1、開(kai)關電源電壓輸(shu)出低的原因(yin)

(1)220V交流電(dian)壓(ya)輸入(ru)和(he)整流濾(lv)波電(dian)路(lu)對開關管供給的作業電(dian)壓(ya)不行，超(chao)出脈寬調整電(dian)路(lu)控制規劃(hua)。

(2)負(fu)載電路存在(zai)過流引(yin)起開關(guan)電源負(fu)載加重而導致輸出(chu)電壓下降。

(3)開／關機切換(huan)錯誤，行掃描(miao)電(dian)(dian)(dian)路剛開始作業瞬間，開關電(dian)(dian)(dian)源(yuan)(yuan)即處于待機狀況，此類缺(que)點適用(yong)于無(wu)準備電(dian)(dian)(dian)源(yuan)(yuan)的(de)機器，CPU電(dian)(dian)(dian)源(yuan)(yuan)取自同一個電(dian)(dian)(dian)源(yuan)(yuan)，非副電(dian)(dian)(dian)源(yuan)(yuan)供給。

(4)開／關(guan)機接口(kou)電路結(jie)束因缺點處(chu)于(yu)開機與待機之間的狀況(kuang)，然后(hou)導(dao)致(zhi)開關(guan)電源輸出電壓低于(yu)正常(chang)值(zhi)高于(yu)待機值(zhi)。

(5)保護電路結束因(yin)缺(que)點進(jin)入導通狀(zhuang)況，使電源進(jin)入弱(ruo)振狀(zhuang)況，引起開關電源輸出電壓下降(jiang)。

(6)整流輸出電(dian)路中二極(ji)管(guan)和濾波電(dian)容(rong)、限流電(dian)阻損壞引起輸出電(dian)壓低。

(7)脈寬調(diao)制電(dian)路缺點，不能對(dui)(dui)開關電(dian)源輸出(chu)(chu)電(dian)壓(ya)(ya)(ya)的改變作(zuo)出(chu)(chu)正確的呼應，對(dui)(dui)開關管(guan)基極電(dian)壓(ya)(ya)(ya)調(diao)整方向不對(dui)(dui)，然后構成開關電(dian)源輸出(chu)(chu)電(dian)壓(ya)(ya)(ya)低。

(8)正(zheng)反(fan)饋(kui)電(dian)路中的正(zheng)反(fan)饋(kui)電(dian)阻(zu)值改變，續流二極管性能蛻變或恒流源(yuan)缺點，使正(zheng)反(fan)饋(kui)量缺乏，導致振動(dong)周期變長，振動(dong)頻率下降，然后引起開關電(dian)源(yuan)輸(shu)出(chu)電(dian)壓(ya)低。

(9)它激式開(kai)關電(dian)(dian)源因未(wei)得到(dao)行(xing)逆程(cheng)脈沖而作業(ye)于低頻狀況，構(gou)成輸(shu)出電(dian)(dian)壓低。

2、判別問題的方法與過程

從上述剖析的(de)原因(yin)看出，引(yin)起(qi)電壓低的(de)原因(yin)涉及到了(le)開關(guan)電源本身的(de)各個(ge)部分和與開關(guan)電源相關(guan)的(de)全部電路，在檢修時應先縮小缺點規劃。

(1)檢測開關管c極電壓，承認開關管供電正常。

(2)依據開關(guan)電源各個輸出(chu)端電壓判(pan)別缺(que)點。

開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)有(you)(you)的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)出(chu)端電(dian)(dian)(dian)(dian)(dian)壓(ya)正(zheng)(zheng)常(chang)(chang)(chang)，有(you)(you)的(de)(de)(de)(de)(de)低(di)于正(zheng)(zheng)常(chang)(chang)(chang)值。缺(que)點(dian)在(zai)輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)低(di)的(de)(de)(de)(de)(de)這(zhe)個整(zheng)(zheng)流(liu)輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，應(ying)對電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中的(de)(de)(de)(de)(de)限流(liu)電(dian)(dian)(dian)(dian)(dian)阻(zu)、整(zheng)(zheng)流(liu)二極管、濾波電(dian)(dian)(dian)(dian)(dian)容進行(xing)(xing)檢查代換，若(ruo)限流(liu)電(dian)(dian)(dian)(dian)(dian)阻(zu)發(fa)燙，說(shuo)(shuo)明(ming)負(fu)(fu)(fu)載(zai)過(guo)流(liu)，查負(fu)(fu)(fu)載(zai)。開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)各(ge)路(lu)(lu)輸(shu)(shu)(shu)出(chu)均低(di)。這(zhe)種狀況說(shuo)(shuo)明(ming)負(fu)(fu)(fu)載(zai)和整(zheng)(zheng)流(liu)輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)均正(zheng)(zheng)常(chang)(chang)(chang)，缺(que)點(dian)在(zai)開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)(de)正(zheng)(zheng)反饋電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)、脈寬調整(zheng)(zheng)、開(kai)(kai)／待機(ji)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)、保(bao)護電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)有(you)(you)的(de)(de)(de)(de)(de)下(xia)降份額大(da)，有(you)(you)的(de)(de)(de)(de)(de)輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)下(xia)降份額小。測量(liang)效果說(shuo)(shuo)明(ming)缺(que)點(dian)在(zai)輸(shu)(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)下(xia)降份額大(da)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。此刻可斷開(kai)(kai)此路(lu)(lu)負(fu)(fu)(fu)載(zai)，假設斷開(kai)(kai)的(de)(de)(de)(de)(de)是行(xing)(xing)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，應(ying)接假負(fu)(fu)(fu)載(zai)。在(zai)斷開(kai)(kai)負(fu)(fu)(fu)載(zai)后，再測開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)各(ge)輸(shu)(shu)(shu)出(chu)端電(dian)(dian)(dian)(dian)(dian)壓(ya)，若(ruo)恢復正(zheng)(zheng)常(chang)(chang)(chang)，可判別所斷電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)(de)(de)(de)負(fu)(fu)(fu)載(zai)有(you)(you)過(guo)流(liu)現(xian)象。若(ruo)仍不正(zheng)(zheng)常(chang)(chang)(chang)，說(shuo)(shuo)明(ming)缺(que)點(dian)在(zai)該(gai)整(zheng)(zheng)流(liu)濾波電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。

3、斷開主負(fu)載(zai)、接(jie)上燈泡，判別是否負(fu)載(zai)缺點

有(you)些收臺(tai)圖(tu)閃、帶負(fu)(fu)載后電壓不穩(wen)的(de)機器(qi)(qi)，難于(yu)鑒別缺點是在電源(yuan)或是負(fu)(fu)載時，能夠(gou)選用(yong)“借(jie)法”，用(yong)此電源(yuan)帶同等(deng)標準、相同B+電壓的(de)另(ling)一臺(tai)機器(qi)(qi)行負(fu)(fu)載，進行判別。

4、保存發(fa)動、正(zheng)反(fan)饋(kui)、軟發(fa)動及負反(fan)饋(kui)電路

逐個吊銷各種保護電(dian)(dian)(dian)路、待機控制電(dian)(dian)(dian)路結束三極管。開(kai)機查詢缺點是否消除，來(lai)逐漸縮小缺點規劃。留心(xin)：兼(jian)有穩壓效(xiao)果的電(dian)(dian)(dian)路不能斷開(kai)(例如光電(dian)(dian)(dian)耦合器)。斷開(kai)保護電(dian)(dian)(dian)路時，須(xu)慎重，并采納防(fang)止電(dian)(dian)(dian)壓升高的辦法。

5、選用替代(dai)法、檢修脈寬調整電(dian)(dian)路(lu)(lu)（用克(ke)己(ji)取樣電(dian)(dian)路(lu)(lu)替代(dai)原取樣電(dian)(dian)路(lu)(lu)，判別缺點(dian)規劃）

(1)代換后，電(dian)壓恢復正常，說(shuo)明缺點在取樣電(dian)路(lu)及光耦電(dian)路(lu)。

(2)電(dian)壓(ya)仍低，則(ze)斷開原取樣電(dian)路B+接入點(dian)(dian)，假設電(dian)壓(ya)還低，則(ze)檢查(cha)B+濾(lv)波電(dian)容，承認良好后(hou)，能夠(gou)圈定缺點(dian)(dian)在熱(re)底板部(bu)分(fen)。先(xian)查(cha)軟發動電(dian)路是否對開關管(guan)B極分(fen)流了。仍不可，查(cha)正反(fan)饋、負(fu)反(fan)饋電(dian)路。查(cha)熱(re)底板部(bu)分(fen)的負(fu)反(fan)饋方法同檢查(cha)電(dian)壓(ya)高的方法附近，選(xuan)用迫使B+輸(shu)出(chu)高的思路(留(liu)心：改變作業點(dian)(dian)不能構成B+過高擴展缺點(dian)(dian))。

總之(zhi)，在電(dian)源(yuan)的修補中，當電(dian)壓(ya)(ya)不(bu)穩時(shi)(shi)可選用逆向(xiang)思維(wei)，電(dian)壓(ya)(ya)高時(shi)(shi)使之(zhi)變低，電(dian)壓(ya)(ya)低時(shi)(shi)使之(zhi)變高，必(bi)要時(shi)(shi)可選用人為改變作(zuo)業點(dian)電(dian)壓(ya)(ya)。以利于查找缺點(dian)點(dian)，在于修補人員活絡把握(wo)。