WO2013187269A1 - Switching power source device - Google Patents

Switching power source device Download PDF

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Publication number
WO2013187269A1
WO2013187269A1 PCT/JP2013/065319 JP2013065319W WO2013187269A1 WO 2013187269 A1 WO2013187269 A1 WO 2013187269A1 JP 2013065319 W JP2013065319 W JP 2013065319W WO 2013187269 A1 WO2013187269 A1 WO 2013187269A1
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Prior art keywords
voltage
circuit
line
diode
drive
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PCT/JP2013/065319
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French (fr)
Japanese (ja)
Inventor
鵜野良之
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株式会社村田製作所
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Priority to JP2014521267A priority Critical patent/JP5825433B2/en
Priority to CN201380030522.XA priority patent/CN104350671B/en
Publication of WO2013187269A1 publication Critical patent/WO2013187269A1/en

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0006—Arrangements for supplying an adequate voltage to the control circuit of converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters

Definitions

  • the present invention relates to a switching power supply device, and more particularly to a switching power supply device including a bootstrap circuit.
  • Patent Document 1 discloses a switching power supply device including a step-down converter. Since the switching element of the step-down converter is a high-side switching element in the circuit, it is necessary to generate a control voltage based on the potential side higher than the ground level for its control. A bootstrap circuit is provided.
  • Patent Document 2 in a circuit for supplying power to a load connected to the midpoint of two switching elements by alternately turning on and off two semiconductor switching elements in series at both ends of a DC power supply by a control signal.
  • a drive circuit using a bootstrap circuit is shown to supply power for driving a switching element connected to the high side of a DC power supply.
  • the capacitor of the bootstrap circuit is charged from the auxiliary power source via the diode.
  • an object of the present invention is to enable charging of the capacitor of the bootstrap circuit even when the input power supply off-period is short, and to enable switching control of the switch element at the start of operation after the off-period. It is an object of the present invention to provide a switching power supply device that can obtain an output voltage of 2.
  • a switching power supply drives a main current line connecting an input terminal and an output terminal, a step-down converter provided on the main current line, having an inductor, a switch element and a first diode, and the switch element
  • a driving circuit for applying a driving voltage to the driving circuit, a capacitor connected between the main current line and the driving voltage line, and an external control voltage input from the outside.
  • the bootstrap diode to be applied to the constant voltage, the voltage of the main current line as a reference, the constant voltage of the input voltage input from the input terminal, to supply a voltage lower than the external control voltage to the drive voltage line And a circuit.
  • the drive voltage based on the main current line is supplied to the drive circuit by the voltage charged in the capacitor of the bootstrap circuit, the voltage necessary for controlling the switch element can be obtained.
  • the potential of the drive voltage line is, for example, the ground potential, such as at the time of initial startup, the capacitor of the bootstrap circuit is charged by the external control voltage. At this time, since the voltage supplied from the constant voltage circuit is lower than the external control voltage, the capacitor of the bootstrap circuit is not charged from the constant voltage circuit.
  • the capacitor of the bootstrap circuit is charged with the external control voltage. Even at this time, since the voltage supplied by the constant voltage circuit is lower than the external control voltage, the capacitor is not charged from the constant voltage circuit. However, after that, when the main current line becomes a steady potential, the capacitor is already charged with the external control voltage, so even at this time, it is not charged from the constant voltage circuit. After that, when the switching power supply is temporarily stopped and the voltage between the output terminals is high (the voltage remains in the smoothing capacitor), the capacitor of the bootstrap circuit cannot be charged with the external control voltage. Since the voltage between the input terminals is higher than the voltage between the output terminals (since it is a step-down converter), the capacitor of the bootstrap circuit is charged by the constant voltage circuit using the main current line as a reference potential.
  • the main current is charged by a constant voltage from a constant voltage circuit using the line as a reference potential, and a driving voltage is applied to the driving circuit, thereby enabling restart. Since the constant voltage circuit does not operate during steady operation, there is no resistance loss in the constant voltage circuit during steady operation, and high efficiency can be achieved.
  • a collector and a base are connected to the input terminal, an emitter is connected to the drive voltage line, an anode is connected to the main current line, and a cathode is connected to the base of the transistor. It is preferable to have a Zener diode.
  • a stabilized constant voltage can be supplied to the drive voltage line with a circuit having a small number of parts.
  • the switching power supply device includes a second diode provided between the input terminal and the constant voltage circuit to prevent a backflow current from the constant voltage circuit.
  • the switching power supply device includes a fourth diode that is provided between the drive voltage line and the constant voltage circuit and prevents application of a reverse bias from the constant voltage circuit.
  • the step-down converter preferably has a configuration in which an LED is connected to the output side.
  • the LED can be reliably turned on even if the LED is turned on and off in a short time.
  • the capacitor of the bootstrap circuit can be charged to a predetermined driving voltage even when the switching power supply device is restarted for a short time after it has been temporarily stopped. For this reason, switching control of the switch element of the step-down converter can be reliably performed at the start of the operation of the switching power supply apparatus, and a desired output can be obtained.
  • FIG. 1 is a circuit diagram of a switching power supply device according to Embodiment 1.
  • FIG. FIG. 4 is a circuit diagram of a switching power supply device according to a second embodiment.
  • FIG. 1 is a circuit diagram of a switching power supply device according to the first embodiment.
  • the switching power supply device 101 steps down the input voltage Vi input from the input terminals Pi (+) and Pi ( ⁇ ) by a step-down converter, and outputs it from the output terminals Po (+) and Po ( ⁇ ).
  • the voltage Vo is output.
  • a DC voltage source E is connected to the input terminals Pi (+) and Pi ( ⁇ ).
  • a constant current driven load such as an LED is connected to the output terminals Po (+) and Po ( ⁇ ).
  • a line connecting the input terminal Pi (+) and the output terminal Po (+) is referred to as a main current line 41.
  • the step-down converter of the switching power supply apparatus 101 includes an n-type MOS-FET (hereinafter referred to as FET) 11, an inductor L1, and a diode D1.
  • FET n-type MOS-FET
  • L1 inductor
  • D1 diode
  • the FET 11 and the inductor L1 are connected in series and provided in the main current line 41. More specifically, the drain of the FET 11 is connected to the input terminal Pi (+), and the source is connected to the output terminal Po (+) via the inductor L1.
  • the cathode of the diode D1 is connected to the connection point of the FET 11 and the inductor L1, and the anode is connected to a ground line connecting the input terminal Pi ( ⁇ ) and the output terminal Po ( ⁇ ).
  • the switching power supply apparatus 101 includes a drive circuit 30, a level shift circuit 31, and a control circuit 32.
  • the drive circuit 30 corresponds to the drive circuit of the present invention.
  • control circuit 32 detects the output current via a resistor (not shown) provided on the ground line and shifts the level of a drive signal for switching the FET 11 so that a predetermined output current Io is obtained. Output to the circuit 31.
  • the control circuit 32 operates with an external control voltage Vcc input through the external power supply line 43.
  • the external power supply line 43 is connected to a decoupling capacitor or a capacitor C2 as a smoothing capacitor.
  • the level shift circuit 31 performs level shift of the drive signal output from the control circuit 32 and outputs it to the drive circuit 30.
  • the drive circuit 30 performs switching control of the FET 11 based on the drive signal level-shifted by the level shift circuit 31. At this time, the drive circuit 30 raises the voltage level of the drive signal by the bootstrap circuit 10 and applies it to the gate of the FET 11. A drive voltage is supplied from the bootstrap circuit 10 to the drive circuit 30 through the drive voltage line 42.
  • the bootstrap circuit 10 has a capacitor C1 and a bootstrap diode D2.
  • the capacitor C ⁇ b> 1 is connected between the drive voltage line 42 and the main current line 41.
  • the bootstrap diode D ⁇ b> 2 has a cathode connected to the drive voltage line 42 and an anode connected to the external power supply line 43.
  • the switching power supply device 101 includes a constant voltage circuit 20 that converts the input voltage Vi to a constant voltage Vb and supplies the input voltage Vi to the drive voltage line 42 with the potential of the main current line 41 as a reference.
  • the constant voltage circuit 20 includes a resistor R1, a transistor 12, and a Zener diode Dz.
  • the transistor 12 has a base connected to the input terminal Pi (+) via the resistor R1, a collector connected to the input terminal Pi (+), and an emitter connected to the drive voltage line 42.
  • the Zener diode Dz has a Zener voltage substantially equal to the constant voltage Vb, an anode connected to the main current line 41, and a cathode connected to the base of the transistor 12.
  • the external control voltage Vcc is set higher than the Zener voltage (constant voltage Vb) of the Zener diode Dz of the constant voltage circuit 20.
  • the input voltage Vi is 80V
  • the output voltage Vo is 50V
  • the external control voltage Vcc is 15V
  • the constant voltage Vb is 12V.
  • the cathode potential of the diode D1 in the main current line 41 which is the reference potential for charging the capacitor C1 varies depending on the on / off state of the FET 11. For example, when the FET 11 is on, the cathode potential of the diode D1 is Vin (80V), and when the FET 11 is off, the cathode potential of the diode D1 is almost the ground potential.
  • the capacitor C1 is charged with the external control voltage Vcc of 15V through the path A passing from the external power supply line 43 through the bootstrap diode D2.
  • the capacitor C1 is not charged from the constant voltage Vb of 12V by the constant voltage circuit 20.
  • the drive circuit 30 can apply the drive voltage between the gate and source of the FET 11, and the FET 11 can be reliably switched.
  • the switching power supply device 101 stops operating and restarts in a short off period, the charge of the capacitor Co may not be completely discharged and the charge may remain in the capacitor Co.
  • the load has a diode characteristic such as an LED, current does not flow unless a voltage higher than a certain level is applied, so that the capacitor Co is difficult to discharge. Therefore, for example, when the potential of the main current line 41 is 13 V, the external power supply line 43 has substantially the same potential as the main current line 41 and the drive voltage line 42. In this case, the bootstrap diode D2 becomes non-conductive until there is no remaining charge in the capacitor Co, and the capacitor C1 is not charged by the external control voltage Vcc.
  • the transistor 12 operates at a potential higher by a Zener voltage (12 V of the constant voltage Vb) with the main current line 41 as a reference potential during the off-period of the FET 11. To do. For this reason, the transistor 12 of the constant voltage circuit 20 operates, and the constant voltage Vb of 12V after the constant voltage of the input voltage Vi of 80V is passed through the capacitor C1 from the transistor 12 and the capacitor C1 has a constant voltage of 12V. The voltage Vb is charged.
  • the drive circuit 30 can stably switch the FET 11.
  • the capacitor C1 is constantly charged with the constant voltage Vb after the constant voltage by the constant voltage circuit 20, a resistance loss occurs in the constant voltage circuit 20.
  • the capacitor C1 is charged from the external control voltage Vcc higher than the voltage after the constant voltage by the constant voltage circuit 20, so the constant voltage circuit 20 does not operate and the resistance loss is reduced. it can.
  • FIG. 2 is a circuit diagram of the switching power supply device according to the second embodiment.
  • the switching power supply apparatus 102 according to the present embodiment has the same basic circuit configuration as that of the first embodiment. Hereinafter, differences from the first embodiment will be described.
  • a diode (second diode of the present invention) D3 and a resistor R2 are provided between the input terminal Pi (+) and the constant voltage circuit 20.
  • the diode D3 has an anode connected to the input terminal Pi (+) and a cathode connected to the base of the transistor 12 via the resistor R2 and the resistor R1.
  • the collector of the transistor 12 is connected to the resistor R2 through the resistor R3.
  • a resistor R4 is connected in series to the bootstrap diode D2 of the bootstrap circuit 10.
  • a diode (a third diode of the present invention) D4 is provided between the emitter of the transistor 12 and the drive voltage line.
  • the diode D3 is intended to prevent a reverse bias from being applied to the constant voltage circuit 20.
  • the input terminal Pi (+) and the cathode of the diode D1 are at the same potential due to the action of the body diode of the FET 11, but when the charge remains in the capacitor C1, the constant voltage circuit A reverse bias is applied to.
  • the diode D3 it is possible to prevent destruction between the base and the emitter of the transistor 12 due to the reverse bias voltage.
  • the resistors R2, R3, and R4 are elements for preventing overcurrent, and the destruction of each element can be prevented.
  • the diode D4 prevents a reverse bias from being applied to the constant voltage circuit 20.
  • the external control voltage Vcc is set to be higher than the Zener voltage (constant voltage Vb) of the Zener diode Dz of the constant voltage circuit 20, and therefore, a reverse bias is applied between the base and emitter of the transistor 12. Applied.
  • Vb constant voltage
  • the diode D4 it is possible to prevent the base 12 and the emitter of the transistor 12 from being destroyed by the reverse bias voltage.

Abstract

A switching power source device comprising: a step-down converter provided to a main current line (41) and having an inductor (L1), an FET (11), and a diode (D1); a drive circuit (30) for driving the FET (11); a drive voltage line (42) for applying and transmitting a drive voltage to be applied to a drive circuit (30); a capacitor (C1) connected between the main current line (41) and the drive voltage line (42); a constant voltage circuit (20) for making an input voltage constant and supplying the voltage to the drive voltage line (42) with the electric potential of the main current line (41) as a reference; and a boot-strap diode (D2) for applying and transmitting to the drive voltage line (42) an externally controlled voltage that is higher than the voltage made constant by the constant voltage circuit (20). A switching power source device is thereby provided, in which switching control of a switching element at operation startup is reliably performed and the desired output voltage is obtained even when the timeframe during which an input power source is off is short.

Description

スイッチング電源装置Switching power supply
　本発明は、スイッチング電源装置に関し、特にブートストラップ回路を備えるスイッチング電源装置に関するものである。 The present invention relates to a switching power supply device, and more particularly to a switching power supply device including a bootstrap circuit.
　従来、降圧コンバータなどのスイッチング電源装置において、ブートストラップ回路を備えたものがある。特許文献１には、降圧コンバータを備えたスイッチング電源装置が開示されている。降圧コンバータのスイッチ素子は回路上、ハイサイドのスイッチ素子であるので、その制御のためには、グランドレベルより高い電位側を基準とする制御電圧を生成する必要があり、そのためにダイオード及びコンデンサを備えたブートストラップ回路が設けられている。 Conventionally, some switching power supply devices such as a step-down converter have a bootstrap circuit. Patent Document 1 discloses a switching power supply device including a step-down converter. Since the switching element of the step-down converter is a high-side switching element in the circuit, it is necessary to generate a control voltage based on the potential side higher than the ground level for its control. A bootstrap circuit is provided.
　特許文献２では、直流電源の両端に直列に２個の半導体スイッチ素子を制御信号により交互にオン／オフさせて、２個のスイッチング素子の中点に接続された負荷に電力を供給する回路において、直流電源のハイサイド側に接続されたスイッチング素子を駆動するための電源を供給するために、ブートストラップ回路を用いた駆動回路が示されている。ローサイド側スイッチング素子がオンすると、補助電源からダイオードを介してブートストラップ回路のキャパシタに充電が行われる。 In Patent Document 2, in a circuit for supplying power to a load connected to the midpoint of two switching elements by alternately turning on and off two semiconductor switching elements in series at both ends of a DC power supply by a control signal. A drive circuit using a bootstrap circuit is shown to supply power for driving a switching element connected to the high side of a DC power supply. When the low-side switching element is turned on, the capacitor of the bootstrap circuit is charged from the auxiliary power source via the diode.
特開平１０－５６７７６号公報Japanese Patent Laid-Open No. 10-56776 特開２００７－６２０７号公報Japanese Patent Laid-Open No. 2007-6207
　しかしながら、特許文献１の回路構成では、ブートストラップ回路のキャパシタには入力電圧が直接充電されるため、ＦＥＴドライブ回路の耐圧を超える大きい入力電圧が入力されるような場合、特許文献１に係る降圧コンバータは適用出来ないといった問題がある。また、特許文献２の回路では、ローサイド側のスイッチング素子がオンすることによりブートストラップ回路のキャパシタに充電が行われるため、このブートストラップ回路をダイオード整流の降圧コンバータに適用した場合、コンバータが一旦停止させて再起動させたような場合であって、出力側にあるキャパシタ又は負荷等の電荷が放電しきれず、電荷が残留している状態で起動された場合には、ブートストラップ回路のキャパシタには入力電圧が充電されなくなり、ブートストラップ回路として機能せず、スイッチ素子を確実に駆動できないといった問題もある。 However, in the circuit configuration of Patent Document 1, since the input voltage is directly charged to the capacitor of the bootstrap circuit, when a large input voltage exceeding the withstand voltage of the FET drive circuit is input, the step-down according to Patent Document 1 is performed. There is a problem that the converter is not applicable. In the circuit of Patent Document 2, since the capacitor of the bootstrap circuit is charged by turning on the low-side switching element, when the bootstrap circuit is applied to a diode rectification step-down converter, the converter is temporarily stopped. If the capacitor on the output side is not fully discharged and is activated with the charge remaining, the capacitor in the bootstrap circuit There is also a problem that the input voltage is not charged, does not function as a bootstrap circuit, and the switch element cannot be driven reliably.
　そこで、本発明の目的は、入力電源のオフ期間が短期間であっても、ブートストラップ回路のキャパシタの充電を可能とし、オフ期間後の動作開始時のスイッチ素子のスイッチング制御を可能とし、所望の出力電圧が得られるスイッチング電源装置を提供することにある。 Therefore, an object of the present invention is to enable charging of the capacitor of the bootstrap circuit even when the input power supply off-period is short, and to enable switching control of the switch element at the start of operation after the off-period. It is an object of the present invention to provide a switching power supply device that can obtain an output voltage of 2.
　本発明に係るスイッチング電源装置は、入力端子及び出力端子を接続する主電流ラインと、前記主電流ラインに設けられ、インダクタ、スイッチ素子及び第１のダイオードを有する降圧コンバータと、前記スイッチ素子を駆動する駆動回路と、前記駆動回路へ駆動電圧を印加する駆動電圧ラインと、前記主電流ライン及び前記駆動電圧ラインの間に接続されたキャパシタと、外部から入力される外部制御電圧を前記駆動電圧ラインへ印加するブートストラップダイオードと、前記主電流ラインの電位を基準とし、前記入力端子から入力される入力電圧を定電圧化して、前記外部制御電圧より低い電圧を前記駆動電圧ラインに供給する定電圧回路とを備えることを特徴とする。 A switching power supply according to the present invention drives a main current line connecting an input terminal and an output terminal, a step-down converter provided on the main current line, having an inductor, a switch element and a first diode, and the switch element A driving circuit for applying a driving voltage to the driving circuit, a capacitor connected between the main current line and the driving voltage line, and an external control voltage input from the outside. The bootstrap diode to be applied to the constant voltage, the voltage of the main current line as a reference, the constant voltage of the input voltage input from the input terminal, to supply a voltage lower than the external control voltage to the drive voltage line And a circuit.
　この構成では、ブートストラップ回路のキャパシタに充電された電圧により、主電流ラインを基準とする駆動電圧が駆動回路に供給されるので、スイッチ素子の制御に必要な電圧を得ることができる。初期の起動時など、駆動電圧ラインの電位が例えばグランド電位であるとき、外部制御電圧によりブートストラップ回路のキャパシタが充電される。このとき定電圧回路が供給する電圧は外部制御電圧よりも低いので、ブートストラップ回路のキャパシタは定電圧回路からは充電されない。 In this configuration, since the drive voltage based on the main current line is supplied to the drive circuit by the voltage charged in the capacitor of the bootstrap circuit, the voltage necessary for controlling the switch element can be obtained. When the potential of the drive voltage line is, for example, the ground potential, such as at the time of initial startup, the capacitor of the bootstrap circuit is charged by the external control voltage. At this time, since the voltage supplied from the constant voltage circuit is lower than the external control voltage, the capacitor of the bootstrap circuit is not charged from the constant voltage circuit.
　また定常動作時においても、スイッチング動作によりブートストラップ回路のキャパシタの基準電位がグランド電位となった際に、外部制御電圧でブートストラップ回路のキャパシタが充電される。このときでも定電圧回路が供給する電圧は外部制御電圧よりも低いので、キャパシタは定電圧回路からは充電されない。しかし、その後、主電流ラインが定常電位となったときは、キャパシタは既に外部制御電圧で充電されているので、このときでも定電圧回路からは充電されない。その後、スイッチング電源装置が一旦停止され、出力端子間電圧が高い（平滑キャパシタに電圧が残留している）状態の場合には、外部制御電圧でブートストラップ回路のキャパシタを充電することはできないが、入力端子間電圧は出力端子間電圧よりも高くなるので（降圧コンバータであるので）、主電流ラインを基準電位とする定電圧回路によってブートストラップ回路のキャパシタが充電される。 Also in the steady operation, when the reference potential of the capacitor of the bootstrap circuit becomes the ground potential by the switching operation, the capacitor of the bootstrap circuit is charged with the external control voltage. Even at this time, since the voltage supplied by the constant voltage circuit is lower than the external control voltage, the capacitor is not charged from the constant voltage circuit. However, after that, when the main current line becomes a steady potential, the capacitor is already charged with the external control voltage, so even at this time, it is not charged from the constant voltage circuit. After that, when the switching power supply is temporarily stopped and the voltage between the output terminals is high (the voltage remains in the smoothing capacitor), the capacitor of the bootstrap circuit cannot be charged with the external control voltage. Since the voltage between the input terminals is higher than the voltage between the output terminals (since it is a step-down converter), the capacitor of the bootstrap circuit is charged by the constant voltage circuit using the main current line as a reference potential.
　このように、スイッチング電源装置が一旦停止した後の短時間での再起動の場合のように、出力端子間電圧が高い（平滑キャパシタに電圧が残留している）状態の場合に限り、主電流ラインを基準電位とする定電圧回路から定電圧化された電圧によってブートストラップ回路のキャパシタが充電され、駆動回路へ駆動電圧が印加されて、再起動が可能となる。定常動作時には定電圧回路が動作しないので、定常動作時における定電圧回路での抵抗損失が無く、高効率化が図れる。 Thus, only when the voltage between the output terminals is high (the voltage remains in the smoothing capacitor) as in the case of restarting in a short time after the switching power supply is temporarily stopped, the main current The capacitor of the bootstrap circuit is charged by a constant voltage from a constant voltage circuit using the line as a reference potential, and a driving voltage is applied to the driving circuit, thereby enabling restart. Since the constant voltage circuit does not operate during steady operation, there is no resistance loss in the constant voltage circuit during steady operation, and high efficiency can be achieved.
　前記定電圧回路は、コレクタ及びベースが前記入力端子に接続され、エミッタが前記駆動電圧ラインに接続されたトランジスタと、アノードが前記主電流ラインに接続され、カソードが前記トランジスタのベースに接続されたツェナーダイオードとを有することが好ましい。 In the constant voltage circuit, a collector and a base are connected to the input terminal, an emitter is connected to the drive voltage line, an anode is connected to the main current line, and a cathode is connected to the base of the transistor. It is preferable to have a Zener diode.
　この構成では、部品数の少ない回路で、かつ、安定化した定電圧を駆動電圧ラインへ供給できる。 In this configuration, a stabilized constant voltage can be supplied to the drive voltage line with a circuit having a small number of parts.
　前記スイッチング電源装置は、前記入力端子と前記定電圧回路との間に設けられ、前記定電圧回路からの逆流電流を防止する第２のダイオードを備えていることが好ましい。 It is preferable that the switching power supply device includes a second diode provided between the input terminal and the constant voltage circuit to prevent a backflow current from the constant voltage circuit.
　この構成では、逆バイアスの印加を防止でき、他の素子の破損等を防ぐことができる。 In this configuration, it is possible to prevent the reverse bias from being applied and to prevent damage to other elements.
　前記スイッチング電源装置は、前記駆動電圧ラインと前記定電圧回路との間に設けられ、前記定電圧回路からの逆バイアスの印加を防止する第４のダイオードを備えていることが好ましい。 Preferably, the switching power supply device includes a fourth diode that is provided between the drive voltage line and the constant voltage circuit and prevents application of a reverse bias from the constant voltage circuit.
　この構成では、逆バイアスの印加を防止でき、他の素子の破損等を防ぐことができる。 In this configuration, it is possible to prevent the reverse bias from being applied and to prevent damage to other elements.
　前記降圧コンバータは、出力側にＬＥＤが接続されている構成が好ましい。 The step-down converter preferably has a configuration in which an LED is connected to the output side.
　この構成では、ＬＥＤを短時間にオンオフさせてもＬＥＤを確実に点灯させることができる。 In this configuration, the LED can be reliably turned on even if the LED is turned on and off in a short time.
　本発明によれば、スイッチング電源装置が一旦停止した後の短期間の再起動時であっても、ブートストラップ回路のキャパシタを所定の駆動電圧に充電できる。このため、スイッチング電源装置の動作開始時に降圧コンバータのスイッチ素子を確実にスイッチング制御でき、所望の出力を得ることができる。 According to the present invention, the capacitor of the bootstrap circuit can be charged to a predetermined driving voltage even when the switching power supply device is restarted for a short time after it has been temporarily stopped. For this reason, switching control of the switch element of the step-down converter can be reliably performed at the start of the operation of the switching power supply apparatus, and a desired output can be obtained.
実施形態１に係るスイッチング電源装置の回路図。1 is a circuit diagram of a switching power supply device according to Embodiment 1. FIG. 実施形態２に係るスイッチング電源装置の回路図。FIG. 4 is a circuit diagram of a switching power supply device according to a second embodiment.
（実施形態１）
　図１は実施形態１に係るスイッチング電源装置の回路図を示す。本実施形態に係るスイッチング電源装置１０１は、入力端子Ｐｉ（＋），Ｐｉ（－）から入力される入力電圧Ｖｉを降圧コンバータで降圧して、出力端子Ｐｏ（＋），Ｐｏ（－）から出力電圧Ｖｏを出力する。入力端子Ｐｉ（＋），Ｐｉ（－）には直流電圧源Ｅが接続されている。出力端子Ｐｏ（＋），Ｐｏ（－）には、ＬＥＤ等、定電流駆動する負荷が接続されている。以下の説明では、入力端子Ｐｉ（＋）と出力端子Ｐｏ（＋）とを接続する線路は、主電流ライン４１という。 (Embodiment 1)
FIG. 1 is a circuit diagram of a switching power supply device according to the first embodiment. The switching power supply device 101 according to the present embodiment steps down the input voltage Vi input from the input terminals Pi (+) and Pi (−) by a step-down converter, and outputs it from the output terminals Po (+) and Po (−). The voltage Vo is output. A DC voltage source E is connected to the input terminals Pi (+) and Pi (−). A constant current driven load such as an LED is connected to the output terminals Po (+) and Po (−). In the following description, a line connecting the input terminal Pi (+) and the output terminal Po (+) is referred to as a main current line 41.
　スイッチング電源装置１０１の降圧コンバータは、ｎ型ＭＯＳ－ＦＥＴ（以下、ＦＥＴという）１１、インダクタＬ１及びダイオードＤ１を備えている。ＦＥＴ１１は本発明のスイッチ素子に相当し、ダイオードＤ１は、本発明の第１のダイオードに相当する。 The step-down converter of the switching power supply apparatus 101 includes an n-type MOS-FET (hereinafter referred to as FET) 11, an inductor L1, and a diode D1. The FET 11 corresponds to the switch element of the present invention, and the diode D1 corresponds to the first diode of the present invention.
　ＦＥＴ１１及びインダクタＬ１は直列接続され、主電流ライン４１に設けられている。より詳しくは、ＦＥＴ１１のドレインは入力端子Ｐｉ（＋）に接続し、ソースはインダクタＬ１を介して出力端子Ｐｏ（＋）に接続している。ダイオードＤ１のカソードはＦＥＴ１１及びインダクタＬ１の接続点に接続し、アノードは、入力端子Ｐｉ（－）と出力端子Ｐｏ（－）とを繋ぐグランドラインに接続している。 The FET 11 and the inductor L1 are connected in series and provided in the main current line 41. More specifically, the drain of the FET 11 is connected to the input terminal Pi (+), and the source is connected to the output terminal Po (+) via the inductor L1. The cathode of the diode D1 is connected to the connection point of the FET 11 and the inductor L1, and the anode is connected to a ground line connecting the input terminal Pi (−) and the output terminal Po (−).
　スイッチング電源装置１０１は、ドライブ回路３０、レベルシフト回路３１及び制御回路３２を備えている。ドライブ回路３０は本発明の駆動回路に相当する。 The switching power supply apparatus 101 includes a drive circuit 30, a level shift circuit 31, and a control circuit 32. The drive circuit 30 corresponds to the drive circuit of the present invention.
　制御回路３２は、例えば、グランドラインに設けられた抵抗（不図示）等を介して出力電流を検出し、所定の出力電流Ｉｏが得られるよう、ＦＥＴ１１をスイッチング制御するための駆動信号をレベルシフト回路３１へ出力する。制御回路３２は、外部電源ライン４３を通じて入力される外部制御電圧Ｖｃｃにより動作する。なお、外部電源ライン４３には、デカップリングコンデンサ又は平滑容量としてのキャパシタＣ２が接続されている。 For example, the control circuit 32 detects the output current via a resistor (not shown) provided on the ground line and shifts the level of a drive signal for switching the FET 11 so that a predetermined output current Io is obtained. Output to the circuit 31. The control circuit 32 operates with an external control voltage Vcc input through the external power supply line 43. The external power supply line 43 is connected to a decoupling capacitor or a capacitor C2 as a smoothing capacitor.
　レベルシフト回路３１は、制御回路３２から出力された駆動信号のレベルシフトを行い、ドライブ回路３０へ出力する。 The level shift circuit 31 performs level shift of the drive signal output from the control circuit 32 and outputs it to the drive circuit 30.
　ドライブ回路３０は、レベルシフト回路３１でレベルシフトされた駆動信号に基づいて、ＦＥＴ１１をスイッチング制御する。このとき、ドライブ回路３０は、ブートストラップ回路１０によって駆動信号の電圧レベルを底上げし、ＦＥＴ１１のゲートへ印加する。ブートストラップ回路１０からドライブ回路３０へは、駆動電圧ライン４２を通じて駆動電圧が供給される。 The drive circuit 30 performs switching control of the FET 11 based on the drive signal level-shifted by the level shift circuit 31. At this time, the drive circuit 30 raises the voltage level of the drive signal by the bootstrap circuit 10 and applies it to the gate of the FET 11. A drive voltage is supplied from the bootstrap circuit 10 to the drive circuit 30 through the drive voltage line 42.
　ブートストラップ回路１０は、キャパシタＣ１及びブートストラップダイオードＤ２を有している。キャパシタＣ１は、駆動電圧ライン４２及び主電流ライン４１の間に接続されている。ブートストラップダイオードＤ２は、カソードが駆動電圧ライン４２に接続され、アノードが外部電源ライン４３に接続されている。 The bootstrap circuit 10 has a capacitor C1 and a bootstrap diode D2. The capacitor C <b> 1 is connected between the drive voltage line 42 and the main current line 41. The bootstrap diode D <b> 2 has a cathode connected to the drive voltage line 42 and an anode connected to the external power supply line 43.
　また、スイッチング電源装置１０１は、主電流ライン４１の電位を基準として、入力電圧Ｖｉを定電圧Ｖｂに定電圧化して駆動電圧ライン４２へ供給する定電圧回路２０を備えている。定電圧回路２０は、抵抗Ｒ１、トランジスタ１２及びツェナーダイオードＤｚを有している。トランジスタ１２は、ベースが抵抗Ｒ１を介して入力端子Ｐｉ（＋）に接続され、コレクタが入力端子Ｐｉ（＋）に接続され、エミッタが駆動電圧ライン４２に接続されている。ツェナーダイオードＤｚは、ツェナー電圧がほぼ定電圧Ｖｂに等しく、アノードが主電流ライン４１に接続され、カソードがトランジスタ１２のベースに接続されている。 Further, the switching power supply device 101 includes a constant voltage circuit 20 that converts the input voltage Vi to a constant voltage Vb and supplies the input voltage Vi to the drive voltage line 42 with the potential of the main current line 41 as a reference. The constant voltage circuit 20 includes a resistor R1, a transistor 12, and a Zener diode Dz. The transistor 12 has a base connected to the input terminal Pi (+) via the resistor R1, a collector connected to the input terminal Pi (+), and an emitter connected to the drive voltage line 42. The Zener diode Dz has a Zener voltage substantially equal to the constant voltage Vb, an anode connected to the main current line 41, and a cathode connected to the base of the transistor 12.
　本実施形態では、外部制御電圧Ｖｃｃは、定電圧回路２０のツェナーダイオードＤｚのツェナー電圧（定電圧Ｖｂ）より高く設定してある。以下、具体的に数値を挙げてスイッチング電源装置１０１の動作を説明する。入力電圧Ｖｉは８０Ｖ、出力電圧Ｖｏは５０Ｖ、外部制御電圧Ｖｃｃは１５Ｖ、定電圧Ｖｂは１２Ｖとする。 In this embodiment, the external control voltage Vcc is set higher than the Zener voltage (constant voltage Vb) of the Zener diode Dz of the constant voltage circuit 20. Hereinafter, the operation of the switching power supply apparatus 101 will be described with specific numerical values. The input voltage Vi is 80V, the output voltage Vo is 50V, the external control voltage Vcc is 15V, and the constant voltage Vb is 12V.
　スイッチング電源装置１０１の定常動作時には、ＦＥＴ１１のスイッチング制御が行われるため、キャパシタＣ１が充電される基準電位となる、主電流ライン４１におけるダイオードＤ１のカソードの電位は、ＦＥＴ１１のオンオフにより変動する。例えば、ＦＥＴ１１がオンの場合、ダイオードＤ１のカソードの電位はＶｉｎ（８０Ｖ）となり、ＦＥＴ１１がオフの場合、ダイオードＤ１のカソードの電位はほぼグランド電位となる。 Since the switching control of the FET 11 is performed during the steady operation of the switching power supply device 101, the cathode potential of the diode D1 in the main current line 41, which is the reference potential for charging the capacitor C1, varies depending on the on / off state of the FET 11. For example, when the FET 11 is on, the cathode potential of the diode D1 is Vin (80V), and when the FET 11 is off, the cathode potential of the diode D1 is almost the ground potential.
　したがって、ＦＥＴ１１がオフのときに、外部電源ライン４３からブートストラップダイオードＤ２を通る経路ＡでキャパシタＣ１には１５Ｖの外部制御電圧Ｖｃｃが充電される。定電圧回路２０による１２Ｖの定電圧Ｖｂからは、キャパシタＣ１は充電されない。このように、スイッチング電源装置１０１の定常動作時には、外部電源ライン４３からキャパシタＣ１に電圧が充電され、その充電電圧が駆動電圧として、ドライブ回路３０に供給される。これにより、ドライブ回路３０に対して駆動電圧が供給され、ドライブ回路３０はＦＥＴ１１のゲート・ソース間にドライブ電圧を印加することができ、ＦＥＴ１１を確実にスイッチング制御できる。 Therefore, when the FET 11 is OFF, the capacitor C1 is charged with the external control voltage Vcc of 15V through the path A passing from the external power supply line 43 through the bootstrap diode D2. The capacitor C1 is not charged from the constant voltage Vb of 12V by the constant voltage circuit 20. Thus, during the steady operation of the switching power supply device 101, the voltage is charged from the external power supply line 43 to the capacitor C1, and the charged voltage is supplied to the drive circuit 30 as the drive voltage. As a result, a drive voltage is supplied to the drive circuit 30, the drive circuit 30 can apply the drive voltage between the gate and source of the FET 11, and the FET 11 can be reliably switched.
　また、スイッチング電源装置１０１が動作停止し、オフ期間が十分に長い場合、キャパシタＣｏの電荷は放電されて、キャパシタＣｏの電荷の残留はないため、ダイオードＤ１のカソード電位はほぼグランド電位となり、キャパシタＣ１には外部電源ライン４３からブートストラップダイオードＤ２を通る経路Ａで１５Ｖの外部制御電圧Ｖｃｃが充電される。 When the switching power supply device 101 stops operating and the off period is sufficiently long, the charge of the capacitor Co is discharged and the charge of the capacitor Co does not remain, so that the cathode potential of the diode D1 becomes almost the ground potential, and the capacitor C1 is charged with an external control voltage Vcc of 15 V along the path A from the external power supply line 43 through the bootstrap diode D2.
　一方で、スイッチング電源装置１０１が動作停止し、短期間のオフ期間で再起動する場合、キャパシタＣｏの電荷が放電しきれずに、キャパシタＣｏに電荷が残留することがある。特に、負荷がＬＥＤ等のダイオード特性を有する場合、一定以上の電圧がかからないと電流が流れないため、キャパシタＣｏは放電しにくい。そのため、例えば主電流ライン４１の電位を１３Ｖとすると、外部電源ライン４３は、主電流ライン４１及び駆動電圧ライン４２とほぼ同電位となる。この場合、ブートストラップダイオードＤ２は、キャパシタＣｏの電荷の残留がなくなるまでの間、非導通となり、キャパシタＣ１には、外部制御電圧Ｖｃｃによっては充電されない。 On the other hand, when the switching power supply device 101 stops operating and restarts in a short off period, the charge of the capacitor Co may not be completely discharged and the charge may remain in the capacitor Co. In particular, when the load has a diode characteristic such as an LED, current does not flow unless a voltage higher than a certain level is applied, so that the capacitor Co is difficult to discharge. Therefore, for example, when the potential of the main current line 41 is 13 V, the external power supply line 43 has substantially the same potential as the main current line 41 and the drive voltage line 42. In this case, the bootstrap diode D2 becomes non-conductive until there is no remaining charge in the capacitor Co, and the capacitor C1 is not charged by the external control voltage Vcc.
　しかし、このように主電流ライン４１の電位が高い場合であっても、ＦＥＴ１１のオフ期間に、トランジスタ１２は主電流ライン４１を基準電位としてツェナー電圧（定電圧Ｖｂの１２Ｖ）分高い電位で動作する。このため、定電圧回路２０のトランジスタ１２が動作し、８０Ｖの入力電圧Ｖｉの定電圧化後の１２Ｖの定電圧Ｖｂが、トランジスタ１２からキャパシタＣ１を通る経路Ｂで、キャパシタＣ１には１２Ｖの定電圧Ｖｂが充電される。 However, even when the potential of the main current line 41 is high as described above, the transistor 12 operates at a potential higher by a Zener voltage (12 V of the constant voltage Vb) with the main current line 41 as a reference potential during the off-period of the FET 11. To do. For this reason, the transistor 12 of the constant voltage circuit 20 operates, and the constant voltage Vb of 12V after the constant voltage of the input voltage Vi of 80V is passed through the capacitor C1 from the transistor 12 and the capacitor C1 has a constant voltage of 12V. The voltage Vb is charged.
　以上のように、スイッチング電源装置１０１が動作停止し、短期間のオフ期間後に再起動する場合であっても、定電圧回路２０によりブートストラップ回路１０のキャパシタＣ１に電圧を充電できる。このため、ドライブ回路３０はＦＥＴ１１を安定的にスイッチング制御できる。 As described above, even when the switching power supply device 101 stops operating and restarts after a short off period, the voltage can be charged to the capacitor C1 of the bootstrap circuit 10 by the constant voltage circuit 20. For this reason, the drive circuit 30 can stably switch the FET 11.
　また、仮に定電圧回路２０による定電圧化後の定電圧ＶｂでキャパシタＣ１を常時充電する構成とした場合、定電圧回路２０で抵抗損失が発生する。しかし、本実施形態では、定常動作時には、定電圧回路２０による定電圧化後の電圧より高い外部制御電圧ＶｃｃからキャパシタＣ１を充電するため、定電圧回路２０は動作せず、前記抵抗損失を低減できる。 Further, if the capacitor C1 is constantly charged with the constant voltage Vb after the constant voltage by the constant voltage circuit 20, a resistance loss occurs in the constant voltage circuit 20. However, in this embodiment, during the steady operation, the capacitor C1 is charged from the external control voltage Vcc higher than the voltage after the constant voltage by the constant voltage circuit 20, so the constant voltage circuit 20 does not operate and the resistance loss is reduced. it can.
（実施形態２）
　図２は実施形態２に係るスイッチング電源装置の回路図を示す。本実施形態に係るスイッチング電源装置１０２は、実施形態１と基本的な回路構成は同じである。以下、実施形態１と相違する点について説明する。 (Embodiment 2)
FIG. 2 is a circuit diagram of the switching power supply device according to the second embodiment. The switching power supply apparatus 102 according to the present embodiment has the same basic circuit configuration as that of the first embodiment. Hereinafter, differences from the first embodiment will be described.
　入力端子Ｐｉ（＋）と定電圧回路２０との間にダイオード（本発明の第２のダイオード）Ｄ３と抵抗Ｒ２が設けられている。ダイオードＤ３は、アノードが入力端子Ｐｉ（＋）に接続され、カソードが抵抗Ｒ２及び抵抗Ｒ１を介してトランジスタ１２のベースに接続されている。また、トランジスタ１２のコレクタは、抵抗Ｒ３を介して抵抗Ｒ２に接続されている。ブートストラップ回路１０のブートストラップダイオードＤ２には、抵抗Ｒ４が直列接続されている。また、トランジスタ１２のエミッタと駆動電圧ライン４２の間にダイオード（本発明の第３のダイオード）Ｄ４が設けられている。 A diode (second diode of the present invention) D3 and a resistor R2 are provided between the input terminal Pi (+) and the constant voltage circuit 20. The diode D3 has an anode connected to the input terminal Pi (+) and a cathode connected to the base of the transistor 12 via the resistor R2 and the resistor R1. The collector of the transistor 12 is connected to the resistor R2 through the resistor R3. A resistor R4 is connected in series to the bootstrap diode D2 of the bootstrap circuit 10. Further, a diode (a third diode of the present invention) D4 is provided between the emitter of the transistor 12 and the drive voltage line.
　上記のダイオードＤ３は、定電圧回路２０に逆バイアスが印加されることを防止することを目的としている。例えば入力電圧Ｖｉが急激に低下した場合、ＦＥＴ１１のボディダイオードの作用により入力端子Ｐｉ（＋）とダイオードＤ１のカソードは同電位になるが、キャパシタＣ１には電荷が残っている場合、定電圧回路に逆バイアスが印加される。しかし、ダイオードＤ３を設けることで、トランジスタ１２のベース・エミッタ間が逆バイアス電圧で破壊されることを防止できる。また、抵抗Ｒ２，Ｒ３，Ｒ４は過電流防止のための素子であり、各素子の破壊を防止できる。 The diode D3 is intended to prevent a reverse bias from being applied to the constant voltage circuit 20. For example, when the input voltage Vi suddenly decreases, the input terminal Pi (+) and the cathode of the diode D1 are at the same potential due to the action of the body diode of the FET 11, but when the charge remains in the capacitor C1, the constant voltage circuit A reverse bias is applied to. However, by providing the diode D3, it is possible to prevent destruction between the base and the emitter of the transistor 12 due to the reverse bias voltage. Further, the resistors R2, R3, and R4 are elements for preventing overcurrent, and the destruction of each element can be prevented.
　ダイオードＤ４は、定電圧回路２０に逆バイアスが印加されることを防止する。実施形態１に記載の通り、外部制御電圧Ｖｃｃは、定電圧回路２０のツェナーダイオードＤｚのツェナー電圧（定電圧Ｖｂ）より高く設定してあるため、トランジスタ１２のベース・エミッタ間には逆バイアスが印加される。しかし、ダイオードＤ４を設けることで、トランジスタ１２のベース・エミッタ間が逆バイアス電圧で破壊されることを防止できる。 The diode D4 prevents a reverse bias from being applied to the constant voltage circuit 20. As described in the first embodiment, the external control voltage Vcc is set to be higher than the Zener voltage (constant voltage Vb) of the Zener diode Dz of the constant voltage circuit 20, and therefore, a reverse bias is applied between the base and emitter of the transistor 12. Applied. However, by providing the diode D4, it is possible to prevent the base 12 and the emitter of the transistor 12 from being destroyed by the reverse bias voltage.
　以上、スイッチング電源装置の具体的構成などは、適宜設計変更可能であり、上述の実施形態に記載された作用及び効果は、本発明から生じる最も好適な作用及び効果を列挙したに過ぎず、本発明による作用及び効果は、上述の実施形態に記載されたものに限定されるものではない。 The specific configuration and the like of the switching power supply device can be appropriately changed as described above, and the operations and effects described in the above-described embodiment are merely a list of the most preferable operations and effects resulting from the present invention. The actions and effects of the invention are not limited to those described in the above embodiment.
１０－ブートストラップ回路
１１－ＦＥＴ（スイッチ素子）
１２－トランジスタ
２０－定電圧回路
３０－ドライブ回路
３１－レベルシフト回路
３２－制御回路
４１－主電流ライン
４２－駆動電圧ライン
４３－外部電源ライン
１０１，１０２－スイッチング電源装置
Ｃ１－キャパシタ
Ｄ１－ダイオード（第１のダイオード）
Ｄ２－ブートストラップダイオード
Ｄ３－ダイオード（第２のダイオード）
Ｄ４－ダイオード（第３のダイオード）
Ｄｚ－ツェナーダイオード
Ｌ１－インダクタ 10-bootstrap circuit 11-FET (switch element)
12-transistor 20-constant voltage circuit 30-drive circuit 31-level shift circuit 32-control circuit 41-main current line 42-drive voltage line 43-external power supply lines 101, 102-switching power supply device C1-capacitor D1-diode ( First diode)
D2-bootstrap diode D3-diode (second diode)
D4-diode (third diode)
Dz-Zener diode L1-Inductor

Claims (5)

  1. 　入力端子及び出力端子を接続する主電流ラインと、
    　前記主電流ラインに設けられ、インダクタ、スイッチ素子及び第１のダイオードを有する降圧コンバータと、
    　前記スイッチ素子を駆動する駆動回路と、
    　前記駆動回路へ駆動電圧を印加する駆動電圧ラインと、
    　前記主電流ライン及び前記駆動電圧ラインの間に接続されたキャパシタと、
    　外部から入力される外部制御電圧を前記駆動電圧ラインへ印加するブートストラップダイオードと、
    　前記主電流ラインの電位を基準とし、前記入力端子から入力される入力電圧を定電圧化して、前記外部制御電圧より低い電圧を前記駆動電圧ラインに供給する定電圧回路と、
    　を備えるスイッチング電源装置。     A main current line connecting the input terminal and the output terminal;
    A step-down converter provided in the main current line and having an inductor, a switch element and a first diode;
    A drive circuit for driving the switch element;
    A drive voltage line for applying a drive voltage to the drive circuit;
    A capacitor connected between the main current line and the driving voltage line;
    A bootstrap diode for applying an external control voltage input from the outside to the drive voltage line;
    A constant voltage circuit that uses the potential of the main current line as a reference, converts the input voltage input from the input terminal to a constant voltage, and supplies a voltage lower than the external control voltage to the drive voltage line;
    A switching power supply device comprising:
  2. 　前記定電圧回路は、
    　コレクタ及びベースが前記入力端子に接続され、エミッタが前記駆動電圧ラインに接続されたトランジスタと、
    　アノードが前記主電流ラインに接続され、カソードが前記トランジスタのベースに接続されたツェナーダイオードと、
    　を有する請求項１に記載のスイッチング電源装置。     The constant voltage circuit is:
    A transistor having a collector and a base connected to the input terminal and an emitter connected to the drive voltage line;
    A Zener diode having an anode connected to the main current line and a cathode connected to the base of the transistor;
    The switching power supply device according to claim 1.
  3. 　前記入力端子と前記定電圧回路との間に設けられ、前記定電圧回路からの逆流電流を防止する第２のダイオードを備える、請求項１又は２に記載のスイッチング電源装置。 3. The switching power supply device according to claim 1, further comprising: a second diode provided between the input terminal and the constant voltage circuit to prevent a backflow current from the constant voltage circuit.
  4. 　前記駆動電圧ラインと前記定電圧回路との間に設けられ、前記定電圧回路からの逆流電流を防止する第３のダイオードを備える、請求項１から３の何れかに記載のスイッチング電源装置。 4. The switching power supply device according to claim 1, further comprising a third diode that is provided between the drive voltage line and the constant voltage circuit and prevents a reverse current from the constant voltage circuit. 5.
  5. 　前記降圧コンバータは、出力側にＬＥＤが接続されている、請求項１から請求項４の何れかに記載のスイッチング電源装置。 The switching power supply device according to any one of claims 1 to 4, wherein the step-down converter has an LED connected to an output side.
PCT/JP2013/065319 2012-06-11 2013-06-03 Switching power source device WO2013187269A1 (en)

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