JP3757577B2

JP3757577B2 - Discharge lamp lighting device

Info

Publication number: JP3757577B2
Application number: JP29472897A
Authority: JP
Inventors: 勝己佐藤; 正弘山中
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 1997-10-28
Filing date: 1997-10-28
Publication date: 2006-03-22
Anticipated expiration: 2017-10-28
Also published as: JPH11135280A

Description

【０００１】
【発明の属する技術分野】
本発明は、直流電力を高周波電力に変換して放電灯に供給するインバータ回路を用いた放電灯点灯装置に関するものである。
【０００２】
【従来の技術】
図１５にインバータ回路１を用いた従来の放電灯点灯装置の一例を示す。交流電源Ｖｓにはダイオードブリッジから成る全波整流器ＤＢの交流入力端子が接続されており、全波整流器ＤＢの直流出力端子には平滑コンデンサＣ₀とスイッチング素子Ｑ₁，Ｑ₂の直列回路が並列に接続されている。また各スイッチング素子Ｑ₁，Ｑ₂には、それぞれダイオードＤ₁，Ｄ₂が逆並列接続されている。
【０００３】
低電位側のスイッチング素子Ｑ₂の両端には直流カット用のコンデンサＣ₃を介して、共振負荷回路２と予熱共振回路３が並列的に接続されている。
共振負荷回路２はインダクタＬ₁とコンデンサＣ₂の直列共振回路と、共振用のコンデンサＣ₂の両端に並列接続された放電灯Ｌａとで構成される。また予熱共振回路３はインダクタＬ₂とコンデンサＣ₄の直列共振回路よりなり、インダクタＬ₂の２次側補助巻線から放電灯Ｌａのフィラメントに予熱電流を供給するようになっている。
【０００４】
この従来装置では、制御回路１０によってスイッチング素子Ｑ₁，Ｑ₂を交互にオン・オフすることにより、ハーフブリッジ型インバータとして動作し、直流カット用のコンデンサＣ₃の出力端に高周波電圧が生成され、共振負荷回路２と予熱共振回路３に印加される。なお、制御回路１０は動作周波数（スイッチング素子Ｑ₁，Ｑ₂をオン・オフする周波数）ｆを制御する周波数制御回路１１と、周波数制御回路１１により制御されてスイッチング素子Ｑ₁，Ｑ₂を駆動するドライブ回路１２とを具備している。
【０００５】
ここで、共振負荷回路２と予熱共振回路３は高周波電圧に対して各々独立しており、各共振回路２，３を流れる電流の位相が別々に設定される。この従来例では、共振形の上記高周波電圧が印加された共振負荷回路２に流れる高周波電流を該高周波電圧に比べて遅れ位相とし、予熱共振回路３に流れる高周波電流を該高周波電圧に比べて進み位相となるようにインダクタＬ₁，Ｌ₂、コンデンサＣ₂，Ｃ₄の設計が行われている。そうすることにより、多くの予熱電流を必要とする先行予熱時に高周波電圧の周波数が高いので、予熱共振回路３から供給される予熱電流が定常時より多く供給され、逆に定常点灯時は子熱電流を低く抑えることで放電灯Ｌａのフィラメントでの損失を少なくできるといった効率の良い予熱が可能な回路構成となっている。
【０００６】
また共振負荷回路２に流れる高周波電流が遅れ位相であるのに対し、予熱共振回路３に流れる高周波電流が進み位相であることから、合成電流としては略同相で力率の高い電流となる。さらにスイッチング素子Ｑ₁，Ｑ₂に流れる電流の実効値は、共振負荷回路２のみの場合の遅れ位相電流よりも低くなり、スイッチング損失も小さくなり、低電流耐量の素子の使用が可能となって装置の小型化並びにコストダウンが実現できる。
【０００７】
【発明が解決しようとする課題】
ところで、上記従来例においては共振負荷回路２と予熱共振回路３がそれぞれ独立しているために、インダクタＬ₂及びコンデンサＣ₄の部品ばらつきによる予熱共振回路３の共振特性には共振負荷回路２と無関係にばらつきが生じる。
例えば、図１６に示すように共振負荷回路２の共振曲線に対し、動作周波数ｆに対する予熱電流Ｉｐｈの共振曲線は曲線Ａ、Ｂ、Ｃのようにばらつきを持つ。ここでｆ₂，ｆ₁，ｆ₃は各々曲線Ａ，Ｂ，Ｃにおける共振周波数であり、ｆ＝１／２π（Ｌ₂・Ｃ₄）^1/2で定められので、インダクタＬ₂とコンデンサＣ₄のばらつきでｆ₂＜ｆ₁＜ｆ₃となる。
【０００８】
ここで、先行予熱時に制御回路１０により定められた一定の動作周波数（予熱周波数）ｆ_phにてインバータ回路１を動作させるとすると、図１６に示すようにＩ_ph(a) ，Ｉ_ph(b) ，Ｉ_ph(c) （Ｉ_ph(b) ＞Ｉ_ph(a) ＞Ｉ_ph(c) ）と予熱電流に大小ができる。この予熱電流の大小は放電灯Ｌａの始動性に影響し、予熱電流が最小となるばらつきの最悪条件（図１６の場合は曲線Ｃ）において、低温時に放電灯Ｌａが点灯しにくいといった問題がある。そのような条件においても確実に放電灯Ｌａを点灯させるためには、始動電圧を高くすることが考えられるが、始動電圧を高く設定すると回路素子にも耐量の高いものを使用する必要が有り、コストアップの要因となっていた。
【０００９】
本発明は上記問題に鑑みて為されたものであり、その目的とするところは、予熱回路の部品ばらつきが生じても常に一定レベル以上の予熱電流を確保し、発振電圧を上げることなく低温時にも確実に放電灯を点灯させることができる放電灯点灯装置を提供することにある。
【００１０】
【課題を解決するための手段】
請求項１の発明は、上記目的を達成するために、交流電源を整流平滑して得られる直流電源と、高周波でオン・オフされる１乃至複数のスイッチング素子を具備して前記直流電源の直流電圧を高周波電圧に変換するインバータ回路と、放電灯を有し前記インバータ回路より印加される高周波電圧に対して遅れ位相となる電流が流れる共振負荷回路と、前記インバータ回路より印加される高周波電圧に対して進み位相となる電流が流れ放電灯のフィラメントに予熱電流を供給する予熱共振回路と、前記放電灯のフィラメントに流れる予熱電流レベルを検出する予熱電流検出回路と、前記スイッチング素子をオン・オフさせてインバータ回路の動作周波数を制御する制御回路とを備え、該制御回路は、放電灯始動時の先行予熱期間に前記予熱電流検出回路で検出された予熱電流レベルが所定のレベル以上となる動作周波数にて所定の時間だけ予熱を行なうように前記インバータ回路の動作周波数を制御して成る放電灯点灯装置であって、前記制御回路は、前記予熱共振回路の共振周波数がばらつきにより最も高くなる周波数よりも高い第１の予熱周波数に動作周波数を設定してインバータ回路の動作を開始させ、前記予熱電流検出回路により検出される予熱電流レベルが前記所定レベルを越える第２の予熱周波数まで前記インバータ回路の動作周波数を変化させ、越えた時点でインバータ回路の動作周波数を第２の予熱周波数に固定して前記所定時間だけ予熱を行なうように制御することを特徴とし、予熱共振回路を構成するインダクタやコンデンサなどの部品ばらつきによって共振特性にばらつきが生じた場合であっても、予熱電流検出回路により予熱電流のレベルを検出しながら、制御回路にて放電灯のフィラメントを予熱するのに充分なレベルの予熱電流が常に供給されるようにインバータ回路の動作周波数を制御するから、常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯の始動時の発振電圧を低く抑えることができる。その結果、従来例に比較して低耐量の素子を使用することができてコストダウンが可能となる。
【００１２】
請求項２の発明は、上記目的を達成するために、交流電源を整流平滑して得られる直流電源と、高周波でオン・オフされる１乃至複数のスイッチング素子を具備して前記直流電源の直流電圧を高周波電圧に変換するインバータ回路と、放電灯を有し前記インバータ回路より印加される高周波電圧に対して遅れ位相となる電流が流れる共振負荷回路と、前記インバータ回路より印加される高周波電圧に対して進み位相となる電流が流れ放電灯のフィラメントに予熱電流を供給する予熱共振回路と、前記放電灯のフィラメントに流れる予熱電流レベルを検出する予熱電流検出回路と、前記スイッチング素子をオン・オフさせてインバータ回路の動作周波数を制御する制御回路とを備え、該制御回路は、放電灯始動時の先行予熱期間に前記予熱電流検出回路で検出された予熱電流レベルが所定のレベル以上となる動作周波数にて所定の時間だけ予熱を行なうように前記インバータ回路の動作周波数を制御して成る放電灯点灯装置であって、前記制御回路が、前記予熱共振回路の共振周波数がばらつきにより最も低くなる周波数よりも低い第１の予熱周波数に動作周波数を設定してインバータ回路の動作を開始させ、前記予熱電流検出回路により検出される予熱電流レベルが前記所定レベルを越える第２の予熱周波数まで前記インバータ回路の動作周波数を変化させ、越えた時点でインバータ回路の動作周波数を第２の予熱周波数に固定して前記所定時間だけ予熱を行なうよう制御することを特徴とし、予熱共振回路を構成するインダクタやコンデンサなどの部品ばらつきによって共振特性にばらつきが生じた場合であっても、予熱電流検出回路により予熱電流のレベルを検出しながら、制御回路にて放電灯のフィラメントを予熱するのに充分なレベルの予熱電流が常に供給されるようにインバータ回路の動作周波数を制御するから、常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯の始動時の発振電圧を低く抑えることができる。その結果、従来例に比較して低耐量の素子を使用することができてコストダウンが可能となる。
【００１３】
請求項３の発明は、上記目的を達成するために、交流電源を整流平滑して得られる直流電源と、高周波でオン・オフされる１乃至複数のスイッチング素子を具備して前記直流電源の直流電圧を高周波電圧に変換するインバータ回路と、放電灯を有し前記インバータ回路より印加される高周波電圧に対して遅れ位相となる電流が流れる共振負荷回路と、前記インバータ回路より印加される高周波電圧に対して進み位相となる電流が流れ放電灯のフィラメントに予熱電流を供給する予熱共振回路と、前記放電灯のフィラメントに流れる予熱電流レベルを検出する予熱電流検出回路と、前記スイッチング素子をオン・オフさせてインバータ回路の動作周波数を制御する制御回路とを備え、該制御回路は、放電灯始動時の先行予熱期間に前記予熱電流検出回路で検出された予熱電流レベルが所定のレベル以上となる動作周波数にて所定の時間だけ予熱を行なうように前記インバータ回路の動作周波数を制御して成る放電灯点灯装置であって、前記制御回路が、前記予熱共振回路の共振周波数のばらつきの中央値に略等しい第１の予熱周波数に動作周波数を設定してインバータ回路の動作を開始させ、第１の予熱周波数よりも高い又は低い第２の予熱周波数に前記インバータ回路の動作周波数を設定するとともに前記予熱電流検出回路にて検出される予熱電流レベルが第１の予熱周波数での動作時の予熱電流レベルよりも高い場合には第１の予熱周波数から第２の予熱周波数への変化方向と同一方向に前記インバータ回路の動作周波数を変化させ、前記予熱電流検出回路にて検出される予熱電流レベルが第１の予熱周波数での動作時の予熱電流レベルよりも低い場合には第１の予熱周波数から第２の予熱周波数への変化方向と逆方向に前記インバータ回路の動作周波数を変化させるように制御し、前記検出される予熱電流レベルが前記所定レベルを越えるまで動作周波数を変化させ、越えた時点でインバータ回路の動作周波数を固定して前記所定時間だけ予熱を行なうよう制御することを特徴とし、予熱共振回路を構成するインダクタやコンデンサなどの部品ばらつきによって共振特性にばらつきが生じた場合であっても、予熱電流検出回路により予熱電流のレベルを検出しながら、制御回路にて放電灯のフィラメントを予熱するのに充分なレベルの予熱電流が常に供給されるようにインバータ回路の動作周波数を制御するから、常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯の始動時の発振電圧を低く抑えることができる。その結果、従来例に比較して低耐量の素子を使用することができてコストダウンが可能となる。
【００１４】
請求項４の発明は、請求項１〜３の何れかの発明において、前記インバータ回路が前記直流電源の出力端間に接続されて交互にオン・オフされる一対のスイッチング素子を具備して成り、該スイッチング素子の一方に前記共振負荷回路及び予熱共振回路を並列に接続して成ることを特徴とし、スイッチング素子におけるスイッチング損失が小さくでき、低電流耐量の素子の使用が可能となって装置の小型化並びにコストダウンが実現できる。
【００１５】
請求項５の発明は、請求項１〜３の何れかの発明において、前記インバータ回路が、平滑コンデンサの直列回路と、ダイオードが逆並列に接続されて交互にオン・オフされる一対のスイッチング素子の直列回路とが互いに並列に前記直流電源の出力端間に接続されて成ることを特徴とし、定常点灯時における予熱電流を抑えて放電灯のフィラメントでの電力損失を低減することができる。
【００１６】
請求項６の発明は、請求項１〜３の何れかの発明において、前記インバータ回路が、前記直流電源の出力端間に一対のスイッチング素子を直列接続し、低電位側の前記スイッチング素子と前記直流電源の出力端との間に第１及び第２のダイオードの直列回路を挿入し、該第１及び第２のダイオードの直列回路の接続点と前記スイッチング素子の接続点との間に前記予熱共振回路及び共振負荷回路を接続するとともにスイッチング素子側に接続された第２のダイオードの両端にコンデンサを接続して成ることを特徴とし、第２のダイオードの両端に接続されたコンデンサで直流電源からの直流入力電圧を昇圧することによって、入力電流高調波を低く抑えることができる。
【００１７】
【発明の実施の形態】
（実施形態１）
図１は本発明の第１の実施形態を示す回路ブロック図である。
ダイオードブリッジから成る全波整流器ＤＢの交流入力端子に交流電源Ｖｓが接続され、全波整流器ＤＢの直流出力端子には平滑用のコンデンサＣ₀を介してインバータ回路１が並列に接続されている。
【００１８】
インバータ回路１は、例えば従来例と同様のハーフブリッジ型やフルブリッジ型等の従来周知の構成を有するものである。このインバータ回路１の出力端には、共振負荷回路２と予熱共振回路３が並列接続され、インバータ回路１から出力される高周波電圧Ｖ₀が両者に印加される。
また、インバータ回路の発振周波数（動作周波数）は制御回路４によって制御される。この制御回路４は、インバータ回路１が具備する１乃至複数のスイッチング素子（図示せず）のオン・オフのタイミングを設定して上記動作周波数を制御する周波数制御回路５と、この周波数制御回路５からの信号を受けてインバータ回路１のスイッチング素子を駆動するドライブ回路６と、放電灯Ｌａのフィラメントに流れる予熱電流レベルを検出する予熱電流検出回路７とを備え、予熱電流検出回路７にて共振負荷回路２又は予熱共振回路３に流れる電流から予熱電流レベルを検出し、周波数制御回路５へフィードバックしている。
【００１９】
共振負荷回路２は、インダクタＬ₁とコンデンサＣ₂の直列共振回路を有し、コンデンサＣ₂の両端に放電灯Ｌａのフィラメントの一端ｆ₂，ｆ₄が接続されており、インバータ回路１から供給される高周波電圧Ｖ₀に対して遅れた位相の電流Ｉ₁が流れるようにインダクタＬ₁のインダクタンス値とコンデンサＣ₂の容量とが設定されている。
【００２０】
一方、予熱共振回路３はインダクタＬ₂とコンデンサＣ₄との直列共振回路から成り、インダクタＬ₂に設けられた補助巻線ｎ₁，ｎ₂がそれぞれ放電灯Ｌａのフィラメントの両端ｆ₁〜ｆ₄に接続されており、インバータ回路１から供給される高周波電圧Ｖ₀に対して進んだ位相の電流Ｉ₂が流れるようにインダクタＬ₂のインダクタンス値とコンデンサＣ₄の容量とが設定されている。
【００２１】
而して、制御回路４によりインバータ回路１を制御して高周波電圧Ｖ₀を共振負荷回路２及び予熱共振回路３に印加し、放電灯Ｌａの予熱から始動及び点灯維持（定常点灯）を行なうものである。
ところが、予熱共振回路３から放電灯Ｌａのフィラメントに供給される予熱電流Ｉ_phは、予熱共振回路３を構成するインダクタＬ₂やコンデンサＣ₄の部品ばらつきにより、図３の曲線Ａ〜Ｃに示すように、その共振特性にもばらつきが生じることになる。
【００２２】
而して、本発明は、このような共振特性のばらつきに対して常に一定以上の予熱電流が確保できるようにしたものである。
次に本実施形態において一定以上の予熱電流を確保する（流す）ための動作について、図２〜図４を参照して説明する。図２は本実施形態における制御回路４の制御動作のタイムチャートを示している。まず、時刻ｔ＝ｔ₀で交流電源Ｖｓが投入されて制御回路４が動作を開始すると、周波数制御回路５は、予熱共振回路３の共振周波数がインダクタＬ₂及びコンデンサＣ₄のばらつきにより最も高くなる周波数（図３におけるｆ₃）よりも高い第１の予熱周波数ｆ_ph1でインバータ回路１の動作を開始させる。
【００２３】
そして、周波数制御回路５は、時刻ｔ＝ｔ₀〜ｔ₁の期間に予熱電流検出回路７によって予熱電流を検出しながら、図４に示すように予熱電流が所定レベルＩ_ph0を越える第２の予熱周波数ｆ_ph2までインバータ回路１の動作周波数ｆを徐々に変化させる（低くする）。ここで、予熱電流が所定レベルＩ_ph0を越える第２の予熱周波数ｆ_ph2は、図４に示すようにインダクタＬ₂及びコンデンサＣ₄によって異なり、曲線Ａで表される共振特性の場合をｆ_ph2(a)、曲線Ｂで表される共振特性の場合をｆ_ph2(b)、曲線Ｃで表される共振特性の場合をｆ_ph2(c)で表すことにする。
【００２４】
周波数制御回路５は、予熱電流検出回路７で検出されるレベルが上記所定レベルＩ_ph0を越えた時点でインバータ回路１の動作周波数ｆを第２の予熱周波数ｆ_ph2(a)又はｆ_ph2(b)又はｆ_ph2(c)に固定し、所定の予熱期間（図２における時刻ｔ＝ｔ₁〜ｔ₂）だけ放電灯Ｌａのフィラメントを予熱する。
そして、周波数制御回路５が、動作周波数ｆを第２の予熱周波数ｆ_ph2(a)…から始動に必要な高電圧が得られる始動周波数ｆ_stにまで低下させ、時刻ｔ＝ｔ₂〜ｔ₃の間（始動期間）だけ始動周波数ｆ_stに固定する（この動作モードを始動モードと呼ぶ。）。その結果、放電灯Ｌａが始動した後（時刻ｔ＝ｔ₃以降）は、周波数制御回路５が放電灯Ｌａを定常点灯させるために始動周波数ｆ_stよりもさらに低い周波数ｆ_CTでインバータ回路１を動作させる（この動作モードを定常点灯モードと呼ぶ。）。
【００２５】
上述のように本実施形態によれば、予熱共振回路３を構成するインダクタＬ₂やコンデンサＣ₄の部品ばらつきによって共振特性にばらつきが生じた場合であっても、予熱電流検出回路７により予熱電流のレベルを検出しながら、周波数制御回路５にて放電灯Ｌａのフィラメントを予熱するのに充分なレベルの予熱電流が常に供給されるようにインバータ回路１の動作周波数ｆを制御するから、常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯Ｌａの始動時の発振電圧を低く抑えることができる。その結果、従来例に比較して低耐量の素子を使用することができてコストダウンが可能となる。
【００２６】
（実施形態２）
図５は本発明の第２の実施形態を示す回路ブロック図である。なお、本実施形態は、図１５に示した従来例と基本的な構成を共通にしているので、共通する部分には同一の符号を付して説明を省略し、本実施形態の特徴となる部分についてのみ説明する。
【００２７】
本実施形態では、予熱共振回路３のインダクタＬ₂の２次側に補助巻線ｎ₃を設けるとともに、補助巻線ｎ₃を通して放電灯Ｌａのフィラメントに供給される予熱電流レベルを検出する予熱電流検出回路７が制御回路４に具備されている。而して、周波数制御回路５、ドライブ回路６及び予熱電流検出回路７で構成される制御回路４が実施形態１と共通の制御動作を行うことにより、本実施形態においても常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯Ｌａの始動時の発振電圧を低く抑えることができる。
【００２８】
インバータ回路１は、ダイオードＤ₁，Ｄ₂が逆並列に接続された一対のスイッチング素子Ｑ₁，Ｑ₂の直列回路が平滑コンデンサＣ₀と並列に全波整流器ＤＢの直流出力端間に接続されて成るものである。
スイッチング素子Ｑ₁，Ｑ₂の接続点と全波整流器ＤＢの低電位側の直流出力端との間には直流カット用のコンデンサＣ₃を介して、共振負荷回路２を構成するインダクタＬ₁及びコンデンサＣ₂が直列接続され、コンデンサＣ₂の両端に放電灯Ｌａのフィラメントの一端ｆ₁，ｆ₃が接続されている。また、スイッチング素子Ｑ₂及びコンデンサＣ₃と並列にインダクタＬ₂とコンデンサＣ₄の直列回路から成る予熱共振回路３が接続されており、インダクタＬ₂に設けられた補助巻線ｎ₁，ｎ₂が放電灯Ｌａのフィラメント両端ｆ₁〜ｆ₄に接続されている。なお、インダクタＬ₂には予熱電流検出用の補助巻線ｎ₃も設けてある。
【００２９】
さらに本実施形態においては、従来例で説明したように共振負荷回路２に流れる高周波電流が遅れ位相であるのに対し、予熱共振回路３に流れる高周波電流が進み位相であることから、合成電流としては略同相で力率の高い電流となり、しかもインバータ回路１のスイッチング素子Ｑ₁，Ｑ₂に流れる電流の実効値が共振負荷回路２のみの場合の遅れ位相電流よりも低くなるので、スイッチング損失も小さくなり、低電流耐量の素子の使用が可能となって装置の小型化並びにコストダウンが実現できる。
【００３０】
（実施形態３）
図６は本発明の第３の実施形態を示す回路ブロック図である。なお、本実施形態の基本構成は実施形態１と共通であるので、共通する部分には同一の符号を付して説明は省略する。
図６に示すように、全波整流器ＤＢの直流出力端子には平滑コンデンサＣ₁₁，Ｃ₁₂の直列回路とダイオードＤ₁，Ｄ₂が逆並列に接続されたスイッチング素子Ｑ₁，Ｑ₂の直列回路とが互いに並列に接続されており、これらスイッチング素子Ｑ₁，Ｑ₂、ダイオードＤ₁，Ｄ₂並びに平滑コンデンサＣ₁₁，Ｃ₁₂にて所謂ハーフブリッジ型のインバータ回路１’を構成している。
【００３１】
スイッチング素子Ｑ₁，Ｑ₂の接続点と平滑コンデンサＣ₁₁，Ｃ₁₂の接続点の間には、直流カット用のコンデンサＣ₃を介してインダクタＬ₁、コンデンサＣ₂及び蛍光灯等の放電灯Ｌａにより構成される共振負荷回路２と、共振負荷回路２と並列接続されたインダクタＬ₂とコンデンサＣ₄の直列回路から成る予熱共振回路３とが接続されている。なお、予熱共振回路３のインダクタＬ₂には、放電灯Ｌａのフィラメントに予熱電流を供給するための補助巻線ｎ₁，ｎ₂と、制御回路４の予熱電流検出回路７にて予熱電流レベルを検出するための補助巻線ｎ₃とが設けてある。
【００３２】
また制御回路４は、インバータ回路１のスイッチング素子Ｑ₁，Ｑ₂のオン・オフのタイミングを設定してインバータ回路１の動作周波数ｆを制御する周波数制御回路５と、この周波数制御回路５からの信号を受けてインバータ回路１のスイッチング素子Ｑ₁，Ｑ₂を駆動するドライブ回路６と、放電灯Ｌａのフィラメントに流れる予熱電流レベルを検出する予熱電流検出回路７とを備え、予熱電流検出回路７にてインダクタＬ₂の補助巻線ｎ₃を通して予熱共振回路３に流れる電流から予熱電流レベルを検出し、周波数制御回路５へフィードバックしている。
【００３３】
而して、本実施形態では、交流電源Ｖｓが投入されると制御回路４によりスイッチング素子Ｑ₁，Ｑ₂が交互にオン、オフされ、インバータ回路１の出力端間に矩形波の高周波電圧が生じる。この高周波電圧が共振負荷回路２のインダクタＬ₁及びコンデンサＣ₂の直列回路による共振作用により昇圧されて放電灯Ｌａの両電極間に印加され、放電灯Ｌａが点灯するのである。
【００３４】
次に本実施形態における予熱から始動及び点灯に至るまでの制御動作について図７〜図９を参照して説明する。図７は本実施形態における制御回路４の制御動作のタイムチャートを示している。まず、時刻ｔ＝ｔ₀で交流電源Ｖｓが投入されて制御回路４が動作を開始すると、周波数制御回路５は、予熱共振回路３の共振周波数がインダクタＬ₂及びコンデンサＣ₄のばらつきにより最も低くなる周波数（図８におけるｆ₂）よりも低い第１の予熱周波数ｆ_ph1でインバータ回路１の動作を開始させる。
【００３５】
そして、周波数制御回路５は、時刻ｔ＝ｔ₀〜ｔ₁の期間に予熱電流検出回路７によって予熱電流を検出しながら、図９に示すように予熱電流が所定レベルＩ_ph0を越える第２の予熱周波数ｆ_ph2までインバータ回路１の動作周波数ｆを徐々に変化させる（高くする）。ここで、予熱電流が所定レベルＩ_ph0を越える第２の予熱周波数ｆ_ph2は、図９に示すようにインダクタＬ₂及びコンデンサＣ₄によって異なり、曲線Ａで表される共振特性の場合をｆ_ph2(a)、曲線Ｂで表される共振特性の場合をｆ_ph2(b)、曲線Ｃで表される共振特性の場合をｆ_ph2(c)で表すことにする。
【００３６】
周波数制御回路５は、予熱電流検出回路７で検出されるレベルが上記所定レベルＩ_ph0を越えた時点でインバータ回路１の動作周波数ｆを第２の予熱周波数ｆ_ph2(a)又はｆ_ph2(b)又はｆ_ph2(c)に固定し、所定の予熱期間（図７における時刻ｔ＝ｔ₁〜ｔ₂）だけ放電灯Ｌａのフィラメントを予熱する。
そして、周波数制御回路５が、動作周波数ｆを第２の予熱周波数ｆ_ph2(a)…から始動に必要な高電圧が得られる始動周波数ｆ_stにまで低下させ、時刻ｔ＝ｔ₂〜ｔ₃の間（始動期間）だけ始動周波数ｆ_stに固定する。その結果、放電灯Ｌａが始動した後（時刻ｔ＝ｔ₃以降）は、周波数制御回路５が放電灯Ｌａを定常点灯させるために始動周波数ｆ_stよりもさらに低い周波数ｆ_CTでインバータ回路１を動作させる。
【００３７】
上述のように本実施形態によれば、予熱共振回路３を構成するインダクタＬ₂やコンデンサＣ₄の部品ばらつきによって共振特性にばらつきが生じた場合であっても、予熱電流検出回路７により予熱電流のレベルを検出しながら、周波数制御回路５にて放電灯Ｌａのフィラメントを予熱するのに充分なレベルの予熱電流が常に供給されるようにインバータ回路１の動作周波数ｆを制御するから、常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯Ｌａの始動時の発振電圧を低く抑えることができる。その結果、従来例に比較して低耐量の素子を使用することができてコストダウンが可能となる。
【００３８】
（実施形態４）
図１０は本発明の第４の実施形態を示す回路ブロック図である。本実施形態は、インバータ回路１”により入力電流高調波を低く抑えることができるとともに、定常点灯時において放電灯Ｌａのフィラメントに供給される予熱電流（以下、「常時予熱電流」と呼ぶ。）を低く抑えることでフィラメントでの損失を低減することができるものであるが、基本的な構成については実施形態１〜３と共通であるので、共通する部分については同一の符号を付して説明を省略する。
【００３９】
本実施形態では、交流電源Ｖｓを全波整流器ＤＢで全波整流した直流電圧をインバータ回路１”に供給する。インバータ回路１”は、全波整流器ＤＢの直流出力端に接続されたコンデンサＣ₁₀、スイッチング素子Ｑ₁，Ｑ₂の直列回路、全波整流器ＤＢの負の出力端子及びスイッチング素子Ｑ₂のソース間に接続されたダイオードＤ₃，Ｄ₄の直列回路、ダイオードＤ₄の両端に接続されたコンデンサＣ₈により構成されている。また、インバータ回路１”の両端にはコンデンサＣ₉が接続されている。
【００４０】
スイッチング素子Ｑ₁，Ｑ₂は電界効果トランジスタから成り、逆並列に接続された寄生ダイオードを具備している。そして、制御回路４のドライブ回路６によってスイッチング素子Ｑ₁，Ｑ₂が交互にオン・オフ駆動される。スイッチング素子Ｑ₁，Ｑ₂の接続点とダイオードＤ₃，Ｄ₄の接続点との間には、直流カット用のコンデンサＣ₃を介して予熱共振回路３”と共振負荷回路２”とが低電位側のスイッチング素子Ｑ₂と並列に接続されている。
【００４１】
共振負荷回路２”は、コンデンサＣ₃とダイオードＤ₃，Ｄ₄の接続点との間に接続されたインダクタＬ₁及びトランスＴ₁の一次巻線ｎ₁の直列回路と、トランスＴ₁の２次巻線ｎ₂の両端に直流カット用のコンデンサＣ₅を介して並列接続された放電灯ＬａとコンデンサＣ₂の並列回路とで構成される。
また予熱共振回路３”は、コンデンサＣ₃を介してスイッチング素子Ｑ₂の両端に接続されたインダクタＬ₂とコンデンサＣ₄の直列回路で構成され、インダクタＬ₂の２次側に放電灯Ｌａのフィラメントに予熱電流を供給するための補助巻線ｎ₁，ｎ₂が設けてある。なお、予熱電流が流れるループ内（放電灯Ｌａのフィラメントの一端ｆ₄）には、予熱電流レベルを検出するために電流トランスＴ₂が挿入してある。
【００４２】
一方、高電位側のスイッチング素子Ｑ₁の両端にはインダクタＬ₃と平滑用コンデンサＣ₀とダイオードＤ₇が直列接続され、ダイオードＤ₇を介して極性が逆方向になるようにダイオードＤ₅が並列接続されている。また、低電位側のスイッチング素子Ｑ₂の両端にはダイオードＤ₇を介して極性が逆方向になるようにダイオードＤ₆が並列接続されており、コンデンサＣ₀とインダクタＬ₃とダイオードＤ₅，Ｄ₇により降圧チョッパ回路が構成されている。
【００４３】
スイッチング素子Ｑ₁，Ｑ₂をオン・オフ制御する制御回路４は、実施形態１〜３と同様に、動作周波数ｆを制御する周波数制御回路５と、スイッチング素子Ｑ₁，Ｑ₂を直接駆動するためのドライブ回路６、電流トランスＴ₂より予熱電流レベルを検出して周波数制御回路５へフィードバックする予熱電流検出回路７とで構成される。
【００４４】
次に本実施形態において入力電流高調波を低く抑える動作について説明する。
まず、スイッチング素子Ｑ₁がオン、スイッチング素子Ｑ₂がオフすると、平滑コンデンサＣ₀からインダクタＬ₃→スイッチング素子Ｑ₁→コンデンサＣ₃→インダクタＬ₁→トランスＴ₁の一次巻線ｎ₁→コンデンサＣ₈→ダイオードＤ₆→平滑コンデンサＣ₀の経路で共振電流が流れ、この共振電流によりコンデンサＣ₈が充電されることによって、コンデンサＣ₈の両端電圧Ｖｃ₈が上昇していく。そして、全波整流器ＤＢの出力電圧（直流電圧）とコンデンサＣ₈の両端電圧Ｖｃ₈との和の電圧が、平滑コンデンサＣ₀からインバータ回路１”に供給される電圧を越えた時点で、交流電源Ｖｓから全波整流器ＤＢ→スイッチング素子Ｑ₁→コンデンサＣ₃→インダクタＬ₁→トランスＴ₁の一次巻線ｎ₁→ダイオードＤ₃→全波整流器ＤＢ→交流電源Ｖｓの経路でも共振電流が流れ、これが全波整流器ＤＢからの入力電流となる。この入力電流が流れる期間は電源電圧Ｖｓの大きさに略比例して変化するので、入力電流が電源電圧Ｖｓに比例した正弦波状となり、入力高調波が低く抑えられる（これを第１の動作モードと呼ぶ。）。
【００４５】
続いて、スイッチング素子Ｑ₁がオフ、スイッチング素子Ｑ₂がオンすると、まず、インダクタＬ₁に蓄積されていたエネルギが放出されることにより、インダクタＬ₁→トランスＴ₁の一次巻線ｎ₁→コンデンサＣ₈→スイッチング素子Ｑ₂の寄生ダイオード→コンデンサＣ₃→インダクタＬ₁の経路で電流が流れ、やがてインダクタＬ₁の蓄積エネルギが放出されると、回生電流によって充電された直流カット用のコンデンサＣ₃を電源として、コンデンサＣ₃→スイッチング素子Ｑ₂→コンデンサＣ₈→トランスＴ₁の一次巻線ｎ₁→インダクタＬ₁→コンデンサＣ₃の経路で電流が流れ、この電流によりコンデンサＣ₈の両端電圧Ｖｃ₈が低下していく（これを第２の動作モードと呼ぶ。）。
【００４６】
さらに続いて、スイッチング素子Ｑ₂がオフ、スイッチング素子Ｑ₁がオンすると、インダクタＬ₁に蓄積されていたエネルギが放出されることにより、インダクタＬ₁→コンデンサＣ₃→スイッチング素子Ｑ₁の寄生ダイオード→コンデンサＣ₉→コンデンサＣ₈→トランスＴ₁の一次巻線ｎ₁→インダクタＬ₁の経路で電流が流れ、コンデンサＣ₈の両端電圧Ｖｃ₈が低下し続ける。コンデンサＣ₈の電荷が完全に放電すると、コンデンサＣ₈を介さずにダイオードＤ₄を介して電流が流れ、やがてインダクタＬ₁の蓄積エネルギが放出されると、上記第１の動作モードに戻る（これを第３の動作モードと呼ぶ。）。
このように第１〜第３の動作モードを繰返すことにより、インバータ回路１”は入力電流の高調波抑制動作を行うとともに高周波発振動作を行い、トランスＴ₁の２次巻線ｎ₂の両端から高周波電圧を印加して放電灯Ｌａを点灯する。また、予熱共振回路３”のインダクタＬ₂とコンデンサＣ₄の共振動作によって、インダクタＬ₂の補助巻線ｎ₁，ｎ₂の両端に高周波電圧が発生し、コンデンサを介して放電灯Ｌａのフィラメントに予熱電流が供給されるのである。
【００４７】
次に降圧チョッパ回路の動作について説明する。
まず、スイッチング素子Ｑ₂がオンすると、交流電源Ｖｓ→全波整流器ＤＢ→インダクタＬ₃→平滑コンデンサＣ₀→スイッチング素子Ｑ₂→ダイオードＤ₄→ダイオードＤ₃→全波整流器ＤＢ→交流電源Ｖｓの経路で平滑コンデンサＣ₀が充電されるとともに、インダクタＬ₃にエネルギが蓄積される。なお、コンデンサＣ₉の放電時には、コンデンサＣ₉→インダクタＬ₃→平滑コンデンサＣ₀→ダイオードＤ₇→スイッチング素子Ｑ₂→コンデンサＣ₉の経路で平滑コンデンサＣ₀が充電される。
【００４８】
続いてスイッチング素子Ｑ₂がオフすると、インダクタＬ₃→平滑コンデンサＣ₀→ダイオードＤ₇→スイッチング素子Ｑ₂の寄生ダイオード→インダクタＬ₃の経路でインダクタＬ₃に蓄積されていたエネルギが放出されて平滑コンデンサＣ₀が充電される。
上記動作を繰り返すことにより、降圧チョッパ回路の出力電圧が平滑コンデンサＣ₀の両端に発生する。
【００４９】
ここで本実施形態では、共振負荷回路２の固有振動周波数ｆ₁と予熱共振回路３の固有振動周波数ｆ₂とのインバータ回路１”（スイッチング素子Ｑ₁，Ｑ₂）の動作周波数ｆに対する関係をｆ₁＜ｆ＜ｆ₂としている。つまり、共振負荷回路２の共振電流がインバータ回路１”の高周波出力電圧に対して遅れ位相となり、予熱共振回路３の共振電流がインバータ回路１”の高周波出力電圧に対して進み位相とすることにより、定常時に放電灯Ｌａのフィラメントに流れる常時予熱電流による電力ロスの低減と、進相電流と遅相電流の合成によるスイッチング素子Ｑ₁，Ｑ₂を流れる電流の低減効果とを得ている。
【００５０】
次に本実施形態における予熱から始動及び点灯に至るまでの制御動作について図１１〜図１３並びに図１４のフローチャートを参照して説明する。図１１は本実施形態における制御回路４の制御動作のタイムチャートを示している。まず、時刻ｔ＝ｔ₀で交流電源Ｖｓが投入されて制御回路４が動作を開始すると、周波数制御回路５は、予熱共振回路３の共振周波数がインダクタＬ₂及びコンデンサＣ₄のばらつきがほぼ中央値のときの固有振動周波数に略等しい第１の予熱周波数ｆ_ph1でインバータ回路１”の動作を開始させる。
【００５１】
そして、周波数制御回路５は、時刻ｔ＝ｔ₀〜ｔ₁の期間に予熱電流検出回路７によって予熱電流Ｉ_ph1を検出して所定レベルＩ_ph0との大小比較を行ない、検出した予熱電流Ｉ_ph1が所定レベルＩ_ph0を越えている（Ｉ_ph1＞Ｉ_ph0）場合には、動作周波数ｆを第１の予熱周波数ｆ_ph1に固定したまま所定時間（例えば、約１秒間）の予熱を行なう。
【００５２】
一方、検出した予熱電流Ｉ_ph1が所定レベルＩ_ph0を下回っている（Ｉ_ph1＜Ｉ_ph0）場合には、周波数制御回路５がインバータ回路１”の動作周波数ｆを第１の予熱周波数ｆ_ph1から第２の予熱周波数ｆ_ph2に下げて共振条件を変更する（ｆ_ph1＞ｆ_ph2）。そして、インバータ回路１”を第２の予熱周波数ｆ_ph2で動作させつつ予熱電流検出回路７によって予熱電流Ｉ_ph2を検出し、第１の予熱周波数ｆ_ph1で動作させたときの予熱電流Ｉ_ph1との大小比較を繰り返して行ない、予熱電流Ｉ_ph2が予熱電流Ｉ_ph1よりも高い（Ｉ_ph2＞Ｉ_ph1）場合には、図１２に示すように更に動作周波数ｆを下げながら所定レベルＩ_ph0との大小比較を繰り返して行ない、検出した予熱電流Ｉ_ph2が所定レベルＩ_ph0を越える（Ｉ_ph2＞Ｉ_ph0）ときの第３の予熱周波数ｆ_ph3にインバータ回路１”の動作周波数ｆを設定して所定時間（例えば、約１秒間）の予熱を行なう。
【００５３】
一方、予熱電流Ｉ_ph2が予熱電流Ｉ_ph1よりも低い（Ｉ_ph2＜Ｉ_ph1）場合には、図１３に示すように逆に動作周波数ｆを上げながら所定レベルＩ_ph0との大小比較を繰り返して行ない、検出した予熱電流Ｉ_ph2が所定レベルＩ_ph0を越える（Ｉ_ph2＞Ｉ_ph0）ときの第３の予熱周波数ｆ_ph3にインバータ回路１”の動作周波数ｆを設定して所定時間（例えば、約１秒間）の予熱を行なう。
【００５４】
而して周波数制御回路５は、時刻ｔ＝ｔ₀〜ｔ₁の期間（予熱期間）に予熱電流が所定レベルＩ_ph0を越えるような第３の予熱周波数ｆ_ph3にインバータ回路１”の動作周波数ｆを設定し、所定の予熱期間（図１１における時刻ｔ＝ｔ₁〜ｔ₂）だけ放電灯Ｌａのフィラメントを予熱する。そして、周波数制御回路５が、動作周波数ｆを第３の予熱周波数ｆ_ph3から始動に必要な高電圧が得られる始動周波数ｆ_stにまで低下させ、時刻ｔ＝ｔ₂〜ｔ₃の間（始動期間）だけ始動周波数ｆ_stに固定する。その結果、放電灯Ｌａが始動した後（時刻ｔ＝ｔ₃以降）は、周波数制御回路５が放電灯Ｌａを定常点灯させるために始動周波数ｆ_stよりもさらに低い周波数ｆ_CTでインバータ回路１”を動作させる。
【００５５】
上述のように本実施形態によれば、予熱共振回路３を構成するインダクタＬ₂やコンデンサＣ₄の部品ばらつきによって共振特性にばらつきが生じた場合であっても、予熱電流検出回路７により予熱電流のレベルを検出しながら、周波数制御回路５にて放電灯Ｌａのフィラメントを予熱するのに充分なレベルの予熱電流が常に供給されるようにインバータ回路１”の動作周波数ｆを制御するから、常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯Ｌａの始動時の発振電圧を低く抑えることができる。その結果、従来例に比較して低耐量の素子を使用することができてコストダウンが可能となる。
【００５６】
なお、本実施形態においては、交流電源Ｖｓを全波整流器ＤＢで全波整流した直流出力電圧と平滑用のコンデンサＣ₀との間に、入力電流高調波低減効果を得るために挿入されたコンデンサＣ₈があるため、全波整流器ＤＢの直流出力電圧が昇圧する。放電灯Ｌａの始動時の発振電圧と上記直流出力電圧の昇圧比は比例関係にあり、発振電圧を高くする（始動時のインバータ回路１”の動作周波数ｆを下げる）と直流出力電圧が高くなるが、本実施形態では放電灯Ｌａの始動時における発振電圧を低く抑えることができ、全波整流器ＤＢの直流出力電圧の昇圧が従来より低く抑えることができるので、低耐圧の素子の使用が可能となってコストダウンが図れるという利点がある。
【００５７】
【発明の効果】
請求項１の発明は、交流電源を整流平滑して得られる直流電源と、高周波でオン・オフされる１乃至複数のスイッチング素子を具備して前記直流電源の直流電圧を高周波電圧に変換するインバータ回路と、放電灯を有し前記インバータ回路より印加される高周波電圧に対して遅れ位相となる電流が流れる共振負荷回路と、前記インバータ回路より印加される高周波電圧に対して進み位相となる電流が流れ放電灯のフィラメントに予熱電流を供給する予熱共振回路と、前記放電灯のフィラメントに流れる予熱電流レベルを検出する予熱電流検出回路と、前記スイッチング素子をオン・オフさせてインバータ回路の動作周波数を制御する制御回路とを備え、該制御回路は、放電灯始動時の先行予熱期間に前記予熱電流検出回路で検出された予熱電流レベルが所定のレベル以上となる動作周波数にて所定の時間だけ予熱を行なうように前記インバータ回路の動作周波数を制御して成る放電灯点灯装置であって、前記制御回路は、前記予熱共振回路の共振周波数がばらつきにより最も高くなる周波数よりも高い第１の予熱周波数に動作周波数を設定してインバータ回路の動作を開始させ、前記予熱電流検出回路により検出される予熱電流レベルが前記所定レベルを越える第２の予熱周波数まで前記インバータ回路の動作周波数を変化させ、越えた時点でインバータ回路の動作周波数を第２の予熱周波数に固定して前記所定時間だけ予熱を行なうように制御するので、予熱共振回路を構成するインダクタやコンデンサなどの部品ばらつきによって共振特性にばらつきが生じた場合であっても、予熱電流検出回路により予熱電流のレベルを検出しながら、制御回路にて放電灯のフィラメントを予熱するのに充分なレベルの予熱電流が常に供給されるようにインバータ回路の動作周波数を制御するから、常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯の始動時の発振電圧を低く抑えることができ、その結果、従来例に比較して低耐量の素子を使用することができてコストダウンが可能となるという効果がある。
【００５９】
請求項２の発明は、交流電源を整流平滑して得られる直流電源と、高周波でオン・オフされる１乃至複数のスイッチング素子を具備して前記直流電源の直流電圧を高周波電圧に変換するインバータ回路と、放電灯を有し前記インバータ回路より印加される高周波電圧に対して遅れ位相となる電流が流れる共振負荷回路と、前記インバータ回路より印加される高周波電圧に対して進み位相となる電流が流れ放電灯のフィラメントに予熱電流を供給する予熱共振回路と、前記放電灯のフィラメントに流れる予熱電流レベルを検出する予熱電流検出回路と、前記スイッチング素子をオン・オフさせてインバータ回路の動作周波数を制御する制御回路とを備え、該制御回路は、放電灯始動時の先行予熱期間に前記予熱電流検出回路で検出された予熱電流レベルが所定のレベル以上となる動作周波数にて所定の時間だけ予熱を行なうように前記インバータ回路の動作周波数を制御して成る放電灯点灯装置であって、前記制御回路が、前記予熱共振回路の共振周波数がばらつきにより最も低くなる周波数よりも低い第１の予熱周波数に動作周波数を設定してインバータ回路の動作を開始させ、前記予熱電流検出回路により検出される予熱電流レベルが前記所定レベルを越える第２の予熱周波数まで前記インバータ回路の動作周波数を変化させ、越えた時点でインバータ回路の動作周波数を第２の予熱周波数に固定して前記所定時間だけ予熱を行なうよう制御するので、予熱共振回路を構成するインダクタやコンデンサなどの部品ばらつきによって共振特性にばらつきが生じた場合であっても、予熱電流検出回路により予熱電流のレベルを検出しながら、制御回路にて放電灯のフィラメントを予熱するのに充分なレベルの予熱電流が常に供給されるようにインバータ回路の動作周波数を制御するから、常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯の始動時の発振電圧を低く抑えることができ、その結果、従来例に比較して低耐量の素子を使用することができてコストダウンが可能となるという効果がある。
【００６０】
請求項３の発明は、交流電源を整流平滑して得られる直流電源と、高周波でオン・オフされる１乃至複数のスイッチング素子を具備して前記直流電源の直流電圧を高周波電圧に変換するインバータ回路と、放電灯を有し前記インバータ回路より印加される高周波電圧に対して遅れ位相となる電流が流れる共振負荷回路と、前記インバータ回路より印加される高周波電圧に対して進み位相となる電流が流れ放電灯のフィラメントに予熱電流を供給する予熱共振回路と、前記放電灯のフィラメントに流れる予熱電流レベルを検出する予熱電流検出回路と、前記スイッチング素子をオン・オフさせてインバータ回路の動作周波数を制御する制御回路とを備え、該制御回路は、放電灯始動時の先行予熱期間に前記予熱電流検出回路で検出された予熱電流レベルが所定のレベル以上となる動作周波数にて所定の時間だけ予熱を行なうように前記インバータ回路の動作周波数を制御して成る放電灯点灯装置であって、前記制御回路が、前記予熱共振回路の共振周波数のばらつきの中央値に略等しい第１の予熱周波数に動作周波数を設定してインバータ回路の動作を開始させ、第１の予熱周波数よりも高い又は低い第２の予熱周波数に前記インバータ回路の動作周波数を設定するとともに前記予熱電流検出回路にて検出される予熱電流レベルが第１の予熱周波数での動作時の予熱電流レベルよりも高い場合には第１の予熱周波数から第２の予熱周波数への変化方向と同一方向に前記インバータ回路の動作周波数を変化させ、前記予熱電流検出回路にて検出される予熱電流レベルが第１の予熱周波数での動作時の予熱電流レベルよりも低い場合には第１の予熱周波数から第２の予熱周波数への変化方向と逆方向に前記インバータ回路の動作周波数を変化させるように制御し、前記検出される予熱電流レベルが前記所定レベルを越えるまで動作周波数を変化させ、越えた時点でインバータ回路の動作周波数を固定して前記所定時間だけ予熱を行なうよう制御するので、予熱共振回路を構成するインダクタやコンデンサなどの部品ばらつきによって共振特性にばらつきが生じた場合であっても、予熱電流検出回路により予熱電流のレベルを検出しながら、制御回路にて放電灯のフィラメントを予熱するのに充分なレベルの予熱電流が常に供給されるようにインバータ回路の動作周波数を制御するから、常に所定のレベル以上の予熱電流を確保する（流す）ことができ、部品ばらつきや低温始動に対しても放電灯の始動時の発振電圧を低く抑えることができ、その結果、従来例に比較して低耐量の素子を使用することができてコストダウンが可能となるという効果がある。
【００６１】
請求項４の発明は、前記インバータ回路が前記直流電源の出力端間に接続されて交互にオン・オフされる一対のスイッチング素子を具備して成り、該スイッチング素子の一方に前記共振負荷回路及び予熱共振回路を並列に接続して成るので、スイッチング素子におけるスイッチング損失が小さくでき、低電流耐量の素子の使用が可能となって装置の小型化並びにコストダウンが実現できるという効果がある。
【００６２】
請求項５の発明は、前記インバータ回路が、平滑コンデンサの直列回路と、ダイオードが逆並列に接続されて交互にオン・オフされる一対のスイッチング素子の直列回路とが互いに並列に前記直流電源の出力端間に接続されて成るので、定常点灯時における予熱電流を抑えて放電灯のフィラメントでの電力損失を低減することができるという効果がある。
【００６３】
請求項６の発明は、前記インバータ回路が、前記直流電源の出力端間に一対のスイッチング素子を直列接続し、低電位側の前記スイッチング素子と前記直流電源の出力端との間に第１及び第２のダイオードの直列回路を挿入し、該第１及び第２のダイオードの直列回路の接続点と前記スイッチング素子の接続点との間に前記予熱共振回路及び共振負荷回路を接続するとともにスイッチング素子側に接続された第２のダイオードの両端にコンデンサを接続して成るので、第２のダイオードの両端に接続されたコンデンサで直流電源からの直流入力電圧を昇圧することによって、入力電流高調波を低く抑えることができるという効果がある。
【図面の簡単な説明】
【図１】実施形態１を示す回路ブロック図である。
【図２】同上の動作を説明するためのタイムチャートである。
【図３】同上における共振負荷回路及び予熱共振回路の共振特性を示す図である。
【図４】同上における共振負荷回路及び予熱共振回路の共振特性を示す図である。
【図５】実施形態２を示す回路ブロック図である。
【図６】実施形態３を示す回路ブロック図である。
【図７】同上の動作を説明するためのタイムチャートである。
【図８】同上における共振負荷回路及び予熱共振回路の共振特性を示す図である。
【図９】同上における共振負荷回路及び予熱共振回路の共振特性を示す図である。
【図１０】実施形態４を示す回路ブロック図である。
【図１１】同上の動作を説明するためのタイムチャートである。
【図１２】同上における共振負荷回路及び予熱共振回路の共振特性を示す図である。
【図１３】同上における共振負荷回路及び予熱共振回路の共振特性を示す図である。
【図１４】同上の動作を説明するためのフローチャートである。
【図１５】従来例を示す回路ブロック図である。
【図１６】同上における共振負荷回路及び予熱共振回路の共振特性を示す図である。
【符号の説明】
１インバータ回路
２共振負荷回路
３予熱共振回路
４制御回路
５周波数制御回路
６ドライブ回路
７予熱電流検出回路
Ｖｓ交流電源
ＤＢ全波整流器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a discharge lamp lighting device using an inverter circuit that converts DC power into high-frequency power and supplies it to a discharge lamp.
[0002]
[Prior art]
FIG. 15 shows an example of a conventional discharge lamp lighting device using the inverter circuit 1. The AC power supply Vs is connected to an AC input terminal of a full-wave rectifier DB composed of a diode bridge. A smoothing capacitor C is connected to a DC output terminal of the full-wave rectifier DB. ₀ And switching element Q ₁ , Q ₂ Are connected in parallel. Each switching element Q ₁ , Q ₂ Respectively, diode D ₁ , D ₂ Are connected in reverse parallel.
[0003]
Switching element Q on the low potential side ₂ DC cut capacitor C at both ends _Three The resonant load circuit 2 and the preheating resonant circuit 3 are connected in parallel.
The resonant load circuit 2 is an inductor L ₁ And capacitor C ₂ Series resonance circuit and resonance capacitor C ₂ And a discharge lamp La connected in parallel to both ends of the lamp. Further, the preheating resonance circuit 3 includes an inductor L ₂ And capacitor C _Four Inductor L ₂ A preheating current is supplied to the filament of the discharge lamp La from the secondary side auxiliary winding.
[0004]
In this conventional apparatus, the switching element Q is controlled by the control circuit 10. ₁ , Q ₂ Are alternately turned on and off to operate as a half-bridge inverter, and a DC-cut capacitor C _Three A high-frequency voltage is generated at the output terminal of the power supply circuit and applied to the resonant load circuit 2 and the preheating resonant circuit 3. The control circuit 10 has an operating frequency (switching element Q ₁ , Q ₂ Frequency control circuit 11 for controlling f), and switching element Q controlled by frequency control circuit 11 ₁ , Q ₂ And a drive circuit 12 for driving.
[0005]
Here, the resonant load circuit 2 and the preheating resonant circuit 3 are independent of each other with respect to the high frequency voltage, and the phases of the currents flowing through the resonant circuits 2 and 3 are set separately. In this conventional example, the high-frequency current flowing through the resonant load circuit 2 to which the resonance type high-frequency voltage is applied is set to a delayed phase compared to the high-frequency voltage, and the high-frequency current flowing through the preheating resonance circuit 3 is advanced compared to the high-frequency voltage. Inductor L to be in phase ₁ , L ₂ , Capacitor C ₂ , C _Four Is being designed. By doing so, since the frequency of the high-frequency voltage is high at the time of pre-heating that requires a large amount of pre-heating current, the pre-heating current supplied from the pre-heating resonance circuit 3 is supplied more than in the steady state, and conversely the child heat during steady lighting The circuit configuration is capable of efficient preheating such that the loss in the filament of the discharge lamp La can be reduced by keeping the current low.
[0006]
Further, since the high-frequency current flowing through the resonant load circuit 2 is in a delayed phase, the high-frequency current flowing through the preheating resonant circuit 3 is in a leading phase, so that the combined current is a current having substantially the same phase and a high power factor. Furthermore, switching element Q ₁ , Q ₂ The effective value of the current flowing in the circuit is lower than the lagging phase current in the case of the resonant load circuit 2 alone, the switching loss is also reduced, and the device with low current resistance can be used, thereby reducing the size and cost of the device. realizable.
[0007]
[Problems to be solved by the invention]
By the way, in the above conventional example, the resonant load circuit 2 and the preheating resonant circuit 3 are independent from each other. ₂ And capacitor C _Four The resonance characteristics of the preheating resonance circuit 3 due to the component variations vary depending on the resonance load circuit 2.
For example, as shown in FIG. 16, the resonance curve of the preheating current Iph with respect to the operating frequency f varies as shown by curves A, B, and C with respect to the resonance curve of the resonant load circuit 2. Where f ₂ , F ₁ , F _Three Are resonance frequencies in curves A, B, and C, respectively, and f = 1 / 2π (L ₂ ・ C _Four ) ^1/2 Inductor L ₂ And capacitor C _Four F ₂ <F ₁ <F _Three It becomes.
[0008]
Here, a constant operating frequency (preheating frequency) f determined by the control circuit 10 during the preceding preheating. _ph If the inverter circuit 1 is operated at the same time, as shown in FIG. _ph (a), I _ph (b), I _ph (c) (I _ph (b)> I _ph (a)> I _ph (c) The preheating current can be increased or decreased. The magnitude of the preheating current affects the startability of the discharge lamp La, and there is a problem that the discharge lamp La is difficult to light at low temperatures in the worst condition of variation in which the preheating current is minimized (curve C in FIG. 16). . To ensure that the discharge lamp La is lit even under such conditions, it is conceivable to increase the starting voltage. However, if the starting voltage is set high, it is necessary to use a circuit element with a high tolerance. It was a factor of cost increase.
[0009]
The present invention has been made in view of the above problems, and the object of the present invention is to always ensure a preheating current of a certain level or more at low temperatures without increasing the oscillation voltage, even if there are variations in the components of the preheating circuit. It is another object of the present invention to provide a discharge lamp lighting device capable of reliably lighting a discharge lamp.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention comprises a DC power source obtained by rectifying and smoothing an AC power source, and one or more switching elements that are turned on and off at a high frequency. An inverter circuit that converts a voltage into a high-frequency voltage, a resonant load circuit that has a discharge lamp and a current that is delayed in phase with respect to the high-frequency voltage applied from the inverter circuit, and a high-frequency voltage that is applied from the inverter circuit On the other hand, a preheating resonance circuit for supplying a preheating current to the filament of the discharge lamp, a preheating current circuit for detecting a preheating current level flowing in the filament of the discharge lamp, and turning on / off the switching element. And a control circuit for controlling the operating frequency of the inverter circuit, the control circuit including the preheating current during a preheating period at the start of the discharge lamp. Controlling the operating frequency of the inverter circuit as preheating current level detected by the circuit performs a pre-heating for a predetermined time at an operating frequency equal to or greater than a predetermined level out In the discharge lamp lighting device, the control circuit sets the operating frequency to a first preheating frequency higher than a frequency at which the resonance frequency of the preheating resonance circuit becomes highest due to variation, and operates the inverter circuit. The operating frequency of the inverter circuit is changed to a second preheating frequency at which the preheating current level detected by the preheating current detection circuit exceeds the predetermined level. The preheating frequency is fixed and controlled to perform preheating for the predetermined time. Even if the resonance characteristics vary due to variations in components such as inductors and capacitors that make up the preheating resonance circuit, the control circuit detects the preheating current level with the preheating current detection circuit. Since the operating frequency of the inverter circuit is controlled so that a preheating current at a level sufficient to preheat the filament of the discharge lamp is always supplied, a preheating current exceeding a predetermined level can always be secured (flowed), The oscillation voltage at the start of the discharge lamp can be kept low even with respect to component variations and low temperature start. As a result, it is possible to use an element having a lower tolerance compared to the conventional example, and the cost can be reduced.
[0012]
Claim 2 The invention of In order to achieve the above object, a DC power source obtained by rectifying and smoothing an AC power source and one or more switching elements that are turned on / off at a high frequency are provided, and the DC voltage of the DC power source is converted into a high frequency voltage. An inverter circuit, a resonant load circuit having a discharge lamp and a current that is delayed in phase with respect to the high-frequency voltage applied from the inverter circuit, and a current that is in a leading phase with respect to the high-frequency voltage applied from the inverter circuit A preheating resonance circuit for supplying a preheating current to the filament of the discharge lamp, a preheating current detection circuit for detecting a preheating current level flowing in the filament of the discharge lamp, and an operating frequency of the inverter circuit by turning on and off the switching element And a control circuit that controls the preheating current detection circuit during the preheating period at the start of the discharge lamp. Preheating current level a the inverter discharge lamp lighting device formed by controlling the operating frequency of the circuit to perform a preheating for a predetermined time at an operating frequency equal to or greater than a predetermined level, The control circuit sets the operating frequency to a first preheating frequency lower than the frequency at which the resonance frequency of the preheating resonance circuit is lowest due to variations, starts the operation of the inverter circuit, and is detected by the preheating current detection circuit. The operating frequency of the inverter circuit is changed to a second preheating frequency at which the preheating current level exceeds the predetermined level, and when it exceeds, the operating frequency of the inverter circuit is fixed at the second preheating frequency and preheated for the predetermined time. It is characterized by controlling to perform, Even if the resonance characteristics vary due to variations in the components such as inductors and capacitors that make up the preheating resonance circuit, the control circuit detects the preheating current level while the preheating current detection circuit detects the preheating current filament. Because the operating frequency of the inverter circuit is controlled so that a preheating current at a level sufficient for preheating is always supplied, A preheating current of a predetermined level or higher can always be secured (flowed), and the oscillation voltage at the start of the discharge lamp can be kept low even with respect to component variations and low temperature start. As a result, it is possible to use an element having a lower tolerance compared to the conventional example, and the cost can be reduced.
[0013]
Claim 3 The invention of In order to achieve the above object, a DC power source obtained by rectifying and smoothing an AC power source and one or more switching elements that are turned on / off at a high frequency are provided, and the DC voltage of the DC power source is converted into a high frequency voltage. An inverter circuit, a resonant load circuit having a discharge lamp and a current that is delayed in phase with respect to the high-frequency voltage applied from the inverter circuit, and a current that is in a leading phase with respect to the high-frequency voltage applied from the inverter circuit A preheating resonance circuit for supplying a preheating current to the filament of the discharge lamp, a preheating current detection circuit for detecting a preheating current level flowing in the filament of the discharge lamp, and an operating frequency of the inverter circuit by turning on and off the switching element And a control circuit that controls the preheating current detection circuit during the preheating period at the start of the discharge lamp. Preheating current level a the inverter discharge lamp lighting device formed by controlling the operating frequency of the circuit to perform a preheating for a predetermined time at an operating frequency equal to or greater than a predetermined level, The control circuit sets the operating frequency to the first preheating frequency substantially equal to the median value of the variation in the resonance frequency of the preheating resonance circuit to start the operation of the inverter circuit, and is higher or lower than the first preheating frequency. When the operating frequency of the inverter circuit is set to the second preheating frequency and the preheating current level detected by the preheating current detection circuit is higher than the preheating current level during operation at the first preheating frequency, The operation frequency of the inverter circuit is changed in the same direction as the change direction from the preheating frequency of 1 to the second preheating frequency, and the preheating current level detected by the preheating current detection circuit is the operation at the first preheating frequency. If the preheating current level is lower than the current preheating current level, the operating frequency of the inverter circuit is changed in the direction opposite to the change direction from the first preheating frequency to the second preheating frequency. The operating frequency is changed until the detected preheating current level exceeds the predetermined level, and when it exceeds, the operating frequency of the inverter circuit is fixed and the preheating is controlled for the predetermined time. age, Even if the resonance characteristics vary due to variations in the components such as inductors and capacitors that make up the preheating resonance circuit, the control circuit detects the preheating current level while the preheating current detection circuit detects the preheating current filament. Because the operating frequency of the inverter circuit is controlled so that a preheating current at a level sufficient for preheating is always supplied, A preheating current of a predetermined level or higher can always be secured (flowed), and the oscillation voltage at the start of the discharge lamp can be kept low even with respect to component variations and low temperature start. As a result, it is possible to use an element having a lower tolerance compared to the conventional example, and the cost can be reduced.
[0014]
Claim 4 The invention of claim 1 Any of ~ 3 In the invention, the inverter circuit includes a pair of switching elements connected between output terminals of the DC power supply and alternately turned on and off, and one of the switching elements includes the resonant load circuit and the preheating resonant circuit. Are connected in parallel, switching loss in the switching element can be reduced, and an element having a low current resistance can be used, so that downsizing and cost reduction of the apparatus can be realized.
[0015]
Claim 5 The invention of claim 1 Any of ~ 3 In the invention, the inverter circuit includes a series circuit of a smoothing capacitor and a series circuit of a pair of switching elements that are alternately turned on and off by connecting a diode in antiparallel between the output terminals of the DC power supply. It is characterized in that the power loss in the filament of the discharge lamp can be reduced by suppressing the preheating current during steady lighting.
[0016]
Claim 6 The invention of claim 1 Any of ~ 3 In the invention, the inverter circuit connects a pair of switching elements in series between the output terminals of the DC power supply, and the first and second switching elements are connected between the switching element on the low potential side and the output terminal of the DC power supply. A series circuit of diodes is inserted, and the preheating resonance circuit and the resonance load circuit are connected between the connection point of the series circuit of the first and second diodes and the connection point of the switching element and connected to the switching element side. A capacitor is connected to both ends of the second diode, and a DC input voltage from a DC power source is boosted by a capacitor connected to both ends of the second diode. It can be kept low.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 is a circuit block diagram showing a first embodiment of the present invention.
An AC power supply Vs is connected to an AC input terminal of a full-wave rectifier DB composed of a diode bridge, and a smoothing capacitor C is connected to a DC output terminal of the full-wave rectifier DB. ₀ The inverter circuit 1 is connected in parallel via
[0018]
The inverter circuit 1 has a conventionally known configuration such as a half-bridge type and a full-bridge type similar to the conventional example. A resonant load circuit 2 and a preheating resonant circuit 3 are connected in parallel to the output terminal of the inverter circuit 1, and a high-frequency voltage V output from the inverter circuit 1. ₀ Is applied to both.
The oscillation frequency (operating frequency) of the inverter circuit is controlled by the control circuit 4. The control circuit 4 includes a frequency control circuit 5 that controls the operating frequency by setting on / off timings of one or more switching elements (not shown) included in the inverter circuit 1, and the frequency control circuit 5. Drive circuit 6 that drives the switching element of inverter circuit 1 in response to the signal from, and a preheating current detection circuit 7 that detects the preheating current level that flows through the filament of discharge lamp La, and resonates in preheating current detection circuit 7. The preheating current level is detected from the current flowing through the load circuit 2 or the preheating resonance circuit 3 and fed back to the frequency control circuit 5.
[0019]
The resonant load circuit 2 includes an inductor L ₁ And capacitor C ₂ Series resonance circuit and capacitor C ₂ One end f of the filament of the discharge lamp La at both ends of ₂ , F _Four Is connected, and the high-frequency voltage V supplied from the inverter circuit 1 is ₀ Phase current I delayed from ₁ Inductor L so that ₁ Inductance value and capacitor C ₂ Capacity is set.
[0020]
On the other hand, the preheating resonance circuit 3 includes an inductor L ₂ And capacitor C _Four Inductor L ₂ Auxiliary winding n provided in ₁ , N ₂ Are both ends f of the filament of the discharge lamp La. ₁ ~ F _Four The high frequency voltage V supplied from the inverter circuit 1 is connected to ₀ Phase current I with respect to ₂ Inductor L so that ₂ Inductance value and capacitor C _Four Capacity is set.
[0021]
Thus, the control circuit 4 controls the inverter circuit 1 to control the high frequency voltage V ₀ Is applied to the resonant load circuit 2 and the preheating resonant circuit 3 to start and maintain the lighting (steady lighting) from the preheating of the discharge lamp La.
However, the preheating current I supplied from the preheating resonance circuit 3 to the filament of the discharge lamp La _ph Is the inductor L constituting the preheating resonance circuit 3 ₂ And capacitor C _Four Due to the component variations, the resonance characteristics also vary as shown by the curves A to C in FIG.
[0022]
Thus, the present invention can always ensure a preheating current of a certain level or more with respect to such variations in resonance characteristics.
Next, an operation for securing (flowing) a preheating current of a certain level or higher in the present embodiment will be described with reference to FIGS. FIG. 2 shows a time chart of the control operation of the control circuit 4 in the present embodiment. First, time t = t ₀ When the AC power source Vs is turned on and the control circuit 4 starts operating, the frequency control circuit 5 determines that the resonance frequency of the preheating resonance circuit 3 is the inductor L. ₂ And capacitor C _Four Frequency (f in FIG. 3) _Three ) Higher first preheating frequency f _ph1 Then, the operation of the inverter circuit 1 is started.
[0023]
Then, the frequency control circuit 5 generates a time t = t ₀ ~ T ₁ While the preheating current is detected by the preheating current detection circuit 7 during this period, the preheating current is reduced to a predetermined level I as shown in FIG. _ph0 The second preheating frequency f exceeding _ph2 Until the operating frequency f of the inverter circuit 1 is gradually changed (lowered). Here, the preheating current is at a predetermined level I _ph0 The second preheating frequency f exceeding _ph2 Is the inductor L as shown in FIG. ₂ And capacitor C _Four The resonance characteristic represented by curve A is f. _ph2 (a) The case of the resonance characteristic represented by curve B is f _ph2 (b) The resonance characteristic represented by the curve C is f _ph2 It will be expressed as (c).
[0024]
In the frequency control circuit 5, the level detected by the preheating current detection circuit 7 is the predetermined level I. _ph0 When the operating frequency f of the inverter circuit 1 exceeds the second preheating frequency f _ph2 (a) or f _ph2 (b) or f _ph2 (c), a predetermined preheating period (time t = t in FIG. 2) ₁ ~ T ₂ ) Only preheat the filament of the discharge lamp La.
Then, the frequency control circuit 5 changes the operating frequency f to the second preheating frequency f. _ph2 (a) The starting frequency f at which a high voltage required for starting is obtained from _st Until time t = t ₂ ~ T _Three The start frequency f only during (start period) _st (This operation mode is referred to as a start mode). As a result, after the discharge lamp La is started (time t = t _Three After), the frequency control circuit 5 causes the discharge lamp La to be steadily lit so that the starting frequency f _st Lower frequency f _CT Then, the inverter circuit 1 is operated (this operation mode is called a steady lighting mode).
[0025]
As described above, according to the present embodiment, the inductor L that constitutes the preheating resonance circuit 3. ₂ And capacitor C _Four Even if the resonance characteristics vary due to component variations, the frequency control circuit 5 is sufficient to preheat the filament of the discharge lamp La while detecting the level of the preheating current with the preheating current detection circuit 7. Since the operating frequency f of the inverter circuit 1 is controlled so that a level of preheating current is always supplied, a preheating current of a predetermined level or higher can be secured (flowed) at all times, and even for component variations and low temperature starting The oscillation voltage at the start of the discharge lamp La can be kept low. As a result, it is possible to use an element having a lower tolerance compared to the conventional example, and the cost can be reduced.
[0026]
(Embodiment 2)
FIG. 5 is a circuit block diagram showing a second embodiment of the present invention. Since this embodiment shares the same basic configuration as the conventional example shown in FIG. 15, common portions are denoted by the same reference numerals, description thereof is omitted, and this embodiment is a feature of this embodiment. Only the part will be described.
[0027]
In the present embodiment, the inductor L of the preheating resonance circuit 3 ₂ Auxiliary winding n on the secondary side of _Three And an auxiliary winding n _Three A preheating current detection circuit 7 for detecting the preheating current level supplied to the filament of the discharge lamp La through the control circuit 4 is provided. Thus, the control circuit 4 including the frequency control circuit 5, the drive circuit 6, and the preheating current detection circuit 7 performs the same control operation as that of the first embodiment, so that a predetermined level or higher is always maintained in this embodiment. The preheating current can be secured (flowed), and the oscillation voltage at the start of the discharge lamp La can be kept low even with respect to component variations and low temperature start.
[0028]
The inverter circuit 1 includes a diode D ₁ , D ₂ Are a pair of switching elements Q connected in antiparallel ₁ , Q ₂ Is a smoothing capacitor C ₀ Connected in parallel with the DC output terminal of the full-wave rectifier DB.
Switching element Q ₁ , Q ₂ And a DC-cut capacitor C between the low-potential side DC output terminal of the full-wave rectifier DB and the full-wave rectifier DB. _Three Through the inductor L constituting the resonant load circuit 2 ₁ And capacitor C ₂ Are connected in series, and the capacitor C ₂ One end f of the filament of the discharge lamp La at both ends of ₁ , F _Three Is connected. The switching element Q ₂ And capacitor C _Three Inductor L in parallel with ₂ And capacitor C _Four Is connected to a preheating resonance circuit 3 composed of a series circuit of the inductor L ₂ Auxiliary winding n provided in ₁ , N ₂ Is the filament ends f of the discharge lamp La ₁ ~ F _Four It is connected to the. Inductor L ₂ Has an auxiliary winding n for preheating current detection _Three Is also provided.
[0029]
Furthermore, in the present embodiment, as described in the conventional example, the high-frequency current flowing through the resonant load circuit 2 has a delayed phase, whereas the high-frequency current flowing through the preheating resonant circuit 3 has a leading phase. Is a current having a high power factor in substantially the same phase, and the switching element Q of the inverter circuit 1 ₁ , Q ₂ Since the effective value of the current flowing through the capacitor is lower than the lagging phase current when only the resonant load circuit 2 is used, the switching loss is reduced, and a device with a low current resistance can be used, thereby reducing the size and cost of the device. realizable.
[0030]
(Embodiment 3)
FIG. 6 is a circuit block diagram showing a third embodiment of the present invention. Since the basic configuration of the present embodiment is the same as that of the first embodiment, common portions are denoted by the same reference numerals and description thereof is omitted.
As shown in FIG. 6, the smoothing capacitor C is connected to the DC output terminal of the full-wave rectifier DB. ₁₁ , C ₁₂ Series circuit and diode D ₁ , D ₂ Are switching elements Q connected in antiparallel ₁ , Q ₂ Are connected in parallel to each other, and these switching elements Q ₁ , Q ₂ , Diode D ₁ , D ₂ And smoothing capacitor C ₁₁ , C ₁₂ Constitutes a so-called half-bridge type inverter circuit 1 '.
[0031]
Switching element Q ₁ , Q ₂ Connection point and smoothing capacitor C ₁₁ , C ₁₂ Between the connection points, a DC cut capacitor C _Three Through inductor L ₁ , Capacitor C ₂ And a resonant load circuit 2 composed of a discharge lamp La such as a fluorescent lamp, and an inductor L connected in parallel with the resonant load circuit 2 ₂ And capacitor C _Four Are connected to a preheating resonance circuit 3 composed of a series circuit. The inductor L of the preheating resonance circuit 3 ₂ Includes an auxiliary winding n for supplying a preheating current to the filament of the discharge lamp La ₁ , N ₂ And an auxiliary winding n for detecting the preheating current level in the preheating current detection circuit 7 of the control circuit 4 _Three Are provided.
[0032]
The control circuit 4 also includes a switching element Q of the inverter circuit 1. ₁ , Q ₂ The frequency control circuit 5 that controls the operating frequency f of the inverter circuit 1 by setting the ON / OFF timing of the inverter circuit 1 and the switching element Q of the inverter circuit 1 in response to a signal from the frequency control circuit 5 ₁ , Q ₂ And a preheating current detection circuit 7 for detecting the preheating current level flowing in the filament of the discharge lamp La. The preheating current detection circuit 7 uses the inductor L ₂ Auxiliary winding n _Three The preheating current level is detected from the current flowing through the preheating resonance circuit 3 through the control circuit 5 and fed back to the frequency control circuit 5.
[0033]
Thus, in the present embodiment, when the AC power source Vs is turned on, the switching element Q is controlled by the control circuit 4. ₁ , Q ₂ Are alternately turned on and off, and a rectangular high-frequency voltage is generated between the output terminals of the inverter circuit 1. This high frequency voltage is applied to the inductor L of the resonant load circuit 2. ₁ And capacitor C ₂ The voltage is boosted by the resonance action of the series circuit and applied between both electrodes of the discharge lamp La, and the discharge lamp La is lit.
[0034]
Next, control operations from preheating to starting and lighting in the present embodiment will be described with reference to FIGS. FIG. 7 shows a time chart of the control operation of the control circuit 4 in the present embodiment. First, time t = t ₀ When the AC power source Vs is turned on and the control circuit 4 starts operating, the frequency control circuit 5 determines that the resonance frequency of the preheating resonance circuit 3 is the inductor L. ₂ And capacitor C _Four (The frequency f in FIG. ₂ ) Lower first preheating frequency f _ph1 Then, the operation of the inverter circuit 1 is started.
[0035]
Then, the frequency control circuit 5 generates a time t = t ₀ ~ T ₁ While the preheating current is detected by the preheating current detection circuit 7 during this period, the preheating current is reduced to a predetermined level I as shown in FIG. _ph0 The second preheating frequency f exceeding _ph2 Until the operating frequency f of the inverter circuit 1 is gradually changed (increased). Here, the preheating current is at a predetermined level I _ph0 The second preheating frequency f exceeding _ph2 Is the inductor L as shown in FIG. ₂ And capacitor C _Four The resonance characteristic represented by curve A is f. _ph2 (a) The case of the resonance characteristic represented by curve B is f _ph2 (b) The resonance characteristic represented by the curve C is f _ph2 It will be expressed as (c).
[0036]
In the frequency control circuit 5, the level detected by the preheating current detection circuit 7 is the predetermined level I. _ph0 When the operating frequency f of the inverter circuit 1 exceeds the second preheating frequency f _ph2 (a) or f _ph2 (b) or f _ph2 (c), a predetermined preheating period (time t = t in FIG. 7) ₁ ~ T ₂ ) Only preheat the filament of the discharge lamp La.
Then, the frequency control circuit 5 changes the operating frequency f to the second preheating frequency f. _ph2 (a) The starting frequency f at which a high voltage required for starting is obtained from _st Until time t = t ₂ ~ T _Three The start frequency f only during (start period) _st To fix. As a result, after the discharge lamp La is started (time t = t _Three After), the frequency control circuit 5 causes the discharge lamp La to be steadily lit so that the starting frequency f _st Lower frequency f _CT Then, the inverter circuit 1 is operated.
[0037]
As described above, according to the present embodiment, the inductor L that constitutes the preheating resonance circuit 3. ₂ And capacitor C _Four Even if the resonance characteristics vary due to component variations, the frequency control circuit 5 is sufficient to preheat the filament of the discharge lamp La while detecting the level of the preheating current with the preheating current detection circuit 7. Since the operating frequency f of the inverter circuit 1 is controlled so that a level of preheating current is always supplied, a preheating current of a predetermined level or higher can be secured (flowed) at all times, and even for component variations and low temperature starting The oscillation voltage at the start of the discharge lamp La can be kept low. As a result, it is possible to use an element having a lower tolerance compared to the conventional example, and the cost can be reduced.
[0038]
(Embodiment 4)
FIG. 10 is a circuit block diagram showing a fourth embodiment of the present invention. In the present embodiment, the inverter circuit 1 ″ can suppress the input current harmonics to a low level, and the preheating current (hereinafter referred to as “always preheating current”) supplied to the filament of the discharge lamp La during steady lighting. Although it is possible to reduce the loss in the filament by keeping it low, the basic configuration is the same as in the first to third embodiments, so the same reference numerals are given to the common parts and the description will be made. Omitted.
[0039]
In the present embodiment, a DC voltage obtained by full-wave rectification of the AC power supply Vs by the full-wave rectifier DB is supplied to the inverter circuit 1 ″. The inverter circuit 1 ″ is a capacitor C connected to the DC output terminal of the full-wave rectifier DB. _Ten , Switching element Q ₁ , Q ₂ Series circuit, negative output terminal of full-wave rectifier DB and switching element Q ₂ D connected between the sources of _Three , D _Four Series circuit of diode D _Four Capacitor C connected to both ends of ₈ It is comprised by. In addition, a capacitor C is connected to both ends of the inverter circuit 1 ″. ₉ Is connected.
[0040]
Switching element Q ₁ , Q ₂ Consists of field effect transistors and has a parasitic diode connected in antiparallel. Then, the switching element Q is driven by the drive circuit 6 of the control circuit 4. ₁ , Q ₂ Are alternately turned on and off. Switching element Q ₁ , Q ₂ Connection point and diode D _Three , D _Four DC cut capacitor C _Three The preheating resonance circuit 3 "and the resonance load circuit 2" are connected to the switching element Q on the low potential side via ₂ Connected in parallel.
[0041]
The resonant load circuit 2 "is a capacitor C _Three And diode D _Three , D _Four Inductor L connected between the connection points of ₁ And transformer T ₁ Primary winding n ₁ Series circuit and transformer T ₁ Secondary winding n ₂ Capacitor C for DC cut at both ends _Five Discharge lamp La and capacitor C connected in parallel via ₂ It is comprised with a parallel circuit.
Further, the preheating resonance circuit 3 ″ has a capacitor C _Three Through the switching element Q ₂ Inductor L connected to both ends of ₂ And capacitor C _Four Inductor L ₂ Auxiliary winding n for supplying a preheating current to the filament of the discharge lamp La on the secondary side of ₁ , N ₂ Is provided. In the loop through which the preheating current flows (one end f of the filament of the discharge lamp La _Four ) Current transformer T to detect preheating current level ₂ Is inserted.
[0042]
On the other hand, the switching element Q on the high potential side ₁ At both ends of the inductor L _Three And smoothing capacitor C ₀ And diode D ₇ Are connected in series and the diode D ₇ Diode D so that the polarity is reversed through _Five Are connected in parallel. Further, the switching element Q on the low potential side ₂ At both ends of the diode D ₇ Diode D so that the polarity is reversed through ₆ Are connected in parallel and the capacitor C ₀ And inductor L _Three And diode D _Five , D ₇ Thus, a step-down chopper circuit is configured.
[0043]
Switching element Q ₁ , Q ₂ As in the first to third embodiments, the control circuit 4 that controls on / off of the frequency control circuit 5 that controls the operating frequency f, and the switching element Q ₁ , Q ₂ Drive circuit 6 for directly driving the current transformer T ₂ The preheating current detection circuit 7 further detects the preheating current level and feeds it back to the frequency control circuit 5.
[0044]
Next, the operation for suppressing the input current harmonics in this embodiment will be described.
First, switching element Q ₁ Is on, switching element Q ₂ Turns off the smoothing capacitor C ₀ To inductor L _Three → Switching element Q ₁ → Capacitor C _Three → Inductor L ₁ → Transformer T ₁ Primary winding n ₁ → Capacitor C ₈ → Diode D ₆ → Smoothing capacitor C ₀ The resonance current flows through the path of the ₈ Is charged, capacitor C ₈ Voltage Vc across ₈ Will rise. And the output voltage (DC voltage) of full wave rectifier DB and capacitor C ₈ Voltage Vc across ₈ The sum of the voltage and the smoothing capacitor C ₀ From the AC power source Vs to the full wave rectifier DB → the switching element Q ₁ → Capacitor C _Three → Inductor L ₁ → Transformer T ₁ Primary winding n ₁ → Diode D _Three → Full-wave rectifier DB → Resonant current also flows through the path of the AC power supply Vs, and this becomes the input current from the full-wave rectifier DB. Since the period during which this input current flows changes approximately in proportion to the magnitude of the power supply voltage Vs, the input current becomes a sine wave proportional to the power supply voltage Vs, and the input harmonics can be suppressed low (this is the first operation mode). Call it.)
[0045]
Subsequently, the switching element Q ₁ Is off, switching element Q ₂ Is turned on, the inductor L ₁ By releasing the energy stored in the inductor L, ₁ → Transformer T ₁ Primary winding n ₁ → Capacitor C ₈ → Switching element Q ₂ Parasitic diode → capacitor C _Three → Inductor L ₁ The current flows through the path, and eventually the inductor L ₁ When the stored energy is released, the direct current cut capacitor C charged by the regenerative current _Three Capacitor C _Three → Switching element Q ₂ → Capacitor C ₈ → Transformer T ₁ Primary winding n ₁ → Inductor L ₁ → Capacitor C _Three The current flows through the path of the ₈ Voltage Vc across ₈ (This is referred to as a second operation mode).
[0046]
Further, switching element Q ₂ Is off, switching element Q ₁ Turns on, inductor L ₁ By releasing the energy stored in the inductor L, ₁ → Capacitor C _Three → Switching element Q ₁ Parasitic diode → capacitor C ₉ → Capacitor C ₈ → Transformer T ₁ Primary winding n ₁ → Inductor L ₁ Current flows through the path of the capacitor C ₈ Voltage Vc across ₈ Continues to decline. Capacitor C ₈ When the electric charge is completely discharged, the capacitor C ₈ Diode D without going through _Four Current flows through the inductor L and eventually the inductor L ₁ When the stored energy is released, the operation returns to the first operation mode (this is called the third operation mode).
By repeating the first to third operation modes as described above, the inverter circuit 1 ″ performs the harmonic suppression operation of the input current and the high-frequency oscillation operation, and the transformer T ₁ Secondary winding n ₂ A high frequency voltage is applied from both ends of the lamp to light the discharge lamp La. Further, the inductor L of the preheating resonance circuit 3 ″ ₂ And capacitor C _Four The resonant operation of the inductor L ₂ Auxiliary winding n ₁ , N ₂ A high frequency voltage is generated at both ends, and a preheating current is supplied to the filament of the discharge lamp La through a capacitor.
[0047]
Next, the operation of the step-down chopper circuit will be described.
First, switching element Q ₂ When turned on, AC power supply Vs → full wave rectifier DB → inductor L _Three → Smoothing capacitor C ₀ → Switching element Q ₂ → Diode D _Four → Diode D _Three → Full-wave rectifier DB → Smoothing capacitor C along the path of AC power supply Vs ₀ Is charged and the inductor L _Three Energy is stored in Capacitor C ₉ When discharging the capacitor C ₉ → Inductor L _Three → Smoothing capacitor C ₀ → Diode D ₇ → Switching element Q ₂ → Capacitor C ₉ Smoothing capacitor C in the path ₀ Is charged.
[0048]
Subsequently, switching element Q ₂ Turns off the inductor L _Three → Smoothing capacitor C ₀ → Diode D ₇ → Switching element Q ₂ Parasitic diode → inductor L _Three Inductor L in the path _Three The energy stored in is discharged and the smoothing capacitor C ₀ Is charged.
By repeating the above operation, the output voltage of the step-down chopper circuit becomes smoothing capacitor C. ₀ Occurs at both ends.
[0049]
In this embodiment, the natural vibration frequency f of the resonant load circuit 2 is here. ₁ And the natural vibration frequency f of the preheating resonance circuit 3 ₂ And inverter circuit 1 "(switching element Q ₁ , Q ₂ ) With respect to the operating frequency f ₁ <F <f ₂ It is said. That is, the resonance current of the resonant load circuit 2 is delayed from the high frequency output voltage of the inverter circuit 1 ″, and the resonance current of the preheating resonance circuit 3 is advanced to the high frequency output voltage of the inverter circuit 1 ″. Switching element Q by reducing power loss due to the constant preheating current flowing through the filament of the discharge lamp La in the steady state, and by combining the fast current and the slow current ₁ , Q ₂ The effect of reducing the current flowing through is obtained.
[0050]
Next, control operations from preheating to starting and lighting in the present embodiment will be described with reference to the flowcharts of FIGS. 11 to 13 and FIG. FIG. 11 shows a time chart of the control operation of the control circuit 4 in the present embodiment. First, time t = t ₀ When the AC power source Vs is turned on and the control circuit 4 starts operating, the frequency control circuit 5 determines that the resonance frequency of the preheating resonance circuit 3 is the inductor L. ₂ And capacitor C _Four The first preheating frequency f that is substantially equal to the natural vibration frequency when the variation of the noise is approximately the median value _ph1 Then, the operation of the inverter circuit 1 "is started.
[0051]
Then, the frequency control circuit 5 generates a time t = t ₀ ~ T ₁ The preheating current I is detected by the preheating current detection circuit 7 during _ph1 Is detected and a predetermined level I is detected. _ph0 The detected preheating current I _ph1 Is the predetermined level I _ph0 (I _ph1 > I _ph0 ), The operating frequency f is set to the first preheating frequency f. _ph1 Preheating is performed for a predetermined time (for example, about 1 second) while being fixed to 1.
[0052]
On the other hand, the detected preheating current I _ph1 Is the predetermined level I _ph0 (I _ph1 <I _ph0 ), The frequency control circuit 5 sets the operating frequency f of the inverter circuit 1 ″ to the first preheating frequency f. _ph1 To the second preheating frequency f _ph2 To change the resonance condition (f _ph1 > F _ph2 ). Then, the inverter circuit 1 ″ is connected to the second preheating frequency f. _ph2 The preheating current detection circuit 7 operates the preheating current I while _ph2 And the first preheating frequency f _ph1 Preheating current I when operated with _ph1 The preheating current I _ph2 Is the preheating current I _ph1 Higher than (I _ph2 > I _ph1 ), A predetermined level I while further lowering the operating frequency f as shown in FIG. _ph0 The detected preheating current I is repeatedly compared with _ph2 Is the predetermined level I _ph0 (I _ph2 > I _ph0 ) When the third preheating frequency f _ph3 Is set to the operating frequency f of the inverter circuit 1 ″ to perform preheating for a predetermined time (for example, about 1 second).
[0053]
On the other hand, preheating current I _ph2 Is the preheating current I _ph1 Lower than (I _ph2 <I _ph1 ), As shown in FIG. 13, on the contrary, while increasing the operating frequency f, the predetermined level I _ph0 The detected preheating current I _ph2 Is the predetermined level I _ph0 (I _ph2 > I _ph0 ) When the third preheating frequency f _ph3 Is set to the operating frequency f of the inverter circuit 1 ″ to perform preheating for a predetermined time (for example, about 1 second).
[0054]
Thus, the frequency control circuit 5 ₀ ~ T ₁ The preheating current is at a predetermined level I during this period (preheating period). _ph0 The third preheating frequency f exceeding _ph3 Is set to the operating frequency f of the inverter circuit 1 ″ and a predetermined preheating period (time t = t in FIG. ₁ ~ T ₂ ) Only preheat the filament of the discharge lamp La. Then, the frequency control circuit 5 changes the operating frequency f to the third preheating frequency f. _ph3 Starting frequency f from which high voltage required for starting can be obtained _st Until time t = t ₂ ~ T _Three The start frequency f only during (start period) _st To fix. As a result, after the discharge lamp La is started (time t = t _Three After), the frequency control circuit 5 causes the discharge lamp La to be steadily lit so that the starting frequency f _st Lower frequency f _CT Inverter circuit 1 "is operated.
[0055]
As described above, according to the present embodiment, the inductor L that constitutes the preheating resonance circuit 3. ₂ And capacitor C _Four Even if the resonance characteristics vary due to component variations, the frequency control circuit 5 is sufficient to preheat the filament of the discharge lamp La while detecting the level of the preheating current with the preheating current detection circuit 7. Since the operating frequency f of the inverter circuit 1 ″ is controlled so that a level of preheating current is always supplied, a preheating current exceeding a predetermined level can be secured (flowed) at all times. In addition, the oscillation voltage at the start of the discharge lamp La can be kept low, and as a result, it is possible to use an element having a low withstand capability as compared with the conventional example, and the cost can be reduced.
[0056]
In this embodiment, the DC output voltage obtained by full-wave rectification of the AC power supply Vs by the full-wave rectifier DB and the smoothing capacitor C ₀ Between the capacitor C and the capacitor C inserted to obtain the input current harmonic reduction effect. ₈ Therefore, the DC output voltage of the full-wave rectifier DB is boosted. The boosting ratio of the starting voltage of the discharge lamp La and the DC output voltage is in a proportional relationship, and the DC output voltage increases when the oscillation voltage is increased (the operating frequency f of the inverter circuit 1 ″ at starting is lowered). However, in this embodiment, the oscillation voltage at the start of the discharge lamp La can be kept low, and the boost of the DC output voltage of the full-wave rectifier DB can be kept lower than before, so that a low withstand voltage element can be used. There is an advantage that the cost can be reduced.
[0057]
【The invention's effect】
The invention of claim 1 comprises a DC power source obtained by rectifying and smoothing an AC power source, and one or a plurality of switching elements that are turned on / off at a high frequency, and an inverter that converts the DC voltage of the DC power source into a high frequency voltage. A circuit, a resonant load circuit having a discharge lamp and a current that is delayed in phase with respect to the high-frequency voltage applied from the inverter circuit, and a current that is in a leading phase with respect to the high-frequency voltage applied from the inverter circuit. A preheating resonance circuit for supplying a preheating current to the filament of the flow discharge lamp, a preheating current detection circuit for detecting a preheating current level flowing through the filament of the discharge lamp, and an operating frequency of the inverter circuit by turning on and off the switching element. A control circuit for controlling the preheating electric current detected by the preheating current detection circuit during the preheating period at the start of the discharge lamp. Level control the operating frequency of the inverter circuit to perform a preheating for a predetermined time at an operating frequency equal to or greater than a predetermined level In the discharge lamp lighting device, the control circuit sets the operating frequency to a first preheating frequency higher than a frequency at which the resonance frequency of the preheating resonance circuit becomes highest due to variation, and operates the inverter circuit. The operating frequency of the inverter circuit is changed to a second preheating frequency at which the preheating current level detected by the preheating current detection circuit exceeds the predetermined level. The preheating frequency is fixed and controlled to perform preheating for the predetermined time. Therefore, even if the resonance characteristics vary due to variations in the components such as inductors and capacitors that make up the preheating resonance circuit, the control circuit detects the level of the preheating current while the preheating current detection circuit detects the level of the discharge lamp. Since the operating frequency of the inverter circuit is controlled so that a preheating current at a level sufficient to preheat the filament is always supplied, a preheating current exceeding a predetermined level can be secured (flowed) at all times. The oscillation voltage at the start of the discharge lamp can be kept low even at a low temperature start. As a result, an element having a low withstand capability can be used as compared with the conventional example, and the cost can be reduced. is there.
[0059]
Claim 2 The invention of A DC power source obtained by rectifying and smoothing an AC power source, an inverter circuit that includes one or a plurality of switching elements that are turned on and off at a high frequency, and converts the DC voltage of the DC power source into a high frequency voltage, and a discharge lamp A resonant load circuit in which a current having a delayed phase flows with respect to the high frequency voltage applied from the inverter circuit, and a current in a leading phase with respect to the high frequency voltage applied from the inverter circuit flows to preheat the filament of the discharge lamp. A preheating resonance circuit for supplying current; a preheating current detection circuit for detecting a preheating current level flowing in the filament of the discharge lamp; and a control circuit for controlling the operating frequency of the inverter circuit by turning on and off the switching element. The control circuit is configured such that the preheating current level detected by the preheating current detection circuit during a preheating period when the discharge lamp is started has a predetermined level. A said formed by controlling the operating frequency of the inverter circuit discharge lamp lighting device that only performs a preheating predetermined time at operation frequencies of Le least, The control circuit sets the operating frequency to a first preheating frequency lower than the frequency at which the resonance frequency of the preheating resonance circuit is lowest due to variation, starts the operation of the inverter circuit, and is detected by the preheating current detection circuit. The operating frequency of the inverter circuit is changed to a second preheating frequency at which the preheating current level exceeds the predetermined level, and when it exceeds, the operating frequency of the inverter circuit is fixed at the second preheating frequency and preheated for the predetermined time. Control to perform Even if the resonance characteristics vary due to variations in the components such as inductors and capacitors that make up the preheating resonance circuit, the control circuit detects the preheating current level while the preheating current detection circuit detects the preheating current filament. Because the operating frequency of the inverter circuit is controlled so that a preheating current at a level sufficient for preheating is always supplied, A preheating current of a predetermined level or higher can be secured (flowed) at all times, and the oscillation voltage at the start of the discharge lamp can be kept low even with respect to component variations and low temperature start. Therefore, there is an effect that a low-resistance element can be used and the cost can be reduced.
[0060]
Claim 3 The invention of A DC power source obtained by rectifying and smoothing an AC power source, an inverter circuit that includes one or a plurality of switching elements that are turned on and off at a high frequency, and converts the DC voltage of the DC power source into a high frequency voltage, and a discharge lamp A resonant load circuit in which a current having a delayed phase flows with respect to the high frequency voltage applied from the inverter circuit, and a current in a leading phase with respect to the high frequency voltage applied from the inverter circuit flows to preheat the filament of the discharge lamp. A preheating resonance circuit for supplying current; a preheating current detection circuit for detecting a preheating current level flowing in the filament of the discharge lamp; and a control circuit for controlling the operating frequency of the inverter circuit by turning on and off the switching element. The control circuit is configured such that the preheating current level detected by the preheating current detection circuit during a preheating period when the discharge lamp is started has a predetermined level. A said formed by controlling the operating frequency of the inverter circuit discharge lamp lighting device that only performs a preheating predetermined time at operation frequencies of Le least, The control circuit sets the operating frequency to the first preheating frequency substantially equal to the median value of the variation in the resonance frequency of the preheating resonance circuit to start the operation of the inverter circuit, and is higher or lower than the first preheating frequency. When the operating frequency of the inverter circuit is set to the second preheating frequency and the preheating current level detected by the preheating current detection circuit is higher than the preheating current level during operation at the first preheating frequency, The operation frequency of the inverter circuit is changed in the same direction as the change direction from the preheating frequency of 1 to the second preheating frequency, and the preheating current level detected by the preheating current detection circuit is the operation at the first preheating frequency. If the preheating current level is lower than the current preheating current level, the operating frequency of the inverter circuit is changed in the direction opposite to the change direction from the first preheating frequency to the second preheating frequency. Controlled, since the the detected preheating current level to change the operating frequency to exceed the predetermined level, controls so as to perform fixing to preheat for the predetermined time the operating frequency of the inverter circuit when it exceeds, Even if the resonance characteristics vary due to variations in the components such as inductors and capacitors that make up the preheating resonance circuit, the control circuit detects the preheating current level while the preheating current detection circuit detects the preheating current filament. Because the operating frequency of the inverter circuit is controlled so that a preheating current at a level sufficient for preheating is always supplied, A preheating current of a predetermined level or higher can be secured (flowed) at all times, and the oscillation voltage at the start of the discharge lamp can be kept low even with respect to component variations and low temperature start. Therefore, there is an effect that a low-resistance element can be used and the cost can be reduced.
[0061]
Claim 4 The present invention comprises a pair of switching elements that are connected between output terminals of the DC power supply and alternately turned on and off, and one of the switching elements includes the resonant load circuit and the preheating resonant circuit. Are connected in parallel, the switching loss in the switching element can be reduced, and the use of an element having a low current resistance can be achieved, so that the apparatus can be reduced in size and cost can be reduced.
[0062]
Claim 5 In the invention, the inverter circuit includes a series circuit of a smoothing capacitor and a series circuit of a pair of switching elements that are alternately turned on and off by connecting a diode in antiparallel between the output terminals of the DC power supply. Therefore, there is an effect that it is possible to suppress the preheating current during steady lighting and reduce the power loss in the filament of the discharge lamp.
[0063]
Claim 6 In the invention, the inverter circuit has a pair of switching elements connected in series between the output terminals of the DC power supply, and the first and second switching elements are connected between the switching element on the low potential side and the output terminal of the DC power supply. A series circuit of diodes is inserted, and the preheating resonance circuit and the resonance load circuit are connected between the connection point of the series circuit of the first and second diodes and the connection point of the switching element and connected to the switching element side. Since the capacitor is connected to both ends of the second diode, the input current harmonics can be suppressed low by boosting the DC input voltage from the DC power source with the capacitor connected to both ends of the second diode. There is an effect that can be.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a first embodiment.
FIG. 2 is a time chart for explaining the operation described above.
FIG. 3 is a diagram showing resonance characteristics of the resonance load circuit and the preheating resonance circuit in the same as above.
FIG. 4 is a diagram showing resonance characteristics of the resonance load circuit and the preheating resonance circuit in the same as above.
FIG. 5 is a circuit block diagram showing a second embodiment.
FIG. 6 is a circuit block diagram showing a third embodiment.
FIG. 7 is a time chart for explaining the operation described above.
FIG. 8 is a diagram showing resonance characteristics of the resonance load circuit and the preheating resonance circuit in the same as above.
FIG. 9 is a diagram showing resonance characteristics of the resonance load circuit and the preheating resonance circuit in the same as above.
FIG. 10 is a circuit block diagram showing a fourth embodiment.
FIG. 11 is a time chart for explaining the operation described above.
FIG. 12 is a diagram showing resonance characteristics of the resonance load circuit and the preheating resonance circuit in the same as above.
FIG. 13 is a diagram showing resonance characteristics of the resonance load circuit and the preheating resonance circuit in the same as above.
FIG. 14 is a flowchart for explaining the operation described above.
FIG. 15 is a circuit block diagram showing a conventional example.
FIG. 16 is a diagram showing resonance characteristics of the resonance load circuit and the preheating resonance circuit in the same as above.
[Explanation of symbols]
1 Inverter circuit
2 Resonant load circuit
3 Preheating resonance circuit
4 Control circuit
5 Frequency control circuit
6 Drive circuit
7 Preheating current detection circuit
Vs AC power supply
DB full-wave rectifier

Claims

A DC power source obtained by rectifying and smoothing an AC power source, an inverter circuit that includes one or a plurality of switching elements that are turned on and off at a high frequency, and converts the DC voltage of the DC power source into a high frequency voltage, and a discharge lamp A resonant load circuit in which a current having a delayed phase flows with respect to the high frequency voltage applied from the inverter circuit, and a current in a leading phase with respect to the high frequency voltage applied from the inverter circuit flows to preheat the filament of the discharge lamp. A preheating resonance circuit for supplying current; a preheating current detection circuit for detecting a preheating current level flowing in the filament of the discharge lamp; and a control circuit for controlling the operating frequency of the inverter circuit by turning on and off the switching element. The control circuit is configured such that the preheating current level detected by the preheating current detection circuit during a preheating period when the discharge lamp is started has a predetermined level. A said formed by controlling the operating frequency of the inverter circuit discharge lamp lighting device that only performs a preheating predetermined time at operation frequencies of Le above, the control circuit, the resonance frequency of the preheating resonant circuit varies The second preheating in which the preheating current level detected by the preheating current detecting circuit exceeds the predetermined level by setting the operating frequency to the first preheating frequency higher than the highest frequency and starting the operation of the inverter circuit. The operating frequency of the inverter circuit is changed up to a frequency, and when it exceeds, the operating frequency of the inverter circuit is fixed to a second preheating frequency, and control is performed so as to perform preheating only for the predetermined time. apparatus.

A DC power source obtained by rectifying and smoothing an AC power source, an inverter circuit that includes one or a plurality of switching elements that are turned on and off at a high frequency, and converts the DC voltage of the DC power source into a high frequency voltage, and a discharge lamp A resonant load circuit in which a current having a delayed phase flows with respect to the high frequency voltage applied from the inverter circuit, and a current in a leading phase with respect to the high frequency voltage applied from the inverter circuit flows to preheat the filament of the discharge lamp. A preheating resonance circuit for supplying current; a preheating current detection circuit for detecting a preheating current level flowing in the filament of the discharge lamp; and a control circuit for controlling the operating frequency of the inverter circuit by turning on and off the switching element. The control circuit is configured such that the preheating current level detected by the preheating current detection circuit during a preheating period when the discharge lamp is started has a predetermined level. A said formed by controlling the operating frequency of the inverter circuit discharge lamp lighting device that only performs a preheating predetermined time at operation frequencies of Le above, the control circuit, the resonance frequency of the preheating resonant circuit varies The second preheating in which the preheating current level detected by the preheating current detecting circuit exceeds the predetermined level by setting the operating frequency to the first preheating frequency lower than the lowest frequency and starting the operation of the inverter circuit. changing the operating frequency of the inverter circuit to the frequency, time in the inverter circuit of the operating frequency of the second feature to discharge lamp lighting device is fixed to preheat frequency to be controlled so as to perform pre-heating for the predetermined time period is exceeded .

A DC power source obtained by rectifying and smoothing an AC power source, an inverter circuit that includes one or a plurality of switching elements that are turned on and off at a high frequency, and converts the DC voltage of the DC power source into a high frequency voltage, and a discharge lamp A resonant load circuit in which a current having a delayed phase flows with respect to the high frequency voltage applied from the inverter circuit, and a current in a leading phase with respect to the high frequency voltage applied from the inverter circuit flows to preheat the filament of the discharge lamp. A preheating resonance circuit for supplying current; a preheating current detection circuit for detecting a preheating current level flowing in the filament of the discharge lamp; and a control circuit for controlling the operating frequency of the inverter circuit by turning on and off the switching element. The control circuit is configured such that the preheating current level detected by the preheating current detection circuit during a preheating period when the discharge lamp is started has a predetermined level. The discharge lamp lighting device formed by controlling the operating frequency of the inverter circuit to perform a preheating for a predetermined time at operation frequencies of Le above, the control circuit, the variation of the resonance frequency of the preheating resonant circuit The operation frequency is set to a first preheating frequency substantially equal to the median value of the inverter circuit to start the operation of the inverter circuit, and the operation frequency of the inverter circuit is set to a second preheating frequency higher or lower than the first preheating frequency. When the preheating current level detected by the preheating current detection circuit is higher than the preheating current level during operation at the first preheating frequency, the direction of change from the first preheating frequency to the second preheating frequency. The operating frequency of the inverter circuit is changed in the same direction as the preheating current level detected by the preheating current detecting circuit is the preheating power when operating at the first preheating frequency. If I level remote low controls to vary the operating frequency of the inverter circuit changes the direction opposite to the second preheat frequency from the first preheat frequency, wherein the detected preheating current level the changing the operating frequency until it exceeds a predetermined level, the time-release lamp lighting apparatus wherein the operating frequency were fixed by controlling to perform preheating by the predetermined time of the inverter circuit is exceeded.

The inverter circuit includes a pair of switching elements connected between output terminals of the DC power supply and alternately turned on and off, and the resonant load circuit and the preheating resonant circuit are connected in parallel to one of the switching elements. the discharge lamp lighting device according to any one of claims 1-3, characterized in that formed by.

In the inverter circuit, a series circuit of a smoothing capacitor and a series circuit of a pair of switching elements that are alternately turned on / off by a diode connected in anti-parallel are connected in parallel with each other between output terminals of the DC power supply. the discharge lamp lighting device according to any one of claims 1-3, characterized by comprising.

The inverter circuit has a pair of switching elements connected in series between output terminals of the DC power supply, and a series circuit of first and second diodes between the switching element on the low potential side and the output terminal of the DC power supply. And the preheating resonant circuit and the resonant load circuit are connected between the connection point of the series circuit of the first and second diodes and the connection point of the switching element, and the second connected to the switching element side The discharge lamp lighting device according to any one of claims 1 to 3 , wherein a capacitor is connected to both ends of the diode .