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    How to check transistor using digital multimeter?

    referred on the title,please save me on this basic theory~XD

    •   Alt12th July 2011, 09:01

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    Re: How to check transistor using digital multimeter?

    Senthilkumar.



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    Re: How to check transistor using digital multimeter?

    thanks for reply XD



    •   Alt12th July 2011, 09:40

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    Re: How to check transistor using digital multimeter?

    To test a transistor using a digital multimeter, all you have to do is check the resistances of the diode junctions of the transistor, as illustrated here, http://www.learningaboutelectronics....t-a-transistor. Measure each of the pairs of diode junctions, Collector-emitter, collector-base, base-emitter. Read the resistance of one junction and then switch the polarity by switching the probes around. One side should read very high resistance, over 1 megohms. And the other should read a moderate resistance, a few hundred thousand ohms. If this is the case for all three junctions, the transistor should be a good working one.



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    Re: How to check transistor using digital multimeter?

    Quote Originally Posted by dlhylton View Post
    To test a transistor using a digital multimeter, all you have to do is check the resistances of the diode junctions of the transistor, as illustrated here, http://www.learningaboutelectronics....t-a-transistor.
    That article is wrong. There is a lot of bad information on that website.

    Measure each of the pairs of diode junctions, Collector-emitter, collector-base, base-emitter. Read the resistance of one junction and then switch the polarity by switching the probes around.
    There is a diode junction between base and emitter, and between base and collector, but there is no diode junction between collector and emitter.



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    Re: How to check transistor using digital multimeter?

    Basically: picture in your mind 2 diodes in series, with cathode connected to cathode, or anode connected to anode (NPN vs. PNP). The common point corresponds with a (bipolar) transistor's base, the other side of the diodes corresponds to collector & emitter.

    Measure accordingly (so diode test function on a multimeter is useful). A diode shouldn't conduct current in reverse direction & thus measure high resistance then, same for collector <-> emitter when base isn't connected to anything. If collector -> emitter (or vice versa) measures a low resistance, transistor is broken.

    FETs are a whole different story, though...



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    Re: How to check transistor using digital multimeter?

    Quote Originally Posted by dlhylton View Post
    To test a transistor using a digital multimeter, all you have to do is check the resistances of the diode junctions of the transistor, as illustrated here, http://www.learningaboutelectronics....t-a-transistor. Measure each of the pairs of diode junctions, Collector-emitter, collector-base, base-emitter. Read the resistance of one junction and then switch the polarity by switching the probes around. One side should read very high resistance, over 1 megohms. And the other should read a moderate resistance, a few hundred thousand ohms. If this is the case for all three junctions, the transistor should be a good working one.
    LOL @ the fact that although the multimeter shown has a dedicated socket for testing transistors (the round blue region), the author didn't use it but instead opted for a more convoluted, less informative, and less reliable approach.

    - - - Updated - - -

    Quote Originally Posted by dlhylton View Post
    To test a transistor using a digital multimeter, all you have to do is check the resistances of the diode junctions of the transistor, as illustrated here, http://www.learningaboutelectronics....t-a-transistor. Measure each of the pairs of diode junctions, Collector-emitter, collector-base, base-emitter. Read the resistance of one junction and then switch the polarity by switching the probes around. One side should read very high resistance, over 1 megohms. And the other should read a moderate resistance, a few hundred thousand ohms. If this is the case for all three junctions, the transistor should be a good working one.
    LOL @ the fact that although the multimeter shown has a dedicated socket for testing transistors (the round blue region), the author didn't use it but instead opted for a more convoluted, less informative, and less reliable approach.



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    Re: How to check transistor using digital multimeter?

    To be fair, that usually serves to measure the amplification factor (hFE). A useful indicator, but doesn't tell you everything.

    I'd do a 'diode test' first to decide whether the transistor still works, then use transistor test socket if I a need a number for that hFE (which -for me personally- is rare, btw).



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