一、二極管工作原理是什么
晶體(ti)二(er)極管(guan)為(wei)一個由p型(xing)半導(dao)體(ti)和(he)n型(xing)半導(dao)體(ti)形成的p-n結,在其界(jie)面(mian)處兩側形成空間(jian)電(dian)(dian)(dian)(dian)(dian)荷層,并(bing)建(jian)(jian)有自建(jian)(jian)電(dian)(dian)(dian)(dian)(dian)場(chang)。當不存在外(wai)(wai)加(jia)(jia)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)時(shi),由于(yu)p-n結兩邊載流(liu)(liu)(liu)子濃度差(cha)引起的擴(kuo)散電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)和(he)自建(jian)(jian)電(dian)(dian)(dian)(dian)(dian)場(chang)引起的漂移電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)相等而處于(yu)電(dian)(dian)(dian)(dian)(dian)平(ping)衡狀態。當外(wai)(wai)界(jie)有正向電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)偏置時(shi),外(wai)(wai)界(jie)電(dian)(dian)(dian)(dian)(dian)場(chang)和(he)自建(jian)(jian)電(dian)(dian)(dian)(dian)(dian)場(chang)的互相抑消作用使載流(liu)(liu)(liu)子的擴(kuo)散電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)增加(jia)(jia)引起了正向電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)。當外(wai)(wai)界(jie)有反向電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)偏置時(shi),外(wai)(wai)界(jie)電(dian)(dian)(dian)(dian)(dian)場(chang)和(he)自建(jian)(jian)電(dian)(dian)(dian)(dian)(dian)場(chang)進一步加(jia)(jia)強,形成在一定反向電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)范圍內(nei)與反向偏置電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)值無(wu)關的反向飽和(he)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)I0。
二、二極管導電特性是怎樣的
二(er)極(ji)(ji)管(guan)最重要的特(te)性(xing)就(jiu)是單方向導電(dian)性(xing)。在電(dian)路(lu)中,電(dian)流只能從二(er)極(ji)(ji)管(guan)的正極(ji)(ji)流入,負極(ji)(ji)流出。下面通過簡單的實驗說明二(er)極(ji)(ji)管(guan)的正向特(te)性(xing)和反向特(te)性(xing)。
1、正向特性
在(zai)電(dian)(dian)(dian)子電(dian)(dian)(dian)路中,將二(er)(er)極(ji)管(guan)(guan)(guan)的(de)(de)正(zheng)(zheng)(zheng)(zheng)極(ji)接在(zai)高電(dian)(dian)(dian)位端,負極(ji)接在(zai)低電(dian)(dian)(dian)位端,二(er)(er)極(ji)管(guan)(guan)(guan)就會導(dao)(dao)通,這(zhe)種連接方(fang)式,稱為(wei)正(zheng)(zheng)(zheng)(zheng)向(xiang)(xiang)偏置。必須說(shuo)明,當(dang)加在(zai)二(er)(er)極(ji)管(guan)(guan)(guan)兩(liang)端的(de)(de)正(zheng)(zheng)(zheng)(zheng)向(xiang)(xiang)電(dian)(dian)(dian)壓(ya)很小時,二(er)(er)極(ji)管(guan)(guan)(guan)仍然不(bu)能導(dao)(dao)通,流過二(er)(er)極(ji)管(guan)(guan)(guan)的(de)(de)正(zheng)(zheng)(zheng)(zheng)向(xiang)(xiang)電(dian)(dian)(dian)流十分微弱。只有當(dang)正(zheng)(zheng)(zheng)(zheng)向(xiang)(xiang)電(dian)(dian)(dian)壓(ya)達到某一(yi)數值(zhi)(這(zhe)一(yi)數值(zhi)稱為(wei)“門檻(jian)電(dian)(dian)(dian)壓(ya)”,鍺(zang)(zang)管(guan)(guan)(guan)約(yue)(yue)為(wei)0.2V,硅管(guan)(guan)(guan)約(yue)(yue)為(wei)0.6V)以后,二(er)(er)極(ji)管(guan)(guan)(guan)才(cai)能直正(zheng)(zheng)(zheng)(zheng)導(dao)(dao)通。導(dao)(dao)通后二(er)(er)極(ji)管(guan)(guan)(guan)兩(liang)端的(de)(de)電(dian)(dian)(dian)壓(ya)基本上保持不(bu)變(bian)(鍺(zang)(zang)管(guan)(guan)(guan)約(yue)(yue)為(wei)0.3V,硅管(guan)(guan)(guan)約(yue)(yue)為(wei)0.7V),稱為(wei)二(er)(er)極(ji)管(guan)(guan)(guan)的(de)(de)“正(zheng)(zheng)(zheng)(zheng)向(xiang)(xiang)壓(ya)降”。
2、反向特性
在電子電路中,二極管的正極接在低電位端,負極接在高電位端,此時二極管中幾乎沒有電流流過,此時二極管處于截止狀態,這種連接方式,稱為反向偏置。二極管處于反向偏置時,仍然會有微弱的反向電流流過二極管,稱為漏電流。當二極管兩端的反向電壓增大到某一數值,反向電流會急劇增大,二極管將失去單方向導電特性,這種狀態稱為二極管的擊穿。
三、二極管的主要參數
用來表示(shi)二(er)極(ji)管(guan)的(de)(de)性(xing)(xing)能好壞和適用范(fan)圍(wei)的(de)(de)技術指(zhi)標,稱為二(er)極(ji)管(guan)的(de)(de)參(can)(can)數(shu)(shu)。不同類型(xing)的(de)(de)二(er)極(ji)管(guan)有不同的(de)(de)特性(xing)(xing)參(can)(can)數(shu)(shu)。對初學者而(er)言,必須了解以下幾個主要參(can)(can)數(shu)(shu):
1、額定正向工作電流
是(shi)指二(er)極管(guan)長期連(lian)續工作時(shi)允許通過(guo)(guo)的(de)最大正(zheng)(zheng)向(xiang)電(dian)流值。因為電(dian)流通過(guo)(guo)管(guan)子時(shi)會使(shi)管(guan)芯發熱,溫(wen)(wen)度(du)上(shang)升,溫(wen)(wen)度(du)超過(guo)(guo)容(rong)許限度(du)(硅管(guan)為140左(zuo)右(you),鍺管(guan)為90左(zuo)右(you))時(shi),就會使(shi)管(guan)芯過(guo)(guo)熱而損壞。所以,二(er)極管(guan)使(shi)用中不要超過(guo)(guo)二(er)極管(guan)額(e)定(ding)正(zheng)(zheng)向(xiang)工作電(dian)流值。例如,常用的(de)IN4001-4007型鍺二(er)極管(guan)的(de)額(e)定(ding)正(zheng)(zheng)向(xiang)工作電(dian)流為1A。
2、最高反向工作電壓
加在二(er)極管(guan)兩端的反(fan)向(xiang)(xiang)電(dian)(dian)壓(ya)(ya)高到一定(ding)值時,會將(jiang)管(guan)子(zi)擊穿,失去(qu)單向(xiang)(xiang)導電(dian)(dian)能力(li)。為(wei)(wei)了保證使用(yong)安全,規定(ding)了最高反(fan)向(xiang)(xiang)工作電(dian)(dian)壓(ya)(ya)值。例如,IN4001二(er)極管(guan)反(fan)向(xiang)(xiang)耐壓(ya)(ya)為(wei)(wei)50V,IN4007反(fan)向(xiang)(xiang)耐壓(ya)(ya)為(wei)(wei)1000V。
3、反向電流
反向電流是指二極管在規定的溫度和最高反向(xiang)電壓作用下(xia),流(liu)過二極管的反(fan)(fan)向(xiang)電流(liu)。反(fan)(fan)向(xiang)電流(liu)越小,管子(zi)的單方向(xiang)導電性能越好。值(zhi)得注(zhu)意的是反(fan)(fan)向(xiang)電流(liu)與(yu)溫度有(you)著密切的關系,大約溫度每(mei)升高(gao)10,反(fan)(fan)向(xiang)電流增大一倍。例如2AP1型鍺二極管,在25時反向電流若為250uA,溫度升高到35,反向電流將上升到500uA,依此類推,在75時,它的反向電流已達8mA,不僅失去了單方向導電特性,還會使管子過熱而損壞。又如,2CP10型硅二極管,25時反向電流僅為5uA,溫度升高到75時,反向電流也不過160uA。故硅二極管比鍺二極管在高溫下具有較好的穩定性。