1277855 九、發明說明： 【發明所屬之技術領域】 本發明係關於一種逆向電流保護電路，並且更特別 . 的是本發明關於一種逆向電流保護電路，其能夠在當交 換式電源供應器的輸入端短路時，保護交換式電源供應 裔内部電路元件，避免遭受由來自輸入濾波電容發出的 逆向電流所造成的傷害。 _ 【先前技術】 圖一顯示根據習知技術的交換式電源供應器的典 ' 型代表圖。圖一所示的交換式電源供應器100係由一輪 、 入電源1〇1(通常為一直流電壓）、一電磁干擾濾波器 (EMI filter) 102、一輸入濾波電容103、一極性偵測 器（polarity detector) 104、一突波電流限制器 (inrush current limiter) 105、一開關裝置 106 以及 一直流/直流轉換器（DC-DC converter) 107所組成。電 φ 磁干擾濾波器102係耦接至輸入電源101且其係用來消 除電路中所形成的差模噪音（differential mode noise) - 或共模噪音（common mode noise)。輸入濾、波電容103 係轉接至電磁干擾濾波器102且其係用來平順（smooth) 由輸入電源10所提供的輸入直流電壓·。開關裝置106 係耦接至輸入濾波電容103且通常係由一串級開關電晶 體電路（cascaded switching transistor circuit)所 完成，其係周來以交替的方式將輸入直流電壓耦接至直 流/直流轉換器107。直流/直流轉換器107係耦接至開 關裝置10 6且用來將輸入直流電壓轉換成一種或多種預 1277855 定的直流電壓以符合一系列的規格要求。極性偵測器 104係用來偵測輸入直流電壓的極性改變並且防止輸入 直流電壓的極性被反接。突波電流限制器105係用來避 免突波電流（inrush current)激增。 在正常工作時，輸入濾波電，容103會被完全充電以 便移除輸入直流電壓中的高頻諧波（high-frequency harmonics)。然而，若交換式電源供應器的輸入端短 路，輸入濾波電容103便會將所儲存的能量釋放出來， 並且在輸入濾波電容103至交換式電源供應器的輸入端 方向上的一個巨大逆向電流，便會經由位於輸入端附近 的内部電路元件流動開來，例如電磁干擾滤波器102、 極性偵測器104、突波電流限制器105以及開關裝置 106。這些内部電路元件對於逆向電流的衝擊浪湧是相 當難以招架的，並且若逆向電流的放電迴路無法立刻切 斷的話，這些内部電路元件將會燒毁。 因此，在輸入端發生短路的情形下，儲存於輸入濾 波電容中的能量便會釋放至交換式電源供應器的輸入 側，並且内部電路元件在沒有安全防護裝置的保護下將 會故障。 是以便有其趨勢來發展一種逆向電流保護電路，其 可在輸入端短路時保護交換式電源供應器的内部電路 元件，避免遭受起源於輸入濾波電容的逆向電流所引起 的傷害。 【發明内容】 本發明的一目的在於提供一逆向電流保護電路，用 1277855 以保護交換式電源供應器的内/ 短路時，避免遭受由輸人濾 ===端 引起的傷害。 久电合所釋放的迚向電流所 本發明的另一目的在於 _ 哭，豆運用 …人 、&供一父換式電源供應 二::Γ電流保護電路來保護内部電路元件避 免a又由於 >丑路的輸入端所引起的傷害。 根據本發明的主要祕，其提出— 應器，包含一輪入電源，用以提供一 jr 4* ^ ^ 3E m . 輸入電力；一電磁 干後濾波益，用以消除存留於電路中BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a reverse current protection circuit, and more particularly to a reverse current protection circuit that can be used at the input of a switched power supply. In the event of a short circuit, the switching circuit power supply internal circuit components are protected from damage caused by the reverse current from the input filter capacitor. _ [Prior Art] FIG. 1 shows a typical representation of a switched power supply according to the prior art. The switching power supply 100 shown in FIG. 1 is composed of a round, input power supply 1〇1 (usually a DC voltage), an electromagnetic interference filter (EMI filter) 102, an input filter capacitor 103, and a polarity detector. A (polarity detector) 104, an inrush current limiter 105, a switching device 106, and a DC-DC converter 107 are formed. The electrical φ magnetic interference filter 102 is coupled to the input power source 101 and is used to cancel differential mode noise formed in the circuit - or common mode noise. The input filter, wave capacitor 103 is switched to the electromagnetic interference filter 102 and is used to smooth the input DC voltage supplied by the input power source 10. The switching device 106 is coupled to the input filter capacitor 103 and is typically implemented by a cascaded switching transistor circuit that couples the input DC voltage to the DC/DC converter in an alternating manner. 107. The DC/DC converter 107 is coupled to the switching device 106 and is used to convert the input DC voltage to one or more pre-1277855 DC voltages to meet a range of specifications. The polarity detector 104 is used to detect the change in polarity of the input DC voltage and to prevent the polarity of the input DC voltage from being reversed. The surge current limiter 105 is used to avoid surges in the inrush current. During normal operation, the input filter is charged and the capacitor 103 is fully charged to remove high-frequency harmonics from the input DC voltage. However, if the input of the switched power supply is shorted, the input filter capacitor 103 will release the stored energy and a large reverse current in the direction of the input filter capacitor 103 to the input of the switched power supply, It will flow through internal circuit components located near the input, such as electromagnetic interference filter 102, polarity detector 104, surge current limiter 105, and switching device 106. These internal circuit components are relatively difficult to withstand surge currents in reverse currents, and if the reverse current discharge loop cannot be cut immediately, these internal circuit components will burn out. Therefore, in the event of a short circuit at the input, the energy stored in the input filter capacitor is released to the input side of the switched power supply, and the internal circuit components will fail without the protection of the safety guard. In order to have a tendency to develop a reverse current protection circuit that protects the internal circuit components of the switched power supply when the input is shorted, avoiding the damage caused by the reverse current originating from the input filter capacitor. SUMMARY OF THE INVENTION It is an object of the present invention to provide a reverse current protection circuit that protects the internal/short circuit of the switched power supply from damage caused by the input filter === terminal when 1277855 is used. Another purpose of the present invention is to cry, the bean use...man, & for a parent-type power supply two:: Γ current protection circuit to protect internal circuit components to avoid a > Damage caused by the input of the ugly road. According to the main secret of the present invention, it is proposed that the device includes a wheeled power supply for providing a jr 4* ^ ^ 3E m . input power; an electromagnetic dry filter benefit for eliminating the remaining in the circuit
噪音；-輪入渡波電容，用以平順該輪入匕曰：直J 轉1以將該輸人電力轉換成—個或多個預 一開關裝置’用來以交替的方式將輸入 包力耦接至直流/直流轉換器；以及一逆向電浐保罐電 路’用以保護内部電路元件避免遭受由 所釋放的逆向電顏引㈣㈣。該逆向電流紐電路 包含一電晶體開關，耦接至該輸入電源且呈伙 (⑽troi terminal)與至少兩個電流傳&導端 (current-conducting terminals); 一監控裝置，耦接 至該電晶體開關，用以監視跨接該電流傳導端的電壓極 性的改變，並且因應跨接該電流傳導端的電壓極性改變 產生一驅動信號；以及一信號耦合器，耦接於該電晶體 開關與該監控裝置之間，用以將該驅動信號耦接至該控 巧知以便將該電晶體開關截止，並且藉此阻斷該逆向電 流的放電迴路。 【實施方式】 1277855 體現本案特徵與優點的一些典型實施例將在後段 的說明中詳細敘述。應理解的是本案能夠在不同的態樣 上具有各種的變化，其皆不脫離本案的範圍，且其中的 說明及圖示在本質上係當作說明之用，而非用以限制本 案。 請參見圖二，其係圖例說明根據本發明的一較佳實 施例之具有逆向電流保護電路的交換式電源供應器的 電路圖。 / 如圖二所示，交換式電源供應器200包含一輸入電 源（通常為一直流電壓）201、一電磁干擾濾波器（EMI filter) 202、一輸入濾波電容203、一突波電流限制器 204、一開關裝置205、一直流-直流轉換器206以及一 逆向電流保護電路207。輸入電源201、電磁干擾濾波 器202、輸入濾波電容203、突波電流限制器204、開關 裝置205以及直流-直流轉換器206的功能與操作原理 皆與圖一的相對應物的功能與操作原理相類似，並且在 此中將他們的說明予以省略。 值得注意的是交換式電源供應器200,包含位於輸入 電源201與輸入濾波電容203之間的逆向電流保護電路 207。該逆向電流保護電路207主要係由一電晶體開關 31、一監控裝置32以及一信號耦合器33所組成。電晶 體開關31 —般係由一個單一的N型MOSFET或一個串級 N 型 MOSFET 電路（cascaded N-channel MOSFE1T circuit) 所組成，其係耦接至輸入電源2〇1。監控裝置32係耦接 至電晶體開關31且較佳者係由一電壓比較器所完成， 其中電壓比較器的一反向輸入端係耦接至電晶體開關 1277855 31 的一電流傳導端（current-conducting terminal) 311並且電壓比較器的一非反向輸入端係耦接至電晶體 開關31的另一個電流傳導端312。監控裝置32係用來 監視跨接於電流傳導端311，312上的電壓極性的改變， - 並且因應跨接於電流傳導端311，312上的電壓極性的改 . 變產生一驅動信號。信號耦合器33係耦接於電晶體開 關31與控裝置32之間，並且較佳者係由一 pNp型雙 極接面電晶體（PNP-type BJT)所完成。信號麵合器33 係用來將由監控裝置32所輸出的驅動信號耦接至電晶 • 體開關31的控制端以便控制電晶體開關31的開/關。 關於根據本發明的一較佳實施例之逆向電流保護電路 • 207的功能與操作原理，將詳細說明如下。 • 在正常操作時，輸入電流係由輸入電源2〇1的正輸 入端211流向負輸入端212,並且電晶體開關31會導通 (turn on)且在順向方向（forward directi〇n)上傳 導電流。也就是說，電流係由電晶體開關31的汲極端 312流向電晶體開關31的源極端311。此時，電晶體開 • 關31的汲極電壓大於電晶體開關31的源極電壓，並^ 因此電壓比較器32輸出一個HIGH信號至PNP型雙極接 • 面電晶體犯，該PNP型雙極接面電晶體33接著會截止 (turn 〇ff)。然而，倘若交換式電源供應器200的輸入 端短路時，輸入濾波電容203便藉由感應出與輸入電流 流動方向相反的一逆向電流來釋放其儲存的能量。因 此，電晶體開關31會導通（turn on)且在逆向方向 (reverse direction)上傳導電流，並且電晶體開關31 的源極電壓大於電晶體開關31的汲極電壓。因此，跨 接於電晶體開關31的電流傳導端上的電壓極性便會改 1277855 變，並且電壓比較器32輸出一個LOW信號作為一驅動 信號至PNP型雙極接面電晶體33。於是，雙極接面電 晶體33便會導通，並且藉此將驅動信號（LOW信號）耦 合至電晶體開關31的閘極端。因此，電晶體開關31會 被驅動信號所驅動且立刻截止。因此，起源於輸入濾波 電容203的逆向電流的放電迴路便會由截止的電晶體開 關31所阻斷，並且交換式電源供應器的内部電路元件 便可避開由於逆向電流的激增所引起的傷害。 縱使本發明已由上述之實施例詳細敘述而可由熟 悉本技藝之人士任施匠思而為諸般修飾，然皆不脫如附 申請專利範圍所欲保護者。 1277855 【圖式簡單說明】 圖一係為顯示根據習知技術的典型交換式電源供 應ι§的電路圖；以及 圖二係為顯示根據本發明之具有逆電流保護電路 / 的交換式電源供應器的一較佳實施例。 【主要元件符號說明】 100, 200交換式電源供應器 • 101，201輸入電源 102,202電磁干擾濾波器（EMI濾波器） — 103, 203輸入濾波電容 104極性偵測器 10 5，2 0 4突波電流限制裔 106,205開關裝置 107,206直流-直流轉換器 2 0 7逆向電流保護電路 31電晶體開關 • 32監控裝置 33信號麵合器 12Noise; - Wheeling into the wave capacitor to smooth the wheel 匕曰: straight J to 1 to convert the input power into one or more pre-switching devices' to force the input package in an alternating manner Connected to the DC/DC converter; and a reverse power tank circuit 'to protect the internal circuit components from being subjected to the reversed electrical junction (4) (4). The reverse current circuit includes a transistor switch coupled to the input power source and configured to (at least two current-conducting terminals) and at least two current-conducting terminals coupled to the power a crystal switch for monitoring a change in a polarity of a voltage across the current conducting end, and generating a driving signal according to a change in a polarity of the voltage across the current conducting end; and a signal coupler coupled to the transistor switch and the monitoring device And a discharge loop for coupling the drive signal to the control to turn off the transistor switch and thereby block the reverse current. [Embodiment] 1277855 Some typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It is to be understood that the present invention is capable of various modifications in the various aspects of the present invention and is not intended to Referring to Figure 2, there is shown a circuit diagram illustrating a switched power supply having a reverse current protection circuit in accordance with a preferred embodiment of the present invention. As shown in FIG. 2, the switching power supply 200 includes an input power source (usually a DC voltage) 201, an EMI filter 202, an input filter capacitor 203, and a surge current limiter 204. A switching device 205, a DC-DC converter 206, and a reverse current protection circuit 207. The functions and operating principles of the input power source 201, the electromagnetic interference filter 202, the input filter capacitor 203, the surge current limiter 204, the switching device 205, and the DC-DC converter 206 are the functions and operating principles of the corresponding objects of FIG. They are similar and their description will be omitted here. It is worth noting that the switched power supply 200 includes a reverse current protection circuit 207 between the input power source 201 and the input filter capacitor 203. The reverse current protection circuit 207 is mainly composed of a transistor switch 31, a monitoring device 32 and a signal coupler 33. The transistor switch 31 is typically comprised of a single N-type MOSFET or a cascaded N-channel MOSFE1T circuit coupled to the input supply 2〇1. The monitoring device 32 is coupled to the transistor switch 31 and is preferably implemented by a voltage comparator, wherein an inverting input of the voltage comparator is coupled to a current conducting end of the transistor switch 127875 31 (current -conducting terminal 311 and a non-inverting input of the voltage comparator is coupled to the other current conducting end 312 of the transistor switch 31. The monitoring device 32 is used to monitor changes in the polarity of the voltage across the current conducting ends 311, 312, and to generate a drive signal in response to changes in the polarity of the voltage across the current conducting ends 311, 312. The signal coupler 33 is coupled between the transistor switch 31 and the control device 32, and is preferably implemented by a pNp type bipolar junction transistor (PNP-type BJT). The signal combiner 33 is used to couple the drive signal outputted by the monitoring device 32 to the control terminal of the electromorph switch 31 to control the on/off of the transistor switch 31. The function and operational principle of the reverse current protection circuit 207 according to a preferred embodiment of the present invention will be described in detail below. • In normal operation, the input current flows from the positive input 211 of the input supply 2〇1 to the negative input 212, and the transistor switch 31 turns on and conducts in the forward direction (forward direct) Current. That is, the current flows from the 汲 terminal 312 of the transistor switch 31 to the source terminal 311 of the transistor switch 31. At this time, the gate voltage of the transistor on/off 31 is larger than the source voltage of the transistor switch 31, and thus the voltage comparator 32 outputs a HIGH signal to the PNP type bipolar junction surface transistor, the PNP type double The pole junction transistor 33 is then turned off (turn 〇 ff). However, if the input of the switched-mode power supply 200 is shorted, the input filter capacitor 203 releases its stored energy by inducing a reverse current that is opposite to the direction of flow of the input current. Therefore, the transistor switch 31 is turned on and conducts current in a reverse direction, and the source voltage of the transistor switch 31 is larger than the gate voltage of the transistor switch 31. Therefore, the polarity of the voltage across the current conducting end of the transistor switch 31 is changed to 1277855, and the voltage comparator 32 outputs a LOW signal as a driving signal to the PNP type bipolar junction transistor 33. Thus, the bipolar junction transistor 33 is turned on, and thereby the drive signal (LOW signal) is coupled to the gate terminal of the transistor switch 31. Therefore, the transistor switch 31 is driven by the drive signal and is turned off immediately. Therefore, the discharge circuit originating from the reverse current of the input filter capacitor 203 is blocked by the cut-off transistor switch 31, and the internal circuit components of the switched power supply can avoid the damage caused by the surge of the reverse current. . The present invention has been described in detail by the above-described embodiments, and may be modified by those skilled in the art, without departing from the scope of the appended claims. 1277855 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a typical switched power supply according to the prior art; and FIG. 2 is a diagram showing a switching power supply having a reverse current protection circuit according to the present invention. A preferred embodiment. [Main component symbol description] 100, 200 switching power supply • 101,201 input power supply 102, 202 electromagnetic interference filter (EMI filter) — 103, 203 input filter capacitor 104 polarity detector 10 5, 2 0 4 surge Current limiting 106,205 switching device 107,206 DC-DC converter 2 0 7 reverse current protection circuit 31 transistor switch 32 monitoring device 33 signal interface 12