傳統的(de)輸入浪涌電(dian)流限(xian)制方法是(shi)串聯負溫(wen)度系數(shu)熱敏(min)限(xian)流電(dian)阻器(qi)(qi)(NTC)，然而這種簡單的(de)方法具有很多缺點：如NTC電(dian)阻器(qi)(qi)的(de)限(xian)流效(xiao)(xiao)果(guo)受(shou)環境溫(wen)度影響較大、限(xian)流效(xiao)(xiao)果(guo)在短暫的(de)輸入主電(dian)網中斷(約幾百毫(hao)秒數(shu)量級)時只能(neng)部分地(di)達到、NTC電(dian)阻器(qi)(qi)的(de)功率(lv)損耗降低(di)了開關電(dian)源的(de)轉換效(xiao)(xiao)率(lv)……。其實上(shang)面提出的(de)這兩個問題可以通過一個“軟啟動電(dian)路”來解決，下(xia)面詳細介紹之(zhi)。

　　1 開關電源浪涌電流產生的原因

　　開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源的(de)(de)輸入(ru)電(dian)(dian)(dian)(dian)(dian)路大(da)(da)都采用電(dian)(dian)(dian)(dian)(dian)容(rong)濾(lv)波型整流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)路，在進線(xian)電(dian)(dian)(dian)(dian)(dian)源合(he)閘瞬間(jian)，由于電(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)(qi)上(shang)的(de)(de)初始電(dian)(dian)(dian)(dian)(dian)壓為零，電(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)(qi)充電(dian)(dian)(dian)(dian)(dian)瞬間(jian)會形成(cheng)很(hen)大(da)(da)的(de)(de)浪(lang)涌(yong)(yong)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，特(te)別是大(da)(da)功率開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源，采用容(rong)量較大(da)(da)的(de)(de)濾(lv)波電(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)(qi)，使(shi)浪(lang)涌(yong)(yong)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)達100A以(yi)(yi)上(shang)。在電(dian)(dian)(dian)(dian)(dian)源接通瞬間(jian)如此(ci)大(da)(da)的(de)(de)浪(lang)涌(yong)(yong)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，重者往往會導(dao)致(zhi)輸入(ru)熔斷器(qi)(qi)(qi)燒斷或合(he)閘開(kai)關(guan)的(de)(de)觸點燒壞，整流(liu)(liu)橋(qiao)過流(liu)(liu)損壞;輕者也會使(shi)空氣開(kai)關(guan)合(he)不上(shang)閘。上(shang)述現象均(jun)會造成(cheng)開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源無(wu)法正常(chang)工作，為此(ci)幾乎所(suo)有的(de)(de)開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源都設(she)置了(le)防止流(liu)(liu)涌(yong)(yong)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)軟啟動電(dian)(dian)(dian)(dian)(dian)路，以(yi)(yi)保證二手機器(qi)(qi)(qi)人電(dian)(dian)(dian)(dian)(dian)源正常(chang)而可(ke)靠運行。

　　2 軟啟動電路(lu)電氣工作原理

　　如果采用“軟啟動電路”來消除開關電源啟動(dong)時的浪(lang)涌(yong)電(dian)(dian)流(liu)，可(ke)以很(hen)(hen)好地避免(mian)上述傳統(tong)浪(lang)涌(yong)電(dian)(dian)流(liu)限制(zhi)方(fang)法的缺點。通(tong)過(guo)“軟啟動(dong)”來控(kong)制(zhi)開關電(dian)(dian)源(yuan)的啟動(dong)以消除(chu)浪(lang)涌(yong)電(dian)(dian)流(liu)，包含這樣兩(liang)條設(she)計(ji)原則：即在(zai)加電(dian)(dian)瞬(shun)間除(chu)去負載、同時限制(zhi)有用的電(dian)(dian)流(liu)。如果不驅動(dong)負載，開關電(dian)(dian)源(yuan)啟動(dong)時一般電(dian)(dian)流(liu)很(hen)(hen)小。在(zai)很(hen)(hen)多情況下(xia)，啟動(dong)電(dian)(dian)流(liu)實際有可(ke)能(neng)要比(bi)利用這種方(fang)法保持的穩(wen)態(tai)工(gong)作電(dian)(dian)流(liu)小。