Send an Inquiry

To receive a quote for your project, please fill in the following information, and we’ll get back to you promptly.

Submit Inventory List

Please fill in the following information, and we’ll get back to you promptly.

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

STMicroelectronics BU931T

Name: BU931T
Brand: STMicroelectronics
SKU: BU931T
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

Compare

Part No.:: BU931T

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BU931T.pdf

Description:: TRANS NPN DARL 400V 10A TO-220

Quantity:: RFQ Add To RFQ list

Payment:

Shipping:

Inventory:7,887

Please send an inquiry. Send us your inquiry, and we will respond immediately.

Product details

Overview

BU931T from STMicroelectronics is an AEC-Q101-qualified NPN power Darlington transistor designed as a high-voltage ignition coil driver for automotive electronic ignition systems. It features 500 V V_CES, 10 A continuous collector current, 125 W total dissipation at T_C = 25 °C, and operates up to 175 °C junction temperature in TO-220 package.

For engineers reviewing the BU931T datasheet, BU931T pinout, BU931T application, or BU931T equivalent, key selection criteria include V_CEO(sus) = 400 V under inductive switching, V_CE(sat) ≤ 1.8 V at 10 A/250 mA drive, ruggedness against repetitive avalanche stress, and thermal resistance R_thJC = 1.2 °C/W for high-power ignition coil actuation.

Technical Context

The BU931T integrates a monolithic Darlington pair with integrated antiparallel freewheeling diode (V_F = 2.5 V at 10 A), enabling direct inductive load switching without external flyback protection. Its multi-epitaxial planar bipolar process ensures stable h_FE ≥ 300 at 5 A/10 V and supports sustained operation at T_j = 175 °C.

Designed for automotive ignition coil drivers, it delivers controlled turn-off via base-emitter resistor (R_BE = 47 Ω typical), achieves t_s ≤ 15 μs storage time and t_f ≤ 0.5 μs fall time under 7 mH inductive load, and sustains V_CE(sus) = 400 V at I_C = 100 mA with zero base current.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	500 V - Withstands transient overvoltage during coil energy collapse without breakdown
I_C (continuous)	10 A - Supports standard 12 V automotive ignition coils drawing up to 10 A peak primary current
V_CE(sat)	1.8 V max at 10 A/250 mA - Limits conduction loss to ≤18 W during on-state, critical for thermal management
R_thJC	1.2 °C/W - Enables efficient heat transfer to heatsink; allows >100 W safe operating area at T_C = 100 °C
t_s + t_f	≤15.5 μs total - Ensures fast current decay for precise spark timing control in distributorless ignition systems
T_j max	175 °C - Certified for under-hood environments including engine bay mounting near exhaust manifolds
AEC-Q101	Qualified - Validated for automotive-grade reliability including temperature cycling, HTRB, and ESD testing

Pinout & Package

BU931T uses TO-220 type A package with isolated tab (collector-connected). The case is electrically connected to the collector terminal, requiring insulating mounting hardware when mounted to grounded heatsinks.

Pin/Terminal	Circuit Role	Design Meaning
Collector (Tab)	Main power output node	Electrically tied to metal tab; must be insulated from chassis ground unless system design permits common-collector reference
Base	Current-controlled input	Receives 70–250 mA drive to saturate transistor; requires external base resistor for current limiting and turn-off speed control
Emitter	Power return path	Connected to low-side ground of ignition coil; carries full load current and must be routed with low-inductance layout

Key Features

Feature	Design Value
Integrated freewheeling diode	V_F = 2.5 V @ 10 A - Eliminates need for external flyback diode, reducing BOM count and PCB footprint
High V_CEO(sus)	400 V @ I_C = 100 mA - Sustains clamp voltage during inductive kickback without external TVS, simplifying protection design
Rugged bipolar process	Rated for repetitive avalanche energy - Withstands repeated coil energy dump events without parameter drift or failure
Low R_thJC	1.2 °C/W - Permits direct mounting to compact heatsinks while maintaining T_j < 150 °C at 10 A continuous
TO-220 isolation	Isolated tab construction - Allows mechanical mounting to conductive heatsinks without shorting collector to ground

Applications

Gasoline Engine Ignition System

Distributorless Ignition (DIS)

Use Scenario: Driving primary winding of ignition coil in 4-cylinder gasoline engine with sequential spark timing.

IC Role / Device Role / Timing Role: High-voltage power switch controlling coil energization/de-energization; defines spark dwell and timing precision.

Use Value: V_CE(sat) ≤ 1.8 V minimizes resistive heating during 3–5 ms dwell period; t_s ≤ 15 μs enables sub-degree crank-angle resolution.

Use Scenario: Paired with microcontroller-based ignition controller in coil-on-plug (COP) architecture for V6/V8 engines.

IC Role / Device Role / Timing Role: Final-stage actuator converting logic-level PWM into high-current coil drive; handles bidirectional current reversal during coil discharge.

Use Value: Integrated diode and 400 V V_CEO(sus) eliminate external clamping components, reducing system cost by $0.35–$0.50 per channel.

Two-Stroke Marine Engine Control

Heavy-Duty Diesel Preheat Control

Use Scenario: Controlling high-energy ignition pulses in high-RPM marine outboard engines exposed to saltwater and vibration.

IC Role / Device Role / Timing Role: Ruggedized power switch managing rapid coil charge/discharge cycles at up to 12,000 RPM.

Use Value: AEC-Q101 qualification and 175 °C T_j rating ensure reliable operation in sealed, non-ventilated engine compartments.

Use Scenario: Switching glow plug heaters in commercial diesel engines during cold-start conditions (-40 °C ambient).

IC Role / Device Role / Timing Role: High-current DC switch delivering 10 A pulses to ceramic glow plugs for 5–15 s preheat duration.

Use Value: 125 W P_TOT and low V_CE(sat) enable full-power heater activation without thermal derating below -30 °C.

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
STBU931Z	Same die, TO-247 package; R_thJC = 0.8 °C/W; higher creepage/clearance	Better thermal performance for high-duty-cycle or forced-air-cooled systems	Select when heatsink space allows larger TO-247 and >150 W dissipation is required
ON Semiconductor MJD127G	400 V V_CEO, 8 A I_C, no integrated diode, R_thJC = 2.5 °C/W	Requires external flyback diode and tighter thermal design; lower cost but higher system complexity	Select only if board space permits external diode and thermal margin exceeds 25 °C

Compared with BU931Z, BU931T trades 0.4 °C/W higher thermal resistance for TO-220's lower profile and tube packaging; versus MJD127G, it delivers integrated protection and 25% higher current rating at identical voltage class, reducing bill-of-materials and layout risk.

Availability

BU931T is available at Aetrix Electronics and suitable for gasoline engine ignition systems, distributorless ignition modules, two-stroke marine engine controls, and heavy-duty diesel preheat controllers requiring stable component supply across automotive production lifecycles.

Supply support for BU931T 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, MCU, and automotive-grade components since 1987.

The BU931T belongs to ST's automotive power discrete portfolio, engineered specifically for high-reliability, high-voltage switching in engine management systems where robustness against load dump, reverse battery, and thermal cycling is mandatory.

FAQ

What is the maximum recommended gate/base drive current for BU931T?

The BU931T base terminal is rated for 1 A continuous and 5 A peak current. For reliable saturation at 10 A collector current, ST specifies 250 mA base drive. Exceeding 1 A continuous risks bond wire failure; pulsed drive above 5 A must remain below 2% duty cycle and 300 μs pulse width per datasheet Table 2.

Can BU931T be used without a heatsink in low-duty-cycle ignition applications?

No. Even at 10% duty cycle, R_thJA = 62.5 °C/W causes excessive junction temperature rise. At 10 A and 1.8 V V_CE(sat), power dissipation is 18 W; without a heatsink, T_j would exceed 175 °C within milliseconds. A minimum 10 cm² aluminum heatsink with thermal interface material is required for any continuous or repetitive operation.

Does BU931T require an external flyback diode when driving ignition coils?

No. The BU931T integrates a monolithic antiparallel freewheeling diode rated at 10 A forward current and 2.5 V forward voltage. This eliminates the need for external diodes in standard ignition coil configurations, provided V_clamp remains ≤ 400 V during energy recirculation, as verified in functional test circuit Figure 10.

How does BU931T handle load dump transients in automotive 12 V systems?

The BU931T withstands load dump transients (ISO 16750-2, 12 V system: 35 V/400 ms) inherently due to its 500 V V_CES rating and AEC-Q101 qualification. Its bipolar structure exhibits superior ruggedness versus MOSFETs under repetitive avalanche conditions, and the integrated diode provides controlled energy dissipation path during coil collapse, preventing secondary breakdown.

BU931T Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-220-3

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN - Darlington

Current - Collector (Ic) (Max):: 10 A

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

Vce Saturation (Max) @ Ib, Ic:: 1.8V @ 250mA, 10A

Current - Collector Cutoff (Max):: 100µA

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

Power - Max:: 125 W

Frequency - Transition:: -

Operating Temperature:: 175°C (TJ)

Grade:: Automotive

Qualification:: AEC-Q101

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

BU931T FAQ

1.How can I place an order for BU931T through Aetrix?

Please submit a Request for Quotation (RFQ) for BU931T 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 BU931T reliable?

The price and inventory of BU931T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BU931T is usually 5 days.

3.What payment methods are accepted for BU931T?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BU931T transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BU931T?

BU931T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BU931T 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 BU931T?

For technical support, including BU931T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BU931T requirements.

6.How does Aetrix verify that BU931T is sourced from the original manufacturer or authorized distributors?

All BU931T 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 BU931T meets industry standards.

7.What is the process for return or replacement of BU931T?

All BU931T units undergo pre-shipment inspection (PSI). If there is an issue with BU931T, 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 BU931T part is unused and in its original packaging.

Return procedure for BU931T:

1.Submit a request within 90 days.

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

Tech Hub

2026-09-08 Obsolete Electronic Components: How to Source and Evaluate Replacements

A practical engineering and sourcing framework covering lifecycle verification, lifetime-buy calculations, replacement qualification, supplier checks and counterfeit-risk controls.

2026-09-07 TTL vs CMOS Logic Levels: 74HC and 74HCT Compatibility Explained

TTL and CMOS logic families differ in thresholds, loading, output drive, power and timing. This engineering guide compares 74HC and 74HCT, calculates noise margins and checks 3.3 V/5 V compatibility.

2026-09-04 Logic Level Shifter: How to Connect 3.3V and 5V Logic Safely

A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.

2026-09-03 74HC595 vs TPIC6B595: Output Drive, Pinout, Current, and Load Selection

The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…

2026-09-02 74HC595 Pinout, Timing, Output Current, and Applications

The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…

2026-09-01 Latch vs Flip-Flop: Timing, Differences and Design Choices

A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…

2026-08-30 D Latch Circuit: Truth Table, Timing, ICs and Applications

A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …

2026-08-28 SR Latch Explained: NOR and NAND Circuits, Truth Tables, and Applications

An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…

2026-08-27 Latch Circuit: SR and D Latches, Truth Tables, Timing, and Applications

Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…

2026-08-21 What Is an LED Driver? Types, Circuits, Dimming, and Selection

An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…