1、開關電(dian)源電(dian)壓輸(shu)出(chu)低的原因(yin)

(1)220V交流(liu)電壓輸入(ru)和整流(liu)濾波電路對開(kai)關管供給的作業(ye)電壓不行(xing)，超(chao)出脈寬(kuan)調整電路控制規劃。

(2)負載(zai)電(dian)路存(cun)在過流引(yin)起開關電(dian)源(yuan)負載(zai)加(jia)重而導(dao)致輸出(chu)電(dian)壓下(xia)降。

(3)開(kai)／關(guan)機切換錯誤，行掃(sao)描(miao)電(dian)路剛開(kai)始(shi)作業瞬間，開(kai)關(guan)電(dian)源(yuan)即處于待(dai)機狀況，此類缺(que)點適用(yong)于無準備(bei)電(dian)源(yuan)的機器，CPU電(dian)源(yuan)取(qu)自同一個電(dian)源(yuan)，非副電(dian)源(yuan)供(gong)給。

(4)開／關機(ji)(ji)(ji)接口電(dian)路結束因缺點處于(yu)(yu)開機(ji)(ji)(ji)與(yu)待機(ji)(ji)(ji)之間(jian)的狀(zhuang)況，然后導(dao)致開關電(dian)源(yuan)輸出電(dian)壓(ya)低于(yu)(yu)正常(chang)值(zhi)高于(yu)(yu)待機(ji)(ji)(ji)值(zhi)。

(5)保護(hu)電(dian)路結束因(yin)缺(que)點進入導通狀況(kuang)，使(shi)電(dian)源(yuan)進入弱振狀況(kuang)，引起(qi)開(kai)關(guan)電(dian)源(yuan)輸出電(dian)壓下(xia)降(jiang)。

(6)整流輸出電(dian)路中二極管和濾波(bo)電(dian)容、限(xian)流電(dian)阻損壞引起輸出電(dian)壓(ya)低(di)。

(7)脈寬調制(zhi)電(dian)(dian)(dian)(dian)路缺點，不(bu)能對(dui)開關(guan)(guan)電(dian)(dian)(dian)(dian)源輸出(chu)電(dian)(dian)(dian)(dian)壓(ya)的(de)改(gai)變作出(chu)正確的(de)呼應，對(dui)開關(guan)(guan)管(guan)基極電(dian)(dian)(dian)(dian)壓(ya)調整方向(xiang)不(bu)對(dui)，然后構成開關(guan)(guan)電(dian)(dian)(dian)(dian)源輸出(chu)電(dian)(dian)(dian)(dian)壓(ya)低。

(8)正(zheng)反(fan)饋(kui)電(dian)(dian)路中的(de)正(zheng)反(fan)饋(kui)電(dian)(dian)阻值(zhi)改變，續(xu)流二極管性(xing)能蛻變或恒(heng)流源(yuan)缺點，使正(zheng)反(fan)饋(kui)量缺乏，導致振動周(zhou)期變長，振動頻率下降，然后(hou)引(yin)起開關電(dian)(dian)源(yuan)輸(shu)出(chu)電(dian)(dian)壓低。

(9)它激式開關電(dian)源因未得到行(xing)逆程脈沖(chong)而作業于低(di)頻狀(zhuang)況，構成(cheng)輸出電(dian)壓低(di)。

2、判別(bie)問(wen)題的(de)方法與過程(cheng)

從(cong)上述剖(pou)析的(de)原因看(kan)出，引起電(dian)壓(ya)低的(de)原因涉及到了開關電(dian)源本身的(de)各個(ge)部分和與開關電(dian)源相關的(de)全部電(dian)路，在(zai)檢修時應先(xian)縮小缺點(dian)規(gui)劃。

(1)檢(jian)測開關(guan)管c極電壓，承認(ren)開關(guan)管供電正常(chang)。

(2)依據開關電源各個輸出端電壓(ya)判別缺點。

開關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)有(you)的輸(shu)(shu)出端電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓正常，有(you)的低(di)于正常值。缺(que)點在(zai)輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓低(di)的這個整(zheng)(zheng)流輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，應(ying)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中的限(xian)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻、整(zheng)(zheng)流二(er)極管、濾(lv)波電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)進行檢(jian)查(cha)(cha)代(dai)換(huan)，若限(xian)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻發燙，說(shuo)明(ming)(ming)負載(zai)(zai)過流，查(cha)(cha)負載(zai)(zai)。開關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)各(ge)路(lu)(lu)輸(shu)(shu)出均(jun)低(di)。這種(zhong)狀況說(shuo)明(ming)(ming)負載(zai)(zai)和(he)整(zheng)(zheng)流輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)均(jun)正常，缺(que)點在(zai)開關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的正反饋(kui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)、脈寬調整(zheng)(zheng)、開／待機電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)、保(bao)護電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓有(you)的下降份(fen)額(e)(e)大(da)(da)，有(you)的輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓下降份(fen)額(e)(e)小。測(ce)量(liang)效果說(shuo)明(ming)(ming)缺(que)點在(zai)輸(shu)(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓下降份(fen)額(e)(e)大(da)(da)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。此刻可斷開此路(lu)(lu)負載(zai)(zai)，假設斷開的是行電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，應(ying)接假負載(zai)(zai)。在(zai)斷開負載(zai)(zai)后，再測(ce)開關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)各(ge)輸(shu)(shu)出端電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓，若恢復正常，可判別所斷電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的負載(zai)(zai)有(you)過流現象(xiang)。若仍不(bu)正常，說(shuo)明(ming)(ming)缺(que)點在(zai)該整(zheng)(zheng)流濾(lv)波電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。

3、斷開(kai)主負載(zai)、接上燈泡(pao)，判別是否負載(zai)缺點

有些收(shou)臺圖閃、帶負載(zai)后(hou)電(dian)(dian)壓不(bu)穩的機器，難于鑒別缺點(dian)是(shi)在(zai)電(dian)(dian)源或是(shi)負載(zai)時，能夠選用“借法”，用此電(dian)(dian)源帶同等標(biao)準(zhun)、相同B+電(dian)(dian)壓的另一臺機器行(xing)負載(zai)，進行(xing)判別。

4、保存發動(dong)、正反(fan)饋、軟發動(dong)及負反(fan)饋電路

逐(zhu)個吊銷(xiao)各(ge)種保護電(dian)路(lu)、待機控制電(dian)路(lu)結束三極(ji)管。開(kai)機查詢缺點是否消除，來逐(zhu)漸縮小缺點規劃。留心：兼有(you)穩壓(ya)效果的電(dian)路(lu)不(bu)能斷開(kai)(例如(ru)光電(dian)耦合器)。斷開(kai)保護電(dian)路(lu)時，須慎(shen)重，并采納防止電(dian)壓(ya)升高的辦法。

5、選用替代(dai)法、檢(jian)修(xiu)脈寬調(diao)整(zheng)電(dian)路（用克己取樣電(dian)路替代(dai)原取樣電(dian)路，判別缺點規劃）

(1)代換(huan)后(hou)，電壓恢(hui)復正(zheng)常，說明缺點在取樣電路及光(guang)耦電路。

(2)電(dian)(dian)壓仍低，則(ze)斷開(kai)原取(qu)樣電(dian)(dian)路(lu)(lu)B+接入點(dian)，假設電(dian)(dian)壓還(huan)低，則(ze)檢查B+濾波電(dian)(dian)容，承認良好后，能夠圈定缺(que)點(dian)在熱底板部分。先(xian)查軟發動電(dian)(dian)路(lu)(lu)是否對開(kai)關管B極分流了。仍不可，查正反(fan)饋、負(fu)反(fan)饋電(dian)(dian)路(lu)(lu)。查熱底板部分的負(fu)反(fan)饋方(fang)法同檢查電(dian)(dian)壓高(gao)的方(fang)法附(fu)近，選用迫(po)使B+輸(shu)出高(gao)的思路(lu)(lu)(留心(xin)：改(gai)變作業點(dian)不能構成(cheng)B+過高(gao)擴(kuo)展缺(que)點(dian))。

總之(zhi)，在(zai)電(dian)源的修補中，當電(dian)壓不穩時可(ke)選用(yong)逆向思維，電(dian)壓高時使之(zhi)變(bian)低，電(dian)壓低時使之(zhi)變(bian)高，必(bi)要時可(ke)選用(yong)人為(wei)改(gai)變(bian)作業點電(dian)壓。以利于查找缺點點，在(zai)于修補人員活(huo)絡把握。