MMBT3904LT1 - 40V NPN General Purpose Transistor SOT-23
MPN: MMBT3904LT1 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.16 | $0.16 |
| 10 | $0.14 | $1.40 |
| 100 | $0.09 | $9.00 |
| 500 | $0.07 | $35.00 |
| 1,000 | $0.05 | $50.00 |
| 3,000 | $0.04 | $120.00 |
MMBT3904LT1 Overview
An NPN bipolar junction transistor is a three-terminal semiconductor device in which a small base current controls a much larger collector current. Within the broader semiconductor taxonomy, the MMBT3904LT1 sits at: BJT -> bipolar transistor -> discrete semiconductor -> semiconductor. NPN devices conduct when the base is biased above the emitter by approximately 0.7 V, making them the natural choice for low-side switching and for sourcing current to a load tied to a positive rail.
Key features include a 40 V collector-emitter breakdown voltage (VCEO), 60 V collector-base breakdown (VCBO), 6 V emitter-base breakdown (VEBO), 200 mA continuous collector current, 300 MHz transition frequency (fT), DC current gain (hFE) of 100 to 300, and an epitaxial planar die construction. The SOT-23 (TO-236) plastic package supports a 350 mW dissipation rating on a minimum 1 inch² copper pad and operates across a -55 °C to +150 °C junction temperature range.
The part uses an epitaxial planar process that yields a high gain-bandwidth product relative to its small footprint. Its low saturation voltage (VCE(sat a few hundred millivolts at moderate IC) makes it efficient as a saturated switch, while its 300 MHz fT supports general-purpose small-signal RF amplification below the VHF band.
Typical applications include low-side switching of LEDs, relays, and logic-level translators, general-purpose small-signal amplification, inverter and interface circuits, and as a driver for higher-power transistors. The complementary MMBT3906 (PNP) is the natural companion for push-pull and level-shifter topologies.
When designing with this device, observe the 200 mW power dissipation limit: at 200 mA collector current the allowable VCE drops to 1 V before derating begins. A minimum 0.5 inch² of copper pad area is recommended to keep the junction within safe thermal limits in continuous operation.
This page synthesizes distributor pricing, drop-in SOT-23 alternatives, and practical design notes not found on the onsemi datasheet alone, with cross-brand equivalents sourced from verified catalog cross-references.
Drop-in alternatives for MMBT3904LT1 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with MMBT3904LT1 (same form factor and footprint) — differing in DC Current Gain (hFE), Package, Power Dissipation (PD), Transition Frequency (fT).
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
MMBT3904LT1G
✅ Drop-In📋 Reference alternative (not in catalog)
MMBT3904LT3G
✅ Drop-In📋 Reference alternative (not in catalog)
SMMBT3904LT1G
✅ Drop-In📋 Reference alternative (not in catalog)
MMBT3904
✅ Drop-In✓ In Stock
$0.04 / Unit
View Datasheet →BC847
✅ Drop-In📋 Reference alternative (not in catalog)
MMBT2222A
✅ Drop-In📋 Reference alternative (not in catalog)
MMBTA05
✅ Drop-In📋 Reference alternative (not in catalog)
MMBT3904LT1 Maximum Ratings & Electrical Characteristics
| Polarity | NPN |
| Collector-Emitter Voltage (Vceo) | 40 V |
| Collector-Base Voltage (Vcbo) | 60 V |
| Emitter-Base Voltage (Vebo) | 6 V |
| Continuous Collector Current (IC) | 200 mA |
| Power Dissipation (PD) | 200 mW (on minimum recommended pad) |
| DC Current Gain (hFE) | 100 to 300 |
| Transition Frequency (ft) | 300 MHz (min) |
| Noise Figure | 5 dB (max) |
| Operating Junction Temperature | -55 °C to +150 °C |
| Package | SOT-23 (TO-236), 3-pin |
| Mounting Type | Surface Mount |
| Die Construction | Epitaxial Planar |
| Complementary PNP Part | MMBT3906 |
| RoHS Status | Compliant (Lead Free version available) |
| AEC-Q101 Qualified | Yes (S-prefix variant) |
MMBT3904LT1 Pin Configuration
| Pin 1 | Emitter — Emitter terminal (grounded for low-side switching) |
| Pin 2 | Base — Base control terminal (current in to turn on) |
| Pin 3 | Collector — Collector terminal (load connection) |
Typical Applications
MMBT3904LT1 is suitable for 6 applications: LED Driver / Low-Side Switch, Logic-Level Translator / Level Shifter, General-Purpose Small-Signal Amplifier, Relay and Solenoid Driver, Inverter and Oscillator Circuits, Sensor Switching and Interface.
LED Driver / Low-Side Switch
The MMBT3904LT1 is widely used as a low-side switch to drive indicator LEDs, optocouplers, and relay coils from 3.3 V or 5 V microcontroller GPIO pins. Its 200 mA collector current comfortably handles single indicator LEDs (10-20 mA) and small signal relays; with hFE of 100-300, a few hundred microamps from the GPIO pin saturates the transistor for clean digital switching. The 40 V VCEO provides substantial headroom above 5 V logic rails, and the SOT-23 footprint saves board space in dense designs. Its 300 ns turn-off time supports PWM dimming above 1 kHz without significant switching loss.
Recommended
Logic-Level Translator / Level Shifter
The MMBT3904LT1 serves as a simple, low-cost logic-level translator between 3.3 V microcontrollers and 5 V peripherals, or between any two rails up to 40 V. Placed in an open-collector configuration with a pull-up resistor on the target rail, it shifts logic levels bidirectionally with no quiescent current beyond the pull-up. The NPN BJT's VBE drop of ~0.7 V and low saturation resistance make it suitable for I2C bus level shifting, GPIO voltage translation, and reset signal buffering. The 200 mA continuous current rating supports driving multiple loads from a single translator stage.
Recommended
General-Purpose Small-Signal Amplifier
The MMBT3904LT1's 300 MHz transition frequency and hFE of 100-300 make it well-suited for general-purpose small-signal AC amplification in audio preamp stages, sensor signal conditioning, and intermediate buffer stages. Its low noise figure (5 dB max) supports microphone preamp and instrumentation front-end designs operating below 100 kHz. The SOT-23 package combined with 200 mW dissipation supports compact analog front-ends on densely populated PCBs where TO-92 packages would be too tall or too large.
Recommended
Relay and Solenoid Driver
For low-power relay and solenoid switching under 200 mA continuous, the MMBT3904LT1 provides a compact driver solution when paired with a flyback diode across the inductive load. Its 40 V VCEO handles typical 12 V and 24 V automotive and industrial relay coils with substantial margin for inductive kick suppression. The high hFE (100-300) means a few milliamps from a logic pin can switch the relay directly, eliminating the need for a Darlington driver in cost-sensitive designs. SOT-23 packaging keeps the BOM compact.
Recommended
Inverter and Oscillator Circuits
The MMBT3904LT1 is a building block for simple astable multivibrators, RC oscillators, and square-wave inverter stages. Its 300 MHz fT supports oscillation frequencies well into the MHz range for crystal-controlled or LC-tank oscillators. Two MMBT3904LT1 transistors plus a complementary MMBT3906 form a classic complementary-pair multivibrator for timing circuits, blinkers, and tone generators. The NPN's 40 V rating also suits use as a line driver in RS-232 / RS-485 interface circuits up to that voltage.
Recommended
Sensor Switching and Interface
The MMBT3904LT1 is widely deployed as a sensor interface switch in industrial controls, automotive ECUs, and consumer electronics. Its low VCE(sat) makes it efficient for switching Hall-effect sensors, reed switches, optocouplers, and thermistor bias networks. In a typical application, it buffers a sensor output to a microcontroller ADC input or digital GPIO, providing isolation and level shifting in one stage. The SMD SOT-23 package supports high-density sensor arrays on compact PCBs.
Recommended
Recommended Products Summary
Engineering reference data for MMBT3904LT1 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MMBT3904LT1G | MMBT3904LT3G | SMMBT3904LT1G | MMBT3904 | BC847 | MMBT2222A | MMBTA05 |
|---|---|---|---|---|---|---|---|---|
| Brand | onsemi | onsemi | onsemi | onsemi | onsemi | NXP Semiconductors | onsemi | onsemi |
| Package | SOT-23 | SOT-23 - same | SOT-23 - same | SOT-23 - same | SOT-23 - same | SOT-23 - same | SOT-23 - same | SOT-23 - same |
| Polarity | NPN | NPN | NPN | NPN | NPN | NPN | NPN | NPN |
| VCEO (max) | 40 V | 40 V | 40 V | 40 V | 40 V | 45 V | 40 V | 60 V |
| Continuous Collector Current | 200 mA | 200 mA | 200 mA | 200 mA | 200 mA | 100 mA | 600-800 mA | 500 mA |
| DC Current Gain (hFE) | 100-300 | 100-300 | 100-300 | 100-300 | 100-300 | 110-800 | 40-300 | 50-300 |
| Transition Frequency (fT) | 300 MHz | 300 MHz | 300 MHz | 300 MHz | 300 MHz | 100-300 MHz | 250-300 MHz | 100 MHz |
| Automotive Qualified (AEC-Q101) | No (S-prefix available) | No (S-prefix available) | No (S-prefix available) | Yes | No | No (BC847A qualified variants exist) | No | No |
Key Differentiators
- Industry-standard SOT-23 NPN with proven second-source ecosystem (vs MMBT2222A)
- Lower collector current rating than BC847 alternative (vs BC847 (NXP))
- Lower VCEO than MMBTA05 alternative (vs MMBTA05)
- AEC-Q101 variant available within the same family (vs BC847)
Design Notes
The MMBT3904LT1 is rated 200 mW continuous dissipation when mounted on a minimum 1 in² copper pad at 25 °C ambient, per the onsemi datasheet MMBT3904LT1/D. Power derates linearly to zero at 150 °C junction. Estimated: at 100 mA IC and 10 V VCE, dissipation is 1 W - well above the 200 mW rating - so duty-cycle limiting or a larger SOT-223/TO-92 package (MPSA18, 2N3904) is required for continuous high-current operation.
Route the base trace as short as possible to minimize stray feedback and switching transients. For switching applications above 10 kHz, place a base resistor (typically 1-10 kΩ) directly at the base pin to dampen input resonance. The SOT-23 thermal pad is the collector lead; do not connect it to high-impedance circuits, and provide at least 0.5 in² copper pour to enhance heat spreading on FR-4.
Do not reverse the emitter and collector - the MMBT3904LT1's forward VCEO is 40 V but reverse VCEO drops to a few volts, and gain in reverse mode is severely degraded. Always include a flyback diode across inductive loads (relays, solenoids) connected between V+ and the collector; the absence of this diode will exceed the 40 V VCEO breakdown on switch-off and destroy the transistor. For logic-level interfacing, ensure VBE(sat) of ~0.7 V is properly overcome by the driving GPIO voltage - 3.3 V logic typically provides adequate margin.
At switching frequencies above 100 kHz, the MMBT3904LT1's transition frequency of 300 MHz provides ~30° of phase margin per stage. For low-distortion small-signal amplifier design, bias the collector at 0.5*VCC and keep the emitter bypass capacitor (typically 10-100 µF) close to the emitter pin to maximize AC gain. The 5 dB noise figure is acceptable for audio applications below 50 kHz but degrades rapidly above the fT/10 corner.
Compliance Information
MMBT3904LT1G suffix guarantees RoHS and lead-free. S-prefix SMMBT3904LT1 is AEC-Q101 qualified and PPAP capable for automotive. Standard MMBT3904LT1 is not AEC-Q100 qualified - choose S-prefix variant for automotive designs.
