JP4251877B2

JP4251877B2 - Power circuit

Info

Publication number: JP4251877B2
Application number: JP2003025397A
Authority: JP
Inventors: 修齊藤; 茂久田
Original assignee: Shindengen Electric Manufacturing Co Ltd
Current assignee: Shindengen Electric Manufacturing Co Ltd
Priority date: 2003-02-03
Filing date: 2003-02-03
Publication date: 2009-04-08
Anticipated expiration: 2023-02-03
Also published as: JP2004234584A

Description

【０００１】
【発明の属する技術分野】
本発明は、電源回路に関するものであって、この電源回路のメインスイッチをオン・オフ動作させ、直流電源電圧を昇降圧させるトランスを駆動するとともに、メインスイッチを流れる電流の過電流を検出する過電流検出回路を備えた電源回路に関するものである。
【０００２】
【従来の技術】
図１８に、従来の過電流検出回路を備えた電源回路の要部を示す。また図１９にこの回路に係る動作波形図を示し、図２０にレベル波形図を示す。この従来の電源回路に備えた過電流保護回路２は過電流検出回路６０と過電流検出抵抗３とを備え、ＭＯＳＦＥＴで構成したメインスイッチ１のソース端子に過電流検出回路６０と過電流検出抵抗３とを接続し、過電流検出回路６０はコンパレータ６１を備え、このコンパレータ６１の正側の入力端子にメインスイッチ１のソース端子を接続し、同じくコンパレータ６１の負側の入力端子に基準電圧生成部６２を接続し、同じくコンパレータ６１の出力端子にメインスイッチ１のオン・オフを制御するように構成してある。
【０００３】
また、メインスイッチを流れる電流の過電流を検出し、その過電流検出信号を出力する過電流検出回路からの過電流検出信号をラッチして、メインスイッチのオン・オフ動作を禁止する動作禁止信号を発生して、メインスイッチのオン・オフ動作を停止させる制御回路における動作禁止信号の発生を継続させるとともに、直流電源の遮断に基づいてそのラッチ動作を解除するラッチ回路を備えた電源回路もある（例えば、特許文献１参照）。
【０００４】
【特許文献１】
特開平１１−６９７９６号公報（第３−５頁、第１図）
【０００５】
【発明が解決しようとする課題】
いずれの電源回路においても、過電流検出抵抗３の端子電圧が基準以上になるとコンパレータ出力がハイになり、メインスイッチ１のゲート端子がリセットされる。電源回路の入力電圧が変わっても過電流保護レベルは常に基準以上で一定であり、電源回路の出力電力は主電圧Ｖinとメインスイッチ１のドレイン電流Ｉdで決まる。よって、入力が高いときは、出力電力が大きくなり、負荷短絡電流も大きくなるという課題が生じた。
【０００６】
本発明は、上記問題に鑑みてなされたものであり、メインスイッチのオン幅に合わせて、過電流保護レベルを変えることができる電源を提供する。
【０００７】
【課題を解決しようとする手段】
上記目的を達成するためになされた本発明は、電源の入力電圧に対する垂下点変動が小さくなる効果がある。出力巻線短絡時のメインスイッチの電流ピークを抑え、メインスイッチの破損を防止することができる。さらに、巻線短絡電流や負荷短絡電流を低減できる。
【０００８】
通常、入力電圧が高くなると垂下点が伸びるため、短絡電流も大きくなるが、本発明によれば、入力が高いときの垂下点を入力が低いときと同程度にできるため、短絡電流の低減ができる。
【０００９】
【発明の実施の形態】
以下、添付図面を用いて本発明電源回路に係る実施例を説明する。本発明に係る電源回路の第一実施例の要部を図１に示し、その動作波形図を図２及び図３に示す。１はメインスイッチ、２は過電流保護回路、３は過電流検出抵抗、１０は過電流検出回路、３０は第二の過電流検出回路である。
【００１０】
本発明に係る電源回路は過電流保護回路２を備えてあり、この第一実施例に係る電源回路に係る過電流保護回路２は過電流検出抵抗３と過電流検出回路１０，３０とを備えてある。過電流検出抵抗３及び過電流検出回路１０，３０をＭＯＳＦＥＴで構成した電源回路のメインスイッチ１のソース端子に接続してある。過電流検出回路１０，３０はコンパレータ１１，３１を備えてある。コンパレータ１１，３１の正側の入力端子にメインスイッチ１のソース端子を接続し、同じくコンパレータ１１，３１の負側の入力端子に基準電圧生成部１２，３２を接続してある。なお、本実施例では過電流検出抵抗３をメインスイッチ１のソース端子に接続してあるが、メインスイッチ１のオン抵抗を利用してもよい。また、本実施例ではメインスイッチ１をＭＯＳＦＥＴで構成してあるが、トランジスタやＩＧＢＴで構成してもよい。
【００１１】
第二の過電流検出回路３０の基準電圧生成部３２は定電圧源のみで構成してあるのに対し、第一の過電流検出回路１０の基準電圧生成部１２は定電圧源１３とスイッチ１４とコンデンサ１５とからなり、定電圧源１３とコンデンサ１５とを直列に接続し、この直列回路にスイッチ１４を並列に接続してあり、メインスイッチ１のオン・オフに応じてレベルが変えられるように構成してある。また、基準電圧生成部１２とコンパレータ１１との間に接続部を設け、この接続部に基準電圧生成部１２に電流を供給する定電流回路１６を接続し、メインスイッチ１のオン幅に合わせてリニアに変えるようにしてある。過電流検出回路１０，３０の出力端子をＯＲ回路３３のそれぞれの入力端子に接続し、ＯＲ回路３３の出力端子を直接若しくは間接的にメインスイッチ１のゲート端子に接続し、メインスイッチ１のオン・オフを制御するように構成してある。
【００１２】
第一実施例は以上のように構成し、以下のような作用をする。メインスイッチ１がオンのとき、第一の過電流検出回路１０に設けたスイッチ１４は同期してオフする。定電流回路１６から電流が流れて、基準電圧生成部１２に設けたコンデンサ１５は充電されるとともに、図２に示すように基準電圧は上昇する。コンパレータ１１において過電流検出抵抗３で検出された信号と基準信号とが比較され、メインスイッチ１のゲートリセット信号として出力する。
【００１３】
一方、第二の過電流検出回路３０の基準電圧は、図３に示すように一定であり、こちらも過電流検出抵抗３で検出された信号と基準信号とが比較され、メインスイッチ１のゲートリセット信号として出力する。これらはＯＲ回路３３により決定され、メインスイッチ１がオンになった段階では、第一の過電流検出回路１０から出力したゲートリセット信号が採用され、図２に示すように、このゲートリセット信号がメインスイッチ１の制御端子に出力され、第一の過電流検出回路１０の基準レベルが第二の過電流検出回路３０の基準レベルより上回ると、第二の過電流検出回路３０から出力したゲートリセット信号が採用され、図３に示すように、このゲートリセット信号がメインスイッチ１に出力される。
【００１４】
メインスイッチ１がオフのとき、第一の過電流検出回路１０に設けたスイッチ１４は同期してオンする。コンデンサ１５は放電し、メインスイッチ１が再びオンした際に、上記の作用が可能になる。
【００１５】
続いて、本発明に係る電源回路の第二実施例の要部を図４に示す。第二実施例に係る電源回路は、過電流保護回路２は過電流検出抵抗３と過電流検出回路１０とを設けた過電流保護回路２を備えてある。過電流検出抵抗３及び過電流検出回路１０を電源回路のメインスイッチ１のソース端子に接続してある。過電流検出回路１０はコンパレータ１１を備えてある。コンパレータ１１の正側の入力端子にメインスイッチ１のソース端子を接続し、同じくコンパレータ１１の負側の入力端子に基準電圧生成部１２を接続してある。この基準電圧生成部１２は定電圧源１３とスイッチ１４とコンデンサ１５とからなり、定電圧源１３とスイッチ１４とを直列に接続し、この直列回路にコンデンサ１５を並列に接続してあり、メインスイッチ１のオン・オフに応じてレベルが変えられるように構成してある。
【００１６】
基準電圧生成部１２とコンパレータ１１との間の接続部に定電流回路１６を接続し、メインスイッチ１のオン幅に合わせてリニアに変えるようにしてある。また、この定電流回路１６の接続部とコンパレータ１１との間に接続部を設け、この接続部にクランプ手段である抵抗１７を接続し、基準電圧生成部１２の最大電圧を制限するようにしてある。なお、抵抗１７の変わりにツェナーダイオードを設けてもよい。また、定電流回路１６の電圧源をある基準に設定することによっても、基準電圧生成部１２の最大電圧を制限するができる。コンパレータ１１の出力端子をメインスイッチ１の制御端子に接続してある。
【００１７】
第二実施例は以上のように構成し、以下のような作用をする。メインスイッチ１がオンのとき、過電流検出回路１０に設けたスイッチ１４は同期してオフする。基準電圧生成部１２に設けたコンデンサ１５は充電して立ち上がり、基準電圧は上昇する。コンパレータ１１で、過電流検出抵抗３で検出された信号と基準信号とが比較され、メインスイッチ１のゲートリセット信号として出力する。
【００１８】
本実施例においては、定電流回路１６の接続部とコンパレータ１１との間の接続部に抵抗１７を接続してあることにより、基準電圧の最大電圧を制限することができる。即ち、抵抗１７によって設定した基準電圧が最大電圧に達すると、コンパレータ１１の基準レベルは抵抗でクランプされた値で一定になる。従って、この抵抗１７を用いたことにより、動作波形が図３で示す第一の実施例の動作波形とほぼ等しくなり、第二の過電流検出回路３０は必要なくなる。
【００１９】
メインスイッチ１がオフのとき、第二の過電流検出回路１０に設けたスイッチ１４は同期してオンする。これにより、コンデンサ１５は定電圧源１３のレベルまで放電し、メインスイッチ１が再びオンした際に、上記の作用が可能になる。
【００２０】
続いて、本発明に係る電源回路の第三実施例の要部を図５に示し、その動作波形図を図６に示す。第三実施例に係る電源回路は、第一実施例と概ね同じ構成であるが、第一の過電流検出回路１０の基準電圧生成部１２とコンパレータ１１との間に接続部を設け、この接続部に定電流回路１６の変わりに抵抗１８を設けてある。
【００２１】
第三実施例は以上のように構成し、以下のような作用をする。メインスイッチ１がオンのとき、第一の過電流検出回路１０に設けたスイッチ１４は同期してオフする。基準電圧生成部１２に設けたコンデンサ１５は充電して立ち上がる。この場合、電流供給回路に抵抗１８を設けたため、抵抗１８とコンデンサ１５との充電特性により、図６に示すように基準電圧は曲線的に上昇する。コンパレータ１１で、過電流検出抵抗３で検出された信号と基準信号とが比較され、メインスイッチ１のゲートリセット信号として出力する。なお、その他の作用は第一実施例とほぼ同様である。
【００２２】
続いて、本発明に係る電源回路の第四実施例の要部を図７に示し、その動作波形図を図８に示す。第四実施例に係る電源回路は、第一実施例と概ね同じ構成であるが、第一の過電流検出回路１０の基準電圧生成部１２を構成する定電圧源１３とコンデンサ１５との直列回路とこの直列回路と並列に接続したスイッチ１４との間に接続部を設け、この接続部に第二の電流供給回路を接続してある。この電流供給回路はスイッチ１９と定電流回路２０とを直列に接続し、メインスイッチ１のオン期間の途中でこのスイッチ１９をオフさせ、第一の過電流検出回路１０の検出レベルを二段階に切り替えられるように構成してある。なお、本実施例では、第一の過電流検出回路１０の検出レベルを二段階に切り替えられるように構成してあるが、基準電圧生成部１２のコンデンサ１５とコンパレータ１１との間に接続部を複数設け、これらにそれぞれ電流供給回路を設けることにより、検出レベルを三段階以上に切り替えることができる。
【００２３】
第四実施例は以上のように構成し、以下のような作用をする。メインスイッチ１がオンのとき、第一の過電流検出回路１０の基準電圧生成部１２に設けたスイッチ１４は同期してオフする。一方、第二の電流供給回路に設けたスイッチ１９はオンし、図８に示すように、基準電圧生成部１２に設けたコンデンサ１５は充電して立ち上がり、基準電圧は上昇する。コンパレータ１１で、過電流検出抵抗３で検出された信号と基準信号とが比較され、メインスイッチ１のゲートリセット信号として出力する。続いて、メインスイッチ１がオンしている途中で第二の電流供給回路に設けたスイッチ１９はオフすると、定電流は１箇所で供給されることになり、電圧の上昇が緩やかになる。即ち、第四実施例は上記構成により、第一の過電流検出回路１０の検出レベルを二段階に切り替えることができる。なお、その他の作用は第一実施例とほぼ同様である。
【００２４】
続いて、本発明に係る電源回路の第五実施例の要部を図９に示し、その動作波形図を図１０に示す。第五実施例に係る電源回路は、第一実施例と概ね同じ構成であるが、第一の過電流検出回路１０の基準電圧生成部１２は、定電圧源１３と直列にコンデンサ１５を接続して直列回路を構成し、コンデンサ１５と並列にスイッチ１４を接続して構成してある。
【００２５】
第五実施例は以上のように構成し、以下のような作用をする。メインスイッチ１がオフのときは、第一の過電流検出回路１０の基準電圧生成部１２に設けたスイッチ１４は同期してオフする。そのため、定電流回路１６から定電流が流れるとともに、コンデンサ１５は充電される。一方、メインスイッチ１がオンのとき、第一の過電流検出回路１０の基準電圧生成部１２に設けたスイッチ１４は同期して瞬時オンする。このとき、検出レベルは下がるが、基準電圧生成部１２に設けたコンデンサ１５は、図１０に示すように第一の過電流検出回路１０の基準電圧Voffsetまでしか下がらない。その後、スイッチ１４が再びオフすると、定電流回路１６から定電流が流れるとともに、コンデンサ１５は充電され、基準電圧は上昇する。なお、その他の作用は第一実施例とほぼ同様である。
【００２６】
続いて、第六実施例について説明する。なお、第六実施例の回路構成は第五実施例と同じである。なお、第六実施例の動作波形図を図１１及び図１２に示す。以上のように構成し、以下のような作用をする。第六実施例では、メインスイッチ１がオフのときに、第一の過電流検出回路１０の基準電圧生成部１２に設けたスイッチ１４は同期してオンさせる。このとき、定電圧源１３の作用により基準電圧は定電圧源１３で決定されるVoffsetで一定の状態になる。一方、メインスイッチ１がオンになると、しばらくの間、第一の過電流検出回路１０の基準電圧生成部１２のスイッチ１４はオンしており、メインスイッチ１がオフのときと同様、基準電圧は定電圧源１３で決定されるVoffsetで一定の状態にある。基準電圧生成部１２のスイッチ１４がオフすると、定電流回路１６より定電流が流れるとともに、コンデンサ１５は充電され、基準電圧は上昇する。基準電圧生成部１２に設けたコンデンサ１５は、図１０に示すように基準電圧Voffsetまでしか下がらない。その後、コンデンサ１５を充電して立ち上がり、基準電圧は上昇する。第一の過電流検出回路１０の基準レベルが第二の過電流検出回路３０の基準レベルより上回ると、第二の過電流検出回路３０から出力したゲートリセット信号が採用され、図１１に示すように、このゲートリセット信号がメインスイッチ１に出力される。
【００２７】
続いて、本発明に係る電源回路の第七実施例の要部を図１３に示す。第七実施例に係る電源回路は、過電流保護回路２は過電流検出抵抗３と過電流検出回路１０とを設けてあり、過電流検出抵抗３を電源回路のメインスイッチ１のソース端子に接続してある。過電流検出回路１０にコンパレータ１１を設け、このコンパレータ１１の正側の入力端子にメインスイッチ１のソース端子を接続し、同じくコンパレータ１１の負側の入力端子に基準電圧生成部１２を接続してある。この基準電圧生成部１２は抵抗２１，２２を直列に接続し、接地側の抵抗２１に並列にスイッチ２３を接続してある。このスイッチ２３の制御端子にタイマー回路４０を接続してある。このタイマー回路４０はメインスイッチ１のオンを検出し、ある一定の時間が経つと、過電流検出回路１０の検出レベルを変化させる回路である。
【００２８】
第七実施例は以上のように構成し、以下のような作用をする。メインスイッチ１がオフのとき、タイマー回路４０はハイ信号を出力し、過電流検出回路１０のスイッチ２３は同期してオンする。逆にメインスイッチ１がオンすると、タイマー回路４０がメインスイッチ１のオンを検出し、ある一定の時間の後、ロー信号を出力する。メインスイッチ１がオンした後、しばらくの間はタイマー回路４０の出力がハイ信号を出力しているため、過電流検出回路１０のスイッチ２３はオンの状態にあるので、定電流回路１６は抵抗２２のみにかかり、図１４に示すように、過電流検出回路１０の基準電圧はＶref2になる。
【００２９】
タイマー回路４０はメインスイッチ1がオンした後、メインスイッチ１のオン時間を検出して、ある一定の時間の後、ロー信号を出力する。タイマー回路４０の出力がロー信号の時、スイッチ２３はオフする。メインスイッチ１がオフするとタイマー回路４０はハイ信号を出力し、スイッチ２３はオンする。
【００３０】
メインスイッチ１がオンし、一定の時間をタイマー回路４０が検出すると、タイマー回路４０はロー信号を出力し、過電流検出回路１０のスイッチ２３がオフする。よって、定電流回路１６は抵抗２１にもかかり、図１４に示すように、過電流検出回路１０の基準電圧はＶref1＋Ｖref2になる。以上より、タイマー回路４０でメインスイッチ１のオンを検出し、ある一定の時間の後、スイッチ２３を制御することで、過電流検出回路１０の検出レベルを変化させることができる。
【００３１】
続いて、本発明に係る電源回路の第八実施例の要部を図１６に示す。第八実施例に係る電源回路は、第七実施例と概ね同じ構成であるが、この実施例に係る電源回路は、コンパレータ１１の負側の入力端子に基準電圧生成部１２を接続してあり、この基準電圧生成部１２は抵抗２１，２２を並列に接続し、一方の抵抗２１と並列に、且つ、他方の抵抗２２と直列にスイッチ２３を接続してある。このスイッチ２３の制御端子に第七実施例と同様にタイマー回路４０を接続してある。
【００３２】
第八実施例は以上のように構成し、以下のような作用をする。メインスイッチ１がオフのとき、タイマー回路４０はハイ信号を出力し、過電流検出回路１０のスイッチ２３はオンの状態にあるので、定電流回路１６は抵抗２１及び抵抗２２にかかり、過電流検出回路１０の基準電圧は抵抗２１，２２の合成抵抗分だけ下がる。
【００３３】
メインスイッチ１がオンすると、タイマー回路４０の出力はハイ信号を出力しており、過電流検出回路１０のスイッチ２３は同期してオン状態にある。このときの基準電圧は抵抗２１及び抵抗２２の合成抵抗で決定される。この後、タイマー回路４０がメインスイッチ１のオンを検出し、ある一定の時間の後、タイマー回路４０はロー信号を出力し、スイッチ２３がオフし、定電流回路１６は抵抗２１のみにかかり、過電流検出回路１０の基準電圧は上昇する。
以上より、タイマー回路４０でメインスイッチ１のオンを検出し、ある一定の時間の後、スイッチ２３を制御することで、過電流検出回路１０の検出レベルを変化させることができる。
【００３４】
続いて、本発明に係る電源回路の第九実施例の要部を図１７に示す。この第九実施例に係る電源回路は、第七実施例と概ね同じ構成であるが、この実施例に係る電源回路は、コンパレータ１１の負側の入力端子に基準電圧生成部１２を接続してあり、この基準電圧生成部１２は抵抗２１，２２，２５を直列に接続し、接地側の抵抗２１に並列にスイッチ２３を接続するとともに、この抵抗２１に接続する抵抗２５にも並列にスイッチ２６を接続してある。これらスイッチ２３，２６の制御端子にタイマー回路４０を接続してある。
【００３５】
第四実施例は以上のように構成し、以下のような作用をする。メインスイッチ１がオフのとき、タイマー回路４０の２つの出力は共にハイ信号を出力し、過電流検出回路１０のスイッチ２３，２６は同期してオンする。過電流検出回路１０のスイッチ２３，２６はオンの状態にあるので、定電流回路１６は抵抗２２のみにかかり、過電流検出回路１０の基準電圧はＶref2になる。
【００３６】
メインスイッチ１がオンすると、タイマー回路４０がメインスイッチ１のオンを検出し、ある一定の時間がたつと、まず、スイッチ２３のみオフさせる。これにより、定電流回路１６は抵抗２２及び２１にかかり、過電流検出回路１０の基準電圧はＶref2＋Ｖref１になる。さらにメインスイッチ１のオン幅が広がると、タイマー回路４０がスイッチ２５をオフさせ、定電流回路１６は抵抗２５にもかかり、過電流検出回路１０の基準電圧はＶref2＋Ｖref１＋Ｖref3になる。第九実施例は上記構成により、過電流検出回路１０の基準電圧を三段階に切り替えることができる。なお、その他の作用は第七実施例とほぼ同様である。
【００３７】
なお、本実施例では、第一の過電流検出回路１０に三つの抵抗を直列に接続することにより、基準電圧生成部１２の電圧を三段階に切り替えられるように構成してあるが、基準電圧生成部１２の抵抗を四つ以上直列に接続して、基準電圧生成部１２の電圧を四段階以上に切り替えることができる。
【００３８】
【発明の効果】
本発明によれば、電源の入力電圧に対する垂下点変動が小さくなる効果がある。出力巻線短絡時のメインスイッチの電流ピークを抑え、メインスイッチの破損を防止することができる効果がある。さらに、巻線短絡電流や負荷短絡電流を低減できる効果がある。
【００３９】
また、通常、入力電圧が高くなると垂下点が伸びるため、短絡電流も大きくなるが、本発明によれば、入力が高いときの垂下点を入力が低いときと同程度にできるため、短絡電流の低減ができる効果がある。
【図面の簡単な説明】
【図１】本発明に係る第一実施例の要部の回路図である。
【図２】第一実施例に係る動作波形図である。
【図３】第一実施例に係るレベル波形図である。
【図４】本発明に係る第二実施例の要部の回路図である。
【図５】本発明に係る第三実施例の要部の回路図である。
【図６】第三実施例に係るレベル波形図である。
【図７】本発明に係る第四実施例を示す要部の回路図である。
【図８】第四実施例に係るレベル波形図である。
【図９】本発明に係る第五及び第六実施例の要部の回路図である。
【図１０】第五実施例に係る動作波形図である。
【図１１】第六実施例に係るレベル波形図である。
【図１２】第六実施例に係る動作波形図である。
【図１３】本発明に係る第七実施例の要部の回路図である。
【図１４】第七実施例に係るレベル波形図である。
【図１５】第七実施例に係る動作波形図である。
【図１６】本発明に係る第八実施例の要部の回路図である。
【図１７】本発明に係る第九実施例の要部の回路図である。
【図１８】従来例の要部の回路図である。
【図１９】従来例に係る動作波形図である。
【図２０】従来例に係るレベル波形図である。
【符号の説明】
１メインスイッチ
２過電流保護回路
３過電流検出抵抗
１０，３０，６０過電流検出回路
１１，３１，４１，６１コンパレータ
１２，３２，４２，６２基準電圧生成部
１３定電圧源
１４，１９，２３，２６，４３スイッチ
１５，４４コンデンサ
１６，２０，４６定電流回路
１７，１８，２１，２２，２４，２５抵抗
３３ＯＲ回路
４０タイマー回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply circuit. The main switch of the power supply circuit is turned on / off to drive a transformer that raises or lowers a DC power supply voltage, and detects an overcurrent of a current flowing through the main switch. The present invention relates to a power supply circuit including a current detection circuit.
[0002]
[Prior art]
FIG. 18 shows a main part of a power supply circuit provided with a conventional overcurrent detection circuit. FIG. 19 shows an operation waveform diagram relating to this circuit, and FIG. 20 shows a level waveform diagram. The overcurrent protection circuit 2 provided in the conventional power supply circuit includes an overcurrent detection circuit 60 and an overcurrent detection resistor 3, and the overcurrent detection circuit 60 and the overcurrent detection resistor are connected to the source terminal of the main switch 1 formed of a MOSFET. 3, the overcurrent detection circuit 60 includes a comparator 61, the source terminal of the main switch 1 is connected to the positive input terminal of the comparator 61, and the reference voltage generation is similarly applied to the negative input terminal of the comparator 61. The unit 62 is connected, and the output terminal of the comparator 61 is also configured to control on / off of the main switch 1.
[0003]
In addition, an over-current detection signal from the over-current detection circuit that detects the over-current of the current flowing through the main switch and outputs the over-current detection signal is latched, and an operation inhibition signal that inhibits the on / off operation of the main switch There is also a power supply circuit provided with a latch circuit that continues the generation of the operation prohibition signal in the control circuit that stops the on / off operation of the main switch and releases the latch operation based on the interruption of the DC power supply. (For example, refer to Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-69796 (page 3-5, FIG. 1)
[0005]
[Problems to be solved by the invention]
In any power supply circuit, when the terminal voltage of the overcurrent detection resistor 3 becomes equal to or higher than the reference, the comparator output becomes high and the gate terminal of the main switch 1 is reset. Even if the input voltage of the power supply circuit changes, the overcurrent protection level is always constant above the reference, and the output power of the power supply circuit is determined by the main voltage Vin and the drain current Id of the main switch 1. Therefore, when the input is high, there is a problem that the output power increases and the load short-circuit current also increases.
[0006]
The present invention has been made in view of the above problems, and provides a power supply capable of changing the overcurrent protection level in accordance with the ON width of the main switch.
[0007]
[Means to solve the problem]
The present invention, which has been made to achieve the above object, has the effect of reducing the droop point variation with respect to the input voltage of the power supply. The current peak of the main switch when the output winding is short-circuited can be suppressed, and the main switch can be prevented from being damaged. Furthermore, the winding short circuit current and the load short circuit current can be reduced.
[0008]
Normally, when the input voltage is increased, the droop point is extended, so that the short circuit current is also increased. it can.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the power supply circuit of the present invention will be described below with reference to the accompanying drawings. The main part of the first embodiment of the power supply circuit according to the present invention is shown in FIG. 1, and the operation waveform diagrams thereof are shown in FIGS. Reference numeral 1 denotes a main switch, 2 an overcurrent protection circuit, 3 an overcurrent detection resistor, 10 an overcurrent detection circuit, and 30 a second overcurrent detection circuit.
[0010]
The power supply circuit according to the present invention includes an overcurrent protection circuit 2, and the overcurrent protection circuit 2 according to the power supply circuit according to the first embodiment includes an overcurrent detection resistor 3 and overcurrent detection circuits 10 and 30. It is. The overcurrent detection resistor 3 and the overcurrent detection circuits 10 and 30 are connected to the source terminal of the main switch 1 of the power supply circuit composed of MOSFETs. The overcurrent detection circuits 10 and 30 are provided with comparators 11 and 31, respectively. The source terminals of the main switch 1 are connected to the positive input terminals of the comparators 11 and 31, and the reference voltage generators 12 and 32 are connected to the negative input terminals of the comparators 11 and 31. Although the overcurrent detection resistor 3 is connected to the source terminal of the main switch 1 in this embodiment, the on-resistance of the main switch 1 may be used. In the present embodiment, the main switch 1 is constituted by a MOSFET, but it may be constituted by a transistor or an IGBT.
[0011]
The reference voltage generation unit 32 of the second overcurrent detection circuit 30 is composed of only a constant voltage source, whereas the reference voltage generation unit 12 of the first overcurrent detection circuit 10 includes a constant voltage source 13 and a switch 14. The constant voltage source 13 and the capacitor 15 are connected in series, and the switch 14 is connected in parallel to the series circuit so that the level can be changed according to the on / off of the main switch 1. It is configured. In addition, a connection portion is provided between the reference voltage generation unit 12 and the comparator 11, and a constant current circuit 16 that supplies current to the reference voltage generation unit 12 is connected to the connection portion so as to match the ON width of the main switch 1. It changes to linear. The output terminals of the overcurrent detection circuits 10 and 30 are connected to the respective input terminals of the OR circuit 33, the output terminal of the OR circuit 33 is connected directly or indirectly to the gate terminal of the main switch 1, and the main switch 1 is turned on. -It is configured to control off.
[0012]
The first embodiment is configured as described above and operates as follows. When the main switch 1 is on, the switch 14 provided in the first overcurrent detection circuit 10 is turned off in synchronization. A current flows from the constant current circuit 16, the capacitor 15 provided in the reference voltage generation unit 12 is charged, and the reference voltage rises as shown in FIG. The comparator 11 compares the signal detected by the overcurrent detection resistor 3 with the reference signal and outputs the signal as a gate reset signal of the main switch 1.
[0013]
On the other hand, the reference voltage of the second overcurrent detection circuit 30 is constant as shown in FIG. 3, and the signal detected by the overcurrent detection resistor 3 is also compared with the reference signal, and the gate of the main switch 1 is compared. Output as a reset signal. These are determined by the OR circuit 33. When the main switch 1 is turned on, the gate reset signal output from the first overcurrent detection circuit 10 is adopted. As shown in FIG. When the reference level of the first overcurrent detection circuit 10 is output to the control terminal of the main switch 1 and exceeds the reference level of the second overcurrent detection circuit 30, the gate reset output from the second overcurrent detection circuit 30 The signal is adopted, and the gate reset signal is output to the main switch 1 as shown in FIG.
[0014]
When the main switch 1 is off, the switch 14 provided in the first overcurrent detection circuit 10 is turned on in synchronization. The capacitor 15 is discharged, and the above-described operation becomes possible when the main switch 1 is turned on again.
[0015]
Next, the main part of the second embodiment of the power supply circuit according to the present invention is shown in FIG. In the power supply circuit according to the second embodiment, the overcurrent protection circuit 2 includes an overcurrent protection circuit 2 provided with an overcurrent detection resistor 3 and an overcurrent detection circuit 10. The overcurrent detection resistor 3 and the overcurrent detection circuit 10 are connected to the source terminal of the main switch 1 of the power supply circuit. The overcurrent detection circuit 10 includes a comparator 11. The source terminal of the main switch 1 is connected to the positive input terminal of the comparator 11, and the reference voltage generator 12 is connected to the negative input terminal of the comparator 11. The reference voltage generator 12 includes a constant voltage source 13, a switch 14, and a capacitor 15. The constant voltage source 13 and the switch 14 are connected in series, and the capacitor 15 is connected in parallel to the series circuit. The level is changed according to whether the switch 1 is turned on or off.
[0016]
A constant current circuit 16 is connected to a connection portion between the reference voltage generation unit 12 and the comparator 11 so as to change linearly according to the ON width of the main switch 1. Further, a connecting portion is provided between the connecting portion of the constant current circuit 16 and the comparator 11, and a resistor 17 as a clamping means is connected to the connecting portion so as to limit the maximum voltage of the reference voltage generating portion 12. is there. A Zener diode may be provided instead of the resistor 17. The maximum voltage of the reference voltage generator 12 can also be limited by setting the voltage source of the constant current circuit 16 to a certain reference. The output terminal of the comparator 11 is connected to the control terminal of the main switch 1.
[0017]
The second embodiment is configured as described above and operates as follows. When the main switch 1 is on, the switch 14 provided in the overcurrent detection circuit 10 is turned off in synchronization. The capacitor 15 provided in the reference voltage generator 12 is charged and rises, and the reference voltage rises. The comparator 11 compares the signal detected by the overcurrent detection resistor 3 with the reference signal and outputs it as a gate reset signal for the main switch 1.
[0018]
In the present embodiment, since the resistor 17 is connected to the connection portion between the connection portion of the constant current circuit 16 and the comparator 11, the maximum voltage of the reference voltage can be limited. That is, when the reference voltage set by the resistor 17 reaches the maximum voltage, the reference level of the comparator 11 becomes constant at a value clamped by the resistor. Therefore, by using this resistor 17, the operation waveform becomes substantially equal to the operation waveform of the first embodiment shown in FIG. 3, and the second overcurrent detection circuit 30 becomes unnecessary.
[0019]
When the main switch 1 is off, the switch 14 provided in the second overcurrent detection circuit 10 is turned on in synchronization. As a result, the capacitor 15 is discharged to the level of the constant voltage source 13, and the above-described operation becomes possible when the main switch 1 is turned on again.
[0020]
Subsequently, the main part of the third embodiment of the power supply circuit according to the present invention is shown in FIG. 5, and its operation waveform diagram is shown in FIG. The power supply circuit according to the third embodiment has substantially the same configuration as that of the first embodiment, but a connection portion is provided between the reference voltage generation unit 12 and the comparator 11 of the first overcurrent detection circuit 10, and this connection A resistor 18 is provided in place of the constant current circuit 16.
[0021]
The third embodiment is configured as described above and operates as follows. When the main switch 1 is on, the switch 14 provided in the first overcurrent detection circuit 10 is turned off in synchronization. The capacitor 15 provided in the reference voltage generator 12 is charged and rises. In this case, since the resistor 18 is provided in the current supply circuit, the reference voltage rises in a curve as shown in FIG. 6 due to the charging characteristics of the resistor 18 and the capacitor 15. The comparator 11 compares the signal detected by the overcurrent detection resistor 3 with the reference signal and outputs it as a gate reset signal for the main switch 1. The other operations are almost the same as in the first embodiment.
[0022]
Next, FIG. 7 shows a main part of a fourth embodiment of the power supply circuit according to the present invention, and FIG. 8 shows an operation waveform diagram thereof. The power supply circuit according to the fourth embodiment has substantially the same configuration as that of the first embodiment, but a series circuit of a constant voltage source 13 and a capacitor 15 constituting the reference voltage generation unit 12 of the first overcurrent detection circuit 10. And a switch 14 connected in parallel to the series circuit, and a second current supply circuit is connected to the connection. In this current supply circuit, a switch 19 and a constant current circuit 20 are connected in series, the switch 19 is turned off during the ON period of the main switch 1, and the detection level of the first overcurrent detection circuit 10 is set in two stages. It is configured to be switched. In the present embodiment, the detection level of the first overcurrent detection circuit 10 is configured to be switched between two levels. However, a connection portion is provided between the capacitor 15 of the reference voltage generation unit 12 and the comparator 11. By providing a plurality and providing each with a current supply circuit, the detection level can be switched to three or more levels.
[0023]
The fourth embodiment is configured as described above and operates as follows. When the main switch 1 is on, the switch 14 provided in the reference voltage generation unit 12 of the first overcurrent detection circuit 10 is turned off in synchronization. On the other hand, the switch 19 provided in the second current supply circuit is turned on, and as shown in FIG. 8, the capacitor 15 provided in the reference voltage generation unit 12 is charged and rises, and the reference voltage rises. The comparator 11 compares the signal detected by the overcurrent detection resistor 3 with the reference signal and outputs it as a gate reset signal for the main switch 1. Subsequently, when the switch 19 provided in the second current supply circuit is turned off while the main switch 1 is turned on, the constant current is supplied at one place, and the voltage rise is moderated. That is, according to the fourth embodiment, the detection level of the first overcurrent detection circuit 10 can be switched in two stages by the above configuration. The other operations are almost the same as in the first embodiment.
[0024]
Next, FIG. 9 shows a main part of a fifth embodiment of the power supply circuit according to the present invention, and FIG. 10 shows an operation waveform diagram thereof. The power supply circuit according to the fifth embodiment has substantially the same configuration as that of the first embodiment, but the reference voltage generation unit 12 of the first overcurrent detection circuit 10 has a capacitor 15 connected in series with the constant voltage source 13. Thus, a series circuit is formed, and a switch 14 is connected in parallel with the capacitor 15.
[0025]
The fifth embodiment is configured as described above and operates as follows. When the main switch 1 is off, the switch 14 provided in the reference voltage generation unit 12 of the first overcurrent detection circuit 10 is turned off in synchronization. Therefore, a constant current flows from the constant current circuit 16 and the capacitor 15 is charged. On the other hand, when the main switch 1 is on, the switch 14 provided in the reference voltage generation unit 12 of the first overcurrent detection circuit 10 is instantaneously turned on in synchronization. At this time, the detection level decreases, but the capacitor 15 provided in the reference voltage generation unit 12 decreases only to the reference voltage Voffset of the first overcurrent detection circuit 10 as shown in FIG. Thereafter, when the switch 14 is turned off again, a constant current flows from the constant current circuit 16, the capacitor 15 is charged, and the reference voltage increases. The other operations are almost the same as in the first embodiment.
[0026]
Subsequently, a sixth embodiment will be described. The circuit configuration of the sixth embodiment is the same as that of the fifth embodiment. The operation waveform diagrams of the sixth embodiment are shown in FIGS. It is configured as described above and operates as follows. In the sixth embodiment, when the main switch 1 is off, the switch 14 provided in the reference voltage generation unit 12 of the first overcurrent detection circuit 10 is turned on synchronously. At this time, the reference voltage becomes constant at Voffset determined by the constant voltage source 13 by the action of the constant voltage source 13. On the other hand, when the main switch 1 is turned on, the switch 14 of the reference voltage generation unit 12 of the first overcurrent detection circuit 10 is on for a while, and the reference voltage is the same as when the main switch 1 is off. It is in a constant state at Voffset determined by the constant voltage source 13. When the switch 14 of the reference voltage generator 12 is turned off, a constant current flows from the constant current circuit 16, and the capacitor 15 is charged, so that the reference voltage increases. As shown in FIG. 10, the capacitor 15 provided in the reference voltage generation unit 12 can be lowered only to the reference voltage Voffset. Thereafter, the capacitor 15 is charged and rises, and the reference voltage rises. When the reference level of the first overcurrent detection circuit 10 exceeds the reference level of the second overcurrent detection circuit 30, the gate reset signal output from the second overcurrent detection circuit 30 is adopted, as shown in FIG. The gate reset signal is output to the main switch 1.
[0027]
Subsequently, FIG. 13 shows a main part of a seventh embodiment of the power supply circuit according to the present invention. In the power supply circuit according to the seventh embodiment, the overcurrent protection circuit 2 is provided with an overcurrent detection resistor 3 and an overcurrent detection circuit 10, and the overcurrent detection resistor 3 is connected to the source terminal of the main switch 1 of the power supply circuit. It is. A comparator 11 is provided in the overcurrent detection circuit 10, the source terminal of the main switch 1 is connected to the positive input terminal of the comparator 11, and the reference voltage generator 12 is connected to the negative input terminal of the comparator 11. is there. The reference voltage generator 12 includes resistors 21 and 22 connected in series, and a switch 23 connected in parallel to the ground-side resistor 21. A timer circuit 40 is connected to the control terminal of the switch 23. The timer circuit 40 is a circuit that detects the ON state of the main switch 1 and changes the detection level of the overcurrent detection circuit 10 after a certain time has passed.
[0028]
The seventh embodiment is configured as described above and operates as follows. When the main switch 1 is off, the timer circuit 40 outputs a high signal, and the switch 23 of the overcurrent detection circuit 10 is turned on in synchronization. Conversely, when the main switch 1 is turned on, the timer circuit 40 detects that the main switch 1 is turned on, and outputs a low signal after a certain time. Since the output of the timer circuit 40 outputs a high signal for a while after the main switch 1 is turned on, the switch 23 of the overcurrent detection circuit 10 is in an on state. As shown in FIG. 14, the reference voltage of the overcurrent detection circuit 10 is Vref2.
[0029]
The timer circuit 40 detects the on-time of the main switch 1 after the main switch 1 is turned on, and outputs a low signal after a certain time. When the output of the timer circuit 40 is a low signal, the switch 23 is turned off. When the main switch 1 is turned off, the timer circuit 40 outputs a high signal and the switch 23 is turned on.
[0030]
When the main switch 1 is turned on and the timer circuit 40 detects a certain time, the timer circuit 40 outputs a low signal, and the switch 23 of the overcurrent detection circuit 10 is turned off. Therefore, the constant current circuit 16 is also applied to the resistor 21, and the reference voltage of the overcurrent detection circuit 10 is Vref1 + Vref2 as shown in FIG. As described above, the detection level of the overcurrent detection circuit 10 can be changed by detecting the ON state of the main switch 1 with the timer circuit 40 and controlling the switch 23 after a certain period of time.
[0031]
Next, FIG. 16 shows a main part of an eighth embodiment of the power supply circuit according to the present invention. The power supply circuit according to the eighth embodiment has substantially the same configuration as that of the seventh embodiment, but the power supply circuit according to this embodiment has a reference voltage generation unit 12 connected to the negative input terminal of the comparator 11. The reference voltage generator 12 includes resistors 21 and 22 connected in parallel, and a switch 23 connected in parallel with one resistor 21 and in series with the other resistor 22. A timer circuit 40 is connected to the control terminal of the switch 23 as in the seventh embodiment.
[0032]
The eighth embodiment is configured as described above and operates as follows. When the main switch 1 is off, the timer circuit 40 outputs a high signal, and the switch 23 of the overcurrent detection circuit 10 is in an on state. Therefore, the constant current circuit 16 is applied to the resistor 21 and the resistor 22, and the overcurrent detection is performed. The reference voltage of the circuit 10 is lowered by the combined resistance of the resistors 21 and 22.
[0033]
When the main switch 1 is turned on, the output of the timer circuit 40 outputs a high signal, and the switch 23 of the overcurrent detection circuit 10 is in an on state in synchronization. The reference voltage at this time is determined by the combined resistance of the resistor 21 and the resistor 22. Thereafter, the timer circuit 40 detects that the main switch 1 is turned on, and after a certain period of time, the timer circuit 40 outputs a low signal, the switch 23 is turned off, the constant current circuit 16 is applied only to the resistor 21, The reference voltage of the overcurrent detection circuit 10 increases.
As described above, the detection level of the overcurrent detection circuit 10 can be changed by detecting the ON state of the main switch 1 with the timer circuit 40 and controlling the switch 23 after a certain period of time.
[0034]
Next, FIG. 17 shows a main part of a ninth embodiment of the power supply circuit according to the present invention. The power supply circuit according to the ninth embodiment has substantially the same configuration as that of the seventh embodiment, but the power supply circuit according to this embodiment is configured by connecting the reference voltage generation unit 12 to the negative input terminal of the comparator 11. The reference voltage generator 12 has resistors 21, 22, and 25 connected in series, and a switch 23 is connected in parallel to the ground-side resistor 21, and a switch 26 is also connected in parallel to the resistor 25 connected to the resistor 21. Is connected. A timer circuit 40 is connected to the control terminals of these switches 23 and 26.
[0035]
The fourth embodiment is configured as described above and operates as follows. When the main switch 1 is off, the two outputs of the timer circuit 40 both output high signals, and the switches 23 and 26 of the overcurrent detection circuit 10 are turned on in synchronization. Since the switches 23 and 26 of the overcurrent detection circuit 10 are in the ON state, the constant current circuit 16 is applied only to the resistor 22, and the reference voltage of the overcurrent detection circuit 10 is Vref2.
[0036]
When the main switch 1 is turned on, the timer circuit 40 detects that the main switch 1 is turned on. When a certain time has elapsed, only the switch 23 is turned off. As a result, the constant current circuit 16 is applied to the resistors 22 and 21, and the reference voltage of the overcurrent detection circuit 10 is Vref2 + Vref1. When the ON width of the main switch 1 further increases, the timer circuit 40 turns off the switch 25, the constant current circuit 16 is also applied to the resistor 25, and the reference voltage of the overcurrent detection circuit 10 becomes Vref2 + Vref1 + Vref3. According to the ninth embodiment, the reference voltage of the overcurrent detection circuit 10 can be switched in three stages with the above configuration. The other operations are almost the same as in the seventh embodiment.
[0037]
In the present embodiment, the voltage of the reference voltage generator 12 can be switched in three stages by connecting three resistors in series to the first overcurrent detection circuit 10, but the reference voltage Four or more resistors of the generation unit 12 can be connected in series to switch the voltage of the reference voltage generation unit 12 to four or more stages.
[0038]
【The invention's effect】
According to the present invention, there is an effect that the droop point variation with respect to the input voltage of the power supply is reduced. There is an effect that the current peak of the main switch when the output winding is short-circuited can be suppressed and the main switch can be prevented from being damaged. Furthermore, there is an effect that the winding short circuit current and the load short circuit current can be reduced.
[0039]
In general, when the input voltage increases, the droop point increases, so the short-circuit current also increases.However, according to the present invention, the droop point when the input is high can be set to the same level as when the input is low. There is an effect that can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a main part of a first embodiment according to the present invention.
FIG. 2 is an operation waveform diagram according to the first embodiment.
FIG. 3 is a level waveform diagram according to the first embodiment.
FIG. 4 is a circuit diagram of a main part of a second embodiment according to the present invention.
FIG. 5 is a circuit diagram of an essential part of a third embodiment according to the present invention.
FIG. 6 is a level waveform diagram according to a third embodiment.
FIG. 7 is a circuit diagram of an essential part showing a fourth embodiment according to the present invention.
FIG. 8 is a level waveform diagram according to a fourth embodiment.
FIG. 9 is a circuit diagram of a main part of fifth and sixth embodiments according to the present invention.
FIG. 10 is an operation waveform diagram according to the fifth embodiment.
FIG. 11 is a level waveform diagram according to the sixth embodiment.
FIG. 12 is an operation waveform diagram according to the sixth embodiment.
FIG. 13 is a circuit diagram of an essential part of a seventh embodiment according to the present invention.
FIG. 14 is a level waveform diagram according to the seventh embodiment.
FIG. 15 is an operation waveform diagram according to the seventh embodiment.
FIG. 16 is a circuit diagram of a main part of an eighth embodiment according to the present invention.
FIG. 17 is a circuit diagram of an essential part of a ninth embodiment according to the present invention.
FIG. 18 is a circuit diagram of a main part of a conventional example.
FIG. 19 is an operation waveform diagram according to a conventional example.
FIG. 20 is a level waveform diagram according to a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main switch 2 Overcurrent protection circuit 3 Overcurrent detection resistor 10, 30, 60 Overcurrent detection circuit 11, 31, 41, 61 Comparator 12, 32, 42, 62 Reference voltage generation part 13 Constant voltage source 14, 19, 23 , 26, 43 Switch 15, 44 Capacitor 16, 20, 46 Constant current circuit 17, 18, 21, 22, 24, 25 Resistor 33 OR circuit 40 Timer circuit

Claims

A power supply circuit comprising an overcurrent protection circuit, the overcurrent protection circuit comprising a resistor for overcurrent detection and an overcurrent detection circuit, and connecting the overcurrent detection circuit to a main switch of the power supply circuit, The overcurrent detection circuit includes a comparator, and is connected to input a signal detected by the overcurrent detection resistor to one input of the comparator, and similarly generates a reference voltage at the other input of the comparator. A generator is connected, and a switch that synchronizes with the main switch is provided in the reference voltage generator, and each time the switch is turned on, the reference voltage is changed continuously or stepwise to control on / off of the main switch. A power supply circuit configured to be configured as described above.

2. The power supply circuit according to claim 1, wherein the main switch is constituted by a MOSFET, and the overcurrent protection circuit is connected to a source terminal or a drain terminal of the main switch.

2. The power supply circuit according to claim 1, wherein the main switch is constituted by a transistor, and the overcurrent protection circuit is connected to an emitter terminal or a collector terminal of the main switch.

2. The power supply circuit according to claim 1, wherein the main switch is constituted by an IGBT, and the overcurrent protection circuit is connected to an emitter terminal or a collector terminal of the main switch.

The reference voltage generator is provided with a capacitor that is charged and discharged by turning on and off the switch, and the reference voltage is continuously changed according to the on width of the main switch. The power supply circuit according to any one of 1 to 4.

6. The power supply according to claim 5, wherein the reference voltage generation unit is configured by connecting a switch in series with a constant voltage source to form a series circuit, and connecting a capacitor in parallel with the series circuit. circuit.

6. The power supply according to claim 5, wherein the reference voltage generator is configured by connecting a capacitor in series with a constant voltage source to form a series circuit, and connecting a switch in parallel with the series circuit. circuit.

6. The power supply circuit according to claim 5, wherein the reference voltage generator is configured by connecting a capacitor in series with a constant voltage source to form a series circuit, and connecting a switch in parallel with the capacitor. .

The reference voltage generator is provided with a resistor in parallel or in series or in parallel and in series with a switch, and a timer is provided at a control terminal of the switch so that the reference voltage is changed stepwise. Item 5. The power supply circuit according to any one of Items 1 to 4.

The power supply circuit according to claim 9, wherein a plurality of switches are connected in series to the reference voltage generation unit, and a resistor is provided in parallel with or in series with or parallel to these switches.

In addition to the overcurrent detection circuit, a second overcurrent detection circuit is connected in parallel to the overcurrent protection circuit. The second overcurrent detection circuit includes a comparator, and the main switch is connected to one input of the comparator. And a reference voltage generator is connected to the other input of the comparator, and an OR circuit is connected to the outputs of the overcurrent detection circuit and the second overcurrent detection circuit. The power supply circuit according to claim 1, wherein the power supply circuit is configured to control on / off of the power supply.

11. A resistor, a Zener diode, or other clamping means for limiting the maximum voltage of the comparator is connected in parallel with a reference voltage generation unit of the overcurrent detection circuit. Power supply circuit.

The connection part is provided between the said reference voltage generation part and the said comparator, The current supply circuit which supplies an electric current to the said reference voltage generation part is connected to this connection part, The Claim 1 thru | or 12 characterized by the above-mentioned. The power circuit according to any one of the above.

The power supply circuit according to claim 13, wherein a constant current flows in the current supply circuit.

15. The power supply circuit according to claim 13, wherein a resistor is provided in the current supply circuit.

14. A configuration in which a plurality of current supply circuits are provided between a capacitor of the reference voltage generation unit and the comparator, and current is supplied to the reference voltage generation unit step by step. 15. The power supply circuit according to any one of 15.

The power supply circuit according to any one of claims 1 to 16, wherein a timer circuit for detecting an ON width of a main switch and changing a level of the overcurrent detection circuit is connected to the switch.