201134092 六、發明說明： 【發明所屬之技術領域】 本發明係關於-種開關電源晶片的啟動檢測保護電 路’特別是指-種在開關電源啟動前對輪出電壓進行檢測 並根據檢測結果適當放電的電路，使得輸出電壓能夠從〇 開始正常完整的啓動。 【先前技術】 請參考第-圖所示，-脈寬調製（PWM)開關電源晶片 的輸出級包含有串接的一主開關電晶體⑴）及一同步電晶 體(12)，兩者在串接節點上連接一輸出電感⑸及輸出電容 ()在輸出電谷上（C)為開關電源的輸出電壓（νουτ)。 爲了防止DC/DC㈤關電源啓動時輸出產生較大的電 f過沖和電感電流産生較大的浪汤電流，會在晶片中加入 -軟啓動控制’使輪出電壓和電感電流緩慢變化到預設 値。常用的-種控制方法是將—誤差放大器（圖中未示）的 正輸入端基準電餘0開始緩慢提升，通過環路調整使得 輪出跟隨基準電難〇逐漸升高至預設值，避免過沖。在 貫際應用中’輸出可能存在殘留電壓，並不是& 〇開始上 :。由於啓動過程屬於閉迴路控制，當晶片檢測到輪出反 貝的電壓高於該誤差放大器緩慢升高的基準電壓時，控制 路止圖通過導通同步電晶體（12)將輸出電壓（VOU 丁）拉 低，將會長時間打開同步電晶體（12)，使輸出經過電感和 同步電晶體（12)持續放電。 在這種情況下，同步電晶體（12)長時間導通，流過同 201134092 步電晶體（12)的反向電流非常大，增大了同步電晶體（12) 的損耗，以至超過其熱限制’嚴重時會損壞同步電晶體 (12)。所以希望能夠防止同步電晶體〇2)導通的時間太久， 持續流過過大的電流。 第二圖是現有的-種解決方案，在晶片準備啓動時對 一輸出反饋信號（FB)和一誤差放大器緩慢變化的基準電虔 (SSREF)進行比較，如果輸出反饋信號（FB)小於基準電壓 (SSREF)，晶片正常啓動；如果輸出反饋信號（fb)大於基 準電壓（SSREF)，則關斷主開關電晶體（24)和同步電晶體 ㈣。基準電壓（SSREF)仍然正常上升，直到高於輸出反 饋信號（FB)時’晶片進人啓動過程，主開關電晶體（2句和 同步電晶體（25)交替導通。這種方法可以避免輸出反饋信 號（FB)大於基準電壓（SSREF)時長時間導通同步電晶體 (叫。但輸出電壓（V0UT)上的預存電壓低於系統設定輸出 時’啓動過程的初始階段關斷輸出’使啓動過程中存在兩 種狀態的切換，容易造成啓動波形的不平滑。如果輸出電 C (VOUT)上的預存電壓高於系統的設定輸出時，在整個軟 啓動周期中關斷輸出，主開關電晶體(24)及同步電晶體(25) 不^開^軟啓動周期結束後才會通過環路將輸出調整 到預設值，調整過程中可能出現過沖。 第三圖是現有的另-種解決方案，利用一比較器（31) 對同步電晶體（34)上的電壓（sw)和接地電璧（gnd)進行比 & > 步電晶體（34)的電流進行檢測，當電流 降至0時關斷同步電晶體(34)，避免同步電晶體(34)反向 '々丨L過電流。但這錄士^ 種方法需要在晶片中增加一個同步電晶體 201134092 零電流檢測電路，增加了電路的複雜程度。 PCT申請案WO 2008/013871描述了 一種新的保護方 案，匕不對輸出電壓進行檢測，而是通過内部邏輯電路控 制同步電晶體的脈寬從小到大逐漸展開，避免同步電晶體 長時間導通。這種方法在輸出反饋信號（FB)高於 (SSREF)時仍可通過環路進行—u的調整，但㈣邏輯 過於複雜，不易實現。 【發明内容】 本發明之主要目的係提供了 一種脈寬調製（pwM)開關 電源晶片的輸出啟動檢測保護電路，㈣路結構簡單易實 現且整合於晶片内部，使晶片整個啓動過程均工作在完全 閉迴路控訂，實;見軟啓動⑽t常工作的平穩 過渡。 本發明包括-輸出反饋電壓檢測模組、一控制邏輯指 組、-放電電阻及一開關電晶體。輸出電壓反饋回來的驾 壓信號輸入到該比較器的負相輸入端，比較器的正相輪入 端接收-基準電壓，比較器的輸出信號送至一 rs正反器 的S端，兵反器的R端接收晶片内部的一使能控制信號 (Μ RS正反器的輸出端接反閘的輸入端，反閘的輪 出端接開關電晶體的柵極’開關電晶體的漏極接放電電阻 的-端，纟電電阻的另外一端接開關電源的一輸出電感。 本發明在啓動前對輸出電壓進行檢測並自輸出電感通 過該放電電阻及開關電晶體對輸出進行接地放電，使得輪 出電壓能夠從0開始正常完整的啓動。電路相對簡單，容 201134092 易實現。 本發明自輸出電感通過該放電電阻及開關電晶體對輸 出進行接地放電，而不是直接由輸出放電。—方面增加了 放電的阻尼係數，另一方面避免了可調輸出架構沒有輸出 (VOUT)璋而無法由輸出直接放電，使得本方法可以同時應 用於固定輸出和可調輸出兩種架構，增加了應用範圍。 【實施方式】 • 4參考第四圖所示，本創作是-開關電源晶片的啟動 輸出檢測保護電路’包含有一輸出反饋電壓檢測模組、一 控制邏輯模組、-放電電阻（44)及一開關電晶體（45)。 該輸出反饋電壓檢測模組由一比較器（41)構成，比較 器（41)的負相輸入端接收一反饋電壓（FB)，正相輸入端接 一内部基準信號（REF)，比較器（41)的輸出作爲該控制邏輯 模組的輸入。 • 該控制邏輯模組由一 RS正反器（42)及一反閘（43)組 成，正反器（42)具有一置位端（s)、一重定端（R)和一輸出 端（Q) ’由前述比較器（41)的輸出信號置位元，由一内部使 能信號（EN)重定，當内部使能信號（EN)為高準位時，晶片 停止工作；當内部使能信號（EN)為低準位時，晶片正常工 作。正反器（42)的輸出連接反閘（43)的輸入，經過反閘（43) 後控制該開關電晶體（45)。 反閘（43)的輸出接開關電晶體（45)的柵極，開關電晶 體（45)的源極接地，漏極接放電電阻（44)的一端，放電電 阻（44)的另一端接一輸出電感（匕）。輸出電感（匕）連接一輸出 201134092 電容⑹，在輸出電容的兩端並聯，電路，該分塵電路 以兩個分遷電阻（46)(47)串聯構成，分壓中點即提供反饋 電屋（FB)給比較器⑷）的負相輸入端。 §反饋電壓（FB)信號;低於内部基準電虔（re㈠時比 較器⑼輪出高電平’ RS正反器（42)輸出爲高電平，經過 反閘(43)反向後爲低電平，關斷放電通路；當反饋電壓㈣ 信號高於内部基準電壓（REF)時，比較器（41)輸出低電平， 正反|5(42)輸出爲低電平，經過反閘⑷)反向後爲高電 ’打開放電通路，通過放電電阻（44)和輸出電感㈨使輸 出對地放電。 前述兩個分廢電阻（46)(47)可整合在晶片内部而構成 冑’提„定式分壓比例；亦可將分壓電阻 )(47)不整合在晶片内部而是連接於晶片外部，構成一 可調式輸出架構，通過改變分壓電阻的比例來調節設定輸 出電壓’輸出電壓通過晶片的FB管腳回饋到内部電路。 雖然本發明經具體實施例作爲示例加以說明，但是應 該明確的是’本發明並不限於此處所公開的實施例，也不 能被認爲是對本發明權利要求的限制，如果其他人員依據 本發明做出了非實質性的改變和改進，皆屬於本發明權利 要求保護的範圍》 【圖式簡單說明】 輸出電感及電 第—圖：脈寬調製開關電源的輸出級和 容的連接電路圖。 第二圖：爲現有技術的啓動保護電路的示意圖 201134092 第三圖：爲現有技術的另一種啓動保護電路的示意 圖。 第四圖：爲本發明啓動輸出檢測保護電路的示意圖。 【主要元件符號說明】 (1 1)主開關電晶體 (12)同步電晶體 (21)誤差放大器 (24) 主開關電晶體 (25) 同步電晶體 (31)比較器 (34)同步電晶體 (41) 比較器 (42) RS正反器 (43) 反閘 (44) 放電電阻 (45) 開關電晶體 (46) (47)分壓電阻 t Si 8201134092 VI. Description of the Invention: [Technical Field] The present invention relates to a startup detection and protection circuit for a switching power supply chip, in particular, a detection of the wheel-out voltage before the switching power supply is started and appropriately discharging according to the detection result. The circuit allows the output voltage to start from a normal full start. [Prior Art] Please refer to the figure - the pulse-width modulation (PWM) switching power supply chip output stage includes a main switch transistor (1) connected in series and a synchronous transistor (12), both in the string An output inductor (5) and an output capacitor () are connected to the output node (C) as the output voltage (νουτ) of the switching power supply. In order to prevent the DC/DC (5) off power supply from starting, the output generates a large electric f overshoot and the inductor current generates a large wave current, and a soft start control is added to the wafer to make the wheel voltage and the inductor current slowly change to the pre- Set up. The commonly used control method is to slowly increase the reference input power residual 0 of the error amplifier (not shown), and adjust the loop to make the wheeling follow the reference power hard to gradually increase to the preset value, avoiding Overshoot. In a continuous application, the output may have a residual voltage, not & Since the startup process is closed loop control, when the wafer detects that the voltage of the anti-bounce is higher than the reference voltage of the error amplifier slowly rising, the control stop diagram outputs the voltage (VOU) by turning on the synchronous transistor (12). Pulling low will open the synchronous transistor (12) for a long time, causing the output to continue to discharge through the inductor and the synchronous transistor (12). In this case, the synchronous transistor (12) is turned on for a long time, and the reverse current flowing through the step transistor (12) of 201134092 is very large, which increases the loss of the synchronous transistor (12) and exceeds its thermal limit. 'Severe damage to the synchronous transistor (12). Therefore, it is desirable to prevent the synchronous transistor 〇2) from being turned on for too long, and excessive current is continuously flowing. The second figure is an existing solution that compares an output feedback signal (FB) with a slowly changing reference voltage (SSREF) when the wafer is ready to start, if the output feedback signal (FB) is less than the reference voltage (SSREF), the chip starts normally; if the output feedback signal (fb) is greater than the reference voltage (SSREF), the main switching transistor (24) and the synchronous transistor (4) are turned off. The reference voltage (SSREF) still rises normally until it is higher than the output feedback signal (FB). When the wafer enters the startup process, the main switching transistor (2 sentences and synchronous transistor (25) are alternately turned on. This method can avoid output feedback. When the signal (FB) is greater than the reference voltage (SSREF), the synchronous transistor is turned on for a long time (called. However, when the pre-stored voltage on the output voltage (V0UT) is lower than the system-set output, the initial phase of the startup process turns off the output]. There are two states of switching, which is easy to cause the starting waveform to be unsmooth. If the pre-stored voltage on the output C (VOUT) is higher than the set output of the system, the output is turned off during the entire soft-start period, the main switch transistor (24) ) and the synchronous transistor (25) will not adjust the output to the preset value through the loop after the soft start period is over, and overshoot may occur during the adjustment process. The third figure is an existing alternative solution. A comparator (31) is used to detect the voltage (sw) and the grounding voltage (gnd) on the synchronous transistor (34) compared to the current of the &> step transistor (34) when the current drops to zero. Shut down Step-up crystal (34), avoiding synchronous transistor (34) reverse '々丨L over-current. But this method requires adding a synchronous transistor 201134092 zero-current detection circuit to the wafer, which increases the complexity of the circuit. PCT Application WO 2008/013871 describes a new protection scheme, which does not detect the output voltage, but controls the pulse width of the synchronous transistor from small to large through internal logic to prevent the synchronous transistor from being turned on for a long time. This method can still perform the adjustment of -u through the loop when the output feedback signal (FB) is higher than (SSREF), but (4) the logic is too complicated and difficult to implement. SUMMARY OF THE INVENTION The main object of the present invention is to provide a The output of the pulse width modulation (pwM) switching power supply chip starts the detection and protection circuit. (4) The structure of the circuit is simple and easy to implement and integrated in the inside of the chip, so that the whole startup process of the wafer works in a completely closed loop control, and the soft start (10) is often worked. Smooth transition. The invention comprises an output feedback voltage detection module, a control logic finger set, a discharge resistor and a switching transistor. The driving feedback signal is input to the negative phase input terminal of the comparator, the normal phase wheel input terminal of the comparator receives the reference voltage, and the output signal of the comparator is sent to the S terminal of the rs positive and negative device, and the transactor is The R terminal receives an enable control signal inside the chip (Μ the output of the RS flip-flop is connected to the input of the reverse gate, and the gate of the reverse gate is connected to the gate of the switch transistor). The drain of the switching transistor is connected to the discharge resistor. The other end of the electric resistance is connected to an output inductor of the switching power supply. The invention detects the output voltage before starting and grounds the output from the output inductor through the discharge resistor and the switching transistor to make the output voltage Ability to start a normal full start from 0. The circuit is relatively simple, and the capacity of 201134092 is easy to implement. The present invention discharges the output from the output inductor through the discharge resistor and the switching transistor instead of directly discharging the output. - The aspect increases the damping coefficient of the discharge, and on the other hand avoids the adjustable output architecture without output (VOUT) 璋 and cannot be directly discharged by the output, so that the method can be applied to both the fixed output and the adjustable output. Application range. [Embodiment] • 4 Referring to the fourth figure, the creation is that the startup output detection protection circuit of the switching power supply chip includes an output feedback voltage detection module, a control logic module, a discharge resistor (44) and a Switch the transistor (45). The output feedback voltage detecting module is composed of a comparator (41), the negative phase input terminal of the comparator (41) receives a feedback voltage (FB), and the positive phase input terminal is connected to an internal reference signal (REF), and the comparator ( The output of 41) is used as an input to the control logic module. • The control logic module is composed of an RS flip-flop (42) and a reverse gate (43). The flip-flop (42) has a set terminal (s), a reset terminal (R) and an output terminal ( Q) 'The output signal of the aforementioned comparator (41) is set by the internal enable signal (EN). When the internal enable signal (EN) is at the high level, the chip stops working; when it is internally enabled When the signal (EN) is low, the chip works normally. The output of the flip-flop (42) is connected to the input of the reverse gate (43), and the switching transistor (45) is controlled after the reverse gate (43). The output of the reverse gate (43) is connected to the gate of the switch transistor (45), the source of the switch transistor (45) is grounded, the drain is connected to one end of the discharge resistor (44), and the other end of the discharge resistor (44) is connected. Output inductance (匕). The output inductor (匕) is connected to an output 201134092 capacitor (6), which is connected in parallel at both ends of the output capacitor. The circuit is formed by connecting two split resistors (46) (47) in series, and the feedback midpoint is provided by the voltage divider. (FB) to the negative phase input of comparator (4)). § Feedback voltage (FB) signal; lower than the internal reference voltage (re (a) when the comparator (9) turns high] RS positive and negative (42) output is high, after the reverse gate (43) reverse is low Ping, turn off the discharge path; when the feedback voltage (4) signal is higher than the internal reference voltage (REF), the comparator (41) outputs a low level, and the positive and negative |5 (42) outputs are low, after the reverse gate (4)) After the reverse, it is high-electrical' to open the discharge path, and the output is discharged to the ground through the discharge resistor (44) and the output inductor (9). The two waste resistors (46) (47) may be integrated into the interior of the wafer to form a predetermined voltage division ratio; or the voltage dividing resistor (47) may be integrated in the interior of the wafer but connected to the outside of the wafer. Forming an adjustable output architecture, adjusting the set output voltage by changing the ratio of the voltage dividing resistors. The output voltage is fed back to the internal circuit through the FB pin of the wafer. Although the invention is illustrated by way of example, it should be clear that The present invention is not limited to the embodiments disclosed herein, and is not to be construed as limiting the scope of the present invention. If other persons make insubstantial changes and improvements in accordance with the present invention, they are claimed. The scope of the figure [Simplified description of the figure] Output inductance and electricity - Figure: Connection diagram of the output stage and capacitance of the pulse width modulation switching power supply. Second figure: Schematic diagram of the startup protection circuit of the prior art 201134092 A schematic diagram of another startup protection circuit of the prior art. Fourth figure: A schematic diagram of the startup output detection protection circuit of the present invention. Main component symbol description] (1 1) main switch transistor (12) synchronous transistor (21) error amplifier (24) main switch transistor (25) synchronous transistor (31) comparator (34) synchronous transistor (41 Comparator (42) RS forward and reverse (43) reverse gate (44) discharge resistor (45) switching transistor (46) (47) voltage divider resistor t Si 8