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

STMicroelectronics BUX348

Name: BUX348
Brand: STMicroelectronics
SKU: BUX348
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUX348

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-204AA, TO-3

Datasheet:: BUX348.pdf

Description:: TRANS NPN 450V 45A TO-3

Quantity:: RFQ Add To RFQ list

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Inventory:8,632

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Product details

Overview

BUX348 from STMicroelectronics is an NPN bipolar power transistor designed for high-voltage, fast-switching off-line applications up to 380 V, with V_CEO = 450 V, I_C = 45 A, P_tot = 300 W at T_case ≤ 25 °C, and R_thj-case = 0.58 °C/W - used in switch-mode power supplies, UPS systems, and DC/AC motor control.

For engineers reviewing the BUX348 datasheet, BUX348 pinout, BUX348 application, or BUX348 equivalent, key selection criteria include its 450 V sustaining voltage under inductive load, 125–250 A/µs di_C/dt rating, 0.7–1.35 V V_CE(sat) at 30 A/6 A, and TO-3 (version "S") metal package thermal performance.

Technical Context

The BUX348 is a ruggedized NPN silicon planar transistor optimized for hard-switched inductive loads without snubbers, featuring a V_CEW of 450 V at T_j = 125 °C and validated dynamic switching parameters including t_s = 2.75–4.5 µs storage time and t_f = 0.12–0.4 µs fall time under standardized 80 µH inductive test conditions.

Its base drive architecture supports high peak base current (I_BM = 15 A, t_p < 5 ms) and fast turn-off via negative base bias (V_BB = −5 V), enabling reliable operation in flyback and forward converter topologies where V_CEV = 850 V provides margin against voltage transients.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	450 V - maximum collector-emitter voltage with open base, defining safe operating voltage ceiling in SMPS primary switches
I_C	45 A - continuous collector current rating at T_case ≤ 25 °C, supporting high-power motor drive stages
P_tot	300 W - total dissipation capability with case temperature ≤ 25 °C, requiring heatsink design per R_thj-case = 0.58 °C/W
di_C/dt	125–250 A/µs - rated rise rate of on-state collector current, critical for minimizing switching losses in hard-switched converters
V_CE(sat)	0.7–1.35 V @ I_C = 30 A, I_B = 6 A - low saturation voltage reduces conduction loss in high-current switching nodes
t_s / t_f	2.75–4.5 µs / 0.12–0.4 µs - verified storage and fall times under 50 V clamp, enabling predictable timing in gate driver design

Pinout & Package

Package: TO-3 (version "S") metal can, with collector connected to case for direct heatsinking and thermal path optimization.

Pin/Terminal	Circuit Role	Design Meaning
Collector (Case)	Main current sink terminal	Electrically and thermally tied to metal housing - must be insulated from chassis unless referenced to system ground
Emitter	Current source terminal	Low-inductance connection point for return path; requires robust PCB trace or busbar routing
Base	Control input terminal	Driven with ≥6 A DC or 15 A pulsed current; negative bias (−5 V) required for fast turn-off

Key Features

Feature	Design Value
Snubberless operation	Rated V_CEW = 450 V under 55 µH inductive load enables elimination of RC snubbers in cost-sensitive UPS designs
High di_C/dt capability	250 A/µs max ensures minimal switching delay and reduced overlap loss in 20–100 kHz SMPS
Rugged thermal design	R_thj-case = 0.58 °C/W allows 300 W dissipation with modest heatsink, reducing thermal interface complexity
Fast dynamic switching	t_c = 0.44–0.7 µs crossover time minimizes shoot-through risk in half-bridge configurations

Applications

Switch-Mode Power Supply Primary Switch

Uninterruptible Power Supply Inverter Stage

Use Scenario: High-efficiency 500–2000 W offline flyback or forward converter operating at 50–100 kHz.

IC Role / Device Role / Timing Role: Main high-voltage switching element handling primary-side energy transfer and transient voltage clamping.

Use Value: 450 V V_CEO and 850 V V_CEV provide margin against reflected spikes; 0.58 °C/W thermal resistance sustains full load without forced air.

Use Scenario: 1–3 kVA double-conversion UPS delivering clean sine-wave output during grid failure.

IC Role / Device Role / Timing Role: Inverter bridge switch managing battery-to-AC conversion with fast turn-off to prevent cross-conduction.

Use Value: 15 A peak base current and −5 V negative bias support sub-microsecond turn-off; t_f < 0.4 µs limits dead-time requirements.

DC Motor Drive H-Bridge Leg

AC Induction Motor Control Inverter

Use Scenario: Industrial 48–110 V DC motor controller with regenerative braking and PWM speeds up to 20 kHz.

IC Role / Device Role / Timing Role: High-side or low-side power switch in half-bridge topology, handling bidirectional current during braking.

Use Value: 45 A I_C and 60 A I_CM support peak torque surges; V_CEW = 450 V accommodates back-EMF spikes up to 380 V.

Use Scenario: Variable-frequency drive for 3-phase AC induction motors in HVAC or pump systems (0.5–5 kW).

IC Role / Device Role / Timing Role: Inverter leg switch in 6-pack configuration, commutating phase currents with precise timing control.

Use Value: Verified t_s/t_f consistency across temperature ensures stable PWM timing at 10–16 kHz; 200 °C T_j rating extends reliability under overload.

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
BU508A	V_CEO = 1000 V, I_C = 12 A, P_tot = 125 W - higher voltage rating but lower current and power	Suitable for lower-power flyback converters where 1 kV margin is prioritized over current handling	Select when V_CE transients exceed 450 V and load current remains below 12 A
2SD1063	V_CEO = 400 V, I_C = 50 A, P_tot = 150 W - lower voltage rating but higher current, TO-218 package	Better suited for high-current, lower-voltage motor drives where heatsinking is less constrained	Choose when system voltage stays ≤ 350 V and thermal budget favors plastic package mounting flexibility

Compared with BU508A and 2SD1063, BUX348 uniquely balances 450 V voltage capability, 45 A current, and 300 W dissipation in a TO-3 metal package - making it optimal for medium-power, high-reliability off-line SMPS and UPS where thermal density and dynamic ruggedness are jointly critical.

Availability

BUX348 is available at Aetrix Electronics and suitable for switch-mode power supplies, uninterruptible power supplies, and DC/AC motor control applications requiring stable component supply and legacy industrial replacement support.

Supply support for BUX348 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, digital, and mixed-signal ICs and discrete power devices for industrial, automotive, and consumer markets.

The BUX348 belongs to ST's legacy high-voltage bipolar transistor family, engineered specifically for ruggedized off-line power conversion where snubberless operation, thermal robustness, and dynamic switching integrity are essential.

FAQ

Is BUX348 still in active production?

No - BUX348 is marked "Obsolete Product(s)" in its official STMicroelectronics datasheet (March 2003 revision). It remains available through authorized legacy distributors and Aetrix Electronics' long-term inventory program for repair, maintenance, and end-of-life industrial equipment support.

Can BUX348 be used without a snubber circuit?

Yes - BUX348 is explicitly characterized for snubberless operation with V_CEW = 450 V under specified inductive load conditions (L_C = 55 µH, I_CWoff = 45 A). This rating is validated per ST's test methodology and permits elimination of external RC snubbers in properly designed 400 V-class systems.

What is the recommended base drive configuration?

ST specifies a two-level base drive: +9 A peak (I_B1) for turn-on and −5 V (V_BB) with 0.4 Ω series resistor for turn-off. This ensures t_s < 4.5 µs and prevents secondary breakdown during inductive switching - critical for UPS and motor control reliability.

How does BUX348's thermal performance compare to modern alternatives?

With R_thj-case = 0.58 °C/W, BUX348 delivers superior thermal conductivity versus most plastic-packaged equivalents (e.g., TO-247 R_thj-case ≈ 0.8–1.2 °C/W). Its metal TO-3 package enables direct mounting to large heatsinks - a key advantage in space-constrained, high-power legacy systems where retrofitting is impractical.

BUX348 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

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

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 45 A

Voltage - Collector Emitter Breakdown (Max):: 450 V

Vce Saturation (Max) @ Ib, Ic:: 900mV @ 6A, 30A

Current - Collector Cutoff (Max):: -

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

Power - Max:: 300 W

Frequency - Transition:: -

Operating Temperature:: 200°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-3

BUX348 FAQ

1.How can I place an order for BUX348 through Aetrix?

Please submit a Request for Quotation (RFQ) for BUX348 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 BUX348 reliable?

The price and inventory of BUX348 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUX348 is usually 5 days.

3.What payment methods are accepted for BUX348?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUX348 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUX348?

BUX348 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUX348 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 BUX348?

For technical support, including BUX348 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUX348 requirements.

6.How does Aetrix verify that BUX348 is sourced from the original manufacturer or authorized distributors?

All BUX348 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 BUX348 meets industry standards.

7.What is the process for return or replacement of BUX348?

All BUX348 units undergo pre-shipment inspection (PSI). If there is an issue with BUX348, 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 BUX348 part is unused and in its original packaging.

Return procedure for BUX348:

1.Submit a request within 90 days.

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

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