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 Specifications Comparison

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.