I’ll research the MMBT3904-TP manufacturer datasheet, verify alternatives and purchasing details, and write a cited application guide in the project files.
I verified the pinout and switching specifications, and found two pin-compatible alternatives with different thermal limits. I’m writing the guide with worked 3.3 V and 5 V drive examples, clearly separating datasheet ratings from design recommendations.
The MCC (Micro Commercial Components) MMBT3904-TP is a general-purpose NPN bipolar junction transistor in a three-terminal SOT-23 surface-mount package, rated for 40 V collector-emitter voltage and 200 mA collector current as separate absolute maxima. Its common practical use is a resistor-driven, low-side switch for indicators and other small loads; it can also provide small-signal amplification with an appropriately designed bias network.
This guide covers the MMBT3904-TP pinout, base-resistor selection, LED switching circuit, PCB footprint considerations, equivalents, and sourcing. **Engineering examples and recommendations below are explicitly distinguished from manu...
Created and checked the MMBT3904-TP Application and Usage Guide in the project files, covering all seven requested sections with citations, 3.3 V/5 V resistor calculations, and two linked alternatives. The guide distinguishes absolute maxima from operating examples and flags unverified sourcing details and replacement thermal differences; no schematic or footprint changes were made.
The MCC (Micro Commercial Components) MMBT3904-TP is a general-purpose NPN bipolar junction transistor in a three-terminal SOT-23 surface-mount package, rated for 40 V collector-emitter voltage and 200 mA collector current as separate absolute maxima. Its common practical use is a resistor-driven, low-side switch for indicators and other small loads; it can also provide small-signal amplification with an appropriately designed bias network.
This guide covers the MMBT3904-TP pinout, base-resistor selection, LED switching circuit, PCB footprint considerations, equivalents, and sourcing. Engineering examples and recommendations below are explicitly distinguished from manufacturer guarantees. Research checked October 7, 2026; no schematic or footprint was changed.
1. Quick Specifications
Table
Parameter
Value and conditions
Classification
Collector-emitter voltage, VCEO
40 V
Absolute maximum; not a recommended supply voltage
Collector-base voltage, VCBO
60 V
Absolute maximum
Emitter-base voltage, VEBO
6 V
Absolute maximum reverse junction voltage; not a forward base-drive voltage
Collector current, IC
200 mA
Absolute maximum; subject to dissipation and drive constraints
Collector power dissipation, PC
350 mW at 25°C; derating curve gives 140 mW at 100°C
Maximum thermal limit, not a normal operating target
Operating junction temperature
−55°C to +150°C
Maximum-rating range; junction temperature, not guaranteed usable ambient range at full power
Storage temperature
−55°C to +150°C
Storage rating
Thermal resistance
RθJA = 357°C/W; RθJC = 185°C/W
Datasheet thermal values; board-dependent performance must be checked
DC current gain, hFE
100–300 at IC = 10 mA, VCE = 1 V; minimum 60 at 50 mA and 30 at 100 mA
Electrical limits at specified test points, not a fixed gain
Collector-emitter saturation voltage
≤0.2 V at IC = 10 mA, IB = 1 mA; ≤0.3 V at IC = 50 mA, IB = 5 mA
Electrical limits at 25°C under stated drive conditions
Base-emitter saturation voltage
0.65–0.85 V at IC = 10 mA, IB = 1 mA; ≤0.95 V at IC = 50 mA, IB = 5 mA
Electrical limits, not a universal 0.7 V constant
Transition frequency, fT
≥300 MHz at VCE = 20 V, IC = 10 mA, measurement frequency = 100 MHz
Small-signal test specification; not a guaranteed 300 MHz switching rate
Package and pad spacing
SOT-23; suggested pad layout has 1.90 mm same-side pad-center spacing and 0.95 mm staggered spacing
Mechanical/layout information; use the complete manufacturer drawing
Example operating point
3.3 V or 5 V load supply, approximately 10 mA collector current
Guide design example, not a manufacturer recommended-operating-condition table
The verified operating-limit section is titled Maximum Ratings @ 25°C Unless Otherwise Specified. A separate recommended-operating-condition table was not verified; select the operating point with voltage, current, thermal, and GPIO-drive margin rather than treating any absolute maximum as a target.
2. Pinout & Connections
Pin numbering below is verified against the MCC pin configuration. Best practices refer specifically to the low-side-switch circuit in Section 3, not every possible amplifier topology.
Table
Pin Number
Pin Name
Description
Best Practice
1
B — Base
Control terminal receiving base current
Drive through a calculated series resistor. Add a 100 kΩ base-emitter pull-down as a starting design choice when the GPIO may float during reset; check GPIO leakage and noise before finalizing it.
2
E — Emitter
Reference/current-return terminal
Tie to GND for a low-side switch; share a reference with the controlling GPIO.
3
C — Collector
Switched load terminal
Connect to the load’s low side; connect its high side to the positive load supply. For an inductive load, provide a flyback clamp.
Check top-view orientation and pad numbering before manufacture. Do not infer pinout from a TO-92 2N3904 or another three-terminal package.
3. Standard Application Circuit
GPIO-controlled low-side switch
Engineering implementation:
Text
+VLOAD ── load ─────────────── C (pin 3)
GPIO ── RB ──┬─────────────── B (pin 1)
└── RBE ── GND
GND ───────────────────────── E (pin 2)
For an LED, the load is +VLOAD → RLED → LED anode; the LED cathode connects to the collector. A high GPIO output turns the load on; the collector goes low. A low output turns it off.
Required passives for this LED example are a base series resistor RB and an LED current-limiting resistor RLED. The 100 kΩ RBE is a recommended reset-state pull-down, not a datasheet requirement. The transistor has no supply pin requiring its own IC-style bypass capacitor; place rail decoupling near the switched-load loop if the supply wiring or switching transient requires it, and size bulk capacitance for the load rather than assigning an arbitrary mandatory value.
Base-resistor calculation for 3.3 V and 5 V logic
The MCC saturation tests use IC/IB = 10 at both the 10 mA and 50 mA test points. Use this forced beta of 10 as the design starting point for the following 10 mA example; do not use the forward-active hFE of 100–300 to guarantee saturation.
Guide-derived equations, including current consumed by the pull-down:
For IC = 10 mA, IB,target = 1 mA. Use the verified 0.85 V VBE(sat) maximum at the 10 mA/1 mA test point as the room-temperature calculation operand.
Table
Assumed GPIO high level
RB upper bound, with RBE = 100 kΩ
Example selection
Calculated base current at VBE = 0.85 V
3.3 V
(3.3 − 0.85)/(1 mA + 8.5 µA) = 2.43 kΩ
2.2 kΩ, 1%
(3.3 − 0.85)/2.2 kΩ − 8.5 µA = 1.105 mA
5.0 V
(5.0 − 0.85)/(1 mA + 8.5 µA) = 4.12 kΩ
3.9 kΩ, 1%
(5.0 − 0.85)/3.9 kΩ − 8.5 µA = 1.056 mA
These are nominal-voltage examples, not validated designs for an unspecified MCU. Replace the assumed logic voltage with the MCU’s guaranteed VOH,min at the required source current; include resistor tolerance, supply tolerance, temperature, GPIO per-pin limits, and total port-current limits. The cited VBE bound is a 25°C test-point value, not a guarantee across the entire temperature range. At 50 mA, the manufacturer’s saturation test requires 5 mA base drive; at higher currents, reconsider whether a logic-level MOSFET or buffer is more appropriate.
A 0.125 W resistor is adequate for the base resistor in these examples: conservatively using the full supply across RB gives less than 7 mW in either case. This is a calculation for these values only.
LED series-resistor calculation
For a hypothetical red LED with VF = 2.0 V, a target LED current of 10 mA, and a 0.2 V transistor-drop design assumption based on the 10 mA/1 mA saturation specification:
A 0.125 W resistor is sufficient for these nominal examples. VF = 2.0 V is an explicit example assumption, not a verified LED specification. For an actual LED, calculate maximum current using maximum supply, minimum LED VF, minimum plausible transistor drop, and minimum resistor tolerance; calculate brightness/current minimum using the opposite corners. The 0.2 V datasheet figure is a maximum at its specified test point, not a typical or minimum drop. The load supply need not equal the GPIO supply; select RB from GPIO voltage and RLED from load-supply voltage independently.
Inductive-load adaptation
For a relay or solenoid, place a flyback diode across the coil with cathode to +VLOAD and anode to collector, so it is reverse-biased while the transistor is on. This is an engineering protection recommendation: select diode reverse-voltage, pulse-current, energy, and recovery capability for the actual coil, keep the clamp below the transistor voltage limit with margin, and verify coil current including turn-on/inrush. A simple diode clamp slows relay release; faster release needs a separately designed clamp. Do not assume the 200 mA collector-current absolute maximum guarantees acceptable coil-drive operation.
4. PCB Layout & Routing Guidelines
The following are engineering recommendations; the datasheet supplies the mechanical reference and thermal limits, not a complete board-layout prescription.
Footprint and orientation: use the MCC SOT-23 drawing and Suggested Solder Pad Layout, including the verified 1.90 mm same-side and 0.95 mm staggered pad-center spacing. Verify pin 1/base, pin 2/emitter, and pin 3/collector in the CAD footprint; do not substitute SOT-323 or SOT-523 because the name contains “3904.” Detailed body-dimension tolerances were not independently validated in this research and are intentionally not reproduced.
Base and emitter routing: place RB and RBE near the transistor, keep the base node short, and route the emitter return directly to the shared ground reference. Avoid sharing a narrow emitter-return segment with sensitive analog references or noisy load currents.
Load-loop width: size collector/emitter traces and vias from actual current, copper thickness, allowable temperature rise, and voltage drop. No universal minimum trace width is specified here. For inductive loads, place the flyback diode close to the load connection and minimize the coil/clamp loop.
Thermal copper and thermal relief: check P ≈ VCE × IC + VBE × IB and estimate TJ ≈ TA + P × RθJA, using the actual PCB’s thermal behavior. MCC lists RθJA = 357°C/W and a power-derating curve. Use copper spreading where needed; avoid overly restrictive thermal-relief spokes if they bottleneck current or heat, while keeping pad solderability balanced. Treat RθJA as a reference, not a board-independent guarantee.
Decoupling and signal integrity: put any load-rail bypass capacitor near the current loop and keep switched collector copper away from sensitive base/analog wiring. This device has no differential interface, so differential-pair routing and impedance matching are not inherent requirements.
5. Common Pitfalls / Things to Watch Out For
Insufficient base drive or uncontrolled reset behavior. Dividing load current by a nominal hFE of 100–300 does not reproduce the saturation test, which uses a forced beta of 10. Always use a base resistor, check GPIO source capability, and establish a safe off state when the controller is high-impedance; a floating base can cause unintended load conduction.
Treating voltage, current, and power maxima as simultaneously usable. For example, 100 mA at VCE = 5 V dissipates approximately 0.5 W in the collector-emitter path alone, already exceeding the 350 mW rating at 25°C. Check linear/transient dissipation, ambient derating, and inductive turn-off protection; do not use the 40 V rating as an unclamped transient target.
6. Popular Alternatives & Equivalents
These are pin-compatible, standard-SOT-23 footprint-compatible candidates, not unconditional electrical/thermal drop-ins. Compare the exact manufacturer package drawing to the existing land pattern and requalify operating corners before changing the BOM; the current project footprint itself was not audited.
Pin-compatible: 1 B, 2 E, 3 C; SOT-23/TO-236 standard-footprint candidate
40 V VCEO and 200 mA continuous IC. VCE(sat) limits match the 0.2 V at 10 mA/1 mA and 0.3 V at 50 mA/5 mA test points. Power rating differs: 225 mW on the specified FR-5 board at 25°C, versus 300 mW on the specified alumina substrate.
Pin-compatible: 1 B, 2 E, 3 C; SOT23 standard-footprint candidate
40 V VCEO and 200 mA IC. VCEsat ≤200 mV at 10 mA/1 mA and ≤300 mV at 50 mA/5 mA, at 25°C. Power rating differs: 250 mW at ambient ≤25°C on the specified single-sided, tin-plated FR4 PCB with standard footprint. The exact ,215 tape/reel ordering convention was not independently verified here; confirm it when buying.
Both exact alternative MPNs were found in the Flux library. Their nominal switching characteristics make them reasonable second-source candidates for the low-current example, but the different thermal test fixtures prevent a simple power-rating equivalence claim. A through-hole 2N3904 is at most functionally similar, not a SOT-23 footprint replacement.
7. Sourcing & Purchasing Guide
Table
Attribute
Details
Primary Distributors
MCC identifies DigiKey and Mouser as authorized global partners on its distribution page. Exact current MMBT3904-TP listings/MOQs at those two distributors were not verified. LCSC lists the exact MCC MMBT3904-TP as C77991; LCSC authorization by MCC was not independently established here.
Packaging Options
Manufacturer -TP = Tape & Reel, 3,000 pieces/reel. Smaller tape quantities are distributor-specific; do not assume every distributor offers one-piece cut tape or a custom reel.
Standard MOQ
Manufacturer full-reel quantity: 3,000. The LCSC listing reports minimum 50 pieces, multiple 50, standard packaging 3,000 when checked. There is no verified universal one-piece MOQ. Confirm checkout quantities because purchasing terms change.
JLCPCB Assembly
JLCPCB lists MMBT3904-TP as C77991, an Extended part. Check assembly stock and fees when placing an order; assembly-library availability is not a guarantee of separately shippable loose components.
Sourcing Advice
Buy direct from MCC or a manufacturer-authorized/franchised distributor with traceability; MCC explicitly recommends authorized sources and states that unauthorized-source purchases receive no MCC warranty coverage or assistance. Match the full MMBT3904-TP ordering code, manufacturer, SOT-23 package, reel/tape format, and assembly orientation. Do not silently replace it with a smaller-package 3904 variant or an unrelated maker’s part.
No live stock quantity or price is promised in this guide. Distributor stock, MOQ, and price must be reconfirmed at purchase.
Sources
MCC manufacturer datasheet:MMBT3904 — SOT-23 NPN General Purpose Amplifier. Verified revision marking Rev.3-6-08182023 (August 18, 2023); maximum ratings, pin configuration, electrical characteristics, pad layout, derating curve, ordering information, and counterfeit warning.
MCC official product page:MMBT3904, including MMBT3904-TP orderable identity and SOT-23 packaging; page revision/date not stated in retrieved content.
MCC official sourcing guidance:Authorized Global Distribution Partners, supporting DigiKey and Mouser authorization; page revision/date not stated in retrieved content.
onsemi manufacturer datasheet:MMBT3904L / SMMBT3904L — MMBT3904LT1/D. Used for pinning, maximum ratings, saturation limits, and substrate-specific dissipation; the revision/date of the exact parsed evidence was not independently confirmed, so no latest-revision claim is made.
Nexperia manufacturer datasheet:MMBT3904. Used for pinning, SOT23 package, limiting values, thermal fixture conditions, and saturation limits; revision/date of the exact parsed evidence was not independently confirmed.
Distributor purchasing source:LCSC C77991 — MCC MMBT3904-TP. Primary source for that distributor’s MOQ, order multiple, and reel quantity; checked October 7, 2026.
Assembly purchasing source:JLCPCB C77991 — MMBT3904-TP. Primary source for that assembler’s listing/classification; checked October 7, 2026.