JP4253809B2

JP4253809B2 - DC-DC converter

Info

Publication number: JP4253809B2
Application number: JP10160599A
Authority: JP
Inventors: 守男佐藤
Original assignee: 大平電子株式会社
Priority date: 1999-03-04
Filing date: 1999-03-04
Publication date: 2009-04-15
Anticipated expiration: 2019-03-04
Also published as: JP2000262046A

Description

【０００１】
【産業上の利用分野】
本発明はスイッチング電源に関し、特にソフトスイッチに関する。
【０００２】
【従来の技術】
従来は、図４に示したようにダイオードにコンデンサを並列に接続し、これによってソフトスイッチ化していた。図４は降圧チョッパ型を例にしているが、昇圧チョッパ型においても同じ。
【０００３】
【発明が解決しようとする課題】
図４において、スイッチ素子１０１が高速でターンオフしてもコンデンサ１０８の電荷の放電はコンデンサ１０８の容量とリアクトル１０２のインダクタンスによって決定される速さで行われるため、コンデンサ１０８の容量をある程度大きくすることによって放電のスピードを遅くさせることができ、スイッチ素子１０１とリアクトル１０２の接続点の電圧の上昇率を緩めることができる。その結果、スイッチ素子１０１の電流と電圧の関係が、電流がほぼゼロになってから電圧が立ち上がることになり、ターンオフ時のスイッチングロスが小さくなる。また、スイッチングノイズを減ずる効果をもたらす。
【０００４】
図４において、コンデンサ１０８の電圧はスイッチ素子１０１がオン状態の間に直流電源１０６の電圧にほぼ等しい電圧まで充電され、スイッチ素子がターンオフすると、ゼロまで下がる。コンデンサ１０８が放電するとき、電荷は負荷側に流れるのでコンデンサ１０８の充電エネルギが損失になることはない。しかし、スイッチ素子１０１がターンオンして、コンデンサ１０８が充電されるとき、スイッチ素子１０１に突入電流が流れ、これがスイッチ素子１０１の電力損失になる。コンデンサ１０８の容量を大きくすればスイッチングノイズを減ずる効果は上がるが、同時にスイッチ素子１０１の突入電流が大きくなり、電力損失が増える。
【０００５】
本発明は、上に示した従来方式の欠点を除去するものでスイッチ素子の突入電流をなくすことを目的としている。
【０００６】
【課題を解決するための手段】
上の目的を達成するために請求項１記載の発明は、従来方式において用いられていたコンデンサ１０８に代わって第２のコンデンサと第２のダイオードからなる直列回路を第１のダイオードに並列に接続し、第２のダイオードによって第１のスイッチ素子がターンオンしたときに第２のコンデンサに突入電流が流れることを防ぎ、更に、第１のスイッチ素子がターンオフする前に第２のコンデンサに、直流電源の電圧に等しい電圧に達する電荷を充電する回路を設けた。
【０００７】
第２のコンデンサを充電する回路は請求項１記載の発明では次のように構成されている。直流電源にトランスの１次巻線と第２のスイッチ素子からなる直列回路を接続し、この第２のスイッチ素子をオン期間一定のパルスによって、第１のスイッチ素子と同期してターンオンさせ、１次巻線によってトランスに蓄積される励磁エネルギを２次巻線とこの２次巻線に直列に接続された第３のダイオードを通して放出して第２のコンデンサを充電する。
【０００８】
【作用】
請求項１記載の発明において、第２のスイッチ素子の１回のオン期間でトランスに蓄積されるエネルギＥは直流電源の電圧をＶ１、１次巻線のインダクタンスをＬ、オン期間をＴ１、１次巻線のピーク電流をＩＰとおくと、次の式で表すことができる。
【０００９】
【数１】

【００１０】
一方、１次巻線によって蓄積された励磁エネルギの全てが第２のコンデンサの充電エネルギになると仮定すれば、充電される電圧Ｖは、第２のコンデンサの容量をＣとおくと、次の式で表すことができる。
【００１１】
【数２】

【００１２】
数２に示されているように、Ｔ１が所定の値に設定されていれば、第２のコンデンサには発振の度に直流電源と同じ電圧が充電され、第１のスイッチ素子がターンオフしたとき、第１のスイッチ素子両端の電圧をゼロからゆっくり上昇させることができる。
【００１３】
請求項２記載の発明は発振の周期が第２のスイッチ素子の制御電極に接続された発振器によって決められるという点で請求項１記載の発明と異なるが、第１のスイッチ素子がターンオフする前に第２のコンデンサを充電するというメカニズムは上に述べた内容と同じ。
【００１４】
請求項３記載の発明においては、第２のコンデンサに充電される電圧が出力電圧に等しくなることによって第１のスイッチ素子両端の電圧がゼロから上昇するようになる。そこで、トランスの１次巻線と第２のスイッチ素子からなる直列回路を出力電圧が充電される第１のコンデンサに接続し、第２のスイッチ素子のオン期間を所定の値に設定して、第２のコンデンサが発振の度に出力電圧に等しい電圧まで充電されるようにした。
【００１５】
請求項４記載の発明は発振の周期が第２のスイッチ素子の制御電極に接続された発振器によって決められるという点で請求項３記載の発明と異なるが、第２のコンデンサを出力電圧に等しい電圧まで充電するメカニズムは請求項３記載の発明と同じ。
【００１６】
【実施例】
図１は請求項１記載の発明に係る実施例を示す回路図である。図１に示した回路において、第１のスイッチ素子１と第２のスイッチ素子１２はほぼ同時にターンオンし、第２のスイッチ素子１２が先にターンオフする。第２のスイッチ素子１２のオン期間に１次巻線１１ａに流れる電流によってトランス１１に励磁エネルギが蓄積され、第２のスイッチ素子１２がターンオフするとその励磁エネルギは２次巻線１１ｂと第３のダイオード１４を通って第２のコンデンサ１６を充電する。
【００１７】
図３は第１のスイッチ素子１のオン期間と第２のスイッチ素子１２のオン期間と２次巻線１１ｂを流れる電流と第２のコンデンサ１６の電圧の波形を示している。２次巻線１１ｂと第３のダイオード１４と第２のコンデンサ１６は半波共振回路を構成するので、２次巻線１１ｂの電流は正弦波の片側だけになり、この電流がゼロになったとき第２のコンデンサ１６の電圧はピークになる。この電圧のピークは作用で述べたように直流電源６の電圧に一致させることができる。第１のスイッチ素子１がターンオフすると、第２のコンデンサ１６の電荷はリアクトルを通り負荷側に流れるが、ターンオフの直後は第１のスイッチ素子１とリアクトル２の接続点の電圧は直流電源６の電圧に等しい電圧から、第２のコンデンサ１６の電荷の放電とともに下がっていくので第１のスイッチ素子１両端の電圧はゼロからゆっくり上昇する。
【００１８】
第２のコンデンサ１６の充電と放電のいずれの場合も、電流経路にインダクタンス成分が存在するので、電流波形は正弦波状になり、突入電流が生じる従来の方式のような電力損失はない。
【００１９】
図２は請求項３記載の発明に係る実施例を示す回路である。図２に示した回路において、第２のコンデンサ１６に充電される電圧は図１の場合と違って、出力電圧に等しい値になる。第１のスイッチ素子１がターンオフした直後はリアクトル２の励磁エネルギの放電は第２のダイオード１５と第２のコンデンサ１６を経由して流れて第１のコンデンサ４を充電するので、リアクトル２と第２のダイオード１５の接続点の電圧はゼロからゆっくり上昇する。すなわち、第１のスイッチ素子１の両端の電圧はゼロからゆっくり上昇する。第２のコンデンサ１６に充電される電圧が出力電圧に等しいという点を除けば、図１に関して図３の波形図を用いて述べた上記の説明をあてはめることができる。
【００２０】
図１及び図２に各々示した回路において、加えられたパルスの立ち上がりから所定のパルス幅のパルスを作る回路１３を、受動部品だけで構成することも、能動素子を組み合わせて作ることも、単安定マルチバイブレータを使うこともできる。
【００２１】
請求項２記載の発明の実施例及び請求項４記載の発明の実施例を示す回路図を省略するが、図１及び図２に示した回路図において、発振制御回路５を外部信号同期端子付き発振制御回路に変更し、加えられたパルスの立ち上がりから所定のパルス幅のパルスを作る回路１３をパルス発生器に変更し、パルス発生器の信号で発振制御回路がトリガされるように構成すれば各々請求項２記載の発明と請求項４記載の発明の実施例を示す回路になる。
【００２２】
図１及び図２に各々示した請求項１及び請求項３記載の発明の実施例において、第１のスイッチ素子１と第２のスイッチ素子１２のいずれにもバイポーラ型トランジスタを用いているが、これらをＭＯＳＦＥＴ等の他のスイッチ素子で置き換えることも可能である。
【００２３】
【発明の効果】
ソフトスイッチングに用いるコンデンサによる突入電流がなくなるため、このコンデンサの容量を大幅に増すことが可能になり、ソフトスイッチングの効果を上げることができる。
【図面の簡単な説明】
【図１】請求項１記載の発明に係るＤＣ−ＤＣコンバータを示す回路図である。
【図２】請求項３記載の発明に係るＤＣ−ＤＣコンバータを示す回路図である。
【図３】図１の主要部の波形を示す波形図である。
【図４】従来方式の一例を示す回路図である。
【符号の説明】
１第１のスイッチ素子
２リアクトル
３第１のダイオード
４第１のコンデンサ
５発振制御回路
６直流電源
７負荷
１１トランス
１１ａ１次巻線
１１ｂ２次巻線
１２第２のスイッチ素子
１３加えられたパルスの立ち上がりから所定のパルス幅のパルスを作る回路
１４第３のダイオード
１５第２のダイオード
１６第２のコンデンサ
１０１スイッチ素子
１０２リアクトル
１０３ダイオード
１０４コンデンサ
１０５発振制御回路
１０６直流電源
１０７負荷[0001]
[Industrial application fields]
The present invention relates to a switching power supply, and more particularly to a soft switch.
[0002]
[Prior art]
Conventionally, as shown in FIG. 4, a capacitor is connected in parallel to a diode, thereby forming a soft switch. Although FIG. 4 shows the step-down chopper type as an example, the same applies to the step-up chopper type.
[0003]
[Problems to be solved by the invention]
In FIG. 4, even when the switch element 101 is turned off at a high speed, the capacitor 108 is discharged at a rate determined by the capacitance of the capacitor 108 and the inductance of the reactor 102. Therefore, the capacitance of the capacitor 108 is increased to some extent. As a result, the discharge speed can be reduced, and the rate of increase in voltage at the connection point of the switch element 101 and the reactor 102 can be reduced. As a result, the relation between the current and voltage of the switch element 101 is that the voltage rises after the current becomes almost zero, and the switching loss at turn-off is reduced. In addition, the switching noise is reduced.
[0004]
In FIG. 4, the voltage of the capacitor 108 is charged to a voltage substantially equal to the voltage of the DC power supply 106 while the switch element 101 is on, and drops to zero when the switch element is turned off. When the capacitor 108 is discharged, the charge flows to the load side, so that the charging energy of the capacitor 108 is not lost. However, when the switch element 101 is turned on and the capacitor 108 is charged, an inrush current flows through the switch element 101, which becomes a power loss of the switch element 101. Increasing the capacitance of the capacitor 108 increases the effect of reducing switching noise, but at the same time, the inrush current of the switch element 101 increases and the power loss increases.
[0005]
The object of the present invention is to eliminate the inrush current of the switch element by eliminating the drawbacks of the conventional method described above.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a series circuit including a second capacitor and a second diode is connected in parallel to the first diode in place of the capacitor 108 used in the conventional system. In addition, when the first switch element is turned on by the second diode, an inrush current is prevented from flowing into the second capacitor, and further, a DC power source is connected to the second capacitor before the first switch element is turned off. A circuit for charging an electric charge reaching a voltage equal to the voltage of is provided.
[0007]
According to the first aspect of the present invention, the circuit for charging the second capacitor is configured as follows. A DC power supply is connected to a series circuit composed of a primary winding of a transformer and a second switch element, and the second switch element is turned on in synchronization with the first switch element by a pulse having a constant ON period. The excitation energy stored in the transformer by the secondary winding is discharged through the secondary winding and a third diode connected in series with the secondary winding to charge the second capacitor.
[0008]
[Action]
According to the first aspect of the present invention, the energy E stored in the transformer in one on period of the second switch element is V1, the voltage of the DC power source is V1, the inductance of the primary winding is L, the on period is T1, If the peak current of the next winding is IP, it can be expressed by the following equation.
[0009]
[Expression 1]

[0010]
On the other hand, if it is assumed that all of the excitation energy accumulated by the primary winding becomes the charging energy of the second capacitor, the charged voltage V can be expressed by the following equation when the capacitance of the second capacitor is C. Can be expressed as
[0011]
[Expression 2]

[0012]
As shown in Equation 2, if T1 is set to a predetermined value, the second capacitor is charged with the same voltage as the DC power source every time it oscillates, and the first switch element is turned off. The voltage across the first switch element can be slowly increased from zero.
[0013]
The invention according to claim 2 is different from the invention according to claim 1 in that the period of oscillation is determined by an oscillator connected to the control electrode of the second switch element, but before the first switch element is turned off. The mechanism for charging the second capacitor is the same as described above.
[0014]
According to the third aspect of the present invention, the voltage charged to the second capacitor becomes equal to the output voltage, whereby the voltage across the first switch element rises from zero. Therefore, a series circuit composed of the primary winding of the transformer and the second switch element is connected to the first capacitor charged with the output voltage, and the ON period of the second switch element is set to a predetermined value, The second capacitor is charged to a voltage equal to the output voltage every time it oscillates.
[0015]
The invention according to claim 4 differs from the invention according to claim 3 in that the oscillation period is determined by an oscillator connected to the control electrode of the second switch element, but the second capacitor is set to a voltage equal to the output voltage. The mechanism for charging up to is the same as that of the third aspect of the invention.
[0016]
【Example】
FIG. 1 is a circuit diagram showing an embodiment according to the first aspect of the present invention. In the circuit shown in FIG. 1, the first switch element 1 and the second switch element 12 are turned on almost simultaneously, and the second switch element 12 is turned off first. Excitation energy is accumulated in the transformer 11 by the current flowing through the primary winding 11a during the ON period of the second switch element 12, and when the second switch element 12 is turned off, the excitation energy is applied to the secondary winding 11b and the third winding 11b. The second capacitor 16 is charged through the diode 14.
[0017]
FIG. 3 shows waveforms of the ON period of the first switch element 1, the ON period of the second switch element 12, the current flowing through the secondary winding 11b, and the voltage of the second capacitor 16. Since the secondary winding 11b, the third diode 14 and the second capacitor 16 constitute a half-wave resonance circuit, the current of the secondary winding 11b is only on one side of the sine wave, and this current becomes zero. Sometimes the voltage on the second capacitor 16 peaks. The peak of this voltage can be matched with the voltage of the DC power source 6 as described in the operation. When the first switch element 1 is turned off, the charge of the second capacitor 16 flows to the load side through the reactor, but immediately after the turn-off, the voltage at the connection point between the first switch element 1 and the reactor 2 is the DC power supply 6 The voltage across the first switch element 1 rises slowly from zero because the voltage drops from the voltage equal to the voltage with the discharge of the charge of the second capacitor 16.
[0018]
In both cases of charging and discharging the second capacitor 16, since an inductance component exists in the current path, the current waveform is sinusoidal and there is no power loss as in the conventional method in which an inrush current occurs.
[0019]
FIG. 2 is a circuit showing an embodiment according to the third aspect of the present invention. In the circuit shown in FIG. 2, the voltage charged in the second capacitor 16 is equal to the output voltage, unlike the case of FIG. Immediately after the first switch element 1 is turned off, the discharge of the excitation energy of the reactor 2 flows through the second diode 15 and the second capacitor 16 to charge the first capacitor 4. The voltage at the connection point of the two diodes 15 rises slowly from zero. That is, the voltage across the first switch element 1 slowly increases from zero. Except for the fact that the voltage charged to the second capacitor 16 is equal to the output voltage, the above description with reference to the waveform diagram of FIG. 3 with respect to FIG. 1 can be applied.
[0020]
In the circuits shown in FIGS. 1 and 2, the circuit 13 for generating a pulse having a predetermined pulse width from the rising edge of the applied pulse can be formed by using only passive components or by combining active elements. A stable multivibrator can also be used.
[0021]
Although the circuit diagrams showing the embodiment of the invention described in claim 2 and the embodiment of the invention described in claim 4 are omitted, the oscillation control circuit 5 is provided with an external signal synchronization terminal in the circuit diagrams shown in FIGS. If the circuit is changed to an oscillation control circuit, the circuit 13 for generating a pulse having a predetermined pulse width from the rising edge of the applied pulse is changed to a pulse generator, and the oscillation control circuit is triggered by the signal of the pulse generator. The circuit according to the second aspect of the present invention and the embodiment of the fourth aspect of the present invention are provided.
[0022]
In the embodiments of the invention according to claim 1 and claim 3 shown in FIGS. 1 and 2, respectively, bipolar transistors are used for both the first switch element 1 and the second switch element 12, It is also possible to replace these with other switching elements such as MOSFETs.
[0023]
【The invention's effect】
Since the inrush current due to the capacitor used for soft switching is eliminated, the capacity of the capacitor can be greatly increased, and the effect of soft switching can be improved.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a DC-DC converter according to a first aspect of the present invention.
FIG. 2 is a circuit diagram showing a DC-DC converter according to a third aspect of the present invention.
FIG. 3 is a waveform diagram showing waveforms of main parts of FIG. 1;
FIG. 4 is a circuit diagram showing an example of a conventional method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st switch element 2 Reactor 3 1st diode 4 1st capacitor 5 Oscillation control circuit 6 DC power supply 7 Load 11 Transformer 11a Primary winding 11b Secondary winding 12 Second switch element 13 Applied pulse A circuit for generating a pulse having a predetermined pulse width from the rising edge of the first diode 15 Third diode 15 Second diode 16 Second capacitor 101 Switch element 102 Reactor 103 Diode 104 Capacitor 105 Oscillation control circuit 106 DC power supply 107 Load

Claims

A direct current power supply, a load that receives power supply from the direct current power supply, a series circuit including a first switch element having a control electrode inserted in series between the direct current power supply and the load, and a reactor, and the reactor A first diode that discharges excitation energy to the load, a first capacitor that smoothes the output current of the reactor, and a control electrode of the first switch element to make the voltage supplied to the load constant. In a step-down chopper type DC-DC converter having a connected oscillation control circuit, a series circuit composed of a second switch element having a primary winding of a transformer and a control electrode is connected to the DC power source, and an applied pulse A circuit for generating a pulse having a predetermined pulse width from the rising edge of the second switching element is connected between the output terminal of the oscillation control circuit and the control electrode of the second switch element, A series circuit composed of a diode and a second capacitor is connected in parallel to the first diode, a secondary winding electromagnetically coupled to the primary winding of the transformer is wound, and the terminal is connected to the third diode. The DC-DC converter is characterized in that the switch operation of the first switch element is made into a soft switch by connecting to the terminal of the second capacitor.

A direct current power supply, a load that receives power supply from the direct current power supply, a series circuit including a first switch element having a control electrode inserted in series between the direct current power supply and the load, and a reactor, and the reactor A first diode that discharges excitation energy to the load, a first capacitor that smoothes the output current of the reactor, and a control electrode of the first switch element to make the voltage supplied to the load constant. In a step-down chopper type DC-DC converter having an oscillation control circuit having a terminal that can synchronize with a connected external signal, a series circuit comprising a second switch element having a primary winding of a transformer and a control electrode is connected to the DC power source. An oscillator that outputs a pulse having a predetermined pulse width is connected to the control electrode of the second switch element, and the output signal of the oscillator is Input to an external signal synchronization terminal of the circuit to synchronize the oscillation of the oscillation control circuit to the oscillator, and connect a series circuit composed of a second diode and a second capacitor in parallel to the first diode; A secondary winding that is electromagnetically coupled to the primary winding of the first winding is wound and the terminal thereof is connected to the terminal of the second capacitor via a third diode, whereby the switching operation of the first switching element is performed. A DC-DC converter characterized by a soft switch.

A DC power source, a load that receives power supply from the DC power source, a series circuit including a first switch element having a control electrode connected to the DC power source and a reactor, and excitation energy of the reactor are discharged to the load. An oscillation control circuit connected to a control electrode of the first switch element in order to make the voltage supplied to the load constant; a first diode that smoothes the output current of the reactor; In a step-up chopper type DC-DC converter provided, a series circuit composed of a second switch element having a primary winding of a transformer and a control electrode is connected to the first capacitor, and a predetermined circuit is applied from the rising edge of the applied pulse. A circuit for generating a pulse having a pulse width is connected between the output terminal of the oscillation control circuit and the control electrode of the second switch element, and a second diode A series circuit composed of a second capacitor is connected in parallel to the first diode, a secondary winding electromagnetically coupled to the primary winding of the transformer is wound, and a terminal thereof is connected via a third diode. A DC-DC converter characterized in that it is connected to a terminal of the second capacitor, whereby the switch operation of the first switch element is made into a soft switch.

A DC power source, a load that receives power supply from the DC power source, a series circuit including a first switch element having a control electrode connected to the DC power source and a reactor, and excitation energy of the reactor are discharged to the load. An oscillation control circuit connected to a control electrode of the first switch element in order to make the voltage supplied to the load constant; a first diode that smoothes the output current of the reactor; In a step-up chopper type DC-DC converter provided, a series circuit including a second switch element having a primary winding of a transformer and a control electrode is connected to the first capacitor, and a pulse having a predetermined pulse width is output. An oscillator is connected to a control electrode of the second switch element, and an output signal of the oscillator is input to an external signal synchronization terminal of the oscillation control circuit to generate the oscillation Control circuit oscillation is synchronized with the oscillator, a series circuit composed of a second diode and a second capacitor is connected in parallel to the first diode, and electromagnetically coupled to the primary winding of the transformer. A DC-DC characterized in that the next winding is wound and its terminal is connected to the terminal of the second capacitor via a third diode, whereby the switch operation of the first switch element is made into a soft switch. converter.