200929818 九、發明說明： * 【發明所屬之技術領域】 本發明是有關於一種升降壓轉換器，特別是指一種直 流電壓轉直流電壓的升降壓轉換器。 【先前技術】 現今的電子設備，例如PDA、MP3 player等可攜式設 備或汽車的電子設備，它們所需的電源電壓各自不同，因 此都需要電壓轉換器來將電池電壓轉換成所需的電源電壓 〇 。 隔離式的升降壓轉換器有相當多種類，例如buck-boost 轉換器、Cuk轉換器、SEPIC轉換器、Zeta轉換器等，以 buck-boost轉換器來說，它工作於連續導通模式（CCM， Continuous Current Mode)時有右半平面零點（One right-half plane zero)，致使它的控制器參數較難設計，穩定性也較差 ，而且負載暫態響應較慢。 另外如Cuk轉換器、SEPIC轉換器、Zeta轉換器，它 © 們不只有上述buck-boost轉換器的缺點，而且還需要兩個 電感來實現電路，如此多增加了轉換器的體積。 【發明内容】 因此，本發明之目的，即在提供一種暫態響應快且輸 出漣波小的升降壓轉換器。 於是，本發明升降壓轉換器是電連接於一電源及一負 載之間，包含一順向導通元件、一第一開關元件、一電感 、一第二開關元件、一第三開關元件、一第一電容、一第 200929818 四開關元件及一第二電容。 順向導通元件具有一與該電源電連接的第一端，及一 第二端。 第一開關元件具有一與該順向導通元件的第二端電連 接的第一端、一第二端，及一與該順向導通元件的第一端 電連接的第三端。 電感具有一與該第一開關元件的第二端電連接的第一 端，及一與該負載電連接的第二端。 〇 第二開關元件，具有一與該順向導通元件的第一端電 連接的第一端，及一第二端。 第三開關元件具有一與該第二開關元件的第二端電連 接的第一端，及一接地的第二端。 第電谷疋電連接於該順向導通元件的第二端與該第 二開關元件的第二端之間。 第四開關元件具有一與該第—開關元件的第二端電連 接的第一端，及一接地的第二端。 Ο 第二電容具有與該負載的兩端電連接的一第一端及一 第二端。 當第二開關元件導通且該第三、第四開關元件不導通 時，該順向導通元件不導通，而該第一開關元件導通，使 得電流由該電源依序流經該第二開關元件、該第一電容及 該第一開關元件而對該電感及該第二電容充電；當第二開 關兀件不導通且該第三、第四開關元件同時導通時，該順 向導通7G件被導通，而該第一開關元件不導通，使得電流 200929818 由該電源依序流經該順向導通元件、該第—電容及該第三 開關兀件而對該第—電容充電，並使該電感產生一反電動 勢向該第二電容充電。 【實施方式】 有關本發明之前述及其他技術内容、特點與功效，在 以下配合參考圖式之一個較佳實施例的詳細說明中，將可 清楚的呈現。 ❹200929818 IX. INSTRUCTIONS: * Technical Field of the Invention The present invention relates to a buck-boost converter, and more particularly to a buck-boost converter for a DC voltage to DC voltage. [Prior Art] Today's electronic devices, such as PDAs, MP3 players and other portable devices or automotive electronic devices, require different power supply voltages, and therefore require a voltage converter to convert the battery voltage to the required power source. Voltage 〇. There are quite a number of isolated buck-boost converters, such as buck-boost converters, Cuk converters, SEPIC converters, Zeta converters, etc. For buck-boost converters, it operates in continuous conduction mode (CCM, Continuous Current Mode) has a right-half plane zero, which makes its controller parameters difficult to design, has poor stability, and has a slow load transient response. In addition, such as Cuk converter, SEPIC converter, Zeta converter, it is not only the shortcomings of the above buck-boost converter, but also requires two inductors to implement the circuit, which increases the size of the converter. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a buck-boost converter having a fast transient response and a small output chopping. Therefore, the buck-boost converter of the present invention is electrically connected between a power source and a load, and includes a forward conducting component, a first switching component, an inductor, a second switching component, a third switching component, and a first A capacitor, a 200929818 four-switch component and a second capacitor. The forward conducting component has a first end electrically coupled to the power source and a second end. The first switching element has a first end electrically connected to the second end of the forward conducting element, a second end, and a third end electrically coupled to the first end of the forward conducting element. The inductor has a first end electrically coupled to the second end of the first switching element and a second end electrically coupled to the load. The second switching element has a first end electrically connected to the first end of the forward conducting element and a second end. The third switching element has a first end electrically coupled to the second end of the second switching element and a grounded second end. The first valley is electrically connected between the second end of the forward conducting element and the second end of the second switching element. The fourth switching element has a first end electrically connected to the second end of the first switching element and a grounded second end. Ο The second capacitor has a first end and a second end electrically connected to both ends of the load. When the second switching element is turned on and the third and fourth switching elements are not turned on, the forward conducting element is not turned on, and the first switching element is turned on, so that current flows from the power source through the second switching element in sequence, The first capacitor and the first switching element charge the inductor and the second capacitor; when the second switch component is non-conducting and the third and fourth switching components are simultaneously turned on, the forward-conducting 7G device is turned on And the first switching element is not turned on, so that the current 200929818 is sequentially flowed by the power source through the forward conducting component, the first capacitor and the third switching component to charge the first capacitor, and the inductor is generated A counter electromotive force charges the second capacitor. The above and other technical contents, features, and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments. ❹
參閱圖1，本發明升降壓轉換器100的較佳實施例是電 連接於-電源91及一負載92之間’其功用是將電源9ι供 給的直流電壓Vin轉換成另一個直流輸出電壓U施加於 負載92上。本實施例升降壓轉換器1〇〇包含一順向導通元 件1、-第-開關元件2、一電感3、一第二開關元件4、 -第三開關元件5、一第一電容6、一第四開關元件7及— 第二電容8。上述的元件皆具有一第一端u、幻、m …、以及-第二端12、22、32、42、52、72、82。(作 第一電容6之兩端未編號) 一順向導通元件1的第—端11是與電源91電連接，其第 一端12是與第一開關元件2 、 叼第端21電連接。在本营 施例中，順向導通元件1為二 +頁 一極體，如飛輪二極體， 第一端11為P極，第二端12為η極。 、 第一開關元件2的第二端a ,# ^ β 是與電感3的第一端31 相連，其還具有一與順向導通.元 干1的第一端11電遠垃 第三端23。在本實施例中，第一 接的 開關兀*件2為Ρ型金 場效電晶體（P-MOS)，其第三^ 2 金氧+ 端23為閘極，第一端以為源 200929818 極，第二端22為汲極，第—端21與第二端22之間更反向 連接一個二極體9，以利未導通時放電之用。 電感3的第一端32是與負載92電連接，且與第二電 谷8的第一端81相連，而第二電容8的第二端82為接地 且與負載92電連接。 第二開關元件4與第三開關元件5為串接，其中，第 二開關元件4的第一端41與順向導通元件丨的第一端u電Referring to Figure 1, a preferred embodiment of the buck-boost converter 100 of the present invention is electrically coupled between a power source 91 and a load 92. The function of which is to convert the DC voltage Vin supplied from the power source 9 to another DC output voltage U. On the load 92. The buck-boost converter 1A of the present embodiment includes a forward conduction element 1, a first-switching element 2, an inductor 3, a second switching element 4, a third switching element 5, a first capacitor 6, and a first The fourth switching element 7 and the second capacitor 8. The above components all have a first end u, a magical, m ..., and - a second end 12, 22, 32, 42, 52, 72, 82. (The two ends of the first capacitor 6 are not numbered.) The first end 11 of the forward conducting element 1 is electrically connected to the power source 91, and the first end 12 thereof is electrically connected to the first switching element 2 and the first end 21. In the present embodiment, the forward conduction element 1 is a two-page one-pole body, such as a flywheel diode, the first end 11 is a P-pole, and the second end 12 is an η-pole. The second end a, #^β of the first switching element 2 is connected to the first end 31 of the inductor 3, and further has a third end 23 electrically connected to the first end 11 of the pass-through element 1 . In this embodiment, the first switch 兀* 2 is a Ρ-type gold field effect transistor (P-MOS), and the third ^ 2 gold oxygen + terminal 23 is a gate, and the first end is a source 200929818 pole The second end 22 is a drain, and a diode 9 is connected in a reverse direction between the first end 21 and the second end 22 to facilitate discharge when not conducting. The first end 32 of the inductor 3 is electrically coupled to the load 92 and to the first end 81 of the second valley 8, while the second end 82 of the second capacitor 8 is grounded and electrically coupled to the load 92. The second switching element 4 and the third switching element 5 are connected in series, wherein the first end 41 of the second switching element 4 and the first end of the forward conducting element u are electrically
連接，其第二端42與第三開關元件5的第一端51電連接 ，而第三開關元件5的第二端52則是接地。在本實施例中 ’第二、第三開關元件4、5皆為N型金氧半場效電晶體 (N MOS)，其第-端41、51皆為源極，第二端42、52皆為 汲極，且皆具有一為閘極的第三端43、53，其閘極皆受一 個控制電路99控制，以決定第二、第三開關元件4、5的Connected, its second end 42 is electrically coupled to the first end 51 of the third switching element 5 and the second end 52 of the third switching element 5 is grounded. In the present embodiment, the second and third switching elements 4 and 5 are all N-type MOS field-effect transistors (N MOS), and the first ends 41 and 51 are all sources, and the second ends 42 and 52 are It is a drain, and both have a third end 43 and 53 which are gates, and their gates are controlled by a control circuit 99 to determine the second and third switching elements 4, 5.
導通與否。另外，它們的第-端41、51與第二端“I 之間皆分別反向連接-個二極體9，以利未導通時放電之用 。而在第二開關元件4與第三開關元件5的串接處電連接 有一個第-電容6,第-電容6的另—端則電連接於順向導 通兀件1的第二端12。 _第四開關元件7的第一端71是與第一開關元件2的第 —端22電連接’其第二端72接地，如同第二、第三開關 :件二、5,第四開關元件7也是㈣金氧半場效電晶體， j 一端為源極’第二端72驗極，另具有—為間極 、第二端73 ’此閘極也受控制電路99控制，以決定第四開 關元件7的導通與否。另外，它的第—端7ι與第二端μ 200929818 之間也反向連接一個二極體9，以利未導通時放電之用。 參閱圖2,圖中的箭頭方向為電流的流動方向，假設第 一電谷6上已具有一等於輸入電壓Vin的跨壓，此時由控制 電路99輸出脈寬調變（PWM)訊號導通第二開關元件4且使 第二、第四開關兀件5、7不導通時，由於第一電容6的跨 壓為電源9丨的輸入電壓Vin且第二開關元件4的兩端41、 42間無壓差’所以第-開關元件2的第一端21(源極）與第 三端23(閘極）間的壓差等於第一電容6的跨壓，第一開 關元件2因此被導通。電流由電源91依序流經第二開關元 件4、第-電容6及第—開關元件2而對電〇及第二電容 8充電，以提供輸出電壓給負載92。下面以交流小訊 號分析電感3的跨壓及流經第二電容8的電流：電感3的 第-端Μ的電壓為第一電容6的跨壓、加上電源Μ輸入Turn on or not. In addition, their first ends 41, 51 and the second end "I are respectively connected in reverse to each of the diodes 9 for the purpose of discharging when not conducting. And in the second switching element 4 and the third switch The series connection of the component 5 is electrically connected to a first capacitor 6, and the other end of the first capacitor 6 is electrically connected to the second end 12 of the forward conduction element 1. The first end 71 of the fourth switching element 7 Is electrically connected to the first terminal 22 of the first switching element 2, the second terminal 72 of which is grounded, like the second and third switches: two, five, the fourth switching element 7 is also (four) gold oxide half field effect transistor, j One end is the source 'second end 72 detector pole, and the other is - the interpole, the second end 73'. This gate is also controlled by the control circuit 99 to determine whether the fourth switching element 7 is turned on or off. A diode 9 is also connected in reverse between the first end 7ι and the second end μ 200929818 to facilitate discharge when not conducting. Referring to Fig. 2, the direction of the arrow is the flow direction of the current, assuming the first electric The valley 6 already has a voltage across the input voltage Vin. At this time, the control circuit 99 outputs a pulse width modulation (PWM) signal to turn on the second switching element 4 and When the second and fourth switching elements 5 and 7 are not turned on, since the voltage across the first capacitor 6 is the input voltage Vin of the power source 9丨 and the voltage difference between the two ends 41 and 42 of the second switching element 4 is The voltage difference between the first terminal 21 (source) and the third terminal 23 (gate) of the switching element 2 is equal to the voltage across the first capacitor 6, and the first switching element 2 is thus turned on. The current is sequentially supplied by the power source 91. The second switching element 4, the first capacitor 6 and the first switching element 2 are passed to charge the power and the second capacitor 8 to provide an output voltage to the load 92. The cross-voltage and current of the inductor 3 are analyzed by an alternating current signal. The current through the second capacitor 8: the voltage at the first terminal of the inductor 3 is the voltage across the first capacitor 6, plus the power supply Μ input
G 以得到電感3的跨壓為l! = 2v dt * ~ 電壓、(即〜)，其第二端32的電壓為輸出電壓，所 • · · (1) ’其中，L為 電感3的值；而流經第二電容8的電流為流經電感3的電 流減去流經負載92的電流，即生^ V(ju 1 . · (2) ’ 其中 ，C為第二電容8的值，r 们值R為負載92的值，i為流經電感3 的電流。 參閱圖 ，圖中的箭頭方向為電流的流動方向， 此時由 9 200929818 . 控制電路99輸出脈寬調變（PWM)訊號導通第三、第四開關 5、7 το件且使第二開關元件4不導通，此時順向導通元件 1被導通’所以第-開關元件2的第一端21(源極）與第三端 23(閘極）間的壓差為零’第一開關元件2因此不導通。電流 由電源91依序流經順向導通元件j、第一電容6及第三開 關％件5而對該第一電容6充冑，同時電感3 0為第一開 〇 關兀件2被關閉而產生一反電動勢向第二電容8持續充電 下面同樣以交流小訊號分析電感3的跨壓及流經第二 電容8的電流：由於第四開關元件7導通，所以電感3兩 端的跨壓就等於負的第二電容8的跨壓（即負的輸出電壓卜 即，所以得到電感3的跨壓為L| = _v_· · ·(3);而流 經第二電容8的電流與前述計算方式相同，即c企:^ = ·G is to obtain the voltage across the inductor 3 as l! = 2v dt * ~ voltage, (ie ~), and the voltage at the second terminal 32 is the output voltage, ? · · · (1) 'where L is the value of the inductor 3 And the current flowing through the second capacitor 8 is the current flowing through the inductor 3 minus the current flowing through the load 92, that is, ^ V (ju 1 . · (2) ' where C is the value of the second capacitor 8, r The value R is the value of the load 92, and i is the current flowing through the inductor 3. Referring to the figure, the direction of the arrow is the flow direction of the current, at this time by 9 200929818. The control circuit 99 outputs the pulse width modulation (PWM). The signal turns on the third and fourth switches 5, 7 and causes the second switching element 4 to be non-conducting. At this time, the forward conducting element 1 is turned on. Therefore, the first end 21 (source) of the first switching element 2 and the first The voltage difference between the three terminals 23 (gate) is zero. The first switching element 2 is therefore not turned on. The current flows from the power source 91 through the forward conduction element j, the first capacitor 6 and the third switch % member 5 in sequence. The first capacitor 6 is charged, and the inductor 30 is turned off to generate a counter electromotive force to the second capacitor 8 to continue charging. The voltage across the inductor 3 and the current flowing through the second capacitor 8 are analyzed: since the fourth switching element 7 is turned on, the voltage across the inductor 3 is equal to the voltage across the negative second capacitor 8 (ie, the negative output voltage) Therefore, the voltage across the inductor 3 is L| = _v_· · · (3); and the current flowing through the second capacitor 8 is the same as the previous calculation, that is, c: ^ =
dt R 私 .·⑷。 假設第二開關元件4的導通週期為D，則第三、第四開 關兀件5、7的導通週期就是卜〇，由於第一開關元件2與 第一開關元件4同步，所以其導通週期也是D。根據伏秒平 衡（即電感3的充電量等於其放電量）及⑴(2)⑶⑷式可以得 到直流輸入電壓vin與直流輸出電壓V()ut間的關係： V〇Ut/Vin=2D。由於導通週期〇的大小是介於〇跟1之間， 所以可以得知輸出電壓與輸入電壓的比是介於0到2之間 ’另外’當導通週期D大於〇.5時，此時2D大於1，所以 10 200929818 • 是升壓，相反地’當導通週期D小於0.5時，2D小於1 , 此時為降壓。 圖4為四個開關元件2、4、5、7的第三端23、43、53 、73 (間極）的驅動訊號’其中⑷為第二開關元件4的閘極 驅動訊號，⑻為第三開關元件5的問極驅動訊號，⑷為第 -開關元件2的閘極驅動訊號，⑷為第四開關元件7的問 極驅動訊號。由圖中可看出，_)的訊號是同步的，表示 帛三、第四開關元件5、7是同時導通同時關閉；另外， ⑷⑷的訊號是同步的，因為第一開關元件2是p_M〇s，第 二開關元件4是N_MOS，所以兩者的閘極驅動訊號的高低 電位恰好相反，當⑷圖是高電位時，⑼圖則是低電位，如 此也表示第-、第二開關元件2、4是同時導通同時關閉的 〇 參閱圖5，圖中⑷為電感3的跨壓圖形，⑻為流經電 感3的電流圖形，⑷為第一電容6的跨壓圖形⑷為流經 Q 第一電容6的電流圖形。由（b)可以觀察到，流經電感3的 電流是連續導通模式（Continuous Current Mode，CCM)，所 以證實本升降壓轉換器100係工作於連續導通模式。 參閱圖6與® 7，在輸入電壓為lov的情況下，圖6⑷ 所示為加載致能訊號，（b)所示為空載至滿載的輸出電壓暫 態波形，圖7(a)所示為卸載致能訊號，（b)所示為滿載至空 載的輸出電壓暫態波形；由圖中可以觀察到，輸出電壓暫 態回復時間相當的短。再參閱圖8與圖9，此兩圖是在輸入 電壓為16V的情況下所量測，其（a)(b)圖形的意義是與圖6 200929818 ' 、圖7的相同，故不贅述，由圖中同樣可以觀察到，輸出 電壓暫態回復時間相當的短。 綜上所述，本發明結構簡單，相當易於實現，且由於 是工作在連續導通模式，所以輸出電壓的漣波可以大大減 小，即使輸入電壓的變動較大也能壓制住輸出電壓的漣波 大小，再者，由圖6〜圖9也可證實其輸出電壓暫態回復時 間相當的短，故確實能達成本發明之目的。 惟以上所述者，僅為本發明之較佳實施例而已，當不 〇 能以此限定本發明實施之範圍，即大凡依本發明申請專利 範圍及發明說明内容所作之簡單的等效變化與修飾，皆仍 屬本發明專利涵蓋之範圍内。 【圖式簡單說明】 圖1疋一電路示意圖，說明本發明的一較佳實施例電 連接於一電源及一負載之間； 圖2是一電路示意圖，說明該較佳實施例的電流流向 9 ® 圖3疋一電路不意圖，說明該較佳實施例的電流流向 9 圖4是一示意圖，說明第一、第二、第三、第四開關 元件的第三端（閘極）的驅動訊號； 圖5是一示意圖，說明電感及第一電容的電壓、電流 圖形； 圖6是一示意圖，說明輸入電壓為1〇v時，輸出電壓 的暫態波形（加載時）； 12 200929818 圖7是一示意圖，說明輸入電壓為10V時，輸出電壓 的暫態波形（卸載時）； 圖8是一示意圖，說明輸入電壓為16V時，輸出電壓 的暫態波形（加載時）；及 圖9是一示意圖，說明輸入電壓為16V時，輸出電壓 的暫態波形（卸載時）。Dt R private .·(4). Assuming that the conduction period of the second switching element 4 is D, the conduction period of the third and fourth switching elements 5, 7 is a dilemma. Since the first switching element 2 is synchronized with the first switching element 4, the conduction period is also D. The relationship between the DC input voltage vin and the DC output voltage V() ut can be obtained according to the volt-second balance (i.e., the amount of charge of the inductor 3 is equal to its discharge amount) and (1)(2)(3)(4): V〇Ut/Vin=2D. Since the conduction period 〇 is between 〇 and 1, it can be known that the ratio of the output voltage to the input voltage is between 0 and 2 'other' when the on-period D is greater than 〇.5, at this time 2D More than 1, so 10 200929818 • is boost, conversely 'when the on-period D is less than 0.5, 2D is less than 1, and this is buck. 4 is a driving signal of the third ends 23, 43, 53, 73 of the four switching elements 2, 4, 5, and 7 (wherein (4) is a gate driving signal of the second switching element 4, and (8) is The gate driving signal of the three switching element 5, (4) is the gate driving signal of the first switching element 2, and (4) is the gate driving signal of the fourth switching element 7. As can be seen from the figure, the signal of _) is synchronous, indicating that the third and fourth switching elements 5, 7 are simultaneously turned on and off at the same time; in addition, the signals of (4) (4) are synchronized because the first switching element 2 is p_M〇 s, the second switching element 4 is N_MOS, so the high and low potentials of the gate driving signals of the two are opposite. When the (4) picture is high, the (9) pattern is low, thus also indicating the first and second switching elements 2 4 is simultaneously turned on and off at the same time. Referring to Figure 5, (4) is the cross-voltage pattern of the inductor 3, (8) is the current pattern flowing through the inductor 3, and (4) is the cross-voltage pattern of the first capacitor 6 (4) is flowing through the Q A current pattern of a capacitor 6. It can be observed from (b) that the current flowing through the inductor 3 is a continuous current mode (CCM), and it is confirmed that the buck-boost converter 100 operates in the continuous conduction mode. Referring to Figures 6 and 7, 7, when the input voltage is lov, Figure 6 (4) shows the load enable signal, and (b) shows the output voltage transient waveform from no load to full load, as shown in Figure 7(a). To unload the enable signal, (b) shows the output voltage transient waveform from full load to no load; as can be seen from the figure, the output voltage transient recovery time is quite short. Referring to FIG. 8 and FIG. 9 again, the two figures are measured under the condition that the input voltage is 16V, and the meaning of the (a)(b) pattern is the same as that of FIG. 6 200929818 ' and FIG. 7, so it will not be described. It can also be observed from the figure that the output voltage transient recovery time is quite short. In summary, the present invention has a simple structure and is relatively easy to implement, and since it operates in a continuous conduction mode, the chopping of the output voltage can be greatly reduced, and the chopping of the output voltage can be suppressed even if the input voltage fluctuates greatly. The size, and further, it can be confirmed from Fig. 6 to Fig. 9 that the output voltage transient recovery time is relatively short, so that the object of the present invention can be achieved. However, the above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, that is, the simple equivalent change of the patent application scope and the description of the invention is Modifications are still within the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram illustrating a preferred embodiment of the present invention electrically connected between a power source and a load; FIG. 2 is a circuit diagram illustrating current flow to the preferred embodiment. FIG. 3 is a schematic diagram showing the current flow direction of the preferred embodiment. FIG. 4 is a schematic diagram showing driving signals of the third end (gate) of the first, second, third, and fourth switching elements. Figure 5 is a schematic diagram showing the voltage and current patterns of the inductor and the first capacitor; Figure 6 is a schematic diagram showing the transient waveform of the output voltage (loading) when the input voltage is 1 〇 v; 12 200929818 Figure 7 A schematic diagram illustrating the transient waveform of the output voltage when the input voltage is 10V (when unloading); Figure 8 is a schematic diagram showing the transient waveform of the output voltage (loading) when the input voltage is 16V; and Figure 9 is a Schematic diagram showing the transient waveform of the output voltage (when unloading) when the input voltage is 16V.
13 20092981813 200929818
【主要元件符號說明】 1 順向導通元件 51 第一端 11 第一端 52 第二端 12 第二端 53 第三端 100 升降壓轉換器 6 第一電容 2 第一開關元件 7 第四開關元件 21 第一端 71 第一端 22 第二端 72 第二端 23 第三端 73 第三端 3 電感 8 第二電容 31 第一端 81 第一端 32 第二端 82 第二端 4 第二開關元件 9 二極體 41 第一端 91 電源 42 第二端 92 負載 43 第三端 99 控制電路 5 第三開關元件 14[Main component symbol description] 1 forward conduction element 51 first end 11 first end 52 second end 12 second end 53 third end 100 buck-boost converter 6 first capacitor 2 first switching element 7 fourth switching element 21 First end 71 First end 22 Second end 72 Second end 23 Third end 73 Third end 3 Inductance 8 Second capacitor 31 First end 81 First end 32 Second end 82 Second end 4 Second switch Element 9 Diode 41 First end 91 Power supply 42 Second end 92 Load 43 Third end 99 Control circuit 5 Third switching element 14