一、二極管工作原理是什么
晶(jing)體(ti)(ti)二極管為一(yi)個由p型(xing)半(ban)導體(ti)(ti)和n型(xing)半(ban)導體(ti)(ti)形(xing)成的(de)p-n結(jie),在(zai)其(qi)界面處兩側形(xing)成空間電(dian)(dian)(dian)(dian)(dian)荷(he)層,并(bing)建(jian)有(you)自(zi)建(jian)電(dian)(dian)(dian)(dian)(dian)場(chang)。當不存在(zai)外加(jia)電(dian)(dian)(dian)(dian)(dian)壓時,由于p-n結(jie)兩邊(bian)載流子濃(nong)度差引起的(de)擴(kuo)散電(dian)(dian)(dian)(dian)(dian)流和自(zi)建(jian)電(dian)(dian)(dian)(dian)(dian)場(chang)引起的(de)漂移電(dian)(dian)(dian)(dian)(dian)流相等而處于電(dian)(dian)(dian)(dian)(dian)平衡狀態。當外界有(you)正向(xiang)電(dian)(dian)(dian)(dian)(dian)壓偏(pian)置(zhi)時,外界電(dian)(dian)(dian)(dian)(dian)場(chang)和自(zi)建(jian)電(dian)(dian)(dian)(dian)(dian)場(chang)的(de)互相抑消作用使載流子的(de)擴(kuo)散電(dian)(dian)(dian)(dian)(dian)流增加(jia)引起了(le)正向(xiang)電(dian)(dian)(dian)(dian)(dian)流。當外界有(you)反向(xiang)電(dian)(dian)(dian)(dian)(dian)壓偏(pian)置(zhi)時,外界電(dian)(dian)(dian)(dian)(dian)場(chang)和自(zi)建(jian)電(dian)(dian)(dian)(dian)(dian)場(chang)進一(yi)步加(jia)強,形(xing)成在(zai)一(yi)定反向(xiang)電(dian)(dian)(dian)(dian)(dian)壓范圍內與反向(xiang)偏(pian)置(zhi)電(dian)(dian)(dian)(dian)(dian)壓值無(wu)關(guan)的(de)反向(xiang)飽和電(dian)(dian)(dian)(dian)(dian)流I0。
二、二極管導電特性是怎樣的
二(er)極管最重要的(de)特(te)性(xing)(xing)就是(shi)單方(fang)向(xiang)導電性(xing)(xing)。在電路(lu)中,電流只能從二(er)極管的(de)正極流入,負極流出。下面通過簡(jian)單的(de)實(shi)驗說明(ming)二(er)極管的(de)正向(xiang)特(te)性(xing)(xing)和反向(xiang)特(te)性(xing)(xing)。
1、正向特性
在電(dian)子電(dian)路中,將二(er)(er)(er)極(ji)管(guan)(guan)(guan)(guan)的正(zheng)極(ji)接在高電(dian)位(wei)端,負極(ji)接在低(di)電(dian)位(wei)端,二(er)(er)(er)極(ji)管(guan)(guan)(guan)(guan)就(jiu)會導通,這種(zhong)連接方式,稱為(wei)正(zheng)向(xiang)偏置。必須說明,當(dang)加在二(er)(er)(er)極(ji)管(guan)(guan)(guan)(guan)兩(liang)端的正(zheng)向(xiang)電(dian)壓(ya)很小(xiao)時(shi),二(er)(er)(er)極(ji)管(guan)(guan)(guan)(guan)仍然不能導通,流(liu)過二(er)(er)(er)極(ji)管(guan)(guan)(guan)(guan)的正(zheng)向(xiang)電(dian)流(liu)十分微弱(ruo)。只有當(dang)正(zheng)向(xiang)電(dian)壓(ya)達到某(mou)一數(shu)值(這一數(shu)值稱為(wei)“門檻電(dian)壓(ya)”,鍺管(guan)(guan)(guan)(guan)約(yue)為(wei)0.2V,硅管(guan)(guan)(guan)(guan)約(yue)為(wei)0.6V)以后,二(er)(er)(er)極(ji)管(guan)(guan)(guan)(guan)才(cai)能直(zhi)正(zheng)導通。導通后二(er)(er)(er)極(ji)管(guan)(guan)(guan)(guan)兩(liang)端的電(dian)壓(ya)基本上(shang)保持不變(鍺管(guan)(guan)(guan)(guan)約(yue)為(wei)0.3V,硅管(guan)(guan)(guan)(guan)約(yue)為(wei)0.7V),稱為(wei)二(er)(er)(er)極(ji)管(guan)(guan)(guan)(guan)的“正(zheng)向(xiang)壓(ya)降(jiang)”。
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
用來表示二(er)極管的性(xing)能(neng)好壞和適用范圍的技(ji)術指標,稱為二(er)極管的參數(shu)(shu)。不同(tong)類(lei)型的二(er)極管有不同(tong)的特性(xing)參數(shu)(shu)。對初學(xue)者而言(yan),必須了解以下幾個主要參數(shu)(shu):
1、額定正向工作電流
是指二極(ji)管(guan)(guan)長期連(lian)續工(gong)作時允(yun)許(xu)通過(guo)(guo)的最(zui)大正向電(dian)(dian)流(liu)(liu)值。因(yin)為電(dian)(dian)流(liu)(liu)通過(guo)(guo)管(guan)(guan)子時會使管(guan)(guan)芯發熱(re),溫度上升,溫度超過(guo)(guo)容許(xu)限(xian)度(硅管(guan)(guan)為140左(zuo)(zuo)右(you),鍺管(guan)(guan)為90左(zuo)(zuo)右(you))時,就會使管(guan)(guan)芯過(guo)(guo)熱(re)而損壞。所以(yi),二極(ji)管(guan)(guan)使用(yong)中(zhong)不(bu)要超過(guo)(guo)二極(ji)管(guan)(guan)額定正向工(gong)作電(dian)(dian)流(liu)(liu)值。例(li)如(ru),常用(yong)的IN4001-4007型鍺二極(ji)管(guan)(guan)的額定正向工(gong)作電(dian)(dian)流(liu)(liu)為1A。
2、最高反向工作電壓
加在(zai)二(er)極管兩(liang)端的反向電(dian)壓高(gao)到(dao)一定值(zhi)時,會將管子(zi)擊穿(chuan),失去單向導電(dian)能力。為了(le)保證(zheng)使(shi)用安全,規定了(le)最高(gao)反向工作電(dian)壓值(zhi)。例(li)如,IN4001二(er)極管反向耐壓為50V,IN4007反向耐壓為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(dian)(dian)(dian)壓作用下,流(liu)過二極(ji)管的(de)反向(xiang)電(dian)(dian)(dian)流(liu)。反向(xiang)電(dian)(dian)(dian)流(liu)越(yue)小,管子的(de)單方向(xiang)導電(dian)(dian)(dian)性能(neng)越(yue)好。值得(de)注意的(de)是反向(xiang)電(dian)(dian)(dian)流(liu)與溫度(du)有著密切的(de)關系,大(da)約溫度(du)每升(sheng)高10,反向(xiang)電(dian)(dian)(dian)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。