1、開關電源(yuan)電壓(ya)輸出低的原因(yin)

(1)220V交(jiao)流電(dian)壓(ya)輸入和整流濾波電(dian)路對開關管供給的作(zuo)業電(dian)壓(ya)不行，超出脈寬調整電(dian)路控制規劃。

(2)負(fu)載(zai)電路存在(zai)過流引起(qi)開關電源(yuan)負(fu)載(zai)加重而導致輸出電壓(ya)下降(jiang)。

(3)開(kai)／關(guan)機(ji)切(qie)換錯誤(wu)，行掃描電路剛(gang)開(kai)始作業瞬間，開(kai)關(guan)電源即處于待機(ji)狀況，此(ci)類缺點適用于無(wu)準備電源的機(ji)器，CPU電源取自同一個電源，非(fei)副電源供給(gei)。

(4)開／關機接口電路結(jie)束因缺點處于(yu)開機與待(dai)機之間(jian)的狀(zhuang)況(kuang)，然(ran)后導致開關電源輸出電壓低于(yu)正常值(zhi)高于(yu)待(dai)機值(zhi)。

(5)保護電(dian)(dian)路結束因缺點(dian)進入導通狀況，使(shi)電(dian)(dian)源(yuan)進入弱振狀況，引起開關電(dian)(dian)源(yuan)輸出(chu)電(dian)(dian)壓下降(jiang)。

(6)整流輸(shu)(shu)出電路中二極管(guan)和濾波電容、限(xian)流電阻損壞引起輸(shu)(shu)出電壓低。

(7)脈寬(kuan)調制(zhi)電(dian)路缺點，不能對開關電(dian)源輸出(chu)電(dian)壓的改變作出(chu)正確(que)的呼應，對開關管基極電(dian)壓調整(zheng)方向(xiang)不對，然后構(gou)成開關電(dian)源輸出(chu)電(dian)壓低。

(8)正反饋電路中的正反饋電阻(zu)值改變(bian)，續流二極管(guan)性能(neng)蛻(tui)變(bian)或恒(heng)流源缺點(dian)，使正反饋量缺乏，導致振動(dong)周期變(bian)長，振動(dong)頻(pin)率(lv)下降，然(ran)后引起開關電源輸出電壓低(di)。

(9)它激式(shi)開(kai)關電源因(yin)未得到(dao)行(xing)逆程脈沖而作業于低(di)頻狀況，構成輸出電壓低(di)。

2、判別(bie)問(wen)題的方法與過程

從上述剖析的原(yuan)因(yin)看出(chu)，引起電壓低的原(yuan)因(yin)涉及到了(le)開(kai)關電源(yuan)本身的各(ge)個(ge)部分和與開(kai)關電源(yuan)相關的全部電路，在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，承認開(kai)關管(guan)供電(dian)正常。

(2)依據開(kai)關(guan)電(dian)源各個輸出端(duan)電(dian)壓判別缺點。

開(kai)關(guan)(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)有的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)端(duan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)正(zheng)常，有的(de)(de)(de)(de)(de)低(di)于(yu)正(zheng)常值。缺點在(zai)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)低(di)的(de)(de)(de)(de)(de)這個整(zheng)(zheng)流(liu)(liu)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)，應(ying)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)中的(de)(de)(de)(de)(de)限(xian)流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻、整(zheng)(zheng)流(liu)(liu)二極管、濾波電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)進行(xing)檢查代(dai)換，若(ruo)限(xian)流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻發燙，說(shuo)明負(fu)載(zai)過流(liu)(liu)，查負(fu)載(zai)。開(kai)關(guan)(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)各路(lu)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)均(jun)低(di)。這種狀況說(shuo)明負(fu)載(zai)和整(zheng)(zheng)流(liu)(liu)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)均(jun)正(zheng)常，缺點在(zai)開(kai)關(guan)(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)(de)正(zheng)反饋(kui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)、脈寬調整(zheng)(zheng)、開(kai)／待機電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)、保(bao)護電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)有的(de)(de)(de)(de)(de)下降(jiang)(jiang)份額(e)(e)大，有的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)下降(jiang)(jiang)份額(e)(e)小。測量效果說(shuo)明缺點在(zai)輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)下降(jiang)(jiang)份額(e)(e)大的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。此刻可斷(duan)(duan)開(kai)此路(lu)負(fu)載(zai)，假(jia)設斷(duan)(duan)開(kai)的(de)(de)(de)(de)(de)是行(xing)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)，應(ying)接(jie)假(jia)負(fu)載(zai)。在(zai)斷(duan)(duan)開(kai)負(fu)載(zai)后(hou)，再測開(kai)關(guan)(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)各輸(shu)(shu)(shu)出(chu)(chu)(chu)(chu)端(duan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，若(ruo)恢復正(zheng)常，可判別所斷(duan)(duan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)的(de)(de)(de)(de)(de)負(fu)載(zai)有過流(liu)(liu)現象(xiang)。若(ruo)仍不(bu)正(zheng)常，說(shuo)明缺點在(zai)該(gai)整(zheng)(zheng)流(liu)(liu)濾波電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

3、斷開主負(fu)載(zai)、接上燈泡，判(pan)別是否負(fu)載(zai)缺點

有些收臺(tai)(tai)圖(tu)閃、帶負(fu)(fu)載(zai)后電(dian)壓不穩的(de)機(ji)器，難于鑒別缺點(dian)是(shi)在電(dian)源或是(shi)負(fu)(fu)載(zai)時，能夠選用“借法”，用此電(dian)源帶同等標準、相同B+電(dian)壓的(de)另一(yi)臺(tai)(tai)機(ji)器行負(fu)(fu)載(zai)，進行判別。

4、保(bao)存(cun)發(fa)動(dong)(dong)、正反饋、軟發(fa)動(dong)(dong)及負反饋電路

逐個吊銷(xiao)各種(zhong)保護電路(lu)、待機(ji)控制電路(lu)結束三極管。開機(ji)查(cha)詢缺點(dian)是否消除，來逐漸縮小缺點(dian)規劃(hua)。留心：兼有穩壓效果的電路(lu)不能斷開(例如(ru)光電耦合(he)器)。斷開保護電路(lu)時，須(xu)慎重，并采納防止電壓升高(gao)的辦法。

5、選用(yong)替代法(fa)、檢修脈(mo)寬調整電(dian)路（用(yong)克(ke)己取(qu)樣(yang)電(dian)路替代原取(qu)樣(yang)電(dian)路，判別缺點規劃）

(1)代換(huan)后，電壓恢復正常，說明(ming)缺點在(zai)取樣電路及(ji)光(guang)耦(ou)電路。

(2)電(dian)(dian)壓仍低(di)，則斷開(kai)原取樣電(dian)(dian)路B+接入點，假(jia)設電(dian)(dian)壓還(huan)低(di)，則檢(jian)查(cha)(cha)B+濾波(bo)電(dian)(dian)容，承認良好后(hou)，能夠圈定缺點在熱底板(ban)(ban)部分。先查(cha)(cha)軟發動電(dian)(dian)路是否對開(kai)關管B極分流了。仍不可，查(cha)(cha)正反饋(kui)(kui)、負反饋(kui)(kui)電(dian)(dian)路。查(cha)(cha)熱底板(ban)(ban)部分的(de)(de)負反饋(kui)(kui)方法同(tong)檢(jian)查(cha)(cha)電(dian)(dian)壓高(gao)(gao)的(de)(de)方法附近，選用迫使B+輸(shu)出高(gao)(gao)的(de)(de)思路(留心：改(gai)變作(zuo)業點不能構(gou)成B+過高(gao)(gao)擴展(zhan)缺點)。

總之(zhi)(zhi)(zhi)，在(zai)電源的修(xiu)補中，當電壓(ya)(ya)不穩時(shi)可(ke)選用逆向思維，電壓(ya)(ya)高(gao)(gao)時(shi)使之(zhi)(zhi)(zhi)變低(di)，電壓(ya)(ya)低(di)時(shi)使之(zhi)(zhi)(zhi)變高(gao)(gao)，必(bi)要時(shi)可(ke)選用人為改變作業點(dian)電壓(ya)(ya)。以利于查找缺點(dian)點(dian)，在(zai)于修(xiu)補人員活絡(luo)把握。