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Can you help me test a transistor

Discussion in 'General Electronics Discussion' started by r2pee3, Oct 5, 2016.

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  1. r2pee3

    r2pee3

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    Oct 5, 2016
    I have a mpsw45a transistor npn . I need to test it with multimeter to see if its good. When I use a multimeter to test it, positive on base and neg on collector I get a value however when I move the neg to emitter there is no value. I am a newb so maybe I am not doing this correctly. Thanks
     
    Last edited by a moderator: Oct 6, 2016
  2. BobK

    BobK

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    Jan 5, 2010
    I assume you mean using the diode test function of your multimeter, correct?

    If so, you should get something like 0.6V on both of those connections. If you get nothing with the base positive and emitter negative, the transistor is bad.

    Oh, and welcome to E.P.

    Bob
     
  3. r2pee3

    r2pee3

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    Oct 5, 2016
    Hello Bob,
    I bought 5 brand new transistor and all of it are testing the same. I have it set on diode test fnction.
    Thanks
     
  4. BobK

    BobK

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    Jan 5, 2010
    Are you sure you are identifying the pins correctly?

    What kind of transistor?

    Bob
     
  5. r2pee3

    r2pee3

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    Oct 5, 2016
    This is a mpsw45a npn darlington ss 1a 50v 1
     
  6. Audioguru

    Audioguru

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    Sep 24, 2016
    The datasheet from Motorola shows the schematic of its insides and its pins.
    It has one silicon junction between its base and its collector with a forward voltage of about 0.65V. It has two silicon junctions in series between its base and emitter with a total forward voltage of about 1.3V that your multimeter diode test might not show.
     

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  7. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    You need to put the transistor in a circuit with a 12v car globe (one of the globes for the inside light. )
    Put 4k7 on the base and the 12v rail. The lamp will illuminate.
    If it was a normal transistor, the lamp would not glow.
    This is a Darlington.
     
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  8. r2pee3

    r2pee3

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    Oct 5, 2016
    That explains why. Thank you very much
     
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