如何判断三极管的类型和极性

用数字式万用表判断基极b和三极管的类型:将万用表欧姆挡置"R×200"或"R×2k"处,先假设三极管的某极为"基极",并把红表笔接在假设的基极上,将黑表笔先后接在其余两个极上,如果两次测得的电阻值都很小(或约为几百欧至几千欧),那么假设的基极是正确的,且被测三极管为NPN型管；同上,如果两次测得的电阻值都很大(约为几千欧至几十千欧),那么假设的基极是正确的,且被测三极管为PNP型管。如果两次测得的电阻值是一大一小,那么原来假设的基极是错误的,这时必须重新假设另一电极为"基极"，再重复上述测试。

②判断集电极c和发射极e:仍将万用表欧姆挡置"R×200"或"R×2k"处,以NPN管为例,把红表笔接在假设的集电极c上,黑表笔接到假设的发射极e上,并用手捏住b和c极(不能使b、c直接接触),通过人体,相当b、C之间接入偏置电阻,读出表头所示的阻值,然后将两表笔反接重测。假设第一次测得的阻值比第二次小,说明原假设成立,因为c、e问电阻值小说明通过万用表的电流大,偏置正常。万用表都有测三极管放大倍数〔Hfe〕的接口。可以估测一下三极管的放大倍数。己知三极管类型及电极,指针式万用表判别晶体管好坏的方法c、c、e的判别电路示意图〔一〕①测NPN三极管:将万用表欧姆挡置"R×200"或"R×2k"处,把红表笔接在基极上,将黑表笔先后接在其余两个极上,如果两次测得的电阻值都较小,再将黑表笔接在基极上,将红表笔先后接在其余两个极上,如果两次测得的电阻值都很大,那么说明三极管是好的。

②测PNP三极管:将万用表欧姆挡置"R×200"或"R×2k"处,把黑表笔接在基极上,将红表笔先后接在其余两个极上,如果两次测得的电阻值都较小,再将红表笔接在基极上,将黑表笔先后接在其余两个极上,如果两次测得的电阻值都很大,那么说明三极管是好的。补充三极管的管型及管脚的判别是电子技术初学者的一项根本功，为了帮助读者迅速掌握测判方法，笔者总结出四句口诀：“三颠倒，找基极；PN结，定管型；顺箭头，偏转大；测不准，动嘴巴。〞下面让我们逐句进行解释吧。测判三极管的口诀一、三颠倒，找基极大家知道，三极管是含有两个PN结的半导体器件。根据两个PN结连接方式不同，可以分为NPN型和PNP型两种不同导电类型的三极管，测试三极管要使用万用电表的欧姆挡，并选择R×100或R×1k挡位。假定我们并不知道被测三极管是NPN型还是PNP型，也分不清各管脚是什么电极。测试的第一步是判断哪个管脚是基极。这时，我们任取两个电极(如这两个电极为1、2)，用万用电表两支表笔颠倒测量它的正、反向电阻，观察表针的偏转角度；接着，再取1、3两个电极和2、3两个电极，分别颠倒测量它们的正、反向电阻，观察表针的偏转角度。在这三次颠倒测量中，必然有两次测量结果相近：即颠倒测量中表针一次偏转大，一次偏转小；剩下一次必然是颠倒测量前后指针偏转角度都很小，这一次未测的那只管脚就是我们要寻找的基极。二、PN结，定管型找出三极管的基极后，我们就可以根据基极与另外两个电极之间PN结的方向来确定管子的导电类型。将万用表的黑表笔接触基极，红表笔接触另外两个电极中的任一电极，假设表头指针偏转角度很大，那么说明被测三极管为NPN型管；假设表头指针偏转角度很小，那么被测管即为PNP型。三、顺箭头，偏转大找出了基极b，另外两个电极哪个是集电极c，哪个是发射极e呢?这时我们可以用测穿透电流ICEO的方法确定集电极c和发射极e。(1)对于NPN型三极管，穿透电流的测量电路如图3所示。根据这个原理，用万用电表的黑、红表笔颠倒测量两极间的正、反向电阻Rce和Rec，虽然两次测量中万用表指针偏转角度都很小，但仔细观察，总会有一次偏转角度稍大，此时电流的流向一定是：黑表笔→c极→b极→e极→红表笔，电流流向正好与三极管符号中的箭头方向一致(“顺箭头〞)，所以此时黑表笔所接的一定是集电极c，红表笔所接的一定是发射极e。(2)对于PNP型的三极管，道理也类似于NPN型，其电流流向一定是：黑表笔→e极→b极→c极→红表笔，其电流流向也与三极管符号中的箭头方向一致，所以此时黑表笔所接的一定是发射极e，红表笔所接的一定是集电极c。四、测不出，动嘴巴假设在“顺箭头，偏转大〞的测量过程中，假设由于颠倒前后的两次测量指针偏转均太小难以区分时，就要“动嘴巴〞了。具体方法是：在“顺箭头，偏转大〞的两次测量中，用两只手分别捏住两表笔与管脚的结合部，用嘴巴含住(或用舌头抵住)基电极b，仍用“顺箭头，偏转大〞的判别方法即可区分开集电极c与发射极e。其中人体起到直流偏置电阻的作用，目的是使效果更加明显。三极管选型一:常用PNP三极管型号及参数表三极管选型一:常用PNP三极管型号及参数表序号型号Pcm[W]Icm[A]Vceo[V]fT[MHz]封装用途说明生产厂商0012SA8570.50.5150140TO-92TV-VAPNPNIP0022SA928A0.25120

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