一、二極管工作原理是什么
晶體(ti)二極管為(wei)一個由(you)p型半導體(ti)和n型半導體(ti)形成(cheng)的(de)(de)p-n結(jie),在其界(jie)面處(chu)(chu)兩側(ce)形成(cheng)空(kong)間電(dian)(dian)(dian)(dian)(dian)荷層(ceng),并建有自(zi)(zi)建電(dian)(dian)(dian)(dian)(dian)場(chang)(chang)。當(dang)不存在外(wai)(wai)(wai)加(jia)電(dian)(dian)(dian)(dian)(dian)壓時,由(you)于p-n結(jie)兩邊載(zai)流(liu)(liu)子濃(nong)度差(cha)引(yin)(yin)起的(de)(de)擴散(san)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)和自(zi)(zi)建電(dian)(dian)(dian)(dian)(dian)場(chang)(chang)引(yin)(yin)起的(de)(de)漂移電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)相等而處(chu)(chu)于電(dian)(dian)(dian)(dian)(dian)平衡狀態。當(dang)外(wai)(wai)(wai)界(jie)有正(zheng)向(xiang)(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)壓偏置(zhi)時,外(wai)(wai)(wai)界(jie)電(dian)(dian)(dian)(dian)(dian)場(chang)(chang)和自(zi)(zi)建電(dian)(dian)(dian)(dian)(dian)場(chang)(chang)的(de)(de)互(hu)相抑(yi)消作用使(shi)載(zai)流(liu)(liu)子的(de)(de)擴散(san)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)增(zeng)加(jia)引(yin)(yin)起了(le)正(zheng)向(xiang)(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。當(dang)外(wai)(wai)(wai)界(jie)有反向(xiang)(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)壓偏置(zhi)時,外(wai)(wai)(wai)界(jie)電(dian)(dian)(dian)(dian)(dian)場(chang)(chang)和自(zi)(zi)建電(dian)(dian)(dian)(dian)(dian)場(chang)(chang)進(jin)一步加(jia)強,形成(cheng)在一定反向(xiang)(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)壓范圍內(nei)與反向(xiang)(xiang)(xiang)偏置(zhi)電(dian)(dian)(dian)(dian)(dian)壓值(zhi)無關的(de)(de)反向(xiang)(xiang)(xiang)飽和電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)I0。
二、二極管導電特性是怎樣的
二極(ji)管(guan)最重要的(de)(de)特性就是單方向(xiang)導電(dian)性。在電(dian)路中,電(dian)流只能從二極(ji)管(guan)的(de)(de)正極(ji)流入(ru),負極(ji)流出。下面(mian)通過簡單的(de)(de)實驗說(shuo)明二極(ji)管(guan)的(de)(de)正向(xiang)特性和反(fan)向(xiang)特性。
1、正向特性
在(zai)電(dian)(dian)子電(dian)(dian)路中(zhong),將二(er)(er)極(ji)管(guan)(guan)(guan)的正極(ji)接在(zai)高電(dian)(dian)位端,負極(ji)接在(zai)低電(dian)(dian)位端,二(er)(er)極(ji)管(guan)(guan)(guan)就會(hui)導(dao)(dao)通(tong),這種連接方(fang)式,稱為(wei)正向偏置。必須說明,當(dang)加在(zai)二(er)(er)極(ji)管(guan)(guan)(guan)兩(liang)端的正向電(dian)(dian)壓很小(xiao)時,二(er)(er)極(ji)管(guan)(guan)(guan)仍然不能導(dao)(dao)通(tong),流過(guo)二(er)(er)極(ji)管(guan)(guan)(guan)的正向電(dian)(dian)流十分微(wei)弱(ruo)。只有當(dang)正向電(dian)(dian)壓達到某一(yi)數(shu)值(這一(yi)數(shu)值稱為(wei)“門檻(jian)電(dian)(dian)壓”,鍺管(guan)(guan)(guan)約(yue)為(wei)0.2V,硅(gui)管(guan)(guan)(guan)約(yue)為(wei)0.6V)以后,二(er)(er)極(ji)管(guan)(guan)(guan)才能直正導(dao)(dao)通(tong)。導(dao)(dao)通(tong)后二(er)(er)極(ji)管(guan)(guan)(guan)兩(liang)端的電(dian)(dian)壓基本(ben)上保持不變(bian)(鍺管(guan)(guan)(guan)約(yue)為(wei)0.3V,硅(gui)管(guan)(guan)(guan)約(yue)為(wei)0.7V),稱為(wei)二(er)(er)極(ji)管(guan)(guan)(guan)的“正向壓降”。
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(yong)來表示二(er)極(ji)管的性(xing)能(neng)好壞和(he)適用(yong)范圍的技術指標,稱為二(er)極(ji)管的參(can)數(shu)。不同(tong)類型的二(er)極(ji)管有不同(tong)的特(te)性(xing)參(can)數(shu)。對初學者而言,必(bi)須(xu)了(le)解(jie)以下(xia)幾(ji)個主要(yao)參(can)數(shu):
1、額定正向工作電流
是指二極(ji)(ji)管(guan)(guan)長期連續(xu)工(gong)作時(shi)(shi)允許通過的最(zui)大正向(xiang)電流值(zhi)。因為電流通過管(guan)(guan)子時(shi)(shi)會使管(guan)(guan)芯發熱,溫度上升,溫度超(chao)過容許限度(硅管(guan)(guan)為140左右,鍺管(guan)(guan)為90左右)時(shi)(shi),就會使管(guan)(guan)芯過熱而損(sun)壞。所以,二極(ji)(ji)管(guan)(guan)使用中不(bu)要超(chao)過二極(ji)(ji)管(guan)(guan)額(e)定正向(xiang)工(gong)作電流值(zhi)。例如,常用的IN4001-4007型鍺二極(ji)(ji)管(guan)(guan)的額(e)定正向(xiang)工(gong)作電流為1A。
2、最高反向工作電壓
加(jia)在二(er)極管兩端的反向(xiang)(xiang)(xiang)電(dian)(dian)壓(ya)高到(dao)一定值時(shi),會(hui)將管子擊穿,失(shi)去單向(xiang)(xiang)(xiang)導電(dian)(dian)能(neng)力。為(wei)了(le)保(bao)證使用(yong)安全,規定了(le)最高反向(xiang)(xiang)(xiang)工作(zuo)電(dian)(dian)壓(ya)值。例(li)如,IN4001二(er)極管反向(xiang)(xiang)(xiang)耐(nai)壓(ya)為(wei)50V,IN4007反向(xiang)(xiang)(xiang)耐(nai)壓(ya)為(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電(dian)(dian)壓作用下,流(liu)過(guo)二極(ji)管的(de)反(fan)向電(dian)(dian)流(liu)。反(fan)向電(dian)(dian)流(liu)越(yue)小,管子的(de)單方向導電(dian)(dian)性能(neng)越(yue)好(hao)。值得注意的(de)是反(fan)向電(dian)(dian)流(liu)與溫度有著密切的(de)關(guan)系(xi),大約溫度每(mei)升(sheng)高10,反(fan)向電(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。