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How to Check PNP Transistor

Transistors are one of the key building blocks in almost all of today's electronic circuits. They can be used as simple electronic switches or to amplify current through a circuit to control relays and sensors. Transistors come as an NPN type or a PNP type, and both will have three leads attached to them, the "emitter," "collector" and the "base." PNP and NPN transistors are wired differently internally but can both be tested the same way.

Things You'll Need

  • Ohmmeter
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Instructions

    • 1

      Identify the base, collector and emitter leads on the transistor. You might need to view the transistor manufacturer's data sheet to determine which lead is which.

    • 2

      Set the ohmmeter to measure resistance, and connect one lead of the meter to the base of the transistor and the other meter lead to the collector of the transistor.

    • 3

      Check the reading on the meter. The meter should read an open (high resistance) or a short (low resistance). Switch the meter leads so the lead on the base is now connected to the collector, and the lead connected to the collector is now connected to the base. The meter should read the opposite, meaning if you had an open before, you should now read a short. If you had a short before, you should now read an open.

    • 4

      Connect one lead of the meter to the base of the transistor and connect the other meter lead to the emitter of the transistor.

    • 5

      Check the reading on the meter. The meter should read an open (high resistance), or a short (low resistance). Switch the meter leads so the lead on the base is now connected to the emitter, and the lead connected to the emitter is now connected to the base. The meter should read the opposite reading.

    • 6

      Disconnect the meter from the transistor. If all readings were correct, the transistor is correct. If any reading was incorrect, the transistor should be replaced.


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