JP3561876B2

JP3561876B2 - Variable output voltage power supply

Info

Publication number: JP3561876B2
Application number: JP33925699A
Authority: JP
Inventors: 哲也山本; 和利渕上; 浩島森
Original assignee: Fujitsu Ltd; Fujitsu Telecom Networks Ltd
Current assignee: Fujitsu Ltd; Fujitsu Telecom Networks Ltd
Priority date: 1999-11-30
Filing date: 1999-11-30
Publication date: 2004-09-02
Anticipated expiration: 2019-11-30
Also published as: JP2001161063A

Description

【０００１】
【発明の属する技術分野】
本発明は、スイッチング制御により出力電圧の安定化を図り、且つ並列運転時の電流バランスがとれるように、出力電圧を制御する出力電圧可変電源装置に関する。
【０００２】
【従来の技術】
図２は従来例の説明図であり、Ｔ１はトランス、Ｑ１はスイッチングトランジスタ、１はパルス幅制御回路（ＰＷＭ）、２は電圧検出部、３は電流検出部、４〜７は演算増幅器、Ｄ１，Ｄ１１，Ｄ１２はダイオード、Ｃ１はコンデンサ、Ｌ１はチョークコイル、ＣＴはカレントトランス、Ｒ１〜Ｒ４，Ｒ８〜Ｒ１２は抵抗、Ｖｒ１，Ｖｒ２は基準電圧、１０は同一構成の出力電圧可変電源装置、ＣＢは電流バランス端子、Ｖｃｃは電源電圧、Ｖｉｎは直流の入力電圧、Ｖｏｕｔは直流の出力電圧を示す。
【０００３】
トランスＴ１の一次巻線にスイッチングトランジスタＱ１を接続し、このスイッチングトランジスタＱ１をパルス幅制御回路１によりオン，オフを制御し、ダイオードＤ１１，Ｄ１２とチョークコイルＬ１とコンデンサＣ１とを含む整流平滑回路により、トランスＴ１の二次巻線の誘起電圧を整流して平滑化し、出力電圧Ｖｏｕｔとして負荷に印加する。又他の出力電圧可変電源装置１０を並列運転して負荷に出力電圧Ｖｏｕｔを印加する場合、電流バランス端子ＣＢを相互に接続する。
【０００４】
又電圧検出部３は、出力電圧Ｖｏｕｔを検出して演算増幅器４に入力し、基準電圧Ｖｒ１を抵抗Ｒ１〜Ｒ３により分圧した値と比較し、差分に対応した出力信号をパルス幅制御回路１に入力する。パルス幅制御回路１は、差分が零となるように、スイッチングトランジスタＱ１のオン期間を制御して、出力電圧Ｖｏｕｔの安定化を図るものである。又基準電圧Ｖｒ１を調整することにより、出力電圧Ｖｏｕｔを所望の値に設定することができる。
【０００５】
又演算増幅器６は、出力電圧Ｖｏｕｔと基準電圧Ｖｒ２とを比較し、出力電圧Ｖｏｕｔが基準電圧Ｖｒ２を超えると、過電圧アラーム信号ＯＶＡを出力する。又演算増幅器７は、出力電圧Ｖｏｕｔと、基準電圧Ｖｒ２を抵抗Ｒ１１，Ｒ１２により分圧した値とを比較し、この分圧値より出力電圧Ｖｏｕｔが低下すると、電圧低下アラーム信号ＵＶＡを出力する。又過電圧アラーム信号ＯＶＡについては、例えば、パルス幅制御回路１に入力して、スイッチングトランジスタＱ１のオン期間を最小とするように制御する。
【０００６】
又カレントトランスＣＴにより負荷に供給する電流を検出して電流検出部２に入力し、電流検出部２からの電流検出値を演算増幅器５に入力する。この電流検出部２は、例えば、カレントトランスＣＴの二次巻線に流れる電流を抵抗により電圧に変換し、その電圧をピーク整流等により直流の検出値として出力する構成を有するものである。又演算増幅器５に接続された抵抗Ｒ８，Ｒ９を同一抵抗値とすると、電流検出部２からの電流検出値と、他の出力電圧可変電源装置１０の電流バランス端子ＣＢからの電流検出値とが同一であると、演算増幅器５の出力信号は０となる。
【０００７】
他の出力電圧可変電源装置１０の電流検出値が大きい場合、演算増幅器５の出力信号は正極性の値となって、抵抗Ｒ４とダイオードＤ１とを介して抵抗Ｒ２，Ｒ３の接続点ａに印加される。それによって、演算増幅器４の抵抗Ｒ１，Ｒ２の接続点ｂの分圧電圧が上昇し、パルス幅制御回路１は、出力電圧Ｖｏｕｔを上昇させる方向にスイッチングトランジスタＱ１のオン期間を長くすることになり、それによって、負荷電流を増加することができるから、他の出力電圧可変電源装置１０との電流バランスをとることができる。
【０００８】
【発明が解決しようとする課題】
前述の従来例に於いては、演算増幅器５の出力信号は、入力される電流検出値の差に対応して０〜Ｖｃｃの範囲に変化する。それによって、抵抗Ｒ２，Ｒ３の接続点ａの電位もそれに対応して変化し、演算増幅器４に対する基準電圧としての抵抗Ｒ１，Ｒ２の接続点ｂの電位を上昇させて、パルス幅制御回路１は、スイッチングトランジスタＱ１のオン期間を必要以上に長くし、出力電圧Ｖｏｕｔを上昇させて過電圧状態となる場合がある。即ち、並列運転時の安定性に問題があった。
【０００９】本発明は、出力電圧可変電源装置に於いて、出力電圧と比較する基準電圧が必要以上に上昇しないように制御して、出力電圧の安定化及び電流バランスを図ることを目的とする。
【００１０】
【課題を解決するための手段】
本発明の出力電圧可変電源装置は、図１を参照して説明すると、（１）出力電圧を検出する電圧検出部３と、この電圧検出部３による電圧検出値と基準値とを比較する出力電圧制御用の演算増幅器４と、この演算増幅器４の出力信号に対応してスイッチング制御を行うパルス幅制御回路１と、トランスＴ１の一次巻線に接続されて、パルス幅制御回路１によりオン，オフ制御されるスイッチングトランジスタＱ１と、トランスＴ１の二次巻線に接続した整流平滑回路と、トランスＴ１の二次巻線に流れる電流を検出する電流検出部２と、この電流検出部２による電流検出値と他の出力電圧可変電源装置の電流検出値とを比較し、比較出力信号を演算増幅器４の基準値に重畳する電流バランス用の演算増幅器５とを含む出力電圧可変電源装置であって、出力電圧制御用の演算増幅器４の基準値を設定するシリーズレギュレータと複数の抵抗とからなる基準電圧回路と、電流バランス用の演算増幅器５の出力信号を、出力電圧制御用の演算増幅器４の基準値に重畳するように接続した第１及び第２の抵抗Ｒ４，Ｒ５と第１のダイオードＤ１との直列回路と、基準電圧回路の所定電位の点と、電流バランス用の演算増幅器５の出力端子に接続した第１の抵抗Ｒ４と第２の抵抗Ｒ５との接続点との間に、該接続点の電位を前記所定電位にクランプするように接続した第２のダイオードＤ２とを備えている。
【００１１】
又（２）基準電圧回路は、抵抗Ｒ６とシリーズレギレータＳＲＧとの接続点の電位を基準電圧とする直列回路と、シリーズレギュレータＳＲＧを制御する可変抵抗ＶＲと、基準電圧を印加する複数の抵抗Ｒ１，Ｒ２，Ｒ３の直列回路とを有し、この直列回路の抵抗分圧点ｂを出力電圧制御用の演算増幅器４の基準値とし、他の抵抗分圧点ａに、電流バランス用の演算増幅器５の出力信号を第１及び第２の抵抗Ｒ４，Ｒ５と第１のダイオードＤ１との直列回路を介して印加する回路と、基準電圧の点を基準電圧回路の所定電位の点として、第１の抵抗Ｒ４と第２の抵抗Ｒ５との接続点との間に、この接続点の電位を所定電位にクランプするように接続した第２のダイオードＤ２とを有する構成とする。
【００１２】
又（３）基準電圧回路の基準電圧を、出力電圧が上昇した時に過電圧アラーム信号ＯＶＡを出力する演算増幅器６と、出力電圧が低下した時に電圧低下アラーム信号ＵＶＡを出力する演算増幅器７との基準電圧とした構成を有するものである。
【００１３】
【発明の実施の形態】
図１は本発明の実施の形態の説明図であり、Ｔ１はトランス、Ｑ１はスイッチングトランジスタ、１はパルス幅制御回路（ＰＷＭ）、２は電圧検出部、３は電流検出部、４〜７は演算増幅器であり、演算増幅器４は出力電圧制御用、演算増幅器５は電流バランス用、演算増幅器６は過電圧アラーム用、演算増幅器７は電圧低下アラーム用である。又Ｄ１，Ｄ２，Ｄ１１，Ｄ１２はダイオード、Ｃ１はコンデンサ、Ｌ１はチョークコイル、ＣＴはカレントトランス、Ｒ１〜Ｒ１２は抵抗、ＶＲは可変抵抗、ＳＲＧはシリーズレギュレータ、ＣＢは電流バランス端子、Ｖ，Ｖｃｃは電源電圧、Ｖｉｎは直流の入力電圧、Ｖｏｕｔは直流の出力電圧を示す。
【００１４】
この実施の形態は、抵抗Ｒ１〜Ｒ３，Ｒ６，Ｒ７と、可変抵抗ＶＲと、シリーズレギュレータＳＲＧとにより基準電圧回路を構成し、抵抗Ｒ６，Ｒ７の接続点ｃの安定化された電位を基準電圧とする。この基準電圧は、可変抵抗ＶＲによりシリーズレギュレータＳＲＧを制御することによって、任意に設定することができる。この基準電圧を抵抗Ｒ１〜Ｒ３の直列回路に印加し、抵抗Ｒ１，Ｒ２の接続点ｂを演算増幅器４に入力する基準値とする。又基準電圧を抵抗Ｒ１１，Ｒ１２に印加し、過電圧アラーム用の演算増幅器６と電圧低下アラーム用の演算増幅器７の基準値とする。
【００１５】
又電流バランス用の演算増幅器５の出力端子に第１，第２の抵抗Ｒ４，Ｒ５と第１のダイオードＤ１とを接続し、この第１のダイオードＤ１を、抵抗Ｒ２，Ｒ３の接続点ａに接続し、第１，第２の抵抗Ｒ４，Ｒ５の接続点と、抵抗Ｒ６，Ｒ７の接続点ｃとの間に第２のダイオードＤ２を接続する。この第２のダイオードＤ２は、第１，第２の抵抗Ｒ４，Ｒ５の接続点の電位を、接続点ｃの電位にクランプできるように接続する。
【００１６】
従って、電流バランス端子ＣＢに、他の出力電圧可変電源装置からの電流検出値が入力されて、この電流検出値が、電流検出部２からの電流検出値より大きい場合に、電流バランス用の演算増幅器５の出力信号は大きくなり、例えば、電源電圧Ｖｃｃ又はそれに近い値となると、第２のダイオードＤ２に対して順方向電圧が印加される状態となり、従って、第１，第２の抵抗Ｒ４，Ｒ５の接続点の電位は、接続点ｃの電位にクランプされる。それにより、接続点ａの電位の上昇が抑制され、それに伴って接続点ｂの電位、即ち、出力電圧制御用の演算増幅器４の基準値の上昇が抑制されて、出力電圧Ｖｏｕｔの極端な上昇を回避することができる。
【００１７】
又基準電圧回路は、可変抵抗ＶＲにより基準電圧を任意に設定可能であり、この基準電圧を、演算増幅器６，７の基準電圧とすることにより、出力電圧Ｖｏｕｔの設定変更に伴って、過電圧アラームの検出基準値及び電圧低下アラームの検出基準値も自動的に変更されるから、基準電圧源の構成を簡単化し、且つ出力電圧Ｖｏｕｔの設定変更が容易となる利点がある。
【００１８】
本発明は、前述の実施の形態のみに限定されるものではなく、種々付加変更することが可能であり、例えば、前述の実施の形態はフォワードコンバータ形式について示すが、フライバックコンバータ形式等の他の形式のコンバータを用いた電源装置にも適用可能である。又基準電源回路は、シリーズレギュレータＳＲＧを用いた場合を示すが、ツェナーダイオード等の他の電圧安定化手段を有する回路を用いることも可能である。又電流検出部２による電流検出値を用いて過電流保護を行う構成を設けることも可能である。
【００１９】
【発明の効果】
以上説明したように、本発明は、スイッチング制御する電源装置に於いて、出力電圧制御用の演算増幅器４の基準値を設定するシリーズレギュレータＳＲＧ等を含む基準電圧回路と、電流バランス用の演算増幅器５の出力信号を、出力電圧制御用の演算増幅器４の基準値に重畳するように接続した第１の抵抗Ｒ４と第１のダイオードＤ１と、基準電圧回路の所定電位の点（接続点ｃ）と、電流バランス用の演算増幅器５の出力端子に接続した第１の抵抗Ｒ４と第２の抵抗Ｒ５との接続点との間に、この接続点の電位をクランプするように接続した第２のダイオードＤ２とを設けたもので、並列運転時の電流検出値の差が大きい時に、電流バランス用の演算増幅器５の出力信号が、電源電圧Ｖｃｃ近くまで上昇可能であるから、それを第２のダイオードＤ２を介して抵抗Ｒ４，Ｒ５の接続点の電位をクランプすることにより、出力電圧Ｖｏｕｔの極端な上昇を回避し、並列運転の安定化を図ることができる利点がある。
【図面の簡単な説明】
【図１】本発明の実施の形態の説明図である。
【図２】従来例の説明図である。
【符号の説明】
１パルス幅制御回路（ＰＷＭ）
２電流検出部
３電圧検出部
４出力電圧制御用の演算増幅器
５電流バランス用の演算増幅器
６過電圧アラーム用の演算増幅器
７電圧低下アラーム用の演算増幅器
Ｔ１トランス
Ｑ１スイッチングトランジスタ
ＳＲＧシリーズレギュレータ
Ｒ１，Ｒ２第１，第２の抵抗
Ｄ１，Ｄ２第１，第２のダイオード
ＣＢ電流バランス端子[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an output voltage variable power supply device that controls an output voltage so as to stabilize an output voltage by switching control and to balance current during parallel operation.
[0002]
[Prior art]
FIG. 2 is an explanatory view of a conventional example, where T1 is a transformer, Q1 is a switching transistor, 1 is a pulse width control circuit (PWM), 2 is a voltage detector, 3 is a current detector, 4 to 7 are operational amplifiers, D1 , D11 and D12 are diodes, C1 is a capacitor, L1 is a choke coil, CT is a current transformer, R1 to R4, R8 to R12 are resistors, Vr1 and Vr2 are reference voltages, 10 is an output voltage variable power supply having the same configuration, CB Denotes a current balance terminal, Vcc denotes a power supply voltage, Vin denotes a DC input voltage, and Vout denotes a DC output voltage.
[0003]
A switching transistor Q1 is connected to the primary winding of the transformer T1, and the switching transistor Q1 is turned on and off by a pulse width control circuit 1, and is controlled by a rectifying and smoothing circuit including diodes D11 and D12, a choke coil L1, and a capacitor C1. Rectifies and smoothes the induced voltage of the secondary winding of the transformer T1, and applies it to the load as the output voltage Vout. When another output voltage variable power supply device 10 is operated in parallel to apply the output voltage Vout to the load, the current balance terminals CB are connected to each other.
[0004]
The voltage detector 3 detects the output voltage Vout, inputs the output voltage Vout to the operational amplifier 4, compares the reference voltage Vr1 with a value obtained by dividing the reference voltage Vr1 by the resistors R1 to R3, and outputs an output signal corresponding to the difference to the pulse width control circuit 1. To enter. The pulse width control circuit 1 controls the ON period of the switching transistor Q1 so that the difference becomes zero, thereby stabilizing the output voltage Vout. Further, by adjusting the reference voltage Vr1, the output voltage Vout can be set to a desired value.
[0005]
The operational amplifier 6 compares the output voltage Vout with the reference voltage Vr2, and outputs an overvoltage alarm signal OVA when the output voltage Vout exceeds the reference voltage Vr2. The operational amplifier 7 compares the output voltage Vout with a value obtained by dividing the reference voltage Vr2 by the resistors R11 and R12, and outputs a voltage drop alarm signal UVA when the output voltage Vout falls below the divided value. The overvoltage alarm signal OVA is input to, for example, the pulse width control circuit 1 to control the ON period of the switching transistor Q1 to be minimized.
[0006]
Further, the current supplied to the load is detected by the current transformer CT and input to the current detection unit 2, and the current detection value from the current detection unit 2 is input to the operational amplifier 5. The current detection unit 2 has a configuration in which, for example, a current flowing through the secondary winding of the current transformer CT is converted into a voltage by a resistor, and the voltage is output as a DC detection value by peak rectification or the like. If the resistors R8 and R9 connected to the operational amplifier 5 have the same resistance value, the current detection value from the current detection unit 2 and the current detection value from the current balance terminal CB of the other output voltage variable power supply 10 will be different. If they are the same, the output signal of the operational amplifier 5 becomes 0.
[0007]
When the current detection value of the other output voltage variable power supply 10 is large, the output signal of the operational amplifier 5 has a positive value and is applied to the connection point a of the resistors R2 and R3 via the resistor R4 and the diode D1. Is done. As a result, the divided voltage at the connection point b between the resistors R1 and R2 of the operational amplifier 4 increases, and the pulse width control circuit 1 lengthens the ON period of the switching transistor Q1 in a direction to increase the output voltage Vout. Accordingly, since the load current can be increased, the current balance with another output voltage variable power supply device 10 can be balanced.
[0008]
[Problems to be solved by the invention]
In the above-described conventional example, the output signal of the operational amplifier 5 changes in the range of 0 to Vcc in accordance with the difference between the input current detection values. Thereby, the potential of the connection point a of the resistors R2 and R3 also changes correspondingly, and the potential of the connection point b of the resistors R1 and R2 as a reference voltage for the operational amplifier 4 is increased, so that the pulse width control circuit 1 In some cases, the on-period of the switching transistor Q1 is made unnecessarily long, and the output voltage Vout is increased, resulting in an overvoltage state. That is, there was a problem in stability during parallel operation.
SUMMARY OF THE INVENTION It is an object of the present invention to stabilize an output voltage and balance current by controlling a reference voltage to be compared with an output voltage not to rise more than necessary in an output voltage variable power supply device. .
[0010]
[Means for Solving the Problems]
The output voltage variable power supply according to the present invention will be described with reference to FIG. 1. (1) A voltage detector 3 for detecting an output voltage, and an output for comparing a voltage detection value of the voltage detector 3 with a reference value. An operational amplifier 4 for voltage control, a pulse width control circuit 1 for performing switching control in response to an output signal of the operational amplifier 4, and a pulse width control circuit 1 connected to the primary winding of the transformer T1 A switching transistor Q1 that is turned off, a rectifying / smoothing circuit connected to the secondary winding of the transformer T1, a current detection unit 2 for detecting a current flowing through the secondary winding of the transformer T1, and a current detected by the current detection unit 2. An output voltage variable power supply including a current balance operational amplifier 5 for comparing a detected value with a current detected value of another output voltage variable power supply and superimposing a comparison output signal on a reference value of the operational amplifier 4. A reference voltage circuit composed of a series regulator for setting a reference value of the operational amplifier 4 for output voltage control and a plurality of resistors, and an output signal of the operational amplifier 5 for current balance are converted into an operational amplifier for output voltage control. 4, a series circuit of the first and second resistors R4, R5 and the first diode D1 connected so as to be superimposed on the reference value, a predetermined potential point of the reference voltage circuit, and an operational amplifier 5 for current balance. A second diode D2 connected between the connection point of the first resistor R4 and the connection point of the second resistor R5 connected to the output terminal of the second diode D2 so as to clamp the potential of the connection point to the predetermined potential. ing.
[0011]
(2) The reference voltage circuit includes a series circuit that uses the potential at the connection point between the resistor R6 and the series regulator SRG as a reference voltage, a variable resistor VR that controls the series regulator SRG, and a plurality of resistors that apply the reference voltage. R1, R2, and a series circuit of R3, a reference value of the operational amplifier 4 for output voltage control resistor voltage dividing point b of the series circuit, the other resistive voltage dividing point a, the calculation of current balance A circuit for applying the output signal of the amplifier 5 through a series circuit of the first and second resistors R4 and R5 and the first diode D1, and a point of the reference voltage as a point of a predetermined potential of the reference voltage circuit. A second diode D2 is connected between a connection point between the first resistor R4 and the second resistor R5 so as to clamp the potential at this connection point to a predetermined potential .
[0012]
(3) The reference voltage of the reference voltage circuit is determined by the operational amplifier 6 that outputs the overvoltage alarm signal OVA when the output voltage rises and the operational amplifier 7 that outputs the voltage drop alarm signal UVA when the output voltage drops. It has a voltage configuration.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is an explanatory view of an embodiment of the present invention, where T1 is a transformer, Q1 is a switching transistor, 1 is a pulse width control circuit (PWM), 2 is a voltage detector, 3 is a current detector, and 4 to 7 are The operational amplifier 4 is for output voltage control, the operational amplifier 5 is for current balance, the operational amplifier 6 is for an overvoltage alarm, and the operational amplifier 7 is for a voltage drop alarm. D1, D2, D11 and D12 are diodes, C1 is a capacitor, L1 is a choke coil, CT is a current transformer, R1 to R12 are resistors, VR is a variable resistor, SRG is a series regulator, CB is a current balance terminal, V and Vcc. Denotes a power supply voltage, Vin denotes a DC input voltage, and Vout denotes a DC output voltage.
[0014]
In this embodiment, a reference voltage circuit is configured by resistors R1 to R3, R6, and R7, a variable resistor VR, and a series regulator SRG, and a stabilized potential at a connection point c between the resistors R6 and R7 is used as a reference voltage. And This reference voltage can be arbitrarily set by controlling the series regulator SRG with the variable resistor VR. This reference voltage is applied to a series circuit of the resistors R1 to R3, and a connection point b between the resistors R1 and R2 is set as a reference value to be input to the operational amplifier 4. Further, a reference voltage is applied to the resistors R11 and R12 to be used as reference values for the operational amplifier 6 for an overvoltage alarm and the operational amplifier 7 for a voltage drop alarm.
[0015]
Also, the first and second resistors R4 and R5 and the first diode D1 are connected to the output terminal of the operational amplifier 5 for current balance, and this first diode D1 is connected to the connection point a between the resistors R2 and R3. And a second diode D2 is connected between a connection point between the first and second resistors R4 and R5 and a connection point c between the resistors R6 and R7. The second diode D2 is connected so that the potential at the connection point between the first and second resistors R4 and R5 can be clamped to the potential at the connection point c.
[0016]
Accordingly, when a current detection value from another output voltage variable power supply device is input to the current balance terminal CB, and this current detection value is larger than the current detection value from the current detection unit 2, the current balance calculation is performed. When the output signal of the amplifier 5 increases and becomes, for example, the power supply voltage Vcc or a value close thereto, a forward voltage is applied to the second diode D2. The potential of the connection point of R5 is clamped at the potential of the connection point c. As a result, a rise in the potential of the connection point a is suppressed, and accordingly, a rise in the potential of the connection point b, that is, the reference value of the operational amplifier 4 for controlling the output voltage is suppressed, so that the output voltage Vout extremely increases. Can be avoided.
[0017]
The reference voltage circuit can arbitrarily set a reference voltage by using a variable resistor VR. By using this reference voltage as the reference voltage of the operational amplifiers 6 and 7, an overvoltage alarm is generated with a change in the setting of the output voltage Vout. And the detection reference value of the voltage drop alarm are automatically changed, so that there is an advantage that the configuration of the reference voltage source is simplified and the setting of the output voltage Vout can be easily changed.
[0018]
The present invention is not limited to the above-described embodiment, and various additions and changes can be made. For example, the above-described embodiment shows the forward converter type, but the present invention is not limited to the flyback converter type. The present invention is also applicable to a power supply device using a converter of the type described above. Although the reference power supply circuit uses a series regulator SRG, a circuit having another voltage stabilizing means such as a Zener diode can be used. It is also possible to provide a configuration for performing overcurrent protection using the current detection value of the current detection unit 2.
[0019]
【The invention's effect】
As described above, according to the present invention, in a power supply device for switching control, a reference voltage circuit including a series regulator SRG for setting a reference value of an operational amplifier 4 for output voltage control, and an operational amplifier for current balance 5, a first resistor R4 and a first diode D1 connected so as to be superimposed on a reference value of the operational amplifier 4 for output voltage control, and a point (connection point c) of a predetermined potential of the reference voltage circuit. And a second node connected between the first resistor R4 and the second resistor R5 connected to the output terminal of the operational amplifier 5 for current balance so as to clamp the potential at the node. When the difference between the current detection values during parallel operation is large, the output signal of the operational amplifier 5 for current balance can rise to near the power supply voltage Vcc. Da By clamping the potential at the connection point of the resistors R4, R5 via the diode D2, avoiding extreme increase in the output voltage Vout, has the advantage that it is possible to stabilize the parallel operation.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a conventional example.
[Explanation of symbols]
1 Pulse width control circuit (PWM)
2 Current detection unit 3 Voltage detection unit 4 Operational amplifier for output voltage control 5 Operational amplifier for current balance 6 Operational amplifier for overvoltage alarm 7 Operational amplifier T1 for voltage drop alarm Transformer Q1 Switching transistor SRG Series regulators R1, R2 1, second resistor D1, D2 first and second diode CB current balance terminal

Claims

A voltage detector for detecting an output voltage, an operational amplifier for controlling an output voltage for comparing a voltage detected by the voltage detector with a reference value, and a pulse width for performing switching control in accordance with an output signal of the operational amplifier A control circuit, a switching transistor connected to the primary winding of the transformer and being turned on and off by the pulse width control circuit, a rectifying and smoothing circuit connected to the secondary winding of the transformer, and a secondary winding of the transformer A current detection unit that detects a current flowing through the current detection unit, and compares a current detection value of the current detection unit with a current detection value of another output voltage variable power supply device, and superimposes a comparison output signal on the reference value of the operational amplifier. In an output voltage variable power supply including an operational amplifier for current balance,
A reference voltage circuit comprising a series regulator and a plurality of resistors for setting the reference value of the output voltage control operational amplifier,
A series circuit of first and second resistors and a first diode connected to superimpose an output signal of the operational amplifier for current balancing on the reference value of the operational amplifier for output voltage control ;
A point of predetermined potential of the reference voltage circuit, between a connection point of the first and the resistor connected to the output terminal and the second resistor of the operational amplifier for the current balance, the potential of the connection point A second diode connected so as to be clamped to the predetermined potential .

The reference voltage circuit is used, the number a series circuit for the potential of the connection point between the resistor and the series regulator and a reference voltage, a variable resistor for controlling the series regulator, and a series circuit of a plurality of resistors for applying the reference voltage and, wherein the resistive voltage dividing point of the series circuit and the reference value of the operational amplifier for the output voltage control, the other resistive voltage dividing point, the first and the output signal of the operational amplifier for the current balancing the A second resistor and a first diode, which are applied through a series circuit ; and a first resistor and a second resistor, wherein a point of the reference voltage is a point of the predetermined potential of the reference voltage circuit. 2. The variable output voltage power supply device according to claim 1, further comprising a second diode connected between the first and second connection points so as to clamp the potential at the connection point to the predetermined potential .

An operational amplifier that compares a reference voltage of the reference voltage circuit with the output voltage and outputs an overvoltage alarm signal when the output voltage increases, and an operational amplifier that outputs a voltage drop alarm signal when the output voltage decreases 3. The variable output voltage power supply device according to claim 1, wherein the output voltage variable power supply device has a configuration in which a reference voltage is used as the reference voltage.