1328921 i心f替換頁 九、發明說明： 【發明所屬之技術領域】 本發明係關於一種電源電路。 【先前技術】 請參閱圖1 ’其係·一種先前技術電源電路的電路結構 示意圖。該電源電路10包括一第一整流滤波電路11、一 ®隔離高頻變壓器14、一第二整流濾波電路15、一電晶體 17、一光耦合器18、一第一電阻121、一第二電阻122、 一過壓保護電路16及一脈寬調變控制器19。其中，該第 一整流濾波電路Π包括二輸入端111、112、一全橋整流 電路113、一濾波電容114及一輸出端115。該隔離高頻變 壓器14包括一初級繞組141及一次級繞組14 2。該第二整 流濾波電路15包括二輸入端151、152及一輸出端150。 B 該過壓保護電路16包括電阻R1、電阻R2、電阻R3、一 穩壓二極體161、一可控式整流器162及一電容163。該光 • 耦合器18包括一發光二極體181及一光電電晶體182。該 ^ 脈寬調變控制器19包括一控制端191、一電壓採樣端192 ： 及一欠壓保護端193。 - 該全橋整流電路113的二輸入端即該第一整流濾波電 路的二輸入端111、112，該全橋整流電路113的正輸出端 即該第一整流濾波電路的輸出端115，該全橋整流電路113 的負輸出端接地，該濾波電容114並聯在該全橋整流電路 1328921 ____ H曰辑替換頁 113的正輸出端及負輸出端之間。該隔離高頻變壓器14的 初級繞組141 一端與該第一整流濾波電路11的輸出端115 電連接，其另一端與該電晶體17的源極電連接。該隔離高 頻變壓器14的次級繞組142與該第二整流濾波電路15的 二輸入端151、152電連接。該電晶體17的閘極與該脈寬 調變控制器19的控制端191電連接，該電晶體17的汲極 藉由一電阻170接地。該電源電路的輸出端150藉由電阻 R1與該發光二極體181的正極電連接，該發光二極體181 ® 的負極與該可控式整流器162的正極電連接，該可控式整 流器162的負極接地，該可控式整流器162的控制極與該 穩壓二極體161的正極電連接。該電源電路的輸出端150 同時藉由電阻R2與該穩壓二極體161的負極電連接，該 穩壓二極體161的正極藉由該電阻R3接地，該電容163 與該電阻R3並聯。該光電電晶體182的集極藉由一電阻（未 標示）與該脈寬調變控制器19的電壓採樣端192連接，該 φ 光電電晶體182的射極接地。該脈寬調變控制器19的欠壓 保護端193藉由該第一電阻121與該全橋整流電路113的 • 正輸出端連接，其同時藉由該第二電阻122接地。 - 在該電晶體17的控制下，外界交流電壓輸入至該第一 : 整流濾波電路11的二輸入端111、112，經過該第一整流 - 濾波電路11、該隔離高頻變壓器14及該第二整流濾波電 路15後從該輸出端150輸出直流電壓。 當輸入端111、112的電壓低於其允許輸入的最小電壓 時，該第二電阻122的電壓隨之發生變化，該電壓反饋至 1328921 参月I燦正替換頁 • Cr ^ 該脈寬調變控制器19的欠壓保護端193，該脈寬調變控制 器19隨即進入鉗位保護狀態。 當輸出端150的電壓超過其允許輸出的最大電壓時， 該穩壓二極體161反向導通，即該穩壓二極體161中會產 生反向導通電流，該電流流經電阻R3，電阻R3二端產生 電壓降，此時，該可控式整流器162的控制極相應產生一 電壓訊號，該可控式整流器162導通，此時，該輸出端150、 該電阻R1、該發光二極體181、該可控式整流器162及地 ®構成一迴路，該迴路中的電流增大，該發光二極體181的 發光強度相應增大，該光電電晶體182的導通電流也相應 增大，反饋至該脈寬調變控制器19的電壓採樣端192的電 壓也相應增大，該脈寬調變控制器19將該反饋電壓與其内 部的參考電壓比較，當高於其内部的參考電壓時，該該脈 寬調變控制器19停止工作，從而實現過壓保護功能。 然，該電源電路10需要用到可控式整流器162及光耦 φ合器18來實現過壓保護功能，故該電源電路10的成本較 高。 ' 【發明内容】 : 有鑑於此，提供一種成本較低的電源電路實為必需。 - 一種電源電路，其包括一第一整流渡波電路、一脈寬 調變控制器、一隔離高頻變壓器、一第二整流濾波電路、 一電晶體、一過壓保護電路、一第一電阻及一第二電阻。 其中，該隔離高頻變壓器包括一輔助繞組，該脈寬調變控 -,r ^ I Bjumt ，制器包括一欠壓保護端。在該電晶體的控制下，外^^一 -電壓&過該第-整流遽波電路、該隔離高頻變堡器及該第 -〜整流濾波電路後輸出直流電壓。當輸出電壓超過其允許 ’輪出的最大電壓時’該輔助繞組的感應電壓藉由該過壓保 -濩電路反饋至該欠壓保護端，該脈寬調變控制器停止工 作j該脈寬調變控制器的欠壓保護端藉由該第一電阻與 該第一整流濾波電路的輸出端電性連接，其同時藉由該 聲第二電阻電性接地，當輸入電壓低於該電源電路允許輸 入的最小電壓時，第二電阻回饋一電壓至該脈寬調變控 制器的欠壓保護端，該脈寬調變控制器進入鉗位保護狀 態。 與先前技術相比’本發明電源電路採用由一二極體、 一雙極電晶體、一穩壓二極體及少量電阻、電容構成的過 壓保護電路即可實現過壓保護功能，從而降低了該電源電 路的成本。且該過壓保護功能利用的是該脈寬調變控制器 _的人壓保護端’該脈寬調變控制器的應用也得到擴展。 【實施方式】 ^ 請參閱圖2 ’其係本發明電源電路的電路結構示意 -圖。該電源電路20包括一第一整流遽波電路21、一脈寬 •調變控制器23、一隔離高頻變壓器24、一第二整流遽波電 路25、一場效電晶體27、一過壓保護電路29、一第一電 阻221、一第二電阻222及一輸出端250。其中，該第一整 流濾波電路21包括二輸入端211、212、一全橋整流電路 11 1328921 :丛嘴職3 213 濾波電容214及一輸出端215。該脈寬^ ί控制器 23包括一控制端231及一欠壓保護端232。該隔離高頻變 壓器24包括一初級繞組241、一次級繞組242及一輔助繞 組243。該過壓保護電路29包括電阻R1、一雙極電晶體 292、一二極體293、一穩壓二極體294及電阻R2。 該全橋整流電路213的二輸入端作為該第一整流濾波 電路21的二輸入端211、212，該全橋整流電路213的正 輸出端作為該第一整流濾波電路213的輸出端215，該全 橋整流電路21的負輸出端接地，該濾波電容214並聯在該 全橋整流電路213的正輸出端及負輸出端之間。該隔離高 頻變壓器24的初級繞組241 —端與該第一整流濾波電路 21的輸出端215電連接，其另一端與該場效電晶體27的 源極電連接。該次級繞組242 —端藉由該第二整流濾波電 路25與該輸出端250連接，其另一端接地。該輔助繞組 243 —端藉由該過壓保護電路29與該脈寬調變控制器23 的欠壓保護端232電連接，其另一端接地。該場效電晶體 27的汲極藉由一限流電阻270接地，該場效電晶體27的 閘極與該脈寬調變控制器23的控制端231電連接。該脈寬 調變控制器23的欠壓保護端232同時藉由該第一電阻221 與該全橋整流電路213的正輸出端連接，其同時藉由該第 二電阻222接地，一電容（未標示）與該第二電阻222並聯。 該二極體293的正極與該隔離高頻變壓器24的輔助繞 組243的一端連接，其負極與該雙極電晶體292的射極連 接，其負極同時藉由一電容（未標示）接地。該雙極電晶體 1328921 292的集極藉由該電阻R1與該脈寬調變控制ft ▲欠壓— 保護端232連接，其基極與該穩壓二極體294的負極連接。 該穩壓二極體294的正極藉由該電阻R2接地。 在該場效電晶體27的控制下，外界交流電壓輸入至該 第一整流濾波電路21的二輸入端211、212，經過該第一 整流濾波電路21、該隔離高頻變壓器24及該第二整流濾 波電路25後從該輸出端250輸出直流電壓。 當輸入端211、212的電壓低於其允許輸入的最小電壓 鲁時，該第二電阻222的電壓隨之發生變化，該電壓反饋至 該脈寬調變控制器23的欠壓保護端232，該脈寬調變控制 器23隨即進入鉗位保護狀態。 當輸出端250的電壓超過其允許輸出的最大電壓時， 該隔離高頻變壓器24的次級繞組242的電壓相應升高，由 於該隔離高頻變壓器24各繞組間的互感作用，該輔助繞組 243的電壓也相應增大’該雙極電晶體292射極的電壓隨 | 之增大，而該穩壓二極體294使該雙極電晶體292的基極 電壓保持不變’故該雙極電晶體292的射極與基極間的電 - 壓差增大，該雙極電晶體292會導通，反饋至該脈寬調變 * 控制器23的欠壓保護端232的電壓也相應增大，該脈寬調 : 變控制器23將該反饋電壓與其内部的鉗位電壓比較，當高 於其内部的鉗位電壓時，該脈寬調變控制器23停止工作， 從而實現過壓保護功能。 與先前技術相比’本發明電源電路20採用由該二極體 293、該雙極電晶體292、該穩壓二極體294及少量電阻、 13 丄J厶 降攸二：的過壓保義電路29即可實現過壓保護切能 -“電源電路20的成本。且該過壓保護功二 =寬調變控制器23的欠厂晴物，該 = 益23的應用也得到擴展。 月及控制 ^所述，本發明確已符合㈣之要件，爰依法提出 月准以上所述者僅為本發明之較佳實施方式， =發月之範圍並不以上述實施方式為限，舉凡熟習本案技 ^之人士援依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】 圖1係一種先前技術電源電路的電路結構示意圖。 圖2係本發明電源電路的電路結構示意圖。 【主要元件符號說明】 電源電路 20 第一整流濾波電路 21 脈寬調變控制器 23 隔離高頻變壓器 24 第二整流濾波電路 25 電晶體 27 過壓保護電路 29 全橋整流電路 213 濾波電容 214 14 1328921 。f替換負丨 第一電阻 221 第二電阻 222 控制端 231 欠壓保護端 232 初級繞組 241 次級繞組 242 辅助繞組 243 限流電阻 270 雙極電晶體 292 二極體 293 穩壓二極體 294 輸入端 211 、 212 輸出端 250 ' 215 151328921 I core f replacement page IX. Description of the invention: TECHNICAL FIELD The present invention relates to a power supply circuit. [Prior Art] Please refer to Fig. 1 '''''''''''''' The power circuit 10 includes a first rectifying and filtering circuit 11 , an isolated high frequency transformer 14 , a second rectifying and filtering circuit 15 , a transistor 17 , an optocoupler 18 , a first resistor 121 , and a second resistor . 122. An overvoltage protection circuit 16 and a pulse width modulation controller 19. The first rectifying and filtering circuit Π includes two input terminals 111 and 112, a full bridge rectifying circuit 113, a filter capacitor 114 and an output terminal 115. The isolated high frequency transformer 14 includes a primary winding 141 and a primary winding 14 2 . The second rectifying and filtering circuit 15 includes two input terminals 151 and 152 and an output terminal 150. B The overvoltage protection circuit 16 includes a resistor R1, a resistor R2, a resistor R3, a voltage stabilizing diode 161, a controllable rectifier 162, and a capacitor 163. The optical coupler 18 includes a light emitting diode 181 and an optoelectronic transistor 182. The pulse width modulation controller 19 includes a control terminal 191, a voltage sampling terminal 192, and an undervoltage protection terminal 193. The two input terminals of the full bridge rectifier circuit 113 are the two input terminals 111, 112 of the first rectifier filter circuit, and the positive output terminal of the full bridge rectifier circuit 113 is the output terminal 115 of the first rectifier filter circuit. The negative output terminal of the bridge rectifier circuit 113 is grounded, and the filter capacitor 114 is connected in parallel between the positive output terminal and the negative output terminal of the full bridge rectifier circuit 1329821 _ _ _ One end of the primary winding 141 of the isolated high frequency transformer 14 is electrically connected to the output terminal 115 of the first rectifying and filtering circuit 11, and the other end thereof is electrically connected to the source of the transistor 17. The secondary winding 142 of the isolated high frequency transformer 14 is electrically coupled to the two input terminals 151, 152 of the second rectifying and filtering circuit 15. The gate of the transistor 17 is electrically coupled to the control terminal 191 of the pulse width modulation controller 19, and the drain of the transistor 17 is grounded via a resistor 170. The output terminal 150 of the power circuit is electrically connected to the anode of the LED 181 via a resistor R1. The cathode of the LED 181 is electrically connected to the anode of the controllable rectifier 162. The controllable rectifier 162 The negative pole is grounded, and the control electrode of the controllable rectifier 162 is electrically connected to the positive pole of the voltage stabilizing diode 161. The output terminal 150 of the power supply circuit is electrically connected to the negative electrode of the voltage stabilizing diode 161 through a resistor R2. The anode of the voltage stabilizing diode 161 is grounded via the resistor R3. The capacitor 163 is connected in parallel with the resistor R3. The collector of the optoelectronic transistor 182 is coupled to the voltage sampling terminal 192 of the pulse width modulation controller 19 by a resistor (not shown), the emitter of which is grounded. The undervoltage protection terminal 193 of the pulse width modulation controller 19 is connected to the positive output terminal of the full bridge rectifier circuit 113 by the first resistor 121, and is simultaneously grounded by the second resistor 122. - under the control of the transistor 17, an external AC voltage is input to the first: two input terminals 111, 112 of the rectifying and filtering circuit 11, passing through the first rectifying-filtering circuit 11, the isolated high-frequency transformer 14, and the The second rectifying and filtering circuit 15 then outputs a DC voltage from the output terminal 150. When the voltage of the input terminals 111, 112 is lower than the minimum voltage of the input enabler, the voltage of the second resistor 122 changes accordingly, and the voltage is fed back to the 13298921 参月Ican positive replacement page • Cr ^ the pulse width modulation The undervoltage protection terminal 193 of the controller 19, the pulse width modulation controller 19 then enters the clamp protection state. When the voltage of the output terminal 150 exceeds the maximum voltage of the allowable output, the voltage stabilizing diode 161 is reverse-conducted, that is, a reverse conducting current is generated in the voltage stabilizing diode 161, and the current flows through the resistor R3, and the resistor A voltage drop is generated at the second end of the R3. At this time, the control electrode of the controllable rectifier 162 generates a voltage signal correspondingly, and the controllable rectifier 162 is turned on. At this time, the output terminal 150, the resistor R1, and the light emitting diode 181. The controllable rectifier 162 and the ground® form a loop. The current in the loop increases, the luminous intensity of the LED 181 increases correspondingly, and the conduction current of the optoelectronic transistor 182 increases accordingly. The voltage to the voltage sampling terminal 192 of the pulse width modulation controller 19 also increases accordingly, and the pulse width modulation controller 19 compares the feedback voltage with its internal reference voltage when it is higher than its internal reference voltage. The pulse width modulation controller 19 stops operating to implement an overvoltage protection function. However, the power supply circuit 10 needs to use the controllable rectifier 162 and the optocoupler φ combiner 18 to implement the overvoltage protection function, so the cost of the power supply circuit 10 is relatively high. [Explanation]: In view of this, it is necessary to provide a power circuit with lower cost. a power supply circuit comprising a first rectification wave circuit, a pulse width modulation controller, an isolated high frequency transformer, a second rectification filter circuit, a transistor, an overvoltage protection circuit, a first resistor, and a second resistor. Wherein, the isolated high frequency transformer comprises an auxiliary winding, the pulse width modulation control -, r ^ I Bjumt, the controller comprises an undervoltage protection end. Under the control of the transistor, the DC voltage is outputted through the first-rectifier chopper circuit, the isolated high-frequency converter, and the first-to-rectification filter circuit. When the output voltage exceeds the maximum voltage that it is allowed to 'round,' the induced voltage of the auxiliary winding is fed back to the undervoltage protection terminal by the overvoltage protection circuit, and the pulse width modulation controller stops working. The undervoltage protection end of the modulation controller is electrically connected to the output end of the first rectifying and filtering circuit by the first resistor, and is electrically grounded by the acoustic second resistor, when the input voltage is lower than the power circuit When the minimum voltage is allowed to be input, the second resistor returns a voltage to the undervoltage protection terminal of the pulse width modulation controller, and the pulse width modulation controller enters the clamp protection state. Compared with the prior art, the power supply circuit of the present invention can realize the overvoltage protection function by using an overvoltage protection circuit composed of a diode, a bipolar transistor, a voltage regulator diode and a small number of resistors and capacitors, thereby reducing the overvoltage protection function. The cost of the power circuit. And the overvoltage protection function utilizes the human voltage protection terminal of the pulse width modulation controller _, and the application of the pulse width modulation controller is also expanded. [Embodiment] ^ Please refer to Fig. 2', which is a schematic diagram of a circuit configuration of a power supply circuit of the present invention. The power circuit 20 includes a first rectifying chopper circuit 21, a pulse width modulation controller 23, an isolated high frequency transformer 24, a second rectifying chopper circuit 25, a field effect transistor 27, and an overvoltage protection. The circuit 29 has a first resistor 221, a second resistor 222 and an output terminal 250. The first rectifying and filtering circuit 21 includes two input terminals 211 and 212 and a full bridge rectifying circuit 11 1328921: a filter capacitor 214 and an output terminal 215. The pulse width controller 23 includes a control terminal 231 and an undervoltage protection terminal 232. The isolated high frequency transformer 24 includes a primary winding 241, a primary winding 242, and an auxiliary winding 243. The overvoltage protection circuit 29 includes a resistor R1, a bipolar transistor 292, a diode 293, a voltage stabilizing diode 294, and a resistor R2. The two input ends of the full-bridge rectifier circuit 213 serve as the two input terminals 211 and 212 of the first rectifier filter circuit 21, and the positive output terminal of the full-bridge rectifier circuit 213 serves as the output terminal 215 of the first rectifier filter circuit 213. The negative output terminal of the full bridge rectifier circuit 21 is grounded, and the filter capacitor 214 is connected in parallel between the positive output terminal and the negative output terminal of the full bridge rectifier circuit 213. The primary winding 241 of the isolated high frequency transformer 24 is electrically connected to the output 215 of the first rectifying and filtering circuit 21, and the other end thereof is electrically connected to the source of the field effect transistor 27. The secondary winding 242 is connected to the output terminal 250 by the second rectifying and filtering circuit 25, and the other end thereof is grounded. The auxiliary winding 243 is electrically connected to the undervoltage protection terminal 232 of the pulse width modulation controller 23 by the overvoltage protection circuit 29, and the other end thereof is grounded. The drain of the field effect transistor 27 is grounded via a current limiting resistor 270, and the gate of the field effect transistor 27 is electrically coupled to the control terminal 231 of the pulse width modulation controller 23. The undervoltage protection terminal 232 of the pulse width modulation controller 23 is simultaneously connected to the positive output terminal of the full bridge rectifier circuit 213 by the first resistor 221, and is simultaneously grounded by the second resistor 222, a capacitor (not Marked) in parallel with the second resistor 222. The anode of the diode 293 is connected to one end of the auxiliary winding 243 of the isolated high frequency transformer 24, the cathode thereof is connected to the emitter of the bipolar transistor 292, and the cathode is simultaneously grounded by a capacitor (not shown). The collector of the bipolar transistor 1328921 292 is connected to the pulse width modulation control ft ▲ undervoltage-protection terminal 232 by the resistor R1, and the base thereof is connected to the cathode of the voltage regulator diode 294. The anode of the voltage stabilizing diode 294 is grounded by the resistor R2. Under the control of the field effect transistor 27, an external AC voltage is input to the two input terminals 211, 212 of the first rectifying and filtering circuit 21, through the first rectifying and filtering circuit 21, the isolated high frequency transformer 24, and the second The rectifying and filtering circuit 25 then outputs a DC voltage from the output terminal 250. When the voltage of the input terminals 211, 212 is lower than the minimum voltage of the input allowable input, the voltage of the second resistor 222 changes accordingly, and the voltage is fed back to the undervoltage protection terminal 232 of the pulse width modulation controller 23, The pulse width modulation controller 23 then enters the clamp protection state. When the voltage of the output terminal 250 exceeds the maximum voltage of the allowable output, the voltage of the secondary winding 242 of the isolated high frequency transformer 24 is correspondingly increased, and the auxiliary winding 243 is affected by the mutual inductance between the windings of the isolated high frequency transformer 24. The voltage is also increased accordingly. 'The voltage of the emitter of the bipolar transistor 292 increases with |, and the Zener diode 294 keeps the base voltage of the bipolar transistor 292 unchanged. The electric-voltage difference between the emitter and the base of the transistor 292 is increased, the bipolar transistor 292 is turned on, and the voltage fed back to the undervoltage protection terminal 232 of the pulse width modulation* controller 23 is also increased accordingly. The pulse width adjustment: the variable controller 23 compares the feedback voltage with its internal clamp voltage. When the clamp voltage is higher than its internal clamp voltage, the pulse width modulation controller 23 stops operating, thereby implementing an overvoltage protection function. . Compared with the prior art, the power supply circuit 20 of the present invention employs an overvoltage protection circuit composed of the diode 293, the bipolar transistor 292, the voltage regulator diode 294, and a small amount of resistors, 13 丄J厶29 can realize the overvoltage protection cut energy - "the cost of the power supply circuit 20. And the overvoltage protection work 2 = the deficiencies of the wide modulation controller 23, the application of the = 23 is also expanded. Month and control ^, the present invention has indeed met the requirements of (4), and the above is only the preferred embodiment of the present invention. The scope of the month is not limited to the above embodiment, and it is familiar with the case. The equivalent modifications or variations made by the person in accordance with the spirit of the present invention are intended to be included in the following claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing the circuit structure of a prior art power supply circuit. Schematic diagram of circuit structure of invention power supply circuit [Description of main component symbols] Power supply circuit 20 First rectification and filtering circuit 21 Pulse width modulation controller 23 Isolated high frequency transformer 24 Second rectification and filtering circuit 25 Transistor 27 Overvoltage protection Guard circuit 29 full bridge rectifier circuit 213 filter capacitor 214 14 1328921. f replace negative 丨 first resistor 221 second resistor 222 control terminal 231 undervoltage protection terminal 232 primary winding 241 secondary winding 242 auxiliary winding 243 current limiting resistor 270 bipolar Transistor 292 Diode 293 Regulator Diode 294 Input 211, 212 Output 250 ' 215 15