1、開關電源電壓輸出低(di)的原(yuan)因

(1)220V交(jiao)流(liu)電(dian)(dian)壓(ya)輸入和整流(liu)濾波電(dian)(dian)路對開關管(guan)供給的作(zuo)業電(dian)(dian)壓(ya)不行(xing)，超出脈寬調(diao)整電(dian)(dian)路控(kong)制規劃。

(2)負(fu)載電路(lu)存在過流引起開(kai)關電源負(fu)載加重而導(dao)致輸出電壓(ya)下降。

(3)開(kai)／關(guan)機(ji)(ji)切(qie)換(huan)錯誤，行掃描電(dian)(dian)路剛開(kai)始(shi)作(zuo)業瞬(shun)間，開(kai)關(guan)電(dian)(dian)源(yuan)即(ji)處于待(dai)機(ji)(ji)狀(zhuang)況，此類缺點適用(yong)于無準備電(dian)(dian)源(yuan)的機(ji)(ji)器，CPU電(dian)(dian)源(yuan)取自同(tong)一個(ge)電(dian)(dian)源(yuan)，非副電(dian)(dian)源(yuan)供給。

(4)開／關機(ji)接口電路結束因缺點處(chu)于(yu)開機(ji)與待(dai)機(ji)之間的狀(zhuang)況(kuang)，然(ran)后導致開關電源(yuan)輸出電壓低(di)于(yu)正常值高于(yu)待(dai)機(ji)值。

(5)保護電路(lu)結束因缺(que)點進入導通狀況，使電源(yuan)進入弱振狀況，引起開(kai)關電源(yuan)輸出電壓下降。

(6)整流輸出(chu)電路中二極管和濾波電容、限(xian)流電阻(zu)損壞(huai)引起輸出(chu)電壓低。

(7)脈(mo)寬(kuan)調(diao)制(zhi)電(dian)路缺點，不能對(dui)開(kai)(kai)關(guan)(guan)(guan)電(dian)源(yuan)輸(shu)出電(dian)壓(ya)的(de)改變作(zuo)出正確的(de)呼(hu)應，對(dui)開(kai)(kai)關(guan)(guan)(guan)管(guan)基極(ji)電(dian)壓(ya)調(diao)整方向不對(dui)，然后構成開(kai)(kai)關(guan)(guan)(guan)電(dian)源(yuan)輸(shu)出電(dian)壓(ya)低。

(8)正反饋(kui)電(dian)(dian)(dian)路中的正反饋(kui)電(dian)(dian)(dian)阻值改變，續流二(er)極管(guan)性能蛻(tui)變或恒流源(yuan)缺(que)點，使(shi)正反饋(kui)量缺(que)乏，導(dao)致振動周期變長，振動頻率下降，然后引起開關電(dian)(dian)(dian)源(yuan)輸出(chu)電(dian)(dian)(dian)壓低。

(9)它激式開關電(dian)源(yuan)因未得到(dao)行(xing)逆(ni)程脈沖而(er)作業于低頻(pin)狀況(kuang)，構成輸出(chu)電(dian)壓低。

2、判(pan)別問(wen)題的(de)方法(fa)與過程

從(cong)上述剖(pou)析的(de)(de)原因(yin)看出(chu)，引(yin)起電(dian)(dian)壓(ya)低的(de)(de)原因(yin)涉(she)及到了開關(guan)電(dian)(dian)源本身的(de)(de)各個部(bu)分和(he)與開關(guan)電(dian)(dian)源相關(guan)的(de)(de)全部(bu)電(dian)(dian)路，在(zai)檢修時應先縮小缺點規劃(hua)。

(1)檢測開(kai)關管(guan)c極電(dian)壓(ya)，承認(ren)開(kai)關管(guan)供(gong)電(dian)正常。

(2)依據開關電(dian)源各個(ge)輸出端電(dian)壓判別缺點。

開(kai)(kai)關電(dian)(dian)(dian)(dian)(dian)(dian)源有(you)(you)的(de)輸出(chu)端電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)正常，有(you)(you)的(de)低(di)于正常值。缺(que)點(dian)在(zai)輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)低(di)的(de)這個整流(liu)(liu)輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)，應(ying)對電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)中的(de)限流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)、整流(liu)(liu)二極管、濾波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)容進行檢查代換，若(ruo)(ruo)限流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)發燙，說(shuo)明(ming)(ming)負(fu)(fu)載(zai)過流(liu)(liu)，查負(fu)(fu)載(zai)。開(kai)(kai)關電(dian)(dian)(dian)(dian)(dian)(dian)源各路(lu)(lu)(lu)(lu)(lu)輸出(chu)均低(di)。這種狀況說(shuo)明(ming)(ming)負(fu)(fu)載(zai)和整流(liu)(liu)輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)均正常，缺(que)點(dian)在(zai)開(kai)(kai)關電(dian)(dian)(dian)(dian)(dian)(dian)源的(de)正反(fan)饋電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)、脈寬調整、開(kai)(kai)／待(dai)機電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)、保護電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)。輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)有(you)(you)的(de)下(xia)降份額大，有(you)(you)的(de)輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)下(xia)降份額小。測量效果說(shuo)明(ming)(ming)缺(que)點(dian)在(zai)輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)下(xia)降份額大的(de)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)。此(ci)刻可斷(duan)開(kai)(kai)此(ci)路(lu)(lu)(lu)(lu)(lu)負(fu)(fu)載(zai)，假設斷(duan)開(kai)(kai)的(de)是行電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)，應(ying)接假負(fu)(fu)載(zai)。在(zai)斷(duan)開(kai)(kai)負(fu)(fu)載(zai)后，再(zai)測開(kai)(kai)關電(dian)(dian)(dian)(dian)(dian)(dian)源各輸出(chu)端電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)，若(ruo)(ruo)恢(hui)復正常，可判別所(suo)斷(duan)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)的(de)負(fu)(fu)載(zai)有(you)(you)過流(liu)(liu)現象(xiang)。若(ruo)(ruo)仍(reng)不正常，說(shuo)明(ming)(ming)缺(que)點(dian)在(zai)該整流(liu)(liu)濾波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)。

3、斷(duan)開主負載、接上燈泡(pao)，判別是否負載缺點(dian)

有(you)些收臺圖閃、帶(dai)負載后(hou)電壓不穩(wen)的機器，難(nan)于鑒別(bie)缺點是在(zai)電源(yuan)或是負載時(shi)，能(neng)夠選用“借法”，用此(ci)電源(yuan)帶(dai)同等標準、相(xiang)同B+電壓的另一臺機器行負載，進行判(pan)別(bie)。

4、保存發動(dong)(dong)、正(zheng)反(fan)饋、軟發動(dong)(dong)及負(fu)反(fan)饋電路

逐個吊銷各種保(bao)護電路、待機(ji)控制電路結束(shu)三(san)極管(guan)。開(kai)機(ji)查詢缺(que)點(dian)是否消除，來逐漸縮小缺(que)點(dian)規劃。留(liu)心：兼有穩壓(ya)效(xiao)果的電路不能斷開(kai)(例如光電耦合(he)器)。斷開(kai)保(bao)護電路時，須(xu)慎(shen)重，并(bing)采(cai)納防止電壓(ya)升高(gao)的辦(ban)法。

5、選用替代法(fa)、檢(jian)修脈寬調整電(dian)路（用克己取樣電(dian)路替代原取樣電(dian)路，判別缺點規劃）

(1)代換后，電(dian)壓恢(hui)復正常，說明缺點(dian)在取樣電(dian)路(lu)及光耦(ou)電(dian)路(lu)。

(2)電壓仍低，則(ze)斷開原取樣電路(lu)B+接入點(dian)，假設(she)電壓還低，則(ze)檢(jian)查(cha)B+濾波電容，承認良(liang)好后，能夠圈(quan)定(ding)缺點(dian)在熱底板部(bu)分。先查(cha)軟(ruan)發動(dong)電路(lu)是否對(dui)開關管B極分流了。仍不(bu)可，查(cha)正反饋(kui)、負(fu)反饋(kui)電路(lu)。查(cha)熱底板部(bu)分的(de)負(fu)反饋(kui)方法同(tong)檢(jian)查(cha)電壓高的(de)方法附(fu)近，選用迫使B+輸出(chu)高的(de)思路(lu)(留心：改變(bian)作業點(dian)不(bu)能構成(cheng)B+過高擴(kuo)展缺點(dian))。

總之，在電(dian)源的修補中，當電(dian)壓(ya)(ya)不穩時(shi)可(ke)(ke)選用(yong)逆向思維，電(dian)壓(ya)(ya)高(gao)時(shi)使之變低，電(dian)壓(ya)(ya)低時(shi)使之變高(gao)，必(bi)要時(shi)可(ke)(ke)選用(yong)人(ren)為改(gai)變作業(ye)點(dian)電(dian)壓(ya)(ya)。以利(li)于(yu)(yu)查找缺點(dian)點(dian)，在于(yu)(yu)修補人(ren)員活絡把握。