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

STMicroelectronics BU941

Name: BU941
Brand: STMicroelectronics
SKU: BU941
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BU941

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-204AA, TO-3

Datasheet:: BU941.pdf

Description:: TRANS NPN DARL 400V 15A TO-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BU941 from STMicroelectronics is an NPN power Darlington transistor with integrated antiparallel collector-emitter diode, rated for 500 V V_CES, 15 A continuous collector current, and 200 °C maximum junction temperature in TO-3 package - designed for high-ruggedness electronic ignition coil driving in automotive and industrial combustion systems.

For engineers reviewing the BU941 datasheet, BU941 pinout, BU941 application, or BU941 equivalent, this device's high V_CEO(sus) (400 V), low V_CE(sat) (1.6–2.0 V at 8–12 A), integrated clamping diode, rugged bipolar construction, and 0.97 °C/W thermal resistance make it critical for inductive load switching where voltage transients and thermal stress dominate design constraints.

Technical Context

The BU941 implements a monolithic NPN Darlington pair with built-in antiparallel diode across C–E to suppress inductive kickback during coil de-energization. It operates with base-driven control (IB ≤ 1 A) and sustains 400 V under inductive switching (L = 7–10 mH) without external snubbers.

Its safe operating area supports DC and pulsed operation up to 30 A peak collector current, with storage time (t_s) ≤ 15 µs and fall time (t_f) ≤ 0.5 µs under specified test conditions - enabling reliable 100–500 Hz ignition timing in distributorless ignition systems (DIS).

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	500 V - Withstands full battery+load dump transients in 24 V automotive systems without breakdown.
I_C (continuous)	15 A - Sustains full primary coil current in high-energy ignition systems (e.g., >50 mJ per spark).
V_CE(sat)	1.6–2.0 V @ 8–12 A - Minimizes conduction loss and self-heating during dwell period.
T_j(max)	200 °C - Enables operation in engine bay environments without derating below 15 A at T_c = 100 °C.
R_thj-case	0.97 °C/W (TO-3) - Allows direct heatsink mounting with <1.5 K/W total thermal path for 180 W dissipation.
t_s/t_f	15 µs / 0.5 µs - Ensures precise spark timing control and fast turn-off for multi-cylinder sequential firing.
Integrated Diode	Antiparallel C–E - Eliminates need for external flyback diode; VF = 2.5 V @ 10 A reduces voltage overshoot.

Pinout & Package

BU941 is supplied in TO-3 metal-can package with isolated tab (collector), pin 1 (base), and pin 2 (emitter). The tab serves as the collector terminal and must be electrically isolated from heatsink unless system ground reference permits.

Pin/Terminal	Circuit Role	Design Meaning
Tab (Mounting Surface)	Collector	Main high-current output node; thermally coupled to heatsink; requires insulating washer if not referenced to system ground.
Pin 1	Base	Current-controlled input; requires 100–300 mA drive for full saturation; sensitive to ESD and transient coupling.
Pin 2	Emiter	Return path for load current; connects to ignition coil primary ground; forms common reference for base drive circuitry.

Key Features

Feature	Design Value
Integrated antiparallel diode	Eliminates discrete flyback diode, reducing BOM count and PCB footprint while ensuring consistent clamping behavior.
200 °C max junction temperature	Enables uninterrupted operation in under-hood environments exceeding 125 °C ambient without thermal shutdown or gain degradation.
0.97 °C/W thermal resistance	Supports 180 W continuous dissipation with standard finned heatsinks, avoiding forced-air or liquid cooling.
400 V sustaining voltage (V_CEO(sus))	Guarantees reliable turn-off under worst-case inductive flyback with L = 7 mH and V_Clamp = 400 V - validated per Figure 4 test circuit.
Low storage time (≤15 µs)	Permits accurate dwell control down to 1 ms intervals, essential for variable-speed DIS and cylinder-cut strategies.

Applications

Automotive Distributorless Ignition (DIS)

Industrial Gas Engine Ignition

Use Scenario: Sequential spark delivery in 4–8 cylinder gasoline engines using individual coil-on-plug (COP) or wasted-spark configurations.

IC Role / Device Role / Timing Role: High-side switch controlling primary current flow into ignition coil; triggered by microcontroller PWM or dedicated ignition driver IC.

Use Value: 500 V V_CES and 400 V V_CEO(sus) prevent failure during load dump; integrated diode ensures repeatable spark energy without external component drift.

Use Scenario: Ignition of large-bore natural gas or biogas engines used in power generation and compression stations.

IC Role / Device Role / Timing Role: Primary-side power switch in high-energy (>100 mJ) ignition modules requiring long dwell times and high thermal endurance.

Use Value: 200 °C T_j(max) and 15 A I_C support continuous operation at elevated ambient temperatures (≥110 °C) without derating.

Motorcycle CDI Systems

Marine Outboard Ignition Modules

Use Scenario: Capacitive discharge ignition in high-RPM two-stroke and four-stroke motorcycle engines.

IC Role / Device Role / Timing Role: Fast-switching Darlington stage discharging capacitor bank into ignition coil primary winding.

Use Value: 15 µs storage time enables precise timing at 12,000 RPM; integrated diode prevents reverse recovery oscillation during rapid recharging cycles.

Use Scenario: Saltwater-exposed outboard motor ignition systems requiring corrosion-resistant packaging and transient immunity.

IC Role / Device Role / Timing Role: Ruggedized primary switch in sealed ignition control units exposed to humidity, vibration, and 12/24 V battery fluctuations.

Use Value: TO-3 metal can provides mechanical robustness and EMI shielding; 0.97 °C/W R_thj-case maintains reliability despite limited heatsinking space.

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage Darlington ignition switch applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BU941Z	Same die, TO-218 package; R_thj-case = 0.97 °C/W but lower P_tot (155 W); identical electrical specs.	Suitable for space-constrained PCB-mount designs where TO-3 mounting is impractical.	Select BU941Z when mechanical integration favors surface-mount heatsink interface over stud-mount TO-3.
BUB941PFI	Same die, ISOWATT218 package; R_thj-case = 2.3 °C/W; T_j(max) = 175 °C; same V_CES/I_C.	Used in cost-sensitive consumer-grade ignition modules where thermal margin is relaxed.	Choose BUB941PFI only when ambient temperature remains ≤85 °C and heatsink capability exceeds 3.5 K/W.

Compared with BU941Z and BUB941PFI, the BU941 delivers superior thermal performance (0.97 °C/W, 200 °C T_j) and higher power handling (180 W), making it the only variant qualified for sustained high-dwell, high-RPM, and under-hood automotive use without thermal throttling.

Availability

BU941 is available at Aetrix Electronics and suitable for automotive ignition systems, industrial gas engine controls, marine outboard modules, and motorcycle CDI units requiring stable component supply across extended production lifecycles.

Supply support for BU941 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, Switzerland, designing and manufacturing analog, power, and microcontroller solutions for automotive, industrial, and consumer markets.

The BU941 belongs to ST's high-voltage power bipolar transistor family, engineered specifically for ruggedized inductive switching in harsh-environment ignition and actuation systems.

FAQ

What is the recommended base drive configuration for BU941 in ignition applications?

Use a current-limited base driver delivering 100–300 mA (depending on I_C) with series resistance selected to limit peak IB to ≤5 A. A 47 Ω resistor between driver and pin 1 is validated per Figure 3 test circuit. Avoid voltage-mode base drive without current limiting to prevent second breakdown.

Can BU941 replace BU941P in existing designs?

Yes - BU941 and BU941P share identical die, pinout, and absolute maximum ratings except for thermal resistance (both 0.97 °C/W) and T_j(max) (200 °C vs. 175 °C). BU941 offers extended thermal headroom and is backward compatible in all TO-3-based ignition modules.

Is the integrated diode rated for continuous conduction?

No - the antiparallel diode is optimized for transient clamping during coil turn-off, not steady-state conduction. Its 2.5 V forward drop at 10 A and lack of specified continuous IF rating indicate pulsed-only use; sustained forward current must be limited by external design.

What mechanical mounting torque is required for the TO-3 package?

Apply 0.8 Nm (recommended) to 1.0 Nm (maximum) torque to the mounting screw. Exceeding 1.0 Nm risks case deformation and internal bond wire damage. Mount on flat, clean heatsink surfaces with thermal compound and insulating washer if collector isolation is required.

BU941 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

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

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN - Darlington

Current - Collector (Ic) (Max):: 15 A

Voltage - Collector Emitter Breakdown (Max):: 400 V

Vce Saturation (Max) @ Ib, Ic:: 2V @ 300mA, 12A

Current - Collector Cutoff (Max):: 100µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 300 @ 5A, 10V

Power - Max:: 180 W

Frequency - Transition:: -

Operating Temperature:: 200°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Chassis Mount

Supplier Device Package:: TO-3

BU941 FAQ

1.How can I place an order for BU941 through Aetrix?

Please submit a Request for Quotation (RFQ) for BU941 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 BU941 reliable?

The price and inventory of BU941 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BU941 is usually 5 days.

3.What payment methods are accepted for BU941?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BU941 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BU941?

BU941 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BU941 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 BU941?

For technical support, including BU941 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BU941 requirements.

6.How does Aetrix verify that BU941 is sourced from the original manufacturer or authorized distributors?

All BU941 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 BU941 meets industry standards.

7.What is the process for return or replacement of BU941?

All BU941 units undergo pre-shipment inspection (PSI). If there is an issue with BU941, 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 BU941 part is unused and in its original packaging.

Return procedure for BU941:

1.Submit a request within 90 days.

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

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