開關(guan)電源(yuan)(yuan)(yuan)的工(gong)作過程相當容易理解，在(zai)線(xian)(xian)性電源(yuan)(yuan)(yuan)中，讓(rang)功(gong)(gong)(gong)(gong)率晶(jing)體(ti)(ti)管(guan)工(gong)作在(zai)線(xian)(xian)性模式(shi)，與線(xian)(xian)性電源(yuan)(yuan)(yuan)不同(tong)的是(shi)，PWM開關(guan)電源(yuan)(yuan)(yuan)是(shi)讓(rang)功(gong)(gong)(gong)(gong)率晶(jing)體(ti)(ti)管(guan)工(gong)作在(zai)導(dao)通(tong)和關(guan)斷的狀態，在(zai)這兩種(zhong)狀態中，加(jia)在(zai)功(gong)(gong)(gong)(gong)率晶(jing)體(ti)(ti)管(guan)上的伏(fu)-安乘積(ji)是(shi)很小的（在(zai)導(dao)通(tong)時，電壓低(di)，電流(liu)大；關(guan)斷時，電壓高，電流(liu)小）/功(gong)(gong)(gong)(gong)率器(qi)件(jian)上的伏(fu)安乘積(ji)就是(shi)功(gong)(gong)(gong)(gong)率半導(dao)體(ti)(ti)器(qi)件(jian)上所產生(sheng)的損耗。

　　與(yu)線性電(dian)(dian)(dian)源相比，PWM開關電(dian)(dian)(dian)源更為有效的(de)(de)工作過(guo)程是通過(guo)“斬波”，即把輸(shu)入的(de)(de)直流電(dian)(dian)(dian)壓(ya)斬成幅值等于輸(shu)入電(dian)(dian)(dian)壓(ya)幅值的(de)(de)脈沖電(dian)(dian)(dian)壓(ya)來實現(xian)的(de)(de)。
脈沖的占空比由開關電源的控制(zhi)器(qi)來(lai)調節。一旦輸(shu)入電壓被斬成交流(liu)方(fang)波(bo)，其幅值就可以(yi)通過變(bian)壓器(qi)來(lai)升(sheng)高(gao)或降低。通過增(zeng)加變(bian)壓器(qi)的二(er)次繞組(zu)數就可以(yi)增(zeng)加輸(shu)出的電壓值。最后這些交流(liu)波(bo)形經過整流(liu)濾波(bo)后就得(de)到直流(liu)輸(shu)出電壓。
控制器(qi)(qi)(qi)的(de)主要(yao)(yao)目(mu)的(de)是(shi)保持輸出電(dian)壓穩定(ding)，其工作過(guo)程(cheng)與線性形式的(de)控制器(qi)(qi)(qi)很類似(si)。也就是(shi)說(shuo)控制器(qi)(qi)(qi)的(de)功能塊、電(dian)壓參考和誤(wu)(wu)差放(fang)大(da)器(qi)(qi)(qi)，可以(yi)設計成(cheng)與線性調節器(qi)(qi)(qi)相(xiang)同。他們(men)的(de)不同之處在于，誤(wu)(wu)差放(fang)大(da)器(qi)(qi)(qi)的(de)輸出（誤(wu)(wu)差電(dian)壓）在驅動功率管(guan)之前(qian)要(yao)(yao)經過(guo)一(yi)個電(dian)壓/脈(mo)沖(chong)寬(kuan)度轉(zhuan)換單元(yuan)。
開(kai)關電源(yuan)有(you)兩種主要的工(gong)作方式(shi)：正激式(shi)變換(huan)和升壓式(shi)變換(huan)。盡(jin)管它們各部(bu)分的布置差別(bie)很小(xiao)，但是(shi)工(gong)作過(guo)程相差很大，在特(te)定的應用場合下各有(you)優(you)點。