How to test a transistor

Summary: Learn all about transistors and how to test them with a multimeter.

A transistor usually comes in one of two different configurations, NPN or PNP. The basic function of a transistor is to amplify current through a circuit.

For example, you could use a transistor to turn a very small current into a large current in order to power relays, lamps, switches and so on.

	Now let's discuss the testing of a transistor. A transistors will have 3 leads attached to it, the "emitter" (E), "collector" (C), and the "base" (B). PNP and NPN transistors are wired differently, but when it comes to testing them it doesn't make a difference. You will test the leads 3 times, first set your meter to the diode setting (found in the resistance section of meter), then test the leads in this order: The base-emitter (BE) junction should behave like a diode and conduct only one way. So for example, when you put the red meter lead on (B), and the black meter lead on (E) you would get an X amount of Ohms. When you swap the meter leads, you would get an open, or no continuity. The base-collector (BC) junction should behave like a diode and conduct only one way. Use the example from above. The collector-emitter (CE) should not conduct either way. If any of your readings do not match the 3 above results, then your transistor is defective and should be replaced. See more how-to articles