1、開關電(dian)源電(dian)壓輸出低的原因

(1)220V交流電(dian)(dian)(dian)(dian)壓輸入和整(zheng)流濾波電(dian)(dian)(dian)(dian)路(lu)對開關管供給的作業電(dian)(dian)(dian)(dian)壓不(bu)行，超(chao)出脈寬調(diao)整(zheng)電(dian)(dian)(dian)(dian)路(lu)控(kong)制(zhi)規劃。

(2)負(fu)載電(dian)路存(cun)在過流引起開(kai)關電(dian)源負(fu)載加(jia)重而導致輸出電(dian)壓(ya)下(xia)降。

(3)開／關(guan)機(ji)切換錯(cuo)誤(wu)，行(xing)掃描電(dian)(dian)路剛(gang)開始(shi)作業瞬間(jian)，開關(guan)電(dian)(dian)源(yuan)(yuan)即處于待機(ji)狀況，此類缺點適(shi)用于無準備(bei)電(dian)(dian)源(yuan)(yuan)的機(ji)器，CPU電(dian)(dian)源(yuan)(yuan)取自(zi)同一個(ge)電(dian)(dian)源(yuan)(yuan)，非副電(dian)(dian)源(yuan)(yuan)供給。

(4)開／關機(ji)接(jie)口電(dian)路結束因缺點處于(yu)開機(ji)與(yu)待機(ji)之間的狀(zhuang)況，然后(hou)導致開關電(dian)源輸(shu)出電(dian)壓低于(yu)正常值高于(yu)待機(ji)值。

(5)保護(hu)電(dian)路結束因缺點進(jin)入導通(tong)狀況(kuang)，使電(dian)源進(jin)入弱振狀況(kuang)，引(yin)起開關電(dian)源輸出電(dian)壓下降。

(6)整流輸出電路中(zhong)二極管(guan)和濾波電容、限流電阻損壞引起輸出電壓低(di)。

(7)脈寬(kuan)調制(zhi)電路(lu)缺點，不能(neng)對(dui)開關(guan)電源輸(shu)出電壓的改變作(zuo)出正確的呼應，對(dui)開關(guan)管(guan)基極電壓調整方(fang)向(xiang)不對(dui)，然后構成開關(guan)電源輸(shu)出電壓低。

(8)正反饋(kui)電路中的正反饋(kui)電阻值改變，續流二極管性能蛻變或(huo)恒流源(yuan)缺(que)點(dian)，使(shi)正反饋(kui)量缺(que)乏，導致振動周期變長(chang)，振動頻率下降，然后引起開(kai)關電源(yuan)輸(shu)出電壓低。

(9)它激式開關電源因(yin)未得到行逆程脈沖而作業于低(di)頻狀況，構成輸出(chu)電壓低(di)。

2、判別問(wen)題的方(fang)法(fa)與過(guo)程

從上(shang)述剖析的原因(yin)看出，引(yin)起(qi)電(dian)(dian)壓低的原因(yin)涉及到了開關(guan)電(dian)(dian)源本身(shen)的各個部分和與(yu)開關(guan)電(dian)(dian)源相關(guan)的全(quan)部電(dian)(dian)路，在檢修時(shi)應(ying)先(xian)縮小缺點規(gui)劃。

(1)檢測開關管c極電壓，承認開關管供電正常。

(2)依據開關電源各個輸出端電壓判別缺點。

開(kai)(kai)(kai)關電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)有的輸(shu)(shu)出(chu)端電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)正(zheng)常(chang)，有的低(di)(di)于正(zheng)常(chang)值。缺點在(zai)輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)低(di)(di)的這個整(zheng)流輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)，應對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)中的限流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻、整(zheng)流二極管、濾波電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容進行(xing)檢查代換，若(ruo)限流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻發(fa)燙，說(shuo)明(ming)負(fu)載(zai)過(guo)流，查負(fu)載(zai)。開(kai)(kai)(kai)關電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)各路(lu)輸(shu)(shu)出(chu)均低(di)(di)。這種狀況說(shuo)明(ming)負(fu)載(zai)和整(zheng)流輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)均正(zheng)常(chang)，缺點在(zai)開(kai)(kai)(kai)關電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的正(zheng)反饋電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)、脈寬調整(zheng)、開(kai)(kai)(kai)／待機電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)、保護電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)有的下降份(fen)額大，有的輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)下降份(fen)額小。測(ce)量效果(guo)說(shuo)明(ming)缺點在(zai)輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)下降份(fen)額大的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。此(ci)刻(ke)可斷開(kai)(kai)(kai)此(ci)路(lu)負(fu)載(zai)，假設斷開(kai)(kai)(kai)的是(shi)行(xing)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)，應接假負(fu)載(zai)。在(zai)斷開(kai)(kai)(kai)負(fu)載(zai)后，再測(ce)開(kai)(kai)(kai)關電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)各輸(shu)(shu)出(chu)端電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，若(ruo)恢復(fu)正(zheng)常(chang)，可判別所(suo)斷電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)的負(fu)載(zai)有過(guo)流現象。若(ruo)仍(reng)不正(zheng)常(chang)，說(shuo)明(ming)缺點在(zai)該整(zheng)流濾波電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

3、斷開主負載、接上燈泡，判別是否負載缺點(dian)

有些收臺(tai)圖閃、帶負(fu)載后電(dian)(dian)壓不穩(wen)的機器，難于鑒別缺點是在(zai)電(dian)(dian)源(yuan)或是負(fu)載時，能夠選用(yong)“借法”，用(yong)此電(dian)(dian)源(yuan)帶同等標(biao)準、相同B+電(dian)(dian)壓的另一臺(tai)機器行負(fu)載，進行判別。

4、保存發(fa)動、正反饋(kui)、軟發(fa)動及負反饋(kui)電路

逐個吊銷各種保護(hu)電(dian)路(lu)(lu)、待機(ji)控制(zhi)電(dian)路(lu)(lu)結束(shu)三極管。開機(ji)查詢(xun)缺(que)點是否(fou)消除，來逐漸(jian)縮小(xiao)缺(que)點規(gui)劃。留心：兼(jian)有(you)穩壓效果的(de)電(dian)路(lu)(lu)不能斷開(例如光電(dian)耦合器(qi))。斷開保護(hu)電(dian)路(lu)(lu)時，須慎重(zhong)，并采納(na)防止電(dian)壓升(sheng)高的(de)辦法。

5、選用替代法、檢(jian)修脈寬(kuan)調整電路（用克(ke)己取樣電路替代原取樣電路，判別(bie)缺點規劃）

(1)代(dai)換后(hou)，電(dian)(dian)壓(ya)恢(hui)復正(zheng)常，說(shuo)明缺點在取樣電(dian)(dian)路及光耦電(dian)(dian)路。

(2)電壓仍(reng)低，則斷開(kai)原取樣電路B+接入(ru)點(dian)，假設電壓還低，則檢查(cha)B+濾波電容(rong)，承(cheng)認良好后，能夠圈定(ding)缺點(dian)在熱(re)(re)底板部分。先(xian)查(cha)軟發動電路是(shi)否(fou)對開(kai)關管B極分流了(le)。仍(reng)不可，查(cha)正反饋、負(fu)反饋電路。查(cha)熱(re)(re)底板部分的(de)(de)負(fu)反饋方法同(tong)檢查(cha)電壓高(gao)(gao)的(de)(de)方法附近，選用迫使B+輸出高(gao)(gao)的(de)(de)思路(留心：改變(bian)作業(ye)點(dian)不能構(gou)成(cheng)B+過高(gao)(gao)擴(kuo)展缺點(dian))。

總(zong)之(zhi)，在(zai)電(dian)源的修補中(zhong)，當電(dian)壓(ya)不穩時(shi)(shi)可選用(yong)逆向思維，電(dian)壓(ya)高時(shi)(shi)使之(zhi)變(bian)(bian)低(di)，電(dian)壓(ya)低(di)時(shi)(shi)使之(zhi)變(bian)(bian)高，必要時(shi)(shi)可選用(yong)人為改變(bian)(bian)作業(ye)點(dian)電(dian)壓(ya)。以(yi)利于查找缺點(dian)點(dian)，在(zai)于修補人員活絡把握(wo)。