201250660 六、發明說明： 【發明所屬之技術領域】 本發明係有關於一種顯示裝置及其背光模組，尤指一種顯示裝 置及其可降低電路板面積需求之背光模組。 【先前技術】 平面顯示裝置(Flat Panel Display ; FPD)是目前廣泛使用的顯示 器，其具有外型輕薄、省電以及低輻射等優點，故被廣泛地應用於 電腦螢幕、行動電話、個人數位助理（PDA)、平面電視等電子產品 上。平面顯示裝置的工作原理係藉由改變晝素的透光性配合背光模 組所提供的光源以顯示影像。亦即，背光模組係為平面顯示裝置執 行顯示運作的關鍵性元件。第1圖為習知背光模組的示意圖。如第 1圖所示’習知背光模組100包含背板10丨、設置於背板1〇1之第一 板面的複數發光單元(未顯示）、以及設置於背板1〇1之第二板面的 印刷電路板110，其中印刷電路板110具有複數電流匯流(current sink) 單元111與直流/直流轉換器112。複數發光單元係透過導電線19〇， 例如軟排線(Flexible Flat Cable ; FFC)而連接至印刷電路板11〇，通 常背板101具有複數開口 120，而每一導電線刚即穿過對應開口 120以連接印刷電路板110與對應發光單元。然而，隨著顯示面板 尺寸的加大，導電線190的數目會因發光單元數量的増加而增加， 此外，為配合發光單元排列，所以印刷電路板110的面積就要隨之 顯著加大，如此會導致高生產成本。此外，若具電流匯流單元m 201250660 與直流/直流轉換器112之印刷電路板110在背板101之第二板面佔 用過多空間，則會限縮具其他功能單元之電路板的設置空間，造成 設計不便。 【發明内容】 依據本發明之實施例，揭露一種背光模組，其包含一背板、至 少一發光單元、一第一電路板、以及一第二電路板。該至少一發光 單元係设置於該背板之一板面。該第一電路板具有至少一電流匯流 單元，每一電流匯流單元係電連接於對應發光單元》該第二電路板 具有一電連接於該至少一電流匯流單元的直流/直流轉換器。 依據本發明之實施例，揭露一種顯示裝置，其包含一具有晝素 陣列的顯示面板以及一用來提供背光源以配合晝素陣列呈現畫面的 背光模組。該背光模組包括一背板、至少一發光單元、一第一電路 板、以及一第二電路板。該至少一發光單元係設置於該背板之面向 該顯示面板的板面。該第一電路板具有至少一電流匯流單元，每一 電流匯流單元係電連接於對應發光單元。該第二電路板具有電連接 於該至少一電流匯流單元的直流/直流轉換器。 【實施方式】 下文依本發明顯示裝置及其背光模組，特舉實施例配合所附圖 式作詳細說明’但所提供之實施例並非用錄制本發明所涵蓋的範 圍。 第2圖為本發明顯示裝置之基本架構示意圖。如第2圖所示， 201250660 顯示裝置200包含顯示面板210與背光模組230,其中顯示面板210 具有晝素陣列215，背光模組230係用來提供背光源以配合畫素陣 列215呈現晝面。第3圖與第4圖分別為第2圖之背光模組230的 第一實施例俯視及仰視示意圖，第5圖為沿第4圖中的A-A線之剖 面示意圖。如第3〜5圖所示，背光模組230_1包含背板240、至少 一第一發光單元251、至少一第一導電線291、第一電路板260、第 二電路板270、第二導電線292、以及第四電路板275。背板240具 有面向第2圖之顯示面板210的第一板面241及反向於第一板面241 的第二板面242。至少一第一發光單元251係設置於背板240之第 一板面241。第一電路板260、第二電路板270及第四電路板275 係設置於背板240之第二板面242，電路板可以例如是印刷電路板 (Printed Circuit Board，PCB)、軟性印刷電路板(Fiexibie Printed Circuit Board，FPCB)。 第一電路板260具有至少一第一電流匯流單元261，每一第一 電流匯流單元261係透過對應第一導電線291而電連接於對應第一 發光單元251。在第3〜5圖所示的實施例中，背板24〇具有至少一 第一開口 245，而每一第一導電線291即穿過對應第一開口 245以 連接對應第一發光單元251與第一電路板260。在另一實施例中， 背板240可省略第一開口 245，而每一第一導電線291係繞過鄰近 第一電路板260的背板240側緣以連接對應第一發光單元251與第 一電路板260。第二電路板270具有電連接於至少一第一電流匯流 單元261的第一直流/直流轉換器271，第一直流/直流轉換器271用 以將一直流電壓轉換為適用於驅動第一電流匯流單元261以及第一 6 201250660 發光單元251之另一直流電壓。第二導電線292係用來將第一電路 板260連接至第二電路板270，據以將至少一第一電流匯流單元26i 電連接至第一直流/直流轉換器271。第四電路板275具有電連接於 第一直流/直流轉換器271的電源供應器276。請注意，電源供應器 276並不限於供電第一直流/直流轉換器271，亦可供電第2圖之顯 示裝置200的其他電子元件。 由於每一第一電流匯流單元261僅具簡單電路，故可設置於相 當小之電路板空間’而配合至少一第一電流匯流單元261之排列佈 局所設計的第一電路板260，在背板240之第二板面242就可只佔 用狹窄的邊緣區域。第二電路板270的第一直流/直流轉換器271可 透過第二導電線292電連接到第一電路板260，再透過第一電路板 260上之導電走線傳輸電源至每一第一電流匯流單元261。此外，第 二電路板270基本上只需提供佈局第一直流/直流轉換器271之電路 所需面積，故第二電路板270之長度/寬度可顯著小於背板24〇之長 度/寬度。亦艮P ’設置於背板240之第二板面242的至少-第-電流 匯流單疋261與第一直流/直流轉換器271所需的電路板面積可顯著 小於上述駕失口印刷電路板11〇之面積。換句話說，本發明背光模組 2MJ的架構可避免習知技術將電流匯流單元111與直流/直流轉換 器112。又置於同一印刷電路板11〇而顯著浪費電路板面積，據以降 低生產成本，並可節省第二板面242之空間以方便設置具其他功能 單元的電路板(譬如具t源供應器276的第四電路板275)。 第6圖與第7圖分別為第2圖之背光模组2扣的第二實施例俯 視及仰視示意圖。如第6圖與第7圖所示，背光模組23G_2包含背 201250660 板340、至少一第一發光单元251、至少一第二發光單元252、至少 一第一導電線29卜至少一第三導電線293、第一電路板26〇、第二 電路板270、第三電路板280、第二導電線292、第四導電線294、 以及第四電路板275。背板340具有面向第2圖之顯示面板210的 第一板面341及反向於第一板面341的第二板面342 〇至少一第一 發光單元251與至少一第二發光單元252係設置於背板340之第一 板面34卜第一電路板260、第二電路板27〇、第三電路板280及第 四電路板275係設置於背板340之第二板面342。 彦光模組230一2基本上類似於第3〜5圖所示的背光模組 230一1 ’主要差異在於另包含至少一第二發光單元252、至少—第三 導電線293、第三電路板280及第四導電線294。第三電路板280 具有至少一第一電流匯流單元281，每一第二電流匯流單元281係 透過對應第三導電線293而電連接於對應第二發光單元252。在第6 圖與第7圖所示的實施例中’背板340具有至少一第二開口 246， 而每一第三導電線293即穿過對應第二開口 246以連接對應第二發 光單元252與第三電路板280。在另一實施例中，背板340可省略 第二開口 246，而每一第三導電線293係繞過鄰近第三電路板280 的背板340側緣以連接對應第二發光單元252與第三電路板280。 第四導電線294係用來將第三電路板280連接至第二電路板270， 據以將至少一第二電流匯流單元281電連接至第一直流/直流轉換器 271。也就是說’至少一第一電流匯流單元261與至少一第二電流匯 流單元281均電連接至第二電路板270之第一直流/直流轉換器271。 同理，由於每一第二電流匯流單元281僅具簡單電路，故可設 201250660 置於相當小之電路板空間，而配合至少一第二電流匯流單元281之 排列佈局所設計的第三電路板280，在背板34〇之第二板面342就 可只佔用狹窄的邊緣區域。因此，第一電路板26〇與第三電路板28〇 係没置於第二板面342之兩對向的狹窄邊緣區域。基於上述說明可 知，設置於背板340之第二板面342的至少一第一電流匯流單元 26卜至少一第二電流匯流單元281及第一直流/直流轉換器271所 需的電路板面積仍可顯著小於習知印刷電路板11〇之面積，據以降 低生產成本’並可節省第二板面342之空間以方便設置具其他功能 單元的電路板(譬如具電源供應器276的第四電路板275)。 第8圖為第2圖之背光模組230的第三實施例仰視示意圖。第 8圖所不之背光模組23〇-3係類似於第6圖與第7圖所示之背光模 組230_2 ’主要差異在於將第二電路板27〇置換為第二電路板37〇， 並將第四電路板275置換為第四電路板375。設置於背板44〇之第 一板面442的第二電路板37〇具有第一直流/直流轉換器371與第二 直流/直流轉換器372。第一直流/直流轉換器仍係透過第二導電線 =2而電連接於至少一第一電流匯流單元％卜第二直流/直流轉換 器372係透過第四導電線294而電連接於至少一第二電流匯流單元 281。没置於背板44〇之第二板面442的第四電路板具有電源供 應器376，且電源供應器376係電連接於第一直流/直流轉換器371 與第二直流/直流轉換器372。請注意，電源供應器376並不限於供 電第一直流/直流轉換器371與第二直流/直流轉換器372,亦可供電 第2圖之顯示裝置的其他電子元件。由於第二電路4反370只需 提仏佈局第-直流/直流轉換器37丨與第二直流/直流轉換器372之電 9 201250660 路所需面積，故設置於背板440之第二板面442的至少一第一電流 匯流單元261、至少一第二電流匯流單元281、第一直流/直流轉換 器371及第二直流/直流轉換器372所需的電路板面積仍可顯著小於 上述習知印刷電路板110之面積，據以降低生產成本，並可節省第 一板面442之空間以方便设置具其他功能單元的電路板(譬如具電 源供應器376的第四電路板375)。 請注意’本發明顯示裝置及其背光模組並不限於上述基於至少 一第一發光單元及/或至少一第二發光單元的結構設計，而可延伸至 基於更多組發光單元配合更多組電流匯流單元之設計。總之，本發 明係將至少一電流匯流單元與直流/直流轉換器分別設置於不同電 路板以避免浪費電路板面積，從而降低生產成本，並可騰出較多板 面空間以方便設置具其他功能單元的電路板。 雖然本發明已以實施例揭露如上，然其並非用以限定本發明， 任何具有本發明所屬技術領域之通常知識者，在不脫離本發明之精 神和範圍内，當可作各種更動與潤飾，因此本發明之保護範圍當視 後附之申請專利範圍所界定者為準。 田 【圖式簡單說明】 第1圖為習知背光模組的示意圖。 第2圖為本發明顯示裝置之基本架構示意圖。 第3圖為第2圖之背光模組的第-實施例俯視示意圖。 第4圖為第2圖之背光模組的第_實施例仰視示意圖。 第5圖為沿第4圖中的Α·Α線之剖面示意圖。 10 201250660 6圖為第2圖之背光模組的第二實施例俯視示意圖。 第7圖為第2圖之背光模組的第二實施例仰視示意圖。 第圖為第2圖之背光模組的第三實施例仰視示意圖。 【主要元件符號說明】 100 背光模組 101 背板 110 印刷電路板 111 電流匯流單元 112 直流/直流轉換器 120 開口 190 導電線 200 顯示裝置 210 顯示面板 215 晝素陣列 230、230J、 背光模組 230J2、230_3 240 > 340'440 背板 241 、 341 第一板面 242、342、442 第二板面 245 第一開口 246 第二開口 201250660 251 第一發光單元 252 第二發光單元 260 第一電路板 261 第一電流匯流單元 270、370 第二電路板 271 、 371 第一直流/直流轉換器 275 ' 375 第四電路板 276 > 376 電源供應 280 第三電路板 281 第二電流匯流單元 291 第一導電線 292 第二導電線 293 第三導電線 294 第四導電線 372 第二直流/直流轉換器 12201250660 VI. Description of the Invention: [Technical Field] The present invention relates to a display device and a backlight module thereof, and more particularly to a display device and a backlight module capable of reducing the area of a circuit board. [Prior Art] Flat Panel Display (FPD) is a widely used display, which has the advantages of slimness, power saving and low radiation, so it is widely used in computer screens, mobile phones, personal digital assistants. (PDA), flat-panel TV and other electronic products. The working principle of the flat display device is to display an image by changing the light transmittance of the element and the light source provided by the backlight module. That is, the backlight module is a key component for the display operation of the flat display device. FIG. 1 is a schematic view of a conventional backlight module. As shown in FIG. 1 , the conventional backlight module 100 includes a back plate 10 , a plurality of light-emitting units (not shown) disposed on the first plate surface of the back plate 1〇1, and a first plate disposed on the back plate 1〇1. A two-sided printed circuit board 110, wherein the printed circuit board 110 has a plurality of current sink units 111 and a DC/DC converter 112. The plurality of light-emitting units are connected to the printed circuit board 11 through a conductive line 19, such as a flexible flat cable (FFC). Usually, the back plate 101 has a plurality of openings 120, and each of the conductive lines just passes through the corresponding opening. 120 to connect the printed circuit board 110 with the corresponding light emitting unit. However, as the size of the display panel increases, the number of conductive lines 190 increases due to the increase in the number of light-emitting units. In addition, in order to match the arrangement of the light-emitting units, the area of the printed circuit board 110 is significantly increased. Will result in high production costs. In addition, if the printed circuit board 110 with the current collecting unit m 201250660 and the DC/DC converter 112 occupies too much space on the second board surface of the back board 101, the setting space of the circuit board with other functional units is limited, resulting in Inconvenient design. SUMMARY OF THE INVENTION According to an embodiment of the invention, a backlight module includes a backplane, at least one light emitting unit, a first circuit board, and a second circuit board. The at least one light emitting unit is disposed on one of the back plates. The first circuit board has at least one current collecting unit, each current collecting unit is electrically connected to the corresponding light emitting unit. The second circuit board has a DC/DC converter electrically connected to the at least one current collecting unit. According to an embodiment of the invention, a display device includes a display panel having a pixel array and a backlight module for providing a backlight to display a picture with a pixel array. The backlight module includes a backplane, at least one light emitting unit, a first circuit board, and a second circuit board. The at least one light emitting unit is disposed on a surface of the backboard facing the display panel. The first circuit board has at least one current collecting unit, and each current collecting unit is electrically connected to the corresponding light emitting unit. The second circuit board has a DC/DC converter electrically coupled to the at least one current sink unit. [Embodiment] Hereinafter, the display device and the backlight module thereof according to the present invention will be described in detail with reference to the drawings, but the embodiments provided are not intended to cover the scope of the present invention. FIG. 2 is a schematic diagram showing the basic structure of the display device of the present invention. As shown in FIG. 2, the display device 200 includes a display panel 210 and a backlight module 230. The display panel 210 has a pixel array 215, and the backlight module 230 is used to provide a backlight to match the pixel array 215. . 3 and 4 are respectively a plan view and a bottom view of the first embodiment of the backlight module 230 of Fig. 2, and Fig. 5 is a cross-sectional view taken along line A-A of Fig. 4; As shown in the third to fifth embodiments, the backlight module 230_1 includes a back plate 240, at least one first light emitting unit 251, at least one first conductive line 291, a first circuit board 260, a second circuit board 270, and a second conductive line. 292, and a fourth circuit board 275. The back plate 240 has a first plate surface 241 facing the display panel 210 of Fig. 2 and a second plate surface 242 opposite to the first plate surface 241. At least one first light emitting unit 251 is disposed on the first plate surface 241 of the back plate 240. The first circuit board 260, the second circuit board 270, and the fourth circuit board 275 are disposed on the second board surface 242 of the back board 240. The circuit board can be, for example, a printed circuit board (PCB) or a flexible printed circuit board. (Fiexibie Printed Circuit Board, FPCB). The first circuit board 260 has at least one first current collecting unit 261, and each of the first current collecting units 261 is electrically connected to the corresponding first light emitting unit 251 through the corresponding first conductive line 291. In the embodiment shown in FIGS. 3~5, the back plate 24A has at least one first opening 245, and each of the first conductive lines 291 passes through the corresponding first opening 245 to connect the corresponding first light emitting unit 251 with The first circuit board 260. In another embodiment, the back plate 240 may omit the first opening 245, and each of the first conductive lines 291 bypasses the side edge of the back plate 240 adjacent to the first circuit board 260 to connect the corresponding first light emitting unit 251 and the first A circuit board 260. The second circuit board 270 has a first DC/DC converter 271 electrically connected to the at least one first current collecting unit 261, and the first DC/DC converter 271 is configured to convert the DC voltage to be suitable for driving the first The current sinking unit 261 and another DC voltage of the first 6 201250660 lighting unit 251. The second conductive line 292 is used to connect the first circuit board 260 to the second circuit board 270 to electrically connect the at least one first current sink unit 26i to the first DC/DC converter 271. The fourth circuit board 275 has a power supply 276 electrically connected to the first DC/DC converter 271. Note that the power supply 276 is not limited to the power supply of the first DC/DC converter 271, but may also supply other electronic components of the display device 200 of Fig. 2. Since each of the first current sinking units 261 has only a simple circuit, the first circuit board 260 can be disposed in a relatively small circuit board space and matched with the arrangement of the at least one first current collecting unit 261. The second plate surface 242 of 240 can occupy only a narrow edge area. The first DC/DC converter 271 of the second circuit board 270 can be electrically connected to the first circuit board 260 through the second conductive line 292, and then transmit power to each of the first through the conductive traces on the first circuit board 260. Current sink unit 261. In addition, the second circuit board 270 basically only needs to provide the area required to lay out the circuit of the first DC/DC converter 271, so that the length/width of the second circuit board 270 can be significantly smaller than the length/width of the back board 24?. The circuit board area required for the at least the first current sinking unit 261 and the first DC/DC converter 271 disposed on the second board surface 242 of the backplane 240 can be significantly smaller than the above-mentioned driver circuit board. 11〇 area. In other words, the architecture of the backlight module 2MJ of the present invention avoids the prior art of the current sink unit 111 and the DC/DC converter 112. The circuit board 11 is placed on the same printed circuit board, which significantly wastes the board area, thereby reducing the production cost, and saving the space of the second board surface 242 to facilitate the setting of the circuit board with other functional units (for example, the t source supply 276) Fourth circuit board 275). Fig. 6 and Fig. 7 are respectively a top view and a bottom view of the second embodiment of the backlight module 2 of Fig. 2. As shown in FIG. 6 and FIG. 7, the backlight module 23G_2 includes a back 201250660 board 340, at least one first light emitting unit 251, at least one second light emitting unit 252, at least one first conductive line 29, and at least one third conductive A line 293, a first circuit board 26, a second circuit board 270, a third circuit board 280, a second conductive line 292, a fourth conductive line 294, and a fourth circuit board 275. The back plate 340 has a first plate surface 341 facing the display panel 210 of FIG. 2 and a second plate surface 342 opposite to the first plate surface 341. The at least one first light emitting unit 251 and the at least one second light emitting unit 252 are The first board surface 34 disposed on the back board 340, the first circuit board 260, the second circuit board 27, the third circuit board 280, and the fourth circuit board 275 are disposed on the second board surface 342 of the back board 340. The light module 230-2 is substantially similar to the backlight module 230-1 shown in FIGS. 3~5. The main difference is that the second light emitting unit 252, at least the third conductive line 293, and the third circuit are further included. Plate 280 and fourth conductive line 294. The third circuit board 280 has at least one first current collecting unit 281, and each of the second current collecting units 281 is electrically connected to the corresponding second lighting unit 252 through the corresponding third conductive line 293. In the embodiment shown in FIGS. 6 and 7, the backplane 340 has at least one second opening 246, and each of the third conductive lines 293 passes through the corresponding second opening 246 to connect the corresponding second light emitting unit 252. With the third circuit board 280. In another embodiment, the back plate 340 can omit the second opening 246, and each of the third conductive lines 293 bypasses the side edge of the back plate 340 adjacent to the third circuit board 280 to connect the corresponding second light emitting unit 252 and the first Three circuit boards 280. The fourth conductive line 294 is used to connect the third circuit board 280 to the second circuit board 270 to electrically connect the at least one second current collecting unit 281 to the first DC/DC converter 271. That is, at least one first current sinking unit 261 and at least one second current sinking unit 281 are electrically connected to the first DC/DC converter 271 of the second circuit board 270. Similarly, since each of the second current collecting units 281 has only a simple circuit, it is possible to set the second board to be placed in a relatively small board space with the 201250660 and the arrangement of the at least one second current collecting unit 281. 280, the second panel surface 342 of the backing plate 34 can occupy only a narrow edge region. Therefore, the first circuit board 26 and the third circuit board 28 are not placed in the opposite narrow edge regions of the second board surface 342. Based on the above description, at least one first current collecting unit 26 disposed on the second board surface 342 of the backplane 340 includes at least one second current collecting unit 281 and a circuit board area required by the first DC/DC converter 271. It can still be significantly smaller than the area of the conventional printed circuit board 11 ,, thereby reducing the production cost 'and saving the space of the second board 342 to facilitate the installation of a circuit board with other functional units (such as the fourth with the power supply 276) Circuit board 275). FIG. 8 is a bottom view showing a third embodiment of the backlight module 230 of FIG. 2. The backlight module 23〇-3 of FIG. 8 is similar to the backlight module 230_2' shown in FIGS. 6 and 7 in that the main difference is that the second circuit board 27〇 is replaced with the second circuit board 37〇. The fourth circuit board 275 is replaced with a fourth circuit board 375. The second circuit board 37A disposed on the first board surface 442 of the backplane 44A has a first DC/DC converter 371 and a second DC/DC converter 372. The first DC/DC converter is still electrically connected to the at least one first current collecting unit by the second conductive line=2, and the second DC/DC converter 372 is electrically connected to the at least one second conductive line 294. A second current sink unit 281. The fourth circuit board not disposed on the second board surface 442 of the backplane 44 has a power supply 376, and the power supply 376 is electrically connected to the first DC/DC converter 371 and the second DC/DC converter. 372. Note that the power supply 376 is not limited to the power supply of the first DC/DC converter 371 and the second DC/DC converter 372, and may also supply other electronic components of the display device of Fig. 2. Since the second circuit 4 is reversed 370, only the layout of the first DC/DC converter 37 and the second DC/DC converter 372 is required, and the second board 4 is disposed on the second board of the backplane 440. The circuit board area required by the at least one first current collecting unit 261, the at least one second current collecting unit 281, the first DC/DC converter 371, and the second DC/DC converter 372 of 442 can still be significantly smaller than the above The area of the printed circuit board 110 is known to reduce the production cost, and the space of the first board surface 442 can be saved to facilitate the installation of a circuit board having other functional units (such as the fourth circuit board 375 with the power supply 376). Please note that the display device of the present invention and the backlight module thereof are not limited to the above-described structural design based on at least one first light emitting unit and/or at least one second light emitting unit, but may be extended to more groups based on more groups of light emitting units. The design of the current sink unit. In summary, the present invention sets at least one current collecting unit and a DC/DC converter on different boards to avoid wasting board area, thereby reducing production cost and freeing up more board space for convenient setting. The board of the unit. The present invention has been disclosed in the above embodiments, and is not intended to limit the present invention. Any of the ordinary skill in the art to which the invention pertains can be modified and modified without departing from the spirit and scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims. Field [Simple description of the drawing] Fig. 1 is a schematic view of a conventional backlight module. FIG. 2 is a schematic diagram showing the basic structure of the display device of the present invention. Fig. 3 is a top plan view showing a first embodiment of the backlight module of Fig. 2. Fig. 4 is a bottom plan view showing the first embodiment of the backlight module of Fig. 2. Fig. 5 is a schematic cross-sectional view taken along line Α·Α in Fig. 4. 10 201250660 6 is a top plan view of a second embodiment of the backlight module of FIG. Fig. 7 is a bottom plan view showing a second embodiment of the backlight module of Fig. 2. The figure is a bottom view of a third embodiment of the backlight module of FIG. [Main component symbol description] 100 backlight module 101 backplane 110 printed circuit board 111 current sink unit 112 DC/DC converter 120 opening 190 conductive line 200 display device 210 display panel 215 pixel array 230, 230J, backlight module 230J2 230_3 240 > 340'440 Backplane 241, 341 First panel 242, 342, 442 Second panel 245 First opening 246 Second opening 201250660 251 First lighting unit 252 Second lighting unit 260 First board 261 first current collecting unit 270, 370 second circuit board 271, 371 first DC/DC converter 275 '375 fourth circuit board 276 > 376 power supply 280 third circuit board 281 second current collecting unit 291 a conductive line 292 a second conductive line 293 a third conductive line 294 a fourth conductive line 372 a second DC/DC converter 12