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WO2018135119A1 - Switching power supply - Google Patents

Switching power supply Download PDF

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Publication number
WO2018135119A1
WO2018135119A1 PCT/JP2017/041327 JP2017041327W WO2018135119A1 WO 2018135119 A1 WO2018135119 A1 WO 2018135119A1 JP 2017041327 W JP2017041327 W JP 2017041327W WO 2018135119 A1 WO2018135119 A1 WO 2018135119A1
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WIPO (PCT)
Prior art keywords
secondary coil
switching element
current
biased
coil
Prior art date
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PCT/JP2017/041327
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French (fr)
Japanese (ja)
Inventor
羽田　正二
Original Assignee
Ntn株式会社
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Application filed by Ntn株式会社 filed Critical Ntn株式会社
Priority to KR1020187018614A priority Critical patent/KR102449387B1/en
Publication of WO2018135119A1 publication Critical patent/WO2018135119A1/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
    • H02M3/22—Conversion of DC power input into DC power output with intermediate conversion into AC
    • H02M3/24—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters
    • H02M3/28—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC
    • H02M3/325—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33592—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
    • 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
    • H02M3/22—Conversion of DC power input into DC power output with intermediate conversion into AC
    • H02M3/24—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters
    • H02M3/28—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC
    • 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
    • H02M3/22—Conversion of DC power input into DC power output with intermediate conversion into AC
    • H02M3/24—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters
    • H02M3/28—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC
    • H02M3/325—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of DC power input into DC power output with intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate AC using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only

Definitions

  • the present invention relates to a forward type switching power supply.
  • Insulating switching power supplies that extract desired DC power from the secondary coil by turning on and off DC power input to the primary coil of the transformer by a switching element are well known.
  • a forward system in an insulating switching power supply is also well known.
  • an exciting current flows in the primary coil during the ON period of the switching element, a load current flows in the secondary coil according to the turns ratio by mutual induction, and a load current also flows in the primary coil correspondingly.
  • the load current of the secondary coil is output through an output diode and an external choke coil, and magnetizes the external choke coil to store magnetic energy.
  • an output current flows through the flywheel diode so as to release the magnetic energy stored in the external choke coil.
  • the forward method requires a reset circuit on the primary side of the transformer in order to release the magnetic energy accumulated in the transformer by the exciting current during the on period.
  • the reset circuit is generally configured by a diode, a capacitor, and a resistor, and there is also a configuration in which a reset coil is added to the primary coil, and various types of reset circuits are known (for example, Patent Document 1).
  • a reset circuit configured to regenerate the reset current to the input side is also known, but power cannot be sent to the secondary side.
  • an object of the present invention is to eliminate the need for a reset circuit in a forward-type switching power supply and to output magnetic energy stored in a transformer as secondary power.
  • the present invention provides the following configuration.
  • symbol in a parenthesis is a code
  • An aspect of the present invention is a switching power supply, A transformer (T), A switching element (Q) having a control end, which is driven on and off to conduct or cut off a current flowing through the primary coil (N1) of the transformer (T) by an input voltage; A choke coil (CH) connected between one end of the secondary coil (N2) of the transformer and the first output end (3); Connected between the other end of the secondary coil (N2) of the transformer (T) and the second output end (4), and occurs at the other end of the secondary coil (N2) when the switching element (Q) is turned on.
  • a transformer (T) A switching element (Q) having a control end, which is driven on and off to conduct or cut off a current flowing through the primary coil (N1) of the transformer (T) by an input voltage
  • a choke coil (CH) connected between one end of the secondary coil (N2) of the transformer and the first output end (3); Connected between the other end of the secondary coil (N2) of the transformer (T) and the second output end (4), and occurs at the
  • a first rectifier (D1) that is forward biased with respect to the potential and reversely biased with respect to the potential generated at the other end of the secondary coil (N2) when turned off; Connected between one end of the secondary coil (N2) of the transformer (T) and the second output end (4), and is generated at one end of the secondary coil (N2) when the switching element (Q) is turned on.
  • a second rectifier (D2) that is reverse-biased with respect to the potential and forward-biased with respect to the potential generated at one end of the secondary coil (N2) when turned off; The other end of the secondary coil (N2) is connected between the other end of the secondary coil (N2) of the transformer (T) and the first output end (3), and the switching element (Q) is turned on.
  • a third rectifying means (D3) which is reverse-biased with respect to the potential generated at the time and is forward-biased with respect to the potential generated at the other end of the secondary coil (N2) when turned off; And a smoothing capacitor (C) connected between the first output terminal (3) and the second output terminal (4).
  • the first rectifying means (D1), the second rectifying means (D2), and the third rectifying means (D3) are diodes.
  • Another aspect of the present invention is connected between the other end of the secondary coil (N2) of the transformer (T) and the second output end (4) instead of the first rectifying means (D1).
  • a second switching element (Q2) having a current path and a control end that is driven on and off to turn on or off the current flowing through the current path;
  • the second switching element (Q2) is preferably driven on / off in synchronization with the switching element (Q).
  • each of the second rectifying means (D2) and the third rectifying means (D3) is a diode.
  • the present invention adds a third rectifying means in addition to the rectifying means corresponding to the conventional choke coil, output diode and flywheel diode as a secondary side component,
  • a current that releases the magnetic energy accumulated in the transformer during the ON period of the switching element can be supplied to the secondary coil during the OFF period and output. Therefore, the utilization efficiency of the transformer is improved.
  • the reset circuit on the primary side in the conventional forward method becomes unnecessary. Therefore, power loss due to the reset circuit does not occur. Further, the reset circuit can be omitted simply by adding one rectifying means which is a diode, so that the entire circuit can be made compact and low in cost. Furthermore, since the magnetic energy stored in the transformer can be output as a current to the secondary side, it is possible to perform a larger power conversion than before.
  • FIG. 1 is a circuit diagram schematically showing a configuration example of a first embodiment of a switching power supply according to the present invention.
  • FIG. 2 is a diagram showing the flow of current during the ON period in the circuit shown in FIG.
  • FIG. 3 is a diagram showing a current flow during an off period in the circuit shown in FIG.
  • FIG. 4 is a diagram schematically showing an example of the temporal change in voltage and current in the circuit diagram shown in FIG.
  • FIG. 5 is a circuit diagram schematically showing a configuration example of the second embodiment of the switching power supply according to the present invention.
  • FIG. 6 is a diagram showing a current flow during the ON period in the circuit shown in FIG.
  • FIG. 7 is a diagram showing a current flow during the off period in the circuit shown in FIG.
  • the switching power supply according to the present invention is an insulating type that performs power conversion between a pair of input terminals and a pair of output terminals via a transformer.
  • DC power is supplied between the pair of input terminals.
  • the supplied DC power may be an output of another arbitrary DC power supply or an output after rectification of the AC power supply. Therefore, the input DC voltage includes not only a constant voltage but also a unipolar variable voltage. For example, pulsating flow after AC rectification, square wave, triangular wave, and the like.
  • a load is connected to the pair of output ends (omitted in the drawing).
  • FIG. 1 is a circuit diagram schematically showing a configuration example of a first embodiment of a switching power supply according to the present invention.
  • DC power is supplied between the input terminal 1 and the input terminal 2. That is, a DC voltage is applied. Further, DC power is output between the output terminal 3 and the output terminal 4.
  • an input voltage at which the input terminal 1 has a positive potential is applied to the input terminal 2 that is the reference potential on the input side, and the output terminal 3 has a positive potential with respect to the output terminal 4 that is the reference potential on the output side. A case where a voltage is output will be described.
  • This circuit has a transformer T having a primary coil N1 and a secondary coil N2.
  • the winding start terminal of each coil is indicated by a black circle (the black circle indicates the polarity of the coil).
  • “one end” and “the other end” include both “winding start terminal” and “winding end terminal”, and “winding end terminal” and “winding start terminal”.
  • the switching power supply of the present invention has a forward circuit as a basic configuration, it is preferable that the primary coil N1 and the secondary coil N2 are tightly coupled, that is, the coupling coefficient of magnetic coupling is close to 1.
  • One end of the primary coil N1 (in this example, the winding start terminal) is connected to the input end 1.
  • the other end of the primary coil N1 (the winding end terminal in this example) is connected to the drain of the switching element Q, which is an N-channel FET, and the source is connected to the input end 2.
  • a pulse voltage having a predetermined switching frequency and duty ratio is input to the gate, which is the control terminal of the switching element Q, as the control voltage Vg.
  • switching element Q a switching element such as an IGBT or a bipolar transistor may be used in addition to the FET.
  • the switching power supply of the present invention has a forward system as a basic configuration, but a reset circuit on the primary side of the transformer that is essential in a general forward system is not provided as shown, and is unnecessary.
  • a choke coil CH is connected between one end of the secondary coil N2 (in this example, the winding start terminal) and the output end 3.
  • a diode D1 is connected between the other end of the secondary coil N2 (winding end terminal in this example) and the output end 4.
  • the polarity of the diode D1 is such that the anode is on the output end 4 side and the cathode is on the other end side of the secondary coil.
  • the diode D1 is forward-biased with respect to the potential generated at the other end of the secondary coil N2 when the switching element Q is turned on, and is reverse-biased with respect to the potential generated at the other end of the secondary coil N2 when the switching element Q is turned off. It is connected in the direction.
  • a diode D2 is connected between one end of the secondary coil N2 and the output end 4.
  • the polarity of the diode D2 is such that the anode is on the output end 4 side and the cathode is on one end side of the secondary coil N2.
  • the diode D2 is reverse-biased with respect to a potential generated at one end of the secondary coil N2 when the switching element Q is turned on, and is forward-biased with respect to a potential generated at one end of the secondary coil N2 when the switching element Q is turned off. Connected in the direction.
  • a diode D3 is connected between the other end of the secondary coil N2 and the output end 3.
  • the polarity of the diode D3 is such that the anode is on the other end side of the secondary coil N2 and the cathode is on the output end 3 side.
  • the diode D3 is reverse-biased with respect to the potential generated at the other end of the secondary coil N2 when the switching element Q is turned on, and forward-biased with respect to the potential generated at the other end of the secondary coil N2 when the switching element Q is turned off. It is connected in the direction.
  • the diodes D1, D2, and D3 are turned on when a forward bias voltage (anode has a high potential with respect to the cathode) is applied, and is blocked with respect to a reverse bias voltage (the anode has a low potential with respect to the cathode).
  • the rectifying means includes a rectifying device or a rectifying circuit equivalent to a diode in addition to a diode which is a rectifying element.
  • a smoothing capacitor C is connected between the output terminal 3 and the output terminal 4.
  • a load is connected between the output terminal 3 and the output terminal 4.
  • an input voltage in which the input terminal 1 is a negative potential may be applied to the input terminal 2 which is the primary side reference potential. In that case, the polarity of each diode on the secondary side is reversed.
  • FIG. 2 is a diagram showing the flow of current during the ON period in the circuit shown in FIG.
  • FIG. 3 is a diagram showing a current flow during an off period in the circuit shown in FIG.
  • FIG. 4 is a diagram schematically showing an example of the temporal change in voltage and current in the circuit diagram shown in FIG.
  • FIG. 2 shows a current flow in the ON period.
  • the control voltage Vg that is a pulse voltage input to the gate of the switching element Q is, for example, as shown in FIG.
  • the control signal Vg When the control signal Vg is turned on, the current path of the switching element Q becomes conductive, a DC voltage is applied to one end of the primary coil N1, and one end of the primary coil N1 has a positive potential and the other end has a negative potential.
  • a current id flows through the path of the input terminal 1 ⁇ the primary coil N1 ⁇ the switching element Q ⁇ the input terminal 2.
  • the change in the on period of the current id is as shown in FIG.
  • the diode D1 becomes forward biased and becomes conductive, and the first current i1 flows through the path of the secondary coil N2, the choke coil CH, the output terminal 3, the load (or the smoothing capacitor C), the output terminal 4, and the diode D1.
  • the change in the ON period of the first current i1 is as shown in FIG.
  • the first current i1 corresponds to the output current during the ON period in the normal forward method.
  • the first current i1 on the secondary side is also an exciting current of the choke coil CH, and thereby magnetic energy is accumulated in the choke coil CH.
  • the current id flowing through the primary coil N1 includes a load current caused by mutual induction with the secondary coil N2 and an exciting current that accumulates magnetic energy in the transformer T. During the ON period, the magnetic flux of the transformer T is increased by the exciting current, and magnetic energy is accumulated.
  • FIG. 3 shows a current flow in the off period.
  • the control signal Vg is turned off, the current path of the switching element Q is interrupted, and the current id flowing through the primary coil N1 disappears. Thereby, back electromotive force is generated in the primary coil N1 and the secondary coil N2.
  • the other end of the secondary coil N2 becomes a positive potential due to the back electromotive force, and the diode D1 is reverse-biased, so the first current i1 does not flow.
  • the second current i2 flows so as to release the magnetic energy accumulated in the choke coil CH.
  • the path of the second current i2 is choke coil CH ⁇ output terminal 3 ⁇ load (or smoothing capacitor) ⁇ output terminal 4 ⁇ diode D2.
  • the change in the off period of the second current i2 is as shown in FIG.
  • the second current i2 corresponds to an output current during an off period in the normal forward method, and the diode D2 functions as a flywheel diode with respect to the second current i2.
  • FIG. 4 (F) shows the total current flowing on the secondary side.
  • the voltage Vo and current Io output between the output terminal 3 and the output terminal 4 are smoothed by the smoothing capacitor C, as shown in FIG.
  • the switching power supply according to the present invention can discharge the magnetic energy accumulated in the transformer during the on period as a secondary output current during the off period by adding the diode D3 while using the forward system as a basic configuration. This eliminates the need for a reset circuit on the primary side. Conventionally, it has been necessary to take a countermeasure against the withstand voltage of the switching element by a spike voltage generated at the time of OFF, but the countermeasure against the spike becomes unnecessary because the magnetic energy is released to the secondary side.
  • FIG. 5 is a circuit diagram schematically showing a configuration example of the second embodiment of the switching power supply according to the present invention.
  • a second switching element Q2 is provided instead of the first diode D1 in the first embodiment.
  • the second switching element Q2 is an N-channel FET in this example.
  • the drain is connected to the other end of the secondary coil N 2, and the source is connected to the output end 4. That is, the current path of the second switching element Q2 is connected between the other end of the secondary coil N2 and the output end 4.
  • the second switching element Q2 is driven on and off in synchronization with the switching element Q connected to the primary coil N1. Accordingly, the same control voltage Vg as that of the switching element Q is input to the gate which is the control end of the second switching element Q2.
  • FIG. 6 shows the current flow during the ON period.
  • the operation on the primary side in the on period is the same as that in the first embodiment.
  • FIG. 7 shows the flow of current during the off period.
  • the operation on the primary side in the on period is the same as that in the first embodiment.
  • the other end of the secondary coil N2 becomes a positive potential due to the back electromotive force.
  • the second switching element Q2 is turned off by the control voltage Vg, the current path is cut off. Therefore, the first current i1 does not flow.
  • the second current i2 and the third current i3 flow as in the first embodiment.
  • the second switching element Q2 may be a P-channel FET instead of an N-channel FET.

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Abstract

A forward switching power supply that does not require a reset circuit and can output, to a secondary side, energy that has been stored at a transistor. A switching power supply that has: a transistor; a switching element Q that is turned on and off so as to conduct or to cut off current that flows in a primary coil; a choke coil that is connected between an output terminal 3 and one end of a secondary coil; a first rectification means that is connected between an output terminal 4 and another end of the secondary coil and that, with respect to the potential of the other end of the secondary coil, is forward-biased when on and reverse-biased when off; a second rectification means that is connected between output terminal 4 and the one end of the secondary coil and that, with respect to the potential of the one end of the secondary coil, is reverse-biased when on and forward-biased when off; a third rectification means that is connected between output terminal 3 and the other end of the secondary coil and that, with respect to the potential of the other end of the secondary coil, is reverse-biased when on and forward-biased when off; and a smoothing capacitor that is between the output terminals.

Description

スイッチング電源Switching power supply
　本発明は、フォワード方式のスイッチング電源に関する。 The present invention relates to a forward type switching power supply.
　トランスの一次コイルに入力される直流電力をスイッチング素子によりオンオフすることにより、二次コイルから所望する直流電力を取り出す絶縁型のスイッチング電源は周知である。絶縁型のスイッチング電源におけるフォワード方式もまた周知である。 Insulating switching power supplies that extract desired DC power from the secondary coil by turning on and off DC power input to the primary coil of the transformer by a switching element are well known. A forward system in an insulating switching power supply is also well known.
　フォワード方式では、スイッチング素子のオン期間に一次コイルに励磁電流が流れ、相互誘導により巻数比に応じて二次コイルに負荷電流が流れ、対応して一次コイルにも負荷電流が流れる。二次コイルの負荷電流は、出力ダイオードと外付けチョークコイルを通して出力されると共に、外付けチョークコイルを励磁して磁気エネルギーを蓄積する。スイッチング素子のオフ期間には外付けチョークコイルに蓄積された磁気エネルギーを放出するようにフライホイールダイオードを通して出力電流が流れる。 In the forward method, an exciting current flows in the primary coil during the ON period of the switching element, a load current flows in the secondary coil according to the turns ratio by mutual induction, and a load current also flows in the primary coil correspondingly. The load current of the secondary coil is output through an output diode and an external choke coil, and magnetizes the external choke coil to store magnetic energy. During the OFF period of the switching element, an output current flows through the flywheel diode so as to release the magnetic energy stored in the external choke coil.
　フォワード方式は、オン期間に励磁電流によりトランスに蓄積された磁気エネルギーをオフ期間に放出するために、トランスの一次側にリセット回路が必要である。リセット回路は、一般的にダイオード、コンデンサ及び抵抗により構成され、また、一次コイルにリセット用コイルを付加した構成もあり、多様な構成のリセット回路が公知である（例えば特許文献１等）。 The forward method requires a reset circuit on the primary side of the transformer in order to release the magnetic energy accumulated in the transformer by the exciting current during the on period. The reset circuit is generally configured by a diode, a capacitor, and a resistor, and there is also a configuration in which a reset coil is added to the primary coil, and various types of reset circuits are known (for example, Patent Document 1).
特開平９－２７５６６８１号公報JP-A-9-2756681
　しかしながら、フォワード方式のスイッチング電源における一般的なリセット回路では、リセット電流がダイオードを通してコンデンサを充電し、コンデンサに蓄積されたエネルギーが抵抗によって消費される構成となっており、電力が無駄に消費されることとなる。また、一次コイルにリセット用コイルを付加した構成は、トランスが大きくなるという欠点がある。 However, in a general reset circuit in a forward-type switching power supply, a reset current charges a capacitor through a diode, and energy stored in the capacitor is consumed by a resistor, so that power is wasted. It will be. Further, the configuration in which the reset coil is added to the primary coil has a disadvantage that the transformer becomes large.
　また、リセット電流を入力側に回生させる構成のリセット回路も公知であるが、二次側に電力を送ることはできない。 A reset circuit configured to regenerate the reset current to the input side is also known, but power cannot be sent to the secondary side.
　以上の問題点に鑑み本発明の目的は、フォワード方式のスイッチング電源においてリセット回路を不要とするとともに、トランスに蓄積された磁気エネルギーを二次側の電力として出力可能とすることである。 In view of the above problems, an object of the present invention is to eliminate the need for a reset circuit in a forward-type switching power supply and to output magnetic energy stored in a transformer as secondary power.
　上記の目的を達成するべく、本発明は、以下の構成を提供する。なお、括弧内の符号は後述する図面中の符号であり、参考のために付するものである。 In order to achieve the above object, the present invention provides the following configuration. In addition, the code | symbol in a parenthesis is a code | symbol in drawing mentioned later, and attaches | subjects it for reference.
・　本発明の態様は、スイッチング電源において、
　トランス（Ｔ）と、
　入力電圧により前記トランス（Ｔ）の一次コイル（Ｎ１）に流れる電流を導通又は遮断するべくオンオフ駆動される、制御端を具備するスイッチング素子（Ｑ）と、
　前記トランスの二次コイル（Ｎ２）の一端と第１出力端（３）の間に接続されたチョークコイル（ＣＨ）と、
　前記トランス（Ｔ）の二次コイル（Ｎ２）の他端と第２出力端（４）の間に接続され、前記スイッチング素子（Ｑ）のオン時に前記二次コイル（Ｎ２）の他端に生じる電位に対して順バイアスとなりかつオフ時に該二次コイル（Ｎ２）の他端に生じる電位に対して逆バイアスとなる第１整流手段（Ｄ１）と、
　前記トランス（Ｔ）の前記二次コイル（Ｎ２）の一端と前記第２出力端（４）の間に接続され、前記スイッチング素子（Ｑ）のオン時に前記二次コイル（Ｎ２）の一端に生じる電位に対して逆バイアスとなりかつオフ時に該二次コイル（Ｎ２）の一端に生じる電位に対して順バイアスとなる第２整流手段（Ｄ２）と、
　前記トランス（Ｔ）の前記二次コイル（Ｎ２）の他端と前記第１出力端（３）の間に接続され、前記スイッチング素子（Ｑ）のオン時に前記二次コイル（Ｎ２）の他端に生じる電位に対して逆バイアスとなりかつオフ時に該二次コイル（Ｎ２）の他端に生じる電位に対して順バイアスとなる第３整流手段（Ｄ３）と、
　前記第１出力端（３）と前記第２出力端（４）の間に接続された平滑コンデンサ（Ｃ）と、を有することを特徴とする。
・　上記態様において、前記第１整流手段（Ｄ１）、前記第２整流手段（Ｄ２）及び前記第３整流手段（Ｄ３）がそれぞれダイオードであることが好適である。
・　本発明の別の態様は、前記第１整流手段（Ｄ１）に替えて、前記トランス（Ｔ）の二次コイル（Ｎ２）の他端と第２出力端（４）の間に接続された電流路と該電流路を流れる電流を導通又は遮断するべくオンオフ駆動される制御端とを具備する第２のスイッチング素子（Ｑ２）を有し、
　前記第２のスイッチング素子（Ｑ２）は前記スイッチング素子（Ｑ）と同期してオンオフ駆動されることが好適である。
・　上記別の態様において、前記第２整流手段（Ｄ２）及び前記第３整流手段（Ｄ３）がそれぞれダイオードであることが好適である。 An aspect of the present invention is a switching power supply,
A transformer (T),
A switching element (Q) having a control end, which is driven on and off to conduct or cut off a current flowing through the primary coil (N1) of the transformer (T) by an input voltage;
A choke coil (CH) connected between one end of the secondary coil (N2) of the transformer and the first output end (3);
Connected between the other end of the secondary coil (N2) of the transformer (T) and the second output end (4), and occurs at the other end of the secondary coil (N2) when the switching element (Q) is turned on. A first rectifier (D1) that is forward biased with respect to the potential and reversely biased with respect to the potential generated at the other end of the secondary coil (N2) when turned off;
Connected between one end of the secondary coil (N2) of the transformer (T) and the second output end (4), and is generated at one end of the secondary coil (N2) when the switching element (Q) is turned on. A second rectifier (D2) that is reverse-biased with respect to the potential and forward-biased with respect to the potential generated at one end of the secondary coil (N2) when turned off;
The other end of the secondary coil (N2) is connected between the other end of the secondary coil (N2) of the transformer (T) and the first output end (3), and the switching element (Q) is turned on. A third rectifying means (D3) which is reverse-biased with respect to the potential generated at the time and is forward-biased with respect to the potential generated at the other end of the secondary coil (N2) when turned off;
And a smoothing capacitor (C) connected between the first output terminal (3) and the second output terminal (4).
In the above aspect, it is preferable that the first rectifying means (D1), the second rectifying means (D2), and the third rectifying means (D3) are diodes.
Another aspect of the present invention is connected between the other end of the secondary coil (N2) of the transformer (T) and the second output end (4) instead of the first rectifying means (D1). A second switching element (Q2) having a current path and a control end that is driven on and off to turn on or off the current flowing through the current path;
The second switching element (Q2) is preferably driven on / off in synchronization with the switching element (Q).
In the other aspect, it is preferable that each of the second rectifying means (D2) and the third rectifying means (D3) is a diode.
　本発明は、フォワード方式のスイッチング電源において、二次側の構成要素として、従来のチョークコイル、出力ダイオード及びフライホイールダイオードに相当する整流手段に加えて、第３の整流手段を追加したことにより、従来のフォワード方式における出力電流に加え、スイッチング素子のオン期間にトランスに蓄積された磁気エネルギーを放出させる電流をオフ期間に二次コイルに流して出力することができる。よってトランスの利用効率が向上する。 In the forward type switching power supply, the present invention adds a third rectifying means in addition to the rectifying means corresponding to the conventional choke coil, output diode and flywheel diode as a secondary side component, In addition to the output current in the conventional forward method, a current that releases the magnetic energy accumulated in the transformer during the ON period of the switching element can be supplied to the secondary coil during the OFF period and output. Therefore, the utilization efficiency of the transformer is improved.
　この結果、トランスの磁気リセットを行うことができるので、従来のフォワード方式における一次側のリセット回路が不要となる。従って、リセット回路による電力損失を生じない。また好適にはダイオードである整流手段を１つ追加するだけでリセット回路を省くことができるので、回路全体をコンパクトとしかつ低コストとすることがる。さらに、トランスに蓄積された磁気エネルギーを二次側に電流として出力することができるので、従来よりも大きな電力変換が可能である。 As a result, since the magnetic reset of the transformer can be performed, the reset circuit on the primary side in the conventional forward method becomes unnecessary. Therefore, power loss due to the reset circuit does not occur. Further, the reset circuit can be omitted simply by adding one rectifying means which is a diode, so that the entire circuit can be made compact and low in cost. Furthermore, since the magnetic energy stored in the transformer can be output as a current to the secondary side, it is possible to perform a larger power conversion than before.
図１は、本発明によるスイッチング電源の第１の実施形態の構成例を概略的に示す回路図である。FIG. 1 is a circuit diagram schematically showing a configuration example of a first embodiment of a switching power supply according to the present invention. 図２は、図１に示した回路におけるオン期間の電流の流れを示した図である。FIG. 2 is a diagram showing the flow of current during the ON period in the circuit shown in FIG. 図３は、図１に示した回路におけるオフ期間の電流の流れを示した図である。FIG. 3 is a diagram showing a current flow during an off period in the circuit shown in FIG. 図４は、図１に示した回路図における電圧及び電流の時間変化の例を模式的に示した図である。FIG. 4 is a diagram schematically showing an example of the temporal change in voltage and current in the circuit diagram shown in FIG. 図５は、本発明によるスイッチング電源の第２の実施形態の構成例を概略的に示す回路図である。FIG. 5 is a circuit diagram schematically showing a configuration example of the second embodiment of the switching power supply according to the present invention. 図６は、図５に示した回路におけるオン期間の電流の流れを示した図である。FIG. 6 is a diagram showing a current flow during the ON period in the circuit shown in FIG. 図７は、図５に示した回路におけるオフ期間の電流の流れを示した図である。FIG. 7 is a diagram showing a current flow during the off period in the circuit shown in FIG.
　以下、図面を参照しつつ、本発明によるスイッチング電源の実施形態について詳細に説明する。 Hereinafter, embodiments of a switching power supply according to the present invention will be described in detail with reference to the drawings.
　本発明によるスイッチング電源は、一対の入力端と一対の出力端の間でトランスを介して電力変換を行う絶縁型のものである。一対の入力端の間に直流電力が供給される。供給される直流電力は、別の任意の直流電源の出力でもよく、交流電源の整流後の出力でもよい。従って入力される直流電圧は、一定電圧の場合の他、一極性の変動する電圧の場合も含まれる。例えば、交流整流後の脈流、方形波、三角波等である。一対の出力端には負荷が接続される（図面では省略）。 The switching power supply according to the present invention is an insulating type that performs power conversion between a pair of input terminals and a pair of output terminals via a transformer. DC power is supplied between the pair of input terminals. The supplied DC power may be an output of another arbitrary DC power supply or an output after rectification of the AC power supply. Therefore, the input DC voltage includes not only a constant voltage but also a unipolar variable voltage. For example, pulsating flow after AC rectification, square wave, triangular wave, and the like. A load is connected to the pair of output ends (omitted in the drawing).
（１）第１の実施形態
＜スイッチング電源の構成＞
　図１は、本発明によるスイッチング電源の第１の実施形態の構成例を概略的に示す回路図である。本回路は、入力端１と入力端２の間に直流電力が供給される。すなわち直流電圧が印加される。また、出力端３と出力端４の間に直流電力が出力される。以下では、入力側の基準電位である入力端２に対して入力端１が正電位となる入力電圧が印加され、出力側の基準電位である出力端４に対して出力端３が正電位となる電圧が出力される場合について説明する。 (1) First Embodiment <Configuration of Switching Power Supply>
FIG. 1 is a circuit diagram schematically showing a configuration example of a first embodiment of a switching power supply according to the present invention. In this circuit, DC power is supplied between the input terminal 1 and the input terminal 2. That is, a DC voltage is applied. Further, DC power is output between the output terminal 3 and the output terminal 4. In the following, an input voltage at which the input terminal 1 has a positive potential is applied to the input terminal 2 that is the reference potential on the input side, and the output terminal 3 has a positive potential with respect to the output terminal 4 that is the reference potential on the output side. A case where a voltage is output will be described.
　本回路は、一次コイルＮ１と二次コイルＮ２を具備するトランスＴを有する。各コイルの巻き始め端子を黒丸で示している（黒丸はコイルの極性を示す）。コイルについて「一端」と「他端」という場合は、「巻き始め端子」と「巻き終わり端子」の場合と、「巻き終わり端子」と「巻き始め端子」の場合の双方が含まれる。 This circuit has a transformer T having a primary coil N1 and a secondary coil N2. The winding start terminal of each coil is indicated by a black circle (the black circle indicates the polarity of the coil). Regarding the coil, “one end” and “the other end” include both “winding start terminal” and “winding end terminal”, and “winding end terminal” and “winding start terminal”.
　本発明のスイッチング電源はフォワード方式の回路を基本構成とするので、一次コイルＮ１と二次コイルＮ２は密結合であること、すなわち磁気結合の結合係数が１に近いことが好適である。 Since the switching power supply of the present invention has a forward circuit as a basic configuration, it is preferable that the primary coil N1 and the secondary coil N2 are tightly coupled, that is, the coupling coefficient of magnetic coupling is close to 1.
　一次コイルＮ１の一端（本例では巻き始め端子）が入力端１に接続されている。一次コイルＮ１の他端（本例では巻き終わり端子）にＮチャネルＦＥＴであるスイッチング素子Ｑのドレインが接続され、ソースが入力端２に接続されている。スイッチング素子Ｑの制御端であるゲートには、制御電圧Ｖｇとして、所定のスイッチング周波数及びデューティ比のパルス電圧が入力される。 One end of the primary coil N1 (in this example, the winding start terminal) is connected to the input end 1. The other end of the primary coil N1 (the winding end terminal in this example) is connected to the drain of the switching element Q, which is an N-channel FET, and the source is connected to the input end 2. A pulse voltage having a predetermined switching frequency and duty ratio is input to the gate, which is the control terminal of the switching element Q, as the control voltage Vg.
　この場合、制御電圧Ｖｇがソース（入力端２）電位に対して正電位のときスイッチング素子Ｑはオンとなり、一次コイルＮ１と入力端２の間の電流路が導通する。制御電圧Ｖｇが零のときスイッチング素子Ｑはオフとなり、一次コイルＮ１と入力端２の間の電流路は遮断される。 In this case, when the control voltage Vg is positive with respect to the source (input terminal 2) potential, the switching element Q is turned on, and the current path between the primary coil N1 and the input terminal 2 is conducted. When the control voltage Vg is zero, the switching element Q is turned off, and the current path between the primary coil N1 and the input terminal 2 is interrupted.
　スイッチング素子Ｑとして、ＦＥＴ以外に例えばＩＧＢＴ又はバイポーラトランジスタ等のスイッチング素子を用いてもよい。 As the switching element Q, a switching element such as an IGBT or a bipolar transistor may be used in addition to the FET.
　本発明のスイッチング電源はフォワード方式を基本構成としているが、一般的なフォワード方式において必須のトランス一次側のリセット回路は、図示の通り設けられておらず、不要である。 The switching power supply of the present invention has a forward system as a basic configuration, but a reset circuit on the primary side of the transformer that is essential in a general forward system is not provided as shown, and is unnecessary.
　二次コイルＮ２の一端（本例では巻き始め端子）と出力端３の間にはチョークコイルＣＨが接続されている。 A choke coil CH is connected between one end of the secondary coil N2 (in this example, the winding start terminal) and the output end 3.
　二次コイルＮ２の他端（本例では巻き終わり端子）と出力端４の間にはダイオードＤ１が接続されている。ダイオードＤ１の極性は、アノードが出力端４側、カソードが二次コイルの他端側となる向きである。ダイオードＤ１は、スイッチング素子Ｑのオン時に二次コイルＮ２の他端に生じる電位に対して順バイアスとなり、かつ、スイッチング素子Ｑのオフ時に二次コイルＮ２の他端に生じる電位に対して逆バイアスとなる向きで接続されている。 A diode D1 is connected between the other end of the secondary coil N2 (winding end terminal in this example) and the output end 4. The polarity of the diode D1 is such that the anode is on the output end 4 side and the cathode is on the other end side of the secondary coil. The diode D1 is forward-biased with respect to the potential generated at the other end of the secondary coil N2 when the switching element Q is turned on, and is reverse-biased with respect to the potential generated at the other end of the secondary coil N2 when the switching element Q is turned off. It is connected in the direction.
　さらに、二次コイルＮ２の一端と出力端４の間にはダイオードＤ２が接続されている。ダイオードＤ２の極性は、アノードが出力端４側、カソードが二次コイルＮ２の一端側となる向きである。ダイオードＤ２は、スイッチング素子Ｑのオン時に二次コイルＮ２の一端に生じる電位に対して逆バイアスとなり、かつ、スイッチング素子Ｑのオフ時に二次コイルＮ２の一端に生じる電位に対して順バイアスとなる向きで接続されている。 Furthermore, a diode D2 is connected between one end of the secondary coil N2 and the output end 4. The polarity of the diode D2 is such that the anode is on the output end 4 side and the cathode is on one end side of the secondary coil N2. The diode D2 is reverse-biased with respect to a potential generated at one end of the secondary coil N2 when the switching element Q is turned on, and is forward-biased with respect to a potential generated at one end of the secondary coil N2 when the switching element Q is turned off. Connected in the direction.
　さらに、二次コイルＮ２の他端と出力端３の間にはダイオードＤ３が接続されている。ダイオードＤ３の極性は、アノードが二次コイルＮ２の他端側、カソードが出力端３側となる向きである。ダイオードＤ３は、スイッチング素子Ｑのオン時に二次コイルＮ２の他端に生じる電位に対して逆バイアスとなり、かつ、スイッチング素子Ｑのオフ時に二次コイルＮ２の他端に生じる電位に対して順バイアスとなる向きで接続されている。 Furthermore, a diode D3 is connected between the other end of the secondary coil N2 and the output end 3. The polarity of the diode D3 is such that the anode is on the other end side of the secondary coil N2 and the cathode is on the output end 3 side. The diode D3 is reverse-biased with respect to the potential generated at the other end of the secondary coil N2 when the switching element Q is turned on, and forward-biased with respect to the potential generated at the other end of the secondary coil N2 when the switching element Q is turned off. It is connected in the direction.
　ダイオードＤ１、Ｄ２、Ｄ３は、順バイアスの電圧（アノードがカソードに対して高電位）が印加されると導通し、逆バイアスの電圧（アノードがカソードに対して低電位）に対して遮断される整流手段の一つである。整流手段には、整流素子であるダイオードの他に、ダイオードと等価の整流デバイス又は整流回路も含まれるものとする。 The diodes D1, D2, and D3 are turned on when a forward bias voltage (anode has a high potential with respect to the cathode) is applied, and is blocked with respect to a reverse bias voltage (the anode has a low potential with respect to the cathode). One of the rectifying means. The rectifying means includes a rectifying device or a rectifying circuit equivalent to a diode in addition to a diode which is a rectifying element.
　出力端３と出力端４の間には平滑コンデンサＣが接続されている。図示しないが、これらの出力端３と出力端４の間には負荷が接続されている。 A smoothing capacitor C is connected between the output terminal 3 and the output terminal 4. Although not shown, a load is connected between the output terminal 3 and the output terminal 4.
　本発明のスイッチング電源の別の構成例として、一次側の基準電位である入力端２に対して入力端１が負電位となる入力電圧を印加する構成とすることもできる。その場合、二次側の各ダイオードの極性を逆向きとする。 As another configuration example of the switching power supply according to the present invention, an input voltage in which the input terminal 1 is a negative potential may be applied to the input terminal 2 which is the primary side reference potential. In that case, the polarity of each diode on the secondary side is reversed.
＜スイッチング電源の動作＞
　図２は、図１に示した回路におけるオン期間の電流の流れを示した図である。図３は、図１に示した回路におけるオフ期間の電流の流れを示した図である。図４は、図１に示した回路図における電圧及び電流の時間変化の例を模式的に示した図である。 <Operation of switching power supply>
FIG. 2 is a diagram showing the flow of current during the ON period in the circuit shown in FIG. FIG. 3 is a diagram showing a current flow during an off period in the circuit shown in FIG. FIG. 4 is a diagram schematically showing an example of the temporal change in voltage and current in the circuit diagram shown in FIG.
・オン期間の動作
　図２は、オン期間の電流の流れを示している。スイッチング素子Ｑのゲートに入力されるパルス電圧である制御電圧Ｖｇは、例えば図４（Ａ）の通りである。制御信号Ｖｇがオンになると、スイッチング素子Ｑの電流路が導通し、直流電圧が一次コイルＮ１の一端に印加され、一次コイルＮ１の一端が正電位、他端が負電位となる。これにより、入力端１→一次コイルＮ１→スイッチング素子Ｑ→入力端２の経路で電流ｉｄが流れる。電流ｉｄのオン期間の変化は、図４（Ｂ）の通りである。 -Operation in ON Period FIG. 2 shows a current flow in the ON period. The control voltage Vg that is a pulse voltage input to the gate of the switching element Q is, for example, as shown in FIG. When the control signal Vg is turned on, the current path of the switching element Q becomes conductive, a DC voltage is applied to one end of the primary coil N1, and one end of the primary coil N1 has a positive potential and the other end has a negative potential. As a result, a current id flows through the path of the input terminal 1 → the primary coil N1 → the switching element Q → the input terminal 2. The change in the on period of the current id is as shown in FIG.
　一次コイルＮ１に電流が流れるとトランスＴのコアを通って二次コイルＮ２を通る磁束が増加し、相互誘導による起電力が二次コイルＮ２に生じ、二次コイルＮ２の一端が正電位、他端が負電位となる。これによりダイオードＤ１が順バイアスとなって導通し、二次コイルＮ２→チョークコイルＣＨ→出力端３→負荷（又は平滑コンデンサＣ）→出力端４→ダイオードＤ１の経路で第１電流ｉ１が流れる。第１電流ｉ１のオン期間の変化は、図４（Ｃ）の通りである。第１電流ｉ１は、通常のフォワード方式におけるオン期間の出力電流に相当する。 When a current flows through the primary coil N1, the magnetic flux passing through the core of the transformer T and the secondary coil N2 increases, an electromotive force due to mutual induction is generated in the secondary coil N2, and one end of the secondary coil N2 has a positive potential. The end is a negative potential. As a result, the diode D1 becomes forward biased and becomes conductive, and the first current i1 flows through the path of the secondary coil N2, the choke coil CH, the output terminal 3, the load (or the smoothing capacitor C), the output terminal 4, and the diode D1. The change in the ON period of the first current i1 is as shown in FIG. The first current i1 corresponds to the output current during the ON period in the normal forward method.
　二次側の第１電流ｉ１は、チョークコイルＣＨの励磁電流でもあり、これによりチョークコイルＣＨに磁気エネルギーが蓄積される。 The first current i1 on the secondary side is also an exciting current of the choke coil CH, and thereby magnetic energy is accumulated in the choke coil CH.
　ダイオードＤ２は、二次コイルＮ２の一端が正電位となり逆バイアスとなるので電流は流れない。ダイオードＤ３も、二次コイルＮ２の他端が負電位となり逆バイアスとなるので電流は流れない。 In the diode D2, since one end of the secondary coil N2 becomes a positive potential and becomes a reverse bias, no current flows. Also in the diode D3, the other end of the secondary coil N2 has a negative potential and is reverse-biased, so no current flows.
　なお、一次コイルＮ１に流れる電流ｉｄは、二次コイルＮ２との相互誘導による負荷電流とトランスＴに磁気エネルギーを蓄積する励磁電流を含むものである。オン期間には、励磁電流によりトランスＴの磁束が増加し磁気エネルギーが蓄積される。 The current id flowing through the primary coil N1 includes a load current caused by mutual induction with the secondary coil N2 and an exciting current that accumulates magnetic energy in the transformer T. During the ON period, the magnetic flux of the transformer T is increased by the exciting current, and magnetic energy is accumulated.
・オフ期間の動作
　図３は、オフ期間の電流の流れを示している。制御信号Ｖｇがオフになると、スイッチング素子Ｑの電流路が遮断され、一次コイルＮ１を流れる電流ｉｄは消失する。これにより、一次コイルＮ１及び二次コイルＮ２に逆起電力が生じる。 -Operation in Off Period FIG. 3 shows a current flow in the off period. When the control signal Vg is turned off, the current path of the switching element Q is interrupted, and the current id flowing through the primary coil N1 disappears. Thereby, back electromotive force is generated in the primary coil N1 and the secondary coil N2.
　逆起電力により二次コイルＮ２の他端が正電位となり、ダイオードＤ１は逆バイアスとなるので第１電流ｉ１は流れない。 The other end of the secondary coil N2 becomes a positive potential due to the back electromotive force, and the diode D1 is reverse-biased, so the first current i1 does not flow.
　一方、二次側では、チョークコイルＣＨに蓄積された磁気エネルギーを放出するように第２電流ｉ２が流れる。第２電流ｉ２の経路は、チョークコイルＣＨ→出力端３→負荷（又は平滑コンデンサ）→出力端４→ダイオードＤ２である。第２電流ｉ２のオフ期間の変化は、図４（Ｄ）の通りである。第２電流ｉ２は、通常のフォワード方式におけるオフ期間の出力電流に相当し、第２電流ｉ２に関してダイオードＤ２はフライホイールダイオードとして機能する。 On the other hand, on the secondary side, the second current i2 flows so as to release the magnetic energy accumulated in the choke coil CH. The path of the second current i2 is choke coil CH → output terminal 3 → load (or smoothing capacitor) → output terminal 4 → diode D2. The change in the off period of the second current i2 is as shown in FIG. The second current i2 corresponds to an output current during an off period in the normal forward method, and the diode D2 functions as a flywheel diode with respect to the second current i2.
　さらに、逆起電力により二次コイルＮ２の一端が負電位、他端が正電位となり、ダイオードＤ２及びダイオードＤ３がいずれも順バイアスとなって導通し、二次コイルＮ２→ダイオードＤ３→出力端３→負荷（又は平滑コンデンサ）→出力端４→ダイオードＤ２の経路で第３電流ｉ３が流れる。第３電流ｉ３のオフ期間の変化は、図４（Ｅ）の通りである。 Further, due to the counter electromotive force, one end of the secondary coil N2 becomes a negative potential and the other end becomes a positive potential, and both the diode D2 and the diode D3 become forward biased and become conductive. The secondary coil N2 → the diode D3 → the output terminal 3 The third current i3 flows through the path of load (or smoothing capacitor) → output terminal 4 → diode D2. The change in the off period of the third current i3 is as shown in FIG.
　従って、オン期間にトランスＴに蓄積された磁気エネルギーは、二次コイルＮ２を通る第３電流ｉ３が流れることにより放出される。第３電流ｉ３も出力電流となるので、トランスの利用効率が向上する。図４（Ｆ）は、二次側に流れる全電流を示す。出力端３と出力端４の間に出力される電圧Ｖｏと電流Ｉｏは、平滑コンデンサＣにより平滑化され、図４（Ｇ）の通りである。 Therefore, the magnetic energy accumulated in the transformer T during the ON period is released by the third current i3 flowing through the secondary coil N2. Since the third current i3 is also an output current, the utilization efficiency of the transformer is improved. FIG. 4 (F) shows the total current flowing on the secondary side. The voltage Vo and current Io output between the output terminal 3 and the output terminal 4 are smoothed by the smoothing capacitor C, as shown in FIG.
　本発明のスイッチング電源は、フォワード方式を基本構成としながら、さらにダイオードＤ３を追加したことにより、オン期間にトランスに蓄積された磁気エネルギーをオフ期間に二次側の出力電流として放出することができるので、一次側のリセット回路が不要となる。従来はオフ時に発生するスパイク電圧によるスイッチング素子の耐圧対策が必要であったが、磁気エネルギーが二次側に放出されることによりスパイク対策も不要となる。 The switching power supply according to the present invention can discharge the magnetic energy accumulated in the transformer during the on period as a secondary output current during the off period by adding the diode D3 while using the forward system as a basic configuration. This eliminates the need for a reset circuit on the primary side. Conventionally, it has been necessary to take a countermeasure against the withstand voltage of the switching element by a spike voltage generated at the time of OFF, but the countermeasure against the spike becomes unnecessary because the magnetic energy is released to the secondary side.
（２）第２の実施形態
　図５～図７を参照して本発明の第２の実施形態を説明する。上述した第１の実施形態と同じ構成については説明を省略する。 (2) Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. The description of the same configuration as that of the first embodiment described above is omitted.
　図５は、本発明によるスイッチング電源の第２の実施形態の構成例を概略的に示す回路図である。第２の実施形態においては、第１の実施形態における第１ダイオードＤ１に替えて、第２のスイッチング素子Ｑ２を有する。 FIG. 5 is a circuit diagram schematically showing a configuration example of the second embodiment of the switching power supply according to the present invention. In the second embodiment, a second switching element Q2 is provided instead of the first diode D1 in the first embodiment.
　第２のスイッチング素子Ｑ２は、この例ではＮチャネルＦＥＴである。ドレインが二次コイルＮ２の他端に接続され、ソースが出力端４に接続されている。すなわち、第２のスイッチング素子Ｑ２の電流路は、二次コイルＮ２の他端と出力端４の間に接続される。第２のスイッチング素子Ｑ２は、一次コイルＮ１に接続されたスイッチング素子Ｑと同期してオンオフ駆動される。従って、第２のスイッチング素子Ｑ２の制御端であるゲートには、スイッチング素子Ｑと同じ制御電圧Ｖｇが入力される。 The second switching element Q2 is an N-channel FET in this example. The drain is connected to the other end of the secondary coil N 2, and the source is connected to the output end 4. That is, the current path of the second switching element Q2 is connected between the other end of the secondary coil N2 and the output end 4. The second switching element Q2 is driven on and off in synchronization with the switching element Q connected to the primary coil N1. Accordingly, the same control voltage Vg as that of the switching element Q is input to the gate which is the control end of the second switching element Q2.
　図６は、オン期間の電流の流れを示している。オン期間における一次側の動作は、第１の実施形態と同じである。 FIG. 6 shows the current flow during the ON period. The operation on the primary side in the on period is the same as that in the first embodiment.
　一次コイルＮ１に電流が流れると、相互誘導による起電力が二次コイルＮ２に生じ、二次コイルＮ２の一端が正電位、他端が負電位となる点も第１の実施形態と同じである。このとき、第２のスイッチング素子Ｑ２は、制御電圧Ｖｇによりオンとなっているので電流路が導通状態である。これにより、二次コイルＮ２→チョークコイルＣＨ→出力端３→負荷（又は平滑コンデンサＣ）→出力端４→第２のスイッチング素子Ｑ２の経路で第１電流ｉ１が流れる。第２のスイッチング素子Ｑ２に置き換えたことにより、第１の実施形態のダイオードＤ１に比べてオン期間の損失が少なくなる。その他の動作については、第１の実施形態と同じである。 When a current flows through the primary coil N1, an electromotive force due to mutual induction is generated in the secondary coil N2, and one end of the secondary coil N2 has a positive potential and the other end has a negative potential, as in the first embodiment. . At this time, since the second switching element Q2 is turned on by the control voltage Vg, the current path is conductive. As a result, the first current i1 flows through the path of the secondary coil N2, the choke coil CH, the output terminal 3, the load (or the smoothing capacitor C), the output terminal 4, and the second switching element Q2. By replacing the second switching element Q2, the loss during the ON period is reduced as compared with the diode D1 of the first embodiment. Other operations are the same as those in the first embodiment.
　図７は、オフ期間の電流の流れを示している。オン期間における一次側の動作は、第１の実施形態と同じである。 FIG. 7 shows the flow of current during the off period. The operation on the primary side in the on period is the same as that in the first embodiment.
　逆起電力により二次コイルＮ２の他端が正電位となる。このとき、第２のスイッチング素子Ｑ２は、制御電圧Ｖｇによりオフとなっているので電流路が遮断状態である。よって第１電流ｉ１は流れない。 The other end of the secondary coil N2 becomes a positive potential due to the back electromotive force. At this time, since the second switching element Q2 is turned off by the control voltage Vg, the current path is cut off. Therefore, the first current i1 does not flow.
　一方、ダイオードＤ２及びダイオードＤ３については、第１の実施形態と同様に、第２電流ｉ２及び第３電流ｉ３が流れる。 On the other hand, as for the diode D2 and the diode D3, the second current i2 and the third current i3 flow as in the first embodiment.
　別の実施例として、第２のスイッチング素子Ｑ２は、ＮチャネルＦＥＴではなくＰチャネルＦＥＴとすることもできる。 As another example, the second switching element Q2 may be a P-channel FET instead of an N-channel FET.
　Ｔ　トランス
　Ｎ１　一次コイル
　Ｎ２　二次コイル
　１、２　入力端
　３、４　出力端
　Ｑ　スイッチング素子
　Ｄ１、Ｄ２、Ｄ３　ダイオード
　Ｃ　平滑コンデンサ T transformer N1 primary coil N2 secondary coil 1, 2 input terminal 3, 4 output terminal Q switching element D1, D2, D3 diode C smoothing capacitor

Claims (4)

  1. 　トランス（Ｔ）と、
    　入力電圧により前記トランス（Ｔ）の一次コイル（Ｎ１）に流れる電流を導通又は遮断するべくオンオフ駆動される、制御端を具備するスイッチング素子（Ｑ）と、
    　前記トランスの二次コイル（Ｎ２）の一端と第１出力端（３）の間に接続されたチョークコイル（ＣＨ）と、
    　前記トランス（Ｔ）の二次コイル（Ｎ２）の他端と第２出力端（４）の間に接続され、前記スイッチング素子（Ｑ）のオン時に前記二次コイル（Ｎ２）の他端に生じる電位に対して順バイアスとなりかつオフ時に該二次コイル（Ｎ２）の他端に生じる電位に対して逆バイアスとなる第１整流手段（Ｄ１）と、
    　前記トランス（Ｔ）の前記二次コイル（Ｎ２）の一端と前記第２出力端（４）の間に接続され、前記スイッチング素子（Ｑ）のオン時に前記二次コイル（Ｎ２）の一端に生じる電位に対して逆バイアスとなりかつオフ時に該二次コイル（Ｎ２）の一端に生じる電位に対して順バイアスとなる第２整流手段（Ｄ２）と、
    　前記トランス（Ｔ）の前記二次コイル（Ｎ２）の他端と前記第１出力端（３）の間に接続され、前記スイッチング素子（Ｑ）のオン時に前記二次コイル（Ｎ２）の他端に生じる電位に対して逆バイアスとなりかつオフ時に該二次コイル（Ｎ２）の他端に生じる電位に対して順バイアスとなる第３整流手段（Ｄ３）と、
    　前記第１出力端（３）と前記第２出力端（４）の間に接続された平滑コンデンサ（Ｃ）と、を有することを特徴とする
    　スイッチング電源。     A transformer (T),
    A switching element (Q) having a control end, which is driven on and off to conduct or cut off a current flowing through the primary coil (N1) of the transformer (T) by an input voltage;
    A choke coil (CH) connected between one end of the secondary coil (N2) of the transformer and the first output end (3);
    Connected between the other end of the secondary coil (N2) of the transformer (T) and the second output end (4), and occurs at the other end of the secondary coil (N2) when the switching element (Q) is turned on. A first rectifier (D1) that is forward biased with respect to the potential and reversely biased with respect to the potential generated at the other end of the secondary coil (N2) when turned off;
    Connected between one end of the secondary coil (N2) of the transformer (T) and the second output end (4), and is generated at one end of the secondary coil (N2) when the switching element (Q) is turned on. A second rectifier (D2) that is reverse-biased with respect to the potential and forward-biased with respect to the potential generated at one end of the secondary coil (N2) when turned off;
    The other end of the secondary coil (N2) is connected between the other end of the secondary coil (N2) of the transformer (T) and the first output end (3), and the switching element (Q) is turned on. A third rectifying means (D3) which is reverse-biased with respect to the potential generated at the time and is forward-biased with respect to the potential generated at the other end of the secondary coil (N2) when turned off;
    A switching power supply comprising a smoothing capacitor (C) connected between the first output terminal (3) and the second output terminal (4).
  2. 　前記第１整流手段（Ｄ１）、前記第２整流手段（Ｄ２）及び前記第３整流手段（Ｄ３）がそれぞれダイオードであることを特徴とする請求項１に記載のスイッチング電源。 The switching power supply according to claim 1, wherein each of the first rectifying means (D1), the second rectifying means (D2), and the third rectifying means (D3) is a diode.
  3. 　前記第１整流手段（Ｄ１）に替えて、前記トランス（Ｔ）の二次コイル（Ｎ２）の他端と第２出力端（４）の間に接続された電流路と該電流路を流れる電流を導通又は遮断するべくオンオフ駆動される制御端とを具備する第２のスイッチング素子（Ｑ２）を有し、
    　前記第２のスイッチング素子（Ｑ２）は前記スイッチング素子（Ｑ）と同期してオンオフ駆動されることを特徴とする
    　請求項１に記載のスイッチング電源。     Instead of the first rectifying means (D1), a current path connected between the other end of the secondary coil (N2) of the transformer (T) and the second output end (4) and a current flowing through the current path And a second switching element (Q2) having a control end that is driven on and off to turn on or off.
    The switching power supply according to claim 1, wherein the second switching element (Q2) is driven on and off in synchronization with the switching element (Q).
  4. 　前記第２整流手段（Ｄ２）及び前記第３整流手段（Ｄ３）がそれぞれダイオードであることを特徴とする請求項３に記載のスイッチング電源。 The switching power supply according to claim 3, wherein each of the second rectifying means (D2) and the third rectifying means (D3) is a diode.
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