1、開關電源電壓輸出低的原因(yin)

(1)220V交流(liu)電(dian)壓(ya)輸入和整流(liu)濾(lv)波電(dian)路(lu)對(dui)開關管供給的作(zuo)業電(dian)壓(ya)不行(xing)，超出脈寬(kuan)調整電(dian)路(lu)控制規劃。

(2)負(fu)載電路存(cun)在過流引起開關(guan)電源負(fu)載加(jia)重而導(dao)致輸出電壓下降。

(3)開(kai)／關機切(qie)換錯誤，行掃描電(dian)(dian)路剛開(kai)始(shi)作業瞬間，開(kai)關電(dian)(dian)源(yuan)即處于待機狀況，此類缺點適用于無(wu)準備電(dian)(dian)源(yuan)的機器，CPU電(dian)(dian)源(yuan)取自(zi)同一(yi)個電(dian)(dian)源(yuan)，非副電(dian)(dian)源(yuan)供給。

(4)開(kai)／關(guan)機(ji)接口電(dian)路結(jie)束因缺點處于開(kai)機(ji)與待機(ji)之間的狀況(kuang)，然后(hou)導致開(kai)關(guan)電(dian)源輸出電(dian)壓低于正常值高于待機(ji)值。

(5)保護電(dian)(dian)路結束(shu)因缺(que)點進(jin)入(ru)(ru)導通(tong)狀(zhuang)況，使電(dian)(dian)源(yuan)進(jin)入(ru)(ru)弱振狀(zhuang)況，引(yin)起開(kai)關電(dian)(dian)源(yuan)輸(shu)出電(dian)(dian)壓下降。

(6)整(zheng)流輸出電(dian)(dian)路中二(er)極(ji)管和濾波電(dian)(dian)容、限流電(dian)(dian)阻(zu)損壞引起輸出電(dian)(dian)壓低(di)。

(7)脈(mo)寬(kuan)調制電(dian)路缺點，不能對開關(guan)電(dian)源輸出(chu)電(dian)壓(ya)的改變作出(chu)正確的呼(hu)應，對開關(guan)管基極(ji)電(dian)壓(ya)調整方向不對，然后構成開關(guan)電(dian)源輸出(chu)電(dian)壓(ya)低。

(8)正(zheng)(zheng)反饋電路中的正(zheng)(zheng)反饋電阻值改變，續流(liu)二極(ji)管性能蛻變或恒流(liu)源缺點，使(shi)正(zheng)(zheng)反饋量缺乏，導致振動(dong)周期變長，振動(dong)頻(pin)率下降，然(ran)后(hou)引起開關電源輸(shu)出電壓低。

(9)它激式開關電(dian)源因未得(de)到行(xing)逆程脈(mo)沖而作業于低頻狀(zhuang)況，構成輸出電(dian)壓低。

2、判別問題的方法與過程(cheng)

從(cong)上述(shu)剖析的原因看出，引起電(dian)壓低的原因涉及到(dao)了開關電(dian)源(yuan)本身(shen)的各個(ge)部(bu)分和與開關電(dian)源(yuan)相關的全部(bu)電(dian)路，在檢修時應先縮(suo)小缺點規劃。

(1)檢(jian)測(ce)開關管c極電壓，承(cheng)認(ren)開關管供電正常。

(2)依據開關電(dian)(dian)源各個輸出端電(dian)(dian)壓判別缺點。

開(kai)(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源有(you)的(de)輸出(chu)(chu)(chu)端電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)正(zheng)常(chang)，有(you)的(de)低于(yu)正(zheng)常(chang)值(zhi)。缺點(dian)在(zai)(zai)輸出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低的(de)這個(ge)整(zheng)流輸出(chu)(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)限流電(dian)(dian)(dian)(dian)(dian)阻(zu)、整(zheng)流二極管、濾(lv)波電(dian)(dian)(dian)(dian)(dian)容進行檢查代換，若限流電(dian)(dian)(dian)(dian)(dian)阻(zu)發燙，說(shuo)明(ming)負載(zai)過流，查負載(zai)。開(kai)(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源各(ge)路(lu)(lu)(lu)輸出(chu)(chu)(chu)均低。這種狀況(kuang)說(shuo)明(ming)負載(zai)和整(zheng)流輸出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)均正(zheng)常(chang)，缺點(dian)在(zai)(zai)開(kai)(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源的(de)正(zheng)反饋(kui)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)、脈寬調整(zheng)、開(kai)(kai)(kai)／待機電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)、保護電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)。輸出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)有(you)的(de)下降份(fen)額(e)大，有(you)的(de)輸出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)下降份(fen)額(e)小。測量(liang)效果說(shuo)明(ming)缺點(dian)在(zai)(zai)輸出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)下降份(fen)額(e)大的(de)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)。此刻(ke)可斷開(kai)(kai)(kai)此路(lu)(lu)(lu)負載(zai)，假(jia)設斷開(kai)(kai)(kai)的(de)是行電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)，應接假(jia)負載(zai)。在(zai)(zai)斷開(kai)(kai)(kai)負載(zai)后，再測開(kai)(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源各(ge)輸出(chu)(chu)(chu)端電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，若恢(hui)復正(zheng)常(chang)，可判別所斷電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)的(de)負載(zai)有(you)過流現象。若仍不正(zheng)常(chang)，說(shuo)明(ming)缺點(dian)在(zai)(zai)該整(zheng)流濾(lv)波電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)。

3、斷開主負(fu)載、接上燈泡，判別(bie)是否(fou)負(fu)載缺(que)點

有些收臺(tai)圖閃(shan)、帶(dai)負(fu)載(zai)后電(dian)壓(ya)不穩的機器(qi)，難于(yu)鑒別缺(que)點是在(zai)電(dian)源或(huo)是負(fu)載(zai)時，能夠選用(yong)(yong)“借法”，用(yong)(yong)此電(dian)源帶(dai)同(tong)等標(biao)準、相同(tong)B+電(dian)壓(ya)的另一臺(tai)機器(qi)行(xing)負(fu)載(zai)，進(jin)行(xing)判(pan)別。

4、保(bao)存發動、正(zheng)反饋(kui)、軟發動及(ji)負反饋(kui)電(dian)路(lu)

逐(zhu)個吊銷各種保(bao)護電(dian)路、待(dai)機控制(zhi)電(dian)路結束三(san)極管。開機查詢(xun)缺點是否(fou)消除，來逐(zhu)漸縮小缺點規劃(hua)。留心：兼有穩壓效果的電(dian)路不能(neng)斷開(例(li)如光電(dian)耦(ou)合器(qi))。斷開保(bao)護電(dian)路時，須慎重，并采(cai)納防止(zhi)電(dian)壓升高的辦法。

5、選用替(ti)代法、檢修脈寬調整電(dian)路（用克己(ji)取(qu)樣電(dian)路替(ti)代原取(qu)樣電(dian)路，判別缺點規劃）

(1)代換后，電壓(ya)恢復(fu)正常(chang)，說(shuo)明缺點在取樣(yang)電路及光耦電路。

(2)電(dian)壓仍低，則斷(duan)開(kai)原取樣電(dian)路(lu)B+接入(ru)點(dian)(dian)，假設電(dian)壓還(huan)低，則檢(jian)查B+濾波電(dian)容，承認良好后，能(neng)夠圈定(ding)缺(que)點(dian)(dian)在熱底板部(bu)分。先查軟(ruan)發動電(dian)路(lu)是否對(dui)開(kai)關管B極分流了。仍不(bu)可，查正反饋、負反饋電(dian)路(lu)。查熱底板部(bu)分的(de)(de)負反饋方法(fa)同檢(jian)查電(dian)壓高的(de)(de)方法(fa)附(fu)近，選用迫使B+輸出高的(de)(de)思(si)路(lu)(留心：改變作(zuo)業點(dian)(dian)不(bu)能(neng)構成(cheng)B+過高擴展(zhan)缺(que)點(dian)(dian))。

總(zong)之(zhi)，在(zai)電源(yuan)的修補中，當電壓不穩時可選用(yong)逆向思維，電壓高時使之(zhi)變低(di)，電壓低(di)時使之(zhi)變高，必要時可選用(yong)人(ren)為(wei)改變作業點電壓。以利于查找缺點點，在(zai)于修補人(ren)員活絡(luo)把握。