JP4118101B2

JP4118101B2 - Power circuit

Info

Publication number: JP4118101B2
Application number: JP2002243554A
Authority: JP
Inventors: 裕之鈴木; 真司谷口
Original assignee: Shindengen Electric Manufacturing Co Ltd
Current assignee: Shindengen Electric Manufacturing Co Ltd
Priority date: 2002-08-23
Filing date: 2002-08-23
Publication date: 2008-07-16
Anticipated expiration: 2022-08-23
Also published as: JP2004088839A

Description

【０００１】
【発明の属する技術分野】
本発明は、一次−二次間が絶縁されたトランスの一次巻線に直列に接続される主スイッチング素子を備え、前記トランスに補助電源回路を接続した電源回路に関するものである。
【０００２】
【従来の技術】
従来の負荷短絡から開放したときに自動復帰する電源装置の補助電源回路を図３に示す。この電源装置は一次−二次間が絶縁されたトランスＴ１の一次巻線ＮＰに直列に接続される主スイッチ素子Ｍ１を備えてある。この主スイッチ素子Ｍ１はＦＥＴで構成してある。また、前記トランスＴ１には補助巻線ＮＳを設けてあり、この補助巻線ＮＳにはフライバック型の補助回路５１を構成してある。この補助回路５１を構成するコンデンサＣ２に並列に集積回路５２を接続してあり、この集積回路５２を主スイッチ素子Ｍ１のゲートに接続してある。また、この補助回路５１の出力側にはドロッパＱ１を設けてあり、このドロッパＱ１を入力電源に接続して、負荷短絡時の電力を確保するよう構成してある。
【０００３】
しかし、前記したようにドロッパＱ１を入力電源に接続すると、ドロッパＱ１にかかる電圧変動が大きくなり、ドロッパＱ１の損失が大きくなる課題が生じた。また定常時にも損失が発生する課題も生じた。ドロッパＱ１の損失が大きくなることから、ドロッパＱ１は大型のトランジスタにしなければいけない課題も生じた。
【０００４】
【発明が解決しようとする課題】
本発明は、上記問題に鑑みてなされたものであり、トランスに補助巻線を設けたフライバック型の補助電源回路で過負荷時並びに短絡時にあっても集積回路に電源を確保することができ、ドロッパの損失を低減することができ、ドロッパを小型のトランジスタにできる新規な電源回路を提供する。
【０００５】
【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、トランスに補助巻線を設け、この補助巻線の一端にカソードを接続した第一整流ダイオードと、前記補助巻線と並列に接続した第一コンデンサとを設けたフライバック型の補助電源回路を備え、前記補助巻線の他端に第二整流ダイオードのアノードを接続し、この第二整流ダイオードのカソードに集積回路を接続し、定常状態では、前記補助電源回路から前記集積回路に電力を供給するようにしてあるとともに、前記補助巻線の他端に過負荷時又は負荷短絡時を検出する検出回路を接続し、前記補助巻線の一端に第三整流ダイオードのアノードを接続し、この第三整流ダイオードのカソードを第二コンデンサに接続し、この第二コンデンサと並列に前記検出回路が過負荷時又は負荷短絡時を検出した際に起動する起動回路に接続し、この起動回路に第二スイッチ素子を設け、この第二スイッチ素子の制御入力端子を前記検出回路に設けた第一スイッチ素子の入力端子に接続し、この第二スイッチ素子の出力端子に第四整流ダイオードのアノードを接続し、この第四整流ダイオードのカソードに前記集積回路を接続して、過負荷時又は負荷短絡時には、前記起動回路から前記集積回路に電力を供給するようにしてあることにより、ドロッパの損失を低減し、二次側が過負荷若しくは短絡しても常に集積回路に電源を確保することができる。
【０００６】
また、補助巻線を直列に二つ設け、この接続部にセンタータップを設け、このセンタータップに前記第三整流ダイオードのアノードを接続してあることにより、ドロッパの電力の低減化を図ることができる。
【０００７】
【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。図１は本発明に係る電源回路の実施例である。１は補助電源回路、２は検出回路、３は起動回路、４は集積回路である。また、Ｃ１は第一コンデンサ、Ｃ２は第二コンデンサ、Ｄ１は第一整流ダイオード，Ｄ２は第二整流ダイオード、Ｄ３は第三整流ダイオード，Ｄ４は第四整流ダイオード、ＤＺ１は第一ツェナーダイオード、ＤＺ２は第二ツェナーダイオード、Ｔｒ１は第一スイッチ素子、Ｔｒ２は第二スイッチ素子、Ｑ３は第三スイッチ素子、Ｒ１，Ｒ２，Ｒ４，Ｒ５，Ｒ６は抵抗、Ｔ１はトランス、ＮＰはトランスＴ１の一次巻線、Ｎ２はトランスＴ１の二次巻線、ＮＳはトランスＴ１の補助巻線、ＳＷは主スイッチ素子である。
【０００８】
図１図示の電源回路は本発明電源回路に係る第一実施例である。この電源回路は、電源装置は一次−二次間が絶縁されたトランスＴ１の一次巻線ＮＰに直列に接続される主スイッチ素子ＳＷを備えてある。また、この電源装置のトランスＴ１は補助巻線ＮＳを設け、この補助巻線ＮＳには補助電源回路１を備えてある。補助電源回路１はフライバック型であり、第一整流ダイオードＤ１と第一コンデンサＣ１を備え、この第一整流ダイオードＤ１のカソードを補助巻線ＮＳの巻き始め側に接続してある。また、この第一整流ダイオードＤ１のアノードを第一コンデンサＣ１の一端に接続し、この他端を抵抗Ｒ１を介して、補助巻線ＮＳの巻き終わり側に接続してある。補助巻線ＮＳの他端に第二整流ダイオードＤ２のアノードを接続してあり、この第二整流ダイオードＤ２のカソードに集積回路４を接続してある。
【０００９】
補助巻線ＮＳの他端に二次側が過負荷若しくは負荷短絡したことを検出する検出回路２を接続してある。この検出回路２は、前記補助巻線ＮＳの一端に抵抗Ｒ４を接続し、この抵抗Ｒ４の他端に第一ツェナーダイオードＤＺ１を接続してあり、この第一ツェナーダイオードＤＺ１のアノードにＮＰＮ型トランジスタで構成した第一スイッチ素子Ｔｒ１のベースを接続して構成してある。
【００１０】
前記補助巻線ＮＳの一端に第三整流ダイオードＤ３を接続し、この第三整流ダイオードＤ３のカソードに第二コンデンサＣ２を接続してある。この第二コンデンサＣ２と並列に、検出回路２が過負荷若しくは負荷短絡を検出した際に起動する起動回路３を備えてある。
【００１１】
この起動回路３にＮＰＮ型トランジスタで構成した第二スイッチ素子Ｔｒ２を設けてある。この第二スイッチ素子Ｔｒ２のベースに第二ツェナーダイオードＤＺ２のカソードを接続し、この第二ツェナーダイオードＤＺ２のアノードを第二コンデンサＣ２の他端に接続してある。この第二スイッチ素子Ｔｒ２のベースを検出回路２の第一スイッチ素子Ｔｒ１のコレクタに接続し、この第二スイッチ素子Ｔｒ２のエミッタに第四整流ダイオードＤ４のアノードを接続して、この第四整流ダイオードＤ４のカソードに集積回路４を接続してある。
【００１２】
本実施例に係る電源回路は、以上のように構成してあり、以下のように作用する。先ず、定常時においては、主電源Ｖinから流れる電流はトランスＴ１を介して補助電源回路１に流れる。補助電源回路１に流れた電流は第二整流ダイオードＤ２に流れて、集積回路４に電源が供給される。このとき、第一コンデンサＣ１間の電圧は、出力電圧に二次巻線Ｎ２と補助巻線ＮＳとの巻数比をかけ合わせた値が発生する。
【００１３】
二次側が過負荷若しくは短絡すると第一コンデンサＣ１間の電圧が低下し、検出回路２に備えた第一ツェナーダイオードＤＺ１に電流が流れなくなり、第一スイッチ素子Ｔｒ１がオンからオフに切り換わる。これに伴い、起動回路３に備えた、第二ツェナーダイオードＤＺ２に電圧がかかり第二スイッチ素子Ｔｒ２がオフからオンに切り換わる。この第二スイッチ素子Ｔｒ２がオンになることにより、起動回路３に電流が流れ、この起動回路３に流れた電流は第四整流ダイオードＤ４に流れて、集積回路４に電源が供給される。このとき、第二コンデンサＣ２間の電圧は、第一コンデンサＣ１間の電圧に加えて、主電源Ｖinの電圧に一次巻線ＮＰと補助巻線ＮＳとの巻数比をかけ合わせた値が発生する。以上より、二次側が過負荷若しくは短絡しても、集積回路４に電源を供給することができる。
【００１４】
図２図示の電源回路は本発明電源回路に係る第二実施例である。この電源回路は、トランスＴ１の補助巻線ＮＳを直列に二つ設け、この接続部にセンタータップを設け、このセンタータップに第三整流ダイオードＤ３のアノードを接続してある。その他の構成については第一実施例とほぼ同様である。
【００１５】
作用についても第一実施例とほぼ同様であるが、補助巻線ＮＳを直列に二つ設け、この接続部にセンタータップを設け、このセンタータップに第三整流ダイオードＤ３のアノードを接続してあることにより、ドロッパの電力の低減化を図ることができる。
【００１６】
【発明の効果】
本発明は、トランスに補助巻線を設け、この補助巻線の一端にカソードを接続した第一整流ダイオードと、前記補助巻線と並列に接続した第一コンデンサとを設けたフライバック型の補助電源回路を備え、前記補助巻線の他端に第二整流ダイオードのアノードを接続し、この第二整流ダイオードのカソードに集積回路を接続し、定常状態では、前記補助電源回路から前記集積回路に電力を供給するようにしてあるとともに、前記補助巻線の他端に過負荷時又は負荷短絡時を検出する検出回路を接続し、前記補助巻線の一端に第三整流ダイオードのアノードを接続し、この第三整流ダイオードのカソードを第二コンデンサに接続し、この第二コンデンサと並列に前記検出回路が過負荷時又は負荷短絡時を検出した際に起動する起動回路に接続し、この起動回路に第二スイッチ素子を設け、この第二スイッチ素子の制御入力端子を前記検出回路に設けた第一スイッチ素子の入力端子に接続し、この第二スイッチ素子の出力端子に第四整流ダイオードのアノードを接続して、この第四整流ダイオードのカソードに前記集積回路を接続してあり過負荷時又は負荷短絡時には、前記起動回路から前記集積回路に電力を供給するようにしてあることにより、ドロッパの損失を低減し、二次側が過負荷若しくは短絡しても常に集積回路に電源を確保することができる効果がある。
【００１７】
また、補助巻線を直列に二つ設け、この接続部にセンタータップを設け、このセンタータップに前記第三整流ダイオードのアノードを接続してあることにより、ドロッパの電力の低減化を図ることができる効果がある。
【図面の簡単な説明】
【図１】本発明に係る一実施例を示す回路図である。
【図２】図１図示実施例とは別の実施例を示す回路図である。
【図３】従来例を示す回路図である。
【符号の説明】
１補助電源回路
２検出回路
３起動回路
４集積回路
Ｃ１第一コンデンサ
Ｃ２第二コンデンサ
Ｄ１第一整流ダイオード
Ｄ２第二整流ダイオード
Ｄ３第三整流ダイオード
Ｄ４第四整流ダイオード
ＤＺ１第一ツェナーダイオード
ＤＺ２第二ツェナーダイオード
Ｔｒ１第一スイッチ素子
Ｔｒ２第二スイッチ素子
Ｑ３第三スイッチ素子
Ｒ１，Ｒ２，Ｒ４，Ｒ５，Ｒ６抵抗
Ｔ１トランス
ＮＰトランスＴ１の一次巻線
Ｎ２トランスＴ１の二次巻線
ＮＳトランスＴ１の補助巻線
ＳＷ主スイッチング素子
Ｖin 主電源[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply circuit including a main switching element connected in series to a primary winding of a transformer in which a primary-secondary is insulated, and an auxiliary power supply circuit connected to the transformer.
[0002]
[Prior art]
FIG. 3 shows an auxiliary power supply circuit of a power supply device that automatically recovers when a conventional load short circuit is released. This power supply device includes a main switch element M1 connected in series to a primary winding NP of a transformer T1 that is insulated between a primary and a secondary. The main switch element M1 is composed of an FET. The transformer T1 is provided with an auxiliary winding NS, and a flyback type auxiliary circuit 51 is formed in the auxiliary winding NS. An integrated circuit 52 is connected in parallel to the capacitor C2 constituting the auxiliary circuit 51, and this integrated circuit 52 is connected to the gate of the main switch element M1. In addition, a dropper Q1 is provided on the output side of the auxiliary circuit 51, and the dropper Q1 is connected to an input power source so as to secure power when the load is short-circuited.
[0003]
However, when the dropper Q1 is connected to the input power source as described above, the voltage fluctuation applied to the dropper Q1 becomes large, which causes a problem that the loss of the dropper Q1 becomes large. In addition, there is a problem that loss occurs even in a steady state. Since the loss of the dropper Q1 is increased, there is a problem that the dropper Q1 has to be a large transistor.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and a flyback type auxiliary power supply circuit in which an auxiliary winding is provided in a transformer can secure a power source in an integrated circuit even at the time of overload and short circuit. A novel power supply circuit that can reduce the loss of the dropper and can make the dropper a small transistor is provided.
[0005]
[Means to solve the problem]
In order to achieve the above object, the present invention provides a first rectifier diode in which an auxiliary winding is provided in a transformer and a cathode is connected to one end of the auxiliary winding, and a first capacitor connected in parallel to the auxiliary winding. Is connected to the other end of the auxiliary winding is connected to the anode of the second rectifier diode, and the cathode of the second rectifier diode is connected to the integrated circuit. Power is supplied from the auxiliary power supply circuit to the integrated circuit, and a detection circuit for detecting an overload or load short-circuit is connected to the other end of the auxiliary winding, and one end of the auxiliary winding is connected. Connect the anode of the third rectifier diode, connect the cathode of the third rectifier diode to the second capacitor, and the detection circuit detects when the load is overloaded or shorted in parallel with the second capacitor. Connected to the start circuit that is activated when the second switch element is provided in the start circuit, the control input terminal of the second switch element is connected to the input terminal of the first switch element provided in the detection circuit, The anode of the fourth rectifier diode is connected to the output terminal of the second switch element, and the integrated circuit is connected to the cathode of the fourth rectifier diode. By supplying power, loss of the dropper can be reduced, and a power source can always be secured in the integrated circuit even if the secondary side is overloaded or short-circuited.
[0006]
Further, two auxiliary windings are provided in series, a center tap is provided at the connection portion, and the anode of the third rectifier diode is connected to the center tap, so that the power of the dropper can be reduced. it can.
[0007]
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. FIG. 1 shows an embodiment of a power supply circuit according to the present invention. Reference numeral 1 denotes an auxiliary power circuit, 2 denotes a detection circuit, 3 denotes a start-up circuit, and 4 denotes an integrated circuit. C1 is a first capacitor, C2 is a second capacitor, D1 is a first rectifier diode, D2 is a second rectifier diode, D3 is a third rectifier diode, D4 is a fourth rectifier diode, DZ1 is a first Zener diode, DZ2 Is a second Zener diode, Tr1 is a first switch element, Tr2 is a second switch element, Q3 is a third switch element, R1, R2, R4, R5 and R6 are resistors, T1 is a transformer, and NP is a primary winding of the transformer T1. N2 is a secondary winding of the transformer T1, NS is an auxiliary winding of the transformer T1, and SW is a main switch element.
[0008]
The power supply circuit shown in FIG. 1 is a first embodiment according to the power supply circuit of the present invention. In this power supply circuit, the power supply device includes a main switch element SW connected in series to the primary winding NP of the transformer T1 in which the primary and secondary are insulated. The transformer T1 of this power supply device is provided with an auxiliary winding NS, and the auxiliary winding NS is provided with an auxiliary power supply circuit 1. The auxiliary power supply circuit 1 is a flyback type and includes a first rectifier diode D1 and a first capacitor C1, and the cathode of the first rectifier diode D1 is connected to the winding start side of the auxiliary winding NS. The anode of the first rectifier diode D1 is connected to one end of the first capacitor C1, and the other end is connected to the winding end side of the auxiliary winding NS via the resistor R1. The anode of the second rectifier diode D2 is connected to the other end of the auxiliary winding NS, and the integrated circuit 4 is connected to the cathode of the second rectifier diode D2.
[0009]
A detection circuit 2 for detecting that the secondary side is overloaded or load short-circuited is connected to the other end of the auxiliary winding NS. In the detection circuit 2, a resistor R4 is connected to one end of the auxiliary winding NS, and a first Zener diode DZ1 is connected to the other end of the resistor R4. An NPN transistor is connected to the anode of the first Zener diode DZ1. The base of the first switch element Tr1 configured as described above is connected.
[0010]
A third rectifier diode D3 is connected to one end of the auxiliary winding NS, and a second capacitor C2 is connected to the cathode of the third rectifier diode D3. In parallel with the second capacitor C2, a startup circuit 3 is provided that starts when the detection circuit 2 detects an overload or a load short circuit.
[0011]
The starter circuit 3 is provided with a second switch element Tr2 composed of an NPN transistor. The cathode of the second Zener diode DZ2 is connected to the base of the second switch element Tr2, and the anode of the second Zener diode DZ2 is connected to the other end of the second capacitor C2. The base of the second switch element Tr2 is connected to the collector of the first switch element Tr1 of the detection circuit 2, the anode of the fourth rectifier diode D4 is connected to the emitter of the second switch element Tr2, and the fourth rectifier diode The integrated circuit 4 is connected to the cathode of D4.
[0012]
The power supply circuit according to the present embodiment is configured as described above and operates as follows. First, in a steady state, a current flowing from the main power source Vin flows to the auxiliary power circuit 1 via the transformer T1. The current flowing through the auxiliary power circuit 1 flows through the second rectifier diode D2, and power is supplied to the integrated circuit 4. At this time, the voltage between the first capacitors C1 is generated by multiplying the output voltage by the turn ratio of the secondary winding N2 and the auxiliary winding NS.
[0013]
When the secondary side is overloaded or short-circuited, the voltage across the first capacitor C1 decreases, and no current flows through the first Zener diode DZ1 provided in the detection circuit 2, so that the first switch element Tr1 is switched from on to off. Accordingly, a voltage is applied to the second Zener diode DZ2 provided in the starting circuit 3, and the second switch element Tr2 is switched from OFF to ON. When the second switch element Tr2 is turned on, a current flows through the starter circuit 3, and the current flowing through the starter circuit 3 flows through the fourth rectifier diode D4 to supply power to the integrated circuit 4. At this time, the voltage between the second capacitors C2 is generated by multiplying the voltage of the main power source Vin by the turn ratio of the primary winding NP and the auxiliary winding NS in addition to the voltage between the first capacitors C1. . As described above, even if the secondary side is overloaded or short-circuited, power can be supplied to the integrated circuit 4.
[0014]
The power supply circuit shown in FIG. 2 is a second embodiment according to the power supply circuit of the present invention. In this power supply circuit, two auxiliary windings NS of the transformer T1 are provided in series, a center tap is provided at the connection portion, and the anode of the third rectifier diode D3 is connected to the center tap. Other configurations are almost the same as those in the first embodiment.
[0015]
The operation is almost the same as in the first embodiment, but two auxiliary windings NS are provided in series, a center tap is provided at this connection portion, and the anode of the third rectifier diode D3 is connected to this center tap. Thus, the power of the dropper can be reduced.
[0016]
【The invention's effect】
The present invention provides a flyback type auxiliary device in which an auxiliary winding is provided in a transformer, a first rectifier diode having a cathode connected to one end of the auxiliary winding, and a first capacitor connected in parallel with the auxiliary winding. A power circuit, and an anode of a second rectifier diode is connected to the other end of the auxiliary winding, an integrated circuit is connected to the cathode of the second rectifier diode, and in a steady state, the auxiliary power circuit is connected to the integrated circuit. In addition to supplying power, the other end of the auxiliary winding is connected to a detection circuit for detecting an overload or load short circuit, and the anode of a third rectifier diode is connected to one end of the auxiliary winding. The cathode of this third rectifier diode is connected to a second capacitor, and in parallel with this second capacitor is connected to a starting circuit that starts when the detection circuit detects an overload or a load short circuit. A second switch element is provided in the starting circuit, a control input terminal of the second switch element is connected to an input terminal of the first switch element provided in the detection circuit, and a fourth rectifier is connected to an output terminal of the second switch element. By connecting the anode of a diode and connecting the integrated circuit to the cathode of the fourth rectifier diode, and supplying power from the start-up circuit to the integrated circuit at the time of overload or load short circuit There is an effect that the loss of the dropper can be reduced and a power source can always be secured in the integrated circuit even if the secondary side is overloaded or short-circuited.
[0017]
Further, two auxiliary windings are provided in series, a center tap is provided at the connection portion, and the anode of the third rectifier diode is connected to the center tap, so that the power of the dropper can be reduced. There is an effect that can be done.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment according to the present invention.
FIG. 2 is a circuit diagram showing an embodiment different from the embodiment shown in FIG.
FIG. 3 is a circuit diagram showing a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Auxiliary power supply circuit 2 Detection circuit 3 Starting circuit 4 Integrated circuit C1 1st capacitor C2 2nd capacitor D1 1st rectifier diode D2 2nd rectifier diode D3 3rd rectifier diode D4 4th rectifier diode DZ1 1st Zener diode DZ2 2nd Zener Diode Tr1 First switch element Tr2 Second switch element Q3 Third switch element R1, R2, R4, R5, R6 Resistor T1 Transformer NP Transformer T1 primary winding N2 Transformer T1 secondary winding NS Transformer T1 auxiliary winding SW Main switching element Vin Main power supply

Claims

In a power supply circuit including a main switching element connected in series to a primary winding of a transformer, the primary and secondary are insulated, an auxiliary winding is provided in the transformer, and a cathode is connected to one end of the auxiliary winding. One rectifier diode and one end of a first capacitor constituting a flyback type auxiliary power supply circuit provided with a first capacitor at the other end of the auxiliary winding are connected, and a second end is connected to the other end of the auxiliary winding. The anode of the rectifier diode is connected, and the integrated circuit is connected to the cathode of the second rectifier diode so that, in a steady state, power is supplied from the auxiliary power circuit to the integrated circuit, and the auxiliary winding the other end of the detection circuit for detecting an overload or when load short-circuit connected to, the detection circuit comprises a resistor and a first switching element, one end of the resistor connecting the other end of the auxiliary winding, this The other end of the resistor connected to the control input terminal of said first switching element, the anode of the third rectifier diode is connected to one end of the auxiliary winding, and a cathode connected to the third rectifier diode to the second capacitor, In parallel with the second capacitor, the detection circuit is connected to a start circuit that starts when an overload or a load short circuit is detected, and the start circuit is provided with a second switch element, and the input terminal of the second switch element while connected to the cathode of the third rectifier diode, is connected to the control input of the second switching element to an input terminal of said first switching element provided in said detection circuit, the output terminal of the second switching device connect the anode of the fourth rectifier diode, with connecting the integrated circuit to the cathode of the fourth rectifier diode, said first switching device to the integrated circuit Connected to the force terminal, at the time of overload or load short, the power supply circuit, characterized in that the said starting circuit are so as to supply power to the integrated circuit.

2. The power supply circuit according to claim 1, wherein winding is started from one end side of the auxiliary winding.

3. The power supply circuit according to claim 1, wherein two auxiliary windings are provided in series, a center tap is provided at the connection portion, and an anode of the third rectifier diode is connected to the center tap. .

The detection circuit is configured by connecting the other end of the resistor to the cathode of the first Zener diode, and connecting the input terminal of the first switch element to the anode of the first Zener diode. 4. The power supply circuit according to claim 1, wherein the power supply circuit is configured to detect that the voltage of the first capacitor has dropped when the load is short-circuited.

The first switch element is an NPN transistor, the anode of the first Zener diode is connected to the base of the first switch element, and the base of the second switch element is connected to the collector of the first switch element. 5. The power supply circuit according to claim 4, wherein the first switch element is configured to be turned off from on during an overload or a load short circuit.

The starting circuit includes a second capacitor connected to the cathode of the third rectifier diode, a second Zener diode having an anode connected to the other end of the second capacitor, and the second switch connected to the cathode of the second Zener diode. 6. The power supply circuit according to claim 1, wherein a base of the element is connected.

The second switch element is an NPN transistor, the cathode of the second Zener diode is connected to the base of the second switch element, the cathode of the third rectifier diode is connected to the collector of the second switch element, 7. The power supply circuit according to claim 6, wherein an anode of the fourth rectifier diode is connected to an emitter of the second switch element.