開關電源不同于線性電源適配器，前者調整管工作在通、斷狀態，后者調整管工作在線性狀態。電源適配器通過控制調整管的通、斷時間實現穩壓。電源適配器的優點是體積小、重量輕、功耗小、穩壓范圍寬，效率可高達80%～90%。調整管功率損耗小，散熱器也隨之減小。英規電源適配器工作頻率在幾十千赫茲甚至幾百千赫茲，濾波電感、電容元件可用較小的容量，允許的環境溫度也可以大大提高，廣泛應用在各種電子設備中。本章主要介紹電源適配器的基本構成、分類及工作原理，讓讀者對電源適配器有一個初步的認識。

　　穩壓電源適配器的比較

　　電(dian)(dian)(dian)子(zi)設(she)備(bei)離(li)不開(kai)電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi)。電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi)供給電(dian)(dian)(dian)子(zi)設(she)備(bei)所(suo)需要的能(neng)(neng)量。電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi)的性(xing)能(neng)(neng)、質量直(zhi)接影響著電(dian)(dian)(dian)子(zi)設(she)備(bei)的安全可靠運行，故此對(dui)電(dian)(dian)(dian)子(zi)設(she)備(bei)電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi)性(xing)能(neng)(neng)、質量的要求也越來越高。現有的電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi)主要有兩大類：串聯(lian)線(xian)性(xing)穩壓電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi)(簡(jian)稱(cheng)線(xian)性(xing)電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi))和開(kai)關穩壓電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi)(簡(jian)稱(cheng)電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi))。這兩類電(dian)(dian)(dian)源(yuan)適(shi)(shi)配器(qi)各具特色而被(bei)廣泛(fan)應用。

　　線性電源適配器的結構與特點

　　線性(xing)電(dian)源適配器通常都是由電(dian)網所(suo)提供的交流(liu)(liu)電(dian)，經(jing)過變壓、整(zheng)流(liu)(liu)、濾(lv)波和穩壓環節而得到。其各(ge)個部分電(dian)路的作(zuo)用如下：

　　①電(dian)源(yuan)適(shi)配(pei)器(qi)變壓(ya)(ya)器(qi)——將220V電(dian)網電(dian)壓(ya)(ya)轉換為(wei)整流電(dian)路(lu)所需要的交(jiao)流電(dian)壓(ya)(ya)值，而少部(bu)分電(dian)路(lu)采用電(dian)容降壓(ya)(ya)，如遙控電(dian)風扇(shan)電(dian)路(lu)。

　　②整(zheng)(zheng)流(liu)(liu)(liu)電(dian)路——將交(jiao)流(liu)(liu)(liu)電(dian)壓轉(zhuan)換為脈動直流(liu)(liu)(liu)電(dian)壓。常(chang)用的整(zheng)(zheng)流(liu)(liu)(liu)電(dian)路有半(ban)波(bo)(bo)整(zheng)(zheng)流(liu)(liu)(liu)電(dian)路、全波(bo)(bo)整(zheng)(zheng)流(liu)(liu)(liu)電(dian)路和橋(qiao)式(shi)整(zheng)(zheng)流(liu)(liu)(liu)電(dian)路。

　　③濾(lv)(lv)波(bo)(bo)電(dian)(dian)路(lu)——將(jiang)脈(mo)動直流(liu)電(dian)(dian)壓轉換(huan)成較為平(ping)滑的直流(liu)電(dian)(dian)壓。線性電(dian)(dian)源適配(pei)器中常用(yong)的濾(lv)(lv)波(bo)(bo)電(dian)(dian)路(lu)有(you)電(dian)(dian)感濾(lv)(lv)波(bo)(bo)、電(dian)(dian)容(rong)濾(lv)(lv)波(bo)(bo)和阻容(rong)濾(lv)(lv)波(bo)(bo)，其(qi)中最常用(yong)的是電(dian)(dian)容(rong)濾(lv)(lv)波(bo)(bo)。

　　④穩(wen)(wen)壓(ya)(ya)(ya)(ya)電(dian)路(lu)——將直流電(dian)源(yuan)(yuan)適配器的(de)(de)輸(shu)出(chu)電(dian)壓(ya)(ya)(ya)(ya)穩(wen)(wen)定(ding)，基(ji)本不受電(dian)網電(dian)壓(ya)(ya)(ya)(ya)或(huo)負載(zai)的(de)(de)影響。在線性電(dian)源(yuan)(yuan)適配器中常(chang)用的(de)(de)穩(wen)(wen)壓(ya)(ya)(ya)(ya)電(dian)路(lu)有(you)二(er)極管穩(wen)(wen)壓(ya)(ya)(ya)(ya)、串(chuan)聯穩(wen)(wen)壓(ya)(ya)(ya)(ya)。其(qi)中，串(chuan)聯穩(wen)(wen)壓(ya)(ya)(ya)(ya)有(you)現成(cheng)(cheng)的(de)(de)集(ji)成(cheng)(cheng)電(dian)路(lu)，如固定(ding)電(dian)壓(ya)(ya)(ya)(ya)輸(shu)出(chu)的(de)(de)集(ji)成(cheng)(cheng)電(dian)路(lu)有(you)LM78××，LM79××等，可調電(dian)壓(ya)(ya)(ya)(ya)輸(shu)出(chu)的(de)(de)集(ji)成(cheng)(cheng)電(dian)路(lu)有(you)LM317和LM337等。

　　4個功能模塊的線性穩壓電源適配器

　　線性(xing)(xing)電(dian)源適配器的優(you)點是穩定性(xing)(xing)好、瞬態響應速度快、可靠性(xing)(xing)高、輸出電(dian)壓(ya)(ya)精度高和輸出紋波電(dian)壓(ya)(ya)小;缺點是工(gong)(gong)作(zuo)頻(pin)率低，所(suo)采用的工(gong)(gong)頻(pin)變(bian)壓(ya)(ya)器、濾波器的體積和重量都(dou)較大。調整管工(gong)(gong)作(zuo)在線性(xing)(xing)狀態，功耗大、效(xiao)率低，需要(yao)加裝散熱器。