How to Read (Test) or Detect a Transistor Terminal

How to Read (Test) a Transistor Using Multimeter

In basic electronics, the know-how or ability to read or been able to detect a transistor terminals is very important as knowing what to do with it. Without knowing or determining the position of individual terminals, you can’t use it properly. You might even end up feeding it with excessive current beyond its rated value and thereby damaging the transistor in the process.

In this discussion I shall show you basic and direct ways to detect a transistor terminal. Also, the diagrams inclusive will guide you so to know what the text is about.

Requirement

First, you would need to have a Multimeter. Below shows a basic Multimeter. Rotate the knob of the multimeter to “Diode” range as seen in the diagram below. The "Diode range" has a "Diode symbol" drawn on it

Secondly, connect your multimeter probe (Red and Black) to any two terminal of your choice. Why I said so is, we need to pick terminal randomly to locate which of the terminals has the highest resistance compare to the other. Also, we will apply basic Diode characteristics.

Thirdly, check your multimeter reading. Did you get any reading? If no! Interchange the multimeter probe (Red to Black and Black to Red). Did you get any reading? If yes, take note of the reading (say, 600 ohms).

Fourthly, make one of the probe static (fixed) and rotate the other probe. For instance, if you choose to make the Red probe static (fixed), then use the Black probe to connect the other idle terminal that has not been connected. Did you get any reading? If Yes, take note of the reading (say 620 ohms). Comparing these results, the one with the highest resistance is the Emitter. While the other terminal wit less resistance is the Collector and the third terminal is the Base. If your reading was No! Then instead of making the Red probe static, make the Black probe static. Did you get any reading? If yes, compare your reading. The terminal with the highest resistance is the Emitter, while the terminal with the lesser resistance is the Collector. Then the third terminal is the Base.

ALTERNATIVE METHOD

Download basic transistor pin configuration online. For instance, C9014 and C9018 series: there Base is at the middle. The collector is at the right hand side when the transistor is standing upright facing you with its value (name tag) facing you. The Emitter is the last terminal by your left hand side.

For C1815 series, the base is at the last right hand side terminal when the transistor is facing you with its name tag in front standing erect. The next terminal (middle terminal) is the collector, and the last terminal by your left hand side is known as the Emitter. Also, you can use your multimeter to confirm these things I just said.

For BC108, BC109 etc, there usually is a Notch or Protruded edge at one side of the transistor. The edge indicates the Emitter. The next terminal usually the next is the Base and the last terminal is the collector.

Please, feel free to contact me if you have any difficulty locating the terminals of your transistor. I shall be delighted in responding ASAP.

Thanks for your time again, lets make it a date tomorrow.

Isaac Johnson

Circuit Design and Technology

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