引言

　　由于移動(dòng)通信等技術(shù)的迅猛發(fā)展，對(duì)車載設(shè)備電源提出了更高的要求。急需一種將汽車電瓶的12V電壓轉(zhuǎn)換為16V,18.5V,24V等多路輸出的電源，要求每路輸出的電流" title="電流">電流可以達(dá)到7A。由于市面上的升壓" title="升壓">升壓DC" title="DC">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" 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title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/" title="DC/">DC/DC達(dá)不到電流需求，目前常采用將12V電瓶電壓逆變到交流220V,再由交流220V產(chǎn)生直流18.5V等多路輸出的方法，雖然其可以達(dá)到電流需求，但電源經(jīng)過兩次轉(zhuǎn)換后，電源效率將大幅度降低，大約只有60%左右，這樣的轉(zhuǎn)換效率對(duì)汽車電瓶供電是很難接受的。

　　針對(duì)這一問題，該文提出基于兩相步進(jìn)升壓型DC/DC控制器LT3782設(shè)計(jì)大電流輸出的升壓型DC/DC模塊的方法。

　　1　LT3782簡介

　　LT3782是美國凌力爾特公司生產(chǎn)的兩相步進(jìn)升壓型DC/DC控制器，28引腳SSOP封裝芯片，開關(guān)頻率在150～500kHz之間可編程，由于采用兩相BOOST拓?fù)浣Y(jié)構(gòu)。對(duì)輸出場效應(yīng)管漏電流和肖特基二極管通過電流的要求都減少一半，即兩個(gè)輸出相位差180°，兩個(gè)輸出間互相抑制輸出紋波電流，輸出紋波是單相BOOST轉(zhuǎn)換電路的1/3。電源效率高，對(duì)散熱的要求小。圖1是LT3782的管腳圖，第29引腳是芯片底部的散熱腳。27引腳連接輸入電源；4引腳接地；11引腳用來設(shè)定開關(guān)頻率；20和23BGATE引腳用來驅(qū)動(dòng)場效應(yīng)管的柵極；8,9,12和13SENSE引腳用來反饋場效應(yīng)管的輸出電流；16引腳是輸出電壓反饋引腳，該腳電壓為2.44V,通過反饋電阻可以設(shè)定輸出電壓值。17引腳是低電壓關(guān)斷引腳，當(dāng)該引腳的電壓大于2.45V時(shí)，器件才開始工作，當(dāng)該引腳的電壓小于0.3V時(shí)，器件進(jìn)入低電壓關(guān)斷模式。14引腳是軟啟動(dòng)引腳，當(dāng)加電時(shí)，輸出電壓從0V漸變到設(shè)定的輸出電壓值，典型的啟動(dòng)時(shí)間可以由下式計(jì)算：

　　式中：C為連接14引腳到地的電容值，單位為μF;t為典型的啟動(dòng)時(shí)間。

　　2　電路實(shí)現(xiàn)

　　2.1　開關(guān)電源總體設(shè)計(jì)

　　電路實(shí)現(xiàn)如圖2所示，12V汽車電瓶電壓經(jīng)過插頭JP1和R5給LT3782供電，LT3782產(chǎn)生的兩相振蕩輸出驅(qū)動(dòng)N溝道場效應(yīng)管Q1和Q2,場效應(yīng)管輸出分別經(jīng)肖特基二極管D1和D2整流后，由電容C7濾波輸出。

　　2.2　開關(guān)電源參數(shù)設(shè)定

　　圖2中，電阻R1用來設(shè)定LT3782的開關(guān)頻率，LT3782的開關(guān)頻率在150～500kHz之間可編程。這里選取開關(guān)頻率為250kHz,參照?qǐng)D3取電阻值R1=75kHz。

　　參照LT3782數(shù)據(jù)手冊(cè)，通過輸入/輸出電壓關(guān)系和占空比可以推算出N溝道場效應(yīng)管的峰值電流約為15A。通過設(shè)定電阻R8和R10的阻值可以設(shè)定電源的限制電流，避免電源電流過大，燒壞后面電路。LT3782的SENSE管腳的域值電壓為60mV,因而電阻R8和R10的阻值為0.004Ω。

　　輸出電壓是通過設(shè)定電阻R13,R7和R11的比例關(guān)系來設(shè)定的，LT3782的FB腳電壓為2.44V參考電壓，這樣輸出電壓可以通過下式計(jì)算：

　　Vout=2.44[1+（R13+R7）/R11]

　　汽車電瓶的過放電保護(hù)是通過設(shè)定該電源的最低工作電壓實(shí)現(xiàn)的。當(dāng)LT3782的RUN管腳電壓高于2.45V時(shí)，該電源才能正常工作，通過電阻R6和R9的分壓，使汽車電瓶電壓在大于10V時(shí)，該電源才能正常工作，避免了電瓶的過放電。

　　3　電路測試

　　為了驗(yàn)證該開關(guān)電源性能，采用如圖4所示的方法進(jìn)行驗(yàn)證。因?yàn)樵撾娫吹妮斎腚娏鬏^大，輸入的直流電源采用安捷倫的6574A2J07。它的輸出電流最高可達(dá)42A,輸出電壓在0～50V范圍內(nèi)可調(diào)，輸出負(fù)載采用建伍的PEL1022201,通過它可以直觀地看到輸出電壓和電流情況。經(jīng)過驗(yàn)證，該電路完全滿足使用單位需求。

　　4　結(jié)語

　　基于美國凌力爾特公司生產(chǎn)的兩相步進(jìn)升壓型DC/DC控制器LT3782,設(shè)計(jì)了一款大電流輸出的升壓型DC/DC模塊。該模塊在12V汽車電瓶供電下，根據(jù)需要可以提供高達(dá)7A電流的24V,18.5V等多種輸出，由于采用兩相DC/DC新技術(shù)，電源效率達(dá)到90%以上。比電源經(jīng)過轉(zhuǎn)換到交流220V后，再轉(zhuǎn)換成所需電壓的方法，效率明顯提高，符合當(dāng)前建設(shè)節(jié)約型社會(huì)的發(fā)展方向，實(shí)用性更強(qiáng)。