The 2N2222 BJT is an iconic jellybean transistor. Since 1962, the original TO-18 and PN2222 TO-92 variants have formed the cornerstone of countless American projects. Let’s explore this versatile and popular transistor family with all its modern surface mount variants.
Celebration!
It’s been 77 years since the transistor was invented in 1947. We pay homage to the Bell Labs pioneers including John Bardeen, Walter Brattain, and William Shockley.
Suppose your team was asked to identify the transistor that best represents our century of progress. My vote is for the 2N2222 (NPN) transistor and the 2N2907 (PNP) complement—arguably the most common and well-loved of all the American Jellybean transistors. For an added flare and nostalgia, let’s use the original TO-18 packaging (Figure 1) with an emphasis on John (Jack) Haenichen’s famous patent 3,226,61 dated 28 Dec 1965 (filed 04 Nov 1963).
Figure 1: Sketch of a TO-18 packaged transistor featured in Jack Haenichen’s patent 3,226,614 dated 28 Dec 1965 (filed 04 Nov 1963).
Beginners corner
The 2N2222 is a legendary transistor that has been featured in projects for over a half century. We call it a Jellybean component because the 2N2222 transistors are as common as jellybeans in a jar. They are everywhere, you simply cannot go wrong using this classic transistor. Chances are, you have already used the transistor in one of your Arduino microcontroller circuits to turn on an LED or activate a relay.
Eliminating the 2222 BJT family naming confusion
One potentially confusing aspect of the 2N2222 transistor is the name itself. The 2N2222 is over 60 years old. Over the decades, many variants have been constructed. For example, the original 2N2222 featured a TO-18 package as shown in Figure 1. To save cost, the silicon was enclosed in the popular TO-92 package as shown in Figure 2. Both devices are referred to as a jellybean 2N2222 as the internal semiconductor die is identical. The 2N2222 has been repackaged into hundreds of unique variants. See the FAQs below for tips on identifying the 2N2222 variants.
Tech Tip: The PN2222 is a play on words. The P indicating a plastic TO-92 package transistor as seen in the KSP2222A part number included as Figure 2. We often see a prefix and suffix to indicate attributes such as lead free, formed leads, or other manufacturer specific information. In most cases we are safe to assume that a transistor with 2222 in the name is a member of the 2N2222 family.
Specifications
The 2N2222 family includes hundreds of variants. Many follow the classic specifications which are included in this onsemi datasheet snipped (Figure 2) for a TO-92 packaged KSP2222A transistor.
Be sure to consult the datasheet as surface mount variants often have lower power dissipation. Also, be sure to review DigiKey’s Transistor Selection Guide for additional information.
Figure 2: Opening image from the onsemi KSP2222A data sheet showing absolute maximum ratings as well as the pinout for the TO-92 packaged 2N2222 transistor.
Tech Tip: The values listed in Figure 2 are absolute design maximums. Think of them as brilliant red lines that should never be crossed, as the transistor will have a short life. Also, avoid pushing the transistor excessively in two dimensions. As a safe starting point, multiply every number by 0.75.
Frequently Asked Questions for the 2N2222
For clarity and easy reading, this engineering brief is composed as a set of FAQs. You can help expand the knowledge by adding your questions and comments in the space below.
For ease of navigation, a page index box is included to your right.
How can I locate a 2N2222 transistor?
The best way to locate jellybean transistors such as the 2N2222 is to search DigiKey using keywords “2N2222 BJT” or “PN2222 BJT”. This search captures the majority of TO-18 and TO-92 packaged parts. From here, you can refine the search using the package / case selection tool.
How can I locate 2N2222 family variants?
The 2N2222 die has been integrated into a wide variety of packages ranging from the original TO-18 to the latest miniature surface-mount form factors. Search for Digikey provided variants using the keywords “2222 BJT”. Casting this wide net will return single as well as transistor arrays. It also includes variants installed in SOT-23, SOT-89, SC-70, and other surface mount options.
This search reveals the true popularity of the 2N2222. We find hundreds of variants with millions of individual devices in DigiKey stock.
Is the 2N2222 obsolete?
No, the 2N2222 is over 60 years old and still a viable transistor. It has a good balance of features applicable to a wide variety of applications.
We recognize that the original TO-18 packaged transistor is slowly fading into history. However, the TO-92 and modern surface mount devices provide robust solutions for your needs. Search DigiKey using keywords “2222 BJT” to see the range and quantity of availability of variants.
Tech Tip: Occasionally, we see an individual 2N2222 listed as obsolete. This confuses the search engine as individual parts are conflated with the greater family of parts. The new AI generated previews are particularly susceptible to this error.
While an individual part number may be obsolete, the family and related devices are readily available. For example, the original lead solder component may be difficult to locate, a ROHS component may be available. Be sure to search DigiKey using keywords “2222 BJT” to see the true availability.
What is the complement of the 2N2222?
Transistors are often offered in complementary pairs with near-identical parameters for the NPN and PNP device. The complement for the 2N2222 (NPN) is the 2N2907 (PNP) transistor. Search for the DigiKey variant parts using keywords “2907 BJT”.
Why is the 2N2222 so popular?
The 2N2222 was unquestionably the correct transistor at the correct time. Designed and released in 1962 it was one of the first silicon transistors with so many desirable features. The robust high speed switching characteristics also provided a transistor with excellent practical value from DC to high-speed amplifier circuits. The 2N2222 is popular because it is a balanced device with attributes suitable for a wide range of projects. The 2N2222 and variants feature:
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High gain typically specified as greater than 100.
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High frequency amplification with operation into the UHF regions up to about 300 MHz.
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Relatively high power dissipation of 1.8 W (case at 25˚ C) or 0.5 W (25˚ C ambient).
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The TO-18 package was physically small. It offered a degree of electromagnetic shielding and facilitated additional heatsink capabilities using a small metal spreader. Surprisingly, DigiKey still has a few purpose built TO-18 heatsinks in stock.
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Relatively high collector current of approximately 500 mA for moderate-power applications.
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Relatively high collector to emitter voltage (30 VDC).
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The device was registered with JEDEC. With this standardization, many manufacturers added the device to their offerings ensuring low cost through robust competition.
Figure 3 presents a good way to visualize the 2N2222 in relationship to other transistors. The arguably subjective radar chart shows the 2N2222 strengths along with the 2N3904 and the TIP41 power transistor. The desirable balance of the 2N2222 transistor is represented by the blue line where we see the 2N2222 scores favorably across many dimensions. The 2N3904 is similar, but slightly less capable across all dimensions except availability and cost where it appears to hold a slight advantage. The TIP41 shows considerable variation. The current is considerably higher at the expense of speed, cost, and current gain.
Figure 3: Subjective measure of transistor attributes on a scale of 1 to 10.
Popularity with amateur radio enthusiasts
Amateur radio enthusiasts (Hams) have taken a keen interest in the 2N2222. This is reflected in over 60 years of literature including the latest American Radio Relay League (ARRL) handbook and a half century of QST and QEX magazines.
From time to time, we see competitions to see what can be done with 2N2222 transistors. Some projects are works of art using the 2N2222 for oscillators, low-signal amplification, signal steering, and even as power amplifier, and transceiver. See examples:
- on Jim Kortge’s (K8IQY) Manhattan Madness pages
- search for keywords 2N2222 along with QRP (low power), and contest
Popularity in education
A quick web search will reveal thousands of articles featuring the 2N2222 transistor. The transistor may also be found in many textbooks and countless introductory articles. It’s safe to say that this device has momentum-of-the-decades ensuring past, present, and future applicability.
What is the difference between a TO-18 and a TO-92 packaged transistor?
The original 2N2222 was packaged in a TO-18 metal can. This is still available for select applications, although it is a relatively expensive options reserved for application requiring the metal case including the natural shielding or the capabilities of a heatsink. It’s also a good option for those seeking an authentic restoration of vintage equipment.
The plastic TO-92 packaged devices are inexpensive and readily available. Quantities of 100 are available for less than $5.00 (U.S. dollar).
Watch out! The TO-18 package has a E-B-C pinout while the TO-92 packaged 2N2222 has a C-B-E pinout. For the metal can, the emitter is located next to the locator tag on the lower part of the can.
What is the equivalent to the 2N2222?
There is no simple answer to this question as we would need to know the application. Yet, we can provide general answers based on the nature of the application including general-purpose and specialized applications.
Non-critical general-purpose applications
For non-critical general purpose work, the jellybean 2N3904 and the jellybean BC547 are perfectly acceptable, provided we pay attention to the pinouts:
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A plastic TO-92 2N2222 transistor has the same E-B-C pinout as the 2N3904.
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A metal TO-18 2N2222 transistor has the same C-B-E pinout as the BC547.
It would be very difficult to recommend one transistor over the other for non-critical applications. Availability, cost, reliability, and performance are all on par. Perhaps the best advice is to continue to use what is already in your shop to minimize the line-item count. It’s perfectly natural to have shop policy to use the 2N2222 (NPN) / 2N2907 (PNP) for all applications unless you have a compelling reason not to.
Tech Tip: Be careful with the BC547X family as the X indicates the gain. To be safe you should use BC547C variants is substituting for a 2N2222 device.
Critical applications
For critical work e.g., higher current, higher frequency, or faster switching, we need to be careful with substitutions. As a general statement, the 2N2222 is a balanced contender optimized to fill its niche. As an example, suppose we chose a 2N2369 or MPSH10 replacement. These related transistors will operate at higher frequencies but have limited voltage capability making it suitable for some but not all applications.
Given the state of transistor logistics, I personally see no reason to shy away from the 2N2222 or any of the other jellybean types. Use transistor X unless you have a justifiable reason not to. For instance, you may need a low noise transistor, higher voltage, higher current, or reduced cost.
Horses for courses.
What is the history of the 2N2222?
The 2N2222 is a Motorola product closely associated with the John (Jack) Haenichen. The earliest reference I could find for the 2N2222 is the 1963 Motorola Switching Transistor Handbook. The datasheet appears on page 333 describing the 2N2222 as a Motorola Epitaxial Star Transistor designed for high-speed switching circuits and DC to UHF amplifier applications.
The Motorola book is an informative read. In some ways, it’s like reading a combined advertisement and textbook focused on the 2N2222. It begins with a description of the epitaxial growth process. It then provides a detailed exploration of circuit reliability and transistor switching circuit including the fascinating description of transistors operating in high-voltage avalanche modes. I personally appreciate the pictures showing the semiconductor manufacturing process.
Tech Tip The term epitaxial is better understood by looking at the roots of the word. The prefix “epi” is familiar using such words as epidermis, epicenter, and epilogue. In all cases we are describing something that is built or overlayed onto an existing structure. With regards to the transistor, we are building a structure upon a crystalline substrate. The root word “taxis” has Greek origins and refers to order and structure as implied in modern words such as syntax and taxonomy. With respect to the transistor, the term “epitaxial” describes a hierarchical ordered structure built upon a crystalline base as shown in Figure 4.
Figure 4: Epitaxial structure of a high voltage transistor from Jack Haenichen’s patent 3,226,614 (Motorola).
What niche was the 2N2222 BJT designed to fill?
Members of the 2N2222 represent a breakthrough in high speed, high voltage silicon transistors. Here, the term high voltage implies a transistor able to operate with an increased collector to base voltage. Please reread the previous line, as high voltage is defined in terms of the collector to base voltage as opposed to the more typical collector to emitter voltage.
To understand the distinction, we need to place the transistor into its historical perspective. It was desirable to increase the switching speed of transistors to meet the demands of the emerging digital equipment. One way to achieve higher speeds is to apply a reverse bias to the base such as when a negative voltage is applied to the base of a NPN transistor. The DC analysis shows that the collector to emitter leakage current is reduced. An AC analysis shows that the transistor will turn off faster.
These attributes are demonstrated in Emitter-Coupled Logic (ECL) circuits where transistors are operated in a long-tailed pair configuration with a negative emitter voltage (constant current source). Without going into the specifics, a digital circuit will cause the current to flow in one, and only one transistor. The beauty of the circuit is that the transistor will not saturate thereby increasing speed. The downside is that the system has a near constant current flow (highly undesirable as the number of transistors increases).
With respect to the 2N2222 and family, the silicon is designed for a wide safety margin in this representative circuit. This prevents unexpected avalanche condition caused by a self-reinforcing current flow from collector to emitter. An avalanched transistor will exhibit SCR latch-like behavior with the flow of current limited by external components.
These ideas are illustrated in the opening paragraphs of Jack Haenichien’s 3,226,614 patent:
It is generally true that compared to transistors which are operable only at low voltages but are otherwise equivalent, high voltage transistors are more dependable devices which are much less limited in the manner in which they may be used.
High voltage transistors are characterized by their higher avalanche voltage characteristic BV (the voltage across the collector-to-base junction at which avalanche breakdown occurs) which enables them to operate over -a wider voltage range from their minimum operable collector voltage up to their higher value of BV Having a higher BV high voltage transistors are more reliable since when used under the same biasing conditions, they have a greater margin of safety against destructive surges of voltage.
Transistors having a high BV demonstrate several desirable characteristics, they may be operated so as to have a higher power output and a higher power gain as compared to lower voltage units. High voltage transistors may often be operated at power line or other source voltages so that voltage reducing components or equipment are unnecessary.
Where can I learn more about the 2N2222’s history?
Historian Jack Ward has done an outstanding job archiving the history of the early transistors at the Semiconductor Museum. His interview with Jack Haenichenprovided) the inspiration behind this post and filled in a few of the missing links specifically, the associations between the 2N2222 family, Motorola, and Jack Haenichien.
Be sure to listen to the audio recordings for a first-hand account of the technology.
Parting thoughts
The 2N2222 is acpopular transistor because it provides a nicely balanced set of attributes suitable for a wide range of projects. It falls into that sweet spot for cost, performance, and availability. While there are certainly more capable devices, the “improvement” often moves the needle into niche application compromising the characteristics that make the 2N2222 attractive in the first place.
Here’s looking forward to the year 2047 and that century-long celebration of the 2N2222. Time will tell the availability of the 2N2222 family. Barring another revolution in electronics, I suspect the 2N2222’s evolution will continue unabated, perhaps with a special 100th anniversary release of the TO-18 packaged device just in time for a friendly design competition.
Please share your favorite 2N2222 application.
What jellybean should we explore next?
Is anyone up for popcorn parts?
Best wishes,
APDahlen
Related information
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About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.