實驗(3)開關穩(wěn)壓電源制作實驗報告

電源技術實訓報告開關穩(wěn)壓電源制作系別：機電工程系專業(yè)：應用電子技術姓名：同組成員：學號：0906020122指導老師：2011年11月 目錄1、任務與要求·············································11.1、任務······················································11.2、要求······················································12、方案論證··············································1 2.1DC-DC主回路拓撲···········································1 2.2控制方法及實現(xiàn)方案·········································13.電路設計···············································2 3.1電路整體設計···············································2 3.2主回路器件的選擇··········································2 3.3控制電路設計···············································3 3.4效率的理論分析及算·········································3 3.5過流/過壓保護電路原理與設計································34．測試方法與數(shù)據(jù)········································44.1測試儀器···················································44.2測試方法···················································45．測試結果分析··········································55.1實驗結果··················································55.2誤差分析···················································55.3改進措施···················································56．電路圖原理圖及PCB圖··································67．參考文獻·············································78.元件清單············································71任務與要求1.1、任務設計并制作如圖1所示開關穩(wěn)壓電源。圖1-1

電路框圖

1.2、要求 在電阻負載條件下，使電源滿足下述要求：基本要求(1)輸出電壓Uo可調范圍：30V-36V;(2)最大輸出電流Iomax：1A；(3)U2從18V變到21V時，計算電壓調整率：Su≤2%；(4)計算DC-DC變換器的效率n(5)具有過流保護功能,動作電流Io(th)=1.3+0.2A;2、方案論證2.1DC-DC主回路拓撲圖2-1 主電路2.2控制方法及實現(xiàn)方案采用電壓型脈寬調制技術，產(chǎn)生頻率固定，脈沖寬度可調整的方波脈沖，采用電壓反饋環(huán)控制系統(tǒng)，它的反饋信息取自輸出電壓，用反饋電壓調整控制器的輸出脈沖寬度，改變脈沖占空比，實現(xiàn)開關電源的穩(wěn)定。3.電路設計3.1電路整體設計通過TL494控制輸出脈寬控制IRF640的開關頻率，使電感儲存電能的時間不同，從而控制輸出電壓的高低。 圖3-1 TL494管腳分布和內部電路圖3.2主回路器件的選擇TL494、IRF640、FR157、600uH電感、220uF/50V電容3.3控制電路設計通過電阻R10、R11、R12分壓采樣反饋到TL494的1腳，然后與2腳的基準電壓比較，從而改變3腳電位的高低，達到控制脈寬的寬窄。通過電阻R14的電壓采樣反饋到TL494的16腳，后與15腳電壓進行比較，改變3腳電位的高低，即可控制脈寬的寬窄。3.4效率的理論分析及計算在U2=18V，輸出電壓UO=45V，輸出電流IO=2A的測試條件下。此電路的額定功率PO=90W，為了使此電路的效率達到%90以上則要求輸入功率為100W，允許損耗的功率為10W。 電路的損耗一般包括電感儲能損耗，整流二極管損耗，開關管的損耗。 （1）儲能電感損耗，儲能電感損耗公式如下： PIND=PCO+PPE=I2rmsRe+△Bm 其大致功率為1.4w。 （2）肖特基二極管的損耗，當二極管導通時流過二極管的電流等于電感電流，約為IO=3.86A，為降低損耗可以采用雙管并聯(lián)的方式，每只二極管的電流約為1.8A，對應其UD=0.42V，二極管導通損耗PD=IOUD=1.8w（3）開關管的損耗包括開關損耗和導通損耗。開關管的損耗直接與開關頻率有關系，其功率損耗的計算公式為 P=I2RTonf+0.5×2∫50i2Rf。 取Ton=T/2,f=50kHz,則開關管得損耗約為1.5W。經(jīng)計算，可得到電路的功率損耗約為4.7W，其效率可達到95.3%3.5過流/過壓保護電路原理與設計過流保護：如圖R14電阻對負載電流進行取樣，返回至TL494的16腳，與15腳電壓進行比較，當16腳電壓超過15腳電壓時，使3腳電壓上升，從而降低輸出的占空比；過壓保護；如圖3與圖4，將可調電阻R14的2腳電壓接至LM339的正端，輸出端接至TL494的4腳，當Uref電壓超過負端電壓時，輸出端為高電平，使TL494的4腳電壓為高電平，從而使TL494輸出占空比為0；圖3-2 過壓保護電路4、測試方法與數(shù)據(jù)4.1測試儀器數(shù)字萬用表、電源4.2測試方法①電路板焊接完后，用萬用表測試電路板是否有短路、斷路；②檢查無誤后，給電路板上電，電壓表打到DC200V檔，紅表筆接TL494的12腳，黑表筆接7腳，測得電壓是否為電源電壓，若不相等，先檢查下電路板；③用示波器測量TL494的5腳，測得為三角波；④用萬用表測量TL494的4腳是否為低電平，若不是，則調整可調電阻R15，使4腳電壓為低電平；⑤調整可調電阻R6，使15腳電壓與16腳電壓進行比較，從而改變輸出的占空比。5、測試結果分析5.1測試結果1) 電源端接18V電壓 2）實測時候5腳和6腳震蕩所產(chǎn)生的鋸齒波圖7-1 電路震蕩波形圖5.2誤差分析溫度變化時，電阻阻值會變化，計算結果會產(chǎn)生誤差。器件的選擇和儀器的選擇不可避免的產(chǎn)生一定的誤差。電路板受外界的電磁干擾也會影響電路的讀數(shù)。在PC