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SOT-23 · MMBT3904
ActiveBJT (NPN General Purpose)
MMBT3904
onsemi · SOT-23 · BJT (NPN General Purpose)
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Overview
The MMBT3904 is the SOT-23 surface-mount version of the legendary 2N3904 NPN bipolar junction transistor. Rated for 40 V collector-emitter, 200 mA continuous collector current, and a gain-bandwidth product of 300 MHz, it is one of the most widely deployed general-purpose NPN transistors in modern electronics — found in virtually every mobile phone, laptop, LED driver, sensor interface and industrial controller manufactured in the last 25 years.
DC current gain (hFE) ranges from 100 to 300 depending on collector current and the specific suffix grade. Saturation voltage is 0.2 V typ at Ic=10 mA, Ib=1 mA, dropping to 0.4 V at Ic=50 mA — good enough for switching but not as low as a MOSFET's Rds(on)×I.
Speed is the standout feature: with fT = 300 MHz and typical switching times under 60 ns, the MMBT3904 handles RF amplification up to VHF and fast digital switching. It is often used as the output stage in class-A preamplifiers, as a level shifter between logic families, and as a small-signal switch in muxing applications.
Complementary PNP: MMBT3906 (40 V, -200 mA, same package, same pinout with E-B-C reversed polarity convention). Use the pair for push-pull amplifiers, complementary level shifters and H-bridge corner drivers.
Fully second-sourced: onsemi (MMBT3904LT1G), Nexperia (MMBT3904,215), Diodes Inc (MMBT3904-7-F), Vishay, ST, and many Asian vendors. Package is SOT-23 with three leads; pinout is Base-Emitter-Collector from left to right when viewed with markings up and leads down.
Our Shenzhen stock: onsemi MMBT3904LT1G MOQ 3,000 pcs on reel; Nexperia MMBT3904 MOQ 3,000 pcs.
Key Features
- 40 V collector-emitter, 200 mA continuous collector current
- 300 MHz gain-bandwidth product for RF and fast switching
- hFE 100-300 across the operating range
- Complementary PNP: MMBT3906 in same package
Typical Applications
- Small-signal amplification in audio preamps and sensor interfaces
- Level shifting between logic families
- Switching small relays, LEDs, and solenoids from MCU GPIOs
- RF amplifiers up to VHF (30-300 MHz)
- Complementary push-pull output stages (with MMBT3906)
Specifications
- Polarity
- NPN
- Collector-Emitter Voltage
- 40 V
- Collector Current
- 200 mA
- DC Current Gain (hFE)
- 100 to 300
- Gain Bandwidth
- 300 MHz
- Power Dissipation
- 350 mW
- Operating Temperature
- -55 to 150 °C
- Mounting Type
- Surface Mount
- RoHS
- Compliant
Procurement Tips
Standardize on MMBT3904 for small-signal and MMBT2222A for switching across your product line — the SOT-23 footprint is identical, so BOM consolidation saves procurement time.
Frequently Asked Questions
MMBT3904 vs 2N3904 — what's the difference?
Electrically identical. 2N3904 is the through-hole TO-92 package; MMBT3904 is the surface-mount SOT-23 package. Same pinout convention (E-B-C from left to right for SOT-23, E-B-C from flat-side for TO-92). Choose based on assembly process.
MMBT3904 vs MMBT2222 — which is better?
MMBT2222A handles higher current (600 mA vs 200 mA) and higher power (350 mW vs 250 mW), but has lower fT (250 MHz vs 300 MHz). Use MMBT3904 for small-signal and RF; use MMBT2222A for higher-current switching (up to 500 mA).
Can I use MMBT3904 as a switch for a 12 V relay?
Only for small relays with coil current under 100 mA. Wire the relay coil between +12 V and collector, add a 1N4148 flyback diode across the coil, drive the base with 1-5 mA through a 2-10 kΩ resistor from your MCU. For larger relays use MMBT2222A or a MOSFET.
What is the pinout of MMBT3904?
SOT-23 viewed with markings up and leads pointing down: pin 1 = Base, pin 2 = Emitter, pin 3 = Collector. Always verify with a multimeter diode test before soldering — some Asian clones swap B and E.
Is it counterfeit-prone?
Moderately. Genuine onsemi/Nexperia parts have laser-etched "M4" or "1AM" marking, matte tin leads, consistent weight. Fakes often use remarked lower-spec dies that fail at 40 V or above 100 mA. Test a sample with a curve tracer if you're buying from an unfamiliar broker.
MOQ and lead time?
MOQ 3,000 pcs on reel for onsemi MMBT3904LT1G, or 100 pcs loose. Shenzhen stock 1-2 days; onsemi authorized 8-16 weeks.
Alternatives & Equivalents
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