一、電阻的種類有哪些
1、按伏安特性分類
可分(fen)為(wei)線性電(dian)阻(zu)和非線性電(dian)阻(zu)。對大多數導體(ti)來說,在一(yi)定的(de)溫(wen)度下,其電(dian)阻(zu)幾乎維持(chi)不變而(er)為(wei)一(yi)定值,這類(lei)電(dian)阻(zu)稱為(wei)線性電(dian)阻(zu)。
有些材料的電(dian)(dian)(dian)(dian)阻(zu)明顯地隨著電(dian)(dian)(dian)(dian)流(或電(dian)(dian)(dian)(dian)壓(ya))而(er)變化,其伏安(an)特(te)(te)性(xing)(xing)(xing)是一條曲線(xian)(xian)(xian),這類電(dian)(dian)(dian)(dian)阻(zu)稱為非(fei)(fei)線(xian)(xian)(xian)性(xing)(xing)(xing)電(dian)(dian)(dian)(dian)阻(zu)。非(fei)(fei)線(xian)(xian)(xian)性(xing)(xing)(xing)電(dian)(dian)(dian)(dian)阻(zu)在(zai)某一給定(ding)的電(dian)(dian)(dian)(dian)壓(ya)(或電(dian)(dian)(dian)(dian)流)作用下,電(dian)(dian)(dian)(dian)壓(ya)與電(dian)(dian)(dian)(dian)流的比值為在(zai)該工作點下的靜態電(dian)(dian)(dian)(dian)阻(zu),伏安(an)特(te)(te)性(xing)(xing)(xing)曲線(xian)(xian)(xian)上(shang)的斜率為動態電(dian)(dian)(dian)(dian)阻(zu)。表達非(fei)(fei)線(xian)(xian)(xian)性(xing)(xing)(xing)電(dian)(dian)(dian)(dian)阻(zu)特(te)(te)性(xing)(xing)(xing)的方式(shi)比較復雜,但這些非(fei)(fei)線(xian)(xian)(xian)性(xing)(xing)(xing)關系在(zai)電(dian)(dian)(dian)(dian)子電(dian)(dian)(dian)(dian)路中得(de)到了廣泛的應用。
2、按材料分類
a.線(xian)(xian)繞電阻(zu)器由電阻(zu)線(xian)(xian)繞成(cheng)電阻(zu)器,用高阻(zu)合(he)金線(xian)(xian)繞在絕(jue)(jue)緣骨架上制(zhi)成(cheng),外面涂(tu)有(you)耐熱的釉絕(jue)(jue)緣層或絕(jue)(jue)緣漆。繞線(xian)(xian)電阻(zu)具有(you)較低的溫度(du)系數,阻(zu)值精度(du)高,穩定性(xing)好,耐熱耐腐蝕,主要做(zuo)精密(mi)大功率電阻(zu)使用,缺點是高頻性(xing)能差,時間(jian)常(chang)數大。
b.碳(tan)合成(cheng)電阻器由(you)碳(tan)及(ji)合成(cheng)塑膠(jiao)壓(ya)制成(cheng)而成(cheng)。
c.碳(tan)膜電阻(zu)器(qi)在瓷(ci)管上(shang)鍍上(shang)一層碳(tan)而成(cheng),將結晶碳(tan)沉積在陶(tao)瓷(ci)棒骨架(jia)上(shang)制成(cheng)。碳(tan)膜電阻(zu)器(qi)成(cheng)本(ben)低、性能穩定、阻(zu)值范圍寬、溫度系數和電壓系數低,是目前應用最廣泛的電阻(zu)器(qi)。
d.金(jin)屬膜(mo)電(dian)阻(zu)器在瓷(ci)管上鍍(du)上一層金(jin)屬而(er)成,用真空(kong)蒸發(fa)的方法將合金(jin)材料蒸鍍(du)于(yu)陶瓷(ci)棒骨(gu)架表面。金(jin)屬膜(mo)電(dian)阻(zu)比(bi)碳膜(mo)電(dian)阻(zu)的精(jing)度(du)(du)高,穩定性(xing)好,噪聲(sheng),溫度(du)(du)系(xi)數小(xiao)。在儀器儀表及(ji)通訊設備中大量采用。
e.金(jin)屬氧化(hua)膜電(dian)阻(zu)器在瓷管上鍍上一層氧化(hua)錫而成,在絕緣(yuan)棒上沉積一層金(jin)屬氧化(hua)物(wu)。由于(yu)其本(ben)身即是氧化(hua)物(wu),所以高(gao)溫(wen)下穩定,耐(nai)熱沖擊(ji),負載能力強。按(an)用途分(fen),有通用、精密、高(gao)頻、高(gao)壓、高(gao)阻(zu)、大(da)功率和電(dian)阻(zu)網絡等(deng)。
3、特殊電阻器
a.保(bao)險電(dian)(dian)阻(zu):又叫熔斷(duan)(duan)電(dian)(dian)阻(zu)器,在(zai)正(zheng)常情(qing)況下起著電(dian)(dian)阻(zu)和保(bao)險絲的(de)雙重作用(yong),當電(dian)(dian)路出現故(gu)障而使其(qi)功(gong)(gong)率超(chao)過額定功(gong)(gong)率時,它會(hui)像保(bao)險絲一樣熔斷(duan)(duan)使連接電(dian)(dian)路斷(duan)(duan)開(kai)。保(bao)險絲電(dian)(dian)阻(zu)一般(ban)電(dian)(dian)阻(zu)值(zhi)都小(xiao)(0.33Ω~10KΩ),功(gong)(gong)率也(ye)較小(xiao)。保(bao)險絲電(dian)(dian)阻(zu)器常用(yong)型(xing)號有:RF10型(xing)、RF111-5保(bao)險絲電(dian)(dian)阻(zu)器的(de)符(fu)號型(xing)、RRD0910型(xing)、RRD0911型(xing)等。
b.敏(min)(min)感(gan)(gan)(gan)(gan)電(dian)阻(zu)器(qi):是指其電(dian)阻(zu)值(zhi)(zhi)對于某(mou)種物(wu)(wu)理量(liang)(liang)(如溫度、濕(shi)度、光照、電(dian)壓、機械力、以及氣體(ti)濃度等)具有(you)敏(min)(min)感(gan)(gan)(gan)(gan)特性,當(dang)這些物(wu)(wu)理量(liang)(liang)發生變化時(shi),敏(min)(min)感(gan)(gan)(gan)(gan)電(dian)阻(zu)的阻(zu)值(zhi)(zhi)就會(hui)隨物(wu)(wu)理量(liang)(liang)變化而發生改變,呈(cheng)現不(bu)(bu)同(tong)的電(dian)阻(zu)值(zhi)(zhi)。根據(ju)對不(bu)(bu)同(tong)物(wu)(wu)理量(liang)(liang)敏(min)(min)感(gan)(gan)(gan)(gan),敏(min)(min)感(gan)(gan)(gan)(gan)電(dian)阻(zu)器(qi)可(ke)分(fen)為(wei)熱敏(min)(min)、濕(shi)敏(min)(min)、光敏(min)(min)、壓敏(min)(min)、力敏(min)(min)、磁敏(min)(min)和氣敏(min)(min)等類型敏(min)(min)感(gan)(gan)(gan)(gan)電(dian)阻(zu)。敏(min)(min)感(gan)(gan)(gan)(gan)電(dian)阻(zu)器(qi)所用的材料幾乎都是半(ban)(ban)導體(ti)材料,這類電(dian)阻(zu)器(qi)也稱為(wei)半(ban)(ban)導體(ti)電(dian)阻(zu)器(qi)。
c.熱敏(min)電(dian)(dian)阻(zu)(zu)(zu)的阻(zu)(zu)(zu)值隨溫(wen)度(du)(du)(du)變化(hua)而變化(hua),溫(wen)度(du)(du)(du)升高(gao)阻(zu)(zu)(zu)為負(fu)(fu)溫(wen)度(du)(du)(du)系(xi)數(shu)(NTC)熱敏(min)電(dian)(dian)阻(zu)(zu)(zu)。應用較(jiao)多的是負(fu)(fu)溫(wen)度(du)(du)(du)系(xi)數(shu)熱敏(min)電(dian)(dian)阻(zu)(zu)(zu),又可分為普通型(xing)負(fu)(fu)溫(wen)度(du)(du)(du)系(xi)數(shu)熱敏(min)電(dian)(dian)阻(zu)(zu)(zu);穩壓型(xing)負(fu)(fu)溫(wen)度(du)(du)(du)系(xi)數(shu)熱敏(min)電(dian)(dian)阻(zu)(zu)(zu);測溫(wen)型(xing)負(fu)(fu)溫(wen)度(du)(du)(du)系(xi)數(shu)熱敏(min)電(dian)(dian)阻(zu)(zu)(zu)等。光(guang)敏(min)電(dian)(dian)阻(zu)(zu)(zu)是電(dian)(dian)阻(zu)(zu)(zu)的阻(zu)(zu)(zu)值隨入(ru)射(she)光(guang)的強(qiang)弱變化(hua)而改變,當入(ru)射(she)光(guang)增強(qiang)時,光(guang)敏(min)電(dian)(dian)阻(zu)(zu)(zu)的減小,入(ru)射(she)光(guang)減弱時電(dian)(dian)阻(zu)(zu)(zu)值增大。
二、電阻器選用的方法
1、固定電阻器的選用
固定電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)有多種類型,選擇哪一種材料和(he)結(jie)構的(de)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi),應根據應用電(dian)(dian)(dian)(dian)路(lu)的(de)具體要(yao)求而(er)定。高頻電(dian)(dian)(dian)(dian)路(lu)應選用分布電(dian)(dian)(dian)(dian)感和(he)分布電(dian)(dian)(dian)(dian)容小的(de)非線繞(rao)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi),例(li)(li)如碳(tan)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)、金(jin)屬(shu)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)和(he)金(jin)屬(shu)氧化膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi),薄膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi),厚膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi),合金(jin)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi),防腐蝕鍍膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)等(deng)。高增益小信號(hao)放大電(dian)(dian)(dian)(dian)路(lu)應選用低(di)噪(zao)聲(sheng)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi),例(li)(li)如金(jin)屬(shu)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)、碳(tan)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)和(he)線繞(rao)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi),而(er)不能使用噪(zao)聲(sheng)較大的(de)合成碳(tan)膜(mo)(mo)(mo)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)和(he)有機(ji)實(shi)心電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)。
所(suo)選電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi)的電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)值應(ying)接近應(ying)用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)路中(zhong)計(ji)算值的一(yi)個標稱值,應(ying)優先選用(yong)標準(zhun)系(xi)列的電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi)。一(yi)般電(dian)(dian)(dian)(dian)(dian)(dian)路使用(yong)的電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi)允許(xu)誤(wu)差為±5%~±10%。精(jing)密(mi)(mi)儀器(qi)(qi)(qi)及特殊電(dian)(dian)(dian)(dian)(dian)(dian)路中(zhong)使用(yong)的電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi),應(ying)選用(yong)精(jing)密(mi)(mi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi),對(dui)精(jing)密(mi)(mi)度(du)為1%以內(nei)的電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu),如0.01%,0.1%,0.5%這些量級的電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)應(ying)采用(yong)捷比信(xin)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)。所(suo)選電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi)的額定功率(lv),要(yao)符合應(ying)用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)路中(zhong)對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi)功率(lv)容量的要(yao)求,一(yi)般不應(ying)隨意(yi)加大或減小電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi)的功率(lv)。
若(ruo)電路要求是功率型電阻器,則(ze)其(qi)額定功率可(ke)高于實際應用(yong)電路要求功率的1~2倍。
2、熔斷電阻器的選用
熔(rong)斷(duan)電(dian)阻器具有保護功能(neng)的電(dian)阻器。選(xuan)用時(shi)應考慮(lv)其雙重(zhong)性能(neng),根據電(dian)路的具體要(yao)求選(xuan)擇其阻值(zhi)和功率等參數。既要(yao)保證(zheng)它在過(guo)負(fu)荷時(shi)能(neng)快速熔(rong)斷(duan),又要(yao)保證(zheng)它在正常(chang)條件下能(neng)長期穩定的工作(zuo)。電(dian)阻值(zhi)過(guo)大或(huo)功率過(guo)大,均(jun)不能(neng)起到保護作(zuo)用。
三、電阻器選用的基本原則
1、選擇通過認(ren)證(zheng)機構(gou)認(ren)證(zheng)的(de)生產線(xian)制造(zao)出的(de)執行高水(shui)平(ping)標準的(de)電阻器。
2、選擇(ze)具備(bei)功能優(you)(you)勢(shi)、質量優(you)(you)勢(shi)、效(xiao)率優(you)(you)勢(shi)、功能價格比優(you)(you)勢(shi)、服務優(you)(you)勢(shi)的制造商生產的電阻(zu)器。
3、選擇能滿足上述要求的上型號目錄的制造商,并向其直接訂購電阻器。