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how to check a MOSFET & BJT

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rabel126

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how we can check a faulty NPN & PNP
and faulty N-cahnnel and P-channel
 

the_edge

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For bjt, if you dont have multimeter with that option, you can use diode checker on your multimeter...
NPN: Connect plus on base and with minus touch collector than emitor, if you see some resistance than it is good. Then you need to check if it will conduct if inverse direction... So connect minus to base, and plus to collector than emitor. If there is some resistance, or you hear beep, your transistor is dead because it conducted current. And the last check is to check if there is connection betwin collector and emitor, so you connect collector to plus and emitor to minus, resistance should be infinity, than connect emitor to plus and collector to minus, and here also should not be connection....

This is because, as you might know, PN connection should conduct current only in one direction... And we can represent NPN transistor as two diodes:

NPN:
C----|<-------->|-------E
               |
              B

PNP:
C---->|--------|<-------E
               |
               B


For PNP it is dual...

So to sumarise:
For NPN:
Step 1: B to plus, C to minus, check numbers on multimeter, than E to minus...
Step 2: B to minus, C to plus, if there is beep or some numbers on multimeter than transistor is dead... if not E to plus, again if there is beep or numbers it is dead...
Step 3: C to plus, E to minus, if no connection, E to plus C to minus. If no connection, tr is OK...

For PNP:
Step 1: B to minus, C to plus, check numbers on multimeter, than E to plus...
Step 2: B to plus, C to minus, if there is beep or some numbers on multimeter than transistor is dead... if not E to minus, again if there is beep or numbers it is dead...
Step 3: C to plus, E to minus, if no connection, E to plus C to minus. If no connection, tr is OK...
 

    rabel126

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A.Anand Srinivasan

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for bjt you can use the multimeter and check it by checking for the β or using diode checker to find the resistance between the different terminals... for N channel and P channel you can find by checking the resistance between the different terminals based on whether the FET is enhancement mode or depletion mode.....
 

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