Blog  /  Transistor Pinouts: A Comprehensive Guide

Transistor Pinouts: A Comprehensive Guide

About Transistor Pinouts,About Transistor Pinouts,An electric circuit is a combination of different electrical devices. These devices work together to ensure that the circuit is not only functional but also stands the test of time. One of these electrical devices is the transistor. 

A transistor is a very important part of an electric circuit. Its function is to convert a weak signal from a low resistance circuit to a high resistance circuit. Pinouts are components of the transistor. This article seeks to discuss them and how they help the transistor perform its function. 


Definition of Transistor Pinouts


The transistor is made up of three components. These components include the base, collector, and emitter. These three components are the transistor pinouts. The emitter is the first pinout and is responsible for the output from the transistor. 

Up next is the base which is the central component of the transistor. Being the central component, the base is responsible for controlling the value and also receives the supply connection. The last part is the collector. It is the biggest component of the transistor. As a result of its size, it has the largest number of carriers in the transistor. 


Configuration of Transistor Pins


Each pinout in a transistor has a configuration. Therefore, there are three pin configurations in a transistor. They include the base configuration, emitter configuration, and collector configuration.


Identification of Transistor Pins


One of the most common problems that professionals face in circuit design is identifying pin connections in many devices. These devices include transistors, TRIAC, SCR, and many other devices. Many technicians have to rely on sources such as datasheets to find the right pin connections and complete the circuit connection.

This section focuses on the guide in identifying transistor pins;


Bipolar Junction Transistor (BJT)


Transistors are usually of two types, NPN or PNP. These two types of transistors are usually available in either plastic casing or metal casing. With the plastic casing, the front side of the transistor is flat and the arrangement of the pins is serial. While trying to identify the pin, keep the front side facing you and start counting the pins. 

More often than not, with NPN Transistors, the first pin is the Collector, the second pin is the Base and the third pin is the Emitter. Thus the configuration is CBE.




However, with PNP transistors, the opposite is the case. The first pin is the Emitter, the second pin is the Base and the last pin is the Collector.

When the transistor uses a metal casing, the pins’ arrangement is circular. To identify the pins in this situation, locate a tab on the rim of the transistor. For NPN transistors, the closest pin to the tab is the Emitter. The pin opposite the emitter is the Collector while the one in the middle is the Base.

With the PNP transistor, the reverse is the case. The pin closest to the tab is the Collector. The one opposite it is the Emitter and the pin in the middle is the Base.

Note: This is not the sacrosanct pin configuration. There could be changes in some cases. However, in most cases, this is the configuration that you will find and work with.


Field Effect Transistor (FET)


The Field Effect Transistor usually has a curved side. While trying to identify the pins in this type of transistor, ensure that the curved side faces you. Then, start counting the pins in an anti-clockwise direction. The first pin you count is the source, the next one is the gate while the last one is the drain.


Metal Oxide Semiconductor Field Effect Transistor (MOSFET)


Just like the Field Effect Transistor, the MOSFET uses the G, D, and S arrangement which stands for Gate, Drain, and Source. To identify the pins in MOSFET, ensure that the flat side is facing you, start counting the pins from left to right. You will find that the pins’ arrangement is Source, Drain, and Gate.

However, this arrangement is also not sacrosanct, so it is advisable to consult the MOSFET datasheet to confirm the identification.


Transistor Pinouts--Insulated Gate Bipolar Transistor- IGBT


To identify the pins on this type of transistor, you need to get a practical IGBT like the GN2470. Now, you need to hold the raised part towards yourself. In this position, the shorter one in the middle is the cathode. The pin on the right is the Emitter, and the one on the left is the Gate.


Transistor Pinouts--Phototransistor


With a practical phototransistor like L14G2, you need to hold the transistor by letting the curved surface facing you and start counting in the clockwise direction. The first pin from this direction is the Collector, the second one is the emitter and the last one is the base.


Transistor Pinouts--Connecting a Transistor to a Circuit


Regardless of the type of transistor, the method of connection is the same. The components needed for the connection include a 2N3906 Transistor, a 330-ohm Resistor, LED, Open Switch, and Dual DC Power Supply or 5 AA batteries.

The connection starts with the connection of the +3V to the emitter of the transistor. You then connect the open switch to the base of the transistor and connect the LED to the base of the transistor. The open switch controls the transistor which in turn controls the LED.




The transistor is quite important in the operation and functionality of the electric circuit. Its components, also known as pinouts, are the functional parts of the transistor. They include the gate, drain, and source in some transistors, and the collector, emitter, and base.

There are two types of transistors, namely, PNP and NPN, and these two types manifest in the five different classes of transistors.