一、電阻的種類有哪些
1、按伏安特性分類
可分為(wei)線(xian)(xian)性(xing)電(dian)(dian)(dian)阻和非線(xian)(xian)性(xing)電(dian)(dian)(dian)阻。對大(da)多數導體來說,在一定的溫(wen)度(du)下,其電(dian)(dian)(dian)阻幾乎維持不變而為(wei)一定值,這類(lei)電(dian)(dian)(dian)阻稱為(wei)線(xian)(xian)性(xing)電(dian)(dian)(dian)阻。
有些(xie)材料的(de)(de)(de)電(dian)(dian)阻(zu)明顯地隨著電(dian)(dian)流(liu)(或電(dian)(dian)壓)而變(bian)化,其伏安(an)特性(xing)是(shi)一條曲線(xian),這(zhe)類電(dian)(dian)阻(zu)稱為(wei)非(fei)線(xian)性(xing)電(dian)(dian)阻(zu)。非(fei)線(xian)性(xing)電(dian)(dian)阻(zu)在某一給定(ding)的(de)(de)(de)電(dian)(dian)壓(或電(dian)(dian)流(liu))作用下,電(dian)(dian)壓與電(dian)(dian)流(liu)的(de)(de)(de)比值(zhi)為(wei)在該工作點下的(de)(de)(de)靜態(tai)電(dian)(dian)阻(zu),伏安(an)特性(xing)曲線(xian)上的(de)(de)(de)斜率(lv)為(wei)動態(tai)電(dian)(dian)阻(zu)。表達非(fei)線(xian)性(xing)電(dian)(dian)阻(zu)特性(xing)的(de)(de)(de)方式比較復雜,但這(zhe)些(xie)非(fei)線(xian)性(xing)關系(xi)在電(dian)(dian)子電(dian)(dian)路中(zhong)得到了(le)廣(guang)泛的(de)(de)(de)應用。
2、按材料分類
a.線繞(rao)(rao)電阻(zu)器(qi)由電阻(zu)線繞(rao)(rao)成(cheng)電阻(zu)器(qi),用(yong)高(gao)(gao)阻(zu)合金(jin)線繞(rao)(rao)在絕緣(yuan)骨架上制成(cheng),外面涂有耐(nai)(nai)熱的釉絕緣(yuan)層或絕緣(yuan)漆(qi)。繞(rao)(rao)線電阻(zu)具(ju)有較低的溫度(du)系數,阻(zu)值精度(du)高(gao)(gao),穩定性好(hao),耐(nai)(nai)熱耐(nai)(nai)腐蝕,主要做精密(mi)大(da)功率(lv)電阻(zu)使(shi)用(yong),缺(que)點是高(gao)(gao)頻性能差,時間(jian)常數大(da)。
b.碳合(he)(he)成(cheng)(cheng)電阻器由碳及(ji)合(he)(he)成(cheng)(cheng)塑膠壓制成(cheng)(cheng)而成(cheng)(cheng)。
c.碳(tan)(tan)膜(mo)電阻(zu)器在(zai)瓷(ci)(ci)管上鍍上一層碳(tan)(tan)而成(cheng)(cheng),將結晶碳(tan)(tan)沉積在(zai)陶(tao)瓷(ci)(ci)棒骨架(jia)上制成(cheng)(cheng)。碳(tan)(tan)膜(mo)電阻(zu)器成(cheng)(cheng)本(ben)低、性能穩定、阻(zu)值范圍寬(kuan)、溫度系數(shu)和電壓系數(shu)低,是目(mu)前應用最廣泛(fan)的電阻(zu)器。
d.金屬(shu)膜(mo)電(dian)阻(zu)器(qi)在瓷管上(shang)鍍上(shang)一層金屬(shu)而成,用(yong)真空(kong)蒸發的方法將合(he)金材料(liao)蒸鍍于陶(tao)瓷棒骨架(jia)表(biao)(biao)面。金屬(shu)膜(mo)電(dian)阻(zu)比碳膜(mo)電(dian)阻(zu)的精度高,穩定性好,噪聲,溫度系數小。在儀器(qi)儀表(biao)(biao)及通訊設備中大量采用(yong)。
e.金屬氧(yang)化膜電(dian)(dian)阻(zu)器在(zai)瓷管(guan)上鍍上一(yi)層(ceng)氧(yang)化錫而成(cheng),在(zai)絕緣棒上沉積一(yi)層(ceng)金屬氧(yang)化物。由于其本(ben)身即是(shi)氧(yang)化物,所以高溫下(xia)穩定,耐熱(re)沖(chong)擊,負載能(neng)力強。按用(yong)途分,有通用(yong)、精密、高頻、高壓、高阻(zu)、大功率和電(dian)(dian)阻(zu)網絡等(deng)。
3、特殊電阻器
a.保(bao)險(xian)(xian)電阻:又(you)叫熔(rong)斷電阻器,在正(zheng)常情(qing)況(kuang)下起著電阻和保(bao)險(xian)(xian)絲(si)(si)的雙重作用(yong),當電路出現故障而使其功(gong)率(lv)超過額(e)定功(gong)率(lv)時,它會像保(bao)險(xian)(xian)絲(si)(si)一(yi)(yi)樣(yang)熔(rong)斷使連接電路斷開。保(bao)險(xian)(xian)絲(si)(si)電阻一(yi)(yi)般電阻值(zhi)都小(0.33Ω~10KΩ),功(gong)率(lv)也較(jiao)小。保(bao)險(xian)(xian)絲(si)(si)電阻器常用(yong)型號有:RF10型、RF111-5保(bao)險(xian)(xian)絲(si)(si)電阻器的符號型、RRD0910型、RRD0911型等。
b.敏(min)(min)(min)感(gan)電(dian)(dian)阻(zu)(zu)器(qi):是指(zhi)其電(dian)(dian)阻(zu)(zu)值對于某種物理量(如溫度(du)、濕度(du)、光照、電(dian)(dian)壓、機械力、以及氣體濃度(du)等)具有敏(min)(min)(min)感(gan)特(te)性(xing),當這些物理量發生(sheng)變(bian)化(hua)時,敏(min)(min)(min)感(gan)電(dian)(dian)阻(zu)(zu)的阻(zu)(zu)值就會隨物理量變(bian)化(hua)而(er)發生(sheng)改(gai)變(bian),呈(cheng)現(xian)不(bu)同的電(dian)(dian)阻(zu)(zu)值。根據(ju)對不(bu)同物理量敏(min)(min)(min)感(gan),敏(min)(min)(min)感(gan)電(dian)(dian)阻(zu)(zu)器(qi)可分為(wei)熱敏(min)(min)(min)、濕敏(min)(min)(min)、光敏(min)(min)(min)、壓敏(min)(min)(min)、力敏(min)(min)(min)、磁敏(min)(min)(min)和氣敏(min)(min)(min)等類型敏(min)(min)(min)感(gan)電(dian)(dian)阻(zu)(zu)。敏(min)(min)(min)感(gan)電(dian)(dian)阻(zu)(zu)器(qi)所(suo)用的材(cai)料幾乎都是半導體材(cai)料,這類電(dian)(dian)阻(zu)(zu)器(qi)也稱為(wei)半導體電(dian)(dian)阻(zu)(zu)器(qi)。
c.熱(re)敏(min)電(dian)(dian)(dian)阻(zu)(zu)(zu)的阻(zu)(zu)(zu)值隨(sui)溫(wen)(wen)(wen)度(du)(du)(du)變(bian)化而變(bian)化,溫(wen)(wen)(wen)度(du)(du)(du)升高阻(zu)(zu)(zu)為負(fu)溫(wen)(wen)(wen)度(du)(du)(du)系(xi)數(shu)(NTC)熱(re)敏(min)電(dian)(dian)(dian)阻(zu)(zu)(zu)。應(ying)用較多的是(shi)(shi)負(fu)溫(wen)(wen)(wen)度(du)(du)(du)系(xi)數(shu)熱(re)敏(min)電(dian)(dian)(dian)阻(zu)(zu)(zu),又可分為普(pu)通型(xing)負(fu)溫(wen)(wen)(wen)度(du)(du)(du)系(xi)數(shu)熱(re)敏(min)電(dian)(dian)(dian)阻(zu)(zu)(zu);穩壓型(xing)負(fu)溫(wen)(wen)(wen)度(du)(du)(du)系(xi)數(shu)熱(re)敏(min)電(dian)(dian)(dian)阻(zu)(zu)(zu);測溫(wen)(wen)(wen)型(xing)負(fu)溫(wen)(wen)(wen)度(du)(du)(du)系(xi)數(shu)熱(re)敏(min)電(dian)(dian)(dian)阻(zu)(zu)(zu)等。光(guang)敏(min)電(dian)(dian)(dian)阻(zu)(zu)(zu)是(shi)(shi)電(dian)(dian)(dian)阻(zu)(zu)(zu)的阻(zu)(zu)(zu)值隨(sui)入(ru)射光(guang)的強弱(ruo)變(bian)化而改變(bian),當(dang)入(ru)射光(guang)增強時,光(guang)敏(min)電(dian)(dian)(dian)阻(zu)(zu)(zu)的減(jian)小(xiao),入(ru)射光(guang)減(jian)弱(ruo)時電(dian)(dian)(dian)阻(zu)(zu)(zu)值增大(da)。
二、電阻器選用的方法
1、固定電阻器的選用
固定(ding)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)有多種類型,選(xuan)擇哪一種材料和(he)(he)結構的(de)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi),應根據應用(yong)電(dian)(dian)(dian)路(lu)的(de)具體(ti)要求而(er)定(ding)。高(gao)(gao)頻電(dian)(dian)(dian)路(lu)應選(xuan)用(yong)分布電(dian)(dian)(dian)感和(he)(he)分布電(dian)(dian)(dian)容小的(de)非線繞(rao)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi),例如碳(tan)膜(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)、金(jin)屬(shu)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)和(he)(he)金(jin)屬(shu)氧(yang)化膜(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi),薄(bo)膜(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi),厚膜(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi),合金(jin)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi),防腐蝕鍍膜(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)等。高(gao)(gao)增益小信號(hao)放大電(dian)(dian)(dian)路(lu)應選(xuan)用(yong)低噪聲電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi),例如金(jin)屬(shu)膜(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)、碳(tan)膜(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)和(he)(he)線繞(rao)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi),而(er)不能使(shi)用(yong)噪聲較大的(de)合成碳(tan)膜(mo)(mo)(mo)電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)和(he)(he)有機實心電(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)。
所(suo)選電(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)(qi)的(de)(de)電(dian)(dian)阻(zu)(zu)(zu)值應(ying)(ying)(ying)(ying)接(jie)近應(ying)(ying)(ying)(ying)用(yong)電(dian)(dian)路(lu)中計算值的(de)(de)一個標稱值,應(ying)(ying)(ying)(ying)優先選用(yong)標準系列的(de)(de)電(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)(qi)。一般電(dian)(dian)路(lu)使用(yong)的(de)(de)電(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)(qi)允許誤差(cha)為±5%~±10%。精(jing)密(mi)儀(yi)器(qi)(qi)(qi)(qi)及(ji)特殊(shu)電(dian)(dian)路(lu)中使用(yong)的(de)(de)電(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)(qi),應(ying)(ying)(ying)(ying)選用(yong)精(jing)密(mi)電(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)(qi),對精(jing)密(mi)度為1%以內的(de)(de)電(dian)(dian)阻(zu)(zu)(zu),如(ru)0.01%,0.1%,0.5%這些量(liang)級的(de)(de)電(dian)(dian)阻(zu)(zu)(zu)應(ying)(ying)(ying)(ying)采用(yong)捷比信電(dian)(dian)阻(zu)(zu)(zu)。所(suo)選電(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)(qi)的(de)(de)額定功(gong)率(lv)(lv),要符合應(ying)(ying)(ying)(ying)用(yong)電(dian)(dian)路(lu)中對電(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)(qi)功(gong)率(lv)(lv)容量(liang)的(de)(de)要求,一般不應(ying)(ying)(ying)(ying)隨意加大或減(jian)小(xiao)電(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)(qi)的(de)(de)功(gong)率(lv)(lv)。
若(ruo)電(dian)路要求是(shi)功(gong)率型電(dian)阻(zu)器(qi),則其(qi)額定(ding)功(gong)率可高于實際應用(yong)電(dian)路要求功(gong)率的1~2倍。
2、熔斷電阻器的選用
熔(rong)斷電(dian)(dian)阻(zu)器具(ju)有保護功能的電(dian)(dian)阻(zu)器。選(xuan)用時應考慮(lv)其雙重性能,根據電(dian)(dian)路的具(ju)體要(yao)求選(xuan)擇其阻(zu)值(zhi)和功率等(deng)參數。既要(yao)保證它在過負荷時能快速熔(rong)斷,又要(yao)保證它在正常條件下能長期穩(wen)定的工作(zuo)。電(dian)(dian)阻(zu)值(zhi)過大(da)(da)或功率過大(da)(da),均不(bu)能起(qi)到保護作(zuo)用。
三、電阻器選用的基本原則
1、選擇通(tong)過認證機構認證的生產線制造出的執行高(gao)水(shui)平標準的電阻器。
2、選擇具備(bei)功(gong)能優(you)勢(shi)、質(zhi)量優(you)勢(shi)、效率優(you)勢(shi)、功(gong)能價格比優(you)勢(shi)、服務優(you)勢(shi)的(de)制造商生產的(de)電阻器。
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。