如何判斷三極管的類型和極性

用數(shù)字式萬用表判斷基極b和三極管的類型:將萬用表歐姆擋置"R×200"或"R×2k"處,先假設(shè)三極管的某極為"基極",并把紅表筆接在假設(shè)的基極上,將黑表筆先后接在其余兩個極上,如果兩次測得的電阻值都很小(或約為幾百歐至幾千歐),那么假設(shè)的基極是正確的,且被測三極管為NPN型管；同上,如果兩次測得的電阻值都很大(約為幾千歐至幾十千歐),那么假設(shè)的基極是正確的,且被測三極管為PNP型管。如果兩次測得的電阻值是一大一小,那么原來假設(shè)的基極是錯誤的,這時必須重新假設(shè)另一電極為"基極"，再重復(fù)上述測試。

②判斷集電極c和發(fā)射極e:仍將萬用表歐姆擋置"R×200"或"R×2k"處,以NPN管為例,把紅表筆接在假設(shè)的集電極c上,黑表筆接到假設(shè)的發(fā)射極e上,并用手捏住b和c極(不能使b、c直接接觸),通過人體,相當(dāng)b、C之間接入偏置電阻,讀出表頭所示的阻值,然后將兩表筆反接重測。假設(shè)第一次測得的阻值比第二次小,說明原假設(shè)成立,因為c、e問電阻值小說明通過萬用表的電流大,偏置正常。萬用表都有測三極管放大倍數(shù)〔Hfe〕的接口?？梢怨罍y一下三極管的放大倍數(shù)。己知三極管類型及電極,指針式萬用表判別晶體管好壞的方法c、c、e的判別電路示意圖〔一〕①測NPN三極管:將萬用表歐姆擋置"R×200"或"R×2k"處,把紅表筆接在基極上,將黑表筆先后接在其余兩個極上,如果兩次測得的電阻值都較小,再將黑表筆接在基極上,將紅表筆先后接在其余兩個極上,如果兩次測得的電阻值都很大,那么說明三極管是好的。

②測PNP三極管:將萬用表歐姆擋置"R×200"或"R×2k"處,把黑表筆接在基極上,將紅表筆先后接在其余兩個極上,如果兩次測得的電阻值都較小,再將紅表筆接在基極上,將黑表筆先后接在其余兩個極上,如果兩次測得的電阻值都很大,那么說明三極管是好的。補充三極管的管型及管腳的判別是電子技術(shù)初學(xué)者的一項根本功，為了幫助讀者迅速掌握測判方法，筆者總結(jié)出四句口訣：“三顛倒，找基極；PN結(jié)，定管型；順箭頭，偏轉(zhuǎn)大；測不準(zhǔn)，動嘴巴。〞下面讓我們逐句進行解釋吧。測判三極管的口訣一、三顛倒，找基極大家知道，三極管是含有兩個PN結(jié)的半導(dǎo)體器件。根據(jù)兩個PN結(jié)連接方式不同，可以分為NPN型和PNP型兩種不同導(dǎo)電類型的三極管，測試三極管要使用萬用電表的歐姆擋，并選擇R×100或R×1k擋位。假定我們并不知道被測三極管是NPN型還是PNP型，也分不清各管腳是什么電極。測試的第一步是判斷哪個管腳是基極。這時，我們?nèi)稳蓚€電極(如這兩個電極為1、2)，用萬用電表兩支表筆顛倒測量它的正、反向電阻，觀察表針的偏轉(zhuǎn)角度；接著，再取1、3兩個電極和2、3兩個電極，分別顛倒測量它們的正、反向電阻，觀察表針的偏轉(zhuǎn)角度。在這三次顛倒測量中，必然有兩次測量結(jié)果相近：即顛倒測量中表針一次偏轉(zhuǎn)大，一次偏轉(zhuǎn)小；剩下一次必然是顛倒測量前后指針偏轉(zhuǎn)角度都很小，這一次未測的那只管腳就是我們要尋找的基極。二、PN結(jié)，定管型找出三極管的基極后，我們就可以根據(jù)基極與另外兩個電極之間PN結(jié)的方向來確定管子的導(dǎo)電類型。將萬用表的黑表筆接觸基極，紅表筆接觸另外兩個電極中的任一電極，假設(shè)表頭指針偏轉(zhuǎn)角度很大，那么說明被測三極管為NPN型管；假設(shè)表頭指針偏轉(zhuǎn)角度很小，那么被測管即為PNP型。三、順箭頭，偏轉(zhuǎn)大找出了基極b，另外兩個電極哪個是集電極c，哪個是發(fā)射極e呢?這時我們可以用測穿透電流ICEO的方法確定集電極c和發(fā)射極e。(1)對于NPN型三極管，穿透電流的測量電路如圖3所示。根據(jù)這個原理，用萬用電表的黑、紅表筆顛倒測量兩極間的正、反向電阻Rce和Rec，雖然兩次測量中萬用表指針偏轉(zhuǎn)角度都很小，但仔細(xì)觀察，總會有一次偏轉(zhuǎn)角度稍大，此時電流的流向一定是：黑表筆→c極→b極→e極→紅表筆，電流流向正好與三極管符號中的箭頭方向一致(“順箭頭〞)，所以此時黑表筆所接的一定是集電極c，紅表筆所接的一定是發(fā)射極e。(2)對于PNP型的三極管，道理也類似于NPN型，其電流流向一定是：黑表筆→e極→b極→c極→紅表筆，其電流流向也與三極管符號中的箭頭方向一致，所以此時黑表筆所接的一定是發(fā)射極e，紅表筆所接的一定是集電極c。四、測不出，動嘴巴假設(shè)在“順箭頭，偏轉(zhuǎn)大〞的測量過程中，假設(shè)由于顛倒前后的兩次測量指針偏轉(zhuǎn)均太小難以區(qū)分時，就要“動嘴巴〞了。具體方法是：在“順箭頭，偏轉(zhuǎn)大〞的兩次測量中，用兩只手分別捏住兩表筆與管腳的結(jié)合部，用嘴巴含住(或用舌頭抵住)基電極b，仍用“順箭頭，偏轉(zhuǎn)大〞的判別方法即可區(qū)分開集電極c與發(fā)射極e。其中人體起到直流偏置電阻的作用，目的是使效果更加明顯。三極管選型一:常用PNP三極管型號及參數(shù)表三極管選型一:常用PNP三極管型號及參數(shù)表序號型號Pcm[W]Icm[A]Vceo[V]fT[MHz]封裝用途說明生產(chǎn)廠商0012SA8570.50.5150140TO-92TV-VAPNPNIP0022SA928A0.25120

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