How to Check a Transistor with a Multimeter

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How to Check a Transistor with a Multimeter

Transistors act as a gate or switch for electrical signals with the ability to regulate voltage or current. They normally have three layers, which are made of semiconductor materials that can carry current. Such semiconductor materials are:

  • Silicon
  • Germanium

How a transistor works

If a small change in voltage or current occurs at the transistor’s inner layers of the semiconductor, a rapid, massive change in current is produced and passes to the entire component. The transistors then act as a switch, closing and opening many times and as an electrical gate.

  • Transistors are used in both combinations called integrated and singly circuits.
  • Transistors used in combination/ integrated circuits are found in equipment such as high-end computers, cell phones, pad devices, laptops, and desktops.
  • During this article, you will get to hear the different types of transistors like PNP and the NPN.
  • A PNP transistor is positive, negative, positive. It is also known as sourcing.
  • An NPN transistor means a negative, positive, negative. It is also known as sinking.

So, what is the difference between these two transistors?

In an NPN transistor, current usually flows from collector to the emitter terminal. A PNP transistor, on the other hand, usually switches ON when no current is flowing at the transistor’s base terminal. In PNP transistor, current often flows from the emitter to the collector terminal.

An NPN transistor will switch ON when there is a high signal while the PNP transistor usually switches ON when there is a very low signal.

Between NPN transistor and PNP transistor, the main difference is usually their correct biasing of their transistor joints. The polarities of voltage and the directions of current are usually in constant reverse to one another.

When it comes to multimeters, they are the most used tools by technicians and professionals. From digital multimeter to analog multimeter, this electrical tool is used in the diagnosing and test of many electrical components and circuits of wide ranges.

When it comes to testing or checking transistors, this versatile component the multimeter is the best to do the job. Most digital multimeters have an in-build transistor testing function. In such cases, the testing of transistors becomes very quick and simple.

How to check transistor using a multimeter with in-build transistor functions

If your digital multimeter has an in-build transistor testing function, then all you need is to follow the below simple steps:

  1. The first step is inserting your transistor to the digital multimeter’s socket.
  2. After that, you need to set your multimeter to the correct mode.
  3. After completing, you will get readings like the gain (hFE). With this reading, you can crosscheck with the fail/pass readings and datasheets.

Testing transistor using a multimeter (diode settings)

For multimeters without the in-build transistors testing function, you can check your transistors using the Diode testing function.

To have an accurate and correct reading, you will need to remove your transistor from the circuit. Below are the steps to follow:

1. Connecting Base to the emitter

The first thing to do in this step is hooking your digital multimeter positive lead to the transistor’s BASE (B).

After that, you then hook your digital multimeter negative lead to the transistor’s EMITTER (E).

If your NPN transistor is in perfect condition, then the digital multimeter should read a voltage drop of around 0.45V to 0.9V. For a PNP transistor, your digital multimeter should give an OL (over limit) reading.

2. Connecting Base to the collector

In this step, you will need to keep your digital multimeter positive, lead to the BASE (B), and then place your digital multimeter negative lead to the COLLECTOR (C).

For a properly functioning NPN transistor, your digital multimeter should read a voltage drop of around 0.45V to 0.9V. For a PNP transistor, your digital multimeter should give an OL (over limit) reading.

3. Connecting emitter to the Base

The first thing to do in this step is hooking your digital multimeter positive lead to the transistor’s EMITTER (E).

After that, you then hook your digital multimeter negative lead to the transistor’s BASE (B)

For a properly functioning NPN transistor, your digital multimeter should give an OL (over limit) reading. For a PNP transistor, your digital multimeter should read a voltage drop of around 0.45V to 0.9V.

4. Connecting the collector to the Base

In this step, you will need to keep your digital multimeter positive lead to the COLLECTOR (C) and then place your digital multimeter negative lead to BASE (B).

For a properly functioning NPN transistor, your digital multimeter should give an OL (over limit) reading. For a PNP transistor, your digital multimeter should read a voltage drop of around 0.45V to 0.9V.

5. Connecting collector to emitter

In this step, you will need to keep your digital multimeter positive lead to the COLLECTOR (C) and then place your digital multimeter negative lead to EMITTER (E).

For a properly functioning NPN and PNP transistor, your digital multimeter should give an OL (over limit) reading.

6. Connecting emitter to collector

Lastly, you will need to keep your digital multimeter positive lead to EMITTER (E) and then place your digital multimeter negative lead to the COLLECTOR (C)

For a properly functioning NPN and PNP transistor, your digital multimeter should give an OL (over limit) reading.

For any faulty transistor, the reading on your digital multimeter will contrast to the above results.

NOTE

Checking your transistor with a multimeter will only identify if your transistor is faulty only; it will not detect if your transistor is working in the range that they should be working.

Tips

When you have a faulty transistor, in these modern days, it is possible to replace them with a Mosfet. Though both Mosfet and transistor may have similar styles, function, and may look alike, they both are different in their configurations and characteristics.

The main difference between the two is that transistors are dependent on current and need to be increased proportionately with load, while the Mosfet is dependent on voltage.

About the Author Dan

Just a random guy who likes to build things. Providing tool knowledge, appliance/device testing tips, and DIY project info in an easy-to read & non-intimidating style.