1、開關電(dian)源電(dian)壓輸出低(di)的原因(yin)

(1)220V交流電(dian)(dian)壓輸入和整流濾波電(dian)(dian)路對開關管(guan)供(gong)給的(de)作業電(dian)(dian)壓不行，超出脈(mo)寬(kuan)調整電(dian)(dian)路控(kong)制規劃。

(2)負載電路存在過流引起(qi)開(kai)關電源負載加重而導致(zhi)輸(shu)出(chu)電壓下降(jiang)。

(3)開／關機切換(huan)錯誤，行掃描電(dian)(dian)路(lu)剛開始(shi)作(zuo)業瞬間，開關電(dian)(dian)源即(ji)處于待機狀況，此類缺點適用(yong)于無準(zhun)備電(dian)(dian)源的機器，CPU電(dian)(dian)源取自同(tong)一個(ge)電(dian)(dian)源，非副電(dian)(dian)源供給。

(4)開(kai)(kai)／關機(ji)(ji)接(jie)口電路結束(shu)因(yin)缺點處于(yu)開(kai)(kai)機(ji)(ji)與待機(ji)(ji)之間(jian)的狀況，然后導致開(kai)(kai)關電源輸(shu)出電壓低于(yu)正常值高于(yu)待機(ji)(ji)值。

(5)保護電(dian)路結(jie)束因缺點進(jin)入導通狀況，使電(dian)源進(jin)入弱振狀況，引起開關電(dian)源輸出電(dian)壓下降。

(6)整(zheng)流輸出電路(lu)中二極管和濾波(bo)電容、限(xian)流電阻損(sun)壞引(yin)起輸出電壓低。

(7)脈寬調制電(dian)路缺點，不能對(dui)開關(guan)電(dian)源(yuan)輸出電(dian)壓的改變作出正確的呼應，對(dui)開關(guan)管基極電(dian)壓調整方向(xiang)不對(dui)，然后構(gou)成開關(guan)電(dian)源(yuan)輸出電(dian)壓低。

(8)正反(fan)饋電(dian)路中的正反(fan)饋電(dian)阻值改變，續流二極(ji)管(guan)性能蛻變或恒流源(yuan)缺(que)點，使正反(fan)饋量(liang)缺(que)乏，導致振(zhen)動周期(qi)變長，振(zhen)動頻率下降，然(ran)后引(yin)起開關電(dian)源(yuan)輸出電(dian)壓(ya)低(di)。

(9)它(ta)激式開關電源因未得到行逆程脈沖而(er)作業于低頻(pin)狀(zhuang)況(kuang)，構成輸出(chu)電壓低。

2、判(pan)別(bie)問(wen)題的(de)方法(fa)與過(guo)程

從上述剖(pou)析的(de)(de)原因看出，引起電(dian)(dian)壓低的(de)(de)原因涉及到了開關電(dian)(dian)源本身(shen)的(de)(de)各(ge)個(ge)部分和(he)與開關電(dian)(dian)源相關的(de)(de)全部電(dian)(dian)路，在檢修時應先縮小缺點規劃。

(1)檢測開(kai)關(guan)管(guan)(guan)c極電壓，承認開(kai)關(guan)管(guan)(guan)供電正(zheng)常。

(2)依據開關(guan)電源各(ge)個輸出端電壓判別(bie)缺點。

開關電(dian)(dian)(dian)(dian)(dian)源(yuan)有(you)的(de)(de)(de)(de)(de)輸(shu)(shu)出(chu)(chu)端(duan)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)正常(chang)，有(you)的(de)(de)(de)(de)(de)低(di)于正常(chang)值。缺(que)點(dian)(dian)(dian)在(zai)輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)低(di)的(de)(de)(de)(de)(de)這(zhe)個(ge)整(zheng)(zheng)流輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)，應對(dui)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)中的(de)(de)(de)(de)(de)限(xian)流電(dian)(dian)(dian)(dian)(dian)阻、整(zheng)(zheng)流二(er)極管(guan)、濾(lv)波電(dian)(dian)(dian)(dian)(dian)容進行檢查(cha)代換，若限(xian)流電(dian)(dian)(dian)(dian)(dian)阻發燙(tang)，說明(ming)負(fu)(fu)載過流，查(cha)負(fu)(fu)載。開關電(dian)(dian)(dian)(dian)(dian)源(yuan)各路(lu)(lu)(lu)輸(shu)(shu)出(chu)(chu)均(jun)(jun)低(di)。這(zhe)種狀況說明(ming)負(fu)(fu)載和整(zheng)(zheng)流輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)均(jun)(jun)正常(chang)，缺(que)點(dian)(dian)(dian)在(zai)開關電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)(de)正反(fan)饋電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)、脈寬(kuan)調整(zheng)(zheng)、開／待機電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)、保護電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)。輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)有(you)的(de)(de)(de)(de)(de)下降份額(e)大，有(you)的(de)(de)(de)(de)(de)輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)下降份額(e)小(xiao)。測量效果說明(ming)缺(que)點(dian)(dian)(dian)在(zai)輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)下降份額(e)大的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)。此(ci)刻(ke)可(ke)斷(duan)(duan)開此(ci)路(lu)(lu)(lu)負(fu)(fu)載，假設斷(duan)(duan)開的(de)(de)(de)(de)(de)是行電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)，應接(jie)假負(fu)(fu)載。在(zai)斷(duan)(duan)開負(fu)(fu)載后，再(zai)測開關電(dian)(dian)(dian)(dian)(dian)源(yuan)各輸(shu)(shu)出(chu)(chu)端(duan)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，若恢復正常(chang)，可(ke)判別所斷(duan)(duan)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)的(de)(de)(de)(de)(de)負(fu)(fu)載有(you)過流現(xian)象。若仍不正常(chang)，說明(ming)缺(que)點(dian)(dian)(dian)在(zai)該整(zheng)(zheng)流濾(lv)波電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)。

3、斷(duan)開主負(fu)(fu)載、接(jie)上(shang)燈(deng)泡，判別是否負(fu)(fu)載缺點

有些收臺圖閃、帶負載后(hou)電(dian)壓不穩的(de)機器(qi)，難于鑒別缺點是在電(dian)源或是負載時(shi)，能夠選用(yong)“借法(fa)”，用(yong)此電(dian)源帶同(tong)等標準、相同(tong)B+電(dian)壓的(de)另一(yi)臺機器(qi)行負載，進行判別。

4、保存發動、正反(fan)饋、軟發動及(ji)負反(fan)饋電路

逐(zhu)(zhu)個(ge)吊銷各種保護電(dian)(dian)路、待機(ji)控制(zhi)電(dian)(dian)路結束三極管(guan)。開機(ji)查詢缺點(dian)(dian)是(shi)否消除，來逐(zhu)(zhu)漸縮小缺點(dian)(dian)規劃。留心：兼有穩壓效果的電(dian)(dian)路不能斷(duan)開(例如光(guang)電(dian)(dian)耦(ou)合器)。斷(duan)開保護電(dian)(dian)路時(shi)，須慎重，并采納防止(zhi)電(dian)(dian)壓升高的辦法。

5、選(xuan)用(yong)(yong)替代(dai)法、檢修脈寬調整電路(lu)（用(yong)(yong)克(ke)己取樣電路(lu)替代(dai)原取樣電路(lu)，判別缺點(dian)規(gui)劃）

(1)代(dai)換(huan)后，電壓(ya)恢復正常(chang)，說明缺點在(zai)取(qu)樣電路(lu)及光耦電路(lu)。

(2)電(dian)(dian)(dian)壓仍低，則(ze)斷開原取樣電(dian)(dian)(dian)路B+接入點，假設電(dian)(dian)(dian)壓還低，則(ze)檢(jian)查(cha)B+濾(lv)波電(dian)(dian)(dian)容，承(cheng)認良好(hao)后，能夠圈(quan)定缺點在熱底(di)板部(bu)分。先查(cha)軟發動電(dian)(dian)(dian)路是否對開關管B極分流了。仍不可(ke)，查(cha)正反饋、負反饋電(dian)(dian)(dian)路。查(cha)熱底(di)板部(bu)分的負反饋方法(fa)同檢(jian)查(cha)電(dian)(dian)(dian)壓高的方法(fa)附(fu)近，選(xuan)用(yong)迫使B+輸出高的思路(留心：改變作業點不能構成B+過(guo)高擴展缺點)。

總(zong)之(zhi)，在(zai)電(dian)(dian)源的修補中，當電(dian)(dian)壓(ya)不穩時(shi)可選用(yong)逆向思維，電(dian)(dian)壓(ya)高時(shi)使(shi)(shi)之(zhi)變(bian)低(di)，電(dian)(dian)壓(ya)低(di)時(shi)使(shi)(shi)之(zhi)變(bian)高，必要時(shi)可選用(yong)人為改(gai)變(bian)作業點(dian)電(dian)(dian)壓(ya)。以利于查找(zhao)缺點(dian)點(dian)，在(zai)于修補人員(yuan)活絡把握。