傳統的(de)(de)(de)(de)輸入浪涌電(dian)(dian)流(liu)(liu)限(xian)制方法(fa)是串聯負溫度系數熱(re)敏限(xian)流(liu)(liu)電(dian)(dian)阻器(qi)(NTC)，然而(er)這(zhe)種簡單的(de)(de)(de)(de)方法(fa)具有很多(duo)缺點：如NTC電(dian)(dian)阻器(qi)的(de)(de)(de)(de)限(xian)流(liu)(liu)效果(guo)受環(huan)境溫度影響較大、限(xian)流(liu)(liu)效果(guo)在(zai)短暫的(de)(de)(de)(de)輸入主電(dian)(dian)網(wang)中斷(約幾(ji)百毫秒數量級)時只能部分(fen)地達到(dao)、NTC電(dian)(dian)阻器(qi)的(de)(de)(de)(de)功率(lv)損耗降(jiang)低(di)了開關電(dian)(dian)源的(de)(de)(de)(de)轉換效率(lv)……。其實上面提出(chu)的(de)(de)(de)(de)這(zhe)兩個問(wen)題可(ke)以通過一個“軟啟動(dong)電(dian)(dian)路”來解(jie)決(jue)，下(xia)面詳細介(jie)紹之。

　　1 開關電(dian)源浪涌電(dian)流(liu)產生的原因(yin)

　　開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)源(yuan)的輸入(ru)電(dian)(dian)(dian)(dian)路(lu)大(da)都采(cai)用電(dian)(dian)(dian)(dian)容濾波(bo)型整流(liu)電(dian)(dian)(dian)(dian)路(lu)，在進線電(dian)(dian)(dian)(dian)源(yuan)合(he)閘(zha)瞬間(jian)，由于電(dian)(dian)(dian)(dian)容器(qi)上(shang)的初(chu)始(shi)電(dian)(dian)(dian)(dian)壓為零(ling)，電(dian)(dian)(dian)(dian)容器(qi)充電(dian)(dian)(dian)(dian)瞬間(jian)會(hui)(hui)形成(cheng)很大(da)的浪(lang)涌(yong)(yong)電(dian)(dian)(dian)(dian)流(liu)，特別是(shi)大(da)功率開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)源(yuan)，采(cai)用容量較(jiao)大(da)的濾波(bo)電(dian)(dian)(dian)(dian)容器(qi)，使浪(lang)涌(yong)(yong)電(dian)(dian)(dian)(dian)流(liu)達100A以(yi)上(shang)。在電(dian)(dian)(dian)(dian)源(yuan)接通瞬間(jian)如此(ci)大(da)的浪(lang)涌(yong)(yong)電(dian)(dian)(dian)(dian)流(liu)，重者(zhe)往往會(hui)(hui)導致輸入(ru)熔斷(duan)器(qi)燒斷(duan)或合(he)閘(zha)開(kai)(kai)關(guan)的觸(chu)點燒壞(huai)，整流(liu)橋過流(liu)損壞(huai);輕者(zhe)也會(hui)(hui)使空氣開(kai)(kai)關(guan)合(he)不上(shang)閘(zha)。上(shang)述(shu)現象均會(hui)(hui)造成(cheng)開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)源(yuan)無法正(zheng)(zheng)常工作，為此(ci)幾乎所有的開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)源(yuan)都設置了防止流(liu)涌(yong)(yong)電(dian)(dian)(dian)(dian)流(liu)的軟啟動電(dian)(dian)(dian)(dian)路(lu)，以(yi)保證二手機器(qi)人電(dian)(dian)(dian)(dian)源(yuan)正(zheng)(zheng)常而可靠運(yun)行。

　　2 軟啟動電(dian)路電(dian)氣工作原理

　　如果采用“軟啟動電路”來消除開關電源啟(qi)動(dong)時的(de)浪(lang)涌電(dian)(dian)流(liu)(liu)，可(ke)以(yi)很(hen)好地避(bi)免上述傳統浪(lang)涌電(dian)(dian)流(liu)(liu)限制(zhi)(zhi)方法的(de)缺點(dian)。通(tong)過“軟啟(qi)動(dong)”來(lai)控制(zhi)(zhi)開關電(dian)(dian)源(yuan)(yuan)的(de)啟(qi)動(dong)以(yi)消除(chu)浪(lang)涌電(dian)(dian)流(liu)(liu)，包含(han)這(zhe)樣兩條設計原則：即在加電(dian)(dian)瞬間(jian)除(chu)去負載(zai)、同時限制(zhi)(zhi)有(you)用的(de)電(dian)(dian)流(liu)(liu)。如果不驅(qu)動(dong)負載(zai)，開關電(dian)(dian)源(yuan)(yuan)啟(qi)動(dong)時一般電(dian)(dian)流(liu)(liu)很(hen)小。在很(hen)多情(qing)況下，啟(qi)動(dong)電(dian)(dian)流(liu)(liu)實(shi)際(ji)有(you)可(ke)能要(yao)比利用這(zhe)種方法保(bao)持的(de)穩態工作電(dian)(dian)流(liu)(liu)小。