200906047 九、發明說明： 【發明所屬之技術領域】 本發明係有關一種返驰式轉換器，特別是具有自驅動式 同步整流器之返驰式轉換器。 【先前技術】 傳統之返驰式轉換器(flyback con verier)主要利用變壓器以及 一極體作為整流器，又稱為二極體整流器，用以將電源之能量傳輸 至外部負載電路。變壓器電路具有分離之一次側線 winding)及二次侧線圈(secondaiy winding)，其中一次側線圈用以連 接外部電源，而二次侧線圈係為一感應線圈，用以感應一次側線圈 之磁通量(magnetic flux)變化而生感應電壓，連接整流器(rectifier)形 成電力電路(power circuit)，用以驅動外部負載電路(i〇ad)。 請參考第1圖，其所示為傳統返馳式轉換器之電路。變壓器 10具有相互分離的一次侧線圈Lp及二次側線圈Ls，一次側線圈Lp 用以連接外部電壓源(power source) ’而二次側線圈ls，經由電力電 路(power circuit)後’連接外部負載電路(l〇ad)。圖中一次側線圈Lp 及二次侧線圈Ls上的黑點表示同極性(同時為正極或負極）。 一次侧線圈Ls連接二極體D!以形成電力電路，其中二極體 〇丨用以整流，又稱為二極體整流器。電力電路之一輸出端為電壓輸 出端，另一端為接地端，於電壓輸出端及接地端之間跨接電容C。， 稱為負載電容(load capacitor)。 首先介紹外部電源的供電方式，其通常區分為連續導通模式 (continuous conduction mode,CCM)及不連續導通模式(discontin_s conduction mode，DCM)。連續導通模式僅為不連續導通模式之特 例，以下說明不連續導通模式。其中輸入電壓以週期性方式供電， 200906047 時間標為t，其定義如下： 1.首先為開啟期間，記為Τωι (0 < t < τοη)，此期間内外部電 源施電壓V^VfHIGH)於一次側線圈Lp，一次側線圈L 儲能’通過一次側線圈Lp線圈之電流漸增至最大值，_P 次側線圈Ls&電流。 2.接著為重置期間’記為Tr (Tcn < t < Ton +Tr)，此期間内外 部電源關閉，二次侧線圈Ls釋能，通過二次側線線圈L 之電流is由最大漸減至0，一次側線圈Lp受到反射輪出 電壓(reflected output voltage) = ，其中 np 及 N 八 別一次側線圈Lp及二次侧線圈Ls“線圈數，一次側線圈 Lp之電流ζ»合^ 形成於一次側電感及一次側線圈^ 的封閉迴路中，彳i通過一次側開關之電流‘(,)=〇。 3_ 最後為延遲期間，記為 Tdead =Ts - T〇n - Tr (T〇n+Tr < t <200906047 IX. Description of the Invention: TECHNICAL FIELD OF THE INVENTION The present invention relates to a flyback converter, and more particularly to a flyback converter having a self-driven synchronous rectifier. [Prior Art] The conventional flyback converter mainly utilizes a transformer and a pole body as a rectifier, which is also called a diode rectifier, for transmitting the energy of the power source to an external load circuit. The transformer circuit has a separated primary side winding and a secondary ai winding, wherein the primary side coil is used to connect an external power source, and the secondary side coil is an induction coil for sensing the magnetic flux of the primary side coil (magnetic Flux changes to generate an induced voltage, and a rectifier is connected to form a power circuit for driving an external load circuit (i〇ad). Please refer to Figure 1, which shows the circuit of a conventional flyback converter. The transformer 10 has a primary side coil Lp and a secondary side coil Ls which are separated from each other, and the primary side coil Lp is for connecting an external voltage source 'and a secondary side coil ls, and is connected to the outside via a power circuit Load circuit (l〇ad). The black dots on the primary side coil Lp and the secondary side coil Ls in the figure indicate the same polarity (simultaneously positive or negative). The primary side coil Ls is connected to the diode D! to form a power circuit in which the diode is used for rectification, also referred to as a diode rectifier. One output of the power circuit is a voltage output terminal, and the other end is a ground terminal, and a capacitor C is connected between the voltage output terminal and the ground terminal. , called the load capacitor. First, the power supply mode of the external power supply will be described. It is generally divided into a continuous conduction mode (CCM) and a discontinuous conduction mode (DCM). The continuous conduction mode is only a special case of the discontinuous conduction mode, and the discontinuous conduction mode is explained below. The input voltage is supplied in a periodic manner, and the 200906047 time is marked as t, which is defined as follows: 1. First, the opening period is denoted as Τωι (0 < t < τοη), during which the external power supply voltage V^VfHIGH) In the primary side coil Lp, the primary side coil L stores 'current through the primary side coil Lp coil to increase to the maximum value, _P secondary side coil Ls & current. 2. Then, during the reset period, it is recorded as Tr (Tcn < t < Ton + Tr). During this period, the internal and external power supplies are turned off, the secondary side coil Ls is released, and the current is passed through the secondary side coil L is reduced by the maximum. To 0, the primary side coil Lp is subjected to a reflected output voltage = , where np and N are the primary side coil Lp and the secondary side coil Ls "the number of coils, and the current of the primary side coil Lp is combined". In the closed loop of the primary side inductance and the primary side coil ^, the current of 彳i through the primary side switch '(,) = 〇. 3_ Finally, the delay period, denoted as Tdead = Ts - T〇n - Tr (T〇n +Tr < t <
Ts)，其中Ts表示開關一周期之期間，延遲期間内外部電 源關閉(V产0)，二次側線圈匕不再釋能，無電流通過—次 側線圈Lp及二次側線圈Ls。 畲感應電流未降至〇(釋能未完全），下一個週期即開始，則 為連續導賴式。配合第丨®，以下說明返馳式轉換器之作^原理。 P撒期間内一次側線圈Lp及二次側線圈Ls上標示里點 點為高壓端，二極MDl為反向偏壓，電力電路未導通，葡 C。提供外部負載電路之電壓V。。 ' ^ 上標示黑點之端點 ’電力於負載電容 重置期間，一次側線圈Lp及二次側線圈L 為低壓端，二極體1^為順向偏壓，電力電路導通 C。及外部負載電路。 延遲期間’-次側線圈Lp及二次側線圈上之電〇，二 極體DA反向偏IV。關閉，由負載電容c。提供外部負載電路^ 200906047 壓v〇。 此種返驰式轉換器之缺點在於二極體整流器將導致嚴重的導 通才貝失(conduction loss)。為降低導通損失，一般採用同步整流器以 替代二極體整流11，例如’氧化金屬半導體場效應電晶體(metal 〇涵 sermeonductor field effect transist〇r，M〇s)常被用來實作同步整流 器’其實作電路請參考第2圖。 比較第2圖與第1圖所示之返馳式轉換器的電路，其不同處在 於採用n-MOS電晶體(n型氧化金屬半導體場效應電晶體)Μι替代二 極體，作為同步整流器，但此種設計需用積體電路控制器 (controller)IC以控制n_M〇S電晶體⑽之導通。 另有相似的返馳式轉換器的設計，請參考第3圖，其與第2圖 電路之不同處在於n_MC)s電晶體城連接於負載線圈之接地端。第 3圖所示之返馳式轉換器稱為低壓端驅動返馳式轉換器(1〇w side dnvenflybackC0nverter) ’而第2圖電路之·1式轉換器稱為高壓端 驅動返馳式轉換器(high side driven flyback converter)。此類設計，因 利用積體電路控制器1C而增加了電路的複雜度及成本。又 為降低導通損失、電路的複雜度及成本，利用不同的電路以 造返驰式轉換器，仍有其需求。 【發明内容】 本發明之一目的係降低返馳式轉換器之導通損失，其 用同步整流器以控制二次側電力線圈之導通。 本發明之另一目的係降低返驰式轉換器電路之複雜 度，其利用二次侧驅動線圈連接一開關控制器， 4要收電 流偵測電路之偵測訊號，開關控制器控制開關之輪出訊號， 進而決定開啟或關閉同步整流器。 ° ~ ’ 200906047 為達上述目的，本發明提供一種返馳式轉換器之實施 例，其包含變壓器、二極體、開關控制器、開關、電流偵測 電路及同步整流器。變壓器包含一次側線圈、二次側驅動線 圈及二次側電力線圈。一次側線圈用以連接外部電源。二次 側電力線圈連接同步整流器構成電力電路，並串接電流偵測 電路，電力電路之輸出端包含一接地端（低壓端），一端為電 壓輸出端（高壓端），電壓輸出端及接地端間跨接負載電容。 二次側驅動線圈串接二極體、開關控制器及開關以形成驅動 電路，開關控制器連接於電流偵測電路以接收偵測訊號。電 流偵測電路串接於電力電路上，用以偵測電力電路之電流， 並傳送偵測訊號給開關控制器，用以控制開關，進而令開關 開啟或關閉同步整流器。 【實施方式】 以下實施例及配合圖式以闡明本發明之精神。 請參考第4圖，說明本發明一實施例之返驰式變壓器 (transformer) 100 電路，其包含一次側線圈（primary winding)Lp、二次側驅動線圈（secondary driving winding)Ld 及二次側電力線圈（secondary power winding)Li，其中一次側 線圈Lp用以連接外部電源Vi。 二次側電力線圈L!連接電力電路(power circuit)，電力 電路串接電流偵測電路700後，提供電壓輸出端（高壓端）及 接地端（低壓端），用以提供驅動外部負載電路(load)(圖上未 示）之電壓V。，於電壓輸出端及接地端間跨接一負載電容 (load capacitor) C。用以穩壓。 200906047 二次側驅動線圈Ld串接驅動電路，驅動電路連接電流 偵測電路700及電力電路，用以接收電流偵測電路700之偵 測訊號，進而導通或斷開控制電力電路。 電流偵測電路700串接於電力電路上，用以偵測電力電 路之電流，其將電流訊號轉為電壓訊號，再傳送此電壓偵測 訊號給驅動電路，驅動電路依據此偵測訊號決定導通或斷開 電力電路。 第5圖為根據本發明之一實施例說明一次側線圈Lp、二 次側驅動線圈Ld、驅動電路以及電流偵測電路700之示意 圖。驅動電路包含二極體D2、開關控制器600及開關200。 開關控制器600具有第一輸入端610、第二輸入端630、參考 端640及輸出端620。開關200具有控制端210、第一電壓連 接端220、第二電壓連接端230及訊號輸出端240。電流偵測 電路700包含電流流入端710、電流流出端730、第一電壓輸 出端720及第二電壓輸出端740。 二次側驅動線圈Ld之第一端連接二極體D2之陽極，二 極體D2之陰極連接開關200之第一電壓連接端220,開關200 之第二電壓連接端230連接二次側驅動線圈Ld之第二端，及 訊號輸出端240用以連接電力電路。 開關控制器600之第一輸入端610及第二輸入端630分 別連接電流偵測電路700之第一電壓輸出端720及第二電壓 輸出端740，用以接收電流偵測電路700之偵測訊號。開關 控制器600之參考端640及輸出端620分別連接開關200之 第一電壓連接端220及控制端210，用以控制開關200之訊 號輸出端240之電位。 電流偵測電路700之電流流入端710及電流流出端730 串接於電力電路上，用以偵測電力電路之電流，並將電流訊 200906047 號轉換為電壓訊號，再藉由第一電壓輸出端720及第二電壓 輸出端740將此電壓訊號傳送給開關控制器600。於開關控 制器600之第二輸入端630及電流偵測電路700之第二電壓 輸出端740間可連接一電阻（圖上未示）以調整其偵測訊號之 電壓值。 第6圖為根據本發明之一實施例說明高壓端具自驅式同 步整流器之自驅返馳式轉換器的一次側線圈Lp、二次側驅動 線圈Ld、驅動電路、二次側電力線圈、電力電路及電流偵 測電路700之示意圖。如圖所示，電力電路包含一同步整流 器300,其具有一控制端310'—流入端320及一流出端330。 二次側電力線圈1^連接同步整流器300之流入端320， 其流出端330串接電流偵測電路700之電流流入端710，再 由電流偵測電路700之電流流出端730連接至電壓輸出端。 驅動電路之開關200的訊號輸出端240及第二電壓連接 端230分別連接同步整流器300的控制端310及流入端320。 根據上述實施例，於電源供電週期内，利用開關控制器 600的輸出端620及參考端640連接開關200之控制端210 及第一電壓連接端220,用以控制開關200之訊號輸出端240 之電位，進而導通或斷開同步整流器300的流入端320與流 出端330。若同步整流器300之控制端310被開啟且流入端 320之電壓高於流出端330之電壓時，電流由流入端320流 向流出端330，並流過電流偵測電路，如此二次側電力線圈 L!充能於負載電容C。並驅動外部負載電路（圖上未示）。若 同步整流器300之控制端3 10被關閉時，流入端320及流出 端330為斷路，電力電路形成開路，由負載電容C。驅動外部 負載電路，此時電流偵測電路之電流亦為0。 200906047 晶體實作同步整流器時，以其基極、集極及射極作為控制端 310、流出端330及流入端320，於流入端320(射極）及流出 端330(集極）之間跨接二極體。 接著，第8圖所示為一低壓端具自驅式同步整流器之自 驅返驰式轉換器實施例之電路圖。如圖所示，同步整流器300 為一 n-MOS電晶體M2。 開關200以一互鎖型電路實作，其包含一 NPN雙極電 晶體Qi、PNP雙極電晶體Q2、電阻R2。雙極電晶體Qi之射 極連接雙極電晶體Q2之射極且連接點定義為訊號輸出端 240。二雙極電晶體Q!、Q2之基極相接且連接點定義為控制 端210。電阻R2跨接在雙極電晶體Q2的集極與基極之間。 雙極電晶體Qi、Q2之集極分別定義為第一電壓連接端220 及第二電壓連接端230。 開關控制器600為一 NPN雙極電晶體Q3，其射極同時 被定義為第一輸入端610及輸出端620，基極及集極分別被 定義為第二輸入端630及參考端640。 電流偵測電路700包含變壓器電路、電阻R5、電容C2 及二極體D3，變壓器電路包含一次側線圈La及二次側線圈 Lb。一次側線圈La之二端被定義為電流流入端710及電流流 出端730，分別連接於同步整流器300之流入端320及電壓 輸出端之間。二次側線圈U之二端分別被定義為第一電壓輸 出端720及第二電壓輸出端740(圖中黑點表示同極性）。二次 側線圈Lb之二端跨接電阻R5，用以將感應電流轉為一電壓 訊號，跨接電容C3用以穩壓，二極體D3之陰極與陽極分別 連接第一電壓輸出端720及第二電壓輸出端740，用以確保 電流方向。 12 200906047 電阻R6連接於電流偵測電路700之第二電壓輸出端 740與開關控制器600之第二輸入端630(雙極電晶體Q3之基 極）之間，用以調整傳送給開關控制器600之電壓值。 電源供電之一週期内的電路之導通情況，電源供電供電 週期區分為開啟期間、重置期間以及延遲期間（定義已於先前 技術t描述）。當應用上述實施例時，其各區間的導通描述如 下： 開啟期間Ton (0 < t < Ton):二極體D2受反向偏壓（reverse biased)而關閉。因n-MOS電晶體M2之本體二極體受反向 偏壓（reverse biased)而關閉，使電流偵測電路700之一次側 線圈La無法導通電流，故電流偵測電路700之二次側線圈 Lb無感應電流’可被視為短路’雙極電晶體Q3之基射極因 無偏壓而關閉，開關200之雙極電晶體亦關閉，n-MOS 電晶體M2被關閉。即使n-MOS電晶體M2之閘極積存電荷， 也會很快地經由開關200之電晶體Q2及電阻R2而釋放，使 n-MOS電晶體M2之閘-源二極的跨壓降為0(VGS=0)，因而關 閉n-MOS電晶體M2。因此，電力電路不導通，由輸出電容 C。驅動外部負載電路之電壓V。。因此，在開啟期間Τοη(0<ί<Τοη) 内’電流由n-MOS電晶體M2之閘極流向電晶體Q2 ’即開關 200之訊號輸出端240提供低電壓訊號。 重置期間Tr (Ton < t < Ton +Tr):二極體D2受順向偏壓 (forward biased)而開啟。因n-MOS電晶體M2之本體二極體 受順向偏壓（forward biased)而開啟，使電流可流入電流债測 電路700之一次側線圈La之黑點端，二次側線圈Lb產生之 感應電流從黑點端流出，經電阻R5轉換為一電壓，此電壓， 經電容C2濾波與二極體D3鉗位後，使雙極電晶體Q3的基-射極間之跨壓為順向偏壓，因而開啟雙極電晶體Q3，開關 13 200906047 200之雙極電晶體仏亦被開啟，而在開關2〇〇之訊號輸出端 240提供一高電位以開啟n_M〇s電晶體，因而導通源極（流 入端320)與汲極（流出端330)，電力電路形成通路。因此，在 重置期間1；(1'。11<^<1'。]1+1；)内’電流由電晶體（^流向1以〇5電 晶體M2之間極，即開關200之訊號輪出端24〇提供高電壓訊號。 延遲期間Tdead (Ton+Tr < t < Ton+Tr+Tdead):返馳式變壓器100之 一次側線圈Lp、二次側驅動線圈Ld以及二次側電力線圈Li 不再釋能且無電流通過，此時二極體D2無偏壓而形成斷路， n-MOS電晶體Μ:被關閉，電力電路不導通，由輸出電容c。 驅動外部負載電路之電壓V。。 高壓端具自驅式同步整流器之自驅返驰式轉換器之原 理同低壓端具自驅式同步整流器之自驅返驰式轉換器，僅需 注意同步整流器之極性需連接正確，此不再贅述。 另一實施例係利用PNP雙極電晶體實作同步整流器3〇〇時，需 外接二極體，以產生流入端320及流出端330之跨壓，其同步整流器 之實施例如第9圖所示。 綜上所述，利用二次側驅動線圈形成一驅動電路，驅動 電路上之開關控制器受電流偵測電路而可控制開關，用以開 啟或關閉電力電路上之同步整流器，電力電路因而形成迴路 或開路，即可完成具自驅式同步整流器之自驅返耽式轉換器。 以上所述之實施例僅係為說明本發明之技術思想及特 點’其目的在使熟習此項技藝之人士能夠瞭解本發明之内容 並據以實施’當不能以之限定本發明之專利範圍，即大凡依 本發明所揭示之精神所作之均等變化或修飾，仍應涵蓋在本 發明之專利範圍内。 14 200906047 【圖式簡單說明】 第1圖所示為習知技術之返馳式轉換器之電路圖。 第2圖所示為習知技術之高壓端驅動返馳式轉換器之電路圖。 第3圖所示為習知技術之低壓端驅動返馳式轉換器電路圖。 第4圖所示為本發明一實施例之反驰式轉換器電路示意圖。 第5圖所示為本發明一實施例之具自驅式同步整流器之自驅返馳式 轉換器的驅動電路示意圖。 第6圖所示為本發明一實施例之高壓端具自驅式同步整流器之 自驅返驰式轉換器電路示意圖。 第7圖所示為本發明一實施例之低壓端具自驅式同步整流器之 自驅返驰式轉換器電路示意圖。 第8圖所示為本發明一實施例之低壓端具自驅式同步整流器之 自麵返馳式轉換器電路圖。 第9圖所示為本發明一實施例之同步整流器，其中以ΡΝΡ雙極電晶 體及二極體實作同步整流器。 【主要元件符號說明】 10 變壓器 、d3 二極體 ^、Ls、Ld、U、La、Lb 線圈 C〇' c3' C2 電容 R2、1、r6 電阻 ' Q2 ' q3 雙極電晶體 15 200906047 Μι ' M2 MOS電晶體 V,'v〇 電壓 IC 積體電路控制器 100 返馳式變壓器 200 開關 210 控制端 220,230 連接端 240 輸出端 300 同步整流器 310 控制端 320 流入端 330 流出端 600 開關控制器 610、630 輸入端 620 輸出端 640 參考端 700 電流偵測電路 710 電流流入端 730 電流流出端 720 第一電壓輸出端 740 第二電壓輸出端 16Ts), where Ts represents a period of one cycle of the switch, the external power supply is turned off during the delay period (V is 0), the secondary side coil turns off, and no current flows through the secondary side coil Lp and the secondary side coil Ls.畲The induced current does not fall to 〇 (release energy is not complete), and the next cycle starts, it is continuous conduction. In conjunction with Dijon®, the following describes the principle of the flyback converter. During the P sprinkling period, the points on the primary side coil Lp and the secondary side coil Ls are the high voltage terminals, the diodes MD1 are reverse biased, and the power circuit is not turned on. Provide the voltage V of the external load circuit. . ' ^ The end point of the black dot is marked. 'Electric power during load capacitor reset. The primary side coil Lp and the secondary side coil L are low voltage terminals, the diode 1 is forward biased, and the power circuit is turned on C. And external load circuit. During the delay period, the electric power on the secondary side coil Lp and the secondary side coil, the diode DA is reversely biased by IV. Off, by load capacitance c. Provide external load circuit ^ 200906047 Pressure v〇. A disadvantage of such a flyback converter is that the diode rectifier will result in severe conduction loss. In order to reduce the conduction loss, a synchronous rectifier is generally used instead of the diode rectification 11, for example, a metal oxide semiconductor field effect transistor (M〇s) is often used to implement a synchronous rectifier. In fact, please refer to Figure 2 for the circuit. Comparing the circuit of the flyback converter shown in FIG. 2 and FIG. 1 , the difference is that an n-MOS transistor (n-type oxidized metal semiconductor field effect transistor) is used instead of the diode as a synchronous rectifier. However, this design requires an integrated circuit controller IC to control the conduction of the n_M〇S transistor (10). For a similar design of the flyback converter, please refer to Figure 3, which differs from the circuit of Figure 2 in that the n_MC)s transistor is connected to the ground of the load coil. The flyback converter shown in Figure 3 is called the low-voltage side drive-back converter (1〇w side dnvenflybackC0nverter)' and the circuit of the second type circuit is called the high-voltage side drive-back converter. (high side driven flyback converter). Such a design increases the complexity and cost of the circuit by using the integrated circuit controller 1C. In order to reduce the conduction loss, the complexity and cost of the circuit, and the use of different circuits for the flyback converter, there is still a need. SUMMARY OF THE INVENTION One object of the present invention is to reduce the conduction loss of a flyback converter, which uses a synchronous rectifier to control the conduction of the secondary side power coil. Another object of the present invention is to reduce the complexity of the flyback converter circuit, which uses a secondary side drive coil to connect a switch controller, 4 to receive a current detection circuit detection signal, and a switch controller to control the switch wheel The signal is sent, and then the synchronous rectifier is turned on or off. ° ~ ' 200906047 To achieve the above object, the present invention provides an embodiment of a flyback converter comprising a transformer, a diode, a switch controller, a switch, a current detecting circuit and a synchronous rectifier. The transformer includes a primary side coil, a secondary side drive coil, and a secondary side power coil. The primary side coil is used to connect to an external power source. The secondary side power coil is connected to the synchronous rectifier to form a power circuit, and the current detecting circuit is connected in series. The output end of the power circuit includes a ground end (low voltage end), one end is a voltage output end (high voltage end), a voltage output end and a ground end. The load capacitor is connected across. The secondary side drive coil is connected in series with the diode, the switch controller and the switch to form a driving circuit, and the switch controller is connected to the current detecting circuit to receive the detection signal. The current detecting circuit is serially connected to the power circuit for detecting the current of the power circuit, and transmitting a detection signal to the switch controller for controlling the switch, thereby turning the switch on or off the synchronous rectifier. [Embodiment] The following embodiments and the accompanying drawings are intended to illustrate the spirit of the invention. Referring to FIG. 4, a flyback transformer 100 circuit according to an embodiment of the present invention includes a primary winding Lp, a secondary driving winding Ld, and a secondary side power line. A secondary power winding Li, wherein the primary side coil Lp is used to connect an external power source Vi. The secondary side power coil L! is connected to a power circuit. After the power circuit is connected in series with the current detecting circuit 700, a voltage output terminal (high voltage terminal) and a ground terminal (low voltage terminal) are provided to provide an external load circuit for driving ( Load) (not shown) voltage V. A load capacitor C is connected across the voltage output terminal and the ground terminal. Used for voltage regulation. 200906047 The secondary side driving coil Ld is connected in series with the driving circuit, and the driving circuit is connected to the current detecting circuit 700 and the power circuit for receiving the detecting signal of the current detecting circuit 700, thereby turning on or off the control power circuit. The current detecting circuit 700 is connected in series to the power circuit for detecting the current of the power circuit. The current signal is converted into a voltage signal, and the voltage detecting signal is transmitted to the driving circuit, and the driving circuit determines the conduction according to the detecting signal. Or disconnect the power circuit. Fig. 5 is a schematic view showing a primary side coil Lp, a secondary side drive coil Ld, a drive circuit, and a current detecting circuit 700 according to an embodiment of the present invention. The driving circuit includes a diode D2, a switch controller 600, and a switch 200. The switch controller 600 has a first input 610, a second input 630, a reference 640, and an output 620. The switch 200 has a control terminal 210, a first voltage connection terminal 220, a second voltage connection terminal 230, and a signal output terminal 240. The current detecting circuit 700 includes a current inflow terminal 710, a current outflow terminal 730, a first voltage output terminal 720, and a second voltage output terminal 740. The first end of the secondary side drive coil Ld is connected to the anode of the diode D2, the cathode of the diode D2 is connected to the first voltage connection end 220 of the switch 200, and the second voltage connection end 230 of the switch 200 is connected to the secondary side drive coil. The second end of the Ld and the signal output end 240 are used to connect to the power circuit. The first input terminal 610 and the second input terminal 630 of the switch controller 600 are respectively connected to the first voltage output terminal 720 and the second voltage output terminal 740 of the current detecting circuit 700 for receiving the detection signal of the current detecting circuit 700. . The reference terminal 640 and the output terminal 620 of the switch controller 600 are respectively connected to the first voltage connection terminal 220 and the control terminal 210 of the switch 200 for controlling the potential of the signal output terminal 240 of the switch 200. The current inflow terminal 710 and the current outflow terminal 730 of the current detecting circuit 700 are connected in series to the power circuit for detecting the current of the power circuit, and converting the current signal 200906047 into a voltage signal, and then using the first voltage output terminal. The 720 and the second voltage output 740 transmit the voltage signal to the switch controller 600. A resistor (not shown) can be connected between the second input terminal 630 of the switch controller 600 and the second voltage output terminal 740 of the current detecting circuit 700 to adjust the voltage value of the detection signal. 6 is a diagram showing a primary side coil Lp, a secondary side drive coil Ld, a drive circuit, and a secondary side power coil of a self-driven flyback converter of a high voltage end-drive self-driven synchronous rectifier according to an embodiment of the present invention. Schematic diagram of power circuit and current detecting circuit 700. As shown, the power circuit includes a synchronous rectifier 300 having a control terminal 310' - an inflow terminal 320 and a first-class outlet 330. The secondary side power coil 1 is connected to the inflow end 320 of the synchronous rectifier 300, and the outflow end 330 is connected in series with the current inflow end 710 of the current detecting circuit 700, and then connected to the voltage output end by the current outflow end 730 of the current detecting circuit 700. . The signal output terminal 240 and the second voltage connection terminal 230 of the switch 200 of the driving circuit are respectively connected to the control terminal 310 and the inflow terminal 320 of the synchronous rectifier 300. According to the above embodiment, the control terminal 210 and the first voltage connection terminal 220 of the switch 200 are connected to the output terminal 620 and the reference terminal 640 of the switch controller 600 for controlling the signal output terminal 240 of the switch 200 during the power supply cycle. The potential, in turn, turns on or off the inflow end 320 and the outflow end 330 of the synchronous rectifier 300. If the control terminal 310 of the synchronous rectifier 300 is turned on and the voltage of the inflow terminal 320 is higher than the voltage of the outflow terminal 330, the current flows from the inflow terminal 320 to the outflow terminal 330 and flows through the current detecting circuit, so that the secondary side power coil L Charged to load capacitor C. And drive the external load circuit (not shown). If the control terminal 3 10 of the synchronous rectifier 300 is turned off, the inflow terminal 320 and the outflow terminal 330 are open, and the power circuit forms an open circuit by the load capacitor C. The external load circuit is driven, and the current of the current detecting circuit is also zero. 200906047 When the crystal is implemented as a synchronous rectifier, its base, collector and emitter are used as the control terminal 310, the outflow terminal 330 and the inflow terminal 320, and span between the inflow terminal 320 (emitter) and the outflow terminal 330 (collector). Connect the diode. Next, Fig. 8 is a circuit diagram showing an embodiment of a self-driven flyback converter of a low voltage end self-driven synchronous rectifier. As shown, the synchronous rectifier 300 is an n-MOS transistor M2. The switch 200 is implemented as an interlocking type circuit comprising an NPN bipolar transistor Qi, a PNP bipolar transistor Q2, and a resistor R2. The emitter of the bipolar transistor Qi is connected to the emitter of the bipolar transistor Q2 and the junction is defined as the signal output 240. The bases of the two bipolar transistors Q!, Q2 are connected and the connection point is defined as the control terminal 210. Resistor R2 is connected across the collector and base of bipolar transistor Q2. The collectors of the bipolar transistors Qi, Q2 are defined as a first voltage connection terminal 220 and a second voltage connection terminal 230, respectively. The switch controller 600 is an NPN bipolar transistor Q3 whose emitter is simultaneously defined as a first input terminal 610 and an output terminal 620. The base and collector are defined as a second input terminal 630 and a reference terminal 640, respectively. The current detecting circuit 700 includes a transformer circuit, a resistor R5, a capacitor C2, and a diode D3. The transformer circuit includes a primary side coil La and a secondary side coil Lb. The two ends of the primary side coil La are defined as a current inflow terminal 710 and a current outflow terminal 730, which are respectively connected between the inflow terminal 320 of the synchronous rectifier 300 and the voltage output terminal. The two ends of the secondary side coil U are defined as a first voltage output terminal 720 and a second voltage output terminal 740, respectively (black dots in the figure indicate the same polarity). The two ends of the secondary side coil Lb are connected to the resistor R5 for converting the induced current into a voltage signal, and the capacitor C3 is used for voltage regulation. The cathode and the anode of the diode D3 are respectively connected to the first voltage output terminal 720 and A second voltage output 740 is used to ensure current direction. 12 200906047 The resistor R6 is connected between the second voltage output terminal 740 of the current detecting circuit 700 and the second input terminal 630 of the switch controller 600 (the base of the bipolar transistor Q3) for adjusting the transmission to the switch controller. 600 voltage value. The conduction of the circuit during one cycle of the power supply is divided into the on period, the reset period, and the delay period (the definition has been described in the prior art t). When the above embodiment is applied, the conduction of each section is as follows: On period Ton (0 < t < Ton): The diode D2 is turned off by reverse biased. Since the body diode of the n-MOS transistor M2 is turned off by reverse biased, the primary side coil La of the current detecting circuit 700 cannot conduct current, so the secondary side coil of the current detecting circuit 700 Lb no induced current 'can be regarded as short circuit' The base emitter of bipolar transistor Q3 is turned off due to no bias, the bipolar transistor of switch 200 is also turned off, and n-MOS transistor M2 is turned off. Even if the gate of the n-MOS transistor M2 accumulates charge, it is quickly released via the transistor Q2 of the switch 200 and the resistor R2, so that the gate-source diode of the n-MOS transistor M2 has a voltage drop of zero. (VGS = 0), thus turning off the n-MOS transistor M2. Therefore, the power circuit is not conducting, and the output capacitor C is used. The voltage V that drives the external load circuit. . Therefore, during the turn-on period, the current flowing from the gate of the n-MOS transistor M2 to the transistor Q2', that is, the signal output terminal 240 of the switch 200, provides a low voltage signal. Reset period Tr (Ton < t < Ton + Tr): The diode D2 is turned on by forward biased. Since the body diode of the n-MOS transistor M2 is turned on by the forward biased, the current can flow into the black point end of the primary side coil La of the current debt measuring circuit 700, and the secondary side coil Lb is generated. The induced current flows from the black point end and is converted into a voltage through the resistor R5. This voltage is clamped by the capacitor C2 and clamped by the diode D3 to make the voltage between the base and the emitter of the bipolar transistor Q3 forward. The bias voltage, thus turning on the bipolar transistor Q3, the bipolar transistor 开关 of the switch 13 200906047 200 is also turned on, and the signal output terminal 240 of the switch 2 提供 provides a high potential to turn on the n_M 〇s transistor, thereby turning on The source (inflow terminal 320) and the drain (outflow terminal 330) form a path for the power circuit. Therefore, during the reset period 1; (1'.11<^<1'.1+1+1;) the current is flown by the transistor (^ flows to 1 to 之间5 between the transistors M2, that is, the switch 200 The signal wheel terminal 24 〇 provides a high voltage signal. The delay period Tdead (Ton+Tr < t < Ton+Tr+Tdead): the primary side coil Lp of the flyback transformer 100, the secondary side drive coil Ld, and the second The side power coil Li is no longer discharged and no current flows. At this time, the diode D2 is unbiased to form an open circuit, the n-MOS transistor is turned off, the power circuit is not turned on, and the output capacitor c is driven by the output capacitor c. The voltage V. The principle of the self-driven flyback converter with self-driven synchronous rectifier at the high voltage end and the self-driven flyback converter with the self-driven synchronous rectifier at the low voltage end, only need to pay attention to the polarity of the synchronous rectifier to be connected. In the other embodiment, when a PNP bipolar transistor is used as the synchronous rectifier 3〇〇, an external diode is required to generate a voltage across the inflow terminal 320 and the outflow terminal 330, and the synchronous rectifier thereof The implementation is as shown in Fig. 9. In summary, a driving power is formed by using the secondary side driving coil. The switch controller on the driving circuit is controlled by the current detecting circuit to open or close the synchronous rectifier on the power circuit, and the power circuit thus forms a loop or an open circuit, thereby completing the self-driven synchronous rectifier. The above-described embodiments are merely illustrative of the technical idea and features of the present invention. The purpose of the present invention is to enable those skilled in the art to understand the contents of the present invention and to implement 'when not </ RTI> </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; Circuit diagram of a technical flyback converter. Fig. 2 is a circuit diagram of a high voltage end driven flyback converter of the prior art. Fig. 3 is a circuit diagram of a low voltage end driven flyback converter of the prior art. Figure 4 is a circuit diagram of a flyback converter according to an embodiment of the present invention. Fig. 5 is a diagram showing a self-driven synchronous rectifier according to an embodiment of the present invention. FIG. 6 is a schematic diagram of a self-driving flyback converter circuit of a high voltage end-conductor self-driven synchronous rectifier according to an embodiment of the present invention. FIG. 7 is a schematic diagram of the present invention. FIG. 8 is a schematic diagram of a self-driven flyback converter of a low voltage end self-driven synchronous rectifier according to an embodiment of the present invention. FIG. Fig. 9 is a schematic diagram showing a synchronous rectifier according to an embodiment of the present invention, in which a synchronous rectifier is implemented by a ΡΝΡ bipolar transistor and a diode. [Main component symbol description] 10 transformer, d3 diode ^, Ls, Ld, U, La, Lb Coil C〇' c3' C2 Capacitor R2, 1, r6 Resistor ' Q2 ' q3 Bipolar transistor 15 200906047 Μι ' M2 MOS transistor V, 'v〇 voltage IC integrated circuit controller 100 Flyback transformer 200 Switch 210 Control terminal 220, 230 Connection terminal 240 Output terminal 300 Synchronous rectifier 310 Control terminal 320 Inflow terminal 330 Outflow terminal 600 Switching controller 610, 630 Input 620 Output terminal 640 Reference 700 current detection circuit 710 a first current flowing terminal 720 current voltage output terminal 730 an outflow end 740 of the second voltage output terminal 16