How to test for NPN and PNP transistors using a multimeter.

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Interpretation of whether a transistor is a PNP or NPN type has kept a lot of people stranded while picking a transistor. Just imagine working on a circuit and needs transistors, but couldn’t know if the type you are having is PNP or NPN type. I can vividly remember those days when they have to label my transistor from the store to help me identify them without knowing with a multimeter only, I could determine if is PNP or NPN transistor. Making me go through rigorous stress checking the label and sometimes the label gets faint to view.

But with knowledge of how to use a multimeter, I was able to identify if a transistor is NPN or PNP transistors, skillfully. So believe me so many people out there who still have the challenge I experience then should go through this particular post, as am sharing the solution to the problem.

Before starting with the main deal, let us reminds ourselves how we can identify the pinout of a transistor.

How to identify the pinout of BJT transistors.

For TO92A, TO92B, and TO92C transistors.

This type of transistor has a three-terminal pinout, the collector, base, and emitter. There is a way we use in determining this pin on a BJT transistor. By placing the transistor flat surface facing upwards, from the left side and label the first pin Emitter, second base, and third collector.

For TO18 transistors.

PNP/NPN transistor

This is the type of transistor that has a round metallic cup case with the terminals under the metallic cup.

to determine the terminal of this type of transistor, pick the transistor and observe around the metallic body is a

small projection. The pin closer to the projection is the emitter while the center one is the base with the last emitter.

For TO220 transistors

These are the type of transistors that looks like a voltage regulator IC. They are normally connected to a cooling sink on circuits for cooling.

In identifying e pinout of this type of transistor. The metallic side of the transistor is made to face the ground, making the other side face upwards. Starting from your left-hand side and number and label the pins. The first is the base, while is second is the collector, and the last, the Emitter.

TO3 transistor type pinout.

PNP and PNP transistor testing.
TO3 transistor type.

this form of the transistor has a metallic case body and two pins under the transistor. The metallic body of the transistor is the emitter, while the remaining two pins are the base and the collector.

How to test electronic diode using a multimeter

How multimeter can be used to determine PNP and NPN of BJT transistors.

having known the pinout of the transistor, the next step is to identify if the transistor is a PNP or NPN type. And that can be done by the simple use of a multimeter or studying the transistors are charts. When testing for a transistor in a circuit, remove the transistor from the circuit before testing.

Steps in identifying the NPN type BJT transistor.

  • Set the multimeter in diode measuring mode. This can be done by rotating the knob and positioning it on the diode mode.
  • Turn ON the multimeter and place the red probe of the meter to the middle pin (base) of the transistor.
  • use the second prob of the meter (black) and touch the first pin, (emitter). Some values of voltage will show up on the meter.
  • leaving the red probe on the base, change the black probe to the collector, the third pin, and record the value of the voltage on the meter.
  • the logic of the NPN test is this, the Emitter(E) in N-type material is the same as the cathode of the diode.
Npn and pnp transistor
testing NPN transistor using a multimeter

the Base (B) in N-type material is the same as the anode of the diode.

the collector(C) in N type material, same as the cathode of the diode.

  • so if the positive probe of the multimeter is connected to the anode and the negative probe to the anode, then the meter will display a voltage between 0.5v to 0.7v. And when the probe is connected the other way round, the meter displays OL meaning open circuit.

Identifying the PNP type BJT transistor

  • Set the multimeter to diode mode.
  • Place the negative probe of the meter to pin 2 ( Base) of the transistor.
  • Touch the positive probe to pin 1(Emitter)of the transistor and the meter will display a voltage. The volt will be between 0.5v -0.7v.
  • Touching the positive probe to pin 3 (Collector). The meter will still display a volt. Between 0.5v – 0.7v.
  • Removing the negative probe from the base and placing it on any other pin. The multimeter will not display OL.

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