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

STMicroelectronics STSA851-AP

Name: STSA851-AP
Brand: STMicroelectronics
SKU: STSA851-AP
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: STSA851-AP

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-226-3, TO-92-3 (TO-226AA) Formed Leads

Datasheet:: STSA851-AP.pdf

Description:: TRANS NPN 60V 5A TO-92AP

Quantity:: RFQ Add To RFQ list

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Product details

Overview

STSA851-AP from STMicroelectronics is a low-voltage, fast-switching NPN power transistor in TO-92AP package, featuring V_CEO = 60 V, I_C = 5 A, V_CE(sat) = 140 mV (IC = 2 A, IB = 50 mA), h_FE = 90 (IC = 5 A), and f_T = 130 MHz - optimized for high-efficiency relay drivers and emergency lighting circuits.

For engineers reviewing the STSA851-AP datasheet, STSA851-AP pinout, STSA851-AP application, or STSA851-AP equivalent, key selection criteria include saturation voltage at high current, DC current gain stability under 5 A load, thermal resistance (R_thj-amb = 114 °C/W), switching speed (t_on = 55 ns, t_f = 120 ns), and TO-92AP mechanical compatibility in space-constrained regulators.

Technical Context

This NPN planar transistor uses a "base island" layout to simultaneously achieve high h_FE (min. 90 at 5 A) and very low V_CE(sat) (140 mV typical at IC = 2 A). Its 130 MHz f_T supports fast digital switching, while the 114 °C/W junction-to-ambient thermal resistance enables operation up to T_J = 150 °C without forced cooling.

The device is rated for V_CBO = 150 V and V_EBO = 7 V, with pulsed I_CM = 20 A (t_P < 5 ms). Saturation behavior is characterized across three current levels (100 mA–5 A), confirming stable low-V_CE(sat) performance essential for low-loss voltage regulation and relay coil drive.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	60 V - maximum safe collector-emitter voltage with base open; defines upper limit for relay driver supply rails
I_C	5 A continuous - supports high-current loads like 24 V solenoids or LED banks without derating at 25 °C ambient
V_CE(sat)	140 mV @ IC = 2 A, IB = 50 mA - enables <0.3 W conduction loss, critical for thermally constrained emergency lighting PCBs
h_FE	90 @ IC = 5 A, V_CE = 1 V - ensures sufficient base drive margin for reliable saturation under full load
f_T	130 MHz - supports sub-100 ns switching transitions, suitable for PWM frequencies up to ~10 MHz
R_thj-amb	114 °C/W - allows 1.1 W dissipation at 25 °C ambient; requires minimal heatsinking in TO-92AP footprint
t_on/t_f	55 ns / 120 ns - enables clean edge control in resistive-load switching applications with minimal overlap loss

Pinout & Package

STSA851-AP is housed in TO-92AP package - a lead-free, ECOPACK®-compliant variant of TO-92 with standardized lead pitch (2.54 mm), body height (4.95 mm max), and ammopack tape-and-reel shipping format (suffix "-AP").

Pin/Terminal	Circuit Role	Design Meaning
Emitter (E)	Current sink terminal	Connected to ground or low-side return path; lowest impedance path for 5 A load current
Base (B)	Control input	Receives 50–200 mA drive to saturate transistor; requires current-limiting resistor per h_FE and V_BE(sat) = 1.15 V
Collector (C)	High-current output	Switches up to 60 V/5 A loads; mounted on PCB copper pour for thermal relief due to R_thj-amb = 114 °C/W

Key Features

Feature	Design Value
Very low V_CE(sat)	140 mV at 2 A enables <0.3 W conduction loss - reduces thermal stress in compact voltage regulators
High h_FE at high current	90 at 5 A ensures robust saturation with modest base drive - simplifies driver circuit design for relay coils
Fast switching (t_on/t_f)	55 ns / 120 ns minimizes transition losses in PWM-controlled low-voltage supplies
ECOPACK® compliance	Lead-free second-level interconnect meets JEDEC JESD97 - supports RoHS-compliant industrial assembly

Applications

Emergency Lighting Control

Voltage Regulator Pass Element

Use Scenario: Standby battery-powered LED arrays activated during AC mains failure.

IC Role / Device Role / Timing Role: NPN switch controlling current path from battery to LED string; operates in saturation during active mode.

Use Value: Low 140 mV V_CE(sat) preserves battery runtime by minimizing dropout loss at 3–5 A load currents.

Use Scenario: Linear post-regulation stage delivering stable 5 V/3 A from unregulated 12 V rail.

IC Role / Device Role / Timing Role: Series pass transistor dissipating excess voltage; biased via error amplifier feedback loop.

Use Value: High h_FE (90 at 5 A) reduces base drive burden and improves regulation accuracy under dynamic load steps.

Relay Driver Circuit

Low-Voltage Switching Power Stage

Use Scenario: Microcontroller GPIO driving 24 V/1 A electromechanical relay coil.

IC Role / Device Role / Timing Role: Digital switch amplifying logic-level signal to full coil current; operates in cutoff/saturation states.

Use Value: Fast 55 ns turn-on ensures precise timing control for safety-critical relay sequencing in industrial PLCs.

Use Scenario: High-efficiency 5–12 V DC-DC converter primary-side switch in non-isolated buck topology.

IC Role / Device Role / Timing Role: Synchronous rectifier or low-side switch handling repetitive 10–100 kHz switching cycles.

Use Value: 130 MHz f_T and low 45 pF C_CBO support clean gate drive coupling and minimal switching delay skew.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BCP56-10T1G	V_CEO = 80 V, I_C = 1 A, h_FE = 100–250 @ 100 mA - lower current rating, higher gain at low current	Not suitable for 5 A loads; limited to <1 A relay coils or signal switching	Select only when base drive is extremely limited and load current ≤ 1 A
MJD127G	V_CEO = 100 V, I_C = 3 A, TO-220 package - higher voltage, lower current, larger footprint	Requires heatsink for >1.5 A; incompatible with TO-92AP board space constraints	Choose for higher-voltage (≥80 V) applications where thermal mass outweighs size penalty

Compared with BCP56-10T1G and MJD127G, STSA851-AP uniquely balances 5 A capability, 60 V rating, and TO-92AP form factor - making it irreplaceable for space-limited, high-current, low-voltage switching where both conduction loss and thermal resistance are design-critical.

Availability

STSA851-AP is available at Aetrix Electronics and suitable for emergency lighting systems, voltage regulators, and relay driver circuits requiring stable component supply and legacy-compatible through-hole packaging.

Supply support for STSA851-AP 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, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The STSA851 belongs to ST's legacy bipolar power transistor product line, engineered specifically for high-gain, low-saturation-voltage switching in cost-sensitive, thermally constrained linear and digital power stages.

FAQ

Is STSA851-AP still in active production?

No - STSA851-AP is marked as Obsolete Product(s) in ST's official documentation (Rev 3, March 2008). Aetrix Electronics maintains limited legacy stock with full traceability and offers engineering support for last-time buy and redesign assistance.

What is the maximum allowable base current for STSA851-AP?

The absolute maximum base current is 1 A (per Table 2). For reliable 5 A collector operation, IB = 200 mA is specified in electrical characteristics - exceeding this risks thermal runaway or bond-wire failure without active current limiting.

Can STSA851-AP replace BC337 in high-current applications?

No - BC337 is rated for 0.5 A continuous collector current and 45 V V_CEO. STSA851-AP delivers 10× higher current and 33% higher voltage rating; substituting it into BC337 designs requires verifying PCB copper area, base drive capability, and thermal relief for 1.1 W dissipation.

Does STSA851-AP require a heatsink in TO-92AP package?

At 25 °C ambient and 1.1 W dissipation, junction temperature reaches ~165 °C (exceeding 150 °C max) without heatsinking. A minimum 2 cm² 1-oz copper pour is recommended; for sustained 5 A operation above 40 °C ambient, external heatsinking or derating below 3 A is required.

STSA851-AP Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-226-3, TO-92-3 (TO-226AA) Formed Leads

Packaging:: Tape & Box (TB)

Product Status:: Obsolete

Transistor Type:: NPN

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

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

Vce Saturation (Max) @ Ib, Ic:: 450mV @ 200mA, 5A

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

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

Power - Max:: 1.1 W

Frequency - Transition:: 130MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92AP

STSA851-AP FAQ

1.How can I place an order for STSA851-AP through Aetrix?

Please submit a Request for Quotation (RFQ) for STSA851-AP 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 STSA851-AP reliable?

The price and inventory of STSA851-AP are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for STSA851-AP is usually 5 days.

3.What payment methods are accepted for STSA851-AP?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for STSA851-AP transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for STSA851-AP?

STSA851-AP orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your STSA851-AP 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 STSA851-AP?

For technical support, including STSA851-AP datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your STSA851-AP requirements.

6.How does Aetrix verify that STSA851-AP is sourced from the original manufacturer or authorized distributors?

All STSA851-AP 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 STSA851-AP meets industry standards.

7.What is the process for return or replacement of STSA851-AP?

All STSA851-AP units undergo pre-shipment inspection (PSI). If there is an issue with STSA851-AP, 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 STSA851-AP part is unused and in its original packaging.

Return procedure for STSA851-AP:

1.Submit a request within 90 days.

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

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