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

STMicroelectronics BUX48

Name: BUX48
Brand: STMicroelectronics
SKU: BUX48
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUX48

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-204AA, TO-3

Datasheet:: BUX48.pdf

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

Quantity:: RFQ Add To RFQ list

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Inventory:8,130

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Product details

Overview

BUX48 from STMicroelectronics is a high-voltage, high-current NPN silicon power transistor in TO-3 metal package, rated for V_CEO = 400 V, I_C = 15 A, and P_tot = 175 W at T_c = 25 °C. It delivers fast switching (t_s = 3 µs, t_f = 0.8 µs under resistive load) and is engineered for single-transistor flyback and forward converters in industrial SMPS.

For engineers reviewing the BUX48 datasheet, BUX48 pinout, BUX48 application, or BUX48 equivalent, key selection criteria include its 400 V V_CEO, 15 A continuous collector current, 175 W thermal dissipation capability, TO-3 mechanical robustness, and verified inductive switching performance at 300 V with 3 µH load.

Technical Context

The BUX48 employs a multiepitaxial mesa structure to achieve high breakdown voltage and low saturation voltage simultaneously. Its base-emitter and collector-emitter junctions are optimized for rugged industrial switching, supporting pulsed operation up to 55 A I_CP with 300 µs pulse width and ≤2% duty cycle.

Designed for mains-connected topologies, it operates reliably across -65 °C to 200 °C junction temperature range and features R_thj-case = 1 °C/W - enabling direct heatsink mounting without isolation washers in TO-3 configuration.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	400 V - Sustains 400 V collector-emitter voltage with zero base current; suitable for 230 VAC-derived DC bus applications.
I_C	15 A continuous - Supports high-power output stages in offline SMPS without parallel devices.
P_tot	175 W at T_c = 25 °C - Enables high-efficiency thermal management using standard TO-3 heatsinks.
V_CE(sat)	1.5 V @ I_C = 10 A, I_B = 2 A - Minimizes conduction loss in hard-switched topologies.
t_s / t_f	3 µs / 0.8 µs (resistive) - Enables switching frequencies up to ~100 kHz in flyback designs with controlled turn-off loss.
R_thj-case	1 °C/W - Allows precise junction temperature estimation from case temperature measurement in thermal design.

Pinout & Package

Package: TO-3 metal case - hermetically sealed, electrically isolated collector tab, screw-mount compatible, 175 W dissipation rating at 25 °C case temperature.

Pin/Terminal	Circuit Role	Design Meaning
Collector (Tab)	Main current path output terminal	Electrically connected to metal case; must be insulated from heatsink unless circuit ground reference permits.
Base (Lead 1)	Control input for transistor biasing	Receives drive current (up to 4 A continuous); requires external base resistor or driver stage for safe switching.
Emitter (Lead 2)	Current return path and reference node	Serves as common emitter node; low-inductance layout critical for minimizing switching oscillation in high-dI/dt applications.

Key Features

Feature	Design Value
Multiepitaxial mesa structure	Enables simultaneous high V_CEO (400 V) and low V_CE(sat) (1.5 V), reducing trade-off between breakdown margin and conduction loss.
TO-3 metal package	Provides superior thermal conductivity (R_thj-case = 1 °C/W) and mechanical stability for high-reliability industrial environments.
Inductive switching validation	Specified storage/fall times (t_s = 5 µs, t_f = 0.4 µs) at V_CC = 300 V, L_B = 3 µH - directly applicable to real-world flyback transformer switching.
High junction temperature rating	200 °C max operating junction temperature - supports operation in enclosed, high-ambient industrial enclosures without derating.

Applications

Switch-Mode Power Supply

Flyback Converter

Use Scenario: 100–200 W offline AC/DC adapter for industrial control systems.

IC Role / Device Role / Timing Role: Main switching transistor in single-transistor flyback topology, driven by UC3842-class controller.

Use Value: 400 V V_CEO provides 2× safety margin over 375 V DC bus; 15 A I_C enables single-device solution without paralleling.

Use Scenario: Isolated auxiliary power supply in PLC backplane modules.

IC Role / Device Role / Timing Role: Primary-side switch handling 65 kHz switching with 300 V clamp voltage during reset.

Use Value: Verified 5 µs storage time at 300 V/10 A ensures predictable turn-off behavior and reduces snubber losses.

Forward Converter

Industrial Motor Drive Snubber

Use Scenario: 150 W regulated DC output for servo amplifier logic supply.

IC Role / Device Role / Timing Role: Single-transistor forward converter switch with synchronous rectification on secondary side.

Use Value: 175 W P_tot and 1 °C/W thermal resistance allow stable operation at full load with passive heatsinking.

Use Scenario: Clamping switch in IGBT gate-drive protection circuits for 3-phase inverters.

IC Role / Device Role / Timing Role: Fast-turn-off crowbar device triggered during overvoltage transients.

Use Value: 0.8 µs fall time ensures sub-microsecond response to dV/dt events, limiting voltage overshoot on sensitive gate drivers.

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage NPN switching transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BUV48A	Same die, TO-218 plastic package; lower P_tot (125 W), higher R_thj-case (1 °C/W → 1.2 °C/W), V_CEO = 450 V.	Preferred where plastic packaging, lighter weight, or lower cost outweighs thermal performance needs.	Select when board-level space constraints preclude TO-3 mounting but 450 V margin is required.
BUV48AFI	ISOWATT218 fully isolated package; P_tot = 55 W, R_thj-case = 2.2 °C/W, V_CEO = 450 V, electrically isolated collector.	Used where collector-to-heatsink isolation is mandatory (e.g., floating bus architectures).	Choose only when galvanic isolation of collector terminal is required - not a thermal or electrical drop-in replacement.

Compared with BUX48, BUV48A trades 30 W dissipation and TO-3 ruggedness for plastic-package cost and weight savings, while BUV48AFI sacrifices >68% power handling to provide collector isolation - making BUX48 the sole choice for high-power, non-isolated, thermally demanding SMPS.

Availability

BUX48 is available at Aetrix Electronics and suitable for switch-mode power supplies, flyback converters, forward converters, and industrial motor drive snubbers requiring stable component supply and long-term manufacturability.

Supply support for BUX48 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, digital, and mixed-signal ICs and discrete power devices.

The BUX48 belongs to ST's high-voltage bipolar power transistor family, developed specifically for ruggedized industrial switching applications including offline SMPS, UPS, and welding equipment.

FAQ

Is BUX48 RoHS compliant?

Yes, BUX48 is RoHS compliant per STMicroelectronics' official product change notification PCN-2006-012. It contains no lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB), or polybrominated diphenyl ethers (PBDE), and meets EU Directive 2011/65/EU requirements.

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

The absolute maximum base peak current (I_BM) is 20 A, but ST recommends limiting continuous base current to ≤4 A and pulsed base drive to ≤10 A with <2% duty cycle. Exceeding these values risks bond wire failure or second breakdown during high-voltage transitions.

Can BUX48 replace BU2508DX in a 120 W flyback design?

No - BU2508DX has V_CEO = 800 V and is designed for higher-input-voltage applications. BUX48's 400 V V_CEO is insufficient for 375 V DC bus with safety margin; use BUX48A (450 V) or BUV48AFI only if isolation is needed, but neither matches BU2508DX's voltage rating.

Does BUX48 require a heatsink in continuous 10 A operation?

Yes - at I_C = 10 A and V_CE(sat) ≈ 1.5 V, conduction loss is ~15 W. With R_thj-case = 1 °C/W and ambient ≤50 °C, junction temperature exceeds 150 °C without heatsinking. A minimum 1.5 K/W heatsink is required to maintain T_j ≤ 125 °C under continuous load.

BUX48 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

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

Packaging:: Bag

Product Status:: Obsolete

Transistor Type:: NPN

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

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

Vce Saturation (Max) @ Ib, Ic:: 5V @ 3A, 15A

Current - Collector Cutoff (Max):: 200µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: -

Power - Max:: 175 W

Frequency - Transition:: -

Operating Temperature:: 200°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Chassis Mount

Supplier Device Package:: TO-3

BUX48 FAQ

1.How can I place an order for BUX48 through Aetrix?

Please submit a Request for Quotation (RFQ) for BUX48 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 BUX48 reliable?

The price and inventory of BUX48 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUX48 is usually 5 days.

3.What payment methods are accepted for BUX48?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUX48 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUX48?

BUX48 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUX48 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 BUX48?

For technical support, including BUX48 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUX48 requirements.

6.How does Aetrix verify that BUX48 is sourced from the original manufacturer or authorized distributors?

All BUX48 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 BUX48 meets industry standards.

7.What is the process for return or replacement of BUX48?

All BUX48 units undergo pre-shipment inspection (PSI). If there is an issue with BUX48, 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 BUX48 part is unused and in its original packaging.

Return procedure for BUX48:

1.Submit a request within 90 days.

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

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