How to Test a PNP Transistor with a Multimeter

This site contains affiliate links to products. We may receive a commission for purchases made through these links.

A human’s brain has nearly 100 billion cells called neurons—the small switches allow us to think and recall things. Computers have billions of small “brain cells,” too. We call them transistors, and they are made from silicon—a chemical element that is normally seen in the sand. One of the typically mentioned transistors is a PNP transistor. 

Did you know that transistors have transformed electronics since they were created more than a half-century ago by William Shockley, Walter Brattain, and John Bardeen? But, what are these really, and how do they work?

Introducing PNP Transistors: What Are They Really? 

A PNP transistor is a kind of transistor in which one n-type material is doped along with two p-type materials. It’s a device controlled by the current. The tiny amount of base current managed both the Collector and the Emitter. Further, two crystal diodes are linked back-to-back in the PNP transistor. You see, the emitter-base diode is then placed on the diode’s left side, whereas the collector-base diode is placed on the right section. 

Keep in mind that the current in the hole is composed of the PNP transistor’s carriers. The hole’s movement makes the current inside the transistor, and the flow of electrons produces the current in the lead of the transistor.

It turns on when a tiny current flows by the base of the PNP transistor. The PNP transistor’s current flows to the Collector from the Emitter.

The voltage needed by the transistor’s base, Collector, and Emitter is specified by the letter of the PNP transistor. Unlike Collector and Emitter, the PNP transistor’s base has been negative at all times. The electrons are also taken from the base terminal. The current entering the base is increased before it reaches the Collector ends. 

How is the Construction of a PNP Transistor?

Commonly, the base and emitter junctions are forward biased. Meanwhile, the base and collector junctions are reverse biased. The former Emitter attracts electrons to the battery, which causes current to flow to the Collector from the Emitter. 

Doped semiconductors are typically seen in three areas of the transistor. There’s a collector on one side, and on the other, there’s an emitter. The base refers to the middle area. The three components of a transistor are explained in detail below. 

  • Collector

This is the section on the Emitter’s opposite side, collecting the charges. When we talk about collecting, the Collector is biased in the opposite course.

  • Base

The transistor’s base is the center forming the two PN-junctions between the Collector and the Emitter. The base-emitter junction is forward biased, which enables the emitter circuit to have low resistance. The collector circuit has a very high resistance because of its reverse bias of the base-collector junction.

  • Emitter

The job of the Emitter is to give charge carriers to the receiver. As opposed to the base, this is forward biased to supply a huge amount of charge carriers. 

So, How Does a PNP Transistor Work?

Take note that the base and emitter junctions are forward biased. Therefore, the Emitter pushes the holes within the base area. The emitter current is composed of such holes. Those electrons united with the electrons when they moved into the N-type base or semiconductor material.

The base of the transistor is extremely thin and doesn’t have more doping. Therefore, only a limited number of holes are moved to the collector space charge layer. This is where the current progresses. 

Moreover, reverse-biased is utilized to link the collector-base region. The Collector attracts or collects the holes collected around the depletion area when exposed to negative polarity. The collector current then progresses as a result of that. The Collector current IC enables the whole emitter current to pass through. 

Where Do You Normally Use these PNP Transistors?

Be informed that we won’t be listing all the circuits that could use PNP transistors. In fact, that would be entirely impossible, as PNP transistors could be utilized in many different ways, even though an NPN transistor might be preferable in most cases.

We will highlight some of PNPs common applications below:

  • A high-side current mirror or active load
  • Complementary amplifier or driver configurations, like the Class AB and Class B output stages
  • They’re also low-dropout regulators. Expending a PNP transistor as the pass element offers the regulator a substantially less dropout voltage. It also raises the quiescent current
  • Drive uses where the load’s one side is grounded. The PNP’s Emitter is linked to the drive voltage, and the load’s other side is connected to the Collector. That configuration is what we refer to as a high-side switch. 

How Do You Test a PNP Transistor?

Before you test your transistor, make sure you know it’s really a PNP transistor. Here’s how you can do that:

Keep your meter on the Diode setting and keep the positive lead to the Pin-1 (Emitter). Touch the negative probe to the center pin (Base), and you’ll notice a voltage on the meter. Touch the negative probe to the center pin (Base) concerning the pin-3 (Collector). You’ll also notice voltage in the meter.

It will show voltage if the meter’s positive probe is attached to the anode and the negative probe is attached to the cathode. It won’t show value if the connections are interchanged. 

Follow the steps below to test your PNP transistor:

  1. Set your digital multimeter in the ohm or continuity mode
  1. The multimeter must show continuity, and the reading should be the same reading obtained when the individual diode was tested across the terminal. 
  1. Connect the negative lead to the Emitter terminal with the positive lead connected to the Base terminal. Connect the negative lead to the Base and the positive lead to the Collector. The meter must show no connectivity or infinity.
  1. Reconnect the positive lead to the Emitter with the negative lead connected to the base. Again, there should be no indication of continuity. 
  1. A forward junction must be indicated when the positive lead is connected to the Emitter or Collector. No continuity should be shown when the negative lead is connected to the Emitter or Collector if the positive lead is connected to the Base of the PNP transistor. 

Final Thoughts

There you have it! With the help of the ideals and steps highlighted above, you can now test your PNP transistor with a digital multimeter.

About The Author