JP3678286B2 - Synchronous rectifier circuit - Google Patents
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【０００１】
【発明の属する技術分野】
この発明は、金属酸化膜電界効果トランジスタ（ＭＯＳＦＥＴ）の低オン抵抗を利用して、交流を直流に高効率に変換する同期整流回路に関する。
【０００２】
【従来の技術】
図８に同期整流回路の従来例を示す。同図において、Ｔｒはトランス、ＲＣ１，ＦＷＲＣはダイオード、ＦＷ１〜ＦＷ４はＭＯＳＦＥＴ、Ｌ0 はリアクトル、Ｃ0 はコンデンサを示す。
ここで、Ｔｒの２次側に正の電圧が生じると、電流はＴｒの２次側→ダイオードＲＣ１→リアクトルＬ0 →コンデンサＣ0 →Ｔｒの２次側の経路で流れる。また、Ｔｒの２次側に負の電圧が生じると、Ｌ0 に流れる電流はリアクトルＬ0 →コンデンサＣ0 →ダイオードＦＷＲＣ→リアクトルＬ0 の経路で還流する。しかし、ダイオードよりもＭＯＳＦＥＴのオン電圧の方が低いので、ＭＯＳＦＥＴ（ＦＷ１〜ＦＷ４）をオンすることで、ＭＯＳＦＥＴ（ＦＷ１〜ＦＷ４）→リアクトルＬ0 の経路で還流させる。このように、ＭＯＳＦＥＴをオンすることで高効率化を図っている。
【０００３】
なお、ダイオードＲＣ１は他のＭＯＳＦＥＴに置き換えても良く、ダイオードとＭＯＳＦＥＴを並列に設けるようにしても良い。ただし、ダイオードの場合はそのアノードを前記トランスの正側に、また、ＭＯＳＦＥＴの場合はそのドレインどうしが接続されるようにそれぞれ挿入することとする。また、ダイオードＦＷＲＣを省略し、ＦＷ１〜ＦＷ４のボディダイオードで代用するようにしても良い。
【０００４】
【発明が解決しようとする課題】
図８の回路では、大きな負荷電流を流しているときのリアクトルＬ0 に流れる電流の還流経路は常にリアクトルＬ0 →コンデンサＣ0 →ダイオードＦＷＲＣまたはＭＯＳＦＥＴ（ＦＷ１〜ＦＷ４）→リアクトルＬ0 の方向である。しかし、負荷電流が小さい軽負荷時では、リアクトル電流は図９（ｃ）に示すように、零付近でリプルを含んだ波形となる。ここで、リアクトル電流がＬ0 →ＦＷ１〜ＦＷ４→Ｃ0 →Ｌ0 の経路で流れているときにＭＯＳＦＥＴをオフすると、リアクトルＬ0 に蓄えられているエネルギーによって、ＭＯＳＦＥＴ（ＦＷ１〜ＦＷ４）のドレイン・ソース間やダイオードＦＷＲＣのアノード・カソード間の電圧が図９（ｄ）に示すように上昇し、素子が破壊するおそれがある。
また、リアクトル電流がＬ0 →ＦＷ１〜ＦＷ４→Ｃ0 →Ｌ0 の方向で流れているときは、出力側のコンデンサＣ0 からエネルギーが放電されており、効率を低下させることになる。
したがって、この発明の課題は、エネルギーの損失を低減し高効率化を図ることにある。
【０００５】
【課題を解決するための手段】
このような課題を解決すべく、請求項１の発明では、トランスの２次側に任意の数の第１の金属酸化膜電界効果トランジスタ（ＭＯＳＦＥＴ）を並列接続し、この第１ＭＯＳＦＥＴのドレインとトランスの正側間に第１ダイオードまたは第２ＭＯＳＦＥＴの少なくとも一方を、ダイオードの場合はそのアノードを前記トランスの正側に、また、ＭＯＳＦＥＴの場合はそのドレインどうしが接続されるようにそれぞれ挿入し、第１ＭＯＳＦＥＴのドレイン・ソース間のドレイン側にカソードが接続されるように第２ダイオードを並列接続するか、または第２ダイオードの役割を第１ＭＯＳＦＥＴのボディダイオードで果たし、さらにトランス２次側に並列接続した第１ＭＯＳＦＥＴのドレイン・ソース間にリアクトルとコンデンサの直列回路を並列接続し、コンデンサ両端間を出力とすることで、トランス２次側に負の電圧が発生したときに第１ＭＯＳＦＥＴをオンさせてリアクトル電流を還流させる同期整流回路において、
前記リアクトルとコンデンサ間、またはコンデンサと第１ＭＯＳＦＥＴのソース間に第３ダイオードを挿入することにより、第１ＭＯＳＦＥＴをオンしたとき、リアクトルにコンデンサから第１ＭＯＳＦＥＴのドレイン・ソース間方向に電流を流さないようにしている。
【０００６】
また、請求項２，３の発明では、トランスの２次側に任意の数の第１の金属酸化膜電界効果トランジスタ（ＭＯＳＦＥＴ）を並列接続し、この第１ＭＯＳＦＥＴのドレインとトランスの正側間に第１ダイオードまたは第２ＭＯＳＦＥＴの少なくとも一方を、ダイオードの場合はそのアノードを前記トランスの正側に、また、ＭＯＳＦＥＴの場合はそのドレインどうしが接続されるようにそれぞれ挿入し、第１ＭＯＳＦＥＴのドレイン・ソース間のドレイン側にカソードが接続されるように第２ダイオードを並列接続するか、または第２ダイオードの役割を第１ＭＯＳＦＥＴのボディダイオードで果たし、さらにトランス２次側に並列接続した第１ＭＯＳＦＥＴのドレイン・ソース間にリアクトルとコンデンサの直列回路を並列接続し、コンデンサ両端間を出力とすることで、トランス２次側に負の電圧が発生したときに第１ＭＯＳＦＥＴをオンさせてリアクトル電流を還流させる同期整流回路において、
前記リアクトルに補助巻線を設けてリアクトルに流れる電流を検出し、これが零になるときに前記第１ＭＯＳＦＥＴをオフする制御手段を設けるか（請求項２の発明）、または、
前記第１ＭＯＳＦＥＴの１つに流れる電流を検出し、これが零になるときに前記第１ＭＯＳＦＥＴをオフする制御手段を設けたことを特徴とする（請求項３の発明）。
【０００７】
さらに、請求項４，５，６の発明では、トランスの２次側に任意の数の第１の金属酸化膜電界効果トランジスタ（ＭＯＳＦＥＴ）を並列接続し、この第１ＭＯＳＦＥＴのドレインとトランスの正側間に第１ダイオードまたは第２ＭＯＳＦＥＴの少なくとも一方を、ダイオードの場合はそのアノードを前記トランスの正側に、また、ＭＯＳＦＥＴの場合はそのドレインどうしが接続されるようにそれぞれ挿入し、第１ＭＯＳＦＥＴのドレイン・ソース間のドレイン側にカソードが接続されるように第２ダイオードを並列接続するか、または第２ダイオードの役割を第１ＭＯＳＦＥＴのボディダイオードで果たし、さらにトランス２次側に並列接続した第１ＭＯＳＦＥＴのドレイン・ソース間にリアクトルとコンデンサの直列回路を並列接続し、コンデンサ両端間を出力とすることで、トランス２次側に負の電圧が発生したときに第１ＭＯＳＦＥＴをオンさせてリアクトル電流を還流させる同期整流回路において、
前記第１ＭＯＳＦＥＴの１つのオン電圧を検出してこれから第１ＭＯＳＦＥＴの１つに流れる電流を推測し、これが零となるときに前記第１ＭＯＳＦＥＴをオフする制御手段を設けるか（請求項４の発明）、または、
前記トランス１次側の電流を検出して負荷率を検出し、負荷率が所定値以下の軽負荷時に前記第１ＭＯＳＦＥＴをオフする制御手段を設けるか（請求項５の発明）、もしくは
前記トランス１次側の電流と同期整流回路の出力電圧とを検出し、リアクトル電流が零となる時間を計算して前記第１ＭＯＳＦＥＴをオフする制御手段を設けたことを特徴とする（請求項６の発明）。
【０００８】
【発明の実施の形態】
図１はこの発明の第１の実施の形態を示す回路図である。
同図からも明らかなように、この例はダイオードＦＷＲＣのカソードとＦＷ１〜ＦＷ４のドレインとの接続点と、コンデンサＣ0 のプラス（＋）端子間にダイオードＲＣ２を挿入した点が特徴である。これにより、リアクトルＬ0 の電流はコンデンサＣ0 →ダイオードＦＷＲＣまたはＭＯＳＦＥＴ（ＦＷ１〜ＦＷ４）→リアクトルＬ0 の方向しか流れなくなる。その結果、Ｌ0 に蓄えられたエネルギーによるＦＷ１〜ＦＷ４やＦＷＲＣ両端間の電圧上昇、Ｃ0 からのエネルギーの放出による軽負荷時の効率低下を抑制することができる。なお、ダイオードＲＣ２はリアクトルＬ0 とコンデンサＣ0 間、若しくはコンデンサＣ0 と第１ＭＯＳＦＥＴのソース間に挿入するようにしても良いことは、言うまでもない。
【０００９】
図２は図１の変形例を示す回路図である。
これは、図１のようにダイオードＲＣ２を挿入する代わりに、電流検出器ＣＴを設けてリアクトルＬ0に流れる電流を検出し、Ｌ0の電流がコンデンサＣ0→リアクトルＬ0→ダイオードＦＷＲＣまたはＭＯＳＦＥＴ（ＦＷ１〜ＦＷ４）→コンデンサＣ0の方向に流れる前の電流、換言すればＬ0の電流が零になったことを検出して、ＦＷ１〜ＦＷ４をオフさせるものである。その結果、Ｌ0の電流はリアクトルＬ0→コンデンサＣ0→ダイオードＦＷＲＣまたはＭＯＳＦＥＴ（ＦＷ１〜ＦＷ４）→リアクトルＬ0の方向にしか流れなくなり、Ｌ0に蓄えられたエネルギーによるＦＷ１〜ＦＷ４やＦＷＲＣ両端間の電圧上昇、Ｃ0からのエネルギー放出による軽負荷時の効率低下を抑制することができる。
【００１０】
図３はこの発明の第２の実施の形態を示す回路図である。
この例は、図１のようにダイオードＲＣ２を挿入する代わりに、Ｌ0に補助巻線Ｌ0’を付加し、その巻数比（Ｌ0：Ｌ0’）からＬ0に流れる電流を検出するもので、安価な電流検出を可能とするものである。なお、電流零を検出したらＦＷ１〜ＦＷ４をオフさせるのは、図１，図２の場合と同様である。
図４はこの発明の第３の実施の形態を示す回路図である。
これは、リアクトルＬ0→コンデンサＣ0→ダイオードＦＷＲＣまたはＭＯＳＦＥＴ（ＦＷ１〜ＦＷ４）→リアクトルＬ0の方向に流れる電流のうち、ＦＷ１〜ＦＷ４のいずれかに流れる電流を電流検出器ＣＴにより検出するものである。この場合、ＭＯＳＦＥＴの並列数分の１の電流を検出すれば良く、電流検出を低コストで実現することができる。なお、電流零を検出したらＦＷ１〜ＦＷ４をオフさせるのは、図１〜図３の場合と同様である。
【００１１】
図５はこの発明の第４の実施の形態を示す回路図である。
これは、図１のようにダイオードＲＣ２を挿入する代わりに、いずれか１つのＭＯＳＦＥＴのドレイン・ソース間電圧の大きさからＭＯＳＦＥＴに流れる電流（零）を検出するものである。電流検出器を用いないので、低コスト化を図ることができる。なお、電流零を検出したらＦＷ１〜ＦＷ４をオフさせるのは、図１〜図４の場合と同様である。
図６はこの発明の第５の実施の形態を示す回路図である。
これは、図１のようにダイオードＲＣ２を挿入する代わりに、トランスＴｒの１次側の電流と負荷電流とが比例関係にあることに着目したもので、トランスＴｒの１次側に電流検出器ＣＴを設けて１次電流の大きさを検出し負荷電流を検出する。そして、この負荷電流が小さい軽負荷時にＦＷ１〜ＦＷ４をオフさせるのは、以上の各場合と同様である。この例では、同期整流器側に検出器を設けなくても済むことになる。
【００１２】
図７はこの発明の第６の実施の形態を示す回路図である。
ここでは、図６と同じくトランスＴｒの１次側に電流検出器を設けて１次電流の大きさを検出し、トランスＴｒの巻数比から２次側に流れるリアクトルＬ0の方向に流れる電流を検出する。すなわち、リアクトル電流のピーク値をＩ0とすると、リアクトル電流Ｉは、次の（１）式で表わされる。
Ｉ＝（ｄｉ／ｄｔ）ｔ＋Ｉ0 …（１）
ただし、ｄｉ／ｄｔは次の（２）式となる。なお、ｔは電流ピーク値からの時間、Ｖ0は出力電圧である。
ｄｉ／ｄｔ＝−Ｖ0／Ｌ0 …（２）
よって、Ｉ＝０となる時間ｔは次の（３）式で表わされる。
ｔ＝Ｌ0Ｉ0／Ｖ0 …（３）
【００１３】
つまり、（３）式よりリアクトル電流が零となるまでの時間は、Ｌ0 ，Ｉ0 ，Ｖ0 の値から計算できることが分かる。図７はリアクトル電流の初期値Ｉ0 から零になるまでの時間ｔを図示している。
そして、この時間ｔをもとにＦＷ１〜ＦＷ４をオフさせるのは、以上の各場合と同様である。また、同期整流器側に検出器を設けなくても済むのは図６の場合と同様である。
【００１４】
【発明の効果】
この発明によれば、軽負荷時における同期整流回路の出力リアクトルに流れる還流電流を逆方向に流さないので、高効率化を図ることができる。また、出力リアクトル電流が逆方向に流れたときに素子をオフするものではないので、素子の耐圧を越えることがなくなり、安全を図ることが可能になるという利点が得られる。
【図面の簡単な説明】
【図１】 この発明の第１の実施の形態を示す構成図である。
【図２】 図１の変形例を示す構成図である。
【図３】 この発明の第２の実施の形態を示す構成図である。
【図４】 この発明の第３の実施の形態を示す構成図である。
【図５】 この発明の第４の実施の形態を示す構成図である。
【図６】 この発明の第５の実施の形態を示す構成図である。
【図７】 この発明の第６の実施の形態を説明するための説明図である。
【図８】 従来例を示す回路図である。
【図９】 図８の動作説明図である。
【符号の説明】
Ｔｒ…トランス、ＲＣ１，ＲＣ２，ＦＷＲＣ…ダイオード、ＦＷ１，ＦＷ２，ＦＷ３，ＦＷ４…ＭＯＳＦＥＴ、Ｌ0，Ｌ0’…リアクトル、Ｃ0…コンデンサ、ＣＴ…電流検出器、Ｐ0…正側出力、Ｎ0…負側出力、Ｉ…電流、ｔ…時間。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a synchronous rectification circuit that converts alternating current into direct current with high efficiency by utilizing the low on-resistance of a metal oxide field effect transistor (MOSFET).
[0002]
[Prior art]
FIG. 8 shows a conventional example of a synchronous rectifier circuit. In the figure, Tr is trans, RC1, FWRC diode, FW1～FW4 the MOSFET, L 0 is the reactor, C 0 denotes a capacitor.
Here, when a positive voltage is generated on the secondary side of Tr, the current flows along a path on the secondary side of the secondary side of Tr → diode RC1 → reactor L 0 → capacitor C 0 → Tr. Further, when a negative voltage on the secondary side of the Tr occurs, the current flowing through the L 0 is refluxed the route of the reactor L 0 → capacitor C 0 → diode FWRC → reactor L 0. However, since the lower the MOSFET on-state voltage than the diode, by turning on the MOSFET (FW1~FW4), it is refluxed in the path of the MOSFET (FW1~FW4) → Reactor L 0. Thus, high efficiency is achieved by turning on the MOSFET.
[0003]
The diode RC1 may be replaced with another MOSFET, and the diode and the MOSFET may be provided in parallel. However, in the case of a diode, its anode is inserted on the positive side of the transformer, and in the case of a MOSFET, its drain is connected to each other. Further, the diode FWRC may be omitted, and the body diodes FW1 to FW4 may be substituted.
[0004]
[Problems to be solved by the invention]
In the circuit of FIG. 8, the return path of the current flowing through the reactor L 0 when a large load current is flowing is always in the direction of the reactor L 0 → capacitor C 0 → diode FWRC or MOSFET (FW1 to FW4) → reactor L 0 . is there. However, at the time of a light load with a small load current, the reactor current has a waveform including ripples near zero as shown in FIG. Here, if the MOSFET is turned off when the reactor current flows along the path of L 0 → FW 1 to FW 4 → C 0 → L 0 , the drains of the MOSFETs (FW 1 to FW 4) are generated by the energy stored in the reactor L 0. The voltage between the sources and between the anode and cathode of the diode FWRC rises as shown in FIG.
Further, when the reactor current flows in the direction of L 0 → FW 1 to FW 4 → C 0 → L 0 , energy is discharged from the output-side capacitor C 0 , and the efficiency is lowered.
Accordingly, an object of the present invention is to reduce energy loss and increase efficiency.
[0005]
[Means for Solving the Problems]
In order to solve such a problem, according to the first aspect of the present invention, an arbitrary number of first metal oxide field effect transistors (MOSFETs) are connected in parallel to the secondary side of the transformer, and the drain of the first MOSFET and the transformer At least one of the first diode and the second MOSFET is inserted between the positive sides of the first and second MOSFETs, and in the case of a diode, the anode thereof is inserted into the positive side of the transformer, and in the case of a MOSFET, the drains thereof are connected to each other. The second diode is connected in parallel so that the cathode is connected to the drain side between the drain and source of the 1MOSFET, or the role of the second diode is played by the body diode of the first MOSFET and further connected in parallel to the transformer secondary side. A series circuit of a reactor and a capacitor between the drain and source of the first MOSFET And column connection, by the output across the capacitor, the synchronous rectifier circuit the second 1MOSFET by turning on recirculating reactor current when the negative voltage is generated in the secondary side of the transformer,
By inserting a third diode between the reactor and the capacitor or between the capacitor and the source of the first MOSFET, when the first MOSFET is turned on, a current is not passed through the reactor from the capacitor to the drain-source direction of the first MOSFET. ing.
[0006]
According to the second and third aspects of the present invention, an arbitrary number of first metal oxide field effect transistors (MOSFETs) are connected in parallel to the secondary side of the transformer, and between the drain of the first MOSFET and the positive side of the transformer. At least one of the first diode and the second MOSFET is inserted so that the anode of the diode is connected to the positive side of the transformer, and the drain of the MOSFET is connected to each other. The second diode is connected in parallel so that the cathode is connected to the drain side between them, or the body diode of the first MOSFET plays the role of the second diode, and further the drain of the first MOSFET connected in parallel to the transformer secondary side Connect a series circuit of a reactor and a capacitor in parallel between the sources, By an output between both ends, in the synchronous rectifier circuit the second 1MOSFET by turning on recirculating reactor current when the negative voltage is generated in the secondary side of the transformer,
Detecting a current flowing through the reactor with an auxiliary winding to the reactor, which Luke provided a control means for turning off said first 1MOSFET when becomes zero (the invention of claim 2), or,
Control means for detecting a current flowing in one of the first MOSFETs and turning off the first MOSFET when the current becomes zero is provided (invention of claim 3).
[0007]
Furthermore, in the inventions of claims 4 , 5 and 6 , an arbitrary number of first metal oxide field effect transistors (MOSFETs) are connected in parallel to the secondary side of the transformer, and the drain of the first MOSFET and the positive side of the transformer In between, at least one of the first diode and the second MOSFET is inserted so that the anode of the diode is connected to the positive side of the transformer, and the drain of the MOSFET is connected to each other. The second diode is connected in parallel so that the cathode is connected to the drain side between the sources, or the body of the first MOSFET plays the role of the second diode and further connected in parallel to the secondary side of the transformer. Connect a series circuit of a reactor and a capacitor in parallel between the drain and source, With output between capacitor ends, the synchronous rectifier circuit the second 1MOSFET by turning on recirculating reactor current when the negative voltage is generated in the secondary side of the transformer,
A control means for detecting one on-voltage of the first MOSFET and estimating a current flowing to one of the first MOSFETs from the first MOSFET and turning off the first MOSFET when the current becomes zero (invention of claim 4); Or
A control means for detecting a current on the primary side of the transformer to detect a load factor and turning off the first MOSFET at a light load when the load factor is a predetermined value or less is provided (invention of claim 5), or
Control means for detecting the current on the primary side of the transformer and the output voltage of the synchronous rectifier circuit, calculating the time when the reactor current becomes zero, and turning off the first MOSFET is provided (Claim 6). Invention).
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a circuit diagram showing a first embodiment of the present invention.
As is apparent from the figure, this example the connection point between the cathode and the drain of FW1~FW4 diode FWRC, that was inserted diode RC2 between positive capacitor C 0 (+) terminal is characterized. Thus, current of the reactor L 0 is not flow only the direction of the capacitor C 0 → diode FWRC or MOSFET (FW1~FW4) → Reactor L 0. As a result, it is possible to suppress an increase in voltage across FW1 to FW4 and FWRC due to the energy stored in L 0 , and a decrease in efficiency at light loads due to the release of energy from C 0 . The diode RC2 is between reactor L 0 and capacitor C 0, or the capacitor C 0 and may be inserted between the source of the 1MOSFET is needless to say.
[0009]
FIG. 2 is a circuit diagram showing a modification of FIG.
This is because, instead of inserting the diode RC2 as shown in FIG. 1, a current detector CT is provided to detect the current flowing through the reactor L 0, and the current of L 0 is the capacitor C 0 → reactor L 0 → diode FWRC or MOSFET The current before flowing in the direction of (FW1 to FW4) → capacitor C 0 , in other words, the current of L 0 becomes zero, and FW1 to FW4 are turned off. As a result, the current of the L 0 is the reactor L 0 → capacitor C 0 → diode FWRC or MOSFET (FW1~FW4) → only not flow in the direction of the reactor L 0, FW1~FW4 and FWRC ends by energy stored in L 0 It is possible to suppress a decrease in efficiency at a light load due to an increase in voltage between them and energy release from C 0 .
[0010]
FIG. 3 is a circuit diagram showing a second embodiment of the present invention.
This example, instead of inserting a diode RC2 shown in FIG. 1, 'adds, the turns ratio (L 0: L 0' L 0 in the auxiliary winding L 0 detects a current flowing from) the L 0 Therefore, an inexpensive current detection is possible. Note that, when zero current is detected, FW1 to FW4 are turned off as in the case of FIGS.
FIG. 4 is a circuit diagram showing a third embodiment of the present invention.
This is because the current detector CT detects a current flowing in any of FW1 to FW4 out of a current flowing in the direction of the reactor L 0 → capacitor C 0 → diode FWRC or MOSFET (FW1 to FW4) → reactor L 0. It is. In this case, it is only necessary to detect a current that is a fraction of the number of parallel MOSFETs, and current detection can be realized at low cost. Note that, when zero current is detected, FW1 to FW4 are turned off as in the case of FIGS.
[0011]
FIG. 5 is a circuit diagram showing a fourth embodiment of the present invention.
This is to detect the current (zero) flowing through the MOSFET from the magnitude of the drain-source voltage of any one MOSFET instead of inserting the diode RC2 as shown in FIG. Since no current detector is used, the cost can be reduced. Note that, when zero current is detected, FW1 to FW4 are turned off as in the case of FIGS.
FIG. 6 is a circuit diagram showing a fifth embodiment of the present invention.
This is because the primary side current of the transformer Tr and the load current are proportional to each other instead of inserting the diode RC2 as shown in FIG. 1, and a current detector is provided on the primary side of the transformer Tr. CT is provided to detect the magnitude of the primary current and to detect the load current. The FW1 to FW4 are turned off at the time of a light load with a small load current as in the above cases. In this example, it is not necessary to provide a detector on the synchronous rectifier side.
[0012]
FIG. 7 is a circuit diagram showing a sixth embodiment of the present invention.
Here, as in FIG. 6, a current detector is provided on the primary side of the transformer Tr to detect the magnitude of the primary current, and the current flowing in the direction of the reactor L 0 flowing from the transformer Tr to the secondary side is determined. To detect. That is, when the peak value of the reactor current is I 0 , the reactor current I is expressed by the following equation (1).
I = (di / dt) t + I 0 (1)
However, di / dt is expressed by the following equation (2). Here, t is the time from the current peak value, and V 0 is the output voltage.
di / dt = −V 0 / L 0 (2)
Therefore, the time t when I = 0 is expressed by the following equation (3).
t = L 0 I 0 / V 0 (3)
[0013]
That is, it can be seen from the equation (3) that the time until the reactor current becomes zero can be calculated from the values of L 0 , I 0 , and V 0 . FIG. 7 shows a time t from the initial value I 0 of the reactor current to zero.
Then, turning off FW1 to FW4 based on this time t is the same as in the above cases. Further, as in the case of FIG. 6, it is not necessary to provide a detector on the side of the synchronous rectifier.
[0014]
【The invention's effect】
According to the present invention, since the return current flowing through the output reactor of the synchronous rectifier circuit at the time of light load is not flowed in the reverse direction, high efficiency can be achieved. Further, since the element is not turned off when the output reactor current flows in the reverse direction, there is an advantage that the breakdown voltage of the element is not exceeded and safety can be achieved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a first embodiment of the present invention.
FIG. 2 is a configuration diagram showing a modification of FIG . 1 ;
FIG. 3 is a block diagram showing a second embodiment of the present invention.
FIG. 4 is a block diagram showing a third embodiment of the present invention.
FIG. 5 is a block diagram showing a fourth embodiment of the present invention.
FIG. 6 is a block diagram showing a fifth embodiment of the present invention.
FIG. 7 is an explanatory diagram for explaining a sixth embodiment of the present invention.
FIG. 8 is a circuit diagram showing a conventional example.
9 is an operation explanatory diagram of FIG. 8. FIG.
[Explanation of symbols]
Tr ... transformer, RC1, RC2, FWRC ... diodes, FW1, FW2, FW3, FW4 ... MOSFET, L 0, L 0 '... reactor, C 0 ... capacitor, CT ... current detector, P 0 ... positive output, N 0 ... negative output, I ... current, t ... time.
Claims (6)
前記リアクトルとコンデンサ間、またはコンデンサと第１ＭＯＳＦＥＴのソース間に第３ダイオードを挿入することにより、第１ＭＯＳＦＥＴをオンしたとき、リアクトルにコンデンサから第１ＭＯＳＦＥＴのドレイン・ソース間方向に電流を流さないようにしたことを特徴とする同期整流回路。An arbitrary number of first metal oxide field effect transistors (MOSFETs) are connected in parallel to the secondary side of the transformer, and at least one of the first diode or the second MOSFET is connected between the drain of the first MOSFET and the positive side of the transformer. In the case of a diode, the anode is inserted to the positive side of the transformer, and in the case of a MOSFET, the drain is connected to each other so that the cathode is connected to the drain side between the drain and source of the first MOSFET. A second diode is connected in parallel, or the role of the second diode is fulfilled by the body diode of the first MOSFET, and a series circuit of a reactor and a capacitor is connected in parallel between the drain and source of the first MOSFET connected in parallel to the transformer secondary side. By connecting and using both ends of the capacitor as output, In synchronous rectifier circuit the second 1MOSFET by turning on recirculating reactor current when the negative voltage is generated in the lance secondary side,
By inserting a third diode between the reactor and the capacitor or between the capacitor and the source of the first MOSFET, when the first MOSFET is turned on, no current flows from the capacitor to the drain-source direction of the first MOSFET when the first MOSFET is turned on. A synchronous rectifier circuit characterized by that.
前記リアクトルに補助巻線を設けてリアクトルに流れる電流を検出し、これが零になるときに前記第１ＭＯＳＦＥＴをオフする制御手段を設けたことを特徴とする同期整流回路。An arbitrary number of first metal oxide field effect transistors (MOSFETs) are connected in parallel to the secondary side of the transformer, and at least one of the first diode or the second MOSFET is connected between the drain of the first MOSFET and the positive side of the transformer. In the case of a diode, the anode is inserted to the positive side of the transformer, and in the case of a MOSFET, the drain is connected to each other so that the cathode is connected to the drain side between the drain and source of the first MOSFET. A second diode is connected in parallel, or the role of the second diode is fulfilled by the body diode of the first MOSFET, and a series circuit of a reactor and a capacitor is connected in parallel between the drain and source of the first MOSFET connected in parallel to the transformer secondary side. By connecting and using both ends of the capacitor as output, In synchronous rectifier circuit the second 1MOSFET by turning on recirculating reactor current when the negative voltage is generated in the lance secondary side,
A synchronous rectifier circuit characterized in that an auxiliary winding is provided in the reactor to detect a current flowing through the reactor, and control means for turning off the first MOSFET when this becomes zero.
前記第１ＭＯＳＦＥＴの１つに流れる電流を検出し、これが零になるときに前記第１ＭＯＳＦＥＴをオフする制御手段を設けたことを特徴とする同期整流回路。 An arbitrary number of first metal oxide field effect transistors (MOSFETs) are connected in parallel to the secondary side of the transformer, and at least one of the first diode or the second MOSFET is connected between the drain of the first MOSFET and the positive side of the transformer. In the case of a diode, the anode is inserted to the positive side of the transformer, and in the case of a MOSFET, the drain is connected to each other so that the cathode is connected to the drain side between the drain and source of the first MOSFET. A second diode is connected in parallel, or the role of the second diode is fulfilled by the body diode of the first MOSFET, and a series circuit of a reactor and a capacitor is connected in parallel between the drain and source of the first MOSFET connected in parallel to the transformer secondary side. By connecting and using both ends of the capacitor as output, In synchronous rectifier circuit the second 1MOSFET by turning on recirculating reactor current when the negative voltage is generated in the lance secondary side,
A synchronous rectifier circuit comprising a control means for detecting a current flowing through one of the first MOSFETs and turning off the first MOSFET when the current becomes zero .
前記第１ＭＯＳＦＥＴの１つのオン電圧を検出してこれから第１ＭＯＳＦＥＴの１つに流れる電流を推測し、これが零となるときに前記第１ＭＯＳＦＥＴをオフする制御手段を設けたことを特徴とする同期整流回路。 An arbitrary number of first metal oxide field effect transistors (MOSFETs) are connected in parallel to the secondary side of the transformer, and at least one of the first diode or the second MOSFET is connected between the drain of the first MOSFET and the positive side of the transformer. In the case of a diode, the anode is inserted to the positive side of the transformer, and in the case of a MOSFET, the drain is connected to each other so that the cathode is connected to the drain side between the drain and source of the first MOSFET. A second diode is connected in parallel, or the role of the second diode is played by the body diode of the first MOS FET, and a series circuit of a reactor and a capacitor is connected between the drain and source of the first MOSFET connected in parallel to the transformer secondary side. By connecting in parallel and using both ends of the capacitor as output, In a synchronous rectifier circuit that turns on the first MOSFET and circulates the reactor current when a negative voltage is generated on the secondary side of the transformer,
A synchronous rectifier circuit comprising: a control means for detecting an ON voltage of one of the first MOSFETs, estimating a current flowing through one of the first MOSFETs, and turning off the first MOSFET when the current becomes zero .
前記トランス１次側の電流を検出して負荷率を検出し、負荷率が所定値以下の軽負荷時に前記第１ＭＯＳＦＥＴをオフする制御手段を設けたことを特徴とする同期整流回路。 An arbitrary number of first metal oxide field effect transistors (MOSFETs) are connected in parallel to the secondary side of the transformer, and at least one of the first diode or the second MOSFET is connected between the drain of the first MOSFET and the positive side of the transformer. In the case of a diode, the anode is inserted to the positive side of the transformer, and in the case of a MOSFET, the drain is connected to each other so that the cathode is connected to the drain side between the drain and source of the first MOSFET. A second diode is connected in parallel, or the role of the second diode is fulfilled by the body diode of the first MOSFET, and a series circuit of a reactor and a capacitor is connected in parallel between the drain and source of the first MOSFET connected in parallel to the transformer secondary side. By connecting and using both ends of the capacitor as output, In synchronous rectifier circuit the second 1MOSFET by turning on recirculating reactor current when the negative voltage is generated in the lance secondary side,
A synchronous rectifier circuit comprising a control means for detecting a current on the primary side of the transformer to detect a load factor and turning off the first MOSFET at a light load when the load factor is a predetermined value or less .
前記トランス１次側の電流と同期整流回路の出力電圧とを検出し、リアクトル電流が零となる時間を計算して前記第１ＭＯＳＦＥＴをオフする制御手段を設けたことを特徴とする同期整流回路。 An arbitrary number of first metal oxide field effect transistors (MOSFETs) are connected in parallel to the secondary side of the transformer, and at least one of the first diode or the second MOSFET is connected between the drain of the first MOSFET and the positive side of the transformer. In the case of a diode, the anode is inserted to the positive side of the transformer, and in the case of a MOSFET, the drain is connected to each other so that the cathode is connected to the drain side between the drain and source of the first MOSFET. A second diode is connected in parallel, or the role of the second diode is fulfilled by the body diode of the first MOSFET, and a series circuit of a reactor and a capacitor is connected in parallel between the drain and source of the first MOSFET connected in parallel to the transformer secondary side. By connecting and using both ends of the capacitor as output, In synchronous rectifier circuit the second 1MOSFET by turning on recirculating reactor current when the negative voltage is generated in the lance secondary side,
A synchronous rectifier circuit comprising a control means for detecting the current on the primary side of the transformer and the output voltage of the synchronous rectifier circuit, calculating a time when the reactor current becomes zero, and turning off the first MOSFET .
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| JP30399897A JP3678286B2 (en) | 1997-11-06 | 1997-11-06 | Synchronous rectifier circuit |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30399897A JP3678286B2 (en) | 1997-11-06 | 1997-11-06 | Synchronous rectifier circuit |
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| JP3678286B2 true JP3678286B2 (en) | 2005-08-03 |
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