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

STMicroelectronics 2ST2121

Name: 2ST2121
Brand: STMicroelectronics
SKU: 2ST2121
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: 2ST2121

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-204AA, TO-3

Datasheet:: 2ST2121.pdf

Description:: TRANS PNP 250V 17A TO-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

2ST2121 from STMicroelectronics is a high-power PNP epitaxial planar bipolar transistor designed for linear audio power amplification, featuring V_CEO = −250 V, I_C = −17 A, P_TOT = 250 W at T_c = 25 °C, f_T = 25 MHz, and R_thj-case = 0.7 °C/W - deployed in Class-AB output stages of high-fidelity audio amplifiers.

For engineers reviewing the 2ST2121 datasheet, 2ST2121 pinout, 2ST2121 application, or 2ST2121 equivalent, key selection criteria include safe operating area (SOA) at elevated case temperatures, gain linearity under large-signal swing, complementary pairing with 2ST5949, and thermal derating compliance up to T_J = 200 °C.

Technical Context

This PNP transistor employs ST's BiT-LA (Bipolar transistor for linear amplifier) process, optimized for low distortion and stable h_FE across collector current (35–160 at I_C = −1 A to −7 A), with verified DC gain linearity and pulsed breakdown robustness (V_(BR)CEO = −250 V, 300 µs pulse, ≤1.5% duty cycle).

It operates with fully characterized parameters at T_case = 125 °C, supporting high-reliability audio output stages where junction temperature stability, saturation voltage control (V_CE(sat) = −3 V at I_C = −8 A/I_B = −800 mA), and emitter-base ruggedness (V_EBO = −6 V) are critical.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	−250 V: Enables operation in high-voltage rail configurations (±100 V supply systems) without secondary breakdown risk.
I_C	−17 A continuous: Supports ≥150 W RMS audio output into 4 Ω loads with appropriate heatsinking.
P_TOT	250 W at T_c = 25 °C: Requires low-thermal-resistance mounting (e.g., TO-3 with thermal pad interface) for sustained power delivery.
f_T	25 MHz typical: Ensures adequate bandwidth for full-audio spectrum (20 Hz–20 kHz) with margin for slew-rate stability.
R_thj-case	0.7 °C/W max: Dictates minimum heatsink thermal resistance (e.g., ≤1.0 °C/W for T_J ≤ 150 °C at 150 W dissipation).
h_FE	35–160: Provides predictable biasing and feedback loop stability across output current range in linear amplifier topologies.

Pinout & Package

Supplied in TO-3 metal package with case-connected collector (standard configuration for high-power PNP devices); base and emitter leads isolated via insulated mounting hardware.

Pin/Terminal	Circuit Role	Design Meaning
Case / Tab	Collector (C)	Electrically connected to collector; must be electrically isolated from chassis unless circuit design requires common-collector topology.
Lead 1	Base (B)	Control terminal for forward-active biasing; requires current-limited drive (e.g., ±800 mA max for V_CE(sat) test condition).
Lead 2	Emitter (E)	Output reference node; carries full load current and defines emitter-follower or common-emitter return path.

Key Features

Feature	Design Value
BiT-LA process technology	Delivers measured gain linearity (h_FE variation <2.5× across I_C = −1 A to −7 A), reducing harmonic distortion in analog output stages.
High-temperature characterization	Full electrical specs validated at T_case = 125 °C, enabling reliable operation in enclosed amplifier cabinets without derating ambiguity.
Complementary pairing	Engineered as direct PNP counterpart to NPN 2ST5949 - matched V_(BR), h_FE spread, and SOA curves for push-pull symmetry.
ECOPACK® packaging	Lead-free second-level interconnect compliant with JEDEC JESD97; supports RoHS-compliant manufacturing without solderability compromise.

Applications

High-Fidelity Audio Amplifier

Professional PA Output Stage

Use Scenario: Dual-rail ±80 V Class-AB power amplifier delivering 200 W into 4 Ω load with THD <0.05% at 1 kHz.

IC Role / Device Role / Timing Role: PNP output transistor in complementary push-pull pair driving loudspeaker load.

Use Value: High V_CEO and SOA integrity prevent secondary breakdown during reactive load transients; low V_CE(sat) minimizes quiescent heating.

Use Scenario: 300 W RMS touring-grade mixer power amplifier with forced-air cooling and thermal foldback protection.

IC Role / Device Role / Timing Role: Primary PNP switching/linear element in high-current output bank.

Use Value: Verified 125 °C case operation enables compact heatsink design; 0.7 °C/W R_thj-case ensures predictable thermal margin under burst program material.

Studio Monitor Power Module

Instrument Amplifier Output

Use Scenario: Active near-field studio monitor requiring wide dynamic range, low noise floor, and DC-coupled output.

IC Role / Device Role / Timing Role: Linear output device in DC-coupled, capacitorless output stage.

Use Value: Stable h_FE and low ICBO (−5 µA) ensure minimal DC offset drift over temperature; BiT-LA linearity preserves transient fidelity.

Use Scenario: Guitar/bass amplifier output stage demanding high headroom, touch-sensitive response, and soft clipping behavior.

IC Role / Device Role / Timing Role: PNP emitter-follower driver in cathode-follower–like topology.

Use Value: Controlled V_BE (−1.5 V at I_C = −7 A) enables precise bias network design; rugged V_EBO (−6 V) withstands grid-leak transient coupling.

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage PNP linear amplifier applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
2SA1943	V_CEO = −230 V (20 V lower); h_FE min = 55 (vs. 35 for 2ST2121); R_thj-case = 0.85 °C/W	Suitable for ≤±90 V rails; slightly higher gain consistency but reduced SOA margin at extreme voltage swing.	Select when legacy board layout uses TO-3P footprint and thermal budget allows +0.15 °C/W penalty.
MJE15034	V_CEO = −200 V; f_T = 15 MHz; P_TOT = 200 W; not characterized above 100 °C	Limited to medium-power audio (<120 W); lacks 125 °C validation and BiT-LA linearity optimization.	Prefer only for cost-sensitive consumer designs where full 200 °C junction rating and THD-critical linearity are non-essential.

Compared with 2SA1943 and MJE15034, the 2ST2121 provides superior high-voltage ruggedness, verified high-temperature performance, and process-tuned gain linearity - making it the preferred choice for professional audio output stages demanding both reliability and signal fidelity.

Availability

2ST2121 is available at Aetrix Electronics and suitable for high-fidelity audio amplifiers, professional PA systems, and studio monitor power modules requiring stable component supply and long-term industrial availability.

Supply support for 2ST2121 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, and microcontroller solutions for industrial, automotive, and consumer markets.

The 2ST2121 belongs to ST's high-power bipolar transistor product line, developed specifically for linear audio and high-fidelity analog power applications where voltage headroom, thermal resilience, and gain linearity are system-critical.

FAQ

Is the 2ST2121 still in active production?

No - STMicroelectronics has marked the 2ST2121 as Obsolete (as confirmed in the November 2008 datasheet revision history and official product status documentation). Aetrix Electronics maintains limited legacy stock with full traceability and offers engineering support for last-time buy and obsolescence mitigation planning.

What is the correct mounting orientation and insulation requirement for the TO-3 case?

The TO-3 case is electrically connected to the collector. It must be mounted using an insulating washer and shoulder washer (e.g., mica or silicone pad) when attached to a grounded heatsink. Mounting torque must not exceed 0.5 N·m to avoid die fracture; flatness tolerance on heatsink surface is ≤0.05 mm.

Can the 2ST2121 be used in parallel configurations?

Yes - but only with emitter-ballasting resistors (typically 0.1–0.22 Ω, 2 W) per device to ensure current sharing. The BiT-LA process improves V_BE matching, yet thermal coupling differences require individual thermal monitoring and symmetrical PCB layout to prevent thermal runaway.

Does the 2ST2121 require a minimum base drive current to avoid saturation artifacts?

Yes - for linear operation, base current must remain within the active region: I_B should be maintained between 1/50 and 1/20 of I_C (e.g., −140 mA to −400 mA at I_C = −7 A). Exceeding this range risks deep saturation, increasing storage time and causing audible "thump" during turn-off in audio applications.

2ST2121 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-204AA, TO-3

Packaging:: Bag

Product Status:: Obsolete

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 17 A

Voltage - Collector Emitter Breakdown (Max):: 250 V

Vce Saturation (Max) @ Ib, Ic:: 3V @ 800mA, 8A

Current - Collector Cutoff (Max):: 5µA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 80 @ 1A, 5V

Power - Max:: 250 W

Frequency - Transition:: 25MHz

Operating Temperature:: 200°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-3

2ST2121 FAQ

1.How can I place an order for 2ST2121 through Aetrix?

Please submit a Request for Quotation (RFQ) for 2ST2121 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 2ST2121 reliable?

The price and inventory of 2ST2121 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 2ST2121 is usually 5 days.

3.What payment methods are accepted for 2ST2121?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 2ST2121 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 2ST2121?

2ST2121 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 2ST2121 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 2ST2121?

For technical support, including 2ST2121 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 2ST2121 requirements.

6.How does Aetrix verify that 2ST2121 is sourced from the original manufacturer or authorized distributors?

All 2ST2121 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 2ST2121 meets industry standards.

7.What is the process for return or replacement of 2ST2121?

All 2ST2121 units undergo pre-shipment inspection (PSI). If there is an issue with 2ST2121, 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 2ST2121 part is unused and in its original packaging.

Return procedure for 2ST2121:

1.Submit a request within 90 days.

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

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