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

STMicroelectronics BU941ZPFI

Name: BU941ZPFI
Brand: STMicroelectronics
SKU: BU941ZPFI
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BU941ZPFI

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-3PF

Datasheet:: BU941ZPFI.pdf

Description:: TRANS NPN DARL 350V 15A TO-3PF

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BU941ZPFI from STMicroelectronics is a high-voltage NPN power Darlington transistor with integrated clamping Zener diode, designed as an ignition coil driver for automotive electronic ignition systems. It features 350 V V_CEO, 15 A continuous collector current, 65 W total dissipation at T_c = 25 °C, 2500 V RMS insulation withstand voltage, and 175 °C maximum operating junction temperature in a fully insulated TO-3 package.

For engineers reviewing the BU941ZPFI datasheet, BU941ZPFI pinout, BU941ZPFI application, or BU941ZPFI equivalent, key selection criteria include clamped inductive switching capability, U.L.-compliant insulation for direct heatsink mounting, ruggedness under repetitive avalanche stress, and thermal performance in engine bay environments.

Technical Context

This device implements a monolithic Darlington pair with built-in Zener clamp across C–E to suppress inductive kickback during coil de-energization. Its Multiepitaxial Planar bipolar process ensures stable gain (h_FE ≥ 300 at I_C = 5 A) and robust safe operating area (SOA) up to 300 µs pulse width.

The TO-3 package provides direct metal tab conduction path for collector, with pin 1 (base), pin 2 (emitter), and collector connected to the insulated metal tab - enabling high-voltage isolation while maintaining low R_thj-case of 0.97 °C/W for thermal management in compact ignition modules.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	350 V - Withstands ignition coil back-EMF without external snubber
I_C (cont.)	15 A - Supports peak primary coil currents in 4–8 cylinder engines
V_CL	350–500 V - Integrated Zener clamps inductive transients to protect downstream circuitry
R_thj-case	0.97 °C/W - Enables efficient heat transfer to heatsink in confined engine compartments
V_CE(sat)	1.8–2.0 V @ I_C = 8–12 A - Minimizes conduction loss and self-heating during dwell period
Visol	2500 V RMS - U.L.-compliant insulation allows direct mounting to chassis/heatsink without insulating washers
T_j(max)	175 °C - Rated for sustained operation near hot engine blocks and exhaust manifolds

Pinout & Package

BU941ZPFI uses a fully insulated TO-3 package (U.L. compliant), with collector connected to the metal tab and electrically isolated from mounting surface. Pin 1 = Base, Pin 2 = Emitter, Pin 3 = Collector tab (isolated).

Pin/Terminal	Circuit Role	Design Meaning
Pin 1	Base	Current-controlled input node requiring ~100–300 mA drive for full saturation
Pin 2	Emitter	Common emitter reference; tied to ground or low-side return path in ignition module
Collector Tab	Collector	Main power output node; electrically isolated from heatsink but thermally coupled via insulated interface

Key Features

Feature	Design Value
Integrated clamping Zener	Enables self-protected inductive switching without external TVS or RC snubbers
U.L.-compliant insulation	Eliminates need for mica washers or silicone pads during mechanical mounting
200 °C storage rating	Supports reflow/reflow-soldering compatibility and long-term under-hood reliability
Rugged SOA (300 µs)	Withstands repeated inductive turn-off stress in high-RPM engine operation
h_FE ≥ 300 @ 5 A	Reduces base drive circuit complexity and power loss in discrete driver stages

Applications

Automotive Electronic Ignition

Industrial Coil Drivers

Use Scenario: Driving primary winding of distributorless ignition system (DIS) coils in gasoline engines.

IC Role / Device Role / Timing Role: High-current, high-voltage switch controlling dwell time and spark timing via microcontroller PWM signal.

Use Value: Integrated Zener clamping eliminates external protection components, reducing BOM count and PCB space in compact ECU modules.

Use Scenario: Controlling solenoid valves and magnetic actuators in oil/gas wellhead control panels.

IC Role / Device Role / Timing Role: Robust power switch handling 350 V inductive loads with fast turn-off and thermal stability at ambient >85 °C.

Use Value: 175 °C T_j(max) and 0.97 °C/W R_thj-case enable reliable operation without forced air cooling in sealed enclosures.

Motorcycle Ignition Modules

Aftermarket Ignition Upgrades

Use Scenario: Compact, fanless ignition units for dual-spark V-twin motorcycles with limited airflow.

IC Role / Device Role / Timing Role: Primary-side switch in CDI (capacitive discharge ignition) circuits with precise timing control.

Use Value: Fully insulated TO-3 package allows direct bolt-on mounting to aluminum frame, simplifying thermal design and EMI shielding.

Use Scenario: High-energy ignition retrofit kits for classic car restorations using modern coil packs.

IC Role / Device Role / Timing Role: Replacement for obsolete discrete drivers in aftermarket ECU interfaces.

Use Value: Pin-compatible upgrade path from BU941Z/BU941ZP with identical footprint and improved thermal derating margin.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BU941Z	Same die, non-insulated TO-3 package; R_thj-case = 0.97 °C/W but no Visol rating	Requires insulating hardware for heatsink mounting; unsuitable where U.L. compliance is mandated	Select BU941Z only when mechanical isolation is handled externally and cost is prioritized
STGD10NB60KD	600 V, 10 A N-channel MOSFET with built-in gate driver; no internal Zener clamp	Higher switching speed but requires external clamping and gate drive optimization	Choose for new designs needing faster switching; avoid in legacy replacements requiring drop-in bipolar behavior

Compared with BU941Z, BU941ZPFI adds certified insulation and retains identical electrical specs; versus STGD10NB60KD, it offers simpler drive requirements and inherent transient protection but lower switching speed - making it optimal for cost-sensitive, thermally constrained ignition modules where reliability trumps frequency.

Availability

BU941ZPFI is available at Aetrix Electronics and suitable for automotive electronic ignition systems, industrial solenoid drivers, and motorcycle CDI modules requiring stable component supply and long-lifecycle support.

Supply support for BU941ZPFI 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, specializing in automotive, industrial, and power discrete technologies.

BU941ZPFI belongs to ST's high-voltage bipolar power transistor family, engineered specifically for rugged, high-temperature ignition actuation in harsh automotive environments.

FAQ

What is the function of the built-in Zener diode in BU941ZPFI?

The integrated Zener diode clamps collector-emitter voltage during inductive turn-off, limiting V_CE to 350–500 V. This protects the transistor from destructive voltage spikes generated by ignition coils, eliminating the need for external snubber networks and improving system reliability in repetitive switching applications.

Can BU941ZPFI be mounted directly to a metal heatsink without insulation hardware?

Yes - BU941ZPFI's TO-3 package is fully insulated per U.L. standards, with 2500 V RMS isolation between all three leads and the external heatsink. This allows direct bolt-on mounting without mica washers or silicone pads, simplifying mechanical assembly and enhancing thermal contact integrity.

How does BU941ZPFI differ from BU941ZP in thermal performance?

BU941ZPFI shares the same 0.97 °C/W R_thj-case as BU941Z but differs from BU941ZP (155 W P_tot, R_thj-case = 0.97 °C/W) in its insulation rating and packaging certification. All three share identical silicon die and electrical characteristics; only mechanical isolation and safety compliance differ.

Is BU941ZPFI suitable for use in 48 V automotive architectures?

Yes - BU941ZPFI's 350 V V_CEO and 175 °C T_j(max) make it compatible with 48 V mild-hybrid systems where ignition coils operate at elevated bus voltages and ambient temperatures. Its rugged SOA and clamping Zener ensure reliable operation under load dump and cranking conditions.

BU941ZPFI Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-3PF

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN - Darlington

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

Voltage - Collector Emitter Breakdown (Max):: 350 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:: 65 W

Frequency - Transition:: -

Operating Temperature:: 175°C (TJ)

Grade:: Automotive

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-3PF

BU941ZPFI FAQ

1.How can I place an order for BU941ZPFI through Aetrix?

Please submit a Request for Quotation (RFQ) for BU941ZPFI 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 BU941ZPFI reliable?

The price and inventory of BU941ZPFI are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BU941ZPFI is usually 5 days.

3.What payment methods are accepted for BU941ZPFI?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BU941ZPFI transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BU941ZPFI?

BU941ZPFI orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BU941ZPFI 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 BU941ZPFI?

For technical support, including BU941ZPFI datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BU941ZPFI requirements.

6.How does Aetrix verify that BU941ZPFI is sourced from the original manufacturer or authorized distributors?

All BU941ZPFI 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 BU941ZPFI meets industry standards.

7.What is the process for return or replacement of BU941ZPFI?

All BU941ZPFI units undergo pre-shipment inspection (PSI). If there is an issue with BU941ZPFI, 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 BU941ZPFI part is unused and in its original packaging.

Return procedure for BU941ZPFI:

1.Submit a request within 90 days.

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

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