The 2N3904 and 2N2222 are two of the most common general-purpose NPN bipolar junction transistors, and they are similar enough in appearance and behavior that they are often treated as alternatives to each other. The main practical difference is current capability — the 2N2222 handles more — alongside differences in packaging and pinout that matter when substituting one for the other. This guide compares their specifications, explains where they are alike and where they differ, covers whether they can be used interchangeably, and sets out how to choose between them.
Table of Contents
Overview of 2N3904 and 2N2222
2N3904 Specifications
The 2N3904 is a silicon NPN bipolar junction transistor built for low-power switching and signal amplification. It is supplied almost exclusively in the plastic TO-92 package, with surface-mount versions sold as the MMBT3904 (SOT-23) and PZT3904 (SOT-223). Its key ratings, taken from the ON Semiconductor 2N3904 datasheet, are:
- Collector–Base Voltage (VCBO): 60 V
- Collector–Emitter Voltage (VCEO): 40 V
- Emitter–Base Voltage (VEBO): 6 V
- Collector Current (IC): 200 mA
- DC Current Gain (hFE): 100–300
- Transition Frequency (fT): 300 MHz
- Power Dissipation (PD): 625 mW
- Package: TO-92
2N2222 Specifications
The 2N2222 is also a silicon NPN BJT, but rated for higher current. The original device shipped in a metal TO-18 can; the plastic TO-92 versions sold for prototyping are the PN2222A and P2N2222A, with the MMBT2222 as the SOT-23 part. Its key ratings, from the P2N2222A datasheet, are:
- Collector–Base Voltage (VCBO): 75 V
- Collector–Emitter Voltage (VCEO): 40 V (the original non-A 2N2222 is rated 30 V)
- Emitter–Base Voltage (VEBO): 6 V
- Collector Current (IC): 800 mA (non-A 2N2222: 600 mA)
- DC Current Gain (hFE): 100–300
- Transition Frequency (fT): 250–300 MHz
- Power Dissipation (PD): 625 mW (TO-92)
- Package: TO-18 metal can / TO-92 (PN2222A, P2N2222A)
2N3904 vs 2N2222 Comparison Table
| Parameter | 2N3904 | 2N2222A |
|---|---|---|
| Type | NPN BJT (silicon) | NPN BJT (silicon) |
| Collector current, IC | 200 mA | 800 mA |
| Collector–emitter voltage, VCEO | 40 V | 40 V |
| Collector–base voltage, VCBO | 60 V | 75 V |
| Emitter–base voltage, VEBO | 6 V | 6 V |
| DC current gain, hFE | 100–300 | 100–300 |
| Transition frequency, fT | 300 MHz | 250–300 MHz |
| Output capacitance, Cobo | ~4 pF | ~8 pF |
| Power dissipation, PD | 625 mW | 625 mW |
| Max junction temperature, TJ | 150 °C | 150 °C |
| Package | TO-92 | TO-18 / TO-92 |
Similarities Between 2N3904 and 2N2222
The two parts share most of their character, which is why they are so often treated as alternatives:
- Both are NPN bipolar junction transistors. A small base current controls a much larger collector current, so they are biased and used the same way in a circuit.
- Both have the same three terminals — emitter, base, and collector — though the order of those pins on the package is not always the same (see Pinout below).
- Comparable voltage handling. Both A-grade parts are rated 40 V collector-to-emitter.
- Comparable gain and speed. Both sit in the 100–300 hFE range and switch at a few hundred megahertz.
- Same thermal ceiling. Both have a maximum junction temperature of 150 °C.
- Overlapping applications. For switching and small-signal amplification under 200 mA, either part does the same job.
Key Differences Between 2N3904 and 2N2222
Collector Current
This is the difference that decides most designs. The 2N2222A passes up to 800 mA — four times the 2N3904’s 200 mA. A small relay or DC motor pulling around 500 mA is well within the 2N2222A’s range, while the same load exceeds the 2N3904’s limit and overheats it.
One caveat: the 800 mA figure is an absolute maximum, not a comfortable continuous point in a TO-92 package. At high current the saturation voltage climbs toward 1 V, so switching near 800 mA dissipates close to 0.8 W — more than the 625 mW the plastic body sheds in free air. The full headroom is most usable in the metal TO-18 version. In TO-92, stay well below the maximum.
Voltage Ratings
Both A-grade parts are rated 40 V collector-to-emitter, so voltage rarely decides the choice. The 2N2222A has a higher collector-to-base rating (75 V vs 60 V), which only matters in unusual high-voltage configurations. The 30 V figure that appears in some tables belongs to the original non-A 2N2222.
Switching Speed and Capacitance
The 2N3904’s transition frequency is about 300 MHz; the 2N2222A’s is roughly 250–300 MHz. In practice the gap is negligible — both are fast enough for high-speed switching, PWM, and small-signal RF. The one place the 2N3904 has a slight edge is output capacitance — around 4 pF against the 2N2222A’s 8 pF — which makes it marginally better suited to low-current high-frequency and RF small-signal stages.
Package: TO-92 vs TO-18
The 2N3904 comes only in plastic TO-92. The 2N2222A comes in both TO-92 (as PN2222A) and the original metal TO-18 can. The metal can dissipates heat far better than plastic, which is what makes the 2N2222A’s higher current rating genuinely usable. The 625 mW figure quoted above is the free-air rating (TA = 25 °C); with the case held at 25 °C the TO-92 part is rated about 1.5 W and the metal TO-18 about 1.8 W, so the metal can sustains noticeably more current before overheating.
Pinout: 2N3904 vs 2N2222
The pinout is where assuming compatibility from the part number goes wrong, because the “2222” parts are not all wired the same way. The 2N3904 in TO-92 reads E-B-C (emitter, base, collector) from left to right with the flat side toward you. The 2N2222 family varies: the PN2222A is also E-B-C, but the P2N2222A is C-B-E — the reverse — and the original TO-18 can uses a circular layout referenced to a locating tab.
Swapping the collector and emitter runs the transistor in reverse, where gain collapses to single digits, or destroys it. Confirm the pinout against the datasheet for the exact part number in your hand, not against the family name.
Applications of 2N3904 and 2N2222
Can You Use the 2N3904 and 2N2222 Interchangeably?
Not unconditionally — and that is exactly why some guides say yes and others say no. Two things decide it:
- Current, and direction. A 2N2222 can stand in for a 2N3904 in almost any circuit, because its ratings meet or exceed the 2N3904’s. The reverse only holds when the load stays inside the 2N3904’s limit — 200 mA absolute, and realistically under about 150 mA continuous once you derate. In a circuit drawing more than that, a 2N3904 cannot replace a 2N2222. Substitution is not symmetric.
- Pinout, and variant. A 2N3904 and a PN2222A share the E-B-C layout and drop in for each other directly. A P2N2222A is wired C-B-E — collector and emitter reversed — and the original metal-can TO-18 2N2222 uses a radial layout. Dropping either into a board laid out for the 2N3904 without rewiring will not work and can destroy the part.
So the two are electrically equivalent for low-current work, but not a guaranteed drop-in. Confirm the load current and the exact part’s pinout before substituting. Working engineers reach the same conditional verdict in the long-running EEVblog thread on choosing between them and in this r/AskElectronics thread on transistor differences: within the current limit and with a matched pinout it makes no difference, and outside those bounds it does.
Common Applications for Both
With current and pinout confirmed, both parts handle the same low-current jobs:
- LED drivers and other small-current load switching
- Microcontroller and logic-level interfacing, where a low base current controls a larger load
- Sensor signal conditioning and small-signal amplification
- Audio preamplification in low-power stages
- Oscillators and timing circuits
- General switching and PWM under 200 mA
How to Choose Between 2N3904 and 2N2222
Voltage and Current Requirements
Start with the load. Both parts handle 40 V collector-to-emitter, so the deciding factor is current. If the load draws under 200 mA, the 2N3904 is sufficient. If it draws between 200 mA and 800 mA — relays, small motors, several LEDs — use the 2N2222A, and prefer the TO-18 package when that current must run continuously.
Frequency and Switching Speed
For high-speed switching, PWM, or small-signal RF, both parts perform almost identically at 250–300 MHz. This factor rarely separates them; if a design depends on higher frequency than that, neither general-purpose part is the right starting point.
Budget and Availability
The 2N3904 is the cheaper, more widely stocked part, which makes it the default for low-power and high-volume designs. The 2N2222A costs slightly more, and its TO-18 metal version more again, but it remains common and is worth the price only when you actually need the extra current or thermal headroom.
2N3904 and 2N2222 Equivalents and Alternatives
2N3904 Equivalents
For the 2N3904 (NPN, ≤200 mA), the 2N3903 is a near-identical sibling and the 2N4401 is a higher-current alternative (~600 mA). The BC547/BC548 and the 2SC945 are functionally close for low-current work but carry less current (roughly 100–150 mA) and use a different pinout, so verify both ratings and pin order before substituting. The SMD version is the MMBT3904, and the PNP complement is the 2N3906.
2N2222 Equivalents
For the 2N2222 (NPN, up to 800 mA), direct equivalents include the PN2222A, P2N2222A, 2N2219A, and MPS2222, with the BC337 as a similar ~800 mA NPN. The SMD version is the MMBT2222, and the PNP complement is the 2N2907.
When You Need More Than 800 mA
Step up rather than overdrive either part: a Darlington such as the TIP120/TIP122 family (~5 A), a power transistor such as the TIP3055 (~15 A), or a logic-level MOSFET for low on-resistance and minimal drive current.
Frequently Asked Questions
What is the main difference between the 2N3904 and 2N2222?
Maximum collector current. The 2N3904 is limited to 200 mA, while the 2N2222A handles up to 800 mA. Their voltage ratings (40 V VCEO), gain (hFE 100–300), and switching speed are otherwise close, so current capability is what separates them.
Can you use the 2N3904 and 2N2222 interchangeably?
Only conditionally. A 2N2222 can replace a 2N3904 in almost any circuit, but a 2N3904 can replace a 2N2222 only when the load stays under about 150–200 mA. You also have to check the pinout: the 2N3904 is E-B-C, while the P2N2222A is C-B-E and the metal-can TO-18 2N2222 is different again.
Which transistor is better for high-speed switching?
They are very close — about 300 MHz for the 2N3904 and 250–300 MHz for the 2N2222A. The 2N3904 has slightly lower output capacitance (~4 pF vs ~8 pF), giving it a marginal edge in low-current high-frequency and RF stages.
Why does the 2N2222 have a metal package option?
The original 2N2222/2N2222A ships in a TO-18 metal can, which dissipates heat far better than the plastic TO-92. That is what lets the 2N2222A sustain its higher current rating, and it suits high-temperature and high-reliability use.
What is the pinout of the 2N3904 and 2N2222?
With the flat side facing you and the leads pointing down, the 2N3904 (TO-92) reads E-B-C left to right. The 2N2222 varies by part: the PN2222A is also E-B-C, the P2N2222A is C-B-E (reversed), and the metal-can TO-18 uses a radial layout. Always confirm against the datasheet for your exact part number.
What can I use to replace the 2N3904 or 2N2222?
For the 2N3904, close NPN substitutes include the 2N3903, 2N4401, and BC547 (lower current and a different pinout). For the 2N2222, use the PN2222A, 2N2219A, or BC337. The 2N3906 and 2N2907 are their PNP complements — useful as partner devices, not as direct replacements.