外部に放射される。
【００１０】
扁平状の放電空間を有する放電装置では一つもしくは二つの放電経路に陽光柱が収縮しやすいということが一般に知られている。特に、キセノンなどの希ガスによる放電は水銀による放電に比べ放電プラズマの収縮現象が起きやすく、放電空間全体に均一な放電プラズマを発生させるためには印加電圧、放電電流条件や駆動周波数、パルス幅、デューティ比、ガス組成、封入圧力等を適当に選ぶことが必要になってくる。
【００１１】
図２は本発明の実施例による放電装置の印加電圧パルスと放電電流の関係を示す図である。図中、（ａ）、（ｂ）は従来の駆動方法による印加電圧と放電電流を示し、（ｃ）、（ｄ）は本発明の実施例による印加電圧と放電電流を示す。図から明らかなように、（ａ）、（ｃ）で示した電圧波形に違いはないが、（ｂ）、（ｄ）の電流波形に大きな違いが見られる。従来の駆動法による放電電流はパルス印加期間前半において最大値をとり、パルス印加期間中に再び零になる。このような電流条件の場合、キセノン混合ガスによる放電プラズマは図４に示したような収縮現象を起こし、放電空間全体に広がらない。一方、本発明の実施例による駆動方法では（ｃ）、（ｄ）に示したように、電圧パルスを印加して放電プラズマを発生させ、前記電圧パルス印加開始から放電電流が最大になるまでの所要時間をｔとした時、電圧パルス印加開始から時刻１．１ｔまでの間に電圧パルスの印加を停止して放電を停止させるよう電圧パルスの幅を適当に選ぶ。この場合、電圧パルスの印加を停止せず、印加電圧を下げて放電を終了させても良い。このような電流条件になるよう電圧パルスの幅を設定することで、放電プラズマは放電空間全体に均一に広がり、キセノン放電のプラズマ中に陽光柱が発生していても平面状の放電プラズマが得られる。
【００１２】
上記電流条件を満足させるには、印加電圧、周波数、パルス幅、デューティ比（パルス幅／周期×１００％）をある範囲に選ぶことが必要になる。
【００１３】
図３はパルス幅をパラメータにした放電電流の時間変化を示した図で、駆動波形は図５に示したと同様な電圧で、周期７０μｓ、１０６０Ｖの矩形波電圧を印加して放電させている。封入ガスはキセノン２８％ーアルゴン７２％の混合ガスで、封入圧力は５．３ｋＰａである。
【００１４】
この条件では、電圧パルス印加後の時間ｔが６．７μｓで放電電流がほぼ最大値になり、この時、パルス幅が４．８μｓから７．３５μｓの間で均一に広がった放電プラズマが得られる。電流が最大値になる時のパルスデューテイ比は９．６％である。パルス幅がこれより広い７．４μｓなると図４に示したように放電プラズマの収縮が発生し全面発光しなくなる。
【００１５】
このように、電圧パルス印加後に放電電流が最大になるまでの所要時間をｔとしたとき、放電プラズマを均一に広がらせておくためには電圧パルスを最大１．１ｔまで印加できる。また、印加時間が短いと放電プラズマは広がるが電力が少ないため発光輝度が低下する。高輝度で、安定な放電を得るための条件は０．９ｔ以上１．１ｔ以下が望ましい。
【００１６】
次に、本発明の実施例による放電装置の駆動波形と電圧条件の例を以下に示す。放電電圧と放電電流は上記した条件を満足している。
【００１７】
図５（ａ）は、本発明の実施例による駆動波形と電圧条件の関係を示す図で、例えば上記平板型放電装置の片方の電極４に正又は負又は０Ｖの直流電圧Ｖ_L1 （本図の例では０Ｖ）に一定の周波数(周期)とパルス幅を有する正の電圧パルス＋Ｖ_H1が重畳された電圧Ｖ１を印加し、他の一方の電極５に加える電圧Ｖ２として、前記電圧パルスＶ_H1とお互いに略半周期位相のずれた、同じかほぼ同じ電圧パルス＋Ｖ_H2が重畳された直流電圧Ｖ_L2（Ｖ_L1と同じかほぼ同じ電圧）を印加して交流放電を行わせる。
【００１８】
図５（ｂ）は、矩形若しくは略矩形電圧パルスとして負の電圧−Ｖ_Ｈ１および−Ｖ_Ｈ２を印加したもので、他の構成は（ａ）と同じである。これらの電圧を印加し、キセノンを含む希ガスを用いて放電空間８全体に均一な放電を発生させるための電圧条件は、Ｖ_Ｌ、Ｖ_Ｈの絶対値でＶ_ＨよりＶ_Ｌが小さくなるように選ぶことが必要である。すなわち、前記電圧の関係を｜Ｖ_Ｌ１｜および｜Ｖ_Ｌ２｜が｜Ｖ_Ｈ１｜および｜Ｖ_Ｈ２｜より小さくなるようにする。このような条件にすることでキセノンと希ガスの混合ガスを放電ガスに用いても陽光柱が放電空間全体に広がり、安定性、均一性の良い発光が得られる。
【００１９】
図６（ａ）、（ｂ）は別の駆動波形を示した図で、上記電極に印加する電圧として、例えば電極４の電圧Ｖ１に０Ｖを含む正又は負の直流電圧Ｖ_L3 （本図の例では０Ｖ）に一定の周波数とパルス幅を有する矩形若しくは略矩形電圧パルスＶ_H3が重畳された電圧とし、他の一方の電極５の電圧Ｖ２にＶ_L3と同じかほぼ同じ直流電圧Ｖ_L4を印加して放電させる例で、（ａ）は電圧パルスＶ_H3、が正の場合、（ｂ）は負の場合を示す。この場合の放電は極性を有する放電となる。
【００２０】
本実施例による電圧の関係は、上記図５の例と同じようにＶ_Ｌ、Ｖ_Ｈの絶対値でＶ_ＨよりＶ_Ｌが小さくなるように選ぶことが必要である。すなわち、前記電圧の関係を｜Ｖ_Ｌ３｜および｜Ｖ_Ｌ４｜が｜Ｖ_Ｈ３｜より小さくなるようにすることでキセノンと希ガスの混合ガスを放電ガスに用いても放電空間全体に放電プラズマが広がり、安定性、均一性の良い放電が得られる。
【００２１】
上記した実験結果からキセノンを含む希ガスを用いて、安定で放電空間全体に均一な放電プラズマが得られる電圧パルスの条件は発光面の大きさや電極間距離、封入ガス組成、圧力により最適な範囲があり、周波数が５ｋＨｚ以上７０ｋＨｚ以下で、パルス幅が０．３μｓ以上１０μｓ以下で、デューテイ比が０．５％以上２５％以下の関係を満足するよう選ぶことが必要である。なお、ここで示したパルス幅は半値幅を用いている。
【００２２】
図７は上記した条件を満足させた駆動条件での放電空間全面均一に放電する安定動作領域を示す図で、横軸はデューテイ比、縦軸は印加電圧で、周期と封入圧力をパラメータにしている。封入ガスはアルゴンーキセノン（２８％）を用いた。ここで、電圧が１１００Ｖ以上は実験用回路の出力電圧の制約から実験を行っていないが、安定動作領域は左上がりの曲線で増加すると推定する。
【００２３】
安定動作領域は、封入ガス圧力を例えば４ｋＰａから６．７ｋＰａに高くすると、同じ周期でデューテイ比が大きい方にシフトする。さらに圧力を高くするとデューテイ比がさらに大きいところで安定動作する。また、周期を大きく（周波数を低く）すると安定動作領域は拡大する。
【００２４】
次に、上記した構造の平板型放電装置の放電電極４、５に図６（ａ）に示した波形の電圧を印加した場合の封入ガス圧と発光効率の関係を示す。周波数は１６ｋＨｚの略矩形の電圧パルスで、上記電流条件を満足するよう点灯させた。図８はキセノンーアルゴン混合ガスを封入した場合、図９はキセノンーアルゴンーネオンの混合ガスを封入した場合で、入力電力は０．７Ｗ一定の条件で、発光効率は相対値で表してある。図７のキセノン混合比は３０％、１５％、７％の３種類の例で、図８は、ａがキセノン２５％ーアルゴン５０％ーネオン２５％で、ｂがキセノン２１％ーアルゴン１６％ーネオン６３％の例である。ネオンを混合することで安定動作領域は高封入圧力にシフトし、効率も向上する。
【００２５】
これらの結果、キセノン混合比と発光効率の関係は、キセノン混合比を増やすに従い発光効率は増加するが、３０％以上でほぼ飽和する。また、キセノンの混合比が３８％までは封入圧力を１，７００Ｐａ以上の適当な値に選べば放電プラズマは放電空間８内全体に広がり全面均一な発光が得られる。しかし、キセノンの混合比を３８％より増やしたり、圧力を１，７００Ｐａより低くすると電流条件や放電電力によらず放電プラズマが収縮して全面発光しない。また、封入ガス組成を変えたり電力を大きくすることで封入ガス圧は高くできるが、１２，６００Ｐａを越えると動作電圧が２．５ｋＶ以上になり、通常の駆動回路では駆動できなくなることや、放電電流が増加して発光効率が大幅に低下するとともに回路の発熱や部品の電流容量等の問題が発生し実用化が難しくなる。
【００２６】
キセノン混合比が７％より少なくなるとキセノンの量が少なすぎて輝度が急激に減少し、実用的な明るさが得られなくなる。
【００２７】
従って、前記した実験結果から安定で均一な放電プラズマを得るために、封入するキセノン混合ガスのキセノン混合比は７％以上、３８％以下で、封入圧力は１，７００Ｐａ以上１２，６００Ｐａ以下が最適な範囲である。
【００２８】
図１０は上記した本発明の実施例による駆動方法を用いて、平板型の放電装置を駆動した場合の発光面の輝度均斉度を示した図である。駆動条件は、電圧１１００Ｖ、周期３５μｓ、パルス幅２．１μｓ、封入ガスはアルゴンーキセノン２８％を用いた。発光面の大きさは５インチで、輝度均斉度は、発光面を９分割して中心部の輝度を１００％とし、それぞれの領域における輝度を測定して求めた。この時の中心輝度は７，０００ｃｄ／ｍ^２であった。図から明らかなように８７％以上の優れた均斉度が得られている。
【００２９】
本発明の実施例による放電装置の駆動方法は、キセノンを含む希ガスを放電ガスに用いた場合、陽光柱の収縮現象を低減し、安定性良く、放電空間全体に均一な放電を発生させることが可能で、高輝度、高発光効率でかつ均斉度の優れた放電装置が得られる。また、水銀を用いない放電装置を使用できるため、放電装置の製造工程が簡略化できる。
【００３０】
【発明の効果】
本発明によれば、従来よりも均斉度のよい放電装置を提供することが可能となる。
【図面の簡単な説明】
【図１】本発明による放電装置の一実施例を示す断面斜視図である。
【図２】本発明による電圧と電流の関係を示す特性図である。
【図３】電流波形を示す特性図である。
【図４】発光の状態を示す図である。
【図５】本発明による放電装置の駆動電圧波形の例を示す図である。
【図６】本発明による放電装置の駆駆動電圧波形の別の例を示す図である。
【図７】安定動作領域を示す特性図である。
【図８】封入ガス圧力と発光効率の関係を示す特性図である。
【図９】封入ガス圧力と発光効率の関係を示す特性図である。
【図１０】均斉度を示す特性図である。
【図１１】従来の駆動電圧波形である。
【符号の説明】
１…密閉容器、２…前面板、３…背面板、４…電極、５…電極、６…誘電体、７…蛍光体、８…放電空間。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a discharge device, a liquid crystal display device, and information equipment, and more particularly to a discharge device that emits visible light, ultraviolet light, and the like, a liquid crystal display device, and information equipment. More specifically, the present invention relates to a discharge device, a liquid crystal display device, and an information device used for backlights for indoor / outdoor illumination, display, equipment, or liquid crystal display devices. Here, the information equipment refers to, for example, a computer, a personal computer, a video camera, a digital camera, a liquid crystal television, or the like that has or incorporates a liquid crystal display device.
[0002]
[Prior art]
There are various methods for driving a light source using discharge, for example, a fluorescent lamp for illumination or display, a flat discharge device, or the like. For example, driving of a general discharge device such as a backlight inverter of a liquid crystal display device or a high-frequency fluorescent lamp uses a high frequency of several tens of kHz. As an example of improving the efficiency of these driving methods, there is a driving method of a discharge device described in, for example, Japanese Patent Laid-Open No. 9-115483.
[0003]
FIG. 11 is a diagram showing a driving voltage waveform according to the driving method of the conventional discharge device. In a discharge device having at least a pair of electrodes, a voltage V1 having a voltage pulse of −Vh is applied to one electrode and the other one is shown. A voltage V2 having a voltage pulse −Vh having a half-cycle phase shift is applied to the electrode of V1 by the same voltage pulse as that of V1, and AC discharge is performed.
[0004]
[Problems to be solved by the invention]
The conventional driving method described above is effective when mercury is used as the discharge gas, and has a feature that a discharge device with good stability, high luminance and high efficiency can be obtained. However, when mercury is eliminated as the discharge gas and xenon or a mixed gas of xenon and other rare gases is used, the discharge plasma becomes unstable with the conventional driving method, and it does not spread uniformly throughout the discharge space, but concentrates on a part of it. There is a problem in that the brightness becomes uneven and the entire discharge space does not emit light uniformly. In particular, in a flat discharge device, a discharge device having a structure in which a gap between electrodes is long and a positive column is generated to emit light has a problem that the conventional driving method does not cause the discharge plasma to spread and the positive column contracts and flat emission does not occur. . There is also a problem that luminance and efficiency are lowered.
[0005]
An object of the present invention is to improve the above-described problems. According to the embodiment of the present invention, even if xenon is not used as a discharge gas and the discharge gas does not have mercury, the discharge plasma spreads over the entire discharge space, and a stable and uniform discharge is obtained. A discharge device with high brightness and high luminous efficiency can be provided.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a discharge device according to an embodiment of the present invention has a pair of electrodes, and a discharge gas (containing no mercury) made of a mixed gas of a rare gas containing xenon is enclosed in the discharge space. The discharge device for discharging between the electrodes has means for repeatedly stopping the discharge after the voltage is applied so that the discharge plasma spreads on the light emitting surface between the electrodes and before the discharge plasma contracts. In addition, in a discharge device having a pair of electrodes, in which a discharge gas composed of a mixed gas of a rare gas containing xenon is sealed in a discharge space, and a discharge is performed between the electrodes, a voltage is applied to generate discharge plasma. When the time when the discharge current becomes maximum from the start of voltage application is t, there is means for repeatedly stopping the discharge by erasing or reducing the voltage between 1.1 t and the start of voltage application. In addition, when the time when the discharge current becomes maximum from the start of the voltage application is t, there is means for repeatedly stopping the discharge by erasing or reducing the voltage between 0.9 t and 1.1 t. In this case, in the discharge device, a positive or negative voltage having a constant frequency and a peak voltage of V _H1 is superimposed on at least one of the electrodes on a DC voltage V _L1 of 0 V or positive or negative with respect to the ground potential. is a voltage was applied was the approximately the same voltage _{V H2} and the other one of the electrode voltage _{V H1} is by applying a DC voltage _{V L2} superimposed, the relationship of the voltage _{| V L1} | and _{| V L2} | Is smaller than | V _H1 | and | V _H2 |. In addition, as a voltage to be applied to the electrode, a positive or negative voltage having a constant frequency and a peak voltage of _VH3 is set to at least one of the electrodes at 0 V or a positive or negative DC voltage _VL3 with respect to the ground potential. Is applied, 0V or a positive or negative DC voltage V _L4 is applied to the other electrode, and | V _L3 | and | V _L4 | are | V _H3 | Make it smaller. Further, the voltage is a rectangular or substantially rectangular voltage pulse. In addition, the voltage pulses applied to the electrodes are voltage pulses that are substantially out of phase with each other. The discharge plasma generated between the electrodes has a positive column. Further, a gas obtained by mixing xenon and one or more other rare gases is used as the discharge gas, and the mixing ratio of xenon is set to 7% or more and 38% or less. Further, the sealing pressure of the discharge gas is set to 1,700 Pa or more and 12,600 Pa or less. Further, as the discharge device, a light-transmitting front plate and a rear plate are positioned substantially parallel to form a sealed container having a flat discharge space, and a phosphor is applied to the inner surface of the sealed container, A flat plate type discharge device is provided in which first and second electrodes are provided over a predetermined length on mutually spaced sides of the discharge space. The electrode is formed on the front plate. A dielectric layer is provided to cover the surface of the electrode.
[0007]
The discharge device according to the embodiment of the present invention is effective as a backlight of a liquid crystal display device, but can also be used as a light source of a direct illumination device.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional perspective view showing an embodiment of a flat plate type discharge device according to the present invention. As shown in the figure, a translucent front plate 2 made of soda glass or the like and a shallow dish-shaped back plate 3 made of soda glass, ceramic, or the like are substantially parallel with, for example, low-melting glass (not shown). A hermetic container 1 having a flat discharge space 8 that is integrally hermetically sealed so as to be positioned is configured. On the inner surface of the front plate 2 serving as the light emitting surface, first and second discharge electrodes 4 and 5 that are substantially parallel to each other extend over the entire length direction along the first and second sides of the discharge space 8 that are separated from each other. Furthermore, a dielectric layer 6 is formed on the surfaces of the discharge electrodes 4 and 5. A phosphor 7 is applied to the inner surfaces of the front plate 2 and the back plate 3, and the discharge space 8 is filled with, for example, a mixed gas of xenon and argon or a mixed gas of xenon, argon, and neon. The size of the light emitting surface is 52 mm × 40 mm when used for a backlight for 2.5 inch liquid crystal, for example. At this time, the distance between the electrodes is about 54 mm, and the height of the discharge space 8 is 1.8 mm, for example, 5 inch. In this case, the size of the light emitting surface is 105 mm × 74 mm. At this time, the distance between the electrodes is about 76 mm, and the height of the discharge space 8 is 2.4 mm.
[0009]
In the flat light source of this structure, a rare gas discharge of xenon is generated in the discharge space 8 by applying a voltage between the discharge electrodes 4 and 5, and the phosphor 7 is caused by the ultraviolet rays emitted from the positive column of xenon. When excited, it emits light and is emitted outside through the front plate.
[0010]
In a discharge device having a flat discharge space, it is generally known that a positive column easily contracts in one or two discharge paths. In particular, discharge due to rare gas such as xenon is more susceptible to discharge plasma contraction than mercury discharge. In order to generate a uniform discharge plasma in the entire discharge space, applied voltage, discharge current conditions, drive frequency, pulse width, etc. It is necessary to appropriately select the duty ratio, gas composition, sealing pressure, and the like.
[0011]
FIG. 2 is a diagram showing the relationship between the applied voltage pulse and the discharge current of the discharge device according to the embodiment of the present invention. In the figure, (a) and (b) show the applied voltage and discharge current according to the conventional driving method, and (c) and (d) show the applied voltage and discharge current according to the embodiment of the present invention. As is clear from the figure, there is no difference in the voltage waveforms shown in (a) and (c), but there are significant differences in the current waveforms in (b) and (d). The discharge current according to the conventional driving method takes the maximum value in the first half of the pulse application period and becomes zero again during the pulse application period. Under such a current condition, the discharge plasma by the xenon mixed gas causes a contraction phenomenon as shown in FIG. 4 and does not spread over the entire discharge space. On the other hand, in the driving method according to the embodiment of the present invention, as shown in (c) and (d), a discharge plasma is generated by applying a voltage pulse, and the discharge current is maximized from the start of the voltage pulse application. When the required time is t, the width of the voltage pulse is appropriately selected so that the application of the voltage pulse is stopped and the discharge is stopped between the start of the voltage pulse application and the time 1.1t. In this case, the discharge may be terminated by lowering the applied voltage without stopping the application of the voltage pulse. By setting the voltage pulse width so as to satisfy such a current condition, the discharge plasma spreads uniformly throughout the discharge space, and a flat discharge plasma is obtained even if a positive column is generated in the xenon discharge plasma. It is done.
[0012]
In order to satisfy the current condition, it is necessary to select the applied voltage, frequency, pulse width, and duty ratio (pulse width / cycle × 100%) within a certain range.
[0013]
FIG. 3 is a diagram showing the change over time of the discharge current with the pulse width as a parameter. The drive waveform is the same voltage as shown in FIG. 5, and a rectangular wave voltage with a period of 70 μs and 1060 V is applied for discharging. The sealing gas is a mixed gas of 28% xenon and 72% argon, and the sealing pressure is 5.3 kPa.
[0014]
Under this condition, the discharge current becomes almost maximum at time 6.7 μs after application of the voltage pulse, and at this time, discharge plasma having a pulse width uniformly spread between 4.8 μs and 7.35 μs is obtained. . The pulse duty ratio when the current reaches the maximum value is 9.6%. When the pulse width is larger than 7.4 μs, the discharge plasma contracts as shown in FIG. 4 and the entire surface does not emit light.
[0015]
Thus, when the time required for the discharge current to become maximum after application of the voltage pulse is t, the voltage pulse can be applied up to 1.1 t in order to spread the discharge plasma uniformly. In addition, when the application time is short, the discharge plasma spreads but the power is low, so that the emission luminance is lowered. The condition for obtaining a high-intensity and stable discharge is preferably 0.9 to 1.1 t.
[0016]
Next, examples of driving waveforms and voltage conditions of the discharge device according to the embodiment of the present invention are shown below. The discharge voltage and discharge current satisfy the above conditions.
[0017]
FIG. 5A is a diagram showing the relationship between the driving waveform and the voltage condition according to the embodiment of the present invention. For example, a positive, negative or 0V DC voltage V _L1 (this figure) is applied to one electrode 4 of the flat plate type discharge device . a constant frequency (by applying a voltage V1 positive voltage pulse + V _H1 is superposed with period) and the pulse width, the voltage V2 applied to the other one of the electrodes 5 to 0V) in the example, the voltage pulse V _H1 And applying a DC voltage V _L2 (same or substantially the same voltage as V _L1 ) on which the same or substantially the same voltage pulse + V _{H2, which} are substantially half-cycle phase shifted from each other, is applied to cause AC discharge.
[0018]
FIG. 5B shows a case where negative voltages −V _H1 and −V _H2 are applied as rectangular or substantially rectangular voltage pulses, and the other configurations are the same as those in FIG. The voltage conditions for applying these voltages and generating a uniform discharge in the entire discharge space 8 using a rare gas containing xenon are such that V _L is smaller than V _{H in} terms of the absolute values of V _L and V _H. It is necessary to choose. That is, the relationship between the voltages is set so that | V _L1 | and | V _L2 | are smaller than | V _H1 | and | V _H2 |. Under such conditions, even if a mixed gas of xenon and a rare gas is used as the discharge gas, the positive column spreads over the entire discharge space, and light emission with good stability and uniformity can be obtained.
[0019]
FIGS. 6A and 6B are diagrams showing other driving waveforms. As a voltage to be applied to the electrode, for example, a positive or negative DC voltage V _L3 including 0 V in the voltage V1 of the electrode 4 (in FIG. In this example, the voltage is a voltage in which a rectangular or substantially rectangular voltage pulse V _H3 having a constant frequency and pulse width is superimposed on 0 V) , and a DC voltage V _L4 that is the same as or substantially the same as V _L3 is applied to the voltage V2 of the other electrode 5. In the example of applying and discharging, (a) shows a case where the voltage pulse V _H3 is positive, and (b) shows a negative case. The discharge in this case is a discharge having polarity.
[0020]
The voltage relationship according to the present embodiment needs to be selected so that V _L is smaller than V _{H in} terms of the absolute values of V _L and V _H as in the example of FIG. That is, by making the voltage relationship | V _L3 | and | V _L4 | smaller than | V _H3 |, even if a mixed gas of xenon and rare gas is used as the discharge gas, the discharge plasma is generated in the entire discharge space. Discharge with good spread, stability and uniformity can be obtained.
[0021]
Based on the above experimental results, the voltage pulse conditions for obtaining a stable and uniform discharge plasma in the entire discharge space using a rare gas containing xenon are in the optimum range depending on the size of the light emitting surface, the distance between electrodes, the composition of the filled gas, and the pressure. It is necessary to select such that the frequency is 5 kHz to 70 kHz, the pulse width is 0.3 μs to 10 μs, and the duty ratio is 0.5% to 25%. The pulse width shown here uses a half width.
[0022]
FIG. 7 is a diagram showing a stable operation region in which the discharge space is uniformly discharged under the driving conditions satisfying the above conditions. The horizontal axis is the duty ratio, the vertical axis is the applied voltage, and the period and the sealing pressure are parameters. Yes. Argon-xenon (28%) was used as the sealing gas. Here, when the voltage is 1100 V or higher, the experiment is not performed due to the limitation of the output voltage of the experimental circuit, but it is estimated that the stable operation region increases with a curve rising to the left.
[0023]
When the sealed gas pressure is increased from 4 kPa to 6.7 kPa, for example, the stable operation region shifts to the larger duty ratio in the same cycle. When the pressure is further increased, stable operation is performed at a higher duty ratio. Further, when the period is increased (frequency is decreased), the stable operation region is expanded.
[0024]
Next, the relationship between the sealed gas pressure and the luminous efficiency when the voltage having the waveform shown in FIG. 6A is applied to the discharge electrodes 4 and 5 of the flat plate type discharge device having the above-described structure is shown. The frequency was set to a substantially rectangular voltage pulse of 16 kHz so that the current condition was satisfied. FIG. 8 shows a case where a xenon-argon mixed gas is sealed, and FIG. 9 shows a case where a xenon-argon-neon mixed gas is sealed, where the input power is 0.7 W and the luminous efficiency is expressed as a relative value. . The xenon mixing ratios in FIG. 7 are 30%, 15%, and 7%, and FIG. 8 shows that a is xenon 25% -argon 50% -neon 25%, and b is xenon 21% -argon 16% -neon 63%. It is an example. By mixing neon, the stable operation region shifts to a high sealing pressure and the efficiency is improved.
[0025]
As a result, the relationship between the xenon mixing ratio and the luminous efficiency increases substantially as the xenon mixing ratio increases, but is nearly saturated at 30% or more. Further, when the mixing pressure of xenon is up to 38%, the discharge plasma spreads in the entire discharge space 8 and uniform light emission can be obtained if the enclosed pressure is selected to an appropriate value of 1,700 Pa or more. However, if the mixing ratio of xenon is increased from 38% or the pressure is decreased from 1,700 Pa, the discharge plasma contracts regardless of the current conditions and the discharge power and the entire surface does not emit light. In addition, the sealed gas pressure can be increased by changing the sealed gas composition or increasing the electric power, but if it exceeds 12,600 Pa, the operating voltage becomes 2.5 kV or more, and it becomes impossible to drive with a normal drive circuit, As the current increases, the luminous efficiency decreases significantly, and problems such as circuit heat generation and current capacity of components occur, making it difficult to put it into practical use.
[0026]
When the xenon mixing ratio is less than 7%, the amount of xenon is too small and the brightness is drastically reduced, so that practical brightness cannot be obtained.
[0027]
Therefore, in order to obtain a stable and uniform discharge plasma from the above experimental results, the xenon mixing ratio of the xenon mixed gas to be sealed is 7% to 38%, and the filling pressure is optimally 1,700 Pa to 12,600 Pa. It is a range.
[0028]
FIG. 10 is a diagram showing the luminance uniformity of the light emitting surface when a flat plate type discharge device is driven using the driving method according to the embodiment of the present invention. The driving conditions were a voltage of 1100 V, a period of 35 μs, a pulse width of 2.1 μs, and an enclosed gas of argon-xenon 28%. The size of the light-emitting surface was 5 inches, and the luminance uniformity was determined by measuring the luminance in each region by dividing the light-emitting surface into 9 parts and setting the luminance at the center to 100%. The central luminance at this time was 7,000 cd / m ² . As is apparent from the figure, an excellent uniformity of 87% or more is obtained.
[0029]
The method of driving the discharge device according to the embodiment of the present invention reduces the shrinkage phenomenon of the positive column when the rare gas containing xenon is used as the discharge gas, and generates a uniform discharge in the entire discharge space with good stability. Therefore, a discharge device having high brightness, high luminous efficiency and excellent uniformity can be obtained. In addition, since a discharge device that does not use mercury can be used, the manufacturing process of the discharge device can be simplified.
[0030]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the discharge device with a better uniformity than before.
[Brief description of the drawings]
FIG. 1 is a cross-sectional perspective view showing an embodiment of a discharge device according to the present invention.
FIG. 2 is a characteristic diagram showing the relationship between voltage and current according to the present invention.
FIG. 3 is a characteristic diagram showing a current waveform.
FIG. 4 is a diagram showing a state of light emission.
FIG. 5 is a diagram showing an example of a driving voltage waveform of the discharge device according to the present invention.
FIG. 6 is a diagram showing another example of the driving voltage waveform of the discharge device according to the present invention.
FIG. 7 is a characteristic diagram showing a stable operation region.
FIG. 8 is a characteristic diagram showing a relationship between an enclosed gas pressure and luminous efficiency.
FIG. 9 is a characteristic diagram showing a relationship between an enclosed gas pressure and luminous efficiency.
FIG. 10 is a characteristic diagram showing uniformity.
FIG. 11 shows a conventional driving voltage waveform.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Sealed container, 2 ... Front plate, 3 ... Back plate, 4 ... Electrode, 5 ... Electrode, 6 ... Dielectric, 7 ... Phosphor, 8 ... Discharge space.

Claims

It has a pair of electrodes, a discharge gas consisting of xenon and other rare gas is sealed in the discharge space, and a voltage is applied between the pair of electrodes so that the discharge plasma spreads on the light emitting surface between the pair of electrodes. And a means for repeatedly stopping the discharge so that the discharge plasma does not substantially contract or stopping the discharge before the discharge plasma substantially contracts.

A discharge gas comprising xenon and other rare gas is enclosed in the discharge space, and a discharge plasma is generated by applying a voltage to the pair of electrodes; Repeatedly stopping the voltage application or stopping the discharge by lowering the applied voltage within a period from the start of voltage application to time 1.1 t, where t is the time required until the discharge current becomes maximum. A discharge device comprising means.

A discharge gas comprising xenon and other rare gas is enclosed in the discharge space, and a discharge plasma is generated by applying a voltage to the pair of electrodes; Means for repeatedly stopping the voltage application or stopping the discharge by lowering the applied voltage within a period of time 0.9t to 1.1t, where t is the time required until the discharge current reaches the maximum. A discharge device characterized by that.

A voltage in which a positive or negative voltage having a predetermined frequency and a peak voltage of V _H1 is superimposed on 0 V or positive or negative DC voltage V _L1 with respect to the ground potential is applied to at least one of the electrodes, A voltage in which a positive or negative voltage having a predetermined frequency and a peak voltage of V _H2 is superimposed on 0 V or a positive or negative DC voltage V _L2 with respect to the ground potential is applied to the electrode of V _H1 , V _H2 have substantially the same value, and | V _L1 | and | V _L2 | are configured to be smaller than | V _H1 | and | V _H2 |, respectively. The discharge device according to any one of the above.

To at least one of the pair of electrodes, a 0V or a positive or voltage positive or negative voltage is superimposed negative DC voltage peak voltage has a constant frequency to the V _L3 is V _H3 with respect to ground potential Then, 0V or a positive or negative DC voltage V _L4 is applied to the other electrode, and the relationship between the voltages is set so that | V _L3 | and | V _L4 | are smaller than | V _H3 |. The discharge device according to any one of claims 1 to 3, wherein the discharge device is provided.

The discharge device according to any one of claims 1 to 5, wherein the voltage applied to the pair of electrodes is a rectangular or substantially rectangular voltage pulse.

7. The discharge device according to claim 1, wherein the voltage applied to the pair of electrodes is a voltage pulse having a substantially half-phase phase shift from each other.

The discharge device according to any one of claims 1 to 7, wherein a positive column exists in the discharge plasma generated between the pair of electrodes.

The discharge device according to any one of claims 1 to 8, wherein a mixing ratio of xenon in the discharge gas is 7% or more and 38% or less.

The discharge device according to any one of claims 1 to 9, wherein a sealing pressure of the discharge gas is 1,700 Pa or more and 12,600 Pa or less.

A hermetic container having a flat discharge space is configured by placing a translucent front plate and a rear plate substantially in parallel, and a phosphor is applied to the inner surface of the hermetic container, and the discharge spaces are separated from each other. The discharge device according to any one of claims 1 to 10, wherein the pair of electrodes are provided on a side over a predetermined length.

The discharge device according to claim 11, wherein the pair of electrodes are formed on the front plate.

The discharge device according to any one of claims 1 to 12, wherein a surface of the electrode is covered with a dielectric layer.

The discharge device according to any one of claims 1 to 13, wherein mercury is not enclosed in the discharge vessel.

A liquid crystal display device comprising a discharge device according to any one of claims 14 claim 1, the liquid crystal display element is provided on the light emitting surface of the discharge device.

Information device to the discharge device according to any one of claims 14 claim 1, characterized in that the liquid crystal display element is provided on the light emitting surface of the discharge device.