一、二極管工作原理是什么
晶體(ti)二(er)極(ji)管(guan)為一個由p型半(ban)導體(ti)和(he)(he)n型半(ban)導體(ti)形成(cheng)的(de)(de)p-n結,在其界(jie)面處兩側形成(cheng)空間電(dian)(dian)(dian)(dian)荷層,并建(jian)有自(zi)(zi)建(jian)電(dian)(dian)(dian)(dian)場(chang)(chang)。當不存在外(wai)加電(dian)(dian)(dian)(dian)壓(ya)時,由于p-n結兩邊(bian)載流(liu)子(zi)濃(nong)度(du)差引(yin)起(qi)的(de)(de)擴散電(dian)(dian)(dian)(dian)流(liu)和(he)(he)自(zi)(zi)建(jian)電(dian)(dian)(dian)(dian)場(chang)(chang)引(yin)起(qi)的(de)(de)漂(piao)移(yi)電(dian)(dian)(dian)(dian)流(liu)相等(deng)而處于電(dian)(dian)(dian)(dian)平衡狀態。當外(wai)界(jie)有正(zheng)向電(dian)(dian)(dian)(dian)壓(ya)偏(pian)(pian)置(zhi)時,外(wai)界(jie)電(dian)(dian)(dian)(dian)場(chang)(chang)和(he)(he)自(zi)(zi)建(jian)電(dian)(dian)(dian)(dian)場(chang)(chang)的(de)(de)互相抑消作用使載流(liu)子(zi)的(de)(de)擴散電(dian)(dian)(dian)(dian)流(liu)增加引(yin)起(qi)了正(zheng)向電(dian)(dian)(dian)(dian)流(liu)。當外(wai)界(jie)有反(fan)向電(dian)(dian)(dian)(dian)壓(ya)偏(pian)(pian)置(zhi)時,外(wai)界(jie)電(dian)(dian)(dian)(dian)場(chang)(chang)和(he)(he)自(zi)(zi)建(jian)電(dian)(dian)(dian)(dian)場(chang)(chang)進一步加強,形成(cheng)在一定反(fan)向電(dian)(dian)(dian)(dian)壓(ya)范(fan)圍內與反(fan)向偏(pian)(pian)置(zhi)電(dian)(dian)(dian)(dian)壓(ya)值(zhi)無關的(de)(de)反(fan)向飽和(he)(he)電(dian)(dian)(dian)(dian)流(liu)I0。
二、二極管導電特性是怎樣的
二(er)極管(guan)最重要的特(te)性(xing)就(jiu)是單(dan)方向導電(dian)性(xing)。在電(dian)路中,電(dian)流只能從(cong)二(er)極管(guan)的正極流入,負(fu)極流出。下面(mian)通過簡(jian)單(dan)的實驗說明二(er)極管(guan)的正向特(te)性(xing)和反向特(te)性(xing)。
1、正向特性
在(zai)(zai)電子(zi)電路中,將二(er)極(ji)(ji)(ji)(ji)管(guan)(guan)的正(zheng)極(ji)(ji)(ji)(ji)接(jie)(jie)在(zai)(zai)高電位端(duan)(duan)(duan),負(fu)極(ji)(ji)(ji)(ji)接(jie)(jie)在(zai)(zai)低(di)電位端(duan)(duan)(duan),二(er)極(ji)(ji)(ji)(ji)管(guan)(guan)就會導(dao)(dao)通(tong),這種連接(jie)(jie)方式,稱(cheng)為(wei)(wei)(wei)正(zheng)向(xiang)(xiang)(xiang)偏置(zhi)。必須說明,當(dang)加(jia)在(zai)(zai)二(er)極(ji)(ji)(ji)(ji)管(guan)(guan)兩(liang)端(duan)(duan)(duan)的正(zheng)向(xiang)(xiang)(xiang)電壓(ya)很小(xiao)時,二(er)極(ji)(ji)(ji)(ji)管(guan)(guan)仍然不能導(dao)(dao)通(tong),流(liu)過二(er)極(ji)(ji)(ji)(ji)管(guan)(guan)的正(zheng)向(xiang)(xiang)(xiang)電流(liu)十分(fen)微弱(ruo)。只有當(dang)正(zheng)向(xiang)(xiang)(xiang)電壓(ya)達到某一數(shu)值(zhi)(這一數(shu)值(zhi)稱(cheng)為(wei)(wei)(wei)“門檻(jian)電壓(ya)”,鍺(zang)管(guan)(guan)約為(wei)(wei)(wei)0.2V,硅管(guan)(guan)約為(wei)(wei)(wei)0.6V)以(yi)后,二(er)極(ji)(ji)(ji)(ji)管(guan)(guan)才(cai)能直(zhi)正(zheng)導(dao)(dao)通(tong)。導(dao)(dao)通(tong)后二(er)極(ji)(ji)(ji)(ji)管(guan)(guan)兩(liang)端(duan)(duan)(duan)的電壓(ya)基本(ben)上(shang)保持不變(鍺(zang)管(guan)(guan)約為(wei)(wei)(wei)0.3V,硅管(guan)(guan)約為(wei)(wei)(wei)0.7V),稱(cheng)為(wei)(wei)(wei)二(er)極(ji)(ji)(ji)(ji)管(guan)(guan)的“正(zheng)向(xiang)(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
用來表示二極(ji)管的性能好(hao)壞和適用范圍的技術(shu)指標,稱為(wei)二極(ji)管的參(can)數(shu)。不(bu)同類型的二極(ji)管有不(bu)同的特性參(can)數(shu)。對初學者(zhe)而言,必須了(le)解以(yi)下幾(ji)個主要(yao)參(can)數(shu):
1、額定正向工作電流
是指(zhi)二(er)(er)極管(guan)(guan)長(chang)期連續工(gong)作(zuo)時允(yun)許(xu)(xu)通(tong)過(guo)的最(zui)大正向電流(liu)(liu)值。因為(wei)電流(liu)(liu)通(tong)過(guo)管(guan)(guan)子時會使(shi)管(guan)(guan)芯(xin)發熱(re),溫度上(shang)升(sheng),溫度超(chao)過(guo)容許(xu)(xu)限度(硅管(guan)(guan)為(wei)140左(zuo)右,鍺管(guan)(guan)為(wei)90左(zuo)右)時,就會使(shi)管(guan)(guan)芯(xin)過(guo)熱(re)而(er)損壞。所(suo)以,二(er)(er)極管(guan)(guan)使(shi)用中不(bu)要超(chao)過(guo)二(er)(er)極管(guan)(guan)額定正向工(gong)作(zuo)電流(liu)(liu)值。例(li)如,常(chang)用的IN4001-4007型鍺二(er)(er)極管(guan)(guan)的額定正向工(gong)作(zuo)電流(liu)(liu)為(wei)1A。
2、最高反向工作電壓
加在二(er)極管兩端(duan)的反(fan)向(xiang)電壓(ya)高到一定值時(shi),會將管子(zi)擊穿,失去單(dan)向(xiang)導(dao)電能力。為(wei)(wei)了保證使用安全,規(gui)定了最高反(fan)向(xiang)工作電壓(ya)值。例如,IN4001二(er)極管反(fan)向(xiang)耐(nai)壓(ya)為(wei)(wei)50V,IN4007反(fan)向(xiang)耐(nai)壓(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)(xiang)(xiang)電(dian)壓作用下(xia),流(liu)過二極管的反(fan)向(xiang)(xiang)(xiang)電(dian)流(liu)。反(fan)向(xiang)(xiang)(xiang)電(dian)流(liu)越小,管子的單方向(xiang)(xiang)(xiang)導電(dian)性能越好。值得(de)注(zhu)意的是反(fan)向(xiang)(xiang)(xiang)電(dian)流(liu)與(yu)溫度有著密(mi)切的關系(xi),大約溫度每(mei)升高10,反(fan)向(xiang)(xiang)(xiang)電(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。