開關電源始(shi)終(zhong)無電(dian)(dian)(dian)壓(ya)輸(shu)出(chu)指開關(guan)(guan)(guan)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)各(ge)輸(shu)出(chu)端(duan)在(zai)按電(dian)(dian)(dian)源(yuan)(yuan)(yuan)開關(guan)(guan)(guan)開機后始(shi)終(zhong)為0V這是開關(guan)(guan)(guan)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)未產(chan)(chan)生(sheng)震蕩(dang)所致。進一步證實測開關(guan)(guan)(guan)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)100UF/400V電(dian)(dian)(dian)容關(guan)(guan)(guan)機后的電(dian)(dian)(dian)壓(ya)，若(ruo)300V之(zhi)后慢慢下降說明開關(guan)(guan)(guan)電(dian)(dian)(dian)源(yuan)(yuan)(yuan)未產(chan)(chan)生(sheng)振蕩(dang)。

1、開關電源始終無電壓輸出的原因

(1)開關管集電極未得到足夠的工作電壓
(2)開關管基極未得到啟動電壓和相關電路漏電
(3)開關管正反饋元件失效

2、判斷故障的方法和步驟

檢修這類故障的首要任務是判斷鼓障在上述三個部位中的哪個部位具體方法是測開關管集電極基極電壓，可能有以下幾種情況：
(1)開關管集電極電壓為0V和低于市電1.4倍開關管沒有正常的工作電壓，如果有1.4倍的電壓說明開關管集電極具備了正常的工作電壓，說明電路工作正常。
(2)開關管的基極電壓為0V(包括開機瞬間)這種情況說明啟動電路對開關管基極未提供啟動(導通)電壓，或基極與發射極之間相關元件擊穿應檢查啟動電路和開關管發射極及相關元件，若電壓為0.6~0.7(包括開幾瞬間)說明啟動電路和開關管發射極元件正常，若在0.7V以上說明啟動電路正常但開關管發射結或元件斷路或阻值變大。
(3)開關(guan)管具備(bei)導通條件：開關(guan)管基(ji)極電(dian)(dian)壓(ya)為0.6~0.7V，集電(dian)(dian)極電(dian)(dian)壓(ya)大于(yu)250V說明(ming)開關(guan)管具備(bei)了工作條件，故(gu)障在正反饋電(dian)(dian)路，包括正反饋電(dian)(dian)阻電(dian)(dian)容續流二極管及(ji)(ji)開關(guan)變壓(ya)器正反饋繞組及(ji)(ji)其之間(jian)的連接應(ying)制板。