The transistor 2N2222 or PN2222 is another of the most used transistors together with BC548. So, if you like DIY and you are a maker, surely at some point you have needed one of these devices. In this case, the PN2222 is a low power silicon transistor and designed for linear amplification and switching applications.
The reason it is so in demand is that it is good at amplifying small currents and small to medium voltages, as well as being able to work at medium high frequencies. That means that it has a general use and is quite popular among radio amateurs. Those who are will know that it is one of the transistors used for the construction of the BITX transceiver, or that it allowed the Norcal Amateur Radio Club to launch in 1999 a challenge to build a radio transceiver with only 22 such transistors without any additional ICs.
Like BC548 it is manufactured by epitaxy processes. It is also a bipolar transistor and NPN type. At present it has several possible encapsulations, such as plastic TO-92, which is usually the most common form of presentation, and also others such as TO-18, SOT-23, SOT-223, etc.
What exactly is a transistor?
Since the radio or transistor was named after this device we talked about, I would like to make a very brief introduction about what a transistor is and a little bit of history. Transistors are nothing more than devices similar to switches and with the ability to amplify the signal. That is to say, they are the substitutes of the primitive vacuum tubes or vacuum valves that gave so many problems.
These valves were similar to traditional light bulbs, so they could melt and had to be replaced frequently. They were also very large and did not allow the creation of small appliances. The heat they generated was also a problem. With the advent of solid-state electronics, that is, semiconductors, they allowed the creation of this type of device that was much cheaper, smaller and more reliable.
The name transistor comes from the union of transfer and resistor, i.e. a transfer resistor in English. Remember that a resistor is a resistor. Moreover, as you know, the invention arises in Europe with the first patents of the physicist Lilienfeld (1925). It was somewhat ahead of its time, since no practical applications were found for it in that decade or the next, and it was a field effect transistor, a more advanced concept even than bipolars.
Oskar Heil also made a similar device in Germany in 1934, and later Robert Pohl and Rudolf Hilsch would also do experiments related to this type of device at a German university. Almost in parallel, in the United States in the Bell Labs of the AT&T experiments were also being done without success, until after World War II the luck changed for them and when they returned from the European battlefield they found the solution by coming up with the “refreshed” ideas.
John Bardeen, Wlater Brattain and William Shockley took the credit for patenting the first transistor in history and winning the Nobel Prize. In 1948 they invented the contact transistor, a very large, very rough and impractical device that was expensive to manufacture and used to fail sometimes and had to be replaced in some cases. From that point they would evolve to the current transistors.
But if you want to know exactly how this device that revolutionized electronics and the technological world works, here I leave you this GIF with a simile of a transistor and a hydraulic system, which I think you will not find better than this example to capture the idea of the operation of a transistor:
It can be seen that when a current is supplied to the base of the NPN transistor the current passes from the collector to the transmitter. But it makes it amplified, because if you look at the image, the water flow from the base and from the collector is added. It is a quite simple similar, although in the electronic system you should replace the water by electrons .
If you want to see a slightly more enlightening picture from the point of view of the operation of the semiconductor zones, i.e. of the load carriers, here is this other picture:
In the picture you can see that when a negative voltage is applied to the emitter, it pushes the negative charge carriers (electrons) and at the base the positive charge carriers (holes) “absorb” electrons so that they can jump into the collector .
In the case of a PNP it would be similar, but it changes the polarizations or ways of connecting the transistor.
Characteristics of 2n2222:
The 2N2222 or PN2222 is often manufactured by Philips Semiconductor, although we can also find other manufacturers such as the historic Fairchild Semiconductor, the German Siemens, COMSET Semiconductor, SEMICOA, etc. It has a variant called 2N2222A.
The 2N2222A is TO-18 metal encapsulated and qualified for use in military applications (MIL-STD) for its ruggedness, acceptable temperature range, etc. If we look at the datasheets provided by these manufacturers, the characteristics that we will find in this transistor are
- Emitter collector voltage at cut-off: 50V
- Constant collector current: 800mA
- Power dissipation: 500mW
- Current gain: >100hFE, typically 150 is reached.
- Working frequency: 250-300 Mhz, which allows its application in high frequency radio
- Type: Bipolar NPN
- Packages: TO-92 plastic, TO-18 metal, SOT-23 and SOT-223, these last two are SMD type.
- Complementary (PNP): 2N2907
- Equivalent: you can use the BC548 we saw in the previous post, but remember to turn it 180º when inverting the collector and emitter pins . You could also use the 2N3904 with very similar characteristics, but it can only carry one tenth of the current supported by the 2N2222. If the circuit is only for small signals, it could be perfectly replaced. Also the 2N2219 is similar, but for more power. In this case, as it has a TO-39 format (up to 3w) and supports up to 300 Mhz, it can be used in transmitters and amplifiers for HF and VHF and even some UHF cases with output powers of 1 to 2 watts.
- SMD equivalent: for surface mounting there is a 2n2222 SMD transistor with SOT-23 encapsulation.
A datasheet is a document, usually a PDF, with the detailed characteristics of the electronic device. They are created by the manufacturer himself with the peculiarities of his product, therefore, we can find that there are not the same parameters in two datasheets on a 2n2222 from different manufacturers. Here you can download some of them:
- On Semiconductor 2n2222A
- STMicroelectronics 2n2222A
- Farnell Multicomp 2n2222A
- Jameco brings us this other one of the mythical Fairchild for the series 2n2222
I hope this guide about 2N222 or PN2222 helped you.