JP4365972B2 - Switching power supply - Google Patents
Switching power supply Download PDFInfo
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- JP4365972B2 JP4365972B2 JP2000037519A JP2000037519A JP4365972B2 JP 4365972 B2 JP4365972 B2 JP 4365972B2 JP 2000037519 A JP2000037519 A JP 2000037519A JP 2000037519 A JP2000037519 A JP 2000037519A JP 4365972 B2 JP4365972 B2 JP 4365972B2
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- 239000003990 capacitor Substances 0.000 claims description 9
- 230000002265 prevention Effects 0.000 claims description 8
- QZZYPHBVOQMBAT-JTQLQIEISA-N (2s)-2-amino-3-[4-(2-fluoroethoxy)phenyl]propanoic acid Chemical compound OC(=O)[C@@H](N)CC1=CC=C(OCCF)C=C1 QZZYPHBVOQMBAT-JTQLQIEISA-N 0.000 description 11
- 238000010586 diagram Methods 0.000 description 5
- 230000003111 delayed effect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 230000020169 heat generation Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
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Description
【０００１】
【発明の属する技術分野】
本発明は、充電回路を備えたスイッチング電源に関するものである。
【０００２】
【従来の技術】
この種のスイッチング電源として、図２のものが提案されているが、図２においては、負荷（バッテリー）Ｘから電源２次側回路への電流の逆流を防止するダイオードＤ１が存在するため、ダイオードの順方向電圧（ＶＦ）による大きな損失が存在する。
【０００３】
【発明が解決しようとする課題】
ダイオードの順方向電圧（ＶＦ）による損失が大きいと、ダイオードに多量の熱が発生するため、かかる損失を低減し、スイッチング電源の効率を改善することができる手段が要求されていた。
【０００４】
【課題を解決するための手段】
本発明は、上記の課題を解決するもので、ダイオードＤ１にＦＥＴ〔Ｑ１〕を並列に接続し、スイッチング電源起動時はダイオードＤ１を起動させ、設定電圧到達後、ＦＥＴ〔Ｑ１〕をオンさせ、ダイオードＤ１の順方向電圧（ＶＦ）による大きな損失から、ＦＥＴ〔Ｑ１〕のオン抵抗による小さな損失に切り換える手段を備えたことを特徴とするスイッチング電源を提供するものである。すなわち、スイッチングトランスの２次側から逆電流防止用ダイオードＤ１を介して負荷に直流電圧を供給する充電回路を備えたスイッチング電源において、前記逆電流防止用ダイオードＤ１と並列に、前記逆電流防止用ダイオードＤ１の順方向抵抗よりオン抵抗が小さいＦＥＴ〔Ｑ１〕を接続し、前記充電回路は、前記スイッチングトランスの２次側の両端子に接続された補助電源Ａと、前記ＦＥＴ〔Ｑ１〕に接続されたトランジスタＱ２と、前記補助電源Ａと前記トランジスタＱ２との間に接続された時定数回路Ｂを有し、起動時は前記逆電流防止用ダイオードＤ１を起動させ、設定電圧到達後、前記ＦＥＴ〔Ｑ１〕をオンさせるスイッチング電源である。
【０００７】
そして、上記の補助電源Ａが、ダイオードＤ２と第１のコンデンサＣ１とからなることを特徴とするスイッチング電源である。
【０００８】
さらに、上記の時定数回路Ｂが、抵抗Ｒ１と第２のコンデンサＣ２とからなることを特徴とするスイッチング電源である。
【０００９】
【発明の実施の形態】
以下、本発明の実施の形態について、図面を参照しながら詳細に説明する。図１は、本発明の実施形態が適用されるスイッチング電源の実施例の回路図である。
この回路は、フライバックコンバータと呼ばれるものであり、出力電圧を安定化するための定電圧検出回路と、バッテリーに一定電流で充電するための定電流検出回路からの制御信号を、１次側の制御回路にフィードバックして動作している。
ダイオードＤ１が、バッテリーから電源の２次回路への電流の逆流を防止するダイオードであり、このダイオードの順方向電圧（ＶＦ）による損失によって発生する熱をいかに抑えるかが問題であった。
【００１０】
上記の問題を解決するため、とられた手段は下記のとおりである。すなわち、（１）ダイオードのＶＦによる損失を低減するオン抵抗が小さいＦＥＴ〔Ｑ１〕をダイオードＤ１と並列に接続し、スイッチング電源起動時はダイオードＤ１を起動させ、設定電圧到達後、ＦＥＴ〔Ｑ１〕をオンさせる。
（２） そのために、ダイオードＤ２とコンデンサＣ１からなる補助電源と、抵抗Ｒ１とコンデンサＣ２からなる時定数回路とを接続して、トランジスタＱ２のベースに印加される電圧を遅延させる。
かかる遅延手段により、トランジスタＱ２が遅れてオンするため、ＦＥＴ〔Ｑ１〕も遅れてオンとなり、ダイオードＤ１に流れる電流がオン抵抗の低いＦＥＴ〔Ｑ１〕に遅れて流れることになる。
その結果、スイッチング電源の出力電流のほとんどがＦＥＴ〔Ｑ１〕側に流れるため、ダイオードＤ１で発生する熱の増加が抑えられ、スイッチング電源の効率が改善できる。
【００１１】
【実施例】
図１の本発明の実施例による回路と、図２の従来例による回路とを作製し、ダイオードＤ１に発生する電圧Ｖの経時変化を調査した。その結果をそれぞれ図３、図４に示す。
実施例においては、図３のように、最初はダイオードＤ１に電流Ｉが流れ、ダイオードの順方向電圧と順方向電流の関係曲線（ＶＦ−ＩＦ特性）のとおり、電流Ｉの増加に伴い電圧Ｖも次第に増加して行くが、次第にその増加の度合がゆるやかになり、ＶＰに達する。
ＦＥＴ〔Ｑ１〕は、図１に示すようにダイオードＤ２とコンデンサＣ１からなる補助電源Ａと、抵抗Ｒ１とコンデンサＣ２からなる時定数回路ＢとにトランジスタＱ２を介して接続されているので、ＦＥＴ〔Ｑ１〕に流れる電流はダイオードＤ１に流れる電流より時間ｔだけ遅れる。
遅延時間ｔ後、ダイオードＤ１に流れていた電流が、並列接続されたオン抵抗の低いＦＥＴ〔Ｑ１〕にほとんど流れてしまう結果、ダイオードＤ１に発生する電圧は（出力電流Ｉ）×（オン抵抗Ｒ）となって、図３に示されているように当初のＶＰを１／１０以下に低下させることができる。
一方、従来例においては、図４のように電圧ＶがＶＰに達するまでは実施例と同様であるが、オン抵抗の低いＦＥＴが並列接続されていないので、電圧はＶＰのままで低下することはない。
このように、ＦＥＴ〔Ｑ１〕をダイオードＤ１に並列接続した実施例による発生電圧は、図３に示すように、ＦＥＴ〔Ｑ１〕を並列接続しない従来例に比べ、遅延時間ｔ後の電圧値を従来例の１／１０以下に低下させることができ、ダイオードＤ１の発熱を抑えることができる。
【００１２】
【発明の効果】
上記したように、本発明によるスイッチング電源は、ダイオードにＦＥＴを並列接続し、かつ、ダイオードより遅延する電流をＦＥＴに流すことにより、ダイオードに発生する電圧を大幅に低下させることができ、ダイオードの発熱を抑えることができるので、スイッチング電源の効率改善を図ることができる。
【図面の簡単な説明】
【図１】本発明の実施例によるスイッチング電源の回路図である。
【図２】従来のスイッチング電源の回路図である。
【図３】図１の回路によるダイオードＤ１の発生電圧の経時変化を示す特性図である。
【図４】図２の回路によるダイオードＤ１の発生電圧の経時変化を示す特性図である。
【符号の説明】
Ｑ１ ＦＥＴ
Ｑ２ トランジスタ
Ｄ１、Ｄ２ ダイオード
Ｒ１ 抵抗
Ｃ１、Ｃ２ コンデンサ
ｔ 遅延時間
Ａ 補助電源
Ｂ 時定数回路
Ｘ 負荷（バッテリー）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply including a charging circuit.
[0002]
[Prior art]
As this type of switching power supply, the one shown in FIG. 2 has been proposed. In FIG. 2, there is a diode D1 for preventing a reverse flow of current from the load (battery) X to the power supply secondary circuit. There is a large loss due to the forward voltage (V F ).
[0003]
[Problems to be solved by the invention]
If the loss due to the forward voltage (V F ) of the diode is large, a large amount of heat is generated in the diode. Therefore, means for reducing such loss and improving the efficiency of the switching power supply has been required.
[0004]
[Means for Solving the Problems]
The present invention solves the above-described problem. The FET [Q1] is connected in parallel to the diode D1, the diode D1 is activated when the switching power supply is activated, the FET [Q1] is turned on after reaching the set voltage, The present invention provides a switching power supply comprising means for switching from a large loss due to the forward voltage (V F ) of the diode D1 to a small loss due to the on-resistance of the FET [Q1]. That is, in a switching power supply including a charging circuit for supplying a DC voltage to the load from the secondary side of the switching transformer via the reverse current prevention diode D1, the reverse current prevention diode is connected in parallel with the reverse current prevention diode D1 . The FET [Q1] having a smaller on-resistance than the forward resistance of the diode D1 is connected, and the charging circuit is connected to the auxiliary power source A connected to both terminals on the secondary side of the switching transformer and the FET [Q1]. Transistor Q2 and a time constant circuit B connected between the auxiliary power source A and the transistor Q2, and when starting, the reverse current prevention diode D1 is started, and after reaching a set voltage, the FET This is a switching power supply for turning on [Q1] .
[0007]
The auxiliary power source A is a switching power source characterized by comprising a diode D2 and a first capacitor C1.
[0008]
Further, the time constant circuit B is a switching power supply characterized by comprising a resistor R1 and a second capacitor C2.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram of an example of a switching power supply to which the embodiment of the present invention is applied.
This circuit is called a flyback converter, and a control signal from a constant voltage detection circuit for stabilizing the output voltage and a constant current detection circuit for charging the battery with a constant current is supplied to the primary side. Operating with feedback to the control circuit.
The diode D1 is a diode that prevents the backflow of current from the battery to the secondary circuit of the power supply, and how to suppress the heat generated by the loss due to the forward voltage (V F ) of this diode has been a problem.
[0010]
In order to solve the above problem, the following measures have been taken. That is, (1) a FET [Q1] ON resistance is small to reduce a loss due to V F of the diode connected in parallel with the diode D1, the switching power supply startup activates the diodes D1, after setting the voltage reached, FET [Q1 ] Is turned on.
(2) For this purpose, an auxiliary power source composed of the diode D2 and the capacitor C1 and a time constant circuit composed of the resistor R1 and the capacitor C2 are connected to delay the voltage applied to the base of the transistor Q2.
With this delay means, the transistor Q2 is turned on with a delay, so that the FET [Q1] is turned on with a delay, and the current flowing through the diode D1 flows with a delay in the FET [Q1] having a low on-resistance.
As a result, since most of the output current of the switching power supply flows to the FET [Q1] side, an increase in heat generated in the diode D1 is suppressed, and the efficiency of the switching power supply can be improved.
[0011]
【Example】
A circuit according to the embodiment of the present invention shown in FIG. 1 and a circuit according to the conventional example shown in FIG. 2 were manufactured, and changes with time of the voltage V generated in the diode D1 were investigated. The results are shown in FIGS. 3 and 4, respectively.
In the embodiment, as shown in FIG. 3, first, a current I flows through the diode D1, as the forward voltage and the relational curve of the forward current of the diode (V F -I F characteristics), with an increase in current I Although the voltage V increases gradually, gradually the degree of the increase is gradual, reaching the V P.
As shown in FIG. 1, the FET [Q1] is connected to the auxiliary power source A composed of the diode D2 and the capacitor C1 and the time constant circuit B composed of the resistor R1 and the capacitor C2 via the transistor Q2. The current flowing in Q1] is delayed by time t from the current flowing in the diode D1.
After the delay time t, the current flowing in the diode D1 almost flows in the FET [Q1] having a low on-resistance connected in parallel. As a result, the voltage generated in the diode D1 is (output current I) × (on-resistance R ) becomes, the initial V P as shown in FIG. 3 can be reduced to 1/10 or less.
On the other hand, in the conventional example, to a voltage V as shown in FIG. 4 reaches V P is the same as the embodiment, since a low on-resistance FET is not connected in parallel, the voltage drop remains V P Never do.
Thus, as shown in FIG. 3, the voltage generated by the embodiment in which the FET [Q1] is connected in parallel to the diode D1 has a voltage value after the delay time t as compared with the conventional example in which the FET [Q1] is not connected in parallel. It can be reduced to 1/10 or less of the conventional example, and the heat generation of the diode D1 can be suppressed.
[0012]
【The invention's effect】
As described above, the switching power supply according to the present invention can significantly reduce the voltage generated in the diode by connecting the FET in parallel to the diode and passing a current delayed from the diode through the FET. Since heat generation can be suppressed, the efficiency of the switching power supply can be improved.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a switching power supply according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of a conventional switching power supply.
FIG. 3 is a characteristic diagram showing a change with time of a voltage generated by a diode D1 by the circuit of FIG. 1;
4 is a characteristic diagram showing a change with time of a voltage generated by a diode D1 by the circuit of FIG. 2; FIG.
[Explanation of symbols]
Q1 FET
Q2 Transistor D1, D2 Diode R1 Resistor C1, C2 Capacitor t Delay time A Auxiliary power supply B Time constant circuit X Load (battery)
Claims (3)
前記逆電流防止用ダイオードと並列に、前記逆電流防止用ダイオードの順方向抵抗よりオン抵抗が小さいＦＥＴを接続し、
前記充電回路は、前記スイッチングトランスの２次側の両端子に接続された補助電源と、前記ＦＥＴに接続されたトランジスタと、前記補助電源と前記トランジスタとの間に接続された時定数回路を有し、起動時は前記逆電流防止用ダイオードを起動させ、設定電圧到達後、前記ＦＥＴをオンさせることを特徴とするスイッチング電源。In a switching power supply having a charging circuit for supplying a DC voltage to a load from a secondary side of a switching transformer via a reverse current prevention diode,
In parallel with the reverse current prevention diode, an FET having an on-resistance smaller than the forward resistance of the reverse current prevention diode is connected ,
The charging circuit includes an auxiliary power source connected to both terminals on the secondary side of the switching transformer, a transistor connected to the FET, and a time constant circuit connected between the auxiliary power source and the transistor. A switching power supply comprising: starting up the reverse current prevention diode at start-up, and turning on the FET after reaching a set voltage .
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000037519A JP4365972B2 (en) | 2000-02-16 | 2000-02-16 | Switching power supply |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000037519A JP4365972B2 (en) | 2000-02-16 | 2000-02-16 | Switching power supply |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2001231254A JP2001231254A (en) | 2001-08-24 |
| JP4365972B2 true JP4365972B2 (en) | 2009-11-18 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2000037519A Expired - Fee Related JP4365972B2 (en) | 2000-02-16 | 2000-02-16 | Switching power supply |
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| Country | Link |
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Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4877072B2 (en) * | 2007-05-28 | 2012-02-15 | パナソニック電工株式会社 | Power transmission equipment |
| JP6031672B2 (en) * | 2012-04-27 | 2016-11-24 | パナソニックＩｐマネジメント株式会社 | In-vehicle power supply device and in-vehicle power supply unit using the same |
| JP6371226B2 (en) * | 2015-01-16 | 2018-08-08 | Fdk株式会社 | Switching power supply with reverse current protection |
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- 2000-02-16 JP JP2000037519A patent/JP4365972B2/en not_active Expired - Fee Related
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| Publication number | Publication date |
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| JP2001231254A (en) | 2001-08-24 |
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