傳統的(de)輸(shu)入浪涌電(dian)(dian)流(liu)限(xian)制(zhi)方法是(shi)串(chuan)聯負溫度系數(shu)熱敏(min)限(xian)流(liu)電(dian)(dian)阻(zu)器(qi)(qi)(NTC)，然而這(zhe)種(zhong)簡單(dan)的(de)方法具有很多缺點(dian)：如NTC電(dian)(dian)阻(zu)器(qi)(qi)的(de)限(xian)流(liu)效(xiao)果受環境溫度影響較大、限(xian)流(liu)效(xiao)果在(zai)短暫的(de)輸(shu)入主(zhu)電(dian)(dian)網(wang)中斷(約幾百毫(hao)秒數(shu)量級)時只能部(bu)分地達到、NTC電(dian)(dian)阻(zu)器(qi)(qi)的(de)功(gong)率損耗降(jiang)低了開關電(dian)(dian)源的(de)轉換(huan)效(xiao)率……。其實(shi)上面(mian)提出(chu)的(de)這(zhe)兩個問題可以通過(guo)一個“軟啟(qi)動電(dian)(dian)路”來解(jie)決，下(xia)面(mian)詳細介紹之。

　　1 開關電(dian)源浪涌電(dian)流產生(sheng)的原因

　　開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)大(da)(da)都采用電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)濾(lv)波型整流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)，在(zai)進線電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)合(he)閘瞬(shun)間(jian)(jian)(jian)，由于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)上的(de)初始(shi)電(dian)(dian)(dian)(dian)(dian)(dian)壓為零，電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)充電(dian)(dian)(dian)(dian)(dian)(dian)瞬(shun)間(jian)(jian)(jian)會(hui)形成(cheng)(cheng)很大(da)(da)的(de)浪(lang)涌電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，特別(bie)是大(da)(da)功(gong)率開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)，采用容(rong)量(liang)較大(da)(da)的(de)濾(lv)波電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)，使浪(lang)涌電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)達(da)100A以上。在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)接通瞬(shun)間(jian)(jian)(jian)如(ru)此大(da)(da)的(de)浪(lang)涌電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，重者(zhe)往(wang)往(wang)會(hui)導致輸入熔斷器(qi)燒斷或合(he)閘開(kai)關(guan)的(de)觸點燒壞，整流(liu)(liu)橋(qiao)過流(liu)(liu)損壞;輕者(zhe)也(ye)會(hui)使空氣開(kai)關(guan)合(he)不上閘。上述(shu)現象均會(hui)造成(cheng)(cheng)開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)無法正常工作，為此幾乎所(suo)有的(de)開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)都設置了(le)防(fang)止(zhi)流(liu)(liu)涌電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)軟啟動電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)，以保證二(er)手機(ji)器(qi)人(ren)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)正常而(er)可靠運行。

　　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(shi)的(de)(de)浪涌電(dian)(dian)(dian)流(liu)(liu)，可以很(hen)好地避免(mian)上述傳統浪涌電(dian)(dian)(dian)流(liu)(liu)限制(zhi)方法的(de)(de)缺點。通過(guo)“軟啟(qi)動(dong)”來控制(zhi)開(kai)關電(dian)(dian)(dian)源(yuan)的(de)(de)啟(qi)動(dong)以消除浪涌電(dian)(dian)(dian)流(liu)(liu)，包(bao)含這(zhe)樣(yang)兩條設計原則：即在加電(dian)(dian)(dian)瞬間(jian)除去負載、同時(shi)限制(zhi)有用的(de)(de)電(dian)(dian)(dian)流(liu)(liu)。如果不(bu)驅動(dong)負載，開(kai)關電(dian)(dian)(dian)源(yuan)啟(qi)動(dong)時(shi)一般電(dian)(dian)(dian)流(liu)(liu)很(hen)小。在很(hen)多(duo)情(qing)況下(xia)，啟(qi)動(dong)電(dian)(dian)(dian)流(liu)(liu)實際有可能要(yao)比利用這(zhe)種方法保持的(de)(de)穩態工(gong)作電(dian)(dian)(dian)流(liu)(liu)小。