JP2004039288A

JP2004039288A - Lighting device

Info

Publication number: JP2004039288A
Application number: JP2002190875A
Authority: JP
Inventors: Yasunori Kawase; 河瀬　靖憲; Hiroyuki Nishino; 西野　博之; Toru Niwa; 丹羽　徹
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 2002-06-28
Filing date: 2002-06-28
Publication date: 2004-02-05
Anticipated expiration: 2022-06-28
Also published as: JP4007096B2

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a light output fluctuation due to power supply fluctuation and an imbalance of light output due to fluctuation of the forward direction voltage in a lighting device that lights a plurality of LEDs with a DC power source such as a battery, and realize a function of lighting off all the LEDs at the disconnection of one LED lamp with a simple structure. <P>SOLUTION: This is the lighting device in which a choke coil L1 and a switch element Tr1 are connected in series to the DC power source Vdc and has a diode D1 and a capacitor C1 for rectifying and smoothing the voltage at both ends of the switching element Tr1 and a boosting circuit constructed of a control circuit 1 and a driving circuit that operate the above switching element Tr1 by high frequency, and the LED unit, in which a plurality of LEDs is connected in series to the output of this boosting circuit, is connected through a resistor R2. The LEDs are connected in series so that the sum of the forward direction voltage of the LEDs may become a voltage or more of the DC power source Vdc, and feed-back control is carried out so that the current flowing to the LEDs may become constant. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は車載用のテールランプ／ストップランプとして利用できる照明装置に関するものである。
【０００２】
【従来の技術】
従来例を図３０〜図３３に示す。図３０は複数のＬＥＤを用いた車載用テール／ストップランプの回路図を示す。図３１はこのようなテール／ストップランプの配置される箇所を図示したものである。図３０において、ＬＥＤ１は第１のＬＥＤユニット、ＬＥＤ２は第２のＬＥＤユニット、Ｄ１，Ｄ２はダイオード、Ｒ１〜Ｒ４は抵抗である。ＧＮＤはグランド端子であり、Ｓｔｏｐはブレーキを踏んだストップランプ点灯状態で通電される端子、Ｔａｉｌはテールランプ点灯状態で通電される端子である。
【０００３】
テールランプ点灯状態ではＬＥＤの光出力を低く抑え、ブレーキを踏んだストップランプ点灯状態ではＬＥＤの光出力を増大させて使用される。このような方式は安価なためによく使われるが、光量確保のために複数のＬＥＤを接続する場合には、ＬＥＤの順方向電圧Ｖｆの和が少なくとも電源電圧以下となるようにＬＥＤを直列に接続したＬＥＤユニットを並列に接続しないと必要数のＬＥＤが接続できない。例えば電源が車で使われるようなバッテリーでは定格が１２Ｖ、電源変動が９Ｖ〜１６Ｖの範囲なので、ＬＥＤの順方向電圧Ｖｆが３Ｖであれば、ＬＥＤは直列に３個しか接続できないことになる。従って、ＬＥＤを６個点灯させたい場合には図３０のように並列に接続して使用する必要がある。
【０００４】
以下、図３０の回路の動作について簡単に説明する。まず、テールランプ点灯状態では図のＴａｉｌ端子とＧＮＤ端子間にバッテリーが接続され、ダイオードＤ２と抵抗Ｒ１を介して複数個直列に接続された第１のＬＥＤユニット（ＬＥＤ１）が、またダイオードＤ２と抵抗Ｒ４を介して複数個直列に接続された第２のＬＥＤユニット（ＬＥＤ２）が点灯し、抵抗Ｒ１とＲ４の抵抗値を等しく設定すれば、ＬＥＤ１とＬＥＤ２は略等しく発光する。
【０００５】
次に、ストップランプ点灯状態では、図のＳｔｏｐ端子とＧＮＤ端子間にバッテリーが接続され、ダイオードＤ１と抵抗Ｒ２を介してＬＥＤ１が、またダイオードＤ１と抵抗Ｒ３を介してＬＥＤ２が点灯し、抵抗Ｒ２とＲ３の抵抗値を等しく且つ抵抗Ｒ１，Ｒ４に対して十分小さく設定すれば、ＬＥＤ１とＬＥＤ２は略等しく高出力で発光する。
【０００６】
【発明が解決しようとする課題】
（課題１）
このような従来例における課題として、上記のような電池などを電源とした時の電源変動による光出力の変化や、ＬＥＤの順方向電圧Ｖｆのばらつきによる並列回路の光出力のばらつきが挙げられる。電池電圧をＶｄｃ、ダイオードＤ１，Ｄ２の順方向電圧をＶｆ０、抵抗値をＲ、ＬＥＤ１の各順方向電圧をＶｆ１１，Ｖｆ１２，Ｖｆ１３、ＬＥＤ２の各順方向電圧をＶｆ２１，Ｖｆ２２，Ｖｆ２３とすれば、ＬＥＤ１及びＬＥＤ２の電流は下式のように表される。
Ｉ（ＬＥＤ１）＝［Ｖｄｃ−Ｖｆ０−（Ｖｆ１１＋Ｖｆ１２＋Ｖｆ１３）］／ＲＩ（ＬＥＤ２）＝［Ｖｄｃ−Ｖｆ０−（Ｖｆ２１＋Ｖｆ２２＋Ｖｆ２３）］／Ｒ
【０００７】
すなわち、電池電圧Ｖｄｃが変動するとＩ（ＬＥＤ１），Ｉ（ＬＥＤ２）は同じように変動するので、最低の電源電圧の時に必要な光出力が得られるようにすると、電源が変動して高くなったときにＬＥＤに過電流が流れ、ＬＥＤ自身が発熱し、寿命に影響を与えたり、限流用の抵抗の消費電力が大きくなり、定格電力の大きい抵抗を使う必要が生じる。また、各ＬＥＤの順方向電圧がばらつくと、特に順方向電圧の総和と電池電圧の差が少ない場合にＬＥＤ１及びＬＥＤ２の電流Ｉ（ＬＥＤ１），Ｉ（ＬＥＤ２）は大きく異なることが予想され、各並列回路の光出力にアンバランスを生じる。
【０００８】
（課題２）
更に車載用特有の課題として、ＬＥＤ断線時に必要最低限の光出力が得られない事態が予想されることから、断線時には全灯とも消灯して識別を容易にする機能が要求される。ところが、上述したようにＬＥＤの数が増えると電源との関係上、並列にせざるをえず、ＬＥＤ回路が並列に接続されていると、ＬＥＤが１灯断線しても全部のＬＥＤを消灯させることはできない。
【０００９】
図３２は前者の課題１に対する一つの解決手段を示すものである。抵抗Ｒ４、コレクタとべースを短絡したトランジスタＴｒ３、抵抗Ｒ３を直列に接続した基準電流回路、ＬＥＤ１と直列に接続されベースが上記トランジスタＴｒ３のベースに接続されたトランジスタＴｒ１と抵抗Ｒ１の直列回路、同様にＬＥＤ２と直列に接続されベースが上記トランジスタＴｒ３のベースに接続されたトランジスタＴｒ２と抵抗Ｒ２の直列回路はカレントミラー回路を構成し、ＬＥＤ１及びＬＥＤ２の回路電流を上記の基準電流に略等しくなるように制御される。このような方策によって、ＬＥＤの順方向電圧がばらついても並列回路の電流を概ね合わせることが可能となり、光出力への影響を回避できる。
【００１０】
図３３は後者の課題２に対する一つの解決手段を示したものである。ＬＥＤ１，ＬＥＤ２には各々電流制限抵抗Ｒ２，Ｒ３が直列に接続され、トータルの電流は抵抗Ｒ１でバイアスされたトランジスタＴｒ１を介して流れる。ＬＥＤ１及びＬＥＤ２が全て正常であればＬＥＤ電流が流れて抵抗Ｒ２，Ｒ３には一定の電圧降下を生じ、コンパレータＣＯＭＰの−端子は基準電源の電圧を抵抗Ｒ４とＲ７で分圧した電位に保たれ、抵抗Ｒ５とＲ８の分圧で決まるコンパレータＣＯＭＰの＋端子の電位を上記−端子の電位以下に設定すれば、コンパレータＣＯＭＰの出力はＬｏｗの状態となり、トランジスタＴｒ１のベース・エミッタ間に接続されたトランジスタＴｒ２はオフ、トランジスタＴｒ１はオンを持続してＬＥＤ１，ＬＥＤ２を点灯する。
【００１１】
ＬＥＤ１，ＬＥＤ２の何れかのＬＥＤが断線すれば、抵抗Ｒ２或いはＲ３の電圧降下が消滅するので、コンパレータＣＯＭＰの−端子電位はダイオードＤ１或いはＤ２を介して接続される抵抗Ｒ２或いはＲ３によって低下し、コンパレータＣＯＭＰの＋端子電位以下となればその出力はＨｉｇｈに反転し、抵抗Ｒ６及びダイオードＤ３を介して＋端子をＨｉｇｈに固定して自己ラッチし、以降コンパレータＣＯＭＰの出力はＨｉｇｈに固定される。従って抵抗Ｒ９を介してトランジスタＴｒ２のベース電流が供給され、トランジスタＴｒ２がオン、トランジスタＴｒ１がオフとなってＬＥＤ１，ＬＥＤ２とも全て消灯する。
【００１２】
上記従来例における２つの課題に対して図３２，図３３で示したような方策を組み合わせる必要があるため、回路構成が複雑となってコスト的な課題を生じたり、ＬＥＤが正常であるにも関わらず、外来ノイズ等による誤動作で全灯消灯するような事態も起こりやすくなって、信頼性の面での課題も生まれる。
【００１３】
（課題３）
また、車載用ではイグニッションを切った時やロードダンプ時や他の機器を電源ＯＮ／ＦＦしたときなどに電源に過渡的なサージ電圧が発生することがある。例えば車載機器の規格である自動車規格（ＪＡＳＯ）では一例としてピーク電圧７０Ｖ、減衰定数２００ｍｓ（最大値の３６．８％まで減衰する時間）等のサージが規定されている。
【００１４】
このようなサージが印加されると図３０の回路ではＬＥＤに過電流が流れ、ＬＥＤが破壊する可能性が考えられる。このようなサージの対策として入力部にパワーツェナーやバリスタ等のサージ対策部品を設けることで対策は可能であるが、前記部品は形状も大きく高価であるという問題がある。
【００１５】
本発明は上述のような従来例の欠点に鑑みてなされたもので、電池などの変動範囲の大きな電源を用いて複数のＬＥＤを点灯する照明装置のＬＥＤ点灯回路において、電源変動による光出力の変動やＬＥＤ光出力のアンバランスを抑制することが可能であり、またＬＥＤが１灯でも断線に至った場合だけ全てのＬＥＤを消灯でき、外乱等による誤動作の可能性を除去できる照明装置を提供することを課題とする。
【００１６】
【課題を解決するための手段】
請求項１の照明装置によれば、上記の課題を解決するために、図１に示すように、直流電源ＶｄｃにチョークコイルＬ１とスイッチング素子Ｔｒ１を直列接続し、スイッチング素子Ｔｒ１の両端の電圧を整流平滑するダイオードＤ１及びコンデンサＣ１と、上記スイッチング素子Ｔｒ１を高周波で動作させる制御回路１及び駆動回路で構成された昇圧回路を備え、この昇圧回路の出力に複数個のＬＥＤが直列に接続されたＬＥＤユニットが抵抗Ｒ２を介して接続された照明装置において、ＬＥＤの順方向電圧の和が直流電源Ｖｄｃの電圧以上となるようにＬＥＤを直列に接続し、ＬＥＤに流れる電流が一定となるようにフィードバック制御したことを特徴とするものである。
【００１７】
請求項２の発明によれば、請求項１において、ＬＥＤの断線時には昇圧回路の出力電圧が一定となるように制御する定電圧制御に切り替えることを特徴とする。
請求項３の発明によれば、請求項１または２において、ＬＥＤユニットに流れる電流を低出力と高出力に切り替える場合に、低出力時には抵抗両端の電圧とＬＥＤの順方向電圧の和が直流電源の電圧以上となるようにＬＥＤを直列に接続し、高出力時には昇圧回路の出力電圧を高くしたことを特徴とする。
【００１８】
請求項４の発明によれば、請求項３において、低出力時に抵抗両端の電圧とＬＥＤの順方向電圧の和が直流電源の電圧以上となるようにＬＥＤを直列に接続し、ＬＥＤユニットと直列に接続された抵抗値を変化させることで高出力と低出力を切り替えることを特徴とする。
請求項５の発明によれば、請求項４において、高出力時に入力電圧範囲を超える異常電圧が入力された時には低出力時の動作に切り替えることを特徴とする。
【００１９】
請求項６の発明によれば、図８に示すように、直流電源Ｖｄｃにスイッチング素子Ｔｒ１とチョークコイルＬ１及びコンデンサＣ１を直列接続し、直流電源Ｖｄｃの負極側からスイッチング素子Ｔｒ１とチョークコイルＬ１の接続点に向けて回生電流を流すようにダイオードＤ１を接続し、上記スイッチング素子Ｔｒ１を高周波で動作させる制御回路１及び駆動回路を有する降圧回路を備え、この降圧回路の出力に複数個のＬＥＤが直列に接続されたＬＥＤユニットが抵抗Ｒ２を介して接続された照明装置において、降圧回路の出力に、前記抵抗Ｒ２の両端の電圧とＬＥＤの順方向電圧の和が直流電源Ｖｄｃの電圧以下となるようにＬＥＤを直列に接続し、ＬＥＤに流れる電流が一定となるようにフィードバック制御したことを特徴とする。
【００２０】
請求項７の発明によれば、請求項６において、ＬＥＤユニットに流れる電流を低出力と高出力に切り替える場合に、高出力時に抵抗両端の電圧とＬＥＤの順方向電圧の和が直流電源の電圧以下となるようにＬＥＤを直列に接続し、高出力時には降圧回路の出力電圧を高くしたことを特徴とする。
請求項８の発明によれば、請求項７において、高出力時に抵抗両端の電圧とＬＥＤの順方向電圧の和が直流電源の電圧以下となるようにＬＥＤを接続し、ＬＥＤと直列に接続された抵抗値を変化させることで低出力と高出力を切り替えること特徴とする。
【００２１】
請求項９の発明によれば、請求項１〜８のいずれかにおいて、ＬＥＤユニットが複数個並列に接続され、それらのＬＥＤユニットがそれぞれ一定周期で点灯するように制御され、各ＬＥＤユニットを切り替える時に複数のＬＥＤユニットが同時に点灯する重複期間を設けたことを特徴とする。
請求項１０の発明によれば、請求項１〜８のいずれかにおいて、負荷として第１及び第２のＬＥＤユニットを並列に接続され、第１のＬＥＤユニットの回路電流で第２のＬＥＤユニットの回路電流を制御する第１のカレントミラー回路と、第２のＬＥＤユニットの回路電流で第１のＬＥＤユニットの回路電流を制御する第２のカレントミラー回路を備えることを特徴とする。
【００２２】
【発明の実施の形態】
（実施形態１）
図１に本発明の第１の実施形態を示す。直流電源Ｖｄｃと直列にチョークコイルＬ１とスイッチング素子Ｔｒ１が接続され、スイッチング素子Ｔｒ１の両端には整流用のダイオードＤ１と平滑用コンデンサＣ１が接続されているいわゆる昇圧チョッパー回路の構成である。コンデンサＣ１の両端には複数個のＬＥＤからなるＬＥＤユニット（以後ＬＥＤと記載する）と、ＬＥＤに流れる電流を検出する抵抗Ｒ２が直列に接続されている。制御回路１は図２のようなエラーアンプ（Ｅ／Ａ）１ａと発振器１ｂと比較器１ｃとからなるいわゆるＰＷＭ制御回路となっており、制御回路１のＩＮ端子の電圧が一定となるように図１のスイッチング素子Ｔｒ１を高周波（数十〜数百ｋＨｚ）でスイッチングしている。
【００２３】
直流電源Ｖｄｃに電池などが使われた場合、例えば自動車用の電池の場合では電圧変動範囲が９〜１６Ｖと広範囲に変動する。従って、ＬＥＤの順方向電圧が仮に３Ｖ／個であると、出力側のＬＥＤは順方向電圧の和が１６Ｖ以上、すなわち最低限６個を直列に接続することで、昇圧回路の出力電圧は電源の変動範囲以上とすることが可能となり、電源が変動した場合でもＬＥＤに流れる電流は一定にすることが可能である。
【００２４】
図３に一変形例を示す。基本構成は図１と同様であり、昇圧回路の出力からツェナーダイオードＺＤ１と抵抗Ｒ５を介してフィードバックループとなる制御回路１のＩＮ端子へ接続する。ＬＥＤが断線した場合には電流が流れないので、ＩＮ端子は略０Ｖとなるため、制御回路１は出力を上げるように、スイッチング素子Ｔｒ１のＯＮデューティを大きくする。そのため出力電圧は上昇するが、出力電圧がツェナー電圧以上となるとツェナーダイオードＺＤ１がオンするので、出力電圧は略ツェナー電圧に制限される。
【００２５】
このように本実施形態では、ＬＥＤを順方向電圧の和が電源電圧以上となるように直列に接続し、昇圧回路を用いてＬＥＤに一定電流が流れるように制御することで、ＬＥＤの順方向電圧のばらつきや従来のような並列回路でのばらつきや電源変動等による光出力のばらつきをなくすことが可能であり、また、ＬＥＤ１灯が断線した時には複雑な回路を必要とせずに全灯を消灯させることが可能であると共に、簡単な構成でＬＥＤが断線した時に回路電圧が異常に上昇することや、スイッチング素子が過負荷状態になることを防止することができる。
【００２６】
（実施形態２）
自動車用のテールランプ／ストップランプのように光出力を切り替える必要が有る場合の実施形態を図４に示す。自動車用のテールランプ／ストップランプでは、テールランプ点灯時には低出力、ストップランプ点灯時には高出力の光出力に切り替える必要がある。Ｔａｉｌ端子から電源が入力されているときは、抵抗Ｒ２の両端に発生する電圧は抵抗Ｒ３，Ｒ４で分圧されて制御回路１のＩＮ端子に入力されており、この電圧が内部の基準電圧Ｖｒｅｆと同じになるようにＬＥＤに流れる電流が制御されて動作している。Ｓｔｏｐ端子から電源が入力されたときには、抵抗Ｒ６を介してトランジスタＴｒ２がオンすることで制御回路１のＩＮ端子の電圧は抵抗Ｒ４と、抵抗Ｒ３，Ｒ５からなる並列回路の分圧に変わるためにＩＮ端子の電圧が低下する。従って、同様に基準電圧Ｖｒｅｆと同じ電圧になるためにはＬＥＤに流れる電流はテールランプ点灯時に比べて大きくなる。すなわち昇圧回路の出力電圧はテールランプ点灯時に比べて高くなる。
【００２７】
他の回路例を図５に示す。Ｔａｉｌ端子から電源が入力されているときは、抵抗Ｒ２の両端に発生する電圧は抵抗Ｒ３，Ｒ４で分圧されて制御回路１のＩＮ端子に入力されており、この電圧が内部の基準電圧Ｖｒｅｆと同じになるようにＬＥＤに流れる電流が制御されて動作している。Ｓｔｏｐ端子から電源が入力されたときには、抵抗Ｒ６を介してトランジスタＴｒ２がオンすることでＬＥＤの電流を制限している抵抗Ｒ２に並列に抵抗Ｒ５が接続され、抵抗値が小さくなるのでＬＥＤに流れる電流は大きくなり、光出力は増大する。制限抵抗が小さくなるので出力電圧が低下するが、ＬＥＤのＶ−Ｉ特性上、ＬＥＤ電流が増加することでＬＥＤの順方向電圧が増加するので、出力電圧は電源電圧に対して高くすることが可能であり、電源電圧変動に対しても確実に制御が可能である。
【００２８】
その他の回路例を図６に示す。Ｓｔｏｐ端子から電源が入力されたときには、抵抗Ｒ６を介してトランジスタＴｒ２がオンすることでＬＥＤの電流を制限している抵抗Ｒ２に並列に抵抗Ｒ５が接続され、抵抗値を切り替えると共に、Ｔａｉｌ端子から電源が入力されているときは、抵抗Ｒ７を介してトランジスタＴｒ３がオンすることで制御回路１のＩＮ端子の電圧の分圧比を切り替える例である。ストップランプ点灯時とテールランプ点灯時の調光比が大きい場合に、ＬＥＤ電流が低下するテールランプ点灯時に、ＬＥＤの順方向電圧がＬＥＤの特性上低くなるので、昇圧回路の出力電圧が低下してしまい、電源変動に対して電源電圧以下となり、制御が出来なくなる、また、抵抗Ｒ２の抵抗値を高くすると、抵抗Ｒ３，Ｒ４の分圧比が高くなり過ぎ、制御回路１が制御できなくなり、電源変動に対して昇圧回路の出力電圧が低下してしまうという可能性がある。これらを防止するためには出力電圧をＬＥＤの順方向電圧の和よりも非常に高く設定する必要があり、電流制限抵抗での損失が大きくなってしまうという問題が生じる。
【００２９】
図６の回路では、Ｓｔｏｐ端子から電源が入力されたときには、トランジスタＴｒ２がオンするので、制限抵抗値が下がるから電流が増加し、Ｔａｉｌ端子から電源が入力されているときには、トランジスタＴｒ３がオンして、抵抗Ｒ３とＲ４の分圧比を変えることで昇圧回路の二次側電圧を必要以上に高くする必要はなく、出力が安定するように制御を行うことができる。
【００３０】
その他の回路例を図７に示す。ダイオードＤ２，Ｄ３のカソードからツェナーダイオードＺＤ１と抵抗Ｒ７、トランジスタＴｒ３からなる過電圧保護回路を設ける。ツェナーダイオードＺＤ１のツェナー電圧は電源電圧範囲以上の電圧、例えば電源電圧が９〜１６Ｖの範囲で変動する電源であれば２４Ｖなどの電圧とする。Ｓｔｏｐ端子から電源入力されている高出力状態でＬＥＤが点灯している時に、入力電源にサージなどにより過電圧が発生し、その過電圧がツェナー電圧以上の電圧であれば、ツェナーダイオードＺＤ１がオンしてトランジスタＴｒ３がオンするので、トランジスタＴｒ２がオフしてＬＥＤユニットの直列抵抗がＲ２のみとなるので、テールランプ点灯時の低い電流に切り替わるから、過電圧に対してもＬＥＤに過電流が流れることは無い。
【００３１】
このように本実施形態では光出力を変化させた時においても低出力時の順方向電圧の和が電源電圧以上となるようにＬＥＤを直列に接続し、昇圧回路の出力を低出力と高出力に変化させ、ＬＥＤに一定電流が流れるように制御することで、光出力が異なる状態においてもＬＥＤの順方向電圧のばらつきや従来のような並列回路でのばらつきや電源変動等による光出力のばらつきをなくすことが可能であり、またＬＥＤ１灯が断線した時には複雑な回路を必要とせずに全灯を消灯させることが可能である。
【００３２】
さらに、図６のような回路では高出力時にも昇圧回路の出力電圧を高くする必要が無いので、部品の耐圧を低くすることが出来、また、制限抵抗での損失を小さくすることができるというメリットが有る。
また、図７のような回路では入力電圧にイグニッション時等のサージ的な過電圧が生じた場合においてもＬＥＤに過電流が流れることが無い。
【００３３】
（実施形態３）
図８に本発明の実施形態３を示す。直流電源Ｖｄｃと直列にスイッチング素子Ｔｒ１とチョークコイルＬ１が接続され、スイッチング素子Ｔｒ１のコレクタとチョークコイルＬ１の接続点に回生用ダイオードＤ１のカソードが接続され、ダイオードＤ１のアノードはグランドに接続され、チョークコイルＬ１の他端に平滑用のコンデンサＣ１が接続された、いわゆる降圧チョッパー回路の構成である。コンデンサＣ１の両端には複数個のＬＥＤからなるＬＥＤユニット（以後ＬＥＤと記載する）とＬＥＤに流れる電流を検出する抵抗Ｒ２が直列に接続されている。制御回路１は図２と同じようないわゆるＰＷＭ制御を行っており、抵抗Ｒ２の両端電圧が一定となるようにスイッチング素子Ｔｒ１を高周波（数十〜数百ｋＨｚ）でスイッチングしている。
【００３４】
直流電源Ｖｄｃに電池などが使われた場合、例えば自動車用の電池の場合では電圧変動範囲が９〜１６Ｖと広範囲に変動する。従って、ＬＥＤの順方向電圧が仮に３Ｖ／個であると出力側のＬＥＤは順方向電圧の和が９Ｖ以下、すなわち最大限３個を直列に接続することで、降圧回路の出力電圧は電源の変動範囲以下とすることが可能となり、電源が変動した場合でもＬＥＤに流れる電流は一定にすることが可能である。
【００３５】
このように本実施形態ではＬＥＤを順方向電圧の和が電源電圧以下となるように直列に接続し、降圧回路を用いてＬＥＤに一定電流が流れるように制御することで、ＬＥＤの順方向電圧のばらつきや電源変動等による光出力のばらつきを無くすことが可能であり、またＬＥＤ１灯が断線した時には複雑な回路を必要とせずに全灯を消灯させることが可能である。本実施形態は電池電圧が例えば４８Ｖ等のように、高い場合に特に有効となる。
【００３６】
（実施形態４）
図９に本発明の実施形態４を示す。自動車用のテールランプのように光出力を切り替える必要が有る場合の例を示す。Ｔａｉｌ端子から電源が入力されているときはトランジスタＴｒ２はオフしており、抵抗Ｒ２の両端に発生する電圧は抵抗Ｒ３，Ｒ４で分圧されて制御回路１のＩＮ端子に入力されており、この電圧が内部の基準電圧Ｖｒｅｆと同じになるようにＬＥＤに流れる電流が制御されて動作している。Ｓｔｏｐ端子から電源が入力されたときには抵抗Ｒ６を介してトランジスタＴｒ２がオンすることで制御回路のＩＮ端子の電圧は抵抗Ｒ４と、抵抗Ｒ３，Ｒ５からなる並列回路の分圧に変わるためにＩＮ端子の電圧が低下する。従って、ＩＮ端子の電圧が基準電圧Ｖｒｅｆと同じ電圧になるためにはＬＥＤに流れる電流はＴａｉｌ端子から電源が入力されているときに比べて大きくなる。
【００３７】
図１０に他の例を示す。Ｔａｉｌ端子から電源が入力されているときは抵抗Ｒ２の両端に発生する電圧は抵抗Ｒ３，Ｒ４で分圧されて制御回路１のＩＮ端子に入力されており、この電圧が内部の基準電圧Ｖｒｅｆと同じになるようにＬＥＤに流れる電流が制御されて動作している。Ｓｔｏｐ端子から電源が入力されたときには抵抗Ｒ６を介してトランジスタＴｒ２がオンすることでＬＥＤの電流を制限している抵抗Ｒ２に並列に抵抗Ｒ５が接続され、制限抵抗が小さくなるのでＬＥＤに流れる電流は大きくなり、光出力は増大する。電流が増加するとＬＥＤの順方向電圧が高くなるので、抵抗値を小さくすることで出力電圧は電源電圧以下にすることが可能であり、電源変動に対しても確実に制御が可能である。
【００３８】
このように本実施形態では光出力を変化させた場合においても高出力時の順方向電圧の和が電源電圧以下となるようにＬＥＤを直列に接続し、降圧回路の出力を低出力と高出力に変化させ、ＬＥＤに一定電流が流れるように制御することで、光出力が異なる状態においてもＬＥＤの順方向電圧のばらつきや従来のような並列回路でのばらつきや電源変動等による光出力のばらつきを無くすことが可能であり、またＬＥＤ１灯が断線した場合には複雑な回路を必要とせずに全灯を消灯させることが可能である。
【００３９】
（実施形態５）
図１１に本発明の実施形態５の回路構成を示す。複数のＬＥＤユニットを点灯する例であり、チョークコイルＬ１、ダイオードＤ１、スイッチング素子Ｔｒ５、コンデンサＣ１、制御回路１からなる昇圧回路の出力に、ＰＮＰ型トランジスタＴｒ１，Ｔｒ２及びエミッタ抵抗Ｒ１，Ｒ２から成る第１のカレントミラー回路（一方のトランジスタ例えばＴｒ２のベース・コレクタ間は短絡される）を構成し、ＰＮＰ型トランジスタＴｒ１及びＴｒ２のコレクタ側にＬＥＤユニット（ＬＥＤ１，ＬＥＤ２）のアノード側が接続され、夫々のカソード側にＮＰＮ型トランジスタＴｒ３，Ｔｒ４及びエミッタ抵抗Ｒ３，Ｒ４からなる第２のカレントミラー回路（ＬＥＤのアノード側のＰＮＰ型トランジスタのベース・コレクタ間が短絡されていない方のトランジスタ、ここではＴｒ３のベース・コレクタ間が短絡される）が接続され、抵抗Ｒ３またはＲ４のどちらかの電圧降下を検出し、この電圧即ち回路電流が一定となるように昇圧回路は定電流制御されている。
【００４０】
上記の２つのカレントミラー回路は、相互に回路電流をミラーし合う関係にあり、双方のＬＥＤ回路電流のバランスをとると同時に、どちらかの電流が無くなれば他方の電流も遮断されることになり、従来例における各回路のＬＥＤ光出力のアンバランスを抑制すると共に、ＬＥＤが１灯でも断線に至った場合に全灯消灯が可能であり、しかも全灯消灯モードを設けていないので外乱等によってそのモードに固定されることも無く、上述の２つの課題を簡単な構成で解決することができる。
【００４１】
図１２にＬＥＤユニットが３つの場合の例を示す。端子Ａ，Ｂ，Ｃが図１１の端子Ａ，Ｂ，Ｃに接続される。このように本実施形態では複数個のＬＥＤユニットを並列に接続した場合でも、ＬＥＤの順方向電圧Ｖｆのばらつきによる光出力のアンバランスを無くすことが出来、またＬＥＤが１灯でも断線すれば全てのＬＥＤを消灯させる機能もそのまま発揮できる。また３つ以上の並列回路にも同様に展開できる。
【００４２】
（実施形態６）
図１３に本発明の実施形態６の回路構成を示す。定電流制御を行っている昇圧回路の出力部にトランジスタＴｒ２，Ｔｒ３を介して複数のＬＥＤからなるＬＥＤユニットＬＥＤ１，ＬＥＤ２が接続されている。トランジスタＴｒ２，Ｔｒ３のベースはそれぞれ抵抗Ｒ５，Ｒ６を介してトランジスタＴｒ４，Ｔｒ５のコレクタに接続されており、トランジスタＴｒ４，Ｔｒ５はそれぞれ制御回路２からの信号Ｓ１，Ｓ２により駆動される。
【００４３】
図１４に示すように信号Ｓ１がＨｉｇｈの時はトランジスタＴｒ４，Ｔｒ２がオンして、ＬＥＤ１が点灯する。信号Ｓ２がＨｉｇｈの時にはトランジスタＴｒ５，Ｔｒ３がオンして、ＬＥＤ２が点灯するいわゆる時分割制御を行っている。信号Ｓ１とＳ２は同時にＨｉｇｈとなる重複期間Ｔ１を設け、この期間では二つのＬＥＤユニットＬＥＤ１，ＬＥＤ２が同時に点灯するように制御されている。
【００４４】
このように複数のＬＥＤユニットを並列に点灯させる場合、それぞれの順方向電圧のばらつきによりＬＥＤユニットの光出力がアンバランスになる可能性があったが、時分割制御を行うことでＬＥＤは１ユニット毎しか点灯しないので、順方向電圧のばらつきによる光出力のアンバランスが生じない。また、トランジスタＴｒ２，Ｔｒ３を切り替える信号Ｓ１，Ｓ２には信号が同時にＨｉｇｈとなる瞬間Ｔ１が設けられており、ＬＥＤ１，ＬＥＤ２を切り替えるときには必ず両方のＬＥＤが点灯する瞬間を設けることで、定電流回路が無負荷となり切替時に異常昇圧が生じることもない。
【００４５】
（実施形態７）
図１５に本発明の実施形態７の回路構成を示す。昇圧回路の出力に複数のＬＥＤを直列に接続し、光出力を変化させる時は複数のＬＥＤの一部を短絡して点灯させないことで光出力を低減させることが出来る。具体的にはチョークコイルＬ１、スイッチング素子Ｔｒ１、ダイオードＤ１、コンデンサＣ１、制御回路１からなる昇圧回路構成の定電流回路の出力部に複数のＬＥＤからなるＬＥＤユニットが接続され、ＬＥＤには定格電流以下の電流で定電流制御されている。光出力の高いストップランプ点灯時にはＳｔｏｐ側の端子に電源が接続されるので、トランジスタＴｒ２，Ｔｒ３がオフしているために出力側のＬＥＤは全灯が点灯している。光出力の低いテールランプ点灯時にはＴａｉｌ側の端子に電源が接続されることでトランジスタＴｒ２，Ｔｒ３がオンするためにＬＥＤの一部が短絡状態となって発光せず、ＬＥＤの一部のみが点灯することになり、結果的に光出力は低下する。
【００４６】
図１６に他の例を示す。昇圧回路の出力部に複数のＬＥＤが直列に接続されたＬＥＤユニットが並列に接続されている。図１５と同様にストップランプ点灯時にはトランジスタＴｒ３がオンするので、ＬＥＤ１，ＬＥＤ２共に点灯するが、テールランプ点灯時にはトランジスタＴｒ３がオフしているので、ＬＥＤ１しか点灯しない。
【００４７】
このように本実施形態では、複数のＬＥＤからなる照明装置で高い光出力を必要とする場合にもＬＥＤに流れる電流を変える必要が無いから、ＬＥＤの温度を上昇させることなく、容易に光出力を変えることが出来るので、ＬＥＤの長寿命化も期待できる。
【００４８】
（実施形態８）
図１７に本発明の実施形態８の回路構成を示す。本実施形態はＬＥＤの近傍に点灯／不点灯を検出するためのセンサを実装したものである。図１８，図１９に本実施形態の実装構造の一例を示す。図１９のようにＬＥＤの近傍に受光素子３が同一基板上に実装され、受光素子３とＬＥＤの一部を覆う形で弧状の遮光板４が設けられており、図１９のような基板５上に構成されている。図１８に示すようにＬＥＤから出た光は遮光板４に当たり受光素子３に当たることで、ＬＥＤが点灯していることが判別でき、外光は遮光板４により、受光素子３に入ることはないので、ＬＥＤが点灯していることだけを検出することが可能である。
【００４９】
図１７に上記構成を用いた回路例を示す。ＬＥＤに電流が流れるとＬＥＤが発光し、個別に設けられた受光素子（ここではフォトトランジスタ）がオンする。全てのＬＥＤが点灯すると全てのフォトトランジスタがオンするのでトランジスタＴｒ２，Ｔｒ３は共にオンする。ＮＯＲ回路ＩＣ１の入力は＜Ｌｏｗ，Ｌｏｗ＞となるので、出力はＨｉｇｈとなり点灯を維持する。
【００５０】
次に仮にＬＥＤ１−１が点灯しなくなったとすると、ＬＥＤ１−１に対応するフォトトランジスタがオフとなり、トランジスタＴｒ２はオフする。そうすると、ＮＯＲ回路ＩＣ１の入力は＜Ｈｉｇｈ，Ｌｏｗ＞となるので、出力はＬｏｗとなり、トランジスタＴｒ４がオフして、トランジスタＴｒ５がオフするからＬＥＤは全て消灯する。なお、電源を入れたときには各ＬＥＤは消灯しているのでフォトトランジスタがオフしているから、ＮＯＲ回路ＩＣ１の出力には遅延回路ＤＬを設けて、電源が入った初期は一定時間Ｈｉｇｈを維持して、ＬＥＤが点灯するようにしている。
【００５１】
実装構造の他の例を図２０，図２１に示す。受光素子３が同一パッケージ６内に設けられた例で、ＬＥＤのチップが基板５上にダイボンディング７等により設けられており、チップ上面からワイヤー８で内部電極に接続されている。内部電極は外部電極Ａ，Ｂにそれぞれに接続されている。受光素子３は同様にもう一方の電極Ｃ，Ｄにワイヤーで接続されている。受光素子３としてはフォトダイオードやフォトトランジスタ等、光により動作する素子であればよい。受光素子３は受光面がＬＥＤのチップ側に向いており、ＬＥＤが発光すると受光面で受光し素子が動作する。
【００５２】
図２２，図２３に他の実施形態を示す。図２３のようにＬＥＤの近傍に温度検出素子９（例えばＮＴＣサーミスタ）などを設け、ＬＥＤの温度を検出して、ＬＥＤが点灯しているかを判断する。ＬＥＤが点灯すると、ＬＥＤにはほぼ同じ電流が流れるので、ＬＥＤの温度は上昇する。ＬＥＤの温度が上昇するとＬＥＤ近傍に設けられたサーミスタの抵抗値が変化するので、ＬＥＤ１のサーミスタ群と抵抗Ｒ７、同様にＬＥＤ２のサーミスタ群と抵抗Ｒ８の分圧比が変わり、ＩＣ１のＡ／Ｄ変換入力端子Ａ／Ｄ１、Ａ／Ｄ２の電圧が変わる。抵抗Ｒ７とＲ８は同じ定数とする。Ａ／Ｄ変換入力端子Ａ／Ｄ１、Ａ／Ｄ２の電圧値は本来同じであるが、点灯していなければ、温度が上昇しないＬＥＤがあるので、サーミスタの抵抗値が変化しない。このため、分圧比が点灯していないＬＥＤユニットとは異なる値になるので、点灯していないＬＥＤがあると判断してＩＣ１のＯＵＴ端子はＬｏｗとなり、トランジスタＴｒ４，Ｔｒ５がオフして消灯する。ＩＣ１はマイコンなどで構成され、電源が入った初期は一定時間Ｈｉｇｈを出力する遅延機能を有している。
【００５３】
このように本実施形態ではＬＥＤ個別にＬＥＤの光や温度を検出することで、ＬＥＤが断線ではなく短絡不良となって点灯しない場合でも点灯しないことを検出することが可能である。
【００５４】
図２４に実施形態１〜８の照明装置を用いたテールランプの器具の例を示す。図２６のように、表面にＬＥＤが実装され、裏面にＬＥＤ点灯回路の電子部品９が実装された照明装置が導光板１１の一端に設けられ、導光板１１の一面には反射板１２を設け、他面が発光するようになっている。図２５のような導光板ユニット１０を構成し、この導光板ユニット１０が図２８のようなケース１３と透過性のある表面パネル１４に組み込まれ、自動車の後部のテールランプを構成している。
【００５５】
その他の例として、図２７のように表面にＬＥＤおよびＬＥＤ点灯回路の電子部品９を実装したような照明装置や、図２９のような表面パネルが無く、ケース１３に導光板ユニット１０が組み込まれたようなテールランプ等も考えられる。
【００５６】
【発明の効果】
本発明によれば、バッテリー等の直流電源で複数のＬＥＤを点灯する照明装置、特に自動車用のテールランプ／ストップランプに用いられる照明装置において課題となる各ＬＥＤ回路の電源変動による光出力変動や順方向電圧のばらつきによる光出力アンバランス及びＬＥＤが１灯でも断線に至った場合にすべてのＬＥＤを消灯する機能を簡単な構成で実現することが可能である。
【図面の簡単な説明】
【図１】本発明の第１の実施形態の回路図である。
【図２】本発明の第１の実施形態に用いる制御回路の回路図である。
【図３】本発明の第１の実施形態の一変形例の回路図である。
【図４】本発明の第２の実施形態の回路図である。
【図５】本発明の第２の実施形態の一変形例の回路図である。
【図６】本発明の第２の実施形態の他の変形例の回路図である。
【図７】本発明の第２の実施形態の別の変形例の回路図である。
【図８】本発明の第３の実施形態の回路図である。
【図９】本発明の第４の実施形態の回路図である。
【図１０】本発明の第４の実施形態の一変形例の回路図である。
【図１１】本発明の第５の実施形態の回路図である。
【図１２】本発明の第５の実施形態の一変形例の回路図である。
【図１３】本発明の第６の実施形態の回路図である。
【図１４】本発明の第６の実施形態の動作説明図である。
【図１５】本発明の第７の実施形態の回路図である。
【図１６】本発明の第７の実施形態の一変形例の回路図である。
【図１７】本発明の第８の実施形態の回路図である。
【図１８】本発明の第８の実施形態の実装構造の一例を示す図であり、（ａ）は平面図、（ｂ）は断面図である。
【図１９】本発明の第８の実施形態の実装構造の一例を示す斜視図である。
【図２０】本発明の第８の実施形態の実装構造の他の例を示す斜視図である。
【図２１】本発明の第８の実施形態の実装構造の他の例を示す断面図である。
【図２２】本発明の第８の実施形態の一変形例の回路図である。
【図２３】本発明の第８の実施形態の一変形例の実装構造の一例を示す斜視図である。
【図２４】本発明の照明装置を用いたテールランプの実装構造の一例を示す分解斜視図である。
【図２５】本発明の照明装置を用いたテールランプの半完成品の外観を示す斜視図である。
【図２６】本発明の照明装置を用いたテールランプの基板上の実装構造の一例を示す図であり、（ａ）は平面図、（ｂ）は側面図、（ｃ）は底面図である。
【図２７】本発明の照明装置を用いたテールランプの基板上の実装構造の他の一例を示す図であり、（ａ）は平面図、（ｂ）は側面図、（ｃ）は底面図である。
【図２８】本発明の照明装置を用いたテールランプの完成品の外観の一例を示す斜視図である。
【図２９】本発明の照明装置を用いたテールランプの完成品の外観の他の一例を示す斜視図である。
【図３０】複数のＬＥＤを用いた従来の照明装置の回路図である。
【図３１】自動車のテールランプ／ストップランプの装着箇所を示す斜視図である。
【図３２】複数のＬＥＤを用いた従来の照明装置に光出力のばらつきを抑制する機能を付加した例を示す回路図である。
【図３３】複数のＬＥＤを用いた従来の照明装置に断線時の全消灯機能を付加した例を示す回路図である。
【符号の説明】
ＬＥＤ　　ＬＥＤ直列回路
Ｖｄｃ　　直流電源
Ｌ１　　　チョークコイル
Ｔｒ１　　スイッチング素子
Ｄ１　　　ダイオード
Ｃ１　　　平滑用コンデンサ
Ｒ２　　　電流制限抵抗
１　　　　制御回路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lighting device that can be used as a tail lamp / stop lamp for a vehicle.
[0002]
[Prior art]
Conventional examples are shown in FIGS. FIG. 30 shows a circuit diagram of an on-vehicle tail / stop lamp using a plurality of LEDs. FIG. 31 illustrates a place where such a tail / stop lamp is arranged. In FIG. 30, LED1 is a first LED unit, LED2 is a second LED unit, D1 and D2 are diodes, and R1 to R4 are resistors. GND is a ground terminal, Stop is a terminal that is energized in a stop lamp lighting state with a brake depressed, and Tail is a terminal that is energized in a tail lamp lighting state.
[0003]
When the tail lamp is lit, the light output of the LED is kept low, and when the stop lamp is lit with the brake depressed, the light output of the LED is increased. Such a method is often used because it is inexpensive, but when connecting a plurality of LEDs to secure the light amount, the LEDs are connected in series so that the sum of the forward voltage Vf of the LEDs is at least equal to or less than the power supply voltage. Unless the connected LED units are connected in parallel, the required number of LEDs cannot be connected. For example, a battery whose power supply is used in a car has a rating of 12 V and a power supply fluctuation of 9 V to 16 V. Therefore, if the forward voltage Vf of the LED is 3 V, only three LEDs can be connected in series. Therefore, when it is desired to light up six LEDs, it is necessary to connect them in parallel as shown in FIG.
[0004]
Hereinafter, the operation of the circuit of FIG. 30 will be briefly described. First, in the tail lamp lighting state, a battery is connected between the Tail terminal and the GND terminal shown in the figure, a plurality of first LED units (LED1) connected in series via a diode D2 and a resistor R1, and a diode D2 and a resistor. When a plurality of second LED units (LED2) connected in series via R4 are turned on and the resistances of the resistors R1 and R4 are set to be equal, the LEDs 1 and 2 emit light substantially equally.
[0005]
Next, in the stop lamp lighting state, a battery is connected between the Stop terminal and the GND terminal in the figure, and LED1 lights up through the diode D1 and the resistor R2, and LED2 lights up through the diode D1 and the resistor R3. If the resistance values of R1 and R3 are equal to each other and are set sufficiently small with respect to the resistances R1 and R4, LED1 and LED2 emit light at substantially the same high output.
[0006]
[Problems to be solved by the invention]
(Issue 1)
Problems in such a conventional example include a change in light output due to power supply fluctuation when a battery or the like is used as a power supply as described above, and a variation in light output of a parallel circuit due to a variation in LED forward voltage Vf. If the battery voltage is Vdc, the forward voltages of the diodes D1 and D2 are Vf0, the resistance value is R, the forward voltages of LED1 are Vf11, Vf12 and Vf13, and the forward voltages of LED2 are Vf21, Vf22 and Vf23, The currents of LED1 and LED2 are represented by the following equations.
I (LED1) = [Vdc-Vf0- (Vf11 + Vf12 + Vf13)] / RI (LED2) = [Vdc-Vf0- (Vf21 + Vf22 + Vf23)] / R
[0007]
That is, when the battery voltage Vdc fluctuates, I (LED1) and I (LED2) fluctuate in the same manner. Therefore, when the required light output is obtained at the lowest power supply voltage, the power supply fluctuates and becomes higher. Occasionally, an overcurrent flows through the LED, causing the LED itself to generate heat, affecting its life, increasing the power consumption of the current limiting resistor, and necessitating the use of a resistor with a large rated power. Also, when the forward voltage of each LED varies, it is expected that the currents I (LED1) and I (LED2) of the LEDs 1 and 2 greatly differ particularly when the difference between the sum of the forward voltages and the battery voltage is small. Unbalance occurs in the optical output of the parallel circuit.
[0008]
(Issue 2)
Further, as a problem specific to the on-vehicle use, since it is expected that a minimum required light output cannot be obtained when the LED is disconnected, a function to facilitate the identification by turning off all the lights when the LED is disconnected is required. However, as described above, if the number of LEDs increases, they must be connected in parallel due to the power supply. If the LED circuits are connected in parallel, all the LEDs are turned off even if one LED is disconnected. It is not possible.
[0009]
FIG. 32 shows one solution to the former problem 1. A resistor R4, a transistor Tr3 having a collector and a base short-circuited, a reference current circuit having a resistor R3 connected in series, a series circuit of a transistor Tr1 and a resistor R1 connected in series with an LED1 and having a base connected to the base of the transistor Tr3; Similarly, a series circuit of the transistor R2 and the resistor R2, which is connected in series with the LED2 and whose base is connected to the base of the transistor Tr3, forms a current mirror circuit, and makes the circuit current of the LED1 and the LED2 substantially equal to the reference current. Is controlled as follows. By such a measure, even if the forward voltage of the LED fluctuates, the current of the parallel circuit can be approximately adjusted, and the influence on the light output can be avoided.
[0010]
FIG. 33 shows one solution to the latter problem 2. Current limiting resistors R2 and R3 are connected in series to LED1 and LED2, respectively, and the total current flows through the transistor Tr1 biased by the resistor R1. If all of LED1 and LED2 are normal, LED current flows, causing a constant voltage drop across resistors R2 and R3, and the negative terminal of comparator COMP is kept at a potential obtained by dividing the voltage of the reference power supply by resistors R4 and R7. If the potential of the + terminal of the comparator COMP determined by the voltage division of the resistors R5 and R8 is set to be equal to or lower than the potential of the-terminal, the output of the comparator COMP becomes a low state, and is connected between the base and the emitter of the transistor Tr1. The transistor Tr2 is kept off, the transistor Tr1 is kept on, and the LEDs 1 and 2 are turned on.
[0011]
If any one of the LEDs LED1 and LED2 is disconnected, the voltage drop of the resistor R2 or R3 disappears, and the negative terminal potential of the comparator COMP is reduced by the resistor R2 or R3 connected via the diode D1 or D2, When the potential becomes equal to or lower than the potential of the + terminal of the comparator COMP, the output is inverted to High, the + terminal is fixed to High via the resistor R6 and the diode D3 and self-latched, and thereafter the output of the comparator COMP is fixed to High. Therefore, the base current of the transistor Tr2 is supplied via the resistor R9, the transistor Tr2 is turned on, the transistor Tr1 is turned off, and both LED1 and LED2 are turned off.
[0012]
Since it is necessary to combine the measures shown in FIGS. 32 and 33 with respect to the two problems in the above-described conventional example, the circuit configuration becomes complicated, causing a cost problem, and even if the LED is normal. Regardless, a situation in which all lights are turned off due to a malfunction due to extraneous noise or the like is likely to occur, and a problem in terms of reliability also arises.
[0013]
(Issue 3)
Also, in the case of a vehicle, a transient surge voltage may be generated in the power supply when the ignition is turned off, when the load is dumped, or when the power of another device is turned ON / FF. For example, in the automotive standard (JASO), which is a standard for in-vehicle equipment, a surge such as a peak voltage of 70 V and a damping constant of 200 ms (time to decay to 36.8% of the maximum value) is specified as an example.
[0014]
When such a surge is applied, in the circuit of FIG. 30, an overcurrent flows through the LED, and it is conceivable that the LED may be destroyed. As a countermeasure against such a surge, a countermeasure can be provided by providing a surge countermeasure component such as a power zener or a varistor in the input portion. However, there is a problem that the component has a large shape and is expensive.
[0015]
The present invention has been made in view of the above-described drawbacks of the conventional example. In an LED lighting circuit of a lighting device that lights a plurality of LEDs using a power supply having a large fluctuation range such as a battery, the light output due to the power fluctuation is reduced. Provided is a lighting device that can suppress fluctuations and unbalance of LED light output, and can turn off all LEDs only when even one LED is disconnected, thereby eliminating the possibility of malfunction due to disturbance or the like. The task is to
[0016]
[Means for Solving the Problems]
According to the lighting device of claim 1, in order to solve the above problem, as shown in FIG. 1, a choke coil L1 and a switching element Tr1 are connected in series to a DC power supply Vdc, and the voltage across the switching element Tr1 is reduced. A booster circuit including a diode D1 and a capacitor C1 for rectifying and smoothing, a control circuit 1 for driving the switching element Tr1 at a high frequency, and a drive circuit, and a plurality of LEDs are connected in series to an output of the booster circuit. In the lighting device in which the LED units are connected via the resistor R2, the LEDs are connected in series so that the sum of the forward voltages of the LEDs is equal to or higher than the voltage of the DC power supply Vdc so that the current flowing through the LEDs is constant. It is characterized by feedback control.
[0017]
According to a second aspect of the present invention, in the first aspect, when the LED is disconnected, the voltage is switched to a constant voltage control for controlling the output voltage of the booster circuit to be constant.
According to the third aspect of the present invention, when the current flowing through the LED unit is switched between a low output and a high output, the sum of the voltage across the resistor and the forward voltage of the LED at the time of the low output is a DC power supply. The LEDs are connected in series so as to have a voltage equal to or higher than the voltage, and the output voltage of the booster circuit is increased at the time of high output.
[0018]
According to the fourth aspect of the present invention, in the third aspect, the LEDs are connected in series so that the sum of the voltage across the resistor and the forward voltage of the LEDs at the time of low output is equal to or higher than the voltage of the DC power supply. The high output and the low output are switched by changing the resistance value connected to.
According to a fifth aspect of the present invention, in the fourth aspect, when an abnormal voltage exceeding the input voltage range is input at a high output, the operation is switched to a low output operation.
[0019]
According to the invention of claim 6, as shown in FIG. 8, the switching element Tr1, the choke coil L1, and the capacitor C1 are connected in series to the DC power supply Vdc, and the switching element Tr1 and the choke coil L1 are connected from the negative side of the DC power supply Vdc. A diode D1 is connected so that a regenerative current flows toward the connection point, and a step-down circuit having a control circuit 1 and a drive circuit for operating the switching element Tr1 at a high frequency is provided. A plurality of LEDs are provided at the output of the step-down circuit. In the lighting device in which the LED units connected in series are connected via the resistor R2, the sum of the voltage across the resistor R2 and the forward voltage of the LED becomes equal to or less than the voltage of the DC power supply Vdc at the output of the step-down circuit. As described above, the LEDs are connected in series, and feedback control is performed so that the current flowing through the LEDs is constant.
[0020]
According to the invention of claim 7, in claim 6, when the current flowing through the LED unit is switched between low output and high output, the sum of the voltage across the resistor and the forward voltage of the LED at high output is the voltage of the DC power supply. The LED is connected in series as described below, and the output voltage of the step-down circuit is increased at the time of high output.
According to the invention of claim 8, in claim 7, the LED is connected so that the sum of the voltage across the resistor and the forward voltage of the LED at the time of high output is equal to or less than the voltage of the DC power supply, and is connected in series with the LED. The low output and the high output are switched by changing the resistance value.
[0021]
According to the ninth aspect of the present invention, in any one of the first to eighth aspects, a plurality of LED units are connected in parallel, and the LED units are controlled so as to be lit at a constant period, and each LED unit is switched. An overlap period in which a plurality of LED units are turned on at the same time is provided.
According to the tenth aspect of the present invention, in any one of the first to eighth aspects, the first and second LED units are connected in parallel as a load, and the second LED unit is turned on by the circuit current of the first LED unit. It is characterized by comprising a first current mirror circuit for controlling a circuit current, and a second current mirror circuit for controlling a circuit current of the first LED unit with a circuit current of the second LED unit.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
FIG. 1 shows a first embodiment of the present invention. A choke coil L1 and a switching element Tr1 are connected in series with the DC power supply Vdc, and a rectifying diode D1 and a smoothing capacitor C1 are connected to both ends of the switching element Tr1 to form a so-called step-up chopper circuit. At both ends of the capacitor C1, an LED unit (hereinafter, referred to as an LED) including a plurality of LEDs and a resistor R2 for detecting a current flowing through the LEDs are connected in series. The control circuit 1 is a so-called PWM control circuit including an error amplifier (E / A) 1a, an oscillator 1b, and a comparator 1c as shown in FIG. 2, so that the voltage of the IN terminal of the control circuit 1 is constant. The switching element Tr1 of FIG. 1 is switched at a high frequency (several tens to several hundreds kHz).
[0023]
When a battery or the like is used as the DC power supply Vdc, for example, in the case of a battery for an automobile, the voltage fluctuation range widely varies from 9 V to 16 V. Therefore, if the forward voltage of the LED is 3 V / piece, the sum of the forward voltages of the LEDs on the output side is 16 V or more, that is, at least six LEDs are connected in series. , And the current flowing through the LED can be kept constant even when the power supply fluctuates.
[0024]
FIG. 3 shows a modification. The basic configuration is the same as that of FIG. 1, and the output of the booster circuit is connected to the IN terminal of the control circuit 1 which forms a feedback loop via the Zener diode ZD1 and the resistor R5. Since no current flows when the LED is disconnected, the IN terminal is at about 0 V, and the control circuit 1 increases the ON duty of the switching element Tr1 so as to increase the output. Therefore, the output voltage rises, but when the output voltage becomes equal to or higher than the zener voltage, the zener diode ZD1 is turned on, so that the output voltage is substantially limited to the zener voltage.
[0025]
As described above, in the present embodiment, the LEDs are connected in series such that the sum of the forward voltages is equal to or higher than the power supply voltage, and a step-up circuit is used to control the LEDs so that a constant current flows. It is possible to eliminate the variation of voltage, the variation of the conventional parallel circuit and the variation of the light output due to the fluctuation of power supply, etc. In addition, when one LED is disconnected, all the lights are turned off without the need for a complicated circuit. It is possible to prevent the circuit voltage from abnormally increasing when the LED is disconnected and to prevent the switching element from being overloaded with a simple configuration.
[0026]
(Embodiment 2)
FIG. 4 shows an embodiment in which the light output needs to be switched like a tail lamp / stop lamp for an automobile. In a tail lamp / stop lamp for an automobile, it is necessary to switch between a low output when the tail lamp is turned on and a high output when the stop lamp is turned on. When power is input from the Tail terminal, the voltage generated at both ends of the resistor R2 is divided by the resistors R3 and R4 and input to the IN terminal of the control circuit 1, and this voltage is applied to the internal reference voltage Vref. The current flowing through the LED is controlled to operate in the same manner as described above. When the power is input from the Stop terminal, the voltage of the IN terminal of the control circuit 1 is changed to the divided voltage of the parallel circuit including the resistor R4 and the resistors R3 and R5 by turning on the transistor Tr2 via the resistor R6. The voltage at the IN terminal decreases. Therefore, similarly, in order to become the same voltage as the reference voltage Vref, the current flowing through the LED becomes larger than when the tail lamp is turned on. That is, the output voltage of the booster circuit is higher than when the tail lamp is turned on.
[0027]
Another circuit example is shown in FIG. When power is input from the Tail terminal, the voltage generated at both ends of the resistor R2 is divided by the resistors R3 and R4 and input to the IN terminal of the control circuit 1, and this voltage is applied to the internal reference voltage Vref. The current flowing through the LED is controlled to operate in the same manner as described above. When power is input from the Stop terminal, the transistor Tr2 is turned on via the resistor R6, so that the resistor R5 is connected in parallel with the resistor R2 that limits the current of the LED, and the resistance value decreases, so that the current flows to the LED. The current increases and the light output increases. Although the output voltage decreases because the limiting resistance decreases, the output voltage can be higher than the power supply voltage because the LED forward voltage increases as the LED current increases due to the VI characteristics of the LED. It is possible, and it is possible to reliably control power supply voltage fluctuations.
[0028]
FIG. 6 shows another example of the circuit. When the power is input from the Stop terminal, the transistor Tr2 is turned on via the resistor R6, so that the resistor R5 is connected in parallel to the resistor R2 which limits the current of the LED, and the resistance value is switched. In this example, when power is input, the transistor Tr3 is turned on via the resistor R7 to switch the voltage division ratio of the voltage at the IN terminal of the control circuit 1. When the dimming ratio between the stop lamp lighting and the tail lamp lighting is large, the LED current decreases when the tail lamp lights. Since the LED forward voltage decreases due to the characteristics of the LED, the output voltage of the booster circuit decreases. When the power supply voltage falls below the power supply voltage, control becomes impossible, and when the resistance value of the resistor R2 is increased, the voltage dividing ratio of the resistors R3, R4 becomes too high, so that the control circuit 1 cannot control the power supply fluctuation. On the other hand, there is a possibility that the output voltage of the booster circuit decreases. In order to prevent these, it is necessary to set the output voltage to be much higher than the sum of the forward voltages of the LEDs, which causes a problem that the loss in the current limiting resistor increases.
[0029]
In the circuit shown in FIG. 6, when power is input from the Stop terminal, the transistor Tr2 is turned on. Therefore, the current increases because the limiting resistance value decreases, and when power is input from the Tail terminal, the transistor Tr3 is turned on. By changing the voltage dividing ratio of the resistors R3 and R4, it is not necessary to increase the secondary voltage of the booster circuit more than necessary, and control can be performed so that the output is stabilized.
[0030]
FIG. 7 shows another circuit example. An overvoltage protection circuit including a Zener diode ZD1, a resistor R7, and a transistor Tr3 is provided from the cathodes of the diodes D2 and D3. The Zener voltage of the Zener diode ZD1 is a voltage higher than the power supply voltage range, for example, a voltage of 24V for a power supply whose power supply voltage varies in a range of 9 to 16V. When the LED is lit in a high output state in which power is input from the Stop terminal, an overvoltage occurs due to a surge or the like in the input power supply, and if the overvoltage is a voltage equal to or higher than the zener voltage, the zener diode ZD1 is turned on. Since the transistor Tr3 is turned on, the transistor Tr2 is turned off and the series resistance of the LED unit is only R2, so that the current is switched to a low current when the tail lamp is turned on. Therefore, no overcurrent flows to the LED even with an overvoltage.
[0031]
As described above, in this embodiment, even when the light output is changed, the LEDs are connected in series so that the sum of the forward voltage at the time of the low output is equal to or higher than the power supply voltage, and the output of the booster circuit is set to the low output and the high output. And control so that a constant current flows through the LED, so that even when the optical output is different, the variation in the forward voltage of the LED, the variation in the parallel circuit as in the past, and the variation in the optical output due to power supply fluctuations, etc. Can be eliminated, and when one LED is disconnected, all the lights can be turned off without requiring a complicated circuit.
[0032]
Further, in the circuit as shown in FIG. 6, it is not necessary to increase the output voltage of the booster circuit even at the time of high output, so that the withstand voltage of components can be reduced and the loss at the limiting resistor can be reduced. There are benefits.
Further, in the circuit as shown in FIG. 7, even when a surge-like overvoltage occurs at the time of ignition or the like, the overcurrent does not flow through the LED.
[0033]
(Embodiment 3)
FIG. 8 shows a third embodiment of the present invention. The switching element Tr1 and the choke coil L1 are connected in series with the DC power supply Vdc, the cathode of the regenerative diode D1 is connected to a connection point between the collector of the switching element Tr1 and the choke coil L1, and the anode of the diode D1 is connected to the ground. This is a so-called step-down chopper circuit configuration in which a smoothing capacitor C1 is connected to the other end of the choke coil L1. At both ends of the capacitor C1, an LED unit (hereinafter, referred to as an LED) including a plurality of LEDs and a resistor R2 for detecting a current flowing through the LEDs are connected in series. The control circuit 1 performs so-called PWM control similar to that of FIG. 2, and switches the switching element Tr1 at a high frequency (several tens to several hundreds kHz) so that the voltage across the resistor R2 is constant.
[0034]
When a battery or the like is used as the DC power supply Vdc, for example, in the case of a battery for an automobile, the voltage fluctuation range widely varies from 9 V to 16 V. Therefore, if the forward voltage of the LED is 3 V / piece, the output side LED has a sum of the forward voltage of 9 V or less, that is, a maximum of three LEDs are connected in series. The current can be kept within the fluctuation range, and the current flowing to the LED can be kept constant even when the power supply fluctuates.
[0035]
As described above, in the present embodiment, the LEDs are connected in series such that the sum of the forward voltages is equal to or less than the power supply voltage, and a step-down circuit is used to control the LED so that a constant current flows. It is possible to eliminate variations in light output due to variations in power supply and fluctuations in power supply, etc., and it is possible to turn off all lights without a complicated circuit when one LED is disconnected. This embodiment is particularly effective when the battery voltage is high, for example, 48V.
[0036]
(Embodiment 4)
FIG. 9 shows a fourth embodiment of the present invention. An example in which light output needs to be switched like a tail lamp for an automobile will be described. When power is input from the Tail terminal, the transistor Tr2 is off, and the voltage generated across the resistor R2 is divided by the resistors R3 and R4 and input to the IN terminal of the control circuit 1. The current flowing through the LED is controlled so that the voltage becomes equal to the internal reference voltage Vref, and the LED operates. When power is input from the Stop terminal, the transistor Tr2 is turned on via the resistor R6, so that the voltage at the IN terminal of the control circuit changes to the divided voltage of the parallel circuit including the resistor R4 and the resistors R3 and R5. Voltage decreases. Therefore, in order for the voltage of the IN terminal to become the same voltage as the reference voltage Vref, the current flowing through the LED becomes larger than when power is input from the Tail terminal.
[0037]
FIG. 10 shows another example. When power is input from the Tail terminal, the voltage generated at both ends of the resistor R2 is divided by the resistors R3 and R4 and input to the IN terminal of the control circuit 1. This voltage is used as the internal reference voltage Vref. The currents flowing through the LEDs are controlled and operated in the same manner. When power is input from the Stop terminal, the transistor Tr2 is turned on via the resistor R6, so that the resistor R5 is connected in parallel with the resistor R2 that limits the current of the LED, and the current flowing through the LED is reduced because the limiting resistance is reduced. And the light output increases. When the current increases, the forward voltage of the LED increases. Therefore, the output voltage can be reduced to the power supply voltage or less by reducing the resistance value, and the power supply fluctuation can be reliably controlled.
[0038]
As described above, in this embodiment, even when the light output is changed, the LEDs are connected in series such that the sum of the forward voltage at the time of high output is equal to or less than the power supply voltage, and the output of the step-down circuit is set to the low output and the high output. And control so that a constant current flows through the LED, so that even when the optical output is different, the variation in the forward voltage of the LED, the variation in the parallel circuit as in the past, and the variation in the optical output due to power supply fluctuations, etc. Can be eliminated, and when one LED is disconnected, all the lights can be turned off without requiring a complicated circuit.
[0039]
(Embodiment 5)
FIG. 11 shows a circuit configuration of the fifth embodiment of the present invention. This is an example in which a plurality of LED units are turned on. The output of a booster circuit including a choke coil L1, a diode D1, a switching element Tr5, a capacitor C1, and a control circuit 1 includes PNP transistors Tr1 and Tr2 and emitter resistors R1 and R2. A first current mirror circuit (one transistor, for example, the base and collector of Tr2 is short-circuited), and the anode sides of the LED units (LED1, LED2) are connected to the collector sides of the PNP transistors Tr1 and Tr2, respectively. A second current mirror circuit (a transistor whose base and collector are not short-circuited between the base and collector of the PNP transistor on the anode side of the LED, Tr3 in this case) is composed of NPN transistors Tr3 and Tr4 and emitter resistors R3 and R4 on the cathode side of the transistor. Base kore Between motor are short-circuited) are connected, detects either the voltage drop of the resistor R3 or R4, the booster circuit as the voltage or the circuit current is constant is the constant current control.
[0040]
The two current mirror circuits described above have a relationship of mirroring circuit currents with each other, so that both LED circuit currents are balanced, and when one of the currents disappears, the other current is cut off. In addition to suppressing the unbalance of the LED light output of each circuit in the conventional example, all the lights can be turned off in the event that even one LED is disconnected. In addition, since all lights are not turned off mode, there is no The above two problems can be solved with a simple configuration without being fixed to the mode.
[0041]
FIG. 12 shows an example in the case of three LED units. Terminals A, B, and C are connected to terminals A, B, and C in FIG. As described above, in the present embodiment, even when a plurality of LED units are connected in parallel, it is possible to eliminate the unbalance of the light output due to the variation in the forward voltage Vf of the LED. The function of turning off the LED can also be exhibited as it is. Further, the present invention can be similarly applied to three or more parallel circuits.
[0042]
(Embodiment 6)
FIG. 13 shows a circuit configuration according to the sixth embodiment of the present invention. LED units LED1 and LED2 composed of a plurality of LEDs are connected via transistors Tr2 and Tr3 to the output section of the booster circuit that performs constant current control. The bases of the transistors Tr2 and Tr3 are connected to the collectors of the transistors Tr4 and Tr5 via the resistors R5 and R6, respectively, and the transistors Tr4 and Tr5 are driven by signals S1 and S2 from the control circuit 2, respectively.
[0043]
As shown in FIG. 14, when the signal S1 is High, the transistors Tr4 and Tr2 are turned on, and the LED1 is turned on. When the signal S2 is High, the transistors Tr5 and Tr3 are turned on, and so-called time-division control for turning on the LED2 is performed. The signals S1 and S2 provide an overlap period T1 in which the signals are simultaneously High, and in this period, the two LED units LED1 and LED2 are controlled so as to be turned on simultaneously.
[0044]
When a plurality of LED units are turned on in parallel in this manner, the light output of the LED units may be unbalanced due to variations in the forward voltage of each LED unit. Since the light is turned on only every time, there is no imbalance in the light output due to the variation in the forward voltage. The signals S1 and S2 for switching the transistors Tr2 and Tr3 are provided with a moment T1 at which the signals are simultaneously High. When switching between the LEDs 1 and LED2, the moment when both the LEDs are turned on is always provided. , And no abnormal pressure rise occurs during switching.
[0045]
(Embodiment 7)
FIG. 15 shows a circuit configuration according to the seventh embodiment of the present invention. When a plurality of LEDs are connected in series to the output of the booster circuit and the light output is changed, the light output can be reduced by short-circuiting some of the plurality of LEDs so that they are not turned on. Specifically, an LED unit including a plurality of LEDs is connected to an output section of a constant current circuit having a booster circuit configuration including a choke coil L1, a switching element Tr1, a diode D1, a capacitor C1, and a control circuit 1. Constant current control is performed with the following currents. When a stop lamp with a high light output is turned on, a power supply is connected to the Stop-side terminal, so that all the LEDs on the output side are turned on because the transistors Tr2 and Tr3 are off. When the tail lamp with a low light output is turned on, the power supply is connected to the terminal on the Tail side to turn on the transistors Tr2 and Tr3, so that part of the LED is short-circuited and does not emit light, and only part of the LED is turned on. As a result, the light output is reduced.
[0046]
FIG. 16 shows another example. An LED unit in which a plurality of LEDs are connected in series is connected in parallel to an output section of the booster circuit. As in FIG. 15, when the stop lamp is turned on, the transistor Tr3 is turned on, so that both the LED1 and the LED2 are turned on. However, when the tail lamp is turned on, only the LED1 is turned on because the transistor Tr3 is turned off.
[0047]
As described above, in the present embodiment, even when a high light output is required in a lighting device including a plurality of LEDs, there is no need to change the current flowing through the LEDs, so that the light output can be easily performed without increasing the temperature of the LEDs. Can be changed, so that a longer life of the LED can be expected.
[0048]
(Embodiment 8)
FIG. 17 shows a circuit configuration of the eighth embodiment of the present invention. In this embodiment, a sensor for detecting lighting / non-lighting is mounted near an LED. 18 and 19 show an example of a mounting structure according to the present embodiment. As shown in FIG. 19, the light receiving element 3 is mounted on the same substrate in the vicinity of the LED, and the arc-shaped light shielding plate 4 is provided so as to cover the light receiving element 3 and a part of the LED. Configured above. As shown in FIG. 18, the light emitted from the LED hits the light-shielding plate 4 and hits the light-receiving element 3, so that it is possible to determine that the LED is turned on, and the external light does not enter the light-receiving element 3 by the light-shielding plate 4. Therefore, it is possible to detect only that the LED is lit.
[0049]
FIG. 17 shows a circuit example using the above configuration. When a current flows through the LED, the LED emits light and the individually provided light receiving element (phototransistor in this case) turns on. When all the LEDs are turned on, all the phototransistors are turned on, so that both the transistors Tr2 and Tr3 are turned on. Since the input of the NOR circuit IC1 becomes <Low, Low>, the output becomes High and the lighting is maintained.
[0050]
Next, assuming that the LED 1-1 does not turn on, the phototransistor corresponding to the LED 1-1 turns off and the transistor Tr2 turns off. Then, since the input of the NOR circuit IC1 becomes <High, Low>, the output becomes Low, the transistor Tr4 is turned off, and the transistor Tr5 is turned off, so that all the LEDs are turned off. When the power is turned on, each LED is turned off and the phototransistor is turned off. Therefore, a delay circuit DL is provided at the output of the NOR circuit IC1 to keep High for a certain period of time when the power is turned on. LED is turned on.
[0051]
Other examples of the mounting structure are shown in FIGS. In the example in which the light receiving element 3 is provided in the same package 6, an LED chip is provided on a substrate 5 by die bonding 7 or the like, and is connected to an internal electrode by a wire 8 from the upper surface of the chip. The internal electrodes are connected to the external electrodes A and B, respectively. The light receiving element 3 is similarly connected to the other electrodes C and D by wires. The light receiving element 3 may be any element that operates by light, such as a photodiode or a phototransistor. The light receiving element 3 has a light receiving surface facing the chip side of the LED. When the LED emits light, the light is received by the light receiving surface and the element operates.
[0052]
22 and 23 show another embodiment. As shown in FIG. 23, a temperature detection element 9 (for example, an NTC thermistor) or the like is provided near the LED, and detects the temperature of the LED to determine whether the LED is turned on. When the LED is turned on, almost the same current flows through the LED, so that the temperature of the LED rises. When the temperature of the LED rises, the resistance value of the thermistor provided in the vicinity of the LED changes, so that the voltage dividing ratio of the thermistor group of the LED 1 and the resistor R7, and similarly, the voltage dividing ratio of the thermistor group of the LED 2 and the resistor R8 change, and A / D conversion of the IC1 The voltages of the input terminals A / D1 and A / D2 change. The resistors R7 and R8 have the same constant. Although the voltage values of the A / D conversion input terminals A / D1 and A / D2 are originally the same, there is an LED whose temperature does not rise if it is not lit, so that the resistance value of the thermistor does not change. For this reason, the voltage division ratio is different from that of the LED unit that is not turned on. Therefore, it is determined that there is an LED that is not turned on, and the OUT terminal of the IC 1 becomes Low, and the transistors Tr4 and Tr5 are turned off and turned off. The IC 1 is configured by a microcomputer or the like, and has a delay function of outputting High for a certain period of time when the power is turned on.
[0053]
As described above, in the present embodiment, by detecting the light and temperature of each LED individually, it is possible to detect that the LED is not turned on even if the LED is not turned on due to a short circuit failure rather than a disconnection.
[0054]
FIG. 24 shows an example of a tail lamp fixture using the lighting devices of the first to eighth embodiments. As shown in FIG. 26, an illumination device in which an LED is mounted on the front surface and an electronic component 9 of the LED lighting circuit is mounted on the back surface is provided at one end of the light guide plate 11, and a reflection plate 12 is provided on one surface of the light guide plate 11. , And the other side emits light. A light guide plate unit 10 as shown in FIG. 25 is formed, and this light guide plate unit 10 is incorporated into a case 13 and a transparent front panel 14 as shown in FIG. 28 to form a tail lamp at the rear of an automobile.
[0055]
As another example, as shown in FIG. 27, a lighting device in which an LED and an electronic component 9 of an LED lighting circuit are mounted on the surface thereof, or a light guide plate unit 10 is incorporated in a case 13 without a surface panel as in FIG. Such tail lamps are also conceivable.
[0056]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the light output fluctuation | variation by the power supply fluctuation | variation of each LED circuit which becomes a subject in the illuminating device which lights several LED with a DC power supply, such as a battery, especially the tail lamp / stop lamp for motor vehicles, which is a subject. It is possible to realize, with a simple configuration, a light output unbalance due to a variation in the directional voltage and a function of turning off all the LEDs when even one LED is disconnected.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a first embodiment of the present invention.
FIG. 2 is a circuit diagram of a control circuit used in the first embodiment of the present invention.
FIG. 3 is a circuit diagram of a modification of the first embodiment of the present invention.
FIG. 4 is a circuit diagram of a second embodiment of the present invention.
FIG. 5 is a circuit diagram of a modification of the second embodiment of the present invention.
FIG. 6 is a circuit diagram of another modification of the second embodiment of the present invention.
FIG. 7 is a circuit diagram of another modification of the second embodiment of the present invention.
FIG. 8 is a circuit diagram of a third embodiment of the present invention.
FIG. 9 is a circuit diagram of a fourth embodiment of the present invention.
FIG. 10 is a circuit diagram of a modified example of the fourth embodiment of the present invention.
FIG. 11 is a circuit diagram according to a fifth embodiment of the present invention.
FIG. 12 is a circuit diagram of a modification of the fifth embodiment of the present invention.
FIG. 13 is a circuit diagram according to a sixth embodiment of the present invention.
FIG. 14 is an operation explanatory diagram of the sixth embodiment of the present invention.
FIG. 15 is a circuit diagram according to a seventh embodiment of the present invention.
FIG. 16 is a circuit diagram of a modification of the seventh embodiment of the present invention.
FIG. 17 is a circuit diagram of an eighth embodiment of the present invention.
FIGS. 18A and 18B are diagrams illustrating an example of a mounting structure according to an eighth embodiment of the present invention, wherein FIG. 18A is a plan view and FIG.
FIG. 19 is a perspective view illustrating an example of a mounting structure according to an eighth embodiment of the present invention.
FIG. 20 is a perspective view showing another example of the mounting structure according to the eighth embodiment of the present invention.
FIG. 21 is a sectional view showing another example of the mounting structure according to the eighth embodiment of the present invention.
FIG. 22 is a circuit diagram of a modification of the eighth embodiment of the present invention.
FIG. 23 is a perspective view showing an example of a mounting structure according to a modification of the eighth embodiment of the present invention.
FIG. 24 is an exploded perspective view showing an example of a mounting structure of a tail lamp using the lighting device of the present invention.
FIG. 25 is a perspective view showing the appearance of a semi-finished tail lamp using the lighting device of the present invention.
26A and 26B are diagrams illustrating an example of a mounting structure of a tail lamp on a substrate using the lighting device of the present invention, wherein FIG. 26A is a plan view, FIG. 26B is a side view, and FIG.
27A and 27B are diagrams illustrating another example of a mounting structure of a tail lamp on a substrate using the lighting device of the present invention, wherein FIG. 27A is a plan view, FIG. 27B is a side view, and FIG. is there.
FIG. 28 is a perspective view showing an example of an appearance of a finished product of a tail lamp using the lighting device of the present invention.
FIG. 29 is a perspective view showing another example of the appearance of a completed tail lamp using the lighting device of the present invention.
FIG. 30 is a circuit diagram of a conventional lighting device using a plurality of LEDs.
FIG. 31 is a perspective view showing a mounting position of a tail lamp / stop lamp of an automobile.
FIG. 32 is a circuit diagram showing an example in which a function of suppressing variation in light output is added to a conventional lighting device using a plurality of LEDs.
FIG. 33 is a circuit diagram showing an example in which a conventional lighting device using a plurality of LEDs is provided with an all-light-off function when a wire is disconnected.
[Explanation of symbols]
LED LED series circuit
Vdc DC power supply
L1 choke coil
Tr1 switching element
D1 diode
C1 Smoothing capacitor
R2 Current limiting resistor
1 control circuit

Claims

A direct-current power supply includes a choke coil and a switching element connected in series, a diode and a capacitor for rectifying and smoothing the voltage across the switching element, and a booster circuit including a control circuit and a drive circuit for operating the switching element at a high frequency. In a lighting device in which an LED unit in which a plurality of LEDs are connected in series to the output of a booster circuit is connected via a resistor, the LEDs are connected in series such that the sum of the forward voltages of the LEDs is equal to or higher than the DC power supply voltage. A lighting device, wherein the lighting device is connected and feedback controlled so that a current flowing through the LED is constant.

2. The lighting device according to claim 1, wherein when the LED is disconnected, the voltage is switched to constant voltage control for controlling the output voltage of the booster circuit to be constant.

In claim 1 or 2, when switching the current flowing through the LED unit between a low output and a high output, the LED is controlled such that the sum of the voltage across the resistor and the forward voltage of the LED at the time of the low output is equal to or higher than the DC power supply voltage. A lighting device characterized in that the output voltage of the booster circuit is increased when the output is high, when they are connected in series.

In claim 3, the LEDs are connected in series such that the sum of the voltage across the resistor and the forward voltage of the LEDs at the time of low output is equal to or higher than the voltage of the DC power supply, and the resistance value connected in series with the LED unit is changed. A lighting device characterized by switching between high output and low output.

5. The lighting device according to claim 4, wherein when an abnormal voltage exceeding the input voltage range is input at a high output, the operation is switched to a low output operation.

A switching element, a choke coil, and a capacitor are connected in series to the DC power supply, and a diode is connected so that a regenerative current flows from the negative side of the DC power supply to the connection point between the switching element and the choke coil. A step-down circuit having a control circuit and a drive circuit to cause the LED unit in which a plurality of LEDs are connected in series to the output of the step-down circuit to be connected via a resistor. An illuminating device wherein LEDs are connected in series such that the sum of the voltage across the resistor and the forward voltage of the LEDs is equal to or less than the voltage of the DC power supply, and feedback control is performed so that the current flowing through the LEDs is constant.

In claim 6, when switching the current flowing through the LED unit between a low output and a high output, the LEDs are connected in series such that the sum of the voltage across the resistor and the forward voltage of the LED at the time of high output is equal to or less than the voltage of the DC power supply. A lighting device, wherein the output voltage of the step-down circuit is increased when the power is high.

8. The LED according to claim 7, wherein the LED is connected such that the sum of the voltage across the resistor and the forward voltage of the LED at the time of high output is equal to or less than the voltage of the DC power supply, and the resistance connected in series with the LED is changed. A lighting device characterized by switching between output and high output.

In any one of claims 1 to 8, a plurality of LED units are connected in parallel, and each of the LED units is controlled so as to be lit at a constant period, and when switching each LED unit, the plurality of LED units are lit at the same time. A lighting device, wherein an overlapping period is provided.

The first current according to any one of claims 1 to 8, wherein a first and a second LED unit are connected in parallel as a load, and the circuit current of the second LED unit is controlled by the circuit current of the first LED unit. An illumination device comprising: a mirror circuit; and a second current mirror circuit that controls a circuit current of the first LED unit with a circuit current of the second LED unit.