How to Identify Transistor Terminals Using a Multimeter

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Would you like to know how you can determine transistor terminals using a digital multimeter? Good news for you because this post got you covered! 

Keeping track of all your electrical circuit’s parts is of utmost importance. You may like to determine the current or voltage sent through resistors and other circuit elements for the sake of ensuring they work with safety and ease. Different tools like a digital multimeter are practical for such situations. 

What is a Transistor? 

In case you didn’t know, a transistor serves as a switch or gate for electrical signals that regulate current or voltage. They typically feature three layers that are made of semiconductor materials, which can bring current. Such semiconductor materials include:

  • Germanium 
  • Silicon 

How Does a Transistor Work?

If a trivial change in current or voltage happens at the transistor’s inner layers of the semiconductor, a fast, massive change in current is generated and passes to the whole component. The transistors then function as a switch, opening and closing many times and as an electric gate as well. 

An NPN transistor provides a negative, positive, negative. It is also referred to as sinking. On the other hand, a PNP transistor is positive, negative, positive. It is also referred to as sourcing. Keep in mind that transistors utilized in integration or combination circuits are seen in equipment like desktops, laptops, pad devices, cell phones, and high-end computers. 

Transistors are utilized in both combinations, known as singly and integrated circuits. These are also used in diodes, circuit elements that allow electricity to follow through in one direction only. Transistors are also widely utilized in amplifying the electrical current to a greater value. 

They are engineered by inserting a small slice of either n-type material between two bigger chunks of p-type material or vice versa. In that setup, the p-type material is positive because of the electron’s absence, while n-type ones are negative because of too many electrons.  

How to Know the Difference Between NPN and PNP Transistors? 

You will find simple ways to determine the difference between the two. The current drifts from the collector to the emitter terminal in an NPN transistor. On the other hand, a PNP transistor switches on without current flowing at the base terminal of the transistor. 

Commonly, an NPN transistor will turn on every time there is a high signal, whereas the PNP transistor will turn on when there’s a low signal. Between these two transistors, the major difference is the proper biasing of its transistor joints. The directions of current and polarities of voltage are in continuous reverse to each other. 

When we talk about multimeters, these devices are typically utilized by electricians and technicians. This electronic tool is utilized in measuring and testing many electrical circuits and components of different types, from analog to a digital multimeter. 

You can use this versatile tool to identify transistor terminals. Many digital multimeters have an in-built transistor testing function. In such scenarios, the testing of transistors becomes simple and fast. 

How to Test Transistor Terminals with a Multimeter? 

You will find five steps to test a transistor in an electric circuit. Those steps involve connecting the base to the emitter, base to collector, emitter to base, collector to base, and collector to emitter.

For your NPN transistor, the emitter is ground along with the collector at the base controls’ voltage. Meanwhile, for a PNP design, the collector is grounded along with the emitter at a voltage. 

Such processes of testing inform you if the transistor is opened or shorted for bipolar transistors. The transistor might still vary in its performance in a particular range.

  1. Detach the transistor from the circuit.
  1. Take your digital multimeter and insert the positive lead to the transistor’s base.
  1. Connect the negative lead to the emitter of your transistor.
  1. Check the reading on your digital multimeter. A PNP transistor must give an over-limit (OL) message. Meanwhile, an NPN transistor that works fine must present a voltage drop between 0.45 volts to 0.9 volts. Any indications on the digital multimeter that contrast from such values could suggest a bad transistor symptom.
  1. Put the negative lead of the digital multimeter to the transistor’s collector. Remember that this is the step for the base to collector. An NPN transistor must present a voltage drop between 0.45 volts to 0.9 volts, while a PNP must be over the limit, the same case with the previous step. 

How to Switch Readings? 

What about the step of the emitter to base? Here are the steps you need to follow:

Link the positive lead of your digital multimeter to the emitter and the negative to the base. The readings, in this case, must be reversed. The NPN transistor must give an OL (over limit) message. For the PNP transistor, it should have a voltage drop of between 0.45 volts to 0.9 volts. 

Likewise, you should get the same results on your digital multimeter with the positive lead attached to the collector and the negative lead connected to the base.

For the last step, make sure you attach the positive lead to the collector and the negative lead to the emitter. Bear in mind that both the NPN and PNP designs must present “over-limit” (OL) messages. You can switch the leads with each other, and you ought to see the same messages. 

It will help if you identify which lead matches to which in an unmarked transistor. You can do that by checking the voltage drops and identifying which ones correspond to which. 

Final Thoughts

Do you notice your circuit not giving results that are as efficient as they could be before? It may be time that you test your transistor. Remember that testing it with a digital multimeter could help you understand if the transistor is working well or not. 

You can use a digital multimeter, a digital tool that can measure different electrical properties for circuit elements. 

We hope you find the answers to your questions in this post. Share your thoughts to us by leaving your comments below!

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