How Do I Find Collector, Emitter, and Base of a Transistor With Multimeter?

Transistors are semiconductors used to switch or amplify power and signals in modern electric or electronic circuits and devices. The transistor usually has three pins or terminals: the emitter, base, and collector. So, how to find the collector, emitter, and base of a transistor? 

How Do I Find Collector, Emitter, and Base of a Transistor?

You can find the transistor’s collector, emitter, and base either using a multimeter or without using it. The multimeter method is general and works for every type of transistor without looking for certain characteristics in the transistor.

Identifying Transistor 3 Pins With Multimeter (PNP)

  1. Grab your multimeter and check that the red cable is connected to the voltage socket while the black cable is connected to the com.
  2. Set the multimeter to diode mode by moving the selecting wheel until it reaches the diode symbol.
  3. Use the red and black probes of your multimeter to test the first lead pin of your transistor.
  4. Put the black probe on the middle pin and then the red probe on the first pin, and wait to observe the reading that appears on the multimeter.
  5. Write down the reading that appeared, and refer to it as the reading of the first pin, “P-N.”
  6. Move the red probe to the pin on the other side while keeping the black probe in the middle.
  7. Observe the reading of the second pin and write it down “N-P.”
  8. The base is the easiest pin to identify because it’s the P-type pin, the one in the middle.
  9. The pin with the highest voltage is the emitter, while the pin remaining or that has the lowest voltage is the collector.

Identifying Transistor 3 Pins With Multimeter (NPN)

  1. Grab your multimeter and check that the red cable is connected to the voltage socket while the black cable is connected to the com.
  2. Set the multimeter to diode mode by moving the selecting wheel until it reaches the diode symbol.
  3. Use the red and black probes of your multimeter to test the first lead pin of your transistor.
  4. Put the red probe on the middle pin and then the black probe on the first pin, and wait to observe the reading that appears on the multimeter.
  5. Write down the reading that appeared, and refer to it as the reading of the first pin, “N-P.”
  6. Move the black probe to the pin on the other side while keeping the red probe on the middle one.
  7. Observe the reading of the second pin and write it down “P-N.”
  8. The base is the easiest pin to identify because it’s the N-type pin, the one in the middle.
  9. The pin with the highest voltage is the emitter, while the pin remaining or that has the lowest voltage is the collector.

How To Differentiate Between PNP and NPN Transistors?

To differentiate between PNP and NPN transistors or the bipolar junction transistors, you must use a multimeter. First, grab the multimeter’s probes (the black and red cables), place the black probe on the middle pin of the transistor, and then put the red probe on any of the pins on the sides.

If it shows reading, then it’s a PNP transistor; you can also place the red probe on the middle pin of the transistor and then put the black probe on any of the pins on the side. If it shows reading, it’s an NPN transistor, but both pins on the side must show reading whether it was a PNP or NPN transistor.

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Identifying Transistor 3 Pins Without Multimeter (PNP or NPN)

The bipolar junction transistor can have either NPN or PNP, and it can have either a plastic or metal casing. The identification process differs from the plastic-cased transistor to the metal-cased transistors, for example:

Plastic-Cased

The plastic-cased transistors have two sides, the first one is a flat side, and it’s called the frontal side, while the second one is concaved and it’s called the backside. So, therefore, the first thing to do is put the resistor on its backside, where its frontal side will be facing you, then label the pins with numbers. 

If you started from the right side, then the first pin is the collector, the second pin is the base, and the third pin is the emitter; meanwhile, If you started from the left side, then the first pin is the emitter, the second pin is the base, and the third pin is collector, and this applies if you have an NPN transistor.

If you have a PNP transistor and start from the right side, the first pin is the collector, the second pin is the base, and the third pin is the emitter; meanwhile, if you start from the left side, the first pin is the collector, the second pin is the base, and the third pin is the emitter. 

Metal-Cased

The metal-cased transistors have a circular-shaped case; the case rim has a tap in it; depending on the closest pin to it, we can identify the transistor’s pins. If you have an NPN transistor, the nearest pin to the tab is the emitter, the middle pin is the base, and the last is the collector; meanwhile, if you have a PNP transistor.

The nearest pin to the tab is the collector, the middle one is the base, and the third is the emitter; however, the pin configuration is not standard in every metal-cased transistor; it can differ according to the transistor model. There’s a table below to make you which model you have and what’s its configuration:

Conclusion

To sum up, you can identify the transistor’s collector, emitter, and base either using a multimeter or not. To use a multimeter, you have to get your multimeter, set it to diode mode, and make sure the red probe is connected to the voltage and the black probe is connected to the com; then follow these steps for the PNP transistor:

  1. Use the red and black probes of your multimeter to test the first lead pin of your transistor.
  2. Put the black probe on the middle pin and then the red probe on the first pin, and wait to observe the reading that appears on the multimeter.
  3. Write down the reading that appeared, and refer to it as the reading of the first pin, “P-N.”
  4. Move the red probe to the pin on the other side while keeping the black probe in the middle.
  5. Observe the reading of the second pin and write it down “N-P.”
  6. The base is the easiest pin to identify because it’s the P-type pin, the one in the middle.
  7. The pin with the highest voltage is the emitter, while the pin remaining or that has the lowest voltage is the collector.

Meanwhile, for the NPN transistor, you will follow similar steps, but there will be some differences because of the different arrangement of the transistor’s pins:

  1. Use the red and black probes of your multimeter to test the first lead pin of your transistor.
  2. Put the red probe on the middle pin and then the black probe on the first pin, and wait to observe the reading that appears on the multimeter.
  3. Write down the reading that appeared, and refer to it as the reading of the first pin, “N-P.”
  4. Move the black probe to the pin on the other side while keeping the red probe on the middle one.
  5. Observe the reading of the second pin and write it down “P-N.”
  6. The base is the easiest pin to identify because it’s the N-type pin, the one in the middle.
  7. The pin with the highest voltage is the emitter, while the pin remaining or that has the lowest voltage is the collector.
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