If you want a quick and simple overview of the 2N2222 Pinout in both TO-92 plastic package and TO-18 metal package, then you have come to the right place! First you should know that the 2N2222 is a BJT (Bipolar Junction Transistor) of the NPN type (Negative, Positive, Negative layer arrangement). So it is important to take this into account when comparing the NPN transistor symbol to the physical 2N2222 pinout.
Looking at the image above we can see that pin number 1 is the collector on the 2N2222 transistor, pin number 2 is the base, and pin number 3 is the emitter. If you need a refresher of what each pin does then read the following.
What does each pin on the 2N2222 pinout do?
Before we go into the details, it’s good to remember the flow of current across all transistor pins. Current enters through the base and collector pins, and exits at the emitter pin. Therefore we know:
iE = iC + iB
We also need to remember that:
iC = hfe * iB
Where hfe is the current gain(sometimes shown as β).
All this takes us to the following simple explanation:
- Base – The base pin on a BJT NPN transistor is used to control the current flowing through the collector, where the amplification factor is defined by the current gain (see transistor datasheet for details).
- Collector – The collector pin on a BJT NPN transistor is what collects the bulk of the electrical current to supply / deliver it to the Emitter.
- Emitter – The emitter pin on a BJT NPN transistor is the outlet of all current entering the transistor.
A very typical application of this transistor is using it as a switch, where the base is used as a signal (with small current) used to determine when the larger current should flow through the collector. This can be helpful when you want to control a load with a controller, but the controller has a current limitation. Example: you want to drive an electrical device whose current exceeds the limit of your Arduino microcontroller, then use the Arduino to send the signal (small current) to the transistor base, and connect the electrical device such that the collector/emitter current define the overall flow through it. If you want some examples, checkout the following posts:
Examples using the 2N2222 transistor
If you’ve read through diyengineers.com, you might notice that I have used the 2N2222 / 2N2222A transistor in several example projects. So I wanted to invite you to take a look at some of them in case you are interested:
- HC-SR501 PIR Sensor – Learn how to use with Arduino
- How to use the 2N2222 Transistor (NPN) (with examples)
- RTC DS3231 – How to use with Arduino
- LDR sensor – How to use a Light Dependent Resistor
- LDR sensor with Arduino – How to use (with examples)
- Rotary Encoder with Arduino – Examples Included
Transistor Kit that you can use for future tests/projects:
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