JP2004234584A

JP2004234584A - Power source circuit

Info

Publication number: JP2004234584A
Application number: JP2003025397A
Authority: JP
Inventors: Osamu Saito; 修齊藤; Shigeru Hisada; 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: 2004-08-19
Anticipated expiration: 2023-02-03
Also published as: JP4251877B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power source capable of changing an overcurrent protective level matched with the on-width of a main switch. <P>SOLUTION: A power source circuit is provided with an overcurrent protective circuit 2 and the overcurrent protective circuit 2 is provided with an overcurrent detection resistor 3 and an overcurrent detection circuit 10. The overcurrent detection circuit 10 is connected to the main switch 1 of the power source circuit and the overcurrent detection circuit 10 is provided with a comparator 11. Connection is performed so as to input signals detected in the overcurrent detection resistor 3 to one input of the comparator 11 and a reference voltage generation part 12 is connected to the other input of the comparator 11 similarly. The reference voltage generation part 12 is provided with a switch 14 synchronized with the main switch 1, a capacitor 15 for performing charging / discharging by the on/off of the switch 14 is provided, and a reference voltage is continuously changed by the charging / discharging of the capacitor 15 and outputted to the main switch 1. <P>COPYRIGHT: (C)2004,JPO&NCIPI

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]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power supply circuit, which turns on and off a main switch of the power supply circuit, drives a transformer for raising and lowering 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 including 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 this 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 composed of a MOSFET. 3, the overcurrent detection circuit 60 includes a comparator 61, and the positive input terminal of the comparator 61 is connected to the source terminal of the main switch 1, and the negative input terminal of the comparator 61 is used to generate the reference voltage. A section 62 is connected, and the output terminal of the comparator 61 is configured to control the on / off of the main switch 1.
[0003]
An operation inhibition signal that detects an overcurrent of the current flowing through the main switch, latches an overcurrent detection signal from an overcurrent detection circuit that outputs the overcurrent detection signal, and inhibits the on / off operation of the main switch. There is also a power supply circuit provided with a latch circuit that causes the control circuit that stops the on / off operation of the main switch to continue generating an operation prohibition signal and releases the latch operation based on the cutoff of the DC power supply. (For example, see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-11-69796 (pages 3-5, FIG. 1)
[0005]
[Problems to be solved by the invention]
In any of the power supply circuits, when the terminal voltage of the overcurrent detection resistor 3 becomes 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 equal to or higher than 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 an overcurrent protection level in accordance with an ON width of a main switch.
[0007]
[Means to solve the problem]
The present invention made to achieve the above object has an effect of reducing a droop point fluctuation with respect to an input voltage of a power supply. It is possible to suppress the current peak of the main switch when the output winding is short-circuited, and prevent the main switch from being damaged. Further, the winding short-circuit current and the load short-circuit current can be reduced.
[0008]
Normally, as the input voltage increases, the droop point increases, and the short-circuit current also increases.However, according to the present invention, the droop point when the input is high can be made about the same as when the input is low, thus reducing the short-circuit current. it can.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the power supply circuit of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a main part of a first embodiment of the power supply circuit according to the present invention, and FIGS. 2 and 3 show operation waveform diagrams thereof. 1 is a main switch, 2 is an overcurrent protection circuit, 3 is an overcurrent detection resistor, 10 is an overcurrent detection circuit, and 30 is a second overcurrent detection circuit.
[0010]
The power supply circuit according to the present invention includes an overcurrent protection circuit 2. 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 a power supply circuit composed of MOSFETs. The overcurrent detection circuits 10 and 30 include comparators 11 and 31. 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, respectively. In this embodiment, the overcurrent detection resistor 3 is connected to the source terminal of the main switch 1, but 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 may be constituted by a transistor or an IGBT.
[0011]
The reference voltage generator 32 of the second overcurrent detection circuit 30 comprises only a constant voltage source, whereas the reference voltage generator 12 of the first overcurrent detection circuit 10 comprises a constant voltage source 13 and a switch 14. A constant voltage source 13 and a capacitor 15 are connected in series, and a switch 14 is connected in parallel with this series circuit so that the level can be changed according to the ON / OFF of the main switch 1. It is configured in. Further, a connection is provided between the reference voltage generator 12 and the comparator 11, and a constant current circuit 16 for supplying a current to the reference voltage generator 12 is connected to this connection. It is changed 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, and the output terminal of the OR circuit 33 is directly or indirectly connected to the gate terminal of the main switch 1 to turn on the main switch 1. -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 turns off synchronously. A current flows from the constant current circuit 16, and the capacitor 15 provided in the reference voltage generator 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 compared with the reference signal. Output as a reset signal. These are determined by the OR circuit 33, and when the main switch 1 is turned on, the gate reset signal output from the first overcurrent detection circuit 10 is adopted, and 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 is reset. 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 turns on in synchronization. When the capacitor 15 is discharged and the main switch 1 is turned on again, the above operation becomes possible.
[0015]
FIG. 4 shows a main part of a second embodiment of the power supply circuit according to the present invention. In the power supply circuit according to the second embodiment, the overcurrent protection circuit 2 includes the overcurrent protection circuit 2 provided with the overcurrent detection resistor 3 and the 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 as well. 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 this series circuit. The level can be changed according to the on / off state of the switch 1.
[0016]
A constant current circuit 16 is connected to a connection between the reference voltage generator 12 and the comparator 11 so as to change linearly in accordance with the ON width of the main switch 1. Further, a connection is provided between the connection of the constant current circuit 16 and the comparator 11, and a resistor 17 serving as a clamp is connected to the connection to limit the maximum voltage of the reference voltage generator 12. is there. Note that 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 turns off synchronously. 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 the signal as a gate reset signal of the main switch 1.
[0018]
In this embodiment, since the resistor 17 is connected to the connection between the connection 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 almost 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 turns on in synchronization. As a result, the capacitor 15 discharges to the level of the constant voltage source 13, and when the main switch 1 is turned on again, the above operation becomes possible.
[0020]
Next, FIG. 5 shows a main part of a third embodiment of the power supply circuit according to the present invention, and FIG. 6 shows an operation waveform diagram thereof. The power supply circuit according to the third embodiment has substantially the same configuration as that of the first embodiment, except that a connection is provided between the reference voltage generator 12 and the comparator 11 of the first overcurrent detection circuit 10, 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 turns off synchronously. 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 the signal as a gate reset signal of the main switch 1. Other operations are almost the same as those of the first embodiment.
[0022]
Subsequently, 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, except that a series circuit of a constant voltage source 13 and a capacitor 15 forming a reference voltage generation unit 12 of the first overcurrent detection circuit 10. A connection is provided between the switch and the switch connected in parallel with the series circuit, and a second current supply circuit is connected to the connection. This current supply circuit connects a switch 19 and a constant current circuit 20 in series, turns off this switch 19 in the middle of the ON period of the main switch 1, and changes the detection level of the first overcurrent detection circuit 10 in two stages. It is configured to be switchable. In the present embodiment, the detection level of the first overcurrent detection circuit 10 is configured to be able to be switched in two stages, but a connection portion is provided between the capacitor 15 of the reference voltage generation unit 12 and the comparator 11. By providing a plurality of the current supply circuits, a detection level can be switched among three or more stages.
[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 generator 12 of the first overcurrent detection circuit 10 turns off synchronously. 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 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 the signal as a gate reset signal of 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 being turned on, the constant current is supplied at one place, and the rise in voltage becomes gentle. That is, in the fourth embodiment, with the above configuration, the detection level of the first overcurrent detection circuit 10 can be switched between two levels. Other operations are almost the same as those of 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, except that the reference voltage generator 12 of the first overcurrent detection circuit 10 connects a capacitor 15 in series with the constant voltage source 13. 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 generator 12 of the first overcurrent detection circuit 10 turns off synchronously. Therefore, the 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 turned on, the switch 14 provided in the reference voltage generator 12 of the first overcurrent detection circuit 10 turns on instantaneously in synchronization. At this time, the detection level drops, but the capacitor 15 provided in the reference voltage generation unit 12 drops 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 rises. Other operations are almost the same as those of the first embodiment.
[0026]
Next, a sixth embodiment will be described. The circuit configuration of the sixth embodiment is the same as that of the fifth embodiment. 11 and 12 show operation waveform diagrams of the sixth embodiment. The configuration described above is performed and the following operation is performed. In the sixth embodiment, when the main switch 1 is off, the switch 14 provided in the reference voltage generator 12 of the first overcurrent detection circuit 10 is turned on in synchronization. At this time, the reference voltage is kept constant at Voffset determined by the constant voltage source 13 due to the operation 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 turned on for a while, and the reference voltage is set to the same value as when the main switch 1 is turned 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, the capacitor 15 is charged, and the reference voltage increases. The capacitor 15 provided in the reference voltage generator 12 drops only to the reference voltage Voffset as shown in FIG. 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 employed, and as shown in FIG. Then, this gate reset signal is output to the main switch 1.
[0027]
Next, 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. I have. A comparator 11 is provided in the overcurrent detection circuit 10, a source terminal of the main switch 1 is connected to a positive input terminal of the comparator 11, and a reference voltage generator 12 is connected to a negative input terminal of the comparator 11 as well. is there. The reference voltage generator 12 has resistors 21 and 22 connected in series, and a switch 23 connected in parallel with a resistor 21 on the ground side. The timer circuit 40 is connected to the control terminal of the switch 23. The timer circuit 40 is a circuit that detects the turning on of the main switch 1 and changes the detection level of the overcurrent detection circuit 10 after a certain period of time.
[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 turns 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 period of 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. Only as shown in FIG. 14, the reference voltage of the overcurrent detection circuit 10 becomes 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 period of 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 also acts on the resistor 21, and the reference voltage of the overcurrent detection circuit 10 becomes 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 of the main switch 1 by 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. However, 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 has 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 resistors 21 and 22 to detect the overcurrent. The reference voltage of the circuit 10 is reduced 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 synchronously on. The reference voltage at this time is determined by the combined resistance of the resistors 21 and 22. Thereafter, the timer circuit 40 detects that the main switch 1 is turned on. After a certain period of time, the timer circuit 40 outputs a low signal, the switch 23 is turned off, and 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 of the main switch 1 by 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. However, the power supply circuit according to the ninth embodiment connects the reference voltage generator 12 to the negative input terminal of the comparator 11. The reference voltage generating unit 12 connects the resistors 21, 22, 25 in series, connects the switch 23 in parallel with the resistor 21 on the ground side, and also connects the switch 26 in parallel with the resistor 25 connected to the resistor 21. Are connected. A timer circuit 40 is connected to the control terminals of the switches 23 and 26.
[0035]
The fourth embodiment is configured as described above and operates as follows. When the main switch 1 is off, both outputs of the timer circuit 40 output a high signal, and the switches 23 and 26 of the overcurrent detection circuit 10 turn 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 becomes Vref2.
[0036]
When the main switch 1 is turned on, the timer circuit 40 detects that the main switch 1 is turned on. After a certain period of time, 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 becomes Vref2 + Vref1. When the ON width of the main switch 1 is further increased, the timer circuit 40 turns off the switch 25, the constant current circuit 16 is applied to the resistor 25, and the reference voltage of the overcurrent detection circuit 10 becomes Vref2 + Vref1 + Vref3. In the ninth embodiment, with the above configuration, the reference voltage of the overcurrent detection circuit 10 can be switched in three stages. The other operations are almost the same as in the seventh embodiment.
[0037]
In the present embodiment, three resistors are connected in series to the first overcurrent detection circuit 10 so that the voltage of the reference voltage generator 12 can be switched in three stages. By connecting four or more resistors of the generator 12 in series, the voltage of the reference voltage generator 12 can be switched in four or more stages.
[0038]
【The invention's effect】
According to the present invention, there is an effect that the droop point fluctuation with respect to the input voltage of the power supply is reduced. This has the effect of suppressing the current peak of the main switch when the output winding is short-circuited and preventing the main switch from being damaged. Further, there is an effect that the winding short-circuit current and the load short-circuit current can be reduced.
[0039]
Also, normally, as the input voltage increases, the droop point increases, so that the short-circuit current also increases.However, according to the present invention, the droop point when the input is high can be made similar to that when the input is low, so that the short-circuit current can be reduced. 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 chart 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 a main part of a third embodiment according to the present invention.
FIG. 6 is a level waveform chart according to a third embodiment.
FIG. 7 is a circuit diagram of a main part showing a fourth embodiment according to the present invention.
FIG. 8 is a level waveform chart according to a fourth embodiment.
FIG. 9 is a circuit diagram of a main part of the 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 chart according to a sixth embodiment.
FIG. 12 is an operation waveform diagram according to the sixth embodiment.
FIG. 13 is a circuit diagram of a main part of a seventh embodiment according to the present invention.
FIG. 14 is a level waveform chart according to a 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 a main 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 chart according to a conventional example.
[Explanation of symbols]
REFERENCE SIGNS LIST 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 generator 13 Constant voltage sources 14, 19, 23 , 26, 43 Switch 15, 44 Capacitor 16, 20, 46 Constant current circuit 17, 18, 21, 22, 24, 25 Resistance 33 OR circuit 40 Timer circuit

Claims

A power supply circuit including an overcurrent protection circuit, wherein the overcurrent protection circuit includes an overcurrent detection resistor and an overcurrent detection circuit, and the overcurrent detection circuit is connected to a main switch of the power supply circuit; The overcurrent detection circuit includes a comparator, which is connected to one input of the comparator so as to input a signal detected by the overcurrent detection resistor, and generates a reference voltage at the other input of the comparator. A generator is connected, and a switch synchronized with the main switch is provided in the reference voltage generator, and the reference voltage is continuously or stepwise changed by turning on / off the switch to turn on / off the main switch. A power supply circuit configured to be controlled.

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

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

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

The reference voltage generator is provided with a capacitor that charges and discharges when the switch is turned on and off, and is configured to continuously change the reference voltage in accordance with the ON width of the main switch. The power supply circuit according to any one of claims 1 to 4.

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

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

10. 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, in series, or in parallel and in series with the switches.

A second overcurrent detection circuit is connected in parallel to the overcurrent protection circuit separately from the overcurrent detection 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 also 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 any one of claims 1 to 10, wherein the power supply circuit is configured to control on / off of the power supply.

11. The device according to claim 1, wherein a resistor, a zener diode, and other clamping means for limiting a maximum voltage of the comparator are connected in parallel with a reference voltage generator of the overcurrent detection circuit. Power circuit.

13. The device according to claim 1, wherein a connection is provided between the reference voltage generator and the comparator, and a current supply circuit that supplies a current to the reference voltage generator is connected to the connection. The power supply circuit according to any one of the above.

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

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

14. A configuration according to claim 13, wherein a plurality of current supply circuits are provided between the capacitor of the reference voltage generation unit and the comparator to supply the current to the reference voltage generation unit in a stepwise manner. The power supply circuit according to any one of the above items 15.

17. The power supply circuit according to claim 1, wherein a timer circuit that detects an ON width of a main switch and changes a level of the overcurrent detection circuit is connected to the switch.