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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

STMicroelectronics STN851

Name: STN851
Brand: STMicroelectronics
SKU: STN851
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: STN851

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-261-4, TO-261AA

Datasheet:: STN851.pdf

Description:: TRANS NPN 60V 5A SOT-223

Quantity:: RFQ Add To RFQ list

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Inventory:2,184

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Product details

Overview

STN851 from STMicroelectronics is a low-voltage, fast-switching NPN power transistor in SOT-223 package, rated for 60 V V_CEO, 5 A continuous collector current, and 1.6 W power dissipation at 25 °C ambient. It delivers V_CE(sat) as low as 50 mV at I_C = 100 mA / I_B = 5 mA and h_FE ≥ 150 at I_C = 10 mA, enabling high-efficiency switching in emergency lighting and relay driver circuits.

For engineers reviewing the STN851 datasheet, STN851 pinout, STN851 application, or STN851 equivalent, key selection criteria include its low saturation voltage under high-current drive, fast turn-on/turn-off timing (t_on = 50 ns, t_f = 120 ns), thermal resistance (78 °C/W), and SOT-223 footprint compatibility with board-level heat sinking.

Technical Context

This planar NPN transistor uses "Base Island" layout to optimize gain uniformity and saturation performance. Its 130 MHz f_T supports fast digital switching, while low V_CE(sat) across I_C = 100 mA–5 A ensures minimal conduction loss in low-voltage DC-DC and load-switching stages.

The device operates up to 150 °C junction temperature and features robust absolute ratings: 150 V V_CBO, 7 V V_EBO, and 10 A I_CM peak current. Thermal derating follows a linear 1.6 W → 0 W over 25–150 °C ambient, validated per JEDEC JESD51-2.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	60 V - maximum safe collector-emitter blocking voltage with base open, suitable for 48 V and lower DC systems
I_C (continuous)	5 A - sustained collector current capability with 1.6 W dissipation on 1 cm² PCB copper area
V_CE(sat) @ I_C=1 A	70 mV - ultra-low conduction loss enabling >95% efficiency in low-dropout switch applications
h_FE @ I_C=2 A	90 - stable current gain at medium load, reducing required base drive current and driver stage complexity
t_f	120 ns - fast fall time minimizes switching transition losses in PWM-controlled loads
R_thj-amb	78 °C/W - thermal resistance enables direct PCB heatsinking without external heatsink below ~1.2 W dissipation
f_T	130 MHz - sufficient bandwidth for high-frequency switching up to ~10 MHz square-wave operation

Pinout & Package

SOT-223 package with exposed emitter pad (pin 2) for enhanced thermal conduction; standard 4-pin configuration where pin 1 = emitter, pin 2 = collector (tab), pin 3 = base, pin 4 = emitter (redundant). Mounting requires minimum 1 cm² copper pour under tab for rated power handling.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1	Emitter	Primary emitter connection; low-inductance path for return current in switching loops
Pin 2 (Tab)	Collector	Electrically connected to collector and thermally coupled to PCB copper; primary heat transfer path
Pin 3	Base	Control input requiring ~200 mA peak drive for full saturation at 5 A I_C
Pin 4	Emitter	Secondary emitter tie for improved current sharing and reduced bond-wire inductance

Key Features

Feature	Design Value
Very low V_CE(sat)	50 mV at I_C = 100 mA - reduces conduction loss by >60% vs. standard general-purpose transistors
High h_FE at high current	90 at I_C = 2 A - enables simplified base drive with low-side logic-level control
Fast switching speed	t_on = 50 ns, t_f = 120 ns - supports PWM frequencies up to 1 MHz with minimal dead-time overhead
Robust thermal design	R_thj-amb = 78 °C/W on 1 cm² PCB - eliminates need for mechanical heatsink in space-constrained industrial modules

Applications

Emergency Lighting Control

Voltage Regulator Pass Element

Use Scenario: Battery-backed LED driver activated during AC mains failure, requiring rapid turn-on and low dropout.

IC Role / Device Role / Timing Role: NPN power switch controlling current to high-brightness LED string via PWM dimming.

Use Value: 50 mV V_CE(sat) at 100 mA preserves battery runtime; 120 ns fall time ensures precise dimming resolution at 1 kHz.

Use Scenario: Linear post-regulation stage in 5 V/3 A supply for noise-sensitive analog circuitry.

IC Role / Device Role / Timing Role: Series pass transistor dissipating up to 1.2 W while maintaining <10 mV output ripple.

Use Value: 90 h_FE at 2 A allows single-stage base drive from op-amp error amplifier; 78 °C/W R_th avoids thermal shutdown.

Relay Driver Stage

Low-Voltage Motor Switch

Use Scenario: Microcontroller-driven 24 V relay coil interface requiring galvanic isolation and surge immunity.

IC Role / Device Role / Timing Role: High-gain NPN switch amplifying GPIO signal to deliver 500 mA coil current with flyback protection.

Use Value: 150 h_FE at 10 mA enables direct MCU drive; 60 V V_CEO withstands 2× coil back-EMF spikes.

Use Scenario: Bidirectional 12 V brushed DC motor control in portable medical pumps using H-bridge half-bridge topology.

IC Role / Device Role / Timing Role: Low-side switching element in one leg of discrete H-bridge, operating at 20 kHz PWM.

Use Value: 130 MHz f_T ensures clean gate drive edge integrity; 5 A I_C rating supports 3 A RMS motor current with margin.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN power switching applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
MJD127	V_CEO = 100 V, V_CE(sat) = 1.2 V @ I_C = 3 A - higher saturation voltage, lower gain at high current	Higher voltage tolerance but unsuitable for ultra-low-loss <1 V drop applications	Prefer STN851 when V_CE(sat) < 100 mV is required at >1 A; MJD127 better for 60–100 V systems with less thermal constraint
ZTX653	h_FE = 100 @ I_C = 1 A, R_thj-amb = 100 °C/W - lower gain, higher thermal resistance than STN851	Less efficient at high current due to higher V_CE(sat) and poorer thermal coupling	STN851 preferred for PCB-area-limited designs needing <80 mV V_CE(sat); ZTX653 acceptable only with external heatsink

Compared with MJD127 and ZTX653, STN851 uniquely combines sub-100 mV saturation, 90+ h_FE at 2 A, and 78 °C/W thermal resistance in SOT-223 - making it optimal for compact, high-efficiency low-voltage switching where conduction loss and board space are critical.

Availability

STN851 is available at Aetrix Electronics and suitable for emergency lighting systems, voltage regulators, and relay drivers requiring stable component supply and long-term industrial availability.

Supply support for STN851 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

The STN851 belongs to ST's high-performance bipolar power transistor family, engineered specifically for low-voltage, high-current switching applications demanding minimal conduction loss and reliable thermal behavior in compact surface-mount packages.

FAQ

What is the maximum safe operating temperature for STN851?

The STN851 has a maximum junction temperature (T_J) of 150 °C and storage temperature range of –65 to +150 °C. Its thermal resistance is 78 °C/W junction-to-ambient on a 1 cm² PCB copper area, so continuous operation at full 5 A load requires careful thermal design to keep T_J ≤ 150 °C.

Can STN851 be used in inductive load switching?

Yes - STN851 is qualified for inductive load switching, with documented waveforms showing t_s = 1.35 µs storage time and robust SOA under inductive turn-off stress. Use with appropriate flyback diode (e.g., 1N4007) and snubber network is recommended for >100 mA inductive currents.

Is STN851 RoHS-compliant and halogen-free?

Yes - STN851 is manufactured in ECOPACK®-compliant SOT-223 packaging, meeting RoHS Directive 2011/65/EU and halogen-free requirements per IEC 61249-2-21. Full compliance documentation is available via ST's quality portal using order code STN851.

How does STN851 compare to standard general-purpose transistors like BC337?

STN851 delivers 5 A continuous current and 1.6 W dissipation - over 10× the current and power capability of BC337 (0.5 A, 0.625 W). Its V_CE(sat) is 50 mV vs. ~200 mV for BC337 at 100 mA, and its h_FE remains ≥90 at 2 A, whereas BC337 drops to <50 above 100 mA - making STN851 a true power-grade replacement.

STN851 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-261-4, TO-261AA

Packaging:: Tape & Reel (TR)

Product Status:: Active

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 5 A

Voltage - Collector Emitter Breakdown (Max):: 60 V

Vce Saturation (Max) @ Ib, Ic:: 500mV @ 200mA, 5A

Current - Collector Cutoff (Max):: 50nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 150 @ 2A, 1V

Power - Max:: 1.6 W

Frequency - Transition:: 130MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-223

STN851 FAQ

1.How can I place an order for STN851 through Aetrix?

Please submit a Request for Quotation (RFQ) for STN851 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for STN851 reliable?

The price and inventory of STN851 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for STN851 is usually 5 days.

3.What payment methods are accepted for STN851?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for STN851 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for STN851?

STN851 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your STN851 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for STN851?

For technical support, including STN851 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your STN851 requirements.

6.How does Aetrix verify that STN851 is sourced from the original manufacturer or authorized distributors?

All STN851 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that STN851 meets industry standards.

7.What is the process for return or replacement of STN851?

All STN851 units undergo pre-shipment inspection (PSI). If there is an issue with STN851, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The STN851 part is unused and in its original packaging.

Return procedure for STN851:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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