JP3728575B2 - Switching power supply with low loss snubber circuit - Google Patents

Description

れる固有インピーダンスが大きくなることから、コンデンサを流れる共振電流のピーク値が下がり、コンデンサの内部直列抵抗成分による電力損失を小さくすることができる。
【００１１】
【実施例】
図１は請求項１記載の発明の実施例に係る低損失スナバ回路付きスイッチング電源装置を示す回路図である。
【００１２】
図２は請求項２記載の発明の実施例に係る低損失スナバ回路付きスイッチング電源装置を示す回路図である。
【００１３】
図３は図１の回路の主要部の波形を示した波形図である。
【００１４】
図１の回路において、スイッチングトランジスタ４両端の電圧は図３（Ａ）に示した波形のように変化し、またリセット巻線１Ｃ両端の電圧は図３（Ｂ）に示した波形のように変化している。コンデンサ３両端の電圧はスイッチングトランス４両端の電圧とリセット巻線１Ｃ両端の電圧の差であり、その値は図３（Ｃ）に示した波形となる。また、コンデンサ３に流れる電流は図３（Ｄ）に示した波形となる。
【００１５】
図３（Ｄ）に示したように、コンデンサ３にはスイッチングトランジスタ４がターンオフした瞬間に電流が流れ、これがスイッチングトランジスタ４に加わるサージ電圧を吸収すると同時に、１次巻線１Ａに流れる電流の変化率を小さくしてノイズの発生を抑えている。また、このターンオフ時にコンデンサに充電された電荷は、その後に生じる共振によって入力側の直流電源９に戻され、スイッチングトランジスタ４がターンオンするときに、このスイッチングトランジスタ４を通って放電することはない。すなわち、電力損失は生じない。
【００１６】
図１及び図２に示した回路は、フライバックコンバータに本発明を実施した例を示しているが、フォワードコンバータにおいて実施することもできる。また、自励方式と他励方式のどちらも応用できる。スイッチングトランジスタ４の代わりにＭＯＳＦＥＴやＩＧＢＴ等の他のスイッチ素子を応用することも可能である。
【００１７】
【発明の効果】
以上のように、本発明によれば、従来のリセット巻線によるスナバ回路の接続を少し変えることによって、ノイズの発生をより効率よく抑えることができるので応用範囲は広い。
【図面の簡単な説明】
【図１】請求項１記載の発明の実施例に係る低損失スナバ回路付きスイッチング電源装置を示す回路図である。
【図２】請求項２記載の発明の実施例に係る低損失スナバ回路付きスイッチング電源装置を示す回路図である。
【図３】図１の回路図の主要部の波形を示す波形図である。
【図４】従来方式の例を示す回路図である。
【符号の説明】
１、１１ トランス
２、１２ ダイオード
３、１３ コンデンサ
４、１４ スイッチ素子
５、１５ 発振制御回路
６、１６ ダイオード
７、１７ コンデンサ
８、１８ 負荷
９、１９ 直流電源
１０ インダクタ
１Ａ、１１Ａ １次巻線
１Ｂ、１１Ｂ ２次巻線
１Ｃ、１１Ｃ リセット巻線[0001]
[Industrial application fields]
The present invention relates to a switching power supply device.
[0002]
[Prior art]
Conventionally, the circuit shown in FIG. 4 is well known as a circuit that absorbs a surge voltage generated when the switch element is turned off. When the switch element 14 is turned off, the voltage generated in the reset winding 11C is clamped by the voltage across the DC power supply 19, so that the surge voltage indirectly generated in the voltage of the primary winding 11A is also suppressed. Since the energy absorbed by the voltage clamp is regenerated by the DC power supply 19, the loss due to absorption of the surge voltage is small.
[0003]
[Problems to be solved by the invention]
The snubber circuit shown in FIG. 4 can absorb the surge voltage generated when the switch element 14 is turned off, but cannot suppress the noise generated by the rapid change in the current flowing through the primary winding 11A. Therefore, a capacitor 13 is connected to both ends of the switch element 14 to attenuate noise. Even if the switch element 14 is turned off at high speed, the current flowing through the primary winding 11A is slowly reduced to zero for the time to charge the capacitor 13, so that the noise is reduced. However, when the switch element 14 is turned on, the electric charge charged in the capacitor 13 flows through the switch element 14 and is discharged, causing power loss.
[0004]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a circuit that attenuates both surge voltage and noise without causing power loss by reducing power loss due to discharge of the capacitor, which reduces noise, to zero.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a reset winding and diode series circuit at both ends of the primary winding and switch element series circuit, the diode end at the primary winding end, and reset. The winding side ends were connected so as to be connected to the switching element side ends, and a capacitor was connected between the connection point of the reset winding and the diode and the connection point of the primary winding and the switching element.
[0006]
[Action]
In the present invention, the polarities of the primary winding and the reset winding are the same at the capacitor side terminals, and the diode becomes conductive when the flyback voltage generated at the reset winding is higher than the input voltage. Therefore, the upper limit voltage is clamped by the value of the input voltage, and the flyback voltage of the primary winding is also clamped, so that the surge voltage applied to the switch element is also limited.
[0007]
For ease of explanation, assuming that the turns ratio of the primary winding and the reset winding is 1: 1, the voltage generated in the reset winding when the switch element is on is equal to the input voltage, Since the voltage on the switch element side of the capacitor is almost zero, the opposite side has a negative input voltage value. Also, when the switch element is off, the voltage on the switch element side of the capacitor is the input voltage plus the flyback voltage, and the other side is the flyback voltage value. Equal to voltage. That is, the voltage across the capacitor is theoretically always constant, so that even when the switch element is turned on, the capacitor charge is not discharged and no power loss occurs.
[0008]
In the case of a flyback converter that oscillates in a current discontinuous mode or a forward converter that has a dead time, a period that is neither an on state nor an off state occurs. During this period, resonance occurs in the series circuit of the capacitor, primary winding, and reset winding, but the polarity of the primary winding and reset winding are opposite to each other, so the inductance is canceled out and only the leakage inductance is The resonance period is determined by the capacitance of the capacitor and the leakage inductance. Since the leakage inductance is a small value compared to the inductance of the primary winding, the resonance period does not become so long even if the capacitor is made sufficiently large.
[0009]
Since the falling slope of the current flowing through the primary winding when the switch element is turned off is determined by the capacitance of the capacitor and the leakage inductance, the slope becomes gentler and the noise becomes smaller as the capacitance of the capacitor is increased.
[0010]
In the invention according to claim 2, the inductor is connected in series to the primary winding.

Since the inherent impedance of the capacitor increases, the peak value of the resonance current flowing through the capacitor decreases, and the power loss due to the internal series resistance component of the capacitor can be reduced.
[0011]
【Example】
FIG. 1 is a circuit diagram showing a switching power supply device with a low loss snubber circuit according to an embodiment of the present invention.
[0012]
FIG. 2 is a circuit diagram showing a switching power supply device with a low loss snubber circuit according to an embodiment of the present invention.
[0013]
FIG. 3 is a waveform diagram showing waveforms of main parts of the circuit of FIG.
[0014]
In the circuit of FIG. 1, the voltage across the switching transistor 4 changes as shown in the waveform shown in FIG. 3A, and the voltage across the reset winding 1C changes as shown in the waveform shown in FIG. are doing. The voltage across the capacitor 3 is the difference between the voltage across the switching transformer 4 and the voltage across the reset winding 1C, and the value has the waveform shown in FIG. Further, the current flowing through the capacitor 3 has a waveform shown in FIG.
[0015]
As shown in FIG. 3D, a current flows through the capacitor 3 at the moment when the switching transistor 4 is turned off. This absorbs a surge voltage applied to the switching transistor 4 and simultaneously changes in the current flowing through the primary winding 1A. The rate is reduced to reduce noise. Further, the electric charge charged in the capacitor at the time of turn-off is returned to the DC power supply 9 on the input side by the resonance that occurs thereafter, and is not discharged through the switching transistor 4 when the switching transistor 4 is turned on. That is, no power loss occurs.
[0016]
The circuit shown in FIGS. 1 and 2 shows an example in which the present invention is implemented in a flyback converter, but it can also be implemented in a forward converter. In addition, both the self-excitation method and the separate excitation method can be applied. Instead of the switching transistor 4, other switching elements such as MOSFET and IGBT can be applied.
[0017]
【The invention's effect】
As described above, according to the present invention, since the generation of noise can be more efficiently suppressed by slightly changing the connection of the snubber circuit by the conventional reset winding, the application range is wide.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a switching power supply device with a low loss snubber circuit according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a switching power supply device with a low loss snubber circuit according to an embodiment of the invention as set forth in claim 2;
3 is a waveform diagram showing waveforms of main parts of the circuit diagram of FIG. 1. FIG.
FIG. 4 is a circuit diagram showing an example of a conventional method.
[Explanation of symbols]
1, 11 Transformer 2, 12 Diode 3, 13 Capacitor 4, 14 Switch element 5, 15 Oscillation control circuit 6, 16 Diode 7, 17 Capacitor 8, 18 Load 9, 19 DC power supply 10 Inductor 1A, 11A Primary winding 1B 11B Secondary winding 1C, 11C Reset winding

Claims (2)

A switching power supply comprising a transformer having a primary winding and a secondary winding, a switch element connected in series to the primary winding of the transformer, and an oscillation control circuit connected to a control electrode of the switch element A reset winding is wound around the transformer, one terminal thereof is connected to an electrode on the opposite side of the electrode to which the primary winding of the switch element is connected, and the other terminal is connected via a diode. And a capacitor connected between the reset winding side electrode of the diode and the primary winding side electrode of the switch element. Is used to attenuate the surge voltage and noise generated when the switch element is turned off without any power loss. Apparatus. The switching power supply with a low loss snubber circuit according to claim 1, wherein an inductor is inserted in series with the primary winding.

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