2N3904 vs BC547: Transistor Comparison & Equivalents
The 2N3904 and BC547 are two of the most popular general-purpose NPN transistors in the world. They appear in countless hobbyist projects, educational kits, and even commercial products. But which one should you choose? Let's compare them side by side.
Quick answer: They are near-identical NPN transistors, but the pinouts differ. The 2N3904 is EBC and handles up to 200 mA. The BC547 is CBE, handles up to 100 mA, and has a higher gain range. Swapping one for the other works in most circuits as long as you rotate the part to match the pins.
Quick Specifications Comparison
| Parameter | 2N3904 | BC547 |
|---|---|---|
| Type | NPN BJT | NPN BJT |
| Max Collector Current (Ic) | 200 mA | 100 mA |
| Max Collector-Emitter Voltage (Vce) | 40V | 45V |
| Max Power Dissipation | 625 mW | 500 mW |
| DC Current Gain (hFE) | 100–300 | 110–800 |
| Transition Frequency (fT) | 300 MHz | 300 MHz |
| Package | TO-92 | TO-92 |
Pinout Differences. Important!
Despite both using the TO-92 package, their pinouts are different:
- 2N3904: Emitter – Base – Collector (EBC)
- BC547: Collector – Base – Emitter (CBE)
This is the most common mistake when substituting one for the other. If you swap them without rotating the component, you'll connect the collector where the emitter should be and vice versa. Always check the datasheet pinout diagram.
When to Use the 2N3904
The 2N3904 is the better choice when you need:
- Higher collector current (up to 200 mA vs 100 mA)
- Higher power dissipation capability
- A transistor that's readily available in North American supply chains
- Compatibility with circuits designed for the JEDEC standard pinout (EBC)
Common applications: LED drivers, relay drivers, small signal amplifiers, switching circuits up to 200 mA.
When to Use the BC547
The BC547 excels when you need:
- Higher voltage capability (45V vs 40V)
- Higher current gain (hFE up to 800 in the BC547C variant)
- Better gain consistency across production batches
- A transistor commonly specified in European and Asian designs
The BC547 also comes in gain-sorted variants (BC547A, B, and C) which makes it easier to select a specific gain range for amplifier circuits.
Can You Substitute One for the Other?
Yes, in most circuits they are interchangeable with one critical caveat: you must account for the different pinout. Physically rotate the transistor 180° or adjust your PCB connections. Electrically, both transistors are similar enough for general-purpose switching and amplification.
For switching applications under 100 mA, either transistor works fine. For currents between 100–200 mA, only the 2N3904 is rated. For amplifier circuits where gain matching matters, the BC547B or BC547C may give more predictable results.
Other Compatible Equivalents
If neither the 2N3904 nor BC547 is available, consider these alternatives:
- 2N2222: Higher current rating (800 mA), same pinout as 2N3904
- BC548: Nearly identical to BC547 with slightly different voltage ratings
- BC337: Higher current (800 mA) with BC547-style pinout
- S8050: Popular in Asian markets, 500 mA, 25V
Practical Advice
For hobby projects and prototyping, keep both transistors in your parts kit. The 2N3904 is the go-to for most switching applications in North American designs, while the BC547 dominates in European circuit books and kits. Understanding both, and especially their pinout differences, will save you debugging time.
Check our component database for detailed specifications, datasheets, and a full list of equivalent parts for both transistors.
Frequently Asked Questions
Can I replace a 2N3904 with a BC547?
Usually yes, for switching and small-signal work below 100 mA. Account for the different pinout (EBC versus CBE), and stay under the BC547's lower 100 mA collector current limit. For anything between 100 and 200 mA, stay with the 2N3904.
What do the A, B and C suffixes on a BC547 mean?
They are gain groups. BC547A has the lowest current gain, BC547B is in the middle, and BC547C has the highest. If a circuit was designed around a specific gain, the suffix matters. For simple on/off switching it rarely does.
Which one is better for driving an LED or relay?
Either works for an LED. For a relay coil that draws more than 100 mA, use the 2N3904 or step up to a higher-current part like the BC337. To pick the LED resistor, see What Resistor Do I Need for My LED?. If you are switching larger loads, a MOSFET is usually the better tool.
Related Guides & Tools
- Component Database with full specs for both parts
- What Is a MOSFET?
- How to Find Equivalent Components
- Ohm's Law Explained
Ready to put this into practice?
View 2N3904 specs & equivalents