JP4151324B2

JP4151324B2 - Light source device and driving method thereof

Info

Publication number: JP4151324B2
Application number: JP2002189801A
Authority: JP
Inventors: 晴生高田; 茂吉田; 均一青木; 藤田　　勉; 勝美田中
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 2002-06-28
Filing date: 2002-06-28
Publication date: 2008-09-17
Anticipated expiration: 2022-06-28
Also published as: JP2004031283A

Description

【０００１】
【発明の属する技術分野】
本発明は、表示器の前面あるいは背面から照明が必要な表示装置、例えば液晶表示装置等に好適な光源装置とその光源の駆動方法に関する。
【０００２】
【従来の技術】
表示器の前面あるいは背面から照明が必要な表示装置、例えば液晶表示装置においては、照明用の光源として冷陰極型の蛍光灯（ＣＦＬ）やエレクトロルミネッセンス素子（ＥＬ）が用いられている。
【０００３】
しかしながら、これらの光源は、通電時間の経過とともにその輝度が低下するという問題を有している。図６は、ＣＦＬの駆動電流別にその累積通電時間に対する輝度の変化を表している。破線（ａ）は駆動電流Ｉ０、破線（ｂ）は駆動電流Ｉ１、破線（ｃ）は駆動電流Ｉ２、破線（ｄ）は駆動電流Ｉ３、破線（ｅ）は駆動電流Ｉ４（Ｉ０＞Ｉ１＞Ｉ２＞Ｉ３＞Ｉ４）を示している。尚、輝度が所定値（Ｋ０）以下の部分は、説明を簡略化するために実際とは異なる急な傾斜によって示している。
【０００４】
図に示すように、初期駆動電流が多いものは輝度が高いがその輝度が光源の交換時期を示す所定輝度（Ｋ０）に低下するまでの時間が短い。初期駆動電流が小さくなるにしたがって、輝度が所定輝度に低下するまでの時間が長くなる。
【０００５】
光源の寿命（交換までの時間）を長くするために、当初は光源の駆動電流を少なくしておき、時間経過とともに輝度が低下すると、段階的に駆動電流を増加させて初期輝度近くまで輝度を増加させることが行われている（例えば特開平１０−２７０１８０号公報）。
【０００６】
ところが、駆動電流を増加させて輝度を増加させることにも限界があり、駆動電流が最大値に達した後は、輝度は時間経過ともに減少するので、いずれにしても光源の輝度低下は避けられない。また、駆動電流の増加によって消費電力が増加するので、電池駆動する携帯型の機器には不適である。また、光源の寿命を延ばすために、初期の駆動電流を少なくすると、初期の輝度も低下するので、当初から暗い照明しか行えない。
【０００７】
また、使用場所に係らず輝度は一定であるので、低輝度で良い暗い場所での使用においても明るい場所での高輝度が維持されるので、無駄な電力を消費することになるとともに、光源の寿命を短くすることになる。
【０００８】
【発明が解決しようとする課題】
そこで本発明は、これらの点を考慮してなされたもので、初期の輝度は高く保ちながら、光源の寿命を延ばすことを課題の１つとする。また、低消費電力化を図ることを課題の1つとする。また、光源駆動電流の切り替えによる輝度の変化を分かりにくくすることを課題の1つとする。
【０００９】
【課題を解決するための手段】
本発明の光源の駆動方法は請求項１に記載のように、光源の累積通電時間を求め、この累積通電時間が長くなるにしたがって、段階的に前記光源の駆動電流を低減することを特徴とする。
【００１０】
本発明の光源の駆動方法は請求項２に記載のように光源の累積通電時間を求め、この累積通電時間が長くなるにしたがって、段階的に前記光源の駆動電流を低減するとともに、周囲の明暗に応じて、前記光源の駆動電流を増減することを特徴とする。
【００１１】
本発明の光源の駆動方法は請求項３に記載のように、光源の累積通電時間を求め、この累積通電時間が長くなるにしたがって、段階的に前記光源の駆動電流を低減する第1の調整と、前記光源の駆動電流を周囲の明るさに応じて増減する第２の調整を行うとともに、前記第1の調整によって前記光源の駆動電流を低減するタイミングを前記第２の調整によって前記光源の駆動電流を低減するタイミングに合わせて行うことを特徴とする。
【００１２】
本発明の光源の駆動方法は請求項４に記載のように、光源の累積通電時間を求め、この累積通電時間が長くなるにしたがって、段階的に前記光源の駆動電流を低減する第1の調整と、前記光源の駆動電流を夜間と昼間とで交互に増減する第３の調整を行うとともに、前記第1の調整によって前記光源の駆動電流を低減するタイミングを前記第３の調整によって前記光源の駆動電流を低減するタイミングに合わせて行うことを特徴とする。
【００１３】
本発明の光源装置は請求項５に記載のように、光源と、その累積通電時間を求める累積通電時間計測手段と、前記光源の駆動を制御する制御手段とを備え、前記制御手段は、前記累積通電時間計測手段の出力に基づいて、前記光源の累積通電時間が長くなるにしたがって、段階的に前記光源の駆動電流を低減することを特徴とする。
【００１４】
本発明の光源装置は請求項６に記載のように、光源と、その累積通電時間を求める累積通電時間計測手段と、周囲の明暗を検出するセンサーと、前記光源の駆動を制御する制御手段とを備え、前記制御手段は、累積通電時間計測手段と前記センサーの出力に基づいて、前記累積通電時間が長くなるにしたがって、段階的に前記光源の駆動電流を低減する第1の調整と、前記光源の駆動電流を周囲の明るさに応じて増減する第２の調整を行うことを特徴とする光源装置。
【００１５】
本発明の光源装置は請求項７に記載のように、光源と、その累積通電時間を求める累積通電時間計測手段と、周囲の明暗を検出するセンサーと、前記光源の駆動を制御する制御手段とを備え、前記制御手段は、累積通電時間計測手段と前記センサーの出力に基づいて、前記累積通電時間が長くなるにしたがって、段階的に前記光源の駆動電流を低減する第1の調整と、前記光源の駆動電流を周囲の明るさに応じて増減する第２の調整を行うとともに、前記第1の調整によって前記光源の駆動電流を低減するタイミングを前記第２の調整によって前記光源の駆動電流を低減するタイミングに合わせて行うことを特徴とする光源装置。
【００１６】
本発明の光源装置は請求項８に記載のように、光源と、その累積通電時間を求める累積通電時間計測手段と、昼間と夜間を判別するタイマーと、前記光源の駆動を制御する制御手段とを備え、前記制御手段は、累積通電時間計測手段と前記タイマーの出力に基づいて、前記累積通電時間が長くなるにしたがって、段階的に前記光源の駆動電流を低減する第1の調整と、前記光源の駆動電流を周囲の明るさに応じて増減する第２の調整を行うとともに、前記第1の調整によって前記光源の駆動電流を低減するタイミングを前記第２の調整によって前記光源の駆動電流を低減するタイミングに合わせて行うことを特徴とする。
【００１７】
【発明の実施の形態】
以下本発明の実施形態を図面を参照して説明する。図１は本発明が実施された光源装置１のブロック図、図２、図３は、光源の駆動方法の実施形態を説明するための特性図、図４、図５は、光源の駆動方法の実施形態を説明するためのフローチャート図である。
【００１８】
光源装置１は、１本あるいは複数本の冷陰極管などで構成される光源２を備えている。この光源２は、時間経過とともに輝度が低下する特性をもつもので、駆動回路３によって駆動される。駆動回路３は電源回路４より電源供給を受け、制御手段５の出力によって制御される。電源回路４は、光源２以外にも装置１の各部に各種の電源を供給する。
【００１９】
駆動回路３に接続した計測手段６によって光源２の通電時間と累積通電時間Ｔが計測される。計測手段６によって計測された光源の通電時間や累積通電時間Ｔは、制御手段５に取り込まれる。制御手段５が計測手段６を兼ねても良い。計測手段６、あるいはそのデータを取り込む制御手段５は、光源装置１の主電源が切られた状態であっても、累積通電時間を保持（バックアップ）できるような構成としておくのが望ましい。
【００２０】
光源装置１には、光源装置１が組み込まれる装置（装着対象物）の周囲の明るさに関する情報を求めるためのセンサー７が配置されている。センサー７は、光源２の影響を受けにくい場所に配置可能な構成とすることが望ましい。センサー７は光源２と遮光される位置に配置するのが好ましい。このセンサー７の出力は、制御手段５に取り込まれる。制御手段５は、センサー７の出力に基づいて、装着対象物の周囲の明るさを判別する。以下の例では、センサー７の出力に基づいて、装着対象物の周囲の明るさが基準輝度（あるいは基準照度）よりも明るいＤａｙモード（以下Ｄモード）と、装着対象物の周囲の明るさが基準輝度（あるいは基準照度）よりも暗いＮｉｇｈｔモード（以下Ｎモード）の２通りの場合分けしかしていないが、２以上の複数の明るさ区分を設けても良い。
【００２１】
光源装置１には、時刻あるいは時間によって昼間と夜間を区別するためのタイマー８が設けられている。このタイマー８の出力によって制御手段５は、昼間と夜間を区別することができる。タイマー８は、計測手段６とその一部を共用することができる。
【００２２】
上記構成の光源装置の動作（駆動方法）の１例について、図２を参照して説明する。図２に示すように、光源２の累積通電時間Ｔがｔ１を経過するまで、光源の駆動電流は最大値もしくは最大値の８０％以上の値のＩ０（破線ａで示す）に設定される。この駆動電流Ｉ０によって、光源は最高輝度あるいは最大輝度付近の輝度で点灯する。駆動電流が同じ同一の条件であっても、時間経過とともに輝度は低下する。
【００２３】
光源２の累積通電時間Ｔがｔ１を経過すると、光源の駆動電流をＩ０からＩ１（破線bで示す）に低下させる。この駆動電流Ｉ１によって、光源２はそれまでよりも一段階程度低い輝度で点灯する。光源２の累積通電時間Ｔがｔ２を経過すると、光源の駆動電流をＩ１からＩ２（破線cで示す）に低下させる。この駆動電流Ｉ２によって、光源２はそれまでよりも一段階程度低い輝度で点灯する。光源２の累積通電時間Ｔがｔ３を経過すると、光源の駆動電流をＩ２からＩ３（破線dで示す）に低下させる。この駆動電流Ｉ３によって、光源２はそれまでよりも一段階程度低い輝度で点灯する。光源２の累積通電時間Ｔがｔ４を経過すると、光源の駆動電流をＩ３からＩ４（破線ｅで示す）に低下させる。この駆動電流Ｉ４によって、光源２はそれまでよりも一段階程度低い輝度、この例では最低レベルの輝度で点灯する。ここで、累積通電時間Ｔに関する時間ｔ１〜ｔ４は、予め定めた時間であり、ｔ１＜ｔ２＜ｔ３＜ｔ４に設定されている。
【００２４】
このように、光源の累積通電時間Ｔを求め、この累積通電時間Ｔが長くなるにしたがって、段階的に前記光源２の駆動電流Ｉを低減する駆動方法を用いるので、初期の輝度は高く保ちながら、光源２の寿命を長くすることができる。光源２の駆動電流Ｉが徐々に低減するので、徐々に増加させる場合に比べて消費電力の低減を図ることができる。
【００２５】
図４は、上述した駆動方法の一例を示すフローチャートで、制御手段５によって実行される動作を示している。
【００２６】
すなわち、制御手段５は、計測手段６の出力に基づき、ステップＳ１にて光源２の累積通電時間Ｔを読み出す。ステップＳ２にて、時間Ｔがｔ１に達していないことを判定すると、ステップＳ３に進み、光源の駆動電流Ｉを最大値もしくは最大値の８０％以上の値のＩ０に設定する。そしてステップＳ１１に進み、駆動回路３を制御することによって、駆動電流Ｉ０が供給され、光源２は最高輝度あるいは最大輝度付近の輝度で点灯する。
【００２７】
ステップＳ２にて、時間Ｔがｔ１に達したことが判定されると、ステップＳ４に進み、ステップＳ４にて、時間Ｔがｔ２に達していないことを判定すると、ステップＳ５に進み、光源の駆動電流ＩをＩ０よりも低いＩ１に設定する。そしてステップＳ１１に進み、駆動回路３を制御することによって、駆動電流Ｉ１が供給され、光源２は先の輝度より一段低い輝度で点灯する。
【００２８】
ステップＳ４にて、時間Ｔがｔ２に達したことが判定されると、ステップＳ６に進み、ステップＳ６にて、時間Ｔがｔ３に達していないことを判定すると、ステップＳ７に進み、光源の駆動電流ＩをＩ１よりも低いＩ２に設定する。そしてステップＳ１１に進み、駆動回路３を制御することによって、駆動電流Ｉ２が供給され、光源２は先の輝度より一段低い輝度で点灯する。
【００２９】
ステップＳ６にて、時間Ｔがｔ３に達したことが判定されると、ステップＳ８に進み、ステップＳ８にて、時間Ｔがｔ４に達していないことを判定すると、ステップＳ９に進み、光源の駆動電流ＩをＩ２よりも低いＩ３に設定する。そしてステップＳ１１に進み、駆動回路３を制御することによって、駆動電流Ｉ３が供給され、光源２は先の輝度より一段低い輝度で点灯する。
【００３０】
ステップＳ８にて、時間Ｔがｔ４に達したことが判定されると、ステップＳ１０に進み、光源２の駆動電流ＩをＩ３よりも低いＩ４に設定する。そしてステップＳ１１に進み、駆動回路３を制御することによって、駆動電流Ｉ４が供給され、光源２は先の輝度より一段階低い輝度、この例では最低レベルの輝度で点灯する。
【００３１】
次に、上記構成の光源装置の動作（駆動方法）の他の例について、図３を参照して説明する。先の例は、累積通電時間Ｔのみをパラメータとして光源２の駆動電流を制御したが、この例は、累積通電時間Ｔに加えて、周囲の明暗に関する情報もパラメータとして光源２の駆動電流Ｉを制御するものである。
【００３２】
図３に示すように、ＤモードとＮモードの何れが設定されているかによって、駆動電流を大きな値と小さな値とに切り替えている。ここでは、Ｄモードを周囲が明るい場合に対応させているので、Ｄモードが選択されると、明るい状態でも見えるように大きな駆動電流Ｉが選択される。また、Ｎモードを周囲が暗い場合に対応させているので、Ｎモードが選択されると、過照明を防止するために小さな駆動電流が選択される。
【００３３】
Ｄモードでの駆動電流は、先の例と同様に累積通電時間Ｔが長くなるにしたがって、段階的に減少させる。ここで特徴的なのが、Ｄモードで駆動中に累積通電時間Ｔが電流切り替えを示す時間ｔに達しても、駆動電流を即座には切り替えずにそれまでの値を維持し、一旦Ｎモードを経てＤモードに復帰する際に、駆動電流を小さな値に切り替えるようにしている点である。このようにすることによって、輝度の急激な変化を防止している。Ｎモードの駆動電流は、最低ランクの一定値を選択しているが、Ｄモードと同様に、累積通電時間Ｔが長くなるにしたがって、徐々に低くすることもできる。
【００３４】
図５は、上述した他の駆動方法の一例を示すフローチャートで、制御手段５によって実行される動作を示している。
【００３５】
すなわち、制御手段５は、センサー７の出力に基づき、ステップＳ２１にてＤモードかＮモードかを判定する。前述したとおり、Ｄモードは、装着対象物の周囲の明るさが基準輝度（あるいは基準照度）よりも明るい場合、Ｎモードは、装着対象物の周囲の明るさが基準輝度（あるいは基準照度）よりも暗い場合としている。Ｄモードが選択されるとステップＳ２２に進み、Ｎモードが選択されるとステップＳ３４に進む。
【００３６】
Ｄモードの選択によってステップＳ２２に進むと、制御手段５は、計測手段６の出力に基づき光源２の累積通電時間Ｔを読み出す。ステップＳ２３にて、時間Ｔがｔ１に達していないことを判定すると、ステップＳ２４に進み、光源の駆動電流Ｉを最大値もしくは最大値の８０％以上の値のＩ０に設定する。そしてステップＳ３５に進み、駆動回路３を制御することによって、駆動電流Ｉ０が供給され、光源２は最高輝度あるいは最大輝度付近の輝度で点灯する。
【００３７】
暗い場所での使用によって、ステップＳ２１にてＮモードが選択されると、ステップＳ３４に進み、光源の駆動電流をＩ０からＩ４（破線ｅで示す）に低下させる。この駆動電流Ｉ４によって、光源２は最低レベルの輝度で点灯する。このようにして、光源２の累積通電時間Ｔがｔ１を経過するまで、光源の駆動電流は最大値もしくは最大値の８０％以上の値のＩ０（破線ａで示す）と最低のＩ４に交互に設定される。
【００３８】
光源２の累積通電時間Ｔがｔ１を経過すると、ステップＳ２３からＳ２５、Ｓ２６に進む。ステップＳ２６では、時間ｔ１経過後にＮモードを経たか否か判定される。Ｎモードを経ていない場合、すなわち、Ｄモード途中に累積通電時間が駆動電流の切り替えの時期を示す値に達した場合は、駆動電流の切り替えを禁止するようにしている。したがって、時間ｔ１経過直後は、ステップＳ２６からステップＳ２４に進み、それまでの駆動電流Ｉ0が保持される。そして、ステップＳ２６にてＮモードを経たことが判定されると、ステップＳ２７に進み、駆動電流Ｉ１が選択される。このようにして、累積通電時間Ｔによる駆動電流の切り替えタイミングをモード切替による駆動電流切り替えタイミングに一致させ、モード途中における輝度変化を防止している。
【００３９】
以下、同様にして、規定の時間ｔ２，ｔ３，ｔ４が経過するごとに、上記と同様な処理がステップＳ２１〜Ｓ３５において実行され、Ｄモードにおける駆動電流が累積通電時間Ｔの経過とともに段階的に減少する。
【００４０】
上記の実施形態では、センサー７によって周囲の明るさを判別し、ＤモードとＮモードを周囲が明るい状態と暗い状態とに対応させたが、さらに別の形態として、タイマー８によって昼間と夜間を判定し、昼前をＤモード、夜間をＮモードに設定し、図５のフローチャートで示す処理を行うこともできる。
【００４１】
上記実施形態は、光源２の駆動電流を変化させる場合を例にとったが、駆動電流の代わりに駆動電圧を制御することもできる。光源２の駆動を電圧によって制御する場合は、先の実施形態における駆動電流を駆動電圧と読み替えれば良い。
【００４２】
【発明の効果】
以上のように、本発明によれば光源の累積通電時間が長くなるに従って駆動電流を段階的に減少させるので、初期の輝度は高く保ちながら、光源の寿命を延ばすことができる。また、消費電力の削減を図ることができる。また、周囲に明るさに応じて駆動電流を増減することができるので、消費電力をより一層削減することができる。また、累積通電時間に基づく駆動電流の切り替え時、輝度の変化を分かりにくくすることができる。
【図面の簡単な説明】
【図１】本発明の光源装置の実施形態を示すブロック図である。
【図２】本発明の一実施形態における輝度と累積通電時間の関係を示す特性図である。
【図３】別の実施形態における輝度と累積通電時間の関係を示す特性図である。
【図４】本発明の一実施形態における動作を示すフローチャート図である。
【図５】別の実施形態における動作を示すフローチャート図である。
【図６】一般的な光源の輝度と累積通電時間の関係を示す特性図である。
【符号の説明】
１光源装置
２光源
３駆動回路
４電源回路
５制御手段
６計測手段
７センサー
８タイマー[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light source device suitable for a display device that needs to be illuminated from the front surface or the back surface of a display, such as a liquid crystal display device, and a driving method of the light source.
[0002]
[Prior art]
In a display device that needs to be illuminated from the front surface or the back surface of the display device, for example, a liquid crystal display device, a cold cathode fluorescent lamp (CFL) or an electroluminescence element (EL) is used as a light source for illumination.
[0003]
However, these light sources have a problem that the luminance decreases with the passage of energization time. FIG. 6 shows the change in luminance with respect to the cumulative energization time for each CFL drive current. The broken line (a) is the driving current I0, the broken line (b) is the driving current I1, the broken line (c) is the driving current I2, the broken line (d) is the driving current I3, and the broken line (e) is the driving current I4 (I0>I1> I2 >I3> I4). Note that the portion where the luminance is equal to or lower than the predetermined value (K0) is indicated by a steep slope different from the actual one for the sake of simplicity.
[0004]
As shown in the figure, the one with a large initial drive current has a high luminance, but the time until the luminance falls to a predetermined luminance (K0) indicating the replacement timing of the light source is short. As the initial drive current decreases, the time until the luminance decreases to the predetermined luminance increases.
[0005]
In order to extend the life of the light source (time until replacement), the drive current of the light source is initially reduced, and when the luminance decreases with time, the drive current is increased step by step to increase the luminance to near the initial luminance. Increasing is performed (for example, JP-A-10-270180).
[0006]
However, there is a limit to increasing the brightness by increasing the drive current, and after the drive current reaches the maximum value, the brightness decreases with time, so any decrease in the brightness of the light source can be avoided in any case. Absent. Further, since the power consumption increases due to an increase in driving current, it is not suitable for a portable device driven by a battery. Further, if the initial driving current is decreased to extend the life of the light source, the initial luminance is also lowered, so that only dark illumination can be performed from the beginning.
[0007]
In addition, since the brightness is constant regardless of the place of use, high brightness is maintained in a bright place even when used in a dark place where low brightness is acceptable. It will shorten the life.
[0008]
[Problems to be solved by the invention]
Therefore, the present invention has been made in consideration of these points, and one of the problems is to extend the life of the light source while keeping the initial luminance high. Another issue is to reduce power consumption. Another object is to make it difficult to understand changes in luminance due to switching of the light source drive current.
[0009]
[Means for Solving the Problems]
The light source driving method according to the present invention is characterized in that, as described in claim 1, the cumulative energization time of the light source is obtained, and the drive current of the light source is gradually reduced as the cumulative energization time becomes longer. To do.
[0010]
According to the light source driving method of the present invention, the cumulative energization time of the light source is obtained as described in claim 2, and as the accumulated energization time becomes longer, the drive current of the light source is reduced step by step and the surrounding light and darkness is increased. The drive current of the light source is increased or decreased according to the above.
[0011]
According to a third aspect of the present invention, there is provided a first light source driving method for obtaining a cumulative energization time of a light source, and reducing the driving current of the light source stepwise as the cumulative energization time increases. And a second adjustment for increasing / decreasing the driving current of the light source in accordance with ambient brightness, and the timing of reducing the driving current of the light source by the first adjustment is adjusted by the second adjustment. It is characterized in that it is performed in accordance with the timing at which the drive current is reduced.
[0012]
According to a fourth aspect of the present invention, there is provided a first light source driving method for obtaining a cumulative energization time of a light source, and reducing the driving current of the light source stepwise as the cumulative energization time increases. And a third adjustment for alternately increasing / decreasing the driving current of the light source at night and daytime, and a timing at which the driving current of the light source is reduced by the first adjustment by the third adjustment. It is characterized in that it is performed in accordance with the timing at which the drive current is reduced.
[0013]
As described in claim 5, the light source device of the present invention includes a light source, a cumulative energization time measuring means for obtaining the cumulative energization time, and a control means for controlling the driving of the light source, Based on the output of the cumulative energization time measuring means, the drive current of the light source is gradually reduced as the cumulative energization time of the light source becomes longer.
[0014]
The light source device according to the present invention includes a light source, a cumulative energization time measuring means for obtaining the cumulative energization time, a sensor for detecting ambient light and darkness, and a control means for controlling driving of the light source. The control means, based on the accumulated energization time measurement means and the output of the sensor, as the accumulated energization time becomes longer, a first adjustment to reduce the drive current of the light source stepwise, and A light source device characterized by performing a second adjustment to increase or decrease a driving current of a light source according to ambient brightness.
[0015]
The light source device according to the present invention includes a light source, a cumulative energization time measuring means for obtaining the cumulative energization time, a sensor for detecting ambient light and darkness, and a control means for controlling driving of the light source. The control means, based on the accumulated energization time measurement means and the output of the sensor, as the accumulated energization time becomes longer, a first adjustment to reduce the drive current of the light source stepwise, and A second adjustment for increasing / decreasing the drive current of the light source according to the surrounding brightness is performed, and the timing for reducing the drive current of the light source by the first adjustment is adjusted to reduce the drive current of the light source by the second adjustment. A light source device, which is performed in accordance with a timing of reduction.
[0016]
The light source device according to the present invention includes a light source, a cumulative energization time measuring means for obtaining the cumulative energization time, a timer for discriminating between daytime and nighttime, and a control means for controlling driving of the light source. And the control means, based on the accumulated energization time measuring means and the output of the timer, a first adjustment to reduce the drive current of the light source stepwise as the accumulated energization time becomes longer, A second adjustment for increasing / decreasing the drive current of the light source according to the surrounding brightness is performed, and the timing for reducing the drive current of the light source by the first adjustment is adjusted to reduce the drive current of the light source by the second adjustment. It is characterized by being performed in accordance with the timing of reduction.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a light source device 1 in which the present invention is implemented, FIGS. 2 and 3 are characteristic diagrams for explaining an embodiment of a light source driving method, and FIGS. 4 and 5 are diagrams of a light source driving method. It is a flowchart for demonstrating embodiment.
[0018]
The light source device 1 includes a light source 2 composed of one or a plurality of cold cathode tubes. The light source 2 has a characteristic that the luminance decreases with time, and is driven by the drive circuit 3. The drive circuit 3 is supplied with power from the power supply circuit 4 and is controlled by the output of the control means 5. In addition to the light source 2, the power supply circuit 4 supplies various power supplies to each part of the apparatus 1.
[0019]
The energizing time and the accumulated energizing time T of the light source 2 are measured by the measuring means 6 connected to the drive circuit 3. The energization time and cumulative energization time T of the light source measured by the measuring unit 6 are taken into the control unit 5. The control means 5 may also serve as the measurement means 6. It is desirable that the measuring means 6 or the control means 5 for taking in the data is configured so that the accumulated energization time can be maintained (backed up) even when the main power source of the light source device 1 is turned off.
[0020]
The light source device 1 is provided with a sensor 7 for obtaining information related to the brightness around the device (mounting object) in which the light source device 1 is incorporated. It is desirable that the sensor 7 has a configuration that can be placed in a place that is not easily affected by the light source 2. The sensor 7 is preferably arranged at a position shielded from the light source 2. The output of the sensor 7 is taken into the control means 5. Based on the output of the sensor 7, the control means 5 determines the brightness around the mounting target. In the following example, on the basis of the output of the sensor 7, the Day mode (hereinafter referred to as D mode) in which the brightness around the mounting target is brighter than the reference luminance (or reference illuminance) and the brightness around the mounting target are Although there are only two cases of Night mode (hereinafter referred to as N mode) darker than the reference luminance (or reference illuminance), two or more brightness categories may be provided.
[0021]
The light source device 1 is provided with a timer 8 for distinguishing between daytime and nighttime according to time or time. The control means 5 can distinguish between daytime and nighttime by the output of the timer 8. The timer 8 can share a part with the measuring means 6.
[0022]
An example of the operation (driving method) of the light source device having the above configuration will be described with reference to FIG. As shown in FIG. 2, until the cumulative energization time T of the light source 2 passes t1, the drive current of the light source is set to the maximum value or I0 (indicated by a broken line a) of 80% or more of the maximum value. With this drive current I0, the light source is turned on with the maximum luminance or a luminance near the maximum luminance. Even under the same driving current and the same conditions, the luminance decreases with time.
[0023]
When the cumulative energization time T of the light source 2 has passed t1, the drive current of the light source is reduced from I0 to I1 (indicated by a broken line b). With this drive current I1, the light source 2 is lit with a brightness that is about one step lower than before. When the cumulative energization time T of the light source 2 has elapsed t2, the driving current of the light source is reduced from I1 to I2 (indicated by a broken line c). Due to this drive current I2, the light source 2 is lit at a brightness that is one step lower than before. When the cumulative energization time T of the light source 2 elapses t3, the driving current of the light source is reduced from I2 to I3 (indicated by a broken line d). Due to this drive current I3, the light source 2 is lit with a brightness one level lower than before. When the cumulative energization time T of the light source 2 elapses t4, the drive current of the light source is reduced from I3 to I4 (indicated by a broken line e). Due to this drive current I4, the light source 2 is lit at a brightness that is one step lower than before, in this example, the lowest level of brightness. Here, the times t1 to t4 related to the cumulative energization time T are predetermined times, and are set to t1 <t2 <t3 <t4.
[0024]
As described above, the cumulative energization time T of the light source is obtained, and a driving method is used in which the drive current I of the light source 2 is reduced step by step as the cumulative energization time T becomes long. The life of the light source 2 can be extended. Since the driving current I of the light source 2 is gradually reduced, the power consumption can be reduced as compared with the case where the driving current I is gradually increased.
[0025]
FIG. 4 is a flowchart showing an example of the driving method described above, and shows an operation executed by the control means 5.
[0026]
That is, the control means 5 reads the accumulated energization time T of the light source 2 in step S1 based on the output of the measurement means 6. If it is determined in step S2 that the time T has not reached t1, the process proceeds to step S3, where the drive current I of the light source is set to the maximum value or I0 of 80% or more of the maximum value. Then, the process proceeds to step S11, where the drive current I0 is supplied by controlling the drive circuit 3, and the light source 2 is lit at the maximum luminance or the luminance near the maximum luminance.
[0027]
If it is determined in step S2 that the time T has reached t1, the process proceeds to step S4. If it is determined in step S4 that the time T has not reached t2, the process proceeds to step S5 to drive the light source. The current I is set to I1 lower than I0. In step S11, the drive circuit 3 is controlled, so that the drive current I1 is supplied, and the light source 2 is lit at a brightness one level lower than the previous brightness.
[0028]
If it is determined in step S4 that the time T has reached t2, the process proceeds to step S6. If it is determined in step S6 that the time T has not reached t3, the process proceeds to step S7 to drive the light source. The current I is set to I2 which is lower than I1. In step S11, the drive circuit 3 is controlled, so that the drive current I2 is supplied, and the light source 2 is lit at a brightness one level lower than the previous brightness.
[0029]
If it is determined in step S6 that the time T has reached t3, the process proceeds to step S8. If it is determined in step S8 that the time T has not reached t4, the process proceeds to step S9 to drive the light source. The current I is set to I3 lower than I2. In step S11, the drive circuit 3 is controlled to supply the drive current I3, and the light source 2 is turned on with a brightness one step lower than the previous brightness.
[0030]
If it is determined in step S8 that the time T has reached t4, the process proceeds to step S10, and the drive current I of the light source 2 is set to I4 lower than I3. Then, the process proceeds to step S11, and the drive current I4 is supplied by controlling the drive circuit 3, and the light source 2 is lit at a level one level lower than the previous level, in this example, the lowest level.
[0031]
Next, another example of the operation (driving method) of the light source device having the above configuration will be described with reference to FIG. In the previous example, the driving current of the light source 2 was controlled using only the cumulative energization time T as a parameter. However, in this example, in addition to the cumulative energization time T, the driving current I of the light source 2 is also used as information about the surrounding light and dark. It is something to control.
[0032]
As shown in FIG. 3, the drive current is switched between a large value and a small value depending on whether the D mode or the N mode is set. Here, since the D mode is associated with a bright surrounding, when the D mode is selected, a large drive current I is selected so that it can be seen even in a bright state. In addition, since the N mode corresponds to the case where the surrounding is dark, when the N mode is selected, a small drive current is selected to prevent overlighting.
[0033]
As in the previous example, the drive current in the D mode is decreased stepwise as the cumulative energization time T increases. What is characteristic here is that even when the cumulative energization time T reaches the time t indicating current switching during driving in the D mode, the current value is maintained without switching the driving current immediately, and the N mode is temporarily switched on. Then, when returning to the D mode, the drive current is switched to a small value. By doing so, a rapid change in luminance is prevented. The N-mode drive current is selected to be a constant value of the lowest rank, but can be gradually lowered as the cumulative energization time T becomes longer as in the D-mode.
[0034]
FIG. 5 is a flowchart showing an example of another driving method described above, and shows an operation executed by the control means 5.
[0035]
That is, the control means 5 determines whether it is D mode or N mode in step S21 based on the output of the sensor 7. As described above, in the D mode, when the brightness around the wearing object is brighter than the reference brightness (or reference illuminance), in the N mode, the brightness around the wearing object is higher than the reference brightness (or reference illuminance). It's also dark. If the D mode is selected, the process proceeds to step S22, and if the N mode is selected, the process proceeds to step S34.
[0036]
When the process proceeds to step S22 due to the selection of the D mode, the control means 5 reads the accumulated energization time T of the light source 2 based on the output of the measurement means 6. If it is determined in step S23 that the time T has not reached t1, the process proceeds to step S24, and the drive current I of the light source is set to the maximum value or I0 of 80% or more of the maximum value. Then, the process proceeds to step S35, where the drive current I0 is supplied by controlling the drive circuit 3, and the light source 2 is lit at the maximum brightness or the brightness near the maximum brightness.
[0037]
When the N mode is selected in step S21 due to use in a dark place, the process proceeds to step S34, and the drive current of the light source is reduced from I0 to I4 (indicated by a broken line e). With this drive current I4, the light source 2 is lit with the lowest level of brightness. In this way, until the cumulative energization time T of the light source 2 has passed t1, the drive current of the light source alternates between the maximum value or 80% or more of the maximum value I0 (indicated by the broken line a) and the minimum I4. Is set.
[0038]
When the cumulative energization time T of the light source 2 has passed t1, the process proceeds from step S23 to S25 and S26. In step S26, it is determined whether the N mode has been passed after the time t1 has elapsed. When the N mode is not passed, that is, when the cumulative energization time reaches a value indicating the timing of switching the driving current during the D mode, switching of the driving current is prohibited. Therefore, immediately after the elapse of time t1, the process proceeds from step S26 to step S24, and the drive current I0 up to that point is held. When it is determined in step S26 that the N mode has been passed, the process proceeds to step S27, and the drive current I1 is selected. In this way, the drive current switching timing based on the cumulative energization time T is made to coincide with the drive current switching timing based on the mode switching, thereby preventing a luminance change during the mode.
[0039]
Thereafter, in the same manner, every time the specified times t2, t3, and t4 elapse, the same processing as described above is executed in steps S21 to S35, and the drive current in the D mode is gradually changed with the elapse of the cumulative energization time T. Decrease.
[0040]
In the above embodiment, the ambient brightness is discriminated by the sensor 7 and the D mode and the N mode are made to correspond to a bright state and a dark state in the surroundings. It is possible to perform the processing shown in the flowchart of FIG. 5 by determining the D mode in the daytime and the N mode in the nighttime.
[0041]
In the above embodiment, the case where the drive current of the light source 2 is changed is taken as an example. However, the drive voltage can be controlled instead of the drive current. When the driving of the light source 2 is controlled by voltage, the driving current in the previous embodiment may be read as the driving voltage.
[0042]
【The invention's effect】
As described above, according to the present invention, the drive current is decreased stepwise as the cumulative energization time of the light source becomes longer, so that the lifetime of the light source can be extended while keeping the initial luminance high. In addition, power consumption can be reduced. In addition, since the drive current can be increased or decreased according to the brightness of the surroundings, power consumption can be further reduced. In addition, it is possible to make it difficult to understand the change in luminance when switching the drive current based on the cumulative energization time.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a light source device of the present invention.
FIG. 2 is a characteristic diagram showing a relationship between luminance and accumulated energization time in an embodiment of the present invention.
FIG. 3 is a characteristic diagram showing a relationship between luminance and accumulated energization time in another embodiment.
FIG. 4 is a flowchart showing an operation in one embodiment of the present invention.
FIG. 5 is a flowchart showing an operation in another embodiment.
FIG. 6 is a characteristic diagram showing a relationship between luminance of a general light source and accumulated energization time.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source device 2 Light source 3 Drive circuit 4 Power supply circuit 5 Control means 6 Measuring means 7 Sensor 8 Timer

Claims

A method for driving a light source, comprising: obtaining an accumulated energization time of the light source, and gradually reducing the drive current of the light source as the accumulated energization time becomes longer.

The accumulated energization time of the light source is obtained, and as the accumulated energization time becomes longer, the drive current of the light source is gradually reduced, and the drive current of the light source is increased or decreased according to the brightness of the surroundings. To drive the light source.

The cumulative energization time of the light source is obtained, and as the cumulative energization time becomes longer, the first adjustment for gradually reducing the drive current of the light source, and the drive current of the light source is increased or decreased according to the ambient brightness. A timing of reducing the driving current of the light source by the first adjustment is adjusted in accordance with a timing of reducing the driving current of the light source by the second adjustment. Driving method.

The cumulative energization time of the light source is obtained, and as the cumulative energization time becomes longer, the first adjustment for gradually reducing the drive current of the light source and the drive current of the light source are increased or decreased alternately at night and daytime. A timing of reducing the driving current of the light source by the first adjustment is adjusted in accordance with a timing of reducing the driving current of the light source by the third adjustment. Driving method.

A light source, a cumulative energization time measuring means for obtaining the cumulative energization time, and a control means for controlling the driving of the light source, the control means accumulating the light source based on the output of the cumulative energization time measuring means. A light source device that reduces the drive current of the light source stepwise as the energization time increases.

A light source, a cumulative energization time measuring means for obtaining the cumulative energization time, a sensor for detecting ambient light and darkness, and a control means for controlling the driving of the light source, wherein the control means includes the cumulative energization time measuring means and the Based on the output of the sensor, as the cumulative energization time becomes longer, a first adjustment for gradually reducing the driving current of the light source, and a first adjustment for increasing or decreasing the driving current of the light source according to ambient brightness. 2. A light source device characterized by performing adjustment of 2.

A light source, a cumulative energization time measuring means for obtaining the cumulative energization time, a sensor for detecting ambient light and darkness, and a control means for controlling the driving of the light source, wherein the control means includes the cumulative energization time measuring means and the Based on the output of the sensor, as the cumulative energization time becomes longer, a first adjustment for gradually reducing the driving current of the light source, and a first adjustment for increasing or decreasing the driving current of the light source according to ambient brightness. The light source device according to claim 1, wherein the timing of reducing the driving current of the light source by the first adjustment is matched with the timing of reducing the driving current of the light source by the second adjustment.

A light source, a cumulative energization time measuring means for obtaining the cumulative energization time, a timer for discriminating between daytime and nighttime, and a control means for controlling driving of the light source, wherein the control means includes the cumulative energization time measuring means and the Based on the output of the timer, as the cumulative energization time becomes longer, a first adjustment for gradually reducing the driving current of the light source, and a first adjustment for increasing / decreasing the driving current of the light source according to ambient brightness The light source device according to claim 1, wherein the timing of reducing the driving current of the light source by the first adjustment is matched with the timing of reducing the driving current of the light source by the second adjustment.