開關電源以(yi)效率高、電壓(ya)適應性(xing)強而得到(dao)廣(guang)泛應用。

     本文介紹一種插頭可伸縮的袖珍式開關電源充電器，其尺寸為６９ｍｍ×４７ｍｍ×２６ｍｍ。該充電器電(dian)(dian)路(lu)采用分立元(yuan)件(jian)和(he)貼片元(yuan)件(jian)相(xiang)結(jie)合(he)，電(dian)(dian)路(lu)設(she)計別致新穎，元(yuan)件(jian)布局嚴謹合(he)理(li)。供電(dian)(dian)電(dian)(dian)壓(ya)原為１１０Ｖ，可方(fang)便(bian)地改為９０～２５０Ｖ工(gong)作；輸出(chu)電(dian)(dian)壓(ya)５Ｖ，可改動為５～１２Ｖ輸出(chu)，特(te)別適合(he)無繩電(dian)(dian)話或手機的３．６Ｖ（或４～９Ｖ）電(dian)(dian)池作快速(su)充電(dian)(dian)之用。電(dian)(dian)路(lu)原理(li)見附圖。其中Ｄ１、Ｌ１以及Ｃ２等組(zu)成市電(dian)(dian)輸入整流濾波電(dian)(dian)路(lu)，Ｃ２兩端產生約３００Ｖ的直(zhi)流高壓(ya)。

     ＶＴ１、ＶＴ２、Ｎ１、Ｎ２等組成(cheng)自激式振(zhen)蕩電(dian)路，Ｒ３、Ｒ４提供啟動(dong)偏置(zhi)電(dian)流(liu)，使ＶＴ１加電(dian)時即導通，主(zhu)回路Ｎ１中(zhong)有(you)電(dian)流(liu)流(liu)過，Ｎ２上產生感(gan)應(ying)電(dian)壓(ya)。當此電(dian)壓(ya)峰值超過３Ｖ時，Ｄ５擊(ji)穿，通過Ｒ８向(xiang)ＶＴ２提供偏流(liu)，使ＶＴ２飽和(he)導通，ＶＴ１因偏置(zhi)電(dian)壓(ya)被(bei)短路而關斷(duan)。

     當Ｎ１中電(dian)(dian)流(liu)(liu)關斷時，Ｎ２感應電(dian)(dian)壓極性反(fan)(fan)相，經Ｄ５、Ｒ８加反(fan)(fan)向偏壓于ＶＴ２基極，ＶＴ２轉(zhuan)變為截止(zhi)狀態，ＶＴ１經Ｒ３、Ｒ４偏置重(zhong)新導(dao)通。如(ru)此循環往復，形(xing)成間歇自激振蕩(dang)。Ｃ５、Ｒ６用以改善(shan)振蕩(dang)波形(xing)，光電(dian)(dian)耦合器(qi)ＯＰＴ１用以調控(kong)振蕩(dang)器(qi)脈沖(chong)寬度。Ｎ３、Ｌ２、Ｃ７等組成整流(liu)(liu)輸(shu)出電(dian)(dian)路，二極管(guan)３Ｓ９０作(zuo)半(ban)波整流(liu)(liu)，ＲＫ１４作(zuo)充電(dian)(dian)隔離，Ｒ１８為輸(shu)出電(dian)(dian)流(liu)(liu)采樣電(dian)(dian)阻。

    當輸(shu)出(chu)電(dian)(dian)流超(chao)載(zai)（大于０．８Ａ）或(huo)短(duan)(duan)路(lu)時，Ｒ１８上產(chan)生較大壓(ya)降，使ＯＰ１輸(shu)出(chu)電(dian)(dian)位(wei)急劇降低，光電(dian)(dian)耦(ou)合(he)器控制(zhi)振蕩脈沖變窄(zhai)，由Ｎ１耦(ou)合(he)到Ｎ３的(de)平均(jun)能量也大幅度減少(shao)。即(ji)使輸(shu)出(chu)短(duan)(duan)路(lu)，輸(shu)出(chu)電(dian)(dian)流也僅有(you)十(shi)幾(ji)毫安，從而避免了(le)輸(shu)出(chu)端超(chao)載(zai)甚至短(duan)(duan)路(lu)對(dui)開關(guan)電(dian)(dian)源自身造成(cheng)的(de)威(wei)脅。

     穩(wen)壓部分(fen)由ＴＬ４３１等周(zhou)邊(bian)電(dian)(dian)(dian)路組成(cheng)，電(dian)(dian)(dian)壓采樣點取(qu)自被充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)池兩端，按圖中Ｒ１３＋Ｒ１４參數值，空載輸(shu)(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)壓為５．２５Ｖ，對(dui)于３．６Ｖ可(ke)充(chong)(chong)電(dian)(dian)(dian)池的(de)最大充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)為０．９５Ａ，適合對(dui)２Ａｈ以上(shang)的(de)鎳鎘或(huo)鋰電(dian)(dian)(dian)池直(zhi)接充(chong)(chong)電(dian)(dian)(dian)。若用它(ta)對(dui)０．７～１Ａｈ的(de)鎳鎘或(huo)鋰電(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)時，充(chong)(chong)電(dian)(dian)(dian)回路內可(ke)串(chuan)接一只(zhi)１．５～２．５Ω、功率０．５Ｗ的(de)限流(liu)電(dian)(dian)(dian)阻(zu)，使充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)被限制(zhi)在(zai)(zai)０．３～０．４Ａ。經(jing)試驗，該電(dian)(dian)(dian)源的(de)輸(shu)(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)壓只(zhi)需(xu)經(jing)小(xiao)改動，即可(ke)使輸(shu)(shu)(shu)出(chu)(chu)為５～１２Ｖ之間的(de)某一電(dian)(dian)(dian)壓值。方法(fa)是：更換帶(dai) 號的(de)電(dian)(dian)(dian)阻(zu)，在(zai)(zai)２４ｋΩ～６２ｋΩ之間取(qu)值。需(xu)要指出(chu)(chu)的(de)是，輸(shu)(shu)(shu)出(chu)(chu)端濾波電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容器標稱耐壓為１０Ｖ，需(xu)要改為１２Ｖ輸(shu)(shu)(shu)出(chu)(chu)時，請更換成(cheng)耐壓為１６Ｖ的(de)電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容。在(zai)(zai)１２Ｖ時，其(qi)最大輸(shu)(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)流(liu)應控制(zhi)在(zai)(zai)０．７Ａ以內。輸(shu)(shu)(shu)出(chu)(chu)端帶(dai)有(you)２米長黑(hei)白(bai)線(xian)，黑(hei)線(xian)為正極，白(bai)線(xian)為負極。