JP2005033853A - Loading driver and portable apparatus - Google Patents

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JP2005033853A
JP2005033853A JP2003192784A JP2003192784A JP2005033853A JP 2005033853 A JP2005033853 A JP 2005033853A JP 2003192784 A JP2003192784 A JP 2003192784A JP 2003192784 A JP2003192784 A JP 2003192784A JP 2005033853 A JP2005033853 A JP 2005033853A
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Prior art keywords
load
voltage
constant current
circuit
driving device
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JP2003192784A
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JP3755770B2 (en
Inventor
Teiichi Murakami
禎一 村上
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Rohm Co Ltd
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Rohm Co Ltd
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Priority to JP2003192784A priority Critical patent/JP3755770B2/en
Priority to DE200460008840 priority patent/DE602004008840T2/en
Priority to EP20040014726 priority patent/EP1499165B1/en
Priority to TW093118447A priority patent/TWI346442B/en
Priority to TW099113230A priority patent/TWI340530B/en
Priority to US10/879,315 priority patent/US7235954B2/en
Priority to CN2010101454408A priority patent/CN101789692B/en
Priority to CN2004100621747A priority patent/CN1578095B/en
Priority to KR1020040052190A priority patent/KR20050006042A/en
Publication of JP2005033853A publication Critical patent/JP2005033853A/en
Application granted granted Critical
Publication of JP3755770B2 publication Critical patent/JP3755770B2/en
Priority to US11/750,894 priority patent/US7541785B2/en
Priority to US12/428,338 priority patent/US7944189B2/en
Priority to US12/731,006 priority patent/US8519680B2/en
Priority to US13/080,498 priority patent/US8242756B2/en
Priority to US13/952,333 priority patent/US8836295B2/en
Priority to US14/454,528 priority patent/US9526138B2/en
Priority to US15/002,275 priority patent/US9526139B2/en
Priority to US15/348,257 priority patent/US9960677B2/en
Priority to US15/924,701 priority patent/US10103625B2/en
Priority to US16/127,571 priority patent/US10396659B2/en
Priority to US16/508,423 priority patent/US10734896B2/en
Priority to US16/909,714 priority patent/US11487310B2/en
Priority to US17/958,840 priority patent/US20230023130A1/en
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Abstract

<P>PROBLEM TO BE SOLVED: To vary a load current for driving a load within a specified range using a DC/DC conversion power supply circuit and to drive a load efficiently by avoiding increase in loss incident to increase in the load current. <P>SOLUTION: A load 10, e.g. an LED, and a constant current source I1 are connected in series between the output voltage Vo1 point of a DC/DC conversion power supply circuit 100 and the ground. Current Io of the constant current source can be regulated and the DC/DC conversion power supply circuit controls the output voltage such that the voltage drop of the constant current source, i.e. a detection voltage Vdet, becomes equal to a reference voltage Vref. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、直流−直流変換型の電源回路を用いて、電源電圧から変換された出力電圧により負荷を駆動する負荷駆動装置及びそれを用いた携帯機器に関する。
【０００２】
【従来の技術】
従来から、電源電圧と異なる電圧を発生する直流−直流変換型の電源回路を用いてＬＥＤなどの負荷を駆動する負荷駆動装置が多く用いられている。この負荷駆動装置は、それを駆動するための電源回路から所定の出力電圧、出力電流を発生させるために、入力電圧または負荷に印加される負荷電圧や負荷に流れる負荷電流を検出して、電源回路の制御回路に帰還させる（特許文献１参照）。
【０００３】
この従来の駆動装置では、制御電圧は入力電圧や負荷電圧を高抵抗で分圧して検出される。また、負荷電流は負荷に直列に接続された抵抗器の電圧降下によって検出される。この制御電圧や負荷電流を基準値と比較して電源回路からの出力電圧や出力電流を所定値に制御している。
【０００４】
【特許文献１】
特開２００１−３１３４２３号公報
【０００５】
【発明が解決しようとする課題】
携帯電話などの携帯型電子機器（携帯機器）においては、負荷を駆動するための負荷電流を、その負荷が設けられる電子機器側の使用上の要請によって、ある範囲内で増加させたり或いは減少させたりする場合がある。例えば、負荷が、発光素子（発光ダイオード等）である場合に、その発光量を任意の値に調整する場合などが考えられる。
【０００６】
このような場合に、負荷と直列に負荷電流検出用抵抗が挿入されていると、負荷電流の増加に応じて、電流検出用抵抗による損失が増加する。したがって、電源回路や負荷を含む電子機器の全体としての効率が、大電流時（即ち、重負荷時）に低下してしまう問題があった。
【０００７】
そこで、本発明は、電源電圧を変換して負荷に供給する、直流−直流変換型電源回路等の出力回路を用いて、負荷を駆動する負荷電流を所定範囲に変化させるとともに、負荷電流の増加に伴う損失の増大を避けて効率よく負荷を駆動することができる負荷駆動装置、及びそれを用いた携帯機器を提供することを目的とする。
【０００８】
【課題を解決するための手段】
請求項１の負荷駆動装置は、電源電圧を変換して所定の出力電圧として負荷に供給する出力回路と、前記負荷に直列に接続されて調整可能な定電流を流す定電流源とを備え、前記出力回路は、前記負荷と前記定電流源との接続点の電圧が一定電圧になるように前記所定の出力電圧を制御することを特徴とする。
【０００９】
請求項２の負荷駆動装置は、請求項１記載の負荷駆動装置において、前記定電流源は、電流可変型の定電流回路と、この定電流回路と直列に接続されたカレントミラー用入力側トランジスタと、このカレントミラー用入力側トランジスタと同じ制御入力が与えられるカレントミラー用出力側トランジスタとを含んでカレントミラー回路が構成されており、前記カレントミラー用出力側トランジスタに前記調整可能な定電流が流されることを特徴とする。
【００１０】
請求項３の負荷駆動装置は、請求項２記載の負荷駆動装置において、前記外部負荷は、少なくとも１つの発光ダイオードを含む発光ダイオード群であることを特徴とする。
【００１１】
請求項４の負荷駆動装置は、請求項２記載の負荷駆動装置において、前記一定電圧は、前記カレントミラー用出力側トランジスタの飽和電圧より高い電圧であることを特徴とする。
【００１２】
請求項５の負荷駆動装置は、請求項１乃至４記載の負荷駆動装置において、前記出力回路は、コイルと、このコイルへの通電をスイッチングするスイッチと、前記コイルと前記スイッチとの接続点と出力端子との間に設けられた整流素子とを有するスイッチング電源回路であることを特徴とする。
【００１３】
請求項６の負荷駆動装置は、請求項５記載の負荷駆動装置において、前記スイッチング電源回路は、さらに、前記整流素子の出力電圧点側に接続された平滑回路と、前記負荷と前記定電流源との接続点の電圧が基準電圧に等しくなるように前記スイッチのオンオフスイッチングを行う制御回路と、を有することを特徴とする。
【００１４】
請求項７の負荷駆動装置は、請求項１記載の負荷駆動装置において、前記負荷及び前記定電流源が複数であり、前記複数の負荷に前記複数の定電流源がそれぞれ直列に接続されてそれぞれ調整可能な定電流を流すとともに、前記複数の負荷と前記複数の定電流源との各接続点の電圧のうちの最も低い電圧が一定電圧になるように前記所定の出力電圧を制御することを特徴とする。
【００１５】
請求項８の負荷駆動装置は、請求項１乃至７記載の負荷駆動装置を用いていることを特徴とする携帯機器。
【００１６】
【発明の実施の形態】
以下、本発明の負荷駆動装置の実施の形態について、図を参照して説明する。図１は、本発明の第１の実施の形態に係る負荷駆動装置の構成を示す図である。
【００１７】
図１において、出力回路であるスイッチング電源回路１００は、入力される電源電圧Ｖｃｃを昇圧して、昇圧された出力電圧Ｖｏ１を出力する昇圧型の電源回路である。
【００１８】
電源電圧Ｖｃｃとグランド間にコイルＬ１とＮ型ＭＯＳトランジスタであるスイッチＱ１が直列に接続される。その直列接続点Ａから、整流用ダイオードＤ１と平滑用コンデンサＣ１とにより、直列接続点Ａの電圧が整流し平滑されて、出力電圧Ｖｏ１として出力される。なお、電圧は、特に断らない場合には、グランドに対する電位である。
【００１９】
出力電圧Ｖｏ１点（Ｐ１）とグランドとの間に、外部負荷１０と定電流源Ｉ１とが直列に接続される。外部負荷１０は、動作させるべき点が流れる電流で決まる負荷であり、外部負荷１０には定電流源Ｉ１で設定された所定の駆動電流Ｉｏが流れる。そして、定電流源Ｉ１の一端Ｐ２に生じる電圧が検出電圧Ｖｄｅｔとなる。
【００２０】
制御回路Ｃｏｎｔは、検出電圧Ｖｄｅｔと基準電圧源Ｂ１からの基準電圧Ｖｒｅｆとが入力され、検出電圧Ｖｄｅｔが基準電圧Ｖｒｅｆに等しくなるように、スイッチＱ１をスイッチング制御するためのスイッチング信号を発生する。ここでは、基準電圧Ｖｒｅｆと検出電圧Ｖｄｅｔとの差を増幅して出力するエラーアンプＥａｍｐと、このエラーアンプＥａｍｐの出力に基づいてＰＷＭ信号を形成してスイッチング信号として出力するパルス幅変調制御回路Ｐｗｍを含んで構成されている。
【００２１】
外部負荷１０は、端子Ｐ１と端子Ｐ２との間に接続される。本発明は、負荷駆動装置の外部負荷をも含めて、携帯機器などの電子機器として構成することができる。この場合には、端子Ｐ１、Ｐ２は省略されることもある。
【００２２】
外部負荷１０としては、発光ダイオードＬＥＤ１〜ＬＥＤ３が用いられる。この発光ダイオードＬＥＤは、例えば白色発光ダイオードであり、ＬＣＤ（液晶表示パネル）やキーのバックライト用等に用いられる。したがって、図１では３個の直列の例を示しているが、異なった数の直列接続、並列接続、或いは直並列接続など、その必要とされる発光エリアや発光量などに応じて、その組み合わせは種々の形態がある。
【００２３】
この発光ダイオードＬＥＤの電流ー電圧特性が図２に示されている。この特性は、白色発光ダイオードＬＥＤの電流Ｉｆ−電圧Ｖｆ特性の例である。この図２は、横軸が対数表示の電流Ｉｆであり、縦軸が電圧Ｖｆである。この発光ダイオードＬＥＤは、電流Ｉｆが２０ｍＡ（図中Ａ点）〜１．５ｍＡ（図中Ｂ点）の範囲で発光する。この電流Ｉｆを変化させることにより、その電流Ｉｆの大きさに応じて発光ダイオードＬＥＤからの発光量が変化する。
【００２４】
電流Ｉｆを２０ｍＡで使用すると、同図中のＡ点で示されるように、順方向電圧Ｖｆが電圧３．４Ｖで動作する。しかし、各々の発光ダイオードＬＥＤの特性は一律でなく、同じ電流２０ｍＡでもその順方向電圧Ｖｆは、例えば３．４Ｖ〜４．０Ｖ程度の範囲でばらつく。このように、一般に白色発光ダイオードＬＥＤは順方向電圧Ｖｆが他色の発光ダイオードＬＥＤよりも高く、これを３個直列に接続して使用するには、出力電圧Ｖｏ１は１２．０Ｖ以上必要になる。
【００２５】
図３は、定電流源Ｉ１の回路構成の例を示す図である。この図３において、電源電圧Ｖｃｃとグランド間に定電流回路Ｉ１１とＮ型ＭＯＳトランジスタ（以下、Ｎ型トランジスタ）Ｑ２とが直列に接続されている。このＮ型トランジスタＱ２のドレインとゲートが直接接続されている。また、駆動電流Ｉｏを流すためにＮ型トランジスタＱ２よりも駆動能力の高いＮ型トランジスタＱ３が設けられている。入力側トランジスタであるＮ型トランジスタＱ２のゲートが、出力側トランジスタであるＮ型トランジスタＱ３のゲートに接続されて、カレントミラー回路を構成している。
【００２６】
この図３で、定電流回路Ｉ１１の電流を調整することにより、Ｎ型トランジスタＱ３を流れる駆動電流Ｉｏの大きさを所望の値に設定する。
【００２７】
再び、図１に戻って説明する。定電流源Ｉ１は、それに使用しているトランジスタ（図３のＮ型トランジスタＱ３）の飽和電圧（約０．３Ｖ）以上の電圧があれば定電流動作できる。その飽和電圧（約０．３Ｖ）を越える部分の電圧は、定電流源Ｉ１の内部での不要な損失分（即ち、損失は、電圧×電流）になる。定電流源Ｉ１の降下電圧Ｖｄｅｔが基準電圧Ｖｒｅｆになるように、電源回路１００の出力電圧Ｖｏ１が制御される。したがって、基準電圧Ｖｒｅｆは、定電流源Ｉ１に使用しているトランジスタの飽和電圧（約０．３Ｖ）に若干の余裕分の電圧を見込んだ値に設定される。
【００２８】
このように構成された負荷駆動装置の動作を、駆動電流Ｉｏと出力電圧Ｖｏ１との特性を示す図４をも参照して説明する。まず、負荷１０である発光ダイオードに流す駆動電流Ｉｏが定電流回路Ｉ１１に設定される。スイッチング電源回路１００は、検出電圧Ｖｄｅｔが基準電圧Ｖｒｅｆに等しくなるように、スイッチＱ１のオンオフスイッチング制御が開始される。これにより、出力電圧Ｖｏ１が徐々に上昇する。
【００２９】
その結果、検出電圧Ｖｄｅｔと基準電圧Ｖｒｅｆとが等しくなり、駆動電流Ｉｏが負荷１０である発光ダイオードＬＥＤ１〜ＬＥＤ３に流れる。これにより、発光ダイオードは、所定の発光量で発光する。
【００３０】
このとき、発光ダイオードＬＥＤ１〜ＬＥＤ３の順方向高電圧Ｖｆの特性がばらついていたとしても、出力電圧Ｖｏ１がそのばらつきに応じて所定値からばらつくだけであり、発光ダイオードＬＥＤ１〜ＬＥＤ３からの発光の制御には格別の影響はない。定電流源Ｉ１１の降下電圧、即ち検出電圧Ｖｄｅｔは一定である。したがって、出力電圧Ｖｏ１は、一定の検出電圧Ｖｄｅｔに、その時点での駆動電流Ｉｏに応じた発光ダイオードＬＥＤ１〜ＬＥＤ３の降下電圧Ｖｌｅｄ（＝３×Ｖｆ）を加えた大きさになる。
【００３１】
次に、発光ダイオードＬＥＤ１〜ＬＥＤ３からの発光量を変更する場合には、駆動電流Ｉｏの大きさを変更する。例えば、駆動電流Ｉｏを大きくすると、それに応じて発光ダイオードＬＥＤ１〜ＬＥＤ３からの発光量が多くなる。これとともに、発光ダイオードＬＥＤ１〜ＬＥＤ３の降下電圧Ｖｌｅｄも、図２の特性に依って大きくなる。なお、図４の出力電圧Ｖｏ１の傾きは、図２のＩｆ−Ｖｆ特性に従う。
【００３２】
したがって、駆動電流Ｉｏの増加に応じて発光ダイオードＬＥＤ１〜ＬＥＤ３の降下電圧Ｖｌｅｄが大きくなるから、出力電圧Ｖｏ１は図４のような特性で大きくなる。しかし、検出電圧Ｖｄｅｔは一定の値を維持するから、発光量を大きくするために駆動電流を大きくしても、定電流源Ｉ１での損失は増加しない。したがって、負荷駆動装置の効率は高く維持される。
【００３３】
図５は、本発明の第２の実施の形態に係る負荷駆動装置の構成を示す図である。図５においては、負荷１０に加えて、他の負荷２０を付加しており、また、負荷が増えたことに伴って、負荷２０に対応して定電流源Ｉ２０を設けている。なお、付加する他の負荷は２以上でも良い。
【００３４】
図５では、負荷１０に直列に定電流源Ｉ１０が設けられ、その直列回路に駆動電流Ｉｏ１が流れる。定電流源Ｉ１０の降下電圧が第１検出電圧Ｖｄｅｔ１になる。同様に、負荷２０に直列に定電流源Ｉ２０が設けられ、その直列回路に駆動電流Ｉｏ２が流れる。定電流源Ｉ２０の降下電圧が第２検出電圧Ｖｄｅｔ２になる。Ｐ１１、Ｐ１２、Ｐ２１、Ｐ２２は、負荷接続用の端子である。
【００３５】
また、制御回路ＣｏｎｔのエラーアンプＥａｍｐは、２つの非反転入力端子（＋）と１つの反転入力端子（−）を持っている。２つの非反転入力端子（＋）には、第１検出電圧Ｖｄｅｔ１及び第２検出電圧Ｖｄｅｔ２がそれぞれ入力され、反転入力端子（−）には基準電圧Ｖｒｅｆが入力される。このエラーアンプＥａｍｐでは、２つの非反転入力端子（＋）に入力される第１検出電圧Ｖｄｅｔ１と第２検出電圧Ｖｄｅｔ２のうちの低い方の電圧が選択されて、基準電圧Ｖｒｅｆと比較される。その他の構成は、図１の第１の実施の形態におけるものと同様である。
【００３６】
この図５の負荷駆動回路では、複数の負荷１０、２０の駆動電流Ｉｏ１、Ｉｏ２を個別に調整することができる。そして、定電流源Ｉ１０、Ｉ２０の降下電圧Ｖｄｅｔ１、Ｖｄｅｔ２のうちの低い方の電圧が自動的に選択されて、電源回路１００のスイッチング制御が行われる。
【００３７】
複数の負荷１０、２０の駆動電流Ｉｏ１、Ｉｏ２を流す定電流源Ｉ１０、Ｉ２０の定電流動作は、確保される。したがって、複数負荷に対しても、第１の実施の形態におけると同様の効果を得ることができる。
【００３８】
【発明の効果】
本発明によれば、出力電圧を出力回路（直流ー直流変換型電源回路）を用いて電源電圧から変換して得るとともに、流れる電流で動作点が決まる負荷、例、発光ダイオード群に直列に電流値が調整できる定電流源を接続するから、負荷側で要求される電流を、安定して負荷に流すことができる。
【００３９】
また、定電流源の降下電圧が、その定電流源が安定して動作できる電圧値に設定された基準電圧に等しくなるように、直流ー直流変換型電源回路の出力電圧が制御される。したがって、負荷である発光ダイオード群に特性のばらつきがあっても予定の発光量のために必要な電流が流れるように、直流ー直流変換型電源回路の出力電圧は、自動調整される。
【００４０】
また、定電流源の降下電圧は、設定した電流値が維持できるように基準電圧に自動的に制御されるから、負荷である発光ダイオード群に流れる電流が大きくなった場合でも、抵抗での電圧検出におけるような、損失の増加はない。したがって、負荷電流の増加に伴う損失が実質的に増加しないから、広い負荷電流の範囲において高効率で負荷を駆動することができる。
【００４１】
また、直流ー直流変換型電源回路は、コイルへの通電をスイッチングして電源電圧を出力電圧に変換するスイッチング電源回路であるから、変換効率が良く、また、必要な高電圧を出力することができる。
【００４２】
また、負荷である発光ダイオード群毎に、対応して可変電流型定電流源が設けられ、かつ、それらの定電流源の降下電圧の低い方の電圧にしたがって直流ー直流変換型電源回路が制御されるから、負荷である発光ダイオード群のそれぞれに所定の定電流を安定して流すことができる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係る負荷駆動装置の構成を示す図
【図２】発光ダイオードＬＥＤの電流ー電圧特性を示す図
【図３】定電流源Ｉ１の回路構成の例を示す図
【図４】駆動電流Ｉｏと出力電圧Ｖｏ１との特性を示す図
【図５】本発明の第２の実施の形態に係る負荷駆動装置の構成を示す図
【符号の説明】
１００ 電源回路
１０、２０ 負荷
ＬＥＤ１〜ＬＥＤ３ 発光ダイオード
Ｌ１ コイル
Ｃ１ 平滑用コンデンサ
Ｄ１ ダイオード
Ｑ１ スイッチ
Ｃｏｎｔ 制御回路
Ｂ１ 基準電圧源
Ｉ１、Ｉ１０、Ｉ２０ 定電流源
Ｉ１１ 定電流回路
Ｑ２、Ｑ３ Ｎ型ＭＯＳトランジスタ
Ｖｃｃ 入力電源電圧
Ｖｏ１ 出力電圧
Ｉｏ、Ｉｏ１、Ｉｏ２ 駆動電流
Ｖｌｅｄ、Ｖｌｅｄ１、Ｖｌｅｄ２ 発光ダイオード降下電圧
Ｖｄｅｔ、Ｖｄｅｔ１、Ｖｄｅｔ２ 検出電圧
Ｖｒｅｆ 基準電圧[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a load driving device that drives a load with an output voltage converted from a power supply voltage using a DC-DC conversion type power supply circuit, and a portable device using the load driving device.
[0002]
[Prior art]
Conventionally, a load driving device that drives a load such as an LED by using a DC-DC conversion type power supply circuit that generates a voltage different from the power supply voltage has been widely used. In order to generate a predetermined output voltage and output current from a power supply circuit for driving the load driving device, the load driving device detects the input voltage or the load voltage applied to the load or the load current flowing through the load, It returns to the control circuit of a circuit (refer patent document 1).
[0003]
In this conventional driving device, the control voltage is detected by dividing the input voltage or the load voltage with a high resistance. The load current is detected by a voltage drop across a resistor connected in series with the load. The control voltage and load current are compared with a reference value to control the output voltage and output current from the power supply circuit to predetermined values.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-313423
[Problems to be solved by the invention]
In a portable electronic device (mobile device) such as a mobile phone, the load current for driving the load is increased or decreased within a certain range depending on the usage on the electronic device side where the load is provided. Sometimes. For example, when the load is a light emitting element (such as a light emitting diode), the light emission amount may be adjusted to an arbitrary value.
[0006]
In such a case, if a load current detection resistor is inserted in series with the load, the loss due to the current detection resistor increases as the load current increases. Therefore, there has been a problem that the efficiency of the electronic apparatus as a whole including the power supply circuit and the load is reduced when the current is large (that is, when the load is heavy).
[0007]
Therefore, the present invention uses an output circuit such as a DC-DC conversion type power supply circuit that converts the power supply voltage and supplies it to the load, and changes the load current for driving the load to a predetermined range and increases the load current. It is an object of the present invention to provide a load driving device capable of efficiently driving a load while avoiding an increase in loss accompanying the above, and a portable device using the load driving device.
[0008]
[Means for Solving the Problems]
The load driving device according to claim 1 includes an output circuit that converts a power supply voltage and supplies the load as a predetermined output voltage to the load, and a constant current source that is connected in series to the load and supplies an adjustable constant current, The output circuit controls the predetermined output voltage so that a voltage at a connection point between the load and the constant current source becomes a constant voltage.
[0009]
The load driving device according to claim 2 is the load driving device according to claim 1, wherein the constant current source includes a current variable type constant current circuit and a current mirror input side transistor connected in series with the constant current circuit. And a current mirror output side transistor to which the same control input as that of the current mirror input side transistor is applied, to form a current mirror circuit, and the adjustable constant current is supplied to the current mirror output side transistor. It is washed away.
[0010]
The load driving device according to claim 3 is the load driving device according to claim 2, wherein the external load is a light emitting diode group including at least one light emitting diode.
[0011]
According to a fourth aspect of the present invention, there is provided the load driving device according to the second aspect, wherein the constant voltage is higher than a saturation voltage of the output transistor for the current mirror.
[0012]
The load driving device according to claim 5 is the load driving device according to any of claims 1 to 4, wherein the output circuit includes a coil, a switch for switching energization to the coil, and a connection point between the coil and the switch. The switching power supply circuit includes a rectifying element provided between the output terminal and the output terminal.
[0013]
The load driving device according to claim 6 is the load driving device according to claim 5, wherein the switching power supply circuit further includes a smoothing circuit connected to an output voltage point side of the rectifying element, the load, and the constant current source. And a control circuit that performs on / off switching of the switch so that a voltage at a connection point between the switch and the switch becomes equal to a reference voltage.
[0014]
The load driving device according to claim 7 is the load driving device according to claim 1, wherein the load and the constant current source are plural, and the plural constant current sources are connected in series to the plural loads, respectively. The predetermined output voltage is controlled so that an adjustable constant current flows and the lowest voltage among the voltages at the connection points of the plurality of loads and the plurality of constant current sources becomes a constant voltage. Features.
[0015]
The load drive device according to claim 8 uses the load drive device according to claims 1 to 7.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a load driving device of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a load driving device according to a first embodiment of the present invention.
[0017]
In FIG. 1, a switching power supply circuit 100 as an output circuit is a boost type power supply circuit that boosts an input power supply voltage Vcc and outputs a boosted output voltage Vo1.
[0018]
A coil L1 and a switch Q1, which is an N-type MOS transistor, are connected in series between the power supply voltage Vcc and the ground. From the series connection point A, the voltage at the series connection point A is rectified and smoothed by the rectifying diode D1 and the smoothing capacitor C1, and output as the output voltage Vo1. Note that the voltage is a potential with respect to the ground unless otherwise specified.
[0019]
The external load 10 and the constant current source I1 are connected in series between the output voltage Vo1 point (P1) and the ground. The external load 10 is a load determined by a current flowing through a point to be operated, and a predetermined drive current Io set by the constant current source I1 flows through the external load 10. The voltage generated at one end P2 of the constant current source I1 becomes the detection voltage Vdet.
[0020]
The control circuit Cont receives the detection voltage Vdet and the reference voltage Vref from the reference voltage source B1, and generates a switching signal for switching the switch Q1 so that the detection voltage Vdet becomes equal to the reference voltage Vref. Here, an error amplifier Eamp that amplifies and outputs the difference between the reference voltage Vref and the detection voltage Vdet, and a pulse width modulation control circuit Pwm that forms a PWM signal based on the output of the error amplifier Eamp and outputs it as a switching signal. It is comprised including.
[0021]
The external load 10 is connected between the terminal P1 and the terminal P2. The present invention can be configured as an electronic device such as a portable device including an external load of a load driving device. In this case, the terminals P1 and P2 may be omitted.
[0022]
As the external load 10, light emitting diodes LED1 to LED3 are used. The light-emitting diode LED is, for example, a white light-emitting diode, and is used for LCD (liquid crystal display panel) and key backlight. Therefore, FIG. 1 shows an example of three series, but different combinations such as series connection, parallel connection, or series-parallel connection, depending on the required light emitting area and light emission amount, etc. There are various forms.
[0023]
The current-voltage characteristics of the light emitting diode LED are shown in FIG. This characteristic is an example of the current If-voltage Vf characteristic of the white light emitting diode LED. In FIG. 2, the horizontal axis represents the logarithmic display current If, and the vertical axis represents the voltage Vf. The light emitting diode LED emits light in a current If range of 20 mA (point A in the figure) to 1.5 mA (point B in the figure). By changing the current If, the amount of light emitted from the light emitting diode LED changes according to the magnitude of the current If.
[0024]
When the current If is used at 20 mA, the forward voltage Vf operates at a voltage of 3.4 V, as indicated by point A in FIG. However, the characteristics of each light emitting diode LED are not uniform, and the forward voltage Vf varies within a range of, for example, about 3.4 V to 4.0 V even with the same current of 20 mA. Thus, in general, the white light emitting diode LED has a higher forward voltage Vf than the light emitting diode LEDs of other colors, and the output voltage Vo1 is required to be 12.0 V or more in order to use three of them in series. .
[0025]
FIG. 3 is a diagram illustrating an example of a circuit configuration of the constant current source I1. In FIG. 3, a constant current circuit I11 and an N-type MOS transistor (hereinafter referred to as an N-type transistor) Q2 are connected in series between a power supply voltage Vcc and the ground. The drain and gate of this N-type transistor Q2 are directly connected. In addition, an N-type transistor Q3 having a driving capability higher than that of the N-type transistor Q2 is provided to allow the drive current Io to flow. The gate of the N-type transistor Q2, which is an input side transistor, is connected to the gate of the N-type transistor Q3, which is an output side transistor, to form a current mirror circuit.
[0026]
In FIG. 3, the magnitude of the drive current Io flowing through the N-type transistor Q3 is set to a desired value by adjusting the current of the constant current circuit I11.
[0027]
Again, returning to FIG. The constant current source I1 can operate at a constant current if there is a voltage equal to or higher than the saturation voltage (about 0.3 V) of the transistor (N-type transistor Q3 in FIG. 3) used therein. The voltage in the portion exceeding the saturation voltage (about 0.3 V) becomes an unnecessary loss in the constant current source I1 (that is, the loss is voltage × current). The output voltage Vo1 of the power supply circuit 100 is controlled so that the voltage drop Vdet of the constant current source I1 becomes the reference voltage Vref. Accordingly, the reference voltage Vref is set to a value that allows a slight margin of voltage to the saturation voltage (about 0.3 V) of the transistor used for the constant current source I1.
[0028]
The operation of the thus configured load driving device will be described with reference to FIG. 4 showing the characteristics of the driving current Io and the output voltage Vo1. First, the drive current Io that flows through the light emitting diode that is the load 10 is set in the constant current circuit I11. In the switching power supply circuit 100, the on / off switching control of the switch Q1 is started so that the detection voltage Vdet becomes equal to the reference voltage Vref. As a result, the output voltage Vo1 gradually increases.
[0029]
As a result, the detection voltage Vdet and the reference voltage Vref become equal, and the drive current Io flows through the light emitting diodes LED1 to LED3 that are the load 10. Thereby, the light emitting diode emits light with a predetermined light emission amount.
[0030]
At this time, even if the characteristics of the forward high voltage Vf of the light emitting diodes LED1 to LED3 vary, the output voltage Vo1 only varies from a predetermined value according to the variation, and the light emission from the light emitting diodes LED1 to LED3 is controlled. Has no special impact. The voltage drop of the constant current source I11, that is, the detection voltage Vdet is constant. Therefore, the output voltage Vo1 has a magnitude obtained by adding the drop voltage Vled (= 3 × Vf) of the light emitting diodes LED1 to LED3 corresponding to the driving current Io at that time to the constant detection voltage Vdet.
[0031]
Next, when the light emission amount from the light emitting diodes LED1 to LED3 is changed, the magnitude of the drive current Io is changed. For example, when the drive current Io is increased, the amount of light emitted from the light emitting diodes LED1 to LED3 increases accordingly. Along with this, the drop voltage Vled of the light emitting diodes LED1 to LED3 also increases depending on the characteristics of FIG. The slope of the output voltage Vo1 in FIG. 4 follows the If-Vf characteristic in FIG.
[0032]
Accordingly, the drop voltage Vled of the light emitting diodes LED1 to LED3 increases as the drive current Io increases, and the output voltage Vo1 increases with the characteristics shown in FIG. However, since the detection voltage Vdet maintains a constant value, the loss in the constant current source I1 does not increase even if the drive current is increased to increase the amount of light emission. Therefore, the efficiency of the load driving device is maintained high.
[0033]
FIG. 5 is a diagram showing a configuration of a load driving device according to the second embodiment of the present invention. In FIG. 5, another load 20 is added in addition to the load 10, and a constant current source I20 is provided corresponding to the load 20 as the load increases. The other load to be added may be two or more.
[0034]
In FIG. 5, a constant current source I10 is provided in series with a load 10, and a drive current Io1 flows through the series circuit. The voltage drop of the constant current source I10 becomes the first detection voltage Vdet1. Similarly, a constant current source I20 is provided in series with the load 20, and a drive current Io2 flows through the series circuit. The voltage drop of the constant current source I20 becomes the second detection voltage Vdet2. P11, P12, P21, and P22 are terminals for load connection.
[0035]
The error amplifier Eamp of the control circuit Cont has two non-inverting input terminals (+) and one inverting input terminal (−). The first detection voltage Vdet1 and the second detection voltage Vdet2 are input to the two non-inverting input terminals (+), respectively, and the reference voltage Vref is input to the inverting input terminal (−). In the error amplifier Eamp, the lower one of the first detection voltage Vdet1 and the second detection voltage Vdet2 input to the two non-inverting input terminals (+) is selected and compared with the reference voltage Vref. Other configurations are the same as those in the first embodiment of FIG.
[0036]
In the load drive circuit of FIG. 5, the drive currents Io1 and Io2 of the plurality of loads 10 and 20 can be individually adjusted. Then, the lower one of the drop voltages Vdet1 and Vdet2 of the constant current sources I10 and I20 is automatically selected, and the switching control of the power supply circuit 100 is performed.
[0037]
The constant current operation of the constant current sources I10 and I20 for flowing the drive currents Io1 and Io2 of the plurality of loads 10 and 20 is ensured. Therefore, the same effect as in the first embodiment can be obtained for a plurality of loads.
[0038]
【The invention's effect】
According to the present invention, an output voltage is obtained by converting an output voltage from a power supply voltage using an output circuit (DC-DC conversion type power supply circuit), and an operating point is determined by a flowing current. Since a constant current source whose value can be adjusted is connected, the current required on the load side can be stably supplied to the load.
[0039]
Further, the output voltage of the DC-DC conversion type power supply circuit is controlled so that the voltage drop of the constant current source becomes equal to a reference voltage set to a voltage value at which the constant current source can stably operate. Accordingly, the output voltage of the DC-DC conversion type power supply circuit is automatically adjusted so that a current necessary for a predetermined light emission amount flows even if there is a variation in characteristics among the light emitting diode groups as the load.
[0040]
In addition, since the voltage drop of the constant current source is automatically controlled to the reference voltage so that the set current value can be maintained, even if the current flowing through the light emitting diode group that is the load becomes large, the voltage across the resistor There is no increase in loss as in detection. Therefore, the loss accompanying the increase in load current does not substantially increase, so that the load can be driven with high efficiency in a wide load current range.
[0041]
In addition, since the DC-DC conversion type power supply circuit is a switching power supply circuit that switches the energization to the coil and converts the power supply voltage to the output voltage, the conversion efficiency is good and the necessary high voltage can be output. it can.
[0042]
Also, a variable current type constant current source is provided for each light emitting diode group that is a load, and the DC-DC conversion type power supply circuit is controlled according to the lower voltage drop of those constant current sources. Therefore, a predetermined constant current can be stably supplied to each of the light emitting diode groups that are loads.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a load driving device according to a first embodiment of the present invention. FIG. 2 is a diagram showing current-voltage characteristics of a light emitting diode LED. FIG. 3 is a circuit configuration of a constant current source I1. FIG. 4 is a diagram showing characteristics of drive current Io and output voltage Vo1. FIG. 5 is a diagram showing a configuration of a load driving device according to a second embodiment of the present invention.
100 Power supply circuit 10, 20 Load LED1 to LED3 Light emitting diode L1 Coil C1 Smoothing capacitor D1 Diode Q1 Switch Cont Control circuit B1 Reference voltage source I1, I10, I20 Constant current source I11 Constant current circuit Q2, Q3 N-type MOS transistor Vcc Input Power supply voltage Vo1 Output voltage Io, Io1, Io2 Drive current Vled, Vled1, Vled2 Light emitting diode drop voltage Vdet, Vdet1, Vdet2 Detection voltage Vref Reference voltage

Claims (8)

電源電圧を変換して所定の出力電圧として負荷に供給する出力回路と、
前記負荷に直列に接続されて調整可能な定電流を流す定電流源とを備え、
前記出力回路は、前記負荷と前記定電流源との接続点の電圧が一定電圧になるように前記所定の出力電圧を制御することを特徴とする負荷駆動装置。An output circuit that converts the power supply voltage and supplies it to the load as a predetermined output voltage;
A constant current source connected in series to the load and supplying an adjustable constant current;
The load driving device, wherein the output circuit controls the predetermined output voltage so that a voltage at a connection point between the load and the constant current source becomes a constant voltage. 前記定電流源は、電流可変型の定電流回路と、この定電流回路と直列に接続されたカレントミラー用入力側トランジスタと、このカレントミラー用入力側トランジスタと同じ制御入力が与えられるカレントミラー用出力側トランジスタとを含んでカレントミラー回路が構成されており、前記カレントミラー用出力側トランジスタに前記調整可能な定電流が流されることを特徴とする、請求項１記載の負荷駆動装置。The constant current source includes a current variable type constant current circuit, a current mirror input side transistor connected in series with the constant current circuit, and a current mirror for which the same control input as the current mirror input transistor is applied. 2. The load driving device according to claim 1, wherein a current mirror circuit is configured including an output side transistor, and the adjustable constant current is supplied to the current mirror output side transistor. 前記外部負荷は、少なくとも１つの発光ダイオードを含む発光ダイオード群であることを特徴とする、請求項２記載の負荷駆動装置。The load driving device according to claim 2, wherein the external load is a light emitting diode group including at least one light emitting diode. 前記一定電圧は、前記カレントミラー用出力側トランジスタの飽和電圧より高い電圧であることを特徴とする、請求項２記載の負荷駆動装置。3. The load driving device according to claim 2, wherein the constant voltage is higher than a saturation voltage of the current mirror output side transistor. 前記出力回路は、コイルと、このコイルへの通電をスイッチングするスイッチと、前記コイルと前記スイッチとの接続点と出力端子との間に設けられた整流素子とを有するスイッチング電源回路であることを特徴とする、請求項１乃至４記載の負荷駆動装置。The output circuit is a switching power supply circuit having a coil, a switch for switching energization to the coil, and a rectifying element provided between a connection point of the coil and the switch and an output terminal. The load driving device according to claim 1, wherein the load driving device is characterized by the following. 前記スイッチング電源回路は、さらに、前記整流素子の出力電圧点側に接続された平滑回路と、前記負荷と前記定電流源との接続点の電圧が基準電圧に等しくなるように前記スイッチのオンオフスイッチングを行う制御回路と、を有することを特徴とする、請求項５記載の負荷駆動装置。The switching power supply circuit further includes on / off switching of the switch so that a voltage at a connection point between the smoothing circuit connected to the output voltage point side of the rectifying element and the load and the constant current source is equal to a reference voltage. The load drive device according to claim 5, further comprising a control circuit that performs the operation. 前記負荷及び前記定電流源が複数であり、前記複数の負荷に前記複数の定電流源がそれぞれ直列に接続されてそれぞれ調整可能な定電流を流すとともに、
前記複数の負荷と前記複数の定電流源との各接続点の電圧のうちの最も低い電圧が一定電圧になるように前記所定の出力電圧を制御することを特徴とする、請求項１記載の負荷駆動装置。The load and the constant current source are a plurality, and the plurality of constant current sources are connected in series to the plurality of loads, respectively, and an adjustable constant current is passed through each,
The said predetermined output voltage is controlled so that the lowest voltage of the voltage of each connection point of these load and said constant current source may become a constant voltage. Load drive device. 請求項１乃至７記載の負荷駆動装置を用いていることを特徴とする携帯機器。A portable device using the load driving device according to claim 1.
JP2003192784A 2003-07-07 2003-07-07 Load drive device and portable device Expired - Lifetime JP3755770B2 (en)

Priority Applications (22)

Application Number Priority Date Filing Date Title
JP2003192784A JP3755770B2 (en) 2003-07-07 2003-07-07 Load drive device and portable device
DE200460008840 DE602004008840T2 (en) 2003-07-07 2004-06-23 A load driving device and portable device using such load driving device
EP20040014726 EP1499165B1 (en) 2003-07-07 2004-06-23 Load driving device and portable apparatus utilizing such driving device
TW093118447A TWI346442B (en) 2003-07-07 2004-06-25 Load driving device and liguid crystal display using such load driving device
TW099113230A TWI340530B (en) 2003-07-07 2004-06-25 Load driving device and liguid crystal display using such load driving device
US10/879,315 US7235954B2 (en) 2003-07-07 2004-06-29 Load driving device and portable apparatus utilizing such driving device
CN2010101454408A CN101789692B (en) 2003-07-07 2004-07-02 Load driving device and liquid crystal apparatus
CN2004100621747A CN1578095B (en) 2003-07-07 2004-07-02 Load driving device and portable apparatus utilizing such driving device
KR1020040052190A KR20050006042A (en) 2003-07-07 2004-07-06 Load driving device and portable equipment
US11/750,894 US7541785B2 (en) 2003-07-07 2007-05-18 Load driving device and portable apparatus utilizing such driving device
US12/428,338 US7944189B2 (en) 2003-07-07 2009-04-22 Load driving device and portable apparatus utilizing such driving device
US12/731,006 US8519680B2 (en) 2003-07-07 2010-03-24 Load driving device, and lighting apparatus and liquid crystal display device using the same
US13/080,498 US8242756B2 (en) 2003-07-07 2011-04-05 Load driving device and portable apparatus utilizing such driving device
US13/952,333 US8836295B2 (en) 2003-07-07 2013-07-26 Load driving device, and lighting apparatus and liquid crystal display device using the same
US14/454,528 US9526138B2 (en) 2003-07-07 2014-08-07 Load driving device, and lighting apparatus and liquid crystal display device using the same
US15/002,275 US9526139B2 (en) 2003-07-07 2016-01-20 Load driving device, and lighting apparatus and liquid crystal display device using the same
US15/348,257 US9960677B2 (en) 2003-07-07 2016-11-10 Load driving device, and lighting apparatus and liquid crystal display device using the same
US15/924,701 US10103625B2 (en) 2003-07-07 2018-03-19 Load driving device, and lighting apparatus and liquid crystal display device using the same
US16/127,571 US10396659B2 (en) 2003-07-07 2018-09-11 Load driving device, and lighting apparatus and liquid crystal display device using the same
US16/508,423 US10734896B2 (en) 2003-07-07 2019-07-11 Load driving device, and lighting apparatus and liquid crystal display device using the same
US16/909,714 US11487310B2 (en) 2003-07-07 2020-06-23 Load driving device, and lighting apparatus and liquid crystal display device using the same
US17/958,840 US20230023130A1 (en) 2003-07-07 2022-10-03 Load driving device, and lighting apparatus and liquid crystal display device using the same

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