1364908 [0001] [0002] [0003] [0004] [0005] 097119121 100年10月26日核正替換頁 發明說明： 【發明所屬之技術領域】 本發明係關於一種開關電源電路。 【先前技術】 開關電源具有損耗小、變換效率高、線性變化小及工作 穩定等特點，因此被廣泛應用於液晶顯示裝置、陰極射 線管顯示裝置等顯示裝置及其它消費性電子產品中。 請參閱圖1，係一種先前技術開關電源電路之電路結構示 意圖。該開關電源電路1包括一第一整流濾波電路1 0、一 保護電路12、一變壓器13、一第二整流濾波電路143、一 第三整流濾波電路144、一反饋電路15、一脈寬調變晶片 16、一整流二極體17及一電晶體18。該脈寬調變晶片16 包括一用於接收工作電壓之電源輸入端161、一用於輸出 脈衝訊號之脈衝輸出端162及一反饋端163。 該第一整流濾波電路10包括二輸入端101、102、一全橋 整流電路103、一第一濾波電容104及一第一輸出端105 。該二輸入端101、102分別與該全橋整流電路103之二 輸入端（未標示）相連接。該全橋整流電路103之正向輸出 端與該第一輸出端105相連接，該全橋整流電路103之負 向輸出端接地。該第一濾波電容104接於該全橋整流電路 103之正向輸出端與負向輸出端之間。 該變壓器13包括一初級繞組131、一輔助繞組132、一第 一次級繞組133及一第二次級繞組134。該變壓器13之初 級繞組131與該保護電路12並聯，該初級繞組131之一端 與該第一輸出端105相連接，另一端與該電晶體18之汲極 表單编號A0101 第4頁/共25頁 1003395824-0 1364908 100年.10月26日梭正替换頁 連接。該電晶體18之源極經由一限流電阻（未標示）接地 。該電晶體18之閘極經由一電阻（未標示）與該脈寬調變 晶片16之脈衝輸出端162相連接。該輔助繞組132之一端 接地，另一端經由該整流二極體17及一電晶體（未標示） 連接於該脈寬調變晶片16之電源輸入端161。 [0006] 該第二整流濾波電路143包括一第二輸出端141，該第三 整流濾波電路144包括一第三輸出端142。該第一次級繞 組133之一端經由該第二整流濾波電路143與該第二輸出 端141連接，其另一端與該第二次級繞組134之一端連接 。該第二次級繞組134之一端接地，其與該第一次級繞組 133連接之一端經由該第三整流濾波電路144與該第三輸 出端142連接。 [0007] 該反饋電路15包括一第一分壓電阻151、一第二分壓電阻 152、一第三分壓電阻153、一保護電阻154、一光耦合 器155及一三端穩壓器158。該第一分壓電阻151之一端 與該第二輸出端141連接，另一端經由該第三分壓電阻 153接地。該第二分壓電阻152之一端與該第三輸出端 142連接，另一端經由該第三分壓電阻153接地。 [0008] 該光耦合器155包括一發光二極體156及一光電電晶體 157。該三端穩壓器158包括一參考端159、一陽極端（未 標示）及一陰極端（未標示）。該參考端159經由該第三分 壓電阻153接地。該陽極端接地，該陰極端與該發光二極 體156之陰極連接。該發光二極體156之陽極經由一電阻（ 未標示）連接於該第三輸出端142。該保護電阻154與該發 光二極體156並聯。該光電電晶體157之一端接地，另一 097119121 表單編號A0101 第5頁/共25頁 1003395824-0 1364908 100年10月26日梭正替換頁 端接於該脈寬調變晶片16之反饋端163。.1364908 [0001] [0001] [0004] [0005] [0005] 097119121 October 26, 100 nuclear replacement page Description of the invention: [Technical Field] The present invention relates to a switching power supply circuit. [Prior Art] Switching power supplies are widely used in display devices such as liquid crystal display devices, cathode ray tube display devices, and other consumer electronic products because of their low loss, high conversion efficiency, small linear variation, and stable operation. Referring to Figure 1, there is shown a schematic diagram of the circuit configuration of a prior art switching power supply circuit. The switching power supply circuit 1 includes a first rectifying and filtering circuit 10, a protection circuit 12, a transformer 13, a second rectifying and filtering circuit 143, a third rectifying and filtering circuit 144, a feedback circuit 15, and a pulse width modulation. The wafer 16, a rectifying diode 17 and a transistor 18 are provided. The pulse width modulation chip 16 includes a power input terminal 161 for receiving an operating voltage, a pulse output terminal 162 for outputting a pulse signal, and a feedback terminal 163. The first rectifying and filtering circuit 10 includes two input terminals 101 and 102, a full bridge rectifying circuit 103, a first filter capacitor 104 and a first output terminal 105. The two input terminals 101, 102 are respectively connected to two input terminals (not shown) of the full bridge rectifier circuit 103. The forward output terminal of the full bridge rectifier circuit 103 is connected to the first output terminal 105, and the negative output terminal of the full bridge rectifier circuit 103 is grounded. The first filter capacitor 104 is connected between the forward output terminal and the negative output terminal of the full bridge rectifier circuit 103. The transformer 13 includes a primary winding 131, an auxiliary winding 132, a first secondary winding 133 and a second secondary winding 134. The primary winding 131 of the transformer 13 is connected in parallel with the protection circuit 12, one end of the primary winding 131 is connected to the first output terminal 105, and the other end is connected to the transistor of the transistor 18. Form number A0101 Page 4 of 25 Page 1003395824-0 1364908 100 years. On October 26th, the shuttle is replacing the page connection. The source of the transistor 18 is grounded via a current limiting resistor (not shown). The gate of the transistor 18 is coupled to the pulse output 162 of the pulse width modulation chip 16 via a resistor (not shown). One end of the auxiliary winding 132 is grounded, and the other end is connected to the power input terminal 161 of the pulse width modulation chip 16 via the rectifying diode 17 and a transistor (not shown). The second rectifying and filtering circuit 143 includes a second output terminal 141, and the third rectifying and filtering circuit 144 includes a third output terminal 142. One end of the first secondary winding 133 is connected to the second output terminal 141 via the second rectifying filter circuit 143, and the other end thereof is connected to one end of the second secondary winding 134. One end of the second secondary winding 134 is grounded, and one end of the second secondary winding 133 is connected to the third output terminal 142 via the third rectifying and filtering circuit 144. The feedback circuit 15 includes a first voltage dividing resistor 151, a second voltage dividing resistor 152, a third voltage dividing resistor 153, a protection resistor 154, an optical coupler 155, and a three-terminal regulator 158. . One end of the first voltage dividing resistor 151 is connected to the second output terminal 141, and the other end is grounded via the third voltage dividing resistor 153. One end of the second voltage dividing resistor 152 is connected to the third output terminal 142, and the other end is grounded via the third voltage dividing resistor 153. The optical coupler 155 includes a light emitting diode 156 and an optoelectronic transistor 157. The three-terminal regulator 158 includes a reference terminal 159, an anode terminal (not shown), and a cathode terminal (not shown). The reference terminal 159 is grounded via the third voltage dividing resistor 153. The anode terminal is grounded, and the cathode terminal is connected to the cathode of the light emitting diode 156. The anode of the LED 156 is coupled to the third output 142 via a resistor (not shown). The protection resistor 154 is connected in parallel with the light-emitting diode 156. One end of the optoelectronic transistor 157 is grounded, another 097119121 Form No. A0101 Page 5 / Total 25 Page 1003395824-0 1364908 On October 26, 100, the shuttle replacement page is terminated on the feedback end 163 of the pulse width modulation chip 16 . .
[0009] 該開關電源電路1之工作原理如下： [0010] 外部交流電壓經由該二輸入端101、102輸入至該第一整 流濾波電路10中，該第一整流濾波電路10對該交流電壓 進行整流濾波，並輸出一直流電壓。該直流電壓依次經 由該初級繞組131、該電晶體18及該限流電阻產生瞬間電 流。該輔助繞組132感應該初級繞組131並藉由該整流二 極體17為該脈寬調變晶片16提供直流工作電壓。該脈寬 調變晶片16藉由該脈衝輸出端162輸出脈衝訊號控制該電 晶體18之開關。當該電晶體18開啟時，該初級繞組131上 有直流電流通過；當該電晶體18截止時，該初級繞組131 上無直流電流通過。該第一次級繞組133及該第二次級繞 組134分別輸出其感應之電訊號，該電訊號分別經由該第 二整流濾波電路143及該第三整流濾波電路144整流、濾 波後產生一 14V直流電壓及一5V直流電壓，並分別藉由該 第二輸出端141及該第三輸出端142輸出。 [0011] 當該第二輸出端141輸出之直流電壓值高於14V，該第三 輸出端142輸出之直流電壓值高於5V時，該第三分壓電阻 153二端之電壓值相應增大。當該第二輸出端141輸出之 直流電壓值低於14V，該第三輸出端142輸出之直流電壓 值低於5V時，該第三分壓電阻153二端之電壓值相應減小 。即該三端穩壓器158之參考端159之電壓值將會相應增 大或減小。該三端穩壓器158之參考端159之電壓值之大 小控制其陽極端及陰極端之電流大小。該參考端159之電 壓值越大，流經該陽極端及該陰極端之電流越大。該參 097119121 表單编號A0101 第6頁/共25頁 1003395824-0 1364908 100年.10月26日按正替¥頁 考端159之電壓值越小，流經該陽極端及該陰極端之電流 越小。因此，該光耦合器155之發光二極體156之電流隨 流經該三端穩壓器158之陽極端及陰極端之電流變化而變 化。該光電電晶體157受到該發光二極體156照射而產生 電流。該發光二極體156之發光強度之變化控制該光電電 晶體157之電流變化。該光電電晶體157將其上之反饋電 流傳送到該反饋端163。該脈寬調變晶片16根據該反饋電 流之變化調節其脈衝輸出端162輸出之脈衝訊號之占空比 ，從而使輸出電壓穩定。 [0012] 該開關電源電路1採用該脈寬調變晶片16產生控制該電晶 體18之脈衝訊號，成本較高，且與該脈寬調變晶片16配 合工作之外部電路結構複雜，涉及元件較多，使採用該 開關電源電路1之電子產品體積較大。且’該反饋電路15 採用該三端穩壓器158反饋，其電路結構複雜，且三端穩 壓器之成本較高。 【發明内容】 [0013] 有鑑於上述内容，有必要提供一種體積較小、電路結構 簡單、成本較低之開關電源電路。 [0014] 一種開關電源電路，其包括一直流電源輸入端、一脈衝 產生電路、一變壓器、一反饋電路及一輸出端。該變壓 器包括一初級繞組、一輔助繞組及一次級繞組；該脈衝 產生電路包括一第一開關元件、一第二開關元件、一電 容、一諧振電阻及串聯於該直流電源輸入端與地之間之 二第一分壓電阻；該反饋電路包括二串聯於該輸出端與 地之間之第二分壓電阻、一第三開關元件及一光耦合器 097119121 表單編號A0101 第7頁/共25頁 1003395824-0 1364908 100年10月26日梭正替換頁 ，該光輕合器包括一發光二極體及一光電電晶體。每一 開關元件包括一控制端、一第一導通端及一第二導通端 ，該第一開關元件之第一導通端連接於該第二開關元件 之控制端，其第二導通端接地，其控制端依次經由該電 容、該諸振電阻及該光電電晶體接地，該第二開關元件 之控制端經由一第一分壓電阻接地；該初級繞組之一端 與該直流電壓輸入端連接，另一端依次經由該第二開關 元件之第一導通端、第二導通端及一限流電阻接地；該 第三開關元件之控制端經由一第二分壓電阻接地，該輸 出端依次經由該第三開關元件之第一導通端、第二導通 端、一限流電阻及該發光二極體接地。 [0015] —種開關電源電路，其包括一直流電源輸入端、一與該 直流電源輸入端連接之變壓器、一與該變壓器配合產生 振盪脈衝之脈衝產生電路、一調節輸出電壓穩定之反饋 電路及一輸出端。該脈衝產生電路包括一反饋端，該反 饋電路包括一分壓電路、一開關元件及一光搞合器，該 開關元件包括一控制端 '一第一導通端、一第二導通端 ，該輸出端輸出之直流電壓經由該分壓電路分壓後傳送 至該開關元件之控制端，該開關元件之一導通端連接該 輸出端，另一導通端經由該光耦合器向該脈衝產生電路 之反饋端反饋電流以反饋輸出端之電壓變化。 [0016] 一種開關電源電路，其包括一直流電源輸入端、一變壓 器、一與該變壓器配合產生振盪脈衝之脈衝產生電路、 —調節輸出電壓穩定之反饋電路、一第一輸出端及一第 二輸出端。該脈衝產生電路包括一反饋端。該反饋電路 097119121 表單编號A0101 第8頁/共25頁 1003395824-0 1364908 ι 100年10月26日桉正替换頁 包括一第一分壓電路、一第二分壓電路、一第一開關元 件、一第二開關元件及一光耦合器，該第一輸出端輸出 之直流電壓經由該第一分壓電路分壓後，依次經由該第 一開關元件及該光耦合器輸入至該脈衝產生電路之反饋 端；該第二輸出端輸出之直流電壓經由該第二分壓電路 分壓後，依次經由該第二開關元件及該光耦合器輸入至 該脈衝產生電路之反饋端。 [0017] 相較於先前技術，本發明之開關電源電路採用該脈衝產 生電路及該變壓器之輔助繞組產生該第一電晶體及該第 二電晶體所需開關脈衝訊號，其電路結構簡單，涉及週 邊元件少。且其不需要脈寬調變晶片，成本較低。該開 關電源電路之反饋電路採用該分壓電路、該開關元件及 該光耦合器進行反饋，其電路結構簡單，且不需要三端 穩壓器，成本較低，滿足目前小型電子產品價格低廉之 需求。 【實施方式】 [0018] 請參閱圖2，係本發明開關電源電路第一實施方式之電路 結構示意圖。該開關電源電路2包括一第一整流濾波電路 20、一脈衝產生電路21、一保護電路22、一變壓器23、 一第二整流濾波電路24及一反饋電路25。該第一整流濾 波電路20包括二第一輸入端201、202、一全橋整流電路 203、一第一電容204及一第一輸出端205。該脈衝產生 電路21包括一第一分壓電阻211、一第二分壓電阻212、 一第一電晶體213、一第二電晶體214、一第二電容215 及一諧振電阻216。該變壓器23包括一初級繞組231、一 097119121 表單編號A0101 第9頁/共25頁 1003395824-0 1364908 100年.10月26日梭正替換頁 輔助繞組232及一次級繞組233。該第二整流濾波電路24 包括一第二輸出端241。該反饋電路25包括一第三電晶體 251、一第三分壓電阻252、一第四分遂電阻253及一光 耦合器254。該光耦合器254包括一發光二極體255及一 光電電晶體256。該第一電晶體213及該第二電晶體214 可以為N型金屬氧化物半導體場效應電晶體。該第三電晶 體251可以為NPN型雙極電晶體。 [0019] 該二第一輸入端201、202分別與該全橋整流電路203之 二輸入端（未標示）相連接。該全橋整流電路2〇3之正向輸 出端與該第一輸出端205相連接，該全橋整流電路203之 負向輸出端接地。該第一電容204連接於該全橋整流電路 20 3之正向輸出端與負向輸出端之間。 [0020] 該第一分壓電阻211及該第二分壓電阻21 2串聯接於該第 一輸出端205與地之間，且該第一分壓電阻211之阻值大 於該第二分壓電阻212之阻值。該第一電晶體213之汲極 與該第二電晶體214之閘極連接，其源極接地。該第二電 晶體214之閘極經由該第二分壓電阻212接地，其源極經 由一限流電阻（未標示）接地。 [0021] 097119121 該初級繞組231與該保護電路22並聯《該初級繞組231之 一端與該第一輸出端205連接，其另—端與該第二電晶體 214之汲極連接。該輔助繞組232之一端接地，其另一端 與戎第一電晶體213之閘極連接。該第一電晶體213之閘 極依次經由該第二電容21 5及該諧振電阻216與該光電電 晶體256之一端連接，定義該諳振電阻216與該光電電晶 體256連接之一端為該脈衝產生電路以之反饋端。該光電 1003395824-0 表單编號A010丨 苐10頁/共25頁 1364908 100年10月26日梭正替換頁 電晶體2 5 6之另一端接地。該次級繞組2 3 3之一端接地， 其另一端經由該第二整流濾波電路24連接於該第二輸出 端 241。 [0022] 該第三分壓電阻252與該第四分壓電阻253串聯接於該第 二輸出端241與地之間。該第三分壓電阻252之電阻值小 於該第四分壓電阻253之電阻值。該第三分壓電阻252與 該第四分壓電阻253組成一分壓電路，用於對該第二輸出 端之輸出電壓進行分壓處理。該第三電晶體251之基極經 由該第四分壓電阻253接地，其集極與該第二輸出端241 連接，其射極經由一限流電阻（未標示）與該發光二極體 255之陽極連接。該發光二極體255之陰極接地。 [0023] 該開關電源電路2之工作原理如下： [0024] 外部交流電壓經由該二第一輸入端201、202輸入至該第 一整流濾波電路20中，該第一整流濾波電路20對該交流 電壓進行整流濾波，並經由該第一輸出端205輸出一第一 直流電壓。由於該第二分壓電阻212之分壓作用，有正電 壓加載至該第二電晶體214之閘極，使該第二電晶體214 導通。此時，該初級繞組2 31上有電流通過。該輔助繞組 232感應該初級繞組231產生電流，並對該第二電容215 充電。當該第二電容215二端之電壓達到該第一電晶體 213之導通電壓時，該第一電晶體213導通。此時，該第 二電晶體214之閘極經由該第一電晶體213之汲極、源極 接地。因此，該第二電晶體214截止，該初級繞組231上 無電流通過。該第二電容21 5充電結束後，其儲存之電能 開始向該輔助繞組232傳遞。當該第二電容215放電使該 097119121 表單编號A0101 第11頁/共25頁 1003395824-0 1364908 100年10月26日梭正替換頁 第一電晶體213之閘極電壓值達到其截止電壓值時，該第 一電晶體21 3截止，該第二電晶體214導通。此時，該初 級繞組2 31上有電流通過。 [0025] 該次級繞組233輸出其感應之電訊號，經由該第二整流濾 波電路24整流、濾波後產生一第二直流電壓，並藉由該 第二輸出端241輸出。因該第三電晶體251之基極電壓始 终小於其集極電壓，當該第二輸出端241有電壓輸出時， 該第三電晶體251始終處於導通狀態。當該第二直流電壓 值大於或小於該直流電源之預定輸出值時，該第四分壓 電阻253二端之電壓相應增大或減小。該第三電晶體251 之基極電流相應增大或減小，從而使其集極電流相應增 大或減小。該第三電晶體251之集極電流之變化傳遞到該 光耦合器254，從而使通過該光電電晶體256之電流增大 或減小。當通過該光電電晶體256之電流增大時，該第二 電容215之充電時間縮短，使該第一電晶體213迅速導通 。同時該第二電晶體214之導通時間相應減小，從而使該 初級繞組231上產生之脈衝訊號之占空比減小，使輸出電 壓值降低。當通過該光電電晶體256之電流減小時，該第 二電容215之充電時間增長，同時該第二電晶體214之導 通時間相應增長，從而使該初級繞組231上產生之脈衝訊 號之占空比增大，使輸出電壓值增大。 [0026] 相較於先前技術，本發明之開關電源電路2採用該脈衝產 生電路21及該變壓器23配合產生該第一電晶體213及該第 二電晶體214所需開關脈衝訊號，其電路結構簡單，涉及 週邊元件少。且其不需要脈寬調變晶片，成本較低。該 097119121 表單编號A0101 第12頁/共25頁 1003395824-0 1364908 100年10月26日修正替換頁 開關電源電路2之反饋電路25採用該分壓電路、該第三電 晶體251及該光耦合器254進行反饋，其電路結構簡單， 且不需要三端穩壓器，成本較低，滿足目前小型電子產 品價格低廉之需求。 [0027] 請參閱圖3，係本發明開關電源電路第二實施方式之電路 結構示意圖。開關電源電路3與該開關電源電路2相比， 其區別點在於：變壓器33包括一第一次級繞組333及一第 二次級繞組334。第二整流濾波電路343包括一第二輸出 端341，第三整流濾波電路344包括一第三輸出端342。 反饋電路35包括一第三分壓電阻352、一第四分壓電阻 353、一第五分壓電阻354、一第三電晶體351及一第四 電晶體355。 [0028] 該第一次級繞組333之一端經由該第二整流濾波電路343 與該第二輸出端341連接，其另一端與該第二次級繞組 334之一端連接。該第二次級繞組334之一端接地，其與 該第一次級繞組3 3 3連接之一端經由該第三整流濾波電路 344與該第三輸出端342連接。 [0029] 該第三分壓電阻352及該第四分壓電阻353串聯接於該第 二輸出端341與地之間。該第三分壓電阻352及該第四分 壓電阻353組成一第一分壓電路。該第五分壓電阻354— 端連接於該第三輸出端342，其另一端經由該第四分壓電 阻353接地。該第五分壓電阻354及該第四分壓電阻353 組成一第二分壓電路。該第三電晶體351之基極經由該第 四分壓電阻353接地，其集極接於該第二輸出端341，其 射極經由一限流電阻（未標示）與光耦合器356之發光二極 097119121 表單編號A0101 第13頁/共25頁 1003395824-0 1364908 _ 100年.10月26日核正替換頁 體357之陽極連接。該第四電晶體邮之基極經由該第四 分壓電阻353接地，其集極接於該第三輸出端⑽，其射 極經由-限流電阻（未標示）與光輕合器挪之發光二極體 357之陽極連接。該開關電源電路3與該開關電源電路2之 原相同纟不同之處在於該開關電源電路3係多路 輸出’可以同時輸出不同電壓值之穩定直流電壓。 [0030] 惟’本發明開關電源電路亦可具其他多種變更設計’如 ‘該反饋電路中之分壓電路亦可以為採用電阻與其他元 件配合之結構或只㈣除電阻外其他元件，該其他元件 可以為電容、f絲晶體管’ P、需達到分壓效果即可。 本說明書中，金魏化物半導體場致應電晶體之閘極及 雙極電晶體之基極統稱為控制端，金屬 效應電晶想之沒極及雙極電晶雜之集枉嶋二 端’金屬氧化物半導體場效應電晶體之源極及雙極電晶 體之射極統稱為第二導通端。 [0031] 综上所述，本發明確已符合發明專利之要件，爰依法提 出專利中請。惟，以上所述者僅為本發明之較佳實施方 式，本發明之範圍並不以上述實施方式為限，舉凡熟悉 本案技藝之人士減本發明之精神所作之等效修飾或變 化’皆應涵蓋於以下申請專利範圍内。 【圖式簡單說明】 [0032] [0033] 圖1係-種先前技術開關電源電路之電略結構示意圖。 圖2係本發明開關電源電路第一實施方式之電路結構示意 圖。 、 097119121 表單編號A0101 第14頁/共25頁 1003395824-0 1364908 [0034] 100年.10月26日核正替換頁 圖3係本發明開關電源電路第二實施方式之電路結構示意 圖 【主要元件符號說明】 [0035] 開關電源電路 2、G 1 [0036] 第一整流濾波電路 20 [0037] 第一輸入端 201 、202 [0038] 全橋整流電路 203 [0039] 第一電容 204 [0040] 第一輸出端 205 [0041] 脈衝產生電路 21 [0042] 第一分壓電阻 211 [0043] 第二分壓電阻 212 [0044] 第一電晶體 213 [0045] 第二電晶體 214 [0046] 第二電容 215 [0047] 諧振電阻 216 [0048] 保護電路 22 [0049] 變壓器 23 ' 33 [0050] 初級繞組 231 [0051] 輔助繞組 232 097119121 表單編號A0101 第15頁/共25頁 1003395824-0 1364908 [0052] 次級繞組 [0053] 第二整流濾波電路 [0054] 第二輸出端 [0055] 反饋電路 [0056] 第三電晶體 [0057] 第三分壓電阻 [0058] 第四分壓電阻 [0059] 光耦合器 [0060] 發光二極體 [0061] 光電電晶體 [0062] 第一次級繞組 [0063] 第二次級繞組 [0064] 第二輸出端 [0065] 第三輸出端 [0066] 第三整流濾波電路 [0067] 第五分壓電阻 [0068] 第四電晶體 100年10月26日接正替换頁 343 35 ' 351 ' 352 ' 353 ' 356 ' 357 097119121 表單编號A0101 第16頁/共25頁 1003395824-0[0009] The operating principle of the switching power supply circuit 1 is as follows: [0010] The external AC voltage is input to the first rectifying and filtering circuit 10 via the two input terminals 101 and 102, and the first rectifying and filtering circuit 10 performs the AC voltage. Rectify and filter, and output the DC voltage. The DC voltage sequentially generates an instantaneous current through the primary winding 131, the transistor 18, and the current limiting resistor. The auxiliary winding 132 senses the primary winding 131 and provides a DC operating voltage to the pulse width modulated wafer 16 by the rectifying diode 17. The pulse width modulation chip 16 controls the switching of the transistor 18 by outputting a pulse signal from the pulse output terminal 162. When the transistor 18 is turned on, a direct current flows through the primary winding 131; when the transistor 18 is turned off, no direct current flows through the primary winding 131. The first secondary winding 133 and the second secondary winding 134 respectively output the induced electrical signals, and the electrical signals are respectively rectified and filtered by the second rectifying and filtering circuit 143 and the third rectifying and filtering circuit 144 to generate a 14V. The DC voltage and a 5V DC voltage are outputted by the second output terminal 141 and the third output terminal 142, respectively. [0011] When the DC voltage value outputted by the second output terminal 141 is higher than 14V, and the DC voltage value outputted by the third output terminal 142 is higher than 5V, the voltage value of the two terminals of the third voltage dividing resistor 153 is correspondingly increased. . When the DC voltage value outputted by the second output terminal 141 is lower than 14V and the DC voltage value outputted by the third output terminal 142 is lower than 5V, the voltage values of the two terminals of the third voltage dividing resistor 153 are correspondingly reduced. That is, the voltage value of the reference terminal 159 of the three-terminal regulator 158 will be correspondingly increased or decreased. The magnitude of the voltage at the reference terminal 159 of the three-terminal regulator 158 controls the magnitude of the current at the anode and cathode terminals. The greater the voltage value of the reference terminal 159, the greater the current flowing through the anode terminal and the cathode terminal. The parameter 097119121 Form No. A0101 Page 6 / Total 25 Page 1003395824-0 1364908 100 years. October 26, according to the positive page, the voltage value of the test terminal 159 is smaller, the current flowing through the anode end and the cathode end The smaller. Therefore, the current of the light-emitting diode 156 of the photocoupler 155 varies with the current flowing through the anode terminal and the cathode terminal of the three-terminal regulator 158. The photovoltaic transistor 157 is irradiated with the light-emitting diode 156 to generate an electric current. The change in the luminous intensity of the light-emitting diode 156 controls the current change of the photovoltaic cell 157. The optoelectronic transistor 157 delivers the feedback current thereon to the feedback terminal 163. The pulse width modulation chip 16 adjusts the duty ratio of the pulse signal outputted from the pulse output terminal 162 according to the change of the feedback current, thereby stabilizing the output voltage. [0012] The switching power supply circuit 1 uses the pulse width modulation chip 16 to generate a pulse signal for controlling the transistor 18. The cost is high, and the external circuit structure working with the pulse width modulation chip 16 is complicated, and the components are relatively In many cases, the electronic product using the switching power supply circuit 1 is bulky. And the feedback circuit 15 is fed back by the three-terminal regulator 158, the circuit structure is complicated, and the cost of the three-terminal voltage regulator is high. SUMMARY OF THE INVENTION [0013] In view of the above, it is necessary to provide a switching power supply circuit that is small in size, simple in circuit structure, and low in cost. [0014] A switching power supply circuit includes a DC power input terminal, a pulse generating circuit, a transformer, a feedback circuit, and an output terminal. The transformer includes a primary winding, an auxiliary winding and a primary winding; the pulse generating circuit includes a first switching element, a second switching element, a capacitor, a resonant resistor and is connected in series between the DC power input terminal and the ground The first voltage dividing resistor comprises: a second voltage dividing resistor connected in series between the output terminal and the ground, a third switching component and an optical coupler 097119121. Form No. A0101 Page 7 of 25 1003395824-0 1364908 On October 26, 100, the shuttle is replacing the page, and the light combiner includes a light emitting diode and a photovoltaic transistor. Each of the switching elements includes a control terminal, a first conductive terminal, and a second conductive terminal. The first conductive terminal of the first switching component is connected to the control terminal of the second switching component, and the second conductive terminal is grounded. The control terminal is grounded via the capacitor, the vibration resistors and the photoelectric transistor in sequence, and the control end of the second switching element is grounded via a first voltage dividing resistor; one end of the primary winding is connected to the DC voltage input end, and the other end is connected The first conductive terminal, the second conductive terminal, and a current limiting resistor are grounded through the second switching element; the control terminal of the third switching component is grounded via a second voltage dividing resistor, and the output terminal sequentially passes through the third switch The first conductive end, the second conductive end, a current limiting resistor and the light emitting diode of the component are grounded. [0015] A switching power supply circuit includes a DC power input terminal, a transformer connected to the DC power input end, a pulse generating circuit that cooperates with the transformer to generate an oscillation pulse, and a feedback circuit that regulates the output voltage stability and An output. The pulse generating circuit includes a feedback terminal, the feedback circuit includes a voltage dividing circuit, a switching component, and a light combiner. The switching component includes a control terminal, a first conductive terminal, and a second conductive terminal. The DC voltage outputted from the output terminal is divided by the voltage dividing circuit and transmitted to the control terminal of the switching element. One of the switching elements is connected to the output end, and the other conductive end is connected to the pulse generating circuit via the optical coupler. The feedback terminal feedback current changes with the voltage at the feedback output. [0016] A switching power supply circuit includes a DC power input terminal, a transformer, a pulse generating circuit that cooperates with the transformer to generate an oscillation pulse, a feedback circuit that regulates output voltage stabilization, a first output terminal, and a second Output. The pulse generating circuit includes a feedback terminal. The feedback circuit 097119121 Form No. A0101 Page 8 / Total 25 Page 1003395824-0 1364908 ι October 26, the replacement page includes a first voltage dividing circuit, a second voltage dividing circuit, a first a switching element, a second switching element, and an optical coupler, wherein the DC voltage outputted by the first output terminal is divided by the first voltage dividing circuit, and then input to the first switching element and the optical coupler through the optical switching device a feedback end of the pulse generating circuit; the DC voltage outputted by the second output terminal is divided by the second voltage dividing circuit, and then input to the feedback end of the pulse generating circuit via the second switching element and the optical coupler. [0017] Compared with the prior art, the switching power supply circuit of the present invention uses the pulse generating circuit and the auxiliary winding of the transformer to generate the switching pulse signals required by the first transistor and the second transistor, and the circuit structure is simple and involves There are few peripheral components. And it does not require a pulse width modulation chip, and the cost is low. The feedback circuit of the switching power supply circuit uses the voltage dividing circuit, the switching element and the optical coupler for feedback, and the circuit structure is simple, and a three-terminal voltage regulator is not needed, and the cost is low, and the current small electronic products are inexpensive. Demand. [Embodiment] [0018] Please refer to FIG. 2, which is a schematic structural diagram of a circuit of a first embodiment of a switching power supply circuit of the present invention. The switching power supply circuit 2 includes a first rectifying and filtering circuit 20, a pulse generating circuit 21, a protection circuit 22, a transformer 23, a second rectifying and filtering circuit 24, and a feedback circuit 25. The first rectifying filter circuit 20 includes two first input terminals 201 and 202, a full bridge rectifying circuit 203, a first capacitor 204 and a first output end 205. The pulse generating circuit 21 includes a first voltage dividing resistor 211, a second voltage dividing resistor 212, a first transistor 213, a second transistor 214, a second capacitor 215, and a resonant resistor 216. The transformer 23 includes a primary winding 231, a 097119121, a form number A0101, a page 9 of 25, 1003395824-0 1364908, a 100. October 26, a shuttle replacement page, an auxiliary winding 232 and a primary winding 233. The second rectifying and filtering circuit 24 includes a second output terminal 241. The feedback circuit 25 includes a third transistor 251, a third voltage dividing resistor 252, a fourth branching resistor 253, and an optical coupler 254. The optical coupler 254 includes a light emitting diode 255 and an optoelectronic transistor 256. The first transistor 213 and the second transistor 214 may be N-type metal oxide semiconductor field effect transistors. The third transistor 251 may be an NPN type bipolar transistor. [0019] The two first input terminals 201, 202 are respectively connected to two input ends (not labeled) of the full bridge rectifier circuit 203. The forward output terminal of the full bridge rectifier circuit 2〇3 is connected to the first output terminal 205, and the negative output terminal of the full bridge rectifier circuit 203 is grounded. The first capacitor 204 is connected between the forward output terminal and the negative output terminal of the full bridge rectifier circuit 203. [0020] The first voltage dividing resistor 211 and the second voltage dividing resistor 21 2 are connected in series between the first output terminal 205 and the ground, and the resistance of the first voltage dividing resistor 211 is greater than the second voltage divider. The resistance of the resistor 212. The drain of the first transistor 213 is connected to the gate of the second transistor 214, and the source thereof is grounded. The gate of the second transistor 214 is grounded via the second voltage dividing resistor 212, and its source is grounded via a current limiting resistor (not shown). [0021] 097119121 The primary winding 231 is connected in parallel with the protection circuit 22. "One end of the primary winding 231 is connected to the first output end 205, and the other end is connected to the drain of the second transistor 214. One end of the auxiliary winding 232 is grounded, and the other end thereof is connected to the gate of the first transistor 213. The gate of the first transistor 213 is connected to one end of the photovoltaic transistor 256 via the second capacitor 21 5 and the resonant resistor 216, and one end of the connection between the resonant resistor 216 and the photovoltaic transistor 256 is defined as the pulse. The circuit is generated with the feedback terminal. The photoelectric 1003395824-0 Form No. A010丨 苐10 pages / Total 25 pages 1364908 October 26, 100 shuttle replacement page The other end of the transistor 2 5 6 is grounded. One end of the secondary winding 2 3 3 is grounded, and the other end thereof is connected to the second output terminal 241 via the second rectifying and filtering circuit 24. [0022] The third voltage dividing resistor 252 and the fourth voltage dividing resistor 253 are connected in series between the second output terminal 241 and the ground. The resistance value of the third voltage dividing resistor 252 is smaller than the resistance value of the fourth voltage dividing resistor 253. The third voltage dividing resistor 252 and the fourth voltage dividing resistor 253 form a voltage dividing circuit for performing voltage division processing on the output voltage of the second output terminal. The base of the third transistor 251 is grounded via the fourth voltage dividing resistor 253, the collector of the third transistor 251 is connected to the second output terminal 241, and the emitter thereof is connected to the light emitting diode 255 via a current limiting resistor (not shown). The anode is connected. The cathode of the light-emitting diode 255 is grounded. [0023] The working principle of the switching power supply circuit 2 is as follows: [0024] The external alternating current voltage is input to the first rectifying and filtering circuit 20 via the two first input terminals 201, 202, and the first rectifying and filtering circuit 20 is connected to the alternating current The voltage is rectified and filtered, and a first DC voltage is output via the first output terminal 205. Due to the voltage division of the second voltage dividing resistor 212, a positive voltage is applied to the gate of the second transistor 214 to turn on the second transistor 214. At this time, current flows through the primary winding 2 31. The auxiliary winding 232 senses that the primary winding 231 generates a current and charges the second capacitor 215. When the voltage at both ends of the second capacitor 215 reaches the turn-on voltage of the first transistor 213, the first transistor 213 is turned on. At this time, the gate of the second transistor 214 is grounded via the drain and source of the first transistor 213. Therefore, the second transistor 214 is turned off, and no current flows through the primary winding 231. After the second capacitor 21 5 is charged, the stored electrical energy begins to be transferred to the auxiliary winding 232. When the second capacitor 215 is discharged, the 097119121 form number A0101 is 11th page/total 25 page 1003395824-0 1364908. On October 26, 100, the shuttle is replacing the gate voltage value of the first transistor 213 to its cutoff voltage value. At this time, the first transistor 21 3 is turned off, and the second transistor 214 is turned on. At this time, current flows through the primary winding 2 31. [0025] The secondary winding 233 outputs the induced electrical signal, and is rectified and filtered by the second rectifying filter circuit 24 to generate a second DC voltage, and is outputted by the second output terminal 241. Since the base voltage of the third transistor 251 is always smaller than its collector voltage, when the second output terminal 241 has a voltage output, the third transistor 251 is always in an on state. When the second DC voltage value is greater than or less than a predetermined output value of the DC power source, the voltage of the two terminals of the fourth voltage dividing resistor 253 is correspondingly increased or decreased. The base current of the third transistor 251 is correspondingly increased or decreased, so that its collector current is correspondingly increased or decreased. The change in the collector current of the third transistor 251 is transmitted to the photocoupler 254, thereby increasing or decreasing the current through the photo transistor 256. When the current through the photo transistor 256 increases, the charging time of the second capacitor 215 is shortened, causing the first transistor 213 to be turned on quickly. At the same time, the on-time of the second transistor 214 is correspondingly reduced, so that the duty ratio of the pulse signal generated on the primary winding 231 is reduced, and the output voltage value is lowered. When the current through the optoelectronic transistor 256 decreases, the charging time of the second capacitor 215 increases, and the on-time of the second transistor 214 increases correspondingly, thereby causing the duty cycle of the pulse signal generated on the primary winding 231. Increase to increase the output voltage value. [0026] Compared with the prior art, the switching power supply circuit 2 of the present invention uses the pulse generating circuit 21 and the transformer 23 to generate the switching pulse signals required by the first transistor 213 and the second transistor 214, and the circuit structure thereof. Simple, involving few peripheral components. And it does not require a pulse width modulation chip, and the cost is low. The 097119121 Form No. A0101 Page 12/Total 25 Page 1003395824-0 1364908 The correction circuit 25 of the replacement page switching power supply circuit 2 is modified on October 26, 100. The voltage dividing circuit, the third transistor 251 and the light are used. The coupler 254 performs feedback, has a simple circuit structure, does not require a three-terminal regulator, and has a low cost, and meets the current low price requirements of small electronic products. Please refer to FIG. 3, which is a schematic diagram of the circuit structure of the second embodiment of the switching power supply circuit of the present invention. The switching power supply circuit 3 is different from the switching power supply circuit 2 in that the transformer 33 includes a first secondary winding 333 and a second secondary winding 334. The second rectifying and filtering circuit 343 includes a second output terminal 341, and the third rectifying and filtering circuit 344 includes a third output terminal 342. The feedback circuit 35 includes a third voltage dividing resistor 352, a fourth voltage dividing resistor 353, a fifth voltage dividing resistor 354, a third transistor 351 and a fourth transistor 355. [0028] One end of the first secondary winding 333 is connected to the second output terminal 341 via the second rectifying filter circuit 343, and the other end thereof is connected to one end of the second secondary winding 334. One end of the second secondary winding 334 is grounded, and one end of the second secondary winding 334 is connected to the third output 342 via the third rectifying and filtering circuit 344. [0029] The third voltage dividing resistor 352 and the fourth voltage dividing resistor 353 are connected in series between the second output terminal 341 and the ground. The third voltage dividing resistor 352 and the fourth voltage dividing resistor 353 constitute a first voltage dividing circuit. The fifth voltage dividing resistor 354 is connected to the third output terminal 342, and the other end thereof is grounded via the fourth voltage dividing resistor 353. The fifth voltage dividing resistor 354 and the fourth voltage dividing resistor 353 form a second voltage dividing circuit. The base of the third transistor 351 is grounded via the fourth voltage dividing resistor 353, and its collector is connected to the second output terminal 341, and the emitter thereof is illuminated by a current limiting resistor (not shown) and the optical coupler 356. Dipole 097119121 Form No. A0101 Page 13 / Total 25 Page 1003395824-0 1364908 _ 100 years. October 26th The anode is replaced by the anode connection of the page body 357. The base of the fourth transistor is grounded via the fourth voltage dividing resistor 353, the collector of which is connected to the third output terminal (10), and the emitter thereof is moved via a current limiting resistor (not labeled) and the light coupling device. The anode of the light-emitting diode 357 is connected. The switching power supply circuit 3 is identical to the switching power supply circuit 2 in that the switching power supply circuit 3 is a multi-output 'stable DC voltage that can simultaneously output different voltage values. [0030] However, the switching power supply circuit of the present invention may have other various design changes. For example, the voltage dividing circuit in the feedback circuit may also be a structure in which a resistor is matched with other components or only (4) other components except a resistor. Other components can be capacitors, f-wire transistors 'P, need to achieve the partial pressure effect. In this specification, the gate of the gold-based semiconductor field-receiving transistor and the base of the bipolar transistor are collectively referred to as the control end, and the metal effect electro-crystals are considered to be the end of the dipole and the bipolar electro-crystals. The source of the metal oxide semiconductor field effect transistor and the emitter of the bipolar transistor are collectively referred to as a second conduction terminal. [0031] In summary, the present invention has indeed met the requirements of the invention patent, and the patent is filed according to law. However, the above description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiments, and equivalent modifications or changes made by those skilled in the art to reduce the spirit of the present invention should be It is covered by the following patent application. BRIEF DESCRIPTION OF THE DRAWINGS [0033] FIG. 1 is a schematic diagram showing the electrical structure of a prior art switching power supply circuit. Fig. 2 is a schematic view showing the circuit configuration of the first embodiment of the switching power supply circuit of the present invention. , 097119121 Form No. A0101 Page 14 / Total 25 Page 1003395824-0 1364908 [0034] 100 years. October 26th nuclear replacement page Figure 3 is a schematic diagram of the circuit structure of the second embodiment of the switching power supply circuit of the present invention [main component symbol [0035] Switching power supply circuit 2, G1 [0036] First rectifying and filtering circuit 20 [0037] First input terminal 201, 202 [0038] Full-bridge rectification circuit 203 [0039] First capacitor 204 [0040] An output terminal 205 [0041] a pulse generating circuit 21 [0042] a first voltage dividing resistor 211 [0043] a first voltage dividing resistor 212 [0044] a first transistor 213 [0045] a second transistor 214 [0046] Capacitor 215 [0047] Resonant Resistor 216 [0048] Protection Circuit 22 [0049] Transformer 23' 33 [0050] Primary Winding 231 [0051] Auxiliary Winding 232 097119121 Form No. A0101 Page 15 of 25 1003395824-0 1364908 [0052 Secondary winding [0053] Second rectifier filter circuit [0054] Second output terminal [0055] Feedback circuit [0056] Third transistor [0057] Third voltage divider resistor [0058] Fourth voltage divider resistor [0059] Optocoupler [0060] illuminating Pole body [0061] Photoelectric transistor [0062] First secondary winding [0063] Second secondary winding [0064] Second output [0065] Third output [0066] Third rectification filter circuit [0067] Five-component resistor [0068] Fourth transistor, October 26, 100, replacement page 343 35 ' 351 ' 352 ' 353 ' 356 ' 357 097119121 Form No. A0101 Page 16 / Total 25 Page 1003395824-0