JP2004229437A - Constant voltage output control method and constant voltage output control device for switching power supply circuit - Google Patents

Abstract

から求めた設定電流Ｉｐ_ｓｅｔに、一次巻線（２ａ）に流れる電流Ｉｐが達した際に、発振用スイッチ素子（３）のオン制御を停止する。その周期での出力電圧は、設定したＶ_{２ｂｓｅｔ}となり、これを繰り返すことにより定電圧出力制御ができる。
【選択図】 図１Provided is a constant voltage output control method and apparatus for a switching power supply circuit capable of controlling an output voltage with a constant voltage with high accuracy even if there are variations in circuit elements and integrated circuits to be used.
The output voltage of a secondary output winding (2b) to be controlled at a constant voltage is V _2bset , the number of turns of a primary winding (2a) is Np, the number of turns of a secondary output winding (2b) is Ns, and When the inductance of the next output winding (2b) is Ls and the output time during which the output appears in the rectifying and smoothing circuits (4, 13) within the oscillation period (T) is T2,
(Equation 1)

When the current Ip flowing through the primary winding (2a) reaches the set current Ip _set determined from the above, the ON control of the oscillation switch element (3) is stopped. The output voltage in that cycle becomes the set _V2bset , and by repeating this, the constant voltage output control can be performed.
[Selection diagram] Fig. 1

Description

から求めた設定電流Ｉｐ_ｓｅｔに、一次巻線に流れる電流Ｉｐが達した際に、発振用スイッチ素子のオン制御を停止し、オン時間を調整することを特徴とする。
【００３６】
請求項２のスイッチング電源回路の定電圧出力制御方法は、一次巻線と二次出力巻線を有するトランスと、一次巻線を励磁する直流電源に、一次巻線と直列に接続された発振用スイッチ素子と、発振用スイッチ素子をオンオフ制御するスイッチ制御回路と、二次出力巻線の出力を整流平滑化する整流平滑化回路とを備えたスイッチング電源回路の発振用スイッチ素子のオン時間を変化させ、整流平滑化回路の出力電圧Ｖ_２ｏを定電圧制御する定電圧出力制御方法であって、
定電圧制御しようとする整流平滑化回路の出力電圧をＶ_{２ｏｓｅｔ}、一次巻線の巻数をＮｐ、二次出力巻線の巻数をＮｓ、二次出力巻線のインダクタンスをＬｓ、発振周期内で整流平滑化回路に出力が表れる出力時間をＴ２、整流平滑化回路のダイオードの順方向電圧降下分の出力電流に対する比例定数をｋとしたときに、
【数７】

から求めた設定電流Ｉｐ_ｓｅｔ´に、一次巻線に流れる電流Ｉｐが達した際に、発振用スイッチ素子のオン制御を停止し、オン時間を調整することを特徴とする。
【００３７】
請求項３のスイッチング電源回路の定電圧出力制御方法は、発振周期内で整流平滑化回路に出力が表れる出力時間Ｔ２を、一次巻線にフライバック電圧が発生してから最初の極性反転時までの時間から検出することを特徴とする。
【００３８】
請求項４のスイッチング電源回路の定電圧出力制御方法は、発振周期内で整流平滑化回路に出力が表れる出力時間Ｔ２を、トランスの副巻き線にフライバック電圧が発生してから最初の極性反転時までの時間から検出する特徴とする。
【００３９】
請求項５のスイッチング電源回路の定電圧出力制御装置は、一次巻線と二次出力巻線を有するトランスと、一次巻線を励磁する直流電源に、一次巻線と直列に接続された発振用スイッチ素子と、発振用スイッチ素子をオンオフ制御するスイッチ制御回路と、二次出力巻線の出力を整流平滑化する整流平滑化回路とを備え、発振用スイッチ素子のオン時間を変化させ、二次出力巻線に表れる出力電圧（Ｖ_２ｂ）を定電圧制御するスイッチング電源回路の定電圧出力制御装置であって、
一次巻線に流れる電流Ｉｐを検出する一次側電流検出部と、発振周期内で整流平滑化回路に出力が表れる出力時間Ｔ２を検出する出力時間検出部と、
定電圧制御しようとする二次出力巻線の出力電圧をＶ_{２ｂｓｅｔ}、一次巻線の巻数をＮｐ、二次出力巻線の巻数をＮｓ、二次出力巻線のインダクタンスをＬｓとし、
出力時間検出部で検出した出力時間Ｔ２と、
【数８】

とから設定電流Ｉｐ_ｓｅｔを求める設定値算出回路と、
一次巻線に流れる電流Ｉｐと設定電流Ｉｐ_ｓｅｔを比較する比較回路とを備え、
スイッチ制御回路は、電流Ｉｐが設定電流Ｉｐ_ｓｅｔに達した際に、発振用スイッチ素子のオン制御を停止し、オン時間を調整することを特徴とする。
【００４０】
請求項６のスイッチング電源回路の定電圧出力制御装置は、一次巻線と二次出力巻線を有するトランスと、一次巻線を励磁する直流電源に、一次巻線と直列に接続された発振用スイッチ素子と、発振用スイッチ素子をオンオフ制御するスイッチ制御回路と、二次出力巻線の出力を整流平滑化する整流平滑化回路とを備え、発振用スイッチ素子のオン時間を変化させ、整流平滑化回路の出力電圧（Ｖ_２ｏ）を定電圧制御するスイッチング電源回路の定電圧出力制御装置であって、
一次巻線に流れる電流Ｉｐを検出する一次側電流検出部と、発振周期内で整流平滑化回路に出力が表れる出力時間Ｔ２を検出する出力時間検出部と、
定電圧制御しようとする整流平滑化回路の出力電圧をＶ_{２ｏｓｅｔ}、一次巻線の巻数をＮｐ、二次出力巻線の巻数をＮｓ、二次出力巻線のインダクタンスをＬｓ、整流平滑化回路のダイオードの順方向電圧降下分の出力電流に対する比例定数をｋとし、
出力時間検出部で検出した出力時間Ｔ２と、
【数９】

とから設定電流Ｉｐ_ｓｅｔ´を求める設定値算出回路と、
一次巻線に流れる電流Ｉｐと設定電流Ｉｐ_ｓｅｔ´を比較する比較回路とを備え、
スイッチ制御回路は、電流Ｉｐが設定電流Ｉｐ_ｓｅｔ´に達した際に、発振用スイッチ素子のオン制御を停止し、オン時間を調整することを特徴とする。
【００４１】
請求項７のスイッチング電源回路の定電圧出力制御装置は、一次巻線の電圧Ｖ_２ａを監視し、フライバック電圧が発生してから最初の極性反転時までの時間を検出する一次巻線電圧監視回路を備え、一次巻線にフライバック電圧が発生してから最初の極性反転時までの時間を、出力時間Ｔ２とすることを特徴とする。
【００４２】
請求項８のスイッチング電源回路の定電圧出力制御装置は、トランスの一次側に更に設けられた副巻き線と、副巻き線の電圧Ｖ_２ｃを監視し、フライバック電圧が発生してから最初の極性反転時までの時間を検出する副巻き線電圧監視回路を備え、副巻き線にフライバック電圧が発生してから最初の極性反転時までの時間を、出力時間Ｔ２とすることを特徴とする。
【００４３】
請求項９のスイッチング電源回路の定電圧出力制御装置は、一次側電流検出部が設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´に達する一次巻線電流Ｉｐを検出した後、発振用スイッチ素子がオン制御を停止するまでの時間差をδｔ、直流電源の電源電圧をＶｃｃ、一次巻線のインダクタンスをＬｐとし、
【数１０】

から求めたＩｐ´を、設定電流Ｉｐｓ_ｅｔ若しくはＩｐ_ｓｅｔ´と比較する電流Ｉｐとすることを特徴とする、
請求項１０のスイッチング電源回路の定電圧出力制御装置は、一次側電流検出部は、一次巻線と直列に抵抗値ｒ_ｉｐのＩｐ検出抵抗を接続し、Ｉｐ検出抵抗による電圧降下Ｖ_ｉｐから電流Ｉｐを検出し、比較回路は、電圧降下Ｖ_ｉｐと、設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´に抵抗値ｒ_ｉｐを乗じて、設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´を表す設定電位Ｖ_ｉｓｅｔを比較し、電流Ｉｐと設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´を比較することを特徴とする。
【００４４】
請求項１と請求項５の発明では、発振周期Ｔ内での整流平滑化回路に出力が表れる出力時間Ｔ２を検出し、（１）式に代入すれば、（１）式から二次出力巻線の出力電圧Ｖ_{２ｂｓｅｔ}を定電圧とする設定電流Ｉｐ_ｓｅｔが得られる。
【００４５】
設定電流Ｉｐ_ｓｅｔに一次巻線に流れる電流Ｉｐが達した際に、発振用スイッチ素子のオン制御を停止しオン時間Ｔ１を調整すると、その周期での電流Ｉｐは設定電流Ｉｐ_ｓｅｔに等しく、二次出力巻線の出力電圧はＶ_{２ｂｓｅｔ}となり、設定した出力電圧とすることができる。
【００４６】
各回路素子の回路定数にばらつきがあっても、出力時間Ｔ２が変化するだけであり、変化する出力時間Ｔ２を求めてから定電圧制御する為の設定電流Ｉｐ_ｓｅｔを得る定電圧制御には影響しない。
【００４７】
また、（１）式の各回路定数を求めておけば、出力電圧Ｖ_{２ｂｓｅｔ}を数値変更するだけで、同一構成のスイッチング電源回路で異なる出力電圧の定電圧制御ができる。
【００４８】
請求項２と請求項６の発明では、発振周期Ｔ内の整流平滑化回路に出力が表れる出力時間Ｔ２を検出し、（２）式に代入すれば、（２）式から整流平滑化回路の出力電圧Ｖ_{２ｏｓｅｔ}を定電圧とする設定電流Ｉｐ_ｓｅｔ´が得られる。
【００４９】
設定電流Ｉｐ_ｓｅｔ´に一次巻線に流れる電流Ｉｐが達した際に、発振用スイッチ素子のオン制御を停止しオン時間Ｔ１を調整すると、その周期での電流Ｉｐは設定電流Ｉｐ_ｓｅｔ´に等しく、ダイオード降下分を考慮した整流平滑化回路の出力電圧はＶ_{２ｏｓｅｔ}となり、精度よく設定した出力電圧とすることができる。
【００５０】
各回路素子の回路定数にばらつきがあっても、出力時間Ｔ２が変化するだけで、変化する出力時間Ｔ２を求めてから定電圧制御する為の設定電流Ｉｐ_ｓｅｔ´を得る定電圧制御には影響しない。
【００５１】
また、（２）式の各回路定数を求めておけば、出力電圧Ｖ_{２ｏｓｅｔ}を数値変更するだけで、同一構成のスイッチング電源回路で異なる出力電圧の定電圧制御ができる。
【００５２】
請求項３と請求項７の発明では、整流平滑化回路に出力が表れる時間Ｔ２は、トランスに蓄積されるエネルギーの放出期間であり、発振用スイッチ素子がターンオフしてから一次巻線に発生するフライバック電圧が減少し固有振動を開始する為にその極性が逆転するまでの時間に等しいので、整流平滑化回路の出力を監視することなく、一次巻線の電位を監視することにより、トランスの一次側から出力時間Ｔ２を検出できる。
【００５３】
従って、二次側の検出結果を一次側へ伝達するための伝達素子を設ける必要がなく、一次側の回路のみで定電圧制御が可能となる。
【００５４】
請求項４と請求項８の発明では、整流平滑化回路に出力が表れる時間Ｔ２は、副巻き線にフライバック電圧が発生してからその極性が逆転するまでの時間に等しく、整流平滑化回路の出力を監視することなく、トランスの一次側の副巻き線の電位を監視することにより、トランスの一次側から出力時間Ｔ２を検出できる。
【００５５】
従って、二次側の検出結果を一次側へ伝達するための伝達素子を設ける必要がなく、一次側の回路のみで定電圧制御が可能となる。
【００５６】
請求項９の発明では、ターンオンした後一次巻線電流Ｉｐは、近似する電源電圧Ｖｃｃ÷Ｌｐに比例して上昇するので、（３）式のδｔ×Ｖｃｃ÷Ｌｐは、一次側電流検出部と発振用スイッチ素子の動作間に遅れδｔによる電流Ｉｐの増加分を表す。
【００５７】
従って、発振用スイッチ素子（３）をターンオフした際の一次巻線電流Ｉｐは、設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´に略等しく、回路素子の遅れがあっても、精度よく定電圧制御ができる。
【００５８】
請求項１０の発明では、一次巻線電流Ｉｐと設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´を、電圧である電圧降下Ｖ_ｉｐと設定電位Ｖ_ｉｓｅｔで表すので、演算処理することなく、コンパレータを用いた比較回路で容易に比較することができる。
【００５９】
【発明の実施の形態】
以下、本発明の一実施の形態について図面を参照して詳細に説明する。これらの図において、図６で示す従来のスイッチング電源回路１００と同一の構成には同一の番号を付している。
【００６０】
図１は、本発明の第１実施の形態に係るスイッチング電源回路５０を示す回路図である。図６の従来のスイッチング電源回路１００と比較して明らかなように、このスイッチング電源回路５０には、出力側の電圧監視回路や光結合素子を用いない簡単な構成となっている。
【００６１】
１は、電圧が変動する可能性のある不安定な直流電源であり、１ａは、その高圧側端子、１ｂは、低圧側端子である。また、２ａは、トランス２の一次巻線、２ｂは、トランス２の二次出力巻線であり、３は、発振用スイッチ素子となる電界効果トランジスタ（以下、スイッチ素子と記す）である。スイッチ素子３は、ここではＭＯＳ形（絶縁ゲート形）ＦＥＴであり、ドレインが一次巻線２ａの一端に、ソースがＩｐ検出抵抗２２を介して低圧側端子１ｂにそれぞれ接続し、ゲートがスイッチ素子３をオンオフ制御するスイッチ制御回路５に接続している。
【００６２】
スイッチ制御回路５は、演算回路５ａとＤ／Ａコンバータ５ｂとＡ／Ｄコンバータ５ｃとが１チップの回路部品に集積化されたもので、Ａ／Ｄコンバータ５ｃのアナログ入力端子Ｖｃｃ、Ｖｄ、Ｉｄは、それぞれ抵抗２１を介して高圧側端子１ａ、抵抗２３を介して一次巻線２ａの低圧側端部、Ｉｐ検出抵抗２２とスイッチ素子３の接続点に接続している。
【００６３】
また、Ｄ／Ａコンバータ５ｂのアナログ出力端子Ｖｇは、スイッチ素子３のゲートに接続し、ゲートに順方向バイアス電圧を所定のタイミングで加えてスイッチ素子３をオンオフ制御し、スイッチング電源回路５０全体を発振制御している。
【００６４】
このスイッチング電源回路５０の基本動作を図２で簡単に説明すると、スイッチ素子３をオン制御し、直列に接続された一次巻線２ａに励磁電流Ｉｐが流れ始めると、トランス２の各巻線に誘導起電力が生じる。
【００６５】
その後所定のオン時間Ｔ１後に、スイッチ制御回路５でスイッチ素子３をオフ制御し、スイッチ素子３がターンオフすると、一次巻線２ａに流れる電流が実質的に遮断され、トランス２の各巻線に、いわゆるフライバック電圧が生じる。このとき、二次出力巻線２ｂに発生するフライバック電圧は、整流用ダイオード４と平滑コンデンサ１３とにより形成される平滑整流回路４、１３により整流平滑化され、出力線２０ａ、２０ｂ間に接続される負荷に供給される電力として出力される。
【００６６】
誘導逆起電力によって二次出力巻線２ｂに蓄積されていた電気的エネルギの放出が終わると、同図（ｃ）の一次巻線２ａの電圧（Ｖ_２ａ）波形に示すように、一次巻線２ａやスイッチ素子３の浮遊容量と一次巻線２ａとの直列共振により、振動を開始しその振幅は次第に減少する。
【００６７】
各巻線に発生していた電圧が降下し、再び周期Ｔ後にスイッチ制御回路５でスイッチ素子３をオン制御し、スイッチ素子３をターンオンさせ、このようにして一連の発振動作が繰り返される。
【００６８】
この発振動作において、二次出力巻線２ｂに発生するピーク電流Ｉｓは、二次出力巻線２ｂの出力電圧をＶ_２ｂ、二次出力巻線２ｂのインダクタンスをＬｓ、発振周期Ｔ内で整流平滑化回路４、１３に出力が表れる出力時間、すなわち二次出力巻線２ｂに電流が流れる時間をＴ２（図２（ｂ）参照）とすれば、
【数１１】

で表すことができる。
【００６９】
また、一次巻線２ａのピーク電流をＩｐ、一次巻線２ａの巻数をＮｐ、二次出力巻線２ｂの巻数をＮｓとすれば、
【数１２】

の関係があり、（４）式と（５）式から
【数１３】

の関係が得られる。
【００７０】
ここで、Ｎｓ、Ｎｐ、Ｌｓは、回路素子により定まる定数であるので、Ｔ２を検出して、その値を（６）式へ代入すれば、一次巻線電流Ｉｐを調整することにより任意の二次出力巻線２ｂの出力電圧Ｖ_２ｂが得られる。
【００７１】
そこで、本実施の形態では、（６）式における出力電圧Ｖ_２ｂを、定電圧制御しようとする二次出力巻線の出力電圧Ｖ_{２ｂｓｅｔ}に設定し、
【数１４】

から得られる設定電流Ｉｐ_ｓｅｔに、一次巻線２ａのピーク電流Ｉｐが一致するようにオン時間Ｔ１を制御するものである。
【００７２】
一次巻線２ａの電流Ｉｐは、ターンオン後に増加するので、増加する一次巻線電流Ｉｐが設定電流Ｉｐ_ｓｅｔに達したときにスイッチ素子３をターンオフ制御することで、一次巻線電流Ｉｐを設定電流Ｉｐ_ｓｅｔに一致させる。
【００７３】
図２に示すように、（ｎ−１）の発振周期Ｔ内での、二次出力巻線２ｂに電流が流れる出力時間Ｔ２（ｎ−１）を検出し、後の発振周期、好ましくはその次の発振周期（ｎ）までに（１）式から設定電流Ｉｐ_ｓｅｔを得て、ターンオン後一次巻線電流Ｉｐが設定電流Ｉｐ_ｓｅｔに達するＴ１（ｎ）で、スイッチ素子３をターンオフ制御する。
【００７４】
以下、この方法を繰り返すことにより、二次出力巻線２ｂの出力電圧Ｖ_２ｂは、常に設定値Ｖ_{２ｂｓｅｔ}で出力され、定電圧制御を行うことができる。
【００７５】
出力時間Ｔ２の検出は、トランス２の二次側のダイオード４に電流が流れる時間を測定することにより容易に得られるが、ここではトランス２の一次側回路のみで定電圧制御を行うために、Ａ／Ｄコンバータ５ｃのアナログ入力端子Ｖｄを、抵抗２３を介して一次巻線２ａの低圧側端部に接続し、一次巻線２ａの電圧（Ｖ_２ａ）を監視し出力時間Ｔ２を検出している。
【００７６】
図２に示すように、二次出力巻線２ｂに出力電流が表れる出力時間Ｔ２は、トランス２に蓄積されるエネルギーの放出期間であり、この時間は、発振用スイッチ素子３がターンオフしてから一次巻線２ａに発生するフライバック電圧が減少し固有振動を開始することにより、一次巻線２ａの両端の極性が逆転し、トランス２への印加電圧を中心に電位が変動するまでの時間に等しい。
【００７７】
従って、スイッチ制御回路５の演算回路５ａが、ターンオフするオフ制御信号をＤ／Ａコンバータ５ｂより出力した後、一次巻線２ａの極性が逆転し、一次巻線電圧Ｖ_２ａ波形の一次巻線２ａの印加電圧に対する電位が最初に逆転するまでの時間から出力時間Ｔ２を検出する。固有振動の際に、一次巻線電圧Ｖ_２ａ波形が最初の極小値に達するまでの時間は、一次巻線２ａの印加電圧に対する電位が最初に逆転するまでの時間に近似するので、オフ制御信号を出力してから、最初の極小値に達するまでの時間を計測し、その時間から出力時間Ｔ２を検出してもよい。
【００７８】
また、スイッチング電源回路５０において、一次巻線電流Ｉｐは、Ａ／Ｄコンバータ５ｃのアナログ入力端子Ｉｄから、一次巻線電流Ｉｐが流れることによるＩｐ検出抵抗２２の電圧降下Ｖ_ｉｐを入力し、検出している。このように電圧換算するのは、電圧降下Ｖ_ｉｐが、Ｉｐ検出抵抗２２の抵抗値をｒ_ｉｐとしてｒ_ｉｐ×Ｉｐで表され、一次巻線電流Ｉｐの換算値として演算回路５ａでの演算処理が可能であり、また、電流Ｉｐの検出に比べて電圧降下Ｖ_ｉｐの検出がより容易なためである。
【００７９】
スイッチ制御回路５の演算回路５ａは、上述した方法で検出した出力時間Ｔ２を、（１）式に代入して、設定電流Ｉｐ_ｓｅｔを算出し、設定電流Ｉｐ_ｓｅｔにＩｐ検出抵抗２２の抵抗値をｒ_ｉｐを乗じた設定電位Ｖ_ｉｓｅｔを、アナログ入力端子Ｉｄから入力される電圧降下Ｖ_ｉｐと比較し、一致する電圧降下Ｖ_ｉｐが入力されたときに、Ｄ／Ａコンバータ５ｂからスイッチ素子３へターンオフするオフ制御信号を出力する。
【００８０】
以上の第１の実施の形態では、二次出力巻線２ｂの出力電圧を設定電圧Ｖ_{２ｂｓｅｔ}に定電圧制御するものであるが、整流平滑化回路４、１３の出力電圧Ｖ_２Ｏは、必ずしも精度よく定電圧とならない。
【００８１】
すなわち、整流平滑化回路４、１３の出力電圧Ｖ_２ｏは、整流平滑化回路のダイオード４の順方向電圧降下分をＶｆとすれば、
【数１５】

で表され、順方向電圧降下分Ｖｆは、通過する電流値、すなわち二次出力巻線２ｂの電流Ｉｓに比例するので、出力電圧Ｖ_２ｂを定電圧制御しても定電圧とはならないからである。
【００８２】
ダイオード４の順方向電圧降下分の出力電流Ｉｓに対する比例定数をｋとすれば、（７）式は、Ｖ_２ｂについて展開した（６）式と、出力電流Ｉｓについて展開した（５）式とから、
【数１６】

となる。ここで、Ｎｐ÷Ｎｓ×ＬｓをＫ１、ｋ÷ＬｓをＫ２とおけば、（８）式は、
【数１７】

となる。
【００８３】
（９）式をＩｐについて展開し、置き換えたＫ１をＮｐ÷Ｎｓ×Ｌｓ、Ｋ２をｋ÷Ｌｓと戻せば、
【数１８】

が得られる。
【００８４】
ここで、Ｎｓ、Ｎｐ、Ｌｓ、ｋは、回路素子により定まる定数であるので、Ｔ２を検出して、その値を（１０）式へ代入すれば、一次巻線電流Ｉｐを調整することにより任意の整流平滑化回路の出力電圧Ｖ_２ｏが得られる。
【００８５】
そこで、この第２実施の形態では、（１０）式における出力電圧Ｖ_２ｏを、定電圧制御しようとする整流平滑化回路４、１３の出力電圧Ｖ_{２ｏｓｅｔ}に設定し、
【数１９】

から得られる設定電流Ｉｐ_ｓｅｔ´に、一次巻線電流Ｉｐが一致するようにオン時間Ｔ１を制御するものである。
【００８６】
一次巻線２ａの電流Ｉｐを、設定電流Ｉｐ_ｓｅｔ´に一致させる方法と、一次巻線電流Ｉｐ及び出力時間Ｔ２の検出方法は、第１実施の形態と同じであるので、その説明を省略する。
【００８７】
特定の発振周期Ｔ内での二次出力巻線２ｂに電流が流れる出力時間Ｔ２を検出し、後の発振周期までに（２）式から設定電流Ｉｐ_ｓｅｔ´を算出し、ターンオン後に一次巻線電流Ｉｐが設定電流Ｉｐ_ｓｅｔ´に達するＴ１時に、スイッチ素子３をターンオフ制御し、以下、この方法を繰り返すことにより、整流平滑化回路４、１３の出力電圧Ｖ_２ｏは、ダイオード４の電圧降下分Ｖｆを考慮して常に設定値Ｖ_{２ｏｓｅｔ}で出力され、定電圧制御を行うことができる。
【００８８】
以上の第１、第２の実施の形態において、Ａ／Ｄコンバータ５ｃのアナログ入力端子Ｉｄより設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´に達する一次巻線電流Ｉｐを表す電圧降下Ｖ_ｉｐを入力してから、設定電位Ｖ_ｉｓｅｔに一致若しくは越えたことを判定し、現実にスイッチ素子３がターンオフするまでには、Ａ／Ｄコンバータ５ｃ、演算回路５ａ、Ｄ／Ａコンバータ５ｂ、スイッチ素子３等の回路素子に固有の遅延が生じている。
【００８９】
一方、一次巻線電流Ｉｐは、一次巻線２ａの電圧をＶ_２ａ、一次巻線２ａのインダクタンスをＬｐとすると、
【数２０】

で表され、ターンオン後に一次巻線２ａに加わえられる電圧に比例して上昇する
。
【００９０】
その結果、図３に示すように、ターンオフの際に一次巻線２ａに流れる電流Ｉｐ´は、設定電位Ｖ_ｉｓｅｔと比較した電圧降下Ｖ_ｉｐの一次巻線電流Ｉｐより増加し、上記回路素子による遅延時間の総和をδｔとすると、その増加分δＩｐは、（１１）式より
【数２１】

となる。
【００９１】
ここで、スイッチ素子３のオン期間に一次巻線２ａに印加される電圧Ｖ_２ａに比べて、回路上の励磁電流による他の電圧降下分を無視すれば、電圧Ｖ_２ａは、直流電源１の電源電圧Ｖｃｃと置き換えることができ、（１２）式の増加分を考慮し、
【数２２】

から求めたＩｐ´を、設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´と比較すれば、設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´に略一致する一次巻線電流Ｉｐが流れているタイミングでターンオフすることができる。
【００９２】
上記実施の形態では、電圧換算した電流Ｉｐを、電圧換算した設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´と比較しているので、アナログ入力端子Ｉｄから入力される電圧降下をＶ_ｉｐとして、（３）式の両辺にｒ_ｉｐを乗じた
【数２３】

の電圧降下Ｖ_ｉｐ´を設定電位Ｖ_ｉｓｅｔと比較する。
【００９３】
図４は、トランス２の一次側に副巻き線２ｃが設けられている場合に、この副巻き線２ｃの電圧Ｖ_２ｃを監視して、出力時間Ｔ２を検出する本発明の第４実施の形態に係るスイッチング電源回路６０を示す回路図である。
【００９４】
スイッチング電源回路６０は、図１に示すスイッチング電源回路５０と比較し、副巻き線２ｃがトランス２に更に設けられ、スイッチ制御回路６のＡ／Ｄコンバータのアナログ入力端子Ｖｄを、抵抗２４を介して副巻き線２ｃの低圧側端部に接続している構成が異なるだけである。
【００９５】
トランス２の副巻き線２ｃには、一次巻線２ａの電圧Ｖ_２ａに対してその巻線比に比例する電圧Ｖ_２ｃが発生するので、ターンオフ後、その極性が反転するまでの時間Ｔ２は副巻き線２ｃにおいても等しく、Ａ／Ｄコンバータのアナログ入力端子Ｖｄから、この副巻き線２ｃの電圧Ｖ_２ｃを継続して入力し、スイッチ制御回路６内の演算回路でＴ２を検出する。他の構成については、上記実施の形態と同一であるので、その説明を省略する。
【００９６】
図５は、本発明の第５実施の形態に係るスイッチング電源回路７０の定電圧出力制御装置７を示す回路図である。
【００９７】
本実施の形態では、スイッチ制御回路５の演算回路５ａで実行していたデジタル演算処理を、定電圧出力制御装置として作用するスイッチ制御回路７において比較回路や論理回路を用いたアナログ処理で実行するものである。従って、上述各実施の形態と異なるスイッチ制御回路７の構成を詳述し、共通する構成については同一の番号を付しその説明を省略する。
【００９８】
図において、７１は、（１３）式のδｔ×Ｖｃｃ÷Ｌｐ×ｒ_ｉｐに相当する補正電圧を出力する遅延補正回路、７２は、スイッチング電源回路７０の発振周期Ｔに等しい周期でクロックを出力する発振器、７３は、一次巻線２ａの電圧Ｖ_２ａの極性を判定するコンパレータ、７４は、出力時間Ｔ２から設定電位Ｖ_ｉｓｅｔに変換する時間−電圧変換回路、７５は、サンプルホールド回路、７６は、設定電位Ｖ_ｉｓｅｔを表す電圧波形を出力するクランプ回路、７７は、一次巻線電流Ｉｐを電圧換算した電圧降下Ｖ_ｉｐに遅延補正回路７１から出力される補正電圧を加える加算器、７８は、補正した電圧降下Ｖ_ｉｐを、設定電位Ｖ_ｉｓｅｔと比較するコンパレータ、７９は、アンドゲートである。
【００９９】
このスイッチ制御回路７の定電圧制御動作を説明すると、始めに発振動作しているスイッチング電源回路７０の出力時間Ｔ２をコンパレータ７３で検出する。コンパレータ７３は、非反転入力を、入力端子Ｖｄから抵抗２３を介して一次巻線２ａの低圧側端部に接続し、一次巻線電圧Ｖ_２ａに比例する分圧された電圧を入力する一方、反転入力には、一次巻線２ａの極性反転の検出が可能となる、直流電源１に比例する分圧された電圧を入力し、一次巻線電圧Ｖ_２ａの極性に応じた波形を出力している。従ってこのコンパレータ７３は、スイッチ素子３がターンオフしたフライバック電圧により「Ｈ」の出力波形を出力し、トランス２のエネルギー放出が完了し極性が反転すると「Ｌ」に転じる。
【０１００】
時間−電圧変換回路７４は、コンパレータ７３から「Ｈ」が出力されている期間を出力時間Ｔ２として、（１）式若しくは（２）式から、Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´を求め、これらの設定電流値にｒ_ｉｐを乗じた設定電位Ｖ_ｉｓｅｔを出力する。設定電流値にＩｐ検出抵抗２２の抵抗値ｒ_ｉｐを乗じるのは、コンパレータ７８において、一次巻線電流Ｉｐに抵抗値ｒ_ｉｐを乗じた電圧降下Ｖ_ｉｐと比較する為である。
【０１０１】
サンプルホールド回路７５は、少なくとも後に定電圧制御しようとする発振周期まで設定電位Ｖ_ｉｓｅｔを保持し、クランプ回路７６へ出力する。
【０１０２】
クランプ回路７６は、サンプルホールド回路７５から出力される設定電位Ｖ_ｉｓｅｔをクランピングし、振幅が設定電位Ｖ_ｉｓｅｔとなるパルス波形を、コンパレータ７８の非反転入力へ出力する。
【０１０３】
発振動作している間に一次巻線２ａに流れる電流Ｉｐは、Ｉｐ検出抵抗２２による電圧降下Ｖ_ｉｐ、すなわちＩｐ×ｒ_ｉｐで表される電圧降下Ｖ_ｉｐとして入力端子Ｉｄから加算器７７の一方に入力される。
【０１０４】
遅延補正回路７１は、図示しない測定値回路などで計測したスイッチ制御回路７及びスイツチ素子３による固有遅延時間の総和δｔと、抵抗２１を介して入力される直流電源１の電源電圧Ｖｃｃとから、（１３）式のδｔ×Ｖｃｃ÷Ｌｐ×ｒ_ｉｐに相当する補正電圧を算出し、加算器７７の他方へ入力する。
【０１０５】
加算器７７は、この補正電圧を電圧降下Ｖ_ｉｐへ加える（１３）式の演算処理を行い、コンパレータ７８の反転入力へ出力する。
【０１０６】
従って、コンパレータ７８へは、回路素子の遅延時間を考慮した電圧降下Ｖ_ｉｐが入力され、設定電位Ｖ_ｉｓｅｔと比較され、加算器７７から出力される電圧降下Ｖ_ｉｐが設定電位Ｖ_ｉｓｅｔ以下である場合には「Ｈ」を、設定電位Ｖ_ｉｓｅｔを越えると「Ｌ」をアンドゲート７９へ出力する。
【０１０７】
アンドゲート７９は、発振器７２とコンパレータ７８からの出力を入力し、出力をスイッチ素子３のゲートに接続するもので、論理積が「Ｈ」の期間のみ、スイッチ素子３をＯＮ制御するように動作する。
【０１０８】
発振器７２から出力されるクロックが「Ｌ」の期間は、スイッチ素子３がＯＦＦ制御され、トランス２の一次巻線２ａに励磁電流が流れない。
【０１０９】
発振器７２から出力されるクロックが「Ｈ」に転じ、コンパレータ７８からの出力も「Ｈ」、すなわち電圧降下Ｖ_ｉｐが設定電位Ｖ_ｉｓｅｔに達しない間は、アンドゲート７９の出力も「Ｈ」となるので、スイッチ素子３がターンオンする。
【０１１０】
その後、オン時間に比例して一次巻線電流Ｉｐを表す電圧降下Ｖ_ｉｐも増加し、電圧降下Ｖ_ｉｐが設定電位Ｖ_ｉｓｅｔを越えると、コンパレータ７８の出力が「Ｌ」となるので、アンドゲート７９の出力も「Ｌ」となり、スイッチ素子３がターンオフする。このターンオフした際の電圧降下Ｖ_ｉｐは、設定電位Ｖ_ｉｓｅｔに等しく、そのときに一次巻線２ａに流れる電流Ｉｐは、（１）式若しくは（２）式のＩｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´となり、設定した出力電圧Ｖ_２ｂ若しくは出力電圧Ｖ_２ｏに略等しい出力が得られる。この制御を、少なくとも発振動作中に繰り返えすことにより、トランス２の二次側で、設定した出力電圧Ｖ_２ｂ若しくは出力電圧Ｖ_２ｏの定電圧出力制御を行うことができる。
【０１１１】
以上の各実施の形態において、スイッチング電源回路全体の発振動作が安定するまでの出力期間Ｔ２は不安定であり、設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´が設定できないので、安定動作するまでは、設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´を初期電流値Ｉｐ_ｄｅｆ（若しくは初期電位Ｖ_ｉｄｅｆ）とし、オン時間Ｔ１を一定にしておくことが望ましい。
【０１１２】
また、出力時間Ｔ２は、必ずしも各周期Ｔ毎に検出する必要はなく、例えば、発振周期Ｔとは異なるより長い周期毎に検出して定電圧制御を行ってもよい。
【０１１３】
更に、本発明によれば、単に設定した基準電圧値に対してこれを越える出力電圧が発生した場合にのみその電圧を低下させるだけでなく、二次出力巻線２ｂ若しくは整流平滑化回路の出力電圧をＶ_２ｂ若しくはＶ_２ｏに設定して、その設定した出力電圧が得られるので、従来例で説明したようなトランス２の二次側に出力検出回路を有し、フォトカプラなどの絶縁された信号伝達素子を介してその検出信号を一次側へ伝送する帰還回路を備えたスイッチング電源回路に対しても適用して、利用することができる。
【０１１４】
【発明の効果】
以上説明したように、本発明によれば、各回路素子の回路定数にばらつきがあっても、出力時間Ｔ２が変化するだけで、変化する出力時間Ｔ２を求めてから定電圧制御する為の設定電流Ｉｐ_ｓｅｔを得る（１）式には影響しないので、量産しても高精度に定電圧制御を行うことができる。
【０１１５】
また、出力電圧の仕様が異なるスイッチング電源回路であっても、同一の回路部品で定電圧出力制御を行うことができる。
【０１１６】
また、トランスの二次側の出力電圧検出回路や光結合素子を設けない一次側の回路のみで、定電圧出力制御できる。
【０１１７】
また、請求項２と請求項６の発明によれば、更に、整流平滑化回路の出力を高精度に定電圧出力制御することかできる。
【０１１８】
更に、請求項３と請求項７の発明によれば、トランスの二次側の検出結果を一次側へ伝達するための信号伝達素子を設ける必要がなく、一次側の回路のみで定電圧制御が可能となる。
【０１１９】
請求項４と請求項８の発明によれば、トランスに副巻き線が設けられている場合には、そのその副巻き線の電位を監視することにより、二次側の定電圧出力制御を行うことができる。
【０１２０】
更に、請求項９の発明によれば、トランスの一次側電流検出部と発振用スイッチ素子の動作間に遅れδｔがあっても、精度よく出力電圧制御を行うことができる。
【０１２１】
更に、請求項１０の発明によれば、電圧である電圧降下Ｖ_ｉｐと設定電位Ｖ_ｉｓｅｔを比較して、ターンオフする際の一次巻線電流Ｉｐを設定電流Ｉｐ_ｓｅｔ若しくはＩｐ_ｓｅｔ´とするので、電流値に換算処理することなく、コンパレータを用いた比較回路で簡単に比較できる。
【図面の簡単な説明】
【図１】本発明の第１実施の形態に係るスイッチング電源回路５０の回路図である。
【図２】スイッチング電源回路５０の各部の電圧若しくは電流波形を拡大して示し、
（ａ）は、トランス２の一次巻線２ａに流れる電流（Ｉｐ）を、
（ｂ）は、トランス２の二次出力巻線２ｂに流れる電流（Ｉｓ）を、
（ｃ）は、トランス２の一次巻線２ａの電圧（Ｖ_２ａ）を、
それぞれ示す波形図である。
【図３】ターンオン後にトランス２の一次巻線２ａに流れる電流（Ｉｐ）と、ターンオン後の時間ｔとの関係を示すグラフである。
【図４】本発明の第４実施の形態に係るスイッチング電源回路６０の回路図である。
【図５】本発明の第５実施の形態に係るスイッチング電源回路７０の定電圧出力制御装置７を示す回路図である。
【図６】従来のスイッチング電源回路１００の回路図である。
【符号の説明】
１ 直流電源
２ トランス
２ａ 一次巻線
２ｂ 二次出力巻線
２ｃ 副巻き線
３ 発振用スイッチ素子
４ 整流用ダイオード（整流平滑化回路）
５、６、７ スイッチ制御回路
１３ 平滑コンデンサ（整流平滑化回路）
２２ Ｉｐ検出抵抗
７３ コンパレータ（出力時間検出部）
７４ 時間−電圧変換回路（設定値算出回路）
Ｔ１ オン時間
Ｔ２ 整流平滑化回路に出力が表れる出力時間
Ｖｃｃ 直流電源の電源電圧
Ｖ_２ｂ 二次出力巻線に表れる出力電圧
Ｖ_{２ｂｓｅｔ} 定電圧制御しようとする二次出力巻線出力電圧
Ｖ_２ｏ 整流平滑化回路の出力電圧
Ｖ_{２ｏｓｅｔ} 定電圧制御しようとする整流平滑化回路の出力電圧
Ｖ_ｉｓｅｔ 設定電位
Ｉｐ 一次巻線電流
Ｉｐ_ｓｅｔ 設定電流
Ｉｐ_ｓｅｔ´ 設定電流
Ｎｐ 一次巻線の巻数
Ｎｓ 二次出力巻線の巻数
Ｌｐ 一次巻線のインダクタンス
Ｌｓ 二次出力巻線のインダクタンス
ｋ 整流用ダイオードの順方向電圧降下分の出力電流に対する比例定数
δ 一次巻線電流Ｉｐを検出した後、発振用スイッチ素子がオン制 御を停止するまでの時間差
ｒ_ｉｐ Ｉｐ検出抵抗の抵抗値[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a constant-voltage output control method and a constant-voltage output control method for performing constant-voltage control on an output voltage output from a secondary side of a transformer of a switching power supply circuit.
[0002]
[Prior art]
The switching power supply circuit supplies an exciting current to the primary winding of the transformer and discharges the energy stored in the transformer as the output of the secondary output winding.It is small, lightweight, and highly efficient as a stabilized power supply. Used in power supply circuits such as battery chargers and AC adapters.
[0003]
Conventionally, this type of switching power supply circuit monitors the output voltage and current of the rectifying / smoothing circuit so as not to generate excessive output power at the output of the secondary-side rectifying / smoothing circuit, and compares the monitoring result with a photocoupler. The signal is transmitted to the primary side using an insulated signal transmission element such as. On the primary side, the oscillation switch element is turned on and off from the transmission signal, and the output voltage is controlled at a constant voltage by controlling the on time (excitation time) and the off time of the excitation current flowing through the primary winding. (For example, see Patent Document 1).
[0004]
[Patent Document 1]
JP 2002-136116 A
[0005]
Hereinafter, the constant voltage control by the conventional switching power supply circuit 100 will be described with reference to the circuit diagram of FIG.
[0006]
Reference numeral 1 denotes an unstable DC power supply including a high-voltage terminal 1a and a low-voltage terminal 1b. Reference numeral 2 denotes a transformer including a primary winding 2a and a secondary output winding 2b. Reference numeral 3 denotes a field-effect transistor. The oscillating switch element 22 is an Ip detection resistor for detecting the current Ip flowing through the primary winding 2a. The oscillation switch element 3 is connected between one end of the primary winding 2a and the low voltage side terminal 1b via the Ip detection resistor 22, and is turned on / off at a predetermined cycle by a switch control circuit 101 connected to the gate. , The entire circuit 100 oscillates.
[0007]
Reference numerals 4 and 13 shown in the secondary output of the transformer 2 are a rectifying diode and a smoothing capacitor constituting a rectifying / smoothing circuit, respectively. The output of the secondary output winding 2b is rectified and smoothed, and the high voltage output is obtained. The signal is output between the line 20a and the low-voltage output line 20b.
[0008]
Between the output lines 20a and 20b, a voltage monitoring circuit that monitors the output voltage and output current and, when any one of them exceeds a predetermined reference voltage or reference current, causes the photocoupler light emitting element 35a in the figure to emit light. An output monitoring circuit including a current monitoring circuit is provided.
[0009]
In the voltage monitoring circuit, voltage dividing resistors 30 and 31 are connected in series between the high voltage side output line 20a and the low voltage side output line 20b, and a voltage division of the output voltage is obtained from an intermediate tap 32 to obtain an error amplifier 33a. Is input to the inverting input terminal. A voltage monitoring reference power supply 34a is connected between the non-inverting input terminal of the error amplifier 33a and the low-voltage side output line 20b, and a first comparator for comparing the output voltage with the divided voltage is connected to the non-inverting input terminal. Voltage is being input. The reference voltage is set to an arbitrary value by changing the resistance values of the voltage dividing resistors 30 and 31 or the first comparison voltage of the voltage monitoring reference power supply 34a.
[0010]
A photocoupler light-emitting element 35 is connected to the output side of the error amplifier 33a. The photocoupler light-emitting element 35a is connected to the high-voltage output line 20a via an electric resistor 36, and is supplied with drive power.
[0011]
Further, the current monitoring circuit has the current detection resistor 43 interposed in the low voltage side output line 20b, one end of the current detection resistor 43 is connected to the inverting input terminal of the error amplifier 33b, and the other end is connected to the current monitoring reference power supply 34b. Input to the non-inverting input terminal.
[0012]
As a result, the output current flowing through the low-voltage side output line 20b is represented by a potential difference between both ends of the current detection resistor 43, and is compared with the second comparison voltage of the current monitoring reference power supply 34b by the error amplifier 33b. It can be determined whether the current has been exceeded. The reference current is set to an arbitrary value by changing the resistance value of the current detection resistor 43 or the second comparison voltage of the current monitoring reference power supply 34b.
[0013]
The output side of the error amplifier 33b is connected to a connection point between the output side of the error amplifier 33a for monitoring the output voltage and the photocoupler light emitting element 35a.
[0014]
The resistor 37a and the capacitor 38a and the resistor 37b and the capacitor 38b connected in series are AC negative feedback elements for stably operating the error amplifier 33a and the error amplifier 33b, respectively.
[0015]
On the primary side of the transformer 2, a photocoupler light receiving element 35 b photocoupled to the photocoupler light emitting element 35 a is connected between the switch control element 101 and the low voltage terminal 1 b of the DC power supply 1.
[0016]
The switch control circuit 101 incorporates a variable reference power supply 101a that outputs a variable voltage according to the collector current of a photocoupler light receiving element 35b composed of a phototransistor, a comparator 101b, an oscillator 101c, and an AND gate 101d. I have.
[0017]
The inverting input of the comparator 101b is connected to the connection point between the oscillating switch element 3 and the Ip detecting resistor 22, and the non-inverting input is connected to the variable reference power source 101a. The current Ip flowing through the primary winding 2a is compared with the amount of received limit signal received by the photocoupler light-receiving element 35b from the photocoupler light-emitting element 35a via the variable reference power supply 101a.
[0018]
The output of the comparator 101b is input to the AND gate 101d together with the output of the oscillator 101c, and the output of the AND gate 101d is connected to the gate of the oscillation switch element 3.
[0019]
The operation of the switching power supply circuit 100 thus configured is performed in a state where the variable reference power supply 101a does not receive the collector current from the photocoupler light-emitting element 35, that is, in a normal operation state where the output is stable. Reference voltage V set to a predetermined value from 101a _set To the non-inverting input of the comparator 101b.
[0020]
On the other hand, the voltage of the Ip detection resistor 22 representing the current Ip flowing through the primary winding 2a is input to the inverting input of the comparator 101b, and after the oscillation switch element 3 is turned on, the primary winding current Ip which rises with time and Be compared. Therefore, the comparator 101b determines that the voltage representing the primary winding current Ip is equal to the reference voltage V _set "H" is output until the reference voltage V _set Is exceeded, "L" is output.
[0021]
The oscillator 101c outputs a clock pulse corresponding to the oscillation cycle T of the switching power supply circuit 100 to the AND gate 101d. As a result, the AND gate 101d outputs the clock pulse of “H” and the output of the comparator 101b becomes “H”. That is, the voltage representing the primary winding current Ip is equal to the reference voltage V _set Until the value reaches “H”, “H” is output, and the oscillation switch element 3 is turned on.
[0022]
On the other hand, when the output voltage exceeds the reference voltage due to the load connected between the high-voltage output line 20a and the low-voltage output line 20b, the partial voltage input to the inverting input terminal of the error amplifier 33a also increases. , The potential difference from the first comparison voltage is inverted and amplified to a potential exceeding the light emission threshold of the photocoupler light emitting element 35.
[0023]
Further, even when the output current exceeds the reference current due to the load connected between the high-voltage output line 20a and the low-voltage output line 20b, the voltage input to the inverting input terminal of the error amplifier 33b increases. The potential difference from the second comparison voltage is inverted and amplified, and becomes a potential exceeding the light emission threshold of the photocoupler light emitting element 35.
[0024]
As a result, when either the output voltage or the output current exceeds the reference voltage or the reference current, the photocoupler light emitting element 35a emits a light emission amount limit signal to the photocoupler light receiving element 35b according to the amount of the excess.
[0025]
When the photocoupler light-receiving element 35b receives the limit signal from the photocoupler light-emitting element 35a, the output voltage of the variable reference power supply 101a is changed to the reference voltage V in accordance with the increase in the amount of received light. _set And the output of the comparator 101b becomes the reference voltage V _set Is turned to "L" earlier than the normal operation in which "."
[0026]
As a result, the oscillation switch element 3 is turned on and the time T1 for exciting the primary winding 2a is shortened, and the energy stored in the transformer 2 in one cycle is reduced. The output voltage or output current naturally decreases and becomes lower than the reference voltage or reference current.
[0027]
As a result, the photocoupler light emitting element 35a stops emitting light, and the photocoupler light receiving element 35b stops receiving the limit signal. _set Is repeated, and a stable output according to the power of the load is obtained.
[0028]
[Problems to be solved by the invention]
However, in the conventional constant voltage output control method of the switching power supply circuit 100, the voltage monitoring circuit includes the voltage dividing resistors 30, 31, the voltage monitoring reference power supply 34a and the switch control circuit 101 , Reference voltage V _set Is provided in series with the primary winding 2a, and the Ip detection resistor 22 is provided in series. However, when the switch control circuit 101 is an integrated circuit, the variation of the circuit constants of these circuit elements and Due to variations in the integrated circuit itself, there is a problem that products having high-precision constant-voltage output characteristics cannot be stably and easily mass-produced.
[0029]
Further, if the output voltage characteristics required for the switching power supply circuit are different, it is necessary to set the above circuit constants and the like each time or replace circuit components, which increases extra design time and circuit component adjustment time, This was causing the cost to rise.
[0030]
Further, the provision of the output voltage detection circuit on the secondary side of the transformer 2 increases the number of circuit components, causing an increase in the size of the entire circuit.
[0031]
Further, in order to correct an increase in the output voltage detected by the output voltage detection circuit on the secondary side of the transformer 2 by controlling the primary side, optical coupling elements such as a photocoupler light emitting element 35a and a photocoupler light receiving element 35b are provided. This necessitates a cost increase and the circuit configuration becomes complicated.
[0032]
The present invention has been made in view of such a problem, and a constant voltage output control method for a switching power supply circuit capable of accurately controlling an output voltage with high accuracy even when circuit elements and integrated circuits used vary. And an apparatus therefor.
[0033]
It is another object of the present invention to provide a constant-voltage output control method and apparatus for a switching power supply circuit capable of mass-producing switching power supply circuits having different output voltage specifications with the same circuit components.
[0034]
Further, it is an object of the present invention to provide a constant voltage output control method for a switching power supply circuit for controlling the output voltage with a constant voltage only by a primary side circuit without a transformer secondary side output voltage detection circuit or an optical coupling element, and a device therefor. Aim.
[0035]
[Means for Solving the Problems]
In order to solve the above problem, a method for controlling a constant voltage output of a switching power supply circuit according to claim 1 includes a transformer having a primary winding and a secondary output winding, a DC power supply for exciting the primary winding, and a primary winding. For oscillating a switching power supply circuit comprising an oscillation switch element connected in series, a switch control circuit for controlling the oscillation switch element to be turned on and off, and a rectification smoothing circuit for rectifying and smoothing the output of the secondary output winding. The output voltage V appearing on the secondary output winding is changed by changing the ON time of the switch element. _2b Constant voltage output control method for controlling the constant voltage
The output voltage of the secondary output winding to be controlled at a constant voltage is V _2bset Where Np is the number of turns of the primary winding, Ns is the number of turns of the secondary output winding, Ls is the inductance of the secondary output winding, and T2 is the output time during which the output appears in the rectification smoothing circuit within the oscillation cycle.
(Equation 6)

Current Ip calculated from _set Furthermore, when the current Ip flowing through the primary winding reaches, the on-control of the oscillation switch element is stopped, and the on-time is adjusted.
[0036]
A constant voltage output control method for a switching power supply circuit according to claim 2, wherein the transformer having a primary winding and a secondary output winding, and a DC power supply for exciting the primary winding are connected to an oscillation connected in series with the primary winding. The on-time of an oscillation switch element of a switching power supply circuit including a switch element, a switch control circuit for controlling on / off of the oscillation switch element, and a rectification smoothing circuit for rectifying and smoothing the output of the secondary output winding is changed. Output voltage V of the rectifying and smoothing circuit. _2o Constant voltage output control method for controlling the constant voltage
The output voltage of the rectifying / smoothing circuit to be controlled at a constant voltage is V _2oset The number of turns of the primary winding is Np, the number of turns of the secondary output winding is Ns, the inductance of the secondary output winding is Ls, the output time during which the output appears in the rectification smoothing circuit within the oscillation period is T2, and the rectification smoothing circuit is used. Where k is the proportional constant to the output current of the forward voltage drop of the diode
(Equation 7)

Current Ip calculated from _set , When the current Ip flowing through the primary winding reaches, the ON control of the oscillation switch element is stopped, and the ON time is adjusted.
[0037]
A constant voltage output control method for a switching power supply circuit according to claim 3, wherein the output time T2 during which the output appears on the rectifying / smoothing circuit within the oscillation cycle is changed from the time when the flyback voltage is generated in the primary winding until the first polarity reversal. Is detected from the time.
[0038]
According to the constant voltage output control method of the switching power supply circuit, the output time T2 during which the output appears on the rectifying / smoothing circuit within the oscillation period is set to the first polarity inversion after the flyback voltage is generated in the sub winding of the transformer. The feature is to detect from the time until the hour.
[0039]
A constant voltage output control device for a switching power supply circuit according to claim 5, further comprising: a transformer having a primary winding and a secondary output winding; and a DC power supply for exciting the primary winding, the oscillation being connected in series with the primary winding. A switching element, a switch control circuit for controlling on / off of the oscillation switch element, and a rectifying / smoothing circuit for rectifying / smoothing the output of the secondary output winding. The output voltage (V _2b A) constant voltage output control device for a switching power supply circuit for constant voltage control,
A primary-side current detection unit that detects a current Ip flowing through the primary winding, an output time detection unit that detects an output time T2 during which an output appears in a rectifying and smoothing circuit within an oscillation cycle,
The output voltage of the secondary output winding to be controlled at a constant voltage is V _2bset , The number of turns of the primary winding is Np, the number of turns of the secondary output winding is Ns, and the inductance of the secondary output winding is Ls,
An output time T2 detected by the output time detector,
(Equation 8)

And the set current Ip _set A set value calculation circuit for determining
Current Ip flowing through primary winding and set current Ip _set And a comparison circuit for comparing
The switch control circuit determines that the current Ip is equal to the set current Ip. _set When the threshold value is reached, the on control of the oscillation switch element is stopped, and the on time is adjusted.
[0040]
A constant voltage output control device for a switching power supply circuit according to claim 6, further comprising: a transformer having a primary winding and a secondary output winding; and a DC power supply for exciting the primary winding. A switch element, a switch control circuit for controlling ON / OFF of the oscillation switch element, and a rectifying / smoothing circuit for rectifying / smoothing the output of the secondary output winding. Output voltage (V _2o A) constant voltage output control device for a switching power supply circuit for constant voltage control,
A primary-side current detection unit that detects a current Ip flowing through the primary winding, an output time detection unit that detects an output time T2 during which an output appears in a rectifying and smoothing circuit within an oscillation cycle,
The output voltage of the rectifying / smoothing circuit to be controlled at a constant voltage is V _2oset Where Np is the number of turns of the primary winding, Ns is the number of turns of the secondary output winding, Ls is the inductance of the secondary output winding, and k is a proportional constant to the output current corresponding to the forward voltage drop of the diode of the rectifying and smoothing circuit. ,
An output time T2 detected by the output time detector,
(Equation 9)

And the set current Ip _set A set value calculation circuit for obtaining the
Current Ip flowing through primary winding and set current Ip _set And a comparison circuit for comparing ′
The switch control circuit determines that the current Ip is equal to the set current Ip. _set When に is reached, the on-control of the oscillation switch element is stopped, and the on-time is adjusted.
[0041]
A constant voltage output control device for a switching power supply circuit according to claim 7, _2a And a primary winding voltage monitoring circuit that detects the time from the occurrence of the flyback voltage to the first polarity reversal, from the occurrence of the flyback voltage on the primary winding to the first polarity reversal Is set as the output time T2.
[0042]
The constant voltage output control device for a switching power supply circuit according to claim 8, further comprising: a sub-winding further provided on the primary side of the transformer; _2c A sub-winding voltage monitoring circuit that monitors the time from when the flyback voltage is generated until the first polarity reversal is provided, and from when the flyback voltage is generated on the sub-winding until the first polarity reversal Is set as the output time T2.
[0043]
In the constant-voltage output control device for a switching power supply circuit according to claim 9, the primary-side current detector detects the set current Ip. _set Or Ip _set After detecting the primary winding current Ip reaching ', the time difference until the oscillation switch element stops the ON control is δt, the power supply voltage of the DC power supply is Vcc, the inductance of the primary winding is Lp,
(Equation 10)

From the set current Ips _et Or Ip _set ′ To be compared with the current Ip,
The constant-voltage output control device for a switching power supply circuit according to claim 10, wherein the primary-side current detection unit has a resistance value r in series with the primary winding. _ip And the voltage drop V due to the Ip detection resistor. _ip From the current Ip, and the comparison circuit detects the voltage drop V _ip And the set current Ip _set Or Ip _set ´ to the resistance value r _ip And the set current Ip _set Or Ip _set Set potential V representing ' _iset Is compared with the current Ip and the set current Ip. _set Or Ip _set ′ Are compared.
[0044]
According to the first and fifth aspects of the present invention, if the output time T2 during which the output appears in the rectifying / smoothing circuit within the oscillation period T is detected and substituted into the equation (1), the secondary output winding is calculated from the equation (1). Line output voltage V _2bset Set current Ip with constant voltage _set Is obtained.
[0045]
Set current Ip _set When the current Ip flowing through the primary winding reaches the threshold value, the ON control of the oscillation switch element is stopped and the ON time T1 is adjusted. _set And the output voltage of the secondary output winding is V _2bset And the output voltage can be set.
[0046]
Even if there is a variation in the circuit constant of each circuit element, only the output time T2 changes, and the set current Ip for controlling the constant voltage after obtaining the changing output time T2. _set Does not affect constant voltage control.
[0047]
If the circuit constants of the equation (1) are determined, the output voltage V _2bset By simply changing the numerical value of, constant voltage control of different output voltages can be performed with the switching power supply circuit having the same configuration.
[0048]
According to the second and sixth aspects of the present invention, if the output time T2 during which the output appears in the rectifying / smoothing circuit within the oscillation period T is detected and substituted into the equation (2), the equation (2) is used to calculate the output time. Output voltage V _2oset Set current Ip with constant voltage _set 'Is obtained.
[0049]
Set current Ip _set When the current Ip flowing through the primary winding reaches the value ', the ON control of the oscillation switch element is stopped and the ON time T1 is adjusted. _set And the output voltage of the rectifying / smoothing circuit in consideration of the diode drop is V _2oset Thus, the output voltage can be accurately set.
[0050]
Even if the circuit constants of the circuit elements vary, the set current Ip for controlling the constant voltage after obtaining the changed output time T2 only by changing the output time T2. _set 'Does not affect the constant voltage control to obtain'.
[0051]
Also, if each circuit constant of the equation (2) is obtained, the output voltage V _2oset By simply changing the numerical value of, constant voltage control of different output voltages can be performed with the switching power supply circuit having the same configuration.
[0052]
According to the third and seventh aspects of the present invention, the time T2 during which the output appears in the rectifying / smoothing circuit is a period during which the energy stored in the transformer is released, and is generated in the primary winding after the oscillation switch element is turned off. By monitoring the potential of the primary winding without monitoring the output of the rectifying / smoothing circuit, it is equal to the time required for the polarity to reverse to reduce the flyback voltage and start natural oscillation. The output time T2 can be detected from the primary side.
[0053]
Therefore, there is no need to provide a transmission element for transmitting the detection result on the secondary side to the primary side, and constant voltage control can be performed only by the circuit on the primary side.
[0054]
According to the fourth and eighth aspects of the present invention, the time T2 during which the output appears in the rectifying / smoothing circuit is equal to the time from when the flyback voltage is generated in the sub winding until the polarity is reversed, and the rectifying / smoothing circuit is used. By monitoring the potential of the secondary winding on the primary side of the transformer without monitoring the output of the transformer, the output time T2 can be detected from the primary side of the transformer.
[0055]
Therefore, there is no need to provide a transmission element for transmitting the detection result on the secondary side to the primary side, and constant voltage control can be performed only by the circuit on the primary side.
[0056]
According to the ninth aspect of the present invention, after the turn-on, the primary winding current Ip increases in proportion to the approximate power supply voltage Vcc ÷ Lp. The increase in the current Ip due to the delay δt during the operation of the oscillation switch element is shown.
[0057]
Therefore, the primary winding current Ip when the oscillation switch element (3) is turned off is equal to the set current Ip. _set Or Ip _set And constant voltage control can be performed with high accuracy even if there is a delay in circuit elements.
[0058]
According to the tenth aspect, the primary winding current Ip and the set current Ip _set Or Ip _set ′ Is the voltage drop V _ip And set potential V _iset Thus, comparison can be easily performed by a comparison circuit using a comparator without performing arithmetic processing.
[0059]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In these figures, the same components as those of the conventional switching power supply circuit 100 shown in FIG. 6 are denoted by the same reference numerals.
[0060]
FIG. 1 is a circuit diagram showing a switching power supply circuit 50 according to the first embodiment of the present invention. As is apparent from comparison with the conventional switching power supply circuit 100 of FIG. 6, the switching power supply circuit 50 has a simple configuration that does not use a voltage monitoring circuit or an optical coupling element on the output side.
[0061]
Reference numeral 1 denotes an unstable DC power supply whose voltage may fluctuate. Reference numeral 1a denotes a high voltage side terminal, and 1b denotes a low voltage side terminal. Reference numeral 2a denotes a primary winding of the transformer 2, 2b denotes a secondary output winding of the transformer 2, and 3 denotes a field-effect transistor (hereinafter, referred to as a switch element) serving as an oscillation switch element. Here, the switch element 3 is a MOS type (insulated gate type) FET. The drain is connected to one end of the primary winding 2a, the source is connected to the low voltage side terminal 1b via the Ip detection resistor 22, and the gate is the switch element. 3 is connected to a switch control circuit 5 for controlling on / off of the switch 3.
[0062]
The switch control circuit 5 includes an arithmetic circuit 5a, a D / A converter 5b, and an A / D converter 5c integrated on a single-chip circuit component. The analog input terminals Vcc, Vd, and Id of the A / D converter 5c are provided. Are connected to the high-voltage side terminal 1a via the resistor 21, the low-voltage side end of the primary winding 2a via the resistor 21, and the connection point between the Ip detection resistor 22 and the switch element 3, respectively.
[0063]
The analog output terminal Vg of the D / A converter 5b is connected to the gate of the switch element 3, and the switch element 3 is turned on and off by applying a forward bias voltage to the gate at a predetermined timing. The oscillation is controlled.
[0064]
The basic operation of the switching power supply circuit 50 will be briefly described with reference to FIG. 2. When the switching element 3 is turned on and the exciting current Ip starts flowing through the primary winding 2a connected in series, induction is applied to each winding of the transformer 2. An electromotive force is generated.
[0065]
Thereafter, after a predetermined ON time T1, the switch element 3 is turned off by the switch control circuit 5, and when the switch element 3 is turned off, the current flowing through the primary winding 2a is substantially cut off. A flyback voltage occurs. At this time, the flyback voltage generated in the secondary output winding 2b is rectified and smoothed by the smoothing rectifier circuits 4, 13 formed by the rectifying diode 4 and the smoothing capacitor 13, and is connected between the output lines 20a, 20b. Is output as electric power supplied to the load.
[0066]
When the release of the electric energy stored in the secondary output winding 2b by the induced back electromotive force is completed, the voltage (V) of the primary winding 2a in FIG. _2a As shown in the waveforms, oscillation starts due to series resonance between the stray capacitance of the primary winding 2a and the switching element 3 and the primary winding 2a, and the amplitude gradually decreases.
[0067]
The voltage generated in each winding drops, and the switch element 3 is turned on again by the switch control circuit 5 after the cycle T, and the switch element 3 is turned on. Thus, a series of oscillation operations is repeated.
[0068]
In this oscillation operation, the peak current Is generated in the secondary output winding 2b changes the output voltage of the secondary output winding 2b to V _2b The inductance of the secondary output winding 2b is represented by Ls, and the output time during which the output appears in the rectifying and smoothing circuits 4 and 13 within the oscillation period T, that is, the time during which the current flows through the secondary output winding 2b is represented by T2 (FIG. )))
[Equation 11]

Can be represented by
[0069]
If the peak current of the primary winding 2a is Ip, the number of turns of the primary winding 2a is Np, and the number of turns of the secondary output winding 2b is Ns,
(Equation 12)

From the equations (4) and (5).
(Equation 13)

Is obtained.
[0070]
Here, Ns, Np, and Ls are constants determined by circuit elements. Therefore, if T2 is detected and its value is substituted into the expression (6), the primary winding current Ip can be adjusted to an arbitrary value. Output voltage V of next output winding 2b _2b Is obtained.
[0071]
Therefore, in the present embodiment, the output voltage V _2b Is the output voltage V of the secondary output winding to be controlled at a constant voltage. _2bset Set to
[Equation 14]

Current Ip obtained from _set In addition, the on-time T1 is controlled so that the peak current Ip of the primary winding 2a matches.
[0072]
Since the current Ip of the primary winding 2a increases after the turn-on, the increasing primary winding current Ip becomes equal to the set current Ip. _set The primary winding current Ip is controlled by turning off the switch element 3 when the _set To match.
[0073]
As shown in FIG. 2, the output time T2 (n-1) in which the current flows through the secondary output winding 2b within the oscillation cycle T of (n-1) is detected, and the subsequent oscillation cycle, preferably, By the next oscillation cycle (n), the set current Ip _set And after the turn-on, the primary winding current Ip becomes equal to the set current Ip _set At T1 (n), the switch element 3 is turned off.
[0074]
Hereinafter, by repeating this method, the output voltage V of the secondary output winding 2b is obtained. _2b Is always the set value V _2bset And constant voltage control can be performed.
[0075]
The detection of the output time T2 can be easily obtained by measuring the time during which the current flows through the diode 4 on the secondary side of the transformer 2. Here, in order to perform the constant voltage control only by the primary side circuit of the transformer 2, The analog input terminal Vd of the A / D converter 5c is connected to the low voltage side end of the primary winding 2a via the resistor 23, and the voltage (V _2a ) Is monitored to detect the output time T2.
[0076]
As shown in FIG. 2, an output time T2 during which the output current appears in the secondary output winding 2b is a period during which the energy stored in the transformer 2 is released. This time is a period after the oscillation switch element 3 is turned off. When the flyback voltage generated in the primary winding 2a decreases and the natural oscillation starts, the polarity at both ends of the primary winding 2a is reversed, and the time until the potential fluctuates around the voltage applied to the transformer 2 is reduced. equal.
[0077]
Therefore, after the arithmetic circuit 5a of the switch control circuit 5 outputs an off control signal for turning off from the D / A converter 5b, the polarity of the primary winding 2a is reversed and the primary winding voltage V _2a The output time T2 is detected from the time until the potential with respect to the voltage applied to the primary winding 2a of the waveform is first reversed. In the case of natural vibration, the primary winding voltage V _2a The time required for the waveform to reach the first minimum value is similar to the time required for the potential of the applied voltage of the primary winding 2a to first reverse, so that the output control signal is output and then the first minimum value is reached. The output time T2 may be detected from the measured time.
[0078]
In the switching power supply circuit 50, the primary winding current Ip is equal to the voltage drop V of the Ip detection resistor 22 due to the primary winding current Ip flowing from the analog input terminal Id of the A / D converter 5c. _ip Enter and detect. The voltage conversion in this manner is based on the voltage drop V _ip Gives the resistance value of the Ip detection resistor 22 as r _ip As r _ip × Ip, which can be calculated by the arithmetic circuit 5a as a converted value of the primary winding current Ip, and the voltage drop V is lower than the detection of the current Ip. _ip Is easier to detect.
[0079]
The arithmetic circuit 5a of the switch control circuit 5 substitutes the output time T2 detected by the above-described method into the equation (1), and sets the set current Ip _set Is calculated and the set current Ip _set The resistance value of the Ip detection resistor 22 to r _ip Potential V multiplied by _iset Is the voltage drop V input from the analog input terminal Id. _ip And the corresponding voltage drop V _ip Is input, the D / A converter 5b outputs an off control signal to turn off the switch element 3.
[0080]
In the first embodiment described above, the output voltage of the secondary output winding 2b is set to the set voltage V _2bset , The output voltage V of the rectifying and smoothing circuits 4 and 13 _2O Does not always have a constant voltage with high accuracy.
[0081]
That is, the output voltage V of the rectifying / smoothing circuits 4 and 13 _2o If Vf is a forward voltage drop of the diode 4 of the rectifying / smoothing circuit,
(Equation 15)

The forward voltage drop Vf is proportional to the passing current value, that is, the current Is of the secondary output winding 2b. _2b Is not a constant voltage even if the constant voltage is controlled.
[0082]
Assuming that a proportional constant to the output current Is corresponding to the forward voltage drop of the diode 4 is k, the equation (7) is _2b From the expression (6) developed for and the expression (5) developed for the output current Is,
(Equation 16)

It becomes. Here, if Np ÷ Ns × Ls is K1 and k ÷ Ls is K2, equation (8) becomes
[Equation 17]

It becomes.
[0083]
If the expression (9) is expanded for Ip and the replaced K1 is returned as Np ÷ Ns × Ls and K2 is returned as k ÷ Ls,
(Equation 18)

Is obtained.
[0084]
Here, Ns, Np, Ls, and k are constants determined by circuit elements. Therefore, if T2 is detected and its value is substituted into equation (10), the primary winding current Ip can be adjusted and adjusted. Output voltage V of the rectifying / smoothing circuit of _2o Is obtained.
[0085]
Therefore, in the second embodiment, the output voltage V _2o To the output voltage V of the rectifying / smoothing circuits 4 and 13 to be controlled at a constant voltage. _2oset Set to
[Equation 19]

Current Ip obtained from _set ', The on-time T1 is controlled so that the primary winding current Ip matches.
[0086]
The current Ip of the primary winding 2a is changed to the set current Ip _set Since the method of matching with 'and the method of detecting the primary winding current Ip and the output time T2 are the same as in the first embodiment, the description thereof will be omitted.
[0087]
An output time T2 during which a current flows through the secondary output winding 2b within a specific oscillation cycle T is detected, and the set current Ip is calculated by the following equation (2) by a later oscillation cycle. _set ′, And after the turn-on, the primary winding current Ip becomes the set current Ip _set 'At T1 when the switch element 3 is turned off, and thereafter, by repeating this method, the output voltage V of the rectifying / smoothing circuits 4 and 13 is reduced. _2o Is always equal to the set value V in consideration of the voltage drop Vf of the diode 4. _2oset And constant voltage control can be performed.
[0088]
In the first and second embodiments, the set current Ip is supplied from the analog input terminal Id of the A / D converter 5c. _set Or Ip _set ', A voltage drop V representing the primary winding current Ip reaching _ip , The set potential V _iset Is determined or exceeded, and a delay inherent to circuit elements such as the A / D converter 5c, the arithmetic circuit 5a, the D / A converter 5b, and the switch element 3 occurs until the switch element 3 is actually turned off. Has occurred.
[0089]
On the other hand, the primary winding current Ip is obtained by changing the voltage of the primary winding 2a to V _2a When the inductance of the primary winding 2a is Lp,
(Equation 20)

And increases in proportion to the voltage applied to the primary winding 2a after the turn-on
.
[0090]
As a result, as shown in FIG. 3, the current Ip ′ flowing through the primary winding 2a at the time of turn-off is changed to the set potential V _iset Voltage drop V compared to _ip Assuming that the total of the delay times due to the above circuit elements is δt, the increase δIp is given by the following equation (11).
(Equation 21)

It becomes.
[0091]
Here, the voltage V applied to the primary winding 2a during the ON period of the switch element 3 _2a By ignoring other voltage drops due to the exciting current on the circuit, the voltage V _2a Can be replaced with the power supply voltage Vcc of the DC power supply 1, and taking into account the increase in equation (12),
(Equation 22)

From the set current Ip _set Or Ip _set ′, The set current Ip _set Or Ip _set ′ Can be turned off at the timing when the primary winding current Ip substantially coincides with ′.
[0092]
In the above embodiment, the voltage-converted current Ip is converted to the voltage-converted set current Ip. _set Or Ip _set ′, The voltage drop input from the analog input terminal Id is V _ip And r on both sides of equation (3) _ip Multiplied by
[Equation 23]

Voltage drop V _ip Is the set potential V _iset Compare with
[0093]
FIG. 4 shows a case where the sub winding 2c is provided on the primary side of the transformer 2 and the voltage V _2c FIG. 10 is a circuit diagram showing a switching power supply circuit 60 according to a fourth embodiment of the present invention, which monitors the output time T2 by monitoring the output power T2.
[0094]
The switching power supply circuit 60 is different from the switching power supply circuit 50 shown in FIG. 1 in that a sub winding 2 c is further provided in the transformer 2, and the analog input terminal Vd of the A / D converter of the switch control circuit 6 is connected via the resistor 24. The only difference is the configuration connected to the low-pressure side end of the sub winding 2c.
[0095]
A voltage V of the primary winding 2a is applied to the sub winding 2c of the transformer 2. _2a Voltage V proportional to the turns ratio _2c Occurs, the time T2 until the polarity is inverted after the turn-off is equal in the sub winding 2c, and the voltage V of the sub winding 2c is supplied from the analog input terminal Vd of the A / D converter. _2c And T2 is detected by the arithmetic circuit in the switch control circuit 6. The other configuration is the same as that of the above-described embodiment, and the description thereof is omitted.
[0096]
FIG. 5 is a circuit diagram showing a constant voltage output control device 7 of a switching power supply circuit 70 according to a fifth embodiment of the present invention.
[0097]
In the present embodiment, the digital operation processing executed by the operation circuit 5a of the switch control circuit 5 is executed by analog processing using a comparison circuit and a logic circuit in the switch control circuit 7 acting as a constant voltage output control device. Things. Therefore, the configuration of the switch control circuit 7 which is different from each of the above-described embodiments will be described in detail.
[0098]
In the figure, reference numeral 71 denotes δt × VccｐLp × r in equation (13). _ip Is a delay correction circuit that outputs a correction voltage corresponding to the following. 72 is an oscillator that outputs a clock with a cycle equal to the oscillation cycle T of the switching power supply circuit 70, and 73 is a voltage V of the primary winding 2a. _2a The comparator 74 determines the polarity of the set potential V from the output time T2. _iset Is a time-voltage conversion circuit, 75 is a sample and hold circuit, and 76 is a set potential V _iset And a clamp circuit 77 for outputting a voltage waveform representing the following equation: _ip The adder 78 adds the correction voltage output from the delay correction circuit 71 to the correction voltage drop V. _ip Is the set potential V _iset The comparator 79 for comparing with is an AND gate.
[0099]
The constant voltage control operation of the switch control circuit 7 will be described. First, the output time T2 of the oscillating switching power supply circuit 70 is detected by the comparator 73. The comparator 73 connects the non-inverting input from the input terminal Vd to the low-voltage side end of the primary winding 2a via the resistor 23, _2a A voltage divided in proportion to the DC power supply 1 that enables detection of polarity inversion of the primary winding 2a is input to the inverting input, and a voltage divided in proportion to the DC power supply 1 is input to the inverting input. Voltage V _2a Output a waveform corresponding to the polarity of. Accordingly, the comparator 73 outputs an output waveform of “H” by the flyback voltage when the switch element 3 is turned off, and changes to “L” when the energy release of the transformer 2 is completed and the polarity is inverted.
[0100]
The time-voltage conversion circuit 74 sets the period during which “H” is output from the comparator 73 as the output time T2 and calculates Ip from the expression (1) or (2). _set Or Ip _set ′, And set these current values to r _ip Potential V multiplied by _iset Is output. The resistance value r of the Ip detection resistor 22 is added to the set current value. _ip Is multiplied by the resistance value r of the primary winding current Ip in the comparator 78. _ip Drop V multiplied by _ip This is to compare with
[0101]
The sample and hold circuit 75 sets the set potential V _iset And outputs the result to the clamp circuit 76.
[0102]
The clamp circuit 76 has a setting potential V output from the sample and hold circuit 75. _iset And the amplitude becomes the set potential V _iset Is output to the non-inverting input of the comparator 78.
[0103]
The current Ip flowing through the primary winding 2a during the oscillating operation is equal to the voltage drop V _ip That is, Ip × r _ip Voltage drop V _ip From the input terminal Id to one of the adders 77.
[0104]
The delay correction circuit 71 calculates the sum δt of the inherent delay times of the switch control circuit 7 and the switch element 3 measured by a measurement circuit (not shown) or the like and the power supply voltage Vcc of the DC power supply 1 input via the resistor 21. Δt × Vcc ÷ Lp × r in equation (13) _ip Is calculated and input to the other end of the adder 77.
[0105]
The adder 77 converts this correction voltage into a voltage drop V _ip (13), and outputs the result to the inverting input of the comparator 78.
[0106]
Therefore, the voltage drop V considering the delay time of the circuit element is supplied to the comparator 78. _ip Is input and the set potential V _iset And the voltage drop V output from the adder 77. _ip Is the set potential V _iset If it is less than or equal to “H”, the set potential V _iset Is exceeded, "L" is output to the AND gate 79.
[0107]
The AND gate 79 receives the output from the oscillator 72 and the comparator 78, and connects the output to the gate of the switch element 3. The AND gate 79 operates so as to control the switch element 3 to be ON only during the period when the logical product is “H”. I do.
[0108]
During a period in which the clock output from the oscillator 72 is “L”, the switch element 3 is turned off, and no exciting current flows through the primary winding 2 a of the transformer 2.
[0109]
The clock output from the oscillator 72 changes to “H”, and the output from the comparator 78 also changes to “H”, that is, the voltage drop V _ip Is the set potential V _iset , The output of the AND gate 79 is also at "H", so that the switch element 3 is turned on.
[0110]
Thereafter, a voltage drop V representing the primary winding current Ip in proportion to the ON time. _ip Also increases, the voltage drop V _ip Is the set potential V _iset Is exceeded, the output of the comparator 78 becomes "L", the output of the AND gate 79 also becomes "L", and the switch element 3 is turned off. Voltage drop V when this turn off _ip Is the set potential V _iset And the current Ip flowing through the primary winding 2a at that time is represented by Ip in the expression (1) or (2). _set Or Ip _set 'And the set output voltage V _2b Or output voltage V _2o Is obtained. By repeating this control at least during the oscillating operation, the set output voltage V _2b Or output voltage V _2o Constant voltage output control can be performed.
[0111]
In each of the above embodiments, the output period T2 until the oscillation operation of the entire switching power supply circuit is stabilized is unstable, and the set current Ip _set Or Ip _set ′ Cannot be set, so that the set current Ip _set Or Ip _set ′ Is the initial current value Ip _def (Or the initial potential V _idef ), And it is desirable to keep the ON time T1 constant.
[0112]
Further, the output time T2 does not necessarily need to be detected for each cycle T. For example, the output time T2 may be detected for each longer cycle different from the oscillation cycle T to perform the constant voltage control.
[0113]
Further, according to the present invention, not only is the voltage reduced only when an output voltage exceeding the set reference voltage value is generated, but also the output voltage of the secondary output winding 2b or the rectifying / smoothing circuit is reduced. Voltage to V _2b Or V _2o And the set output voltage is obtained, so that an output detection circuit is provided on the secondary side of the transformer 2 as described in the conventional example, and the output detection circuit is provided via an insulated signal transmission element such as a photocoupler. The present invention can be applied to a switching power supply circuit having a feedback circuit for transmitting a detection signal to the primary side, and can be used.
[0114]
【The invention's effect】
As described above, according to the present invention, even if there is variation in the circuit constants of the circuit elements, only the output time T2 changes, and the setting for performing the constant voltage control after obtaining the changing output time T2. Current Ip _set Since this does not affect the equation (1), the constant voltage control can be performed with high accuracy even in mass production.
[0115]
Further, even in the case of switching power supply circuits having different output voltage specifications, constant voltage output control can be performed with the same circuit components.
[0116]
Further, the constant voltage output can be controlled only by the output voltage detection circuit on the secondary side of the transformer or the primary side circuit without the optical coupling element.
[0117]
Further, according to the second and sixth aspects of the present invention, the output of the rectifying / smoothing circuit can be controlled at a constant voltage with high accuracy.
[0118]
Further, according to the third and seventh aspects of the present invention, it is not necessary to provide a signal transmission element for transmitting the detection result of the secondary side of the transformer to the primary side, and the constant voltage control can be performed only by the primary side circuit. It becomes possible.
[0119]
According to the fourth and eighth aspects of the invention, when the transformer is provided with a sub winding, the secondary side constant voltage output control is performed by monitoring the potential of the sub winding. be able to.
[0120]
Furthermore, according to the ninth aspect of the invention, even if there is a delay δt between the operation of the primary current detector of the transformer and the operation of the oscillating switch element, it is possible to accurately control the output voltage.
[0121]
Further, according to the tenth aspect of the present invention, the voltage drop V _ip And set potential V _iset And the primary winding current Ip at the time of turning off is set to the set current Ip _set Or Ip _set ', The comparison can be easily performed by a comparison circuit using a comparator without converting the current value.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a switching power supply circuit 50 according to a first embodiment of the present invention.
FIG. 2 is an enlarged view showing a voltage or current waveform of each part of the switching power supply circuit 50;
(A) shows the current (Ip) flowing through the primary winding 2a of the transformer 2;
(B) shows the current (Is) flowing through the secondary output winding 2b of the transformer 2,
(C) shows the voltage (V) of the primary winding 2a of the transformer 2; _2a ),
It is a waveform diagram shown respectively.
FIG. 3 is a graph showing a relationship between a current (Ip) flowing through a primary winding 2a of a transformer 2 after turning on and a time t after turning on.
FIG. 4 is a circuit diagram of a switching power supply circuit 60 according to a fourth embodiment of the present invention.
FIG. 5 is a circuit diagram showing a constant voltage output control device 7 of a switching power supply circuit 70 according to a fifth embodiment of the present invention.
FIG. 6 is a circuit diagram of a conventional switching power supply circuit 100.
[Explanation of symbols]
1 DC power supply
2 transformer
2a Primary winding
2b Secondary output winding
2c Secondary winding
3 Oscillation switch element
4 Rectifier diode (rectifier smoothing circuit)
5, 6, 7 switch control circuit
13. Smoothing capacitor (rectifying and smoothing circuit)
22 Ip detection resistor
73 Comparator (output time detector)
74 time-voltage conversion circuit (set value calculation circuit)
T1 ON time
T2 Output time during which the output appears on the rectification smoothing circuit
Vcc DC power supply voltage
V _2b Output voltage appearing on the secondary output winding
V _2bset Secondary output winding output voltage to be controlled by constant voltage
V _2o Output voltage of rectification smoothing circuit
V _2oset Output voltage of rectifying and smoothing circuit to be controlled by constant voltage
V _iset Set potential
Ip Primary winding current
Ip _set Set current
Ip _set ´ Set current
Np Number of turns of primary winding
Ns Number of turns of secondary output winding
Lp Inductance of primary winding
Ls Inductance of secondary output winding
k Constant of proportionality to output current of forward voltage drop of rectifier diode
δ Time difference from when the primary winding current Ip is detected to when the oscillation switch element stops ON control
r _ip Resistance value of Ip detection resistor

Claims (10)

A transformer (2) having a primary winding (2a) and a secondary output winding (2b);
An oscillation switch element (3) connected in series with the primary winding (2a) to a DC power supply (1) for exciting the primary winding (2a);
A switch control circuit (5) for controlling ON / OFF of the oscillation switch element (3);
The on-time (T1) of the oscillation switch element (3) of the switching power supply circuit including the rectifying and smoothing circuits (4, 13) for rectifying and smoothing the output of the secondary output winding (2b) is changed. A constant voltage output control method for constant voltage control of an output voltage V _2b appearing in a next output winding (2b),
The output voltage of the secondary output winding (2b) to be controlled at a constant voltage is V _2bset , the number of turns of the primary winding (2a) is Np, the number of turns of the secondary output winding (2b) is Ns, the secondary output winding When the inductance of (2b) is Ls, and the output time during which the output appears in the rectifying / smoothing circuits (4, 13) within the oscillation period (T) is T2,

When the current Ip flowing through the primary winding (2a) reaches the set current Ip _set determined from the above, the on-control of the oscillation switch element (3) is stopped and the on-time (T1) is adjusted. A constant voltage output control method for a switching power supply circuit. A transformer (2) having a primary winding (2a) and a secondary output winding (2b);
An oscillation switch element (3) connected in series with the primary winding (2a) to a DC power supply (1) for exciting the primary winding (2a);
A switch control circuit (5) for controlling ON / OFF of the oscillation switch element (3);
Rectification by changing the on-time (T1) of the oscillation switch element (3) of the switching power supply circuit including the rectification smoothing circuits (4, 13) for rectifying and smoothing the output of the secondary output winding (2b). A constant voltage output control method for constant voltage control of an output voltage _V2o of a smoothing circuit,
The output voltage of the rectifying / smoothing circuits (4, 13) to be controlled at a constant voltage is V _2oset , the number of turns of the primary winding (2a) is Np, the number of turns of the secondary output winding (2b) is Ns, and the secondary output winding is The inductance of the line (2b) is Ls, the output time during which the output appears in the rectifying / smoothing circuit (4, 13) within the oscillation period (T) is T2, and the forward voltage drop of the diode (4) in the rectifying / smoothing circuit is T2. When the proportional constant to the output current is k,

When the current Ip flowing through the primary winding (2a) reaches the set current Ip _set ′ obtained from the above, the ON control of the oscillation switch element (3) is stopped and the ON time (T1) is adjusted. A constant voltage output control method for a switching power supply circuit. The output time (T2) during which the output appears in the rectifying / smoothing circuits (4, 13) within the oscillation cycle (T) is the time from when the flyback voltage is generated in the primary winding (2a) until the first polarity inversion. The constant voltage output control method for a switching power supply circuit according to claim 1, wherein the constant voltage output is detected from the control signal. The output time (T2) during which the output appears in the rectifying / smoothing circuits (4, 13) within the oscillation period (T) is determined by the first polarity after the flyback voltage is generated in the sub winding (2c) of the transformer (2). 3. The constant voltage output control method for a switching power supply circuit according to claim 1, wherein the detection is performed from a time until the inversion. A transformer (2) having a primary winding (2a) and a secondary output winding (2b);
An oscillation switch element (3) connected in series with the primary winding (2a) to a DC power supply (1) for exciting the primary winding (2a);
A switch control circuit (7) for controlling ON / OFF of the oscillation switch element (3);
Rectifying and smoothing circuits (4, 13) for rectifying and smoothing the output of the secondary output winding (2b);
A constant-voltage output control device for a switching power supply circuit, wherein the on-time (T1) of the oscillation switch element (3) is changed to control the output voltage (V _2b ) appearing in the secondary output winding (2b) at a constant voltage. ,
A primary side current detector (Id) for detecting a current Ip flowing through the primary winding (2a) and an output time (T2) during which an output appears in the rectifying and smoothing circuits (4, 13) within the oscillation period (T). An output time detecting unit (73) for performing
The output voltage of the secondary output winding (2b) to be controlled at a constant voltage is V _2bset , the number of turns of the primary winding (2a) is Np, the number of turns of the secondary output winding (2b) is Ns, the secondary output winding Let Ls be the inductance of (2b),
An output time T2 detected by the output time detector,

A set value calculation circuit (74) for obtaining a _set current Ip _set from
A comparison circuit (78) for comparing the current Ip flowing through the primary winding (2a) with the set current Ip _set ;
When the current Ip reaches the set current Ip _set , the switch control circuit (7) stops the ON control of the oscillation switch element (3) and adjusts the ON time (T1). Circuit constant voltage output control device. A transformer (2) having a primary winding (2a) and a secondary output winding (2b);
An oscillation switch element (3) connected in series with the primary winding (2a) to a DC power supply (1) for exciting the primary winding (2a);
A switch control circuit (7) for controlling ON / OFF of the oscillation switch element (3);
Rectifying and smoothing circuits (4, 13) for rectifying and smoothing the output of the secondary output winding (2b);
A constant-voltage output control device for a switching power supply circuit for changing an on-time (T1) of an oscillation switch element (3) and controlling an output voltage (V _2o ) of a rectifying / smoothing circuit (4, 13) at a constant voltage. ,
A primary current detector (Id) for detecting a current Ip flowing through the primary winding (2a);
An output time detector (73) for detecting an output time (T2) during which an output appears in the rectifying / smoothing circuits (4, 13) within the oscillation cycle (T);
The output voltage of the rectifying / smoothing circuits (4, 13) to be controlled at a constant voltage is V _2oset , the number of turns of the primary winding (2a) is Np, the number of turns of the secondary output winding (2b) is Ns, and the secondary output winding is Let Ls be the inductance of the line (2b) and k be a proportional constant to the output current of the forward voltage drop of the diode (4) of the rectifying / smoothing circuit.
An output time T2 detected by the output time detection unit (73);

A set value calculation circuit (74) for obtaining a _set current Ip _set ′ from
A comparison circuit (78) for comparing the current Ip flowing through the primary winding (2a) with the set current Ip _set ′;
When the current Ip reaches the set current Ip _set ′, the switch control circuit (7) stops the ON control of the oscillation switch element (3) and adjusts the ON time (T1). Constant voltage output control device for power supply circuit. Monitors the voltage V _2a of the primary winding (2a), comprising a primary winding voltage monitoring circuit that detects (73) the time from the flyback voltage is generated until the first polarity reversal,
7. The switching power supply circuit according to claim 5, wherein a time from when a flyback voltage is generated in the primary winding to when the first polarity inversion occurs is defined as an output time (T2). Voltage output control device. A secondary winding (2c) further provided on the primary side of the transformer (2);
A sub-winding voltage monitoring circuit that monitors the voltage V _2c of the sub-winding (2c) and detects the time from when the flyback voltage is generated until the first polarity inversion,
7. The switching power supply circuit according to claim 5, wherein the time from when the flyback voltage is generated in the sub winding (2c) until the first polarity inversion is set as the output time (T2). Voltage output control device. After the primary current detector detects the primary winding current Ip reaching the _set current Ip _set or Ip _set ′, the time difference until the oscillation switch element (3) stops ON control is δt, and the DC power supply (1) Vcc, the inductance of the primary winding (2a) is Lp,

7. The constant voltage output control device for a switching power supply circuit according to claim 5, wherein Ip ′ obtained from the above is set as a set current Ip _set or a current Ip to be compared with Ip _set ′. The primary-side current detection unit connects an Ip detection resistor (22) having a resistance value r _{ip in} series with the primary winding (2a), detects a current Ip from a voltage drop V _ip caused by the Ip detection resistor (22),
Comparison circuit, 'multiplied by the resistance value _{r ip,} the set current _{Ip The set} or _{Ip The set'} and the voltage drop _{V ip,} set current _{Ip The set} or _{Ip The set} compares the set potential _{V iset} that represents the current Ip and the set current The constant voltage output control device for a switching power supply circuit according to claim 5, wherein Ip _set or Ip _set ′ is compared.

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