丄项265 九、發明說明： 【發明所屬之技術領域】 本發明係關於一種背光保護電路。 【先前技術】 液晶顯示器具輕、薄 '耗電小等優點，因此被廣泛應 :於筆記型電腦、行動電話、個人數位助理等現代化資訊 設備。由於液晶顯示器中之液晶分子本身並不發光，因此 液晶顯示ϋ需借助-背紐組發光來實現圖像顯示，通常 =光模組需要一背光保護電路來驅動工作，當背光模組之 月光燈苔工作出現思外，造成該背光保護電路之負載開路 時，該脈寬調變積體電路需一背光開路保護電路使其停止 工作。 一請參閱圖1，係一種先前技術背光保護電路之電路結 冓示〜、囷°亥月光保濩電路1〇〇包括一脈寬調變積體電路 110、一逆變器13〇、一背光燈組15〇、一第一反饋電路1糾、 一第二反饋電路160及一保護控制電路170。該脈寬調變 積體電路110輸出背光調節訊號至該逆變器130，該逆變 益130接收該背光調節訊號以驅動該背光燈組15〇發光， ^第一、第二反饋電路14〇、16〇分別反饋該背光燈組15〇 高壓端的電壓及低壓端的電流以輸出一第一反饋訊號及一 第一反饋sfl號至該脈寬調變積體電路丨丨〇。該脈寬調變積 體電路110依據該第二反饋訊號調節輸入該背光燈組15〇 之工作電壓’且依據該第一反饋訊號於該背光燈組150開 路時開啟該保護控制電路170。 1379265 該背光燈組150包括一第一燈管151及一第二燈管 152。該第一燈管151及該第二燈管152均包括一高壓端及 一低壓端。該脈寬調變積體電路11〇包括一訊號輪出端 111、一電流反饋端113、一保護輸出端115及一電壓反饋 端116。該訊號輸出端ln連接至該逆變器13〇。該電壓反 饋端116連接該第一反饋電路14〇，該電流反饋端ii3連 接至該第二反饋電路160，該保護輸出端115則連接至該 保護控制電路170。 Λ 該逆變器130分別驅動該背光燈組15〇之第一燈管 151及第二燈管152,其包括一訊號接收端131、一第一驅 動端132及一第二驅動端133。該訊號接收端ΐ3ι與該脈 寬調變積體電路110之訊號輸出端i丨丨連接以接收該背光 調節訊號。該第一驅動端132連接該第一燈管151之高壓 端，驅動該第一燈管151，該第一燈管151接收為15( 的高壓交流電。該第二驅動端133連接該第二燈管152之 咼壓端’驅動該第二燈管152,該第二燈管152接收負15卯 伏的反向高壓交流電。 、 該第一反饋電路140包括二高壓反饋接收端141及一 高壓反饋輸出端142。該高壓反饋接收端141連接气第— 燈管⑸及-第二燈管152之高壓端，該高壓反饋：出端 142則連接該脈寬調變積體電路11()之電壓反饋端lb。 即，該第一反饋電路140分別接收該第一燈管151及一第 二燈管152高壓端之電壓’並轉換為第—反饋訊號輸出至 該脈寬調變積體電路no之電壓反饋端116。 1379265 該該第二反饋電路160包括一電流接收端161及一低 壓反饋輸出端162。該電流接收端161連接該第一燈管151 及第一燈管152之低壓端，該低壓反饋輸出端162則連 接該脈寬調變積體電路11〇之電流反饋端113,第二反饋 電路160分別接收該第一及第二燈管15卜152之低壓端之 電流，亚輸出與該工作電流對應之第二反饋訊號至該脈寬 調變積體電路11 〇。 該保護控制電路170包括一第一電阻171及一電容 172。該第一電阻171 一端連接該脈寬調變積體電路之保護 輸出端115，另一端經由該電容172接地。該第一電阻i7i 用以控制該電容17 2之充電時間。 當该背光燈組150之一燈管損壞，該背光保護電路1〇〇 出現背光開路狀況時，該電流接收端161接收之電流降 低，則5亥第二反饋電路i 6〇輸出至該脈寬調變積體電路工i 〇 之第二反饋訊號變低’該脈寬調變積體電路丨1()判別該第 二反饋訊號低於其内設之低壓參考電壓後，將調高其輸出 之该背光調節訊號之占空比’以使該逆變器13〇輸出更高 之工作電壓至該背光燈組150，從而該背光燈組150第一 燈官151之高壓端與第二燈管152之高壓端之電壓差變 大。同時’該第一反饋電路14〇將對應增大之第一反饋訊 號輸出至該脈寬調變積體電路11〇,該脈寬調變積體電路 110判斷該第一反饋訊號高於其内設之高壓壓參考電壓， 其藉由該保護輪出端115輸出充電訊號，開始對該保護控 制電路170之電容172進行充電’當該電容172充滿時， 8 1379265 該脈寬調變積體電路110之保護輪出端ιΐ5之電壓達到3 伏^脈^調變積體電路110停止輸出背光調節訊號至該 ，該逆變器13G停止為該背光燈組i5Q提供工 電壓，該背先二燈組150停止工作以保護該背光燈組15〇。 料惟：電容172需要一定充電時間才能被充滿電，以 吏:玄脈寬調變積體電路u。停止輸出充電訊號至該電容 亚停止輸出背光調節訊號。&，在此充電時間内，該 =調電路U〇仍然根據該第二反饋訊號過小，繼 ^南其輸出之背光調節訊號之占空比，從而進—步增大 且150同壓南壓端之電壓。過於增大的電壓將易 光燈組15G高_的打火放電，使得該背光保護 電路100之可靠性較低。 【發明内容】 有鑑於此’提供一種可靠性較高之背光保護電路實為 〇 :背光保護電路’編一背光燈組、一脈寬調變積 _ 第一反饋電路、一逆變器及一保護控制電路， =寬=變積體電路輸出背光調節訊號；該逆變器接收該 二光調節況唬以輪出驅動電壓驅動該背光燈組；該第一反 二電路根據°亥月光燈組高壓端之電壓產生—第一反饋訊 =姓β玄保4控制電路分別與該脈寬調變積體電路及該第一 貝電路电連接，且其内部設置一參考電壓丨該保護控制 二路於°亥帛反饋訊號高於該參考電壓時，控制該脈寬調 邊積體電路停止輸出背光調節訊號。 1379265 一背光保護電路，其包括一背光燈組、一脈寬調變積 體電路、一第一反饋電路、一逆變器及一保護控制電路， 該脈寬調變積體電路輸出背光調節訊號；該逆變器接收該 背光調節訊號以輸出驅動電壓驅動該背光燈組；該第一反 饋電路根據該背光燈組高壓端之電壓產生一第一反饋訊 號；該保護控制電路接收該第一反饋電路輸出之第一反饋 訊號以控制該脈寬調變積體電路是否直接停止輸出背光調 節訊號。 相較於先前技術，該背光保護電路之保護控制電路於 該第一反饋訊號高於該參考電壓時，控制該脈寬調變積體 電路直接停止輸出背光調節訊號，無須等待一段充電時 間’防止發生在充電時間内該脈寬調變積體電路繼績調rfj 該背光燈組之工作電壓而引發的背光電路發生打火放電的 現象，從而提高該背光保護電路之可靠性。 【實施方式】 請參閱圖2，係背光保護電路第一實施方式之電路結 構示意圖。該背光保護電路200包括一脈寬調變積體電路 210、一逆變器230、一背光燈組250、一第一反饋電路240、 一第二反饋電路260及一保護控制電路270。該脈寬調變 積體電路210輸出背光調節訊號至該逆變器230，該逆變 器230接收該背光調節訊號以驅動該背光燈組250發光。 該第一反饋電路240根據該背光燈組250之高壓端之電壓 輸出第一反饋訊號至該脈寬調變積體電路210及該保護控 制電路270。該第二反饋電路260根據該背光燈組25 0之 1379265 ％流輪出—第二反饋訊號至該脈寬調變積體電路 =脈見調變積體電路21G依據該第二反饋訊號調節輸 上月，燈組250之工作電壓。該脈寬調變積體電路21〇 二制電路270依據該第一反镇訊號於該背光燈組 250開路時保護該背光燈組250。 該背光燈組250包括一第一燈管251及一第二燈管 252 ^第燈官251及該第二燈管252均包括一高壓端及 一低壓端。、該服寬調變積體電路21〇包括一訊號輸出端 211 电机反饋端213、一保護輸出端215及一電壓反饋 ，216，且其内部設置一低壓參考電壓及一高壓壓參考電 ，。該訊號輸出端211連接至該逆變器23〇 ;該電流反饋 端213連接該第二反饋電路26〇，以接收該第二反饋訊號； 忒電壓反饋端216連接該第一反饋電路24〇，以接收該第 一反饋訊號；該保護輸出端215則連接至該保護控制電路 270。遠脈寬調變積體電路21〇係採用型號為〇z9938之積 體電路。 s亥逆變器230包括一訊號接收端23 1、一第一驅動端 232及一第二驅動端233。該訊號接收端231與該脈寬調變 積體電路210之訊號輸出端211連接以接收該背光調節訊 號。该第一驅動端232連接該第一燈管251之高壓端，用 于輸出驅動電歷至該第一燈管251之高壓端，該驅動電壓 一般為1500伏的尚壓交流電。該第二驅動端233連接該第 一燈管252之南壓’用于輸出反向的驅動電壓至該第二 燈管252之向壓知’该反向的驅動電壓一般為負1500伏的 11 1379265 高壓交流電。 古該第一反饋電路240包括二高壓反饋接收端241及一 同=反饋輸出端242。該高壓反饋接收端241連接該第一 燈& 251及—第二燈管252之高壓端，該高壓反饋輪出端 242則連接該脈寬調變積體電路21〇之電壓反饋端216。 該第二反饋電路260包括一電流反饋端261及一低壓 反饋輸出端262。該電流反饋端261連接該第一燈管251 及第二燈管252之低壓端，該低壓反饋輸出端262則連 接5亥脈寬調變積體電路210之電流反饋端213。 該保護控制電路270包括一充電支路i及一比較電路 272。該比較電路272控制該充電支路1導通或斷開。該充 電支路1包括一限流電阻271、一開關單元278及一充電 電谷279。該限流電阻271 —端連接該脈寬調變積體電路 210之保護輸出端2丨5 ’另一端依序經由該開關單元278 及該充電電容279接地。該開關單元278為一二極體，其 包括一正極（未標示）及一負極（未標示），該正極與該限流電 阻271連接，該負極連接該比較電路272及該充電電容 279。 該比較電珞272包括一比較器273、一第一分壓電阻 R11、一第二分壓電阻R12及一高壓訊號端277。該比較器 273包括一正向輸入端274、一反向輸入端275及一輸出端 276。該高壓訊號端277經由該第一分壓電阻R11及該第 二分壓電阻R12接地，該比較器273之正向輸入端274連 接於該第一分壓電阻Rl 1及該第二分壓電阻R12之間，以 12 1379265 此言又疋该正向輸人端274為πϋ-參考 電壓大於或等於該脈寬調變積體電路21〇内之高壓壓參考 電壓。該比較器273之反向輸入端275則連接至該第二反 饋電路240之高壓反饋輸出端242以接 饋訊號:該比較器273之輸出端276連接;== 之開關單元278與該充電電容279之間。 ^該背光燈組250之任意一燈管損壞，該背光保護電 路200出現背光開路狀況時，該第二反饋電路26〇接收之 该背光燈組250之低壓端之電流變低，則該第二反饋電路 260輸出之第二反饋訊號對應變小，該脈寬調變積體電路 21〇接收該第二反饋訊號，並與其内設之低壓參考電壓進 仃比對，判斷該第二反饋訊號低於該低壓參考電壓，該脈 寬=變積體電路210輸出之背光調節訊號的占空比變大， 以提高該背光燈組250高壓端之電壓。同時，該第一反饋 私路240反饋該背光燈組25〇之高壓端之電壓，並輸出與 其對應的第一反饋訊號至該脈寬調變積體電路21〇之電壓 反饋端216及該比較電路272之反向輸入端275。該脈寬 調=積體電路210判斷該第一反饋訊號高於該高壓壓參考 ^壓’該脈寬調變積體電路21〇啟動高壓保護，藉由其保 瘦輪出端215輸出充電訊號至該保護控制電路27〇，即該 =電訊號經由該限流電阻271及該開關單元278對該充電 ，容279進行充電。同時，該比較電路272亦對其接收之 第。反饋訊號進行判別’當該第一反饋訊號高於該第一參 考電壓時’該比較器273輸出高電壓至該開關單元278， 13 1379265 該開關單it 278反向截止，則該脈寬調變積體電路2ι〇停 止輸出充電訊號至該充電支路丨，從而該脈寬調變積體電 路210之内部電路將控制其保護輸出端215之電壓迅速到 達3伏，該脈寬調變積體電路21〇停止輸出背光調節訊號 至該逆變器230 ’則該背光燈組25〇關閉，從而防止該背 光燈組250之高壓端出現打火放電。 相較於先前技術，該背光保護電路2〇〇之保護控制電 路270，括一比較電路272及一開關單元278，該比較= 路272藉由比較該第一反饋訊號與其内設置第一參考電壓 的大小，以控制該充電支路丨於該第一反饋訊號大於該第 參考電壓時斷開，該脈寬調變積體電路2丨〇停止輸出背 光調節訊號，則該背光燈組250關閉’其高壓端的電壓不 會繼續升高而出現放電的現象，從而提高該背光保護電路 200之可靠性。 “請參閱圖3，係本發明背光保護電路第二實施方式之 電路結構示意圖。該背光保護電路则較該背光保護電路 200之不同之處在於：該保護控制電路37〇包括一限流電 阻37卜-比較電路372、一開關單元378及―充電電^ 37\該限流電阻371 一端連接該脈寬調變積體電路則 之保護輸出端315，另一端依序經由該充電電容379及該 開關單元378接地以形成-充電支路2。胃比較電路奶 控制該充電支路2導通或斷開。該開關單元378為開關電 晶體，其為- NM0S型晶體管，包括—閘極、—源極及一 汲極，其閘極與該比較電路372連接，其汲極連接至該充 1379265 電電容379，其源極直接接地。 «•亥保濩控制電路37〇之比較電路372接收哕 電路州輸出之第-反饋訊號，並與其 ^ = ^ =比較’當該第一反饋訊號大於該第一丄壓：電 。比較電路372截止該開關電晶體，以斷開該第二 :二=脈寬調變積體電路310停止輸出充電訊號i 以充電支路2’從而該脈寬調變積體電路3i〇之 將控制其保護输出端315之電壓迅速到達3伏，該脈= 變積體電路21G停止輸出背光調節訊號至該逆變器33〇了 則該背光燈組350關閉’從而防止該背光燈組 端出現打火放電。 (冋& 惟丄本發明不限於上述實施方式，該背光保護電路之 電电谷了 „又置於戎開關單元3 7 8與該接地端之間，只須 保證，充電支路的導通或斷開受該比較電路的控制即^。、 綜上所述，本發明確已符合發明專利之要件，爰依法 提出申請專利。惟’以上所述者僅係本發明之較佳實施方 式，士發明之範圍並不以上述實施方式爲限，舉凡熟悉本 2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係先前技術之背光保護電路之電路結構示意圖。 Θ 2係本發明背光保護電路第一實施方式之電路結構示意 圖0 圖3係本發明背光保護電路第二實施方式之電路結構示意 15 1379265 圖。 【主要元件符號說明】 充電支路 脈寬調變積體電路210、 電流反饋端 電壓反饋端 訊號接收端 弟—驅動端 第一燈管 高壓反饋接收端 第二燈管 電流反饋端 保護控制電路 270、 比較電路 272、 正向輸入端 輸出端 開關單元 m 第一分壓電阻 背光保護電路 訊號輸出端 保護輸出端 逆變器 第一驅動端 第一反饋電路 高壓反饋輸出端 第一燈管 第二反饋電路 低壓反饋輸出端 背光保護電路 200 ' 300 訊號輪出端 211 保護輸出端 215 ' 315 逆變器 230 、 330 第一驅動端 232 背光燈組 250 ' 350 第一反饋電路 240 ' 340 高壓反饋輸出端 242 第二反饋電路 260 低壓反饋輪出端 262 限流電阻 271 、 371 比較器 273 反向輸入端 275 高壓訊號端 277 充電電容 279 ' 379 第二分壓電阻 R12 脈寬調變積體電路 i J 〇 電流反饋端 113 電壓反饋端 116 訊號接收端 131 第.一驅動端 133 高壓反饋接收端 141 背光燈組 150 第二燈管 152 電流接收端 161 保護控制電路 170 1379265 172 第一電阻 171 電容 17Item 265 IX. Description of the Invention: [Technical Field of the Invention] The present invention relates to a backlight protection circuit. [Prior Art] Liquid crystal display devices are light and thin, and have low power consumption. Therefore, they are widely used: modern information devices such as notebook computers, mobile phones, and personal digital assistants. Since the liquid crystal molecules in the liquid crystal display do not emit light by themselves, the liquid crystal display does not need to be illuminated by the back-group illumination, and usually the optical module needs a backlight protection circuit to drive the work, and the backlight module is used as a moonlight. When the work of the moss is unexpected, when the load of the backlight protection circuit is open, the pulse width modulation integrated circuit needs a backlight open circuit protection circuit to stop working. Please refer to FIG. 1 , which is a circuit diagram of a prior art backlight protection circuit. The 亥°海月光保濩 circuit 1〇〇 includes a pulse width modulation integrated circuit 110, an inverter 13〇, and a backlight. The lamp group 15A, a first feedback circuit 1 and a second feedback circuit 160 and a protection control circuit 170. The pulse width modulation integrated circuit 110 outputs a backlight adjustment signal to the inverter 130, and the inverter benefit 130 receives the backlight adjustment signal to drive the backlight group 15 to emit light, and the first and second feedback circuits 14〇 And 16〇 respectively feedback the voltage of the high voltage end of the backlight group 15〇 and the current of the low voltage end to output a first feedback signal and a first feedback sfl number to the pulse width modulation integrated circuit 丨丨〇. The pulse width modulation integrated circuit 110 adjusts the input voltage of the backlight group 15 依据 according to the second feedback signal and turns on the protection control circuit 170 when the backlight group 150 is opened according to the first feedback signal. 1379265 The backlight unit 150 includes a first tube 151 and a second tube 152. The first lamp tube 151 and the second lamp tube 152 each include a high voltage end and a low voltage end. The pulse width modulation integrated circuit 11A includes a signal wheel output terminal 111, a current feedback terminal 113, a protection output terminal 115 and a voltage feedback terminal 116. The signal output terminal ln is connected to the inverter 13A. The voltage feedback terminal 116 is coupled to the first feedback circuit 14A, the current feedback terminal ii3 is coupled to the second feedback circuit 160, and the protection output terminal 115 is coupled to the protection control circuit 170. The inverter 130 drives the first lamp 151 and the second lamp 152 of the backlight unit 15 respectively, and includes a signal receiving end 131, a first driving end 132 and a second driving end 133. The signal receiving terminal ΐ3ι is connected to the signal output terminal i of the pulse width modulation integrated circuit 110 to receive the backlight adjustment signal. The first driving end 132 is connected to the high voltage end of the first lamp tube 151 to drive the first lamp tube 151. The first lamp tube 151 receives 15 high voltage alternating current. The second driving end 133 is connected to the second lamp. The second end of the tube 152 drives the second tube 152, and the second tube 152 receives a reverse high voltage alternating current of 15 volts. The first feedback circuit 140 includes two high voltage feedback receiving ends 141 and a high voltage feedback. The high-voltage feedback receiving end 141 is connected to the high-voltage end of the gas-light tube (5) and the second tube 152, and the high-voltage feedback: the output end 142 is connected to the voltage of the pulse width modulation integrated circuit 11 () The feedback terminal lb, that is, the first feedback circuit 140 receives the voltages of the high voltage terminals of the first lamp tube 151 and the second lamp tube 152 respectively, and converts them into a first feedback signal output to the pulse width modulation integrated circuit no. The voltage feedback terminal 116. The second feedback circuit 160 includes a current receiving end 161 and a low voltage feedback output end 162. The current receiving end 161 is connected to the low voltage end of the first lamp tube 151 and the first lamp tube 152. The low voltage feedback output terminal 162 is connected to the pulse width modulation integrated circuit 1 a current feedback terminal 113, the second feedback circuit 160 receives the currents of the low voltage terminals of the first and second lamps 15 152, and outputs a second feedback signal corresponding to the working current to the pulse width modulation. The protection circuit 170 includes a first resistor 171 and a capacitor 172. The first resistor 171 has one end connected to the protection output 115 of the pulse width modulation integrated circuit, and the other end is grounded via the capacitor 172. The first resistor i7i is used to control the charging time of the capacitor 17 2. When one of the backlights 150 is damaged, the backlight receiving circuit 1 receives a backlight open condition, and the current receiving terminal 161 receives the current. When the voltage is lowered, the second feedback circuit i 6 〇 output to the pulse width modulation circuit circuit i 第二 second feedback signal goes low 'the pulse width modulation integrated circuit 丨 1 () discriminates the second feedback After the signal is lower than the built-in low voltage reference voltage, the duty ratio of the output of the backlight adjustment signal is increased to enable the inverter 13 to output a higher operating voltage to the backlight group 150, thereby Backlight group 150 first lamp officer 151 high voltage The voltage difference from the high voltage terminal of the second lamp tube 152 becomes larger. At the same time, the first feedback circuit 14 outputs a correspondingly increased first feedback signal to the pulse width modulation integrated circuit 11 〇, the pulse width modulation The expansion circuit 110 determines that the first feedback signal is higher than the built-in high voltage reference voltage, and the protection wheel output terminal 115 outputs a charging signal to start charging the capacitor 172 of the protection control circuit 170. When the capacitor 172 is full, 8 1379265, the voltage of the protection wheel terminal ιΐ5 of the pulse width modulation integrated circuit 110 reaches 3 volts, and the modulation integrated circuit 110 stops outputting the backlight adjustment signal to the inverter 13G. The backlight group i5Q is supplied with a working voltage, and the back first lamp group 150 stops working to protect the backlight group 15〇. Note: Capacitor 172 requires a certain charging time to be fully charged, so that: 玄: Xuan pulse wide adjustment variable body circuit u. Stop outputting the charging signal to the capacitor to stop outputting the backlight adjustment signal. &, during this charging time, the = adjustment circuit U 〇 is still too small according to the second feedback signal, followed by the output of the backlight adjustment signal duty cycle, thereby increasing step by step and 150 pressing south pressure The voltage at the end. An excessively large voltage discharges the ignition light of the light group 15G high, making the backlight protection circuit 100 less reliable. SUMMARY OF THE INVENTION In view of the present invention, a backlight protection circuit with high reliability is provided: a backlight protection circuit ́s a backlight group, a pulse width modulation product _ a first feedback circuit, an inverter and a Protection control circuit, = width = variable integrated circuit output backlight adjustment signal; the inverter receives the two light adjustment condition to drive the backlight group by driving the driving voltage; the first inverse two circuit is based on the moonlight group The voltage of the high voltage terminal is generated - the first feedback signal = the last name of the β Xuanbao 4 control circuit is electrically connected to the pulse width modulation integrated circuit and the first shell circuit, and a reference voltage is internally set. The protection control circuit When the feedback signal is higher than the reference voltage, the pulse width adjustment integrated circuit stops controlling the output of the backlight adjustment signal. 1379265 A backlight protection circuit comprising a backlight group, a pulse width modulation integrated circuit, a first feedback circuit, an inverter and a protection control circuit, wherein the pulse width modulation integrated circuit outputs a backlight adjustment signal Receiving the backlight adjustment signal to output the driving voltage to drive the backlight group; the first feedback circuit generates a first feedback signal according to the voltage of the high voltage end of the backlight group; the protection control circuit receives the first feedback The first feedback signal of the circuit output controls whether the pulse width modulation integrated circuit directly stops outputting the backlight adjustment signal. Compared with the prior art, the protection control circuit of the backlight protection circuit controls the pulse width modulation integrated circuit to directly stop outputting the backlight adjustment signal when the first feedback signal is higher than the reference voltage, without waiting for a charging time to prevent The phenomenon that the backlight circuit generates a sparking discharge caused by the operating voltage of the backlight group during the charging time of the pulse width modulation integrated circuit is adjusted, thereby improving the reliability of the backlight protection circuit. [Embodiment] Please refer to FIG. 2, which is a schematic diagram of a circuit structure of a first embodiment of a backlight protection circuit. The backlight protection circuit 200 includes a pulse width modulation integrated circuit 210, an inverter 230, a backlight group 250, a first feedback circuit 240, a second feedback circuit 260, and a protection control circuit 270. The pulse width modulation circuit 210 outputs a backlight adjustment signal to the inverter 230. The inverter 230 receives the backlight adjustment signal to drive the backlight group 250 to emit light. The first feedback circuit 240 outputs a first feedback signal to the pulse width modulation integrated circuit 210 and the protection control circuit 270 according to the voltage of the high voltage terminal of the backlight group 250. The second feedback circuit 260 flows out according to the 1379265% of the backlight group 25—the second feedback signal to the pulse width modulation integrated circuit=the pulse modulation integrated circuit 21G adjusts the input according to the second feedback signal. Last month, the operating voltage of the lamp set 250. The pulse width modulation integrated circuit 21 保护 the second circuit 270 protects the backlight group 250 when the backlight group 250 is opened according to the first reverse signal. The backlight unit 250 includes a first tube 251 and a second tube 252. The second lamp unit 251 and the second tube 252 each include a high voltage end and a low voltage end. The service wide adjustment variable circuit 21 includes a signal output terminal 211, a motor feedback terminal 213, a protection output terminal 215, and a voltage feedback 216, and a low voltage reference voltage and a high voltage reference power are internally disposed. The signal output terminal 211 is connected to the inverter 23〇; the current feedback terminal 213 is connected to the second feedback circuit 26〇 to receive the second feedback signal; and the voltage feedback terminal 216 is connected to the first feedback circuit 24〇. The first feedback signal is received; the protection output 215 is connected to the protection control circuit 270. The far-wave wide-width transformer circuit 21 is an integrated circuit of the type 〇z9938. The s-inverter 230 includes a signal receiving end 23 1 , a first driving end 232 and a second driving end 233 . The signal receiving end 231 is coupled to the signal output terminal 211 of the pulse width modulation transformer circuit 210 to receive the backlight adjustment signal. The first driving end 232 is connected to the high voltage end of the first lamp tube 251 for outputting the driving power to the high voltage end of the first lamp tube 251. The driving voltage is generally 1500 volts of AC voltage. The second driving end 233 is connected to the south voltage of the first lamp tube 252 for outputting a reverse driving voltage to the second lamp tube 252. The driving voltage of the reverse direction is generally negative 1500 volts. 1379265 High voltage alternating current. The first feedback circuit 240 includes two high voltage feedback receiving ends 241 and a same = feedback output terminal 242. The high voltage feedback receiving end 241 is connected to the high voltage end of the first lamp & 251 and the second lamp tube 252. The high voltage feedback wheel output end 242 is connected to the voltage feedback end 216 of the pulse width modulation integrated circuit 21〇. The second feedback circuit 260 includes a current feedback terminal 261 and a low voltage feedback output 262. The current feedback terminal 261 is connected to the low voltage terminals of the first lamp tube 251 and the second lamp tube 252. The low voltage feedback output terminal 262 is connected to the current feedback terminal 213 of the 5th pulse width modulation integrated circuit 210. The protection control circuit 270 includes a charging branch i and a comparison circuit 272. The comparison circuit 272 controls the charging branch 1 to be turned on or off. The charging branch 1 includes a current limiting resistor 271, a switching unit 278, and a charging valley 279. The current limiting resistor 271 is connected to the protection output terminal 2丨5 ′ of the pulse width modulation integrated circuit 210, and the other end is grounded via the switching unit 278 and the charging capacitor 279 in sequence. The switch unit 278 is a diode including a positive electrode (not shown) and a negative electrode (not shown). The positive electrode is connected to the current limiting resistor 271, and the negative electrode is connected to the comparison circuit 272 and the charging capacitor 279. The comparator 272 includes a comparator 273, a first voltage dividing resistor R11, a second voltage dividing resistor R12 and a high voltage signal terminal 277. The comparator 273 includes a forward input 274, an inverted input 275, and an output 276. The high voltage signal terminal 277 is grounded via the first voltage dividing resistor R11 and the second voltage dividing resistor R12. The forward input terminal 274 of the comparator 273 is connected to the first voltage dividing resistor R11 and the second voltage dividing resistor. Between R12 and 12 1379265, the forward input terminal 274 is π ϋ - the reference voltage is greater than or equal to the high voltage reference voltage in the pulse width modulation integrated circuit 21 〇. The inverting input terminal 275 of the comparator 273 is connected to the high voltage feedback output terminal 242 of the second feedback circuit 240 to receive the signal: the output terminal 276 of the comparator 273 is connected; the switching unit 278 of the == and the charging capacitor Between 279. ^ Any one of the backlights of the backlight unit 250 is damaged. When the backlight protection circuit 200 is in an open state, the second feedback circuit 26 receives the current of the low voltage terminal of the backlight unit 250, and the second The second feedback signal outputted by the feedback circuit 260 is correspondingly small. The pulse width modulation integrated circuit 21 receives the second feedback signal and compares it with the low voltage reference voltage set therein to determine that the second feedback signal is low. At the low voltage reference voltage, the duty cycle of the backlight adjustment signal output by the pulse width=variable circuit circuit 210 is increased to increase the voltage of the high voltage terminal of the backlight group 250. At the same time, the first feedback private path 240 feeds back the voltage of the high voltage end of the backlight group 25〇, and outputs a corresponding first feedback signal to the voltage feedback end 216 of the pulse width modulation integrated circuit 21〇 and the comparison. Inverting input 275 of circuit 272. The pulse width adjustment=the integrated circuit 210 determines that the first feedback signal is higher than the high voltage reference voltage, and the pulse width modulation integrated circuit 21 starts the high voltage protection, and outputs the charging signal through the thin wheel output end 215 thereof. To the protection control circuit 27, that is, the = electrical signal is charged by the current limiting resistor 271 and the switching unit 278, and the capacitor 279 is charged. At the same time, the comparison circuit 272 also receives the first. The feedback signal determines that 'when the first feedback signal is higher than the first reference voltage', the comparator 273 outputs a high voltage to the switch unit 278, 13 1379265, the switch unit it 278 is reverse-cut, and the pulse width modulation The integrated circuit 2 〇 stops outputting the charging signal to the charging branch 丨, so that the internal circuit of the pulse width modulation integrated circuit 210 controls the voltage of the protection output terminal 215 to rapidly reach 3 volts, and the pulse width modulation integrated body The circuit 21 〇 stops outputting the backlight adjustment signal to the inverter 230 ′, and the backlight group 25 〇 is turned off, thereby preventing the high-voltage end of the backlight group 250 from being spark-discharged. Compared with the prior art, the protection control circuit 270 of the backlight protection circuit 2 includes a comparison circuit 272 and a switch unit 278. The comparison = path 272 is set by comparing the first feedback signal with a first reference voltage. The size of the backlight group is controlled to be turned off when the first feedback signal is greater than the first reference voltage, and the pulse width modulation integrated circuit 2 stops outputting the backlight adjustment signal, and the backlight group 250 is turned off. The voltage at the high voltage end does not continue to rise and a discharge phenomenon occurs, thereby improving the reliability of the backlight protection circuit 200. Please refer to FIG. 3 , which is a schematic diagram of a circuit structure of a second embodiment of the backlight protection circuit of the present invention. The backlight protection circuit is different from the backlight protection circuit 200 in that the protection control circuit 37 includes a current limiting resistor 37 . a comparison circuit 372, a switching unit 378, and a charging current controller 371 are connected at one end to the protection output terminal 315 of the pulse width modulation integrated circuit, and the other end is sequentially connected via the charging capacitor 379 and the The switch unit 378 is grounded to form a charging branch 2. The stomach comparison circuit milk controls the charging branch 2 to be turned on or off. The switching unit 378 is a switching transistor, which is a -NMOS transistor, including a gate, a source a pole and a drain, the gate of which is connected to the comparison circuit 372, the drain of which is connected to the charge 1379265 capacitor 379, the source of which is directly grounded. «•Haibao control circuit 37〇 comparison circuit 372 receives the circuit The state outputs a feedback signal and compares it with ^ = ^ = 'When the first feedback signal is greater than the first voltage: electricity. The comparison circuit 372 turns off the switching transistor to turn off the second: two = pulse Wide adjustment The circuit 310 stops outputting the charging signal i to charge the branch 2' so that the pulse width modulation integrated circuit 3i will control the voltage of its protection output terminal 315 to quickly reach 3 volts, and the pulse=variant circuit 21G stops outputting the backlight When the inverter signal 33 is adjusted, the backlight group 350 is turned off to prevent the ignition group from being ignited and discharged. (冋& However, the present invention is not limited to the above embodiment, and the backlight protection circuit is electrically The electric valley is placed between the switch unit 377 and the ground terminal, and it is only necessary to ensure that the conduction or disconnection of the charging branch is controlled by the comparison circuit, that is, the present invention does Having met the requirements of the invention patent, and applying for a patent according to law. However, the above description is only a preferred embodiment of the present invention, and the scope of the invention is not limited to the above embodiment, and those who are familiar with the second technology # Equivalent modifications or variations made 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 backlight protection circuit of the prior art. FIG. 3 is a schematic diagram of a circuit structure of a second embodiment of a backlight protection circuit according to the present invention. FIG. 3 is a schematic diagram of a circuit structure of a second embodiment of the present invention. [Characteristics of Symbols of Main Components] A charging branch pulse width modulation integrated circuit 210, Current feedback terminal voltage feedback terminal signal receiving terminal - driving terminal first lamp high voltage feedback receiving terminal second lamp tube current feedback terminal protection control circuit 270, comparison circuit 272, forward input terminal output terminal switching unit m first partial pressure Resistance backlight protection circuit signal output protection output inverter inverter first drive terminal first feedback circuit high voltage feedback output terminal first lamp second feedback circuit low voltage feedback output terminal backlight protection circuit 200 '300 signal wheel output 211 protection output End 215 '315 inverter 230, 330 first drive end 232 backlight set 250' 350 first feedback circuit 240' 340 high voltage feedback output 242 second feedback circuit 260 low voltage feedback wheel output 262 current limiting resistor 271, 371 Comparator 273 Inverting input 275 High voltage signal terminal 277 Charging capacitor 279 ' 379 Dividing resistor R12 Pulse width modulation integrated circuit i J 〇 Current feedback terminal 113 Voltage feedback terminal 116 Signal receiving terminal 131 First driving terminal 133 High voltage feedback receiving terminal 141 Backlight group 150 Second lamp 152 Current receiving end 161 Protection Control Circuit 170 1379265 172 First Resistor 171 Capacitor 17