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

onsemi BUT11A

Name: BUT11A
Brand: onsemi
SKU: BUT11A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUT11A

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BUT11A.pdf

Description:: TRANS NPN 450V 5A TO-220-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BUT11A from STMicroelectronics is a high-voltage, fast-switching NPN power transistor in TO-220 package, rated for 450 V V_CEO, 5 A continuous collector current, and 83 W power dissipation at T_c ≤ 25 °C; designed for flyback and forward single-transistor low-power converters in AC/DC adapters and offline SMPS.

For engineers reviewing the BUT11A datasheet, BUT11A pinout, BUT11A application, or BUT11A equivalent, key selection criteria include V_CEO(sus) = 450 V, t_on/t_s/t_f = 1/4/0.8 µs (resistive load), V_CE(sat) = 1.5 V @ 2.5 A/0.5 A, h_FE ≥ 10 @ 5 mA, and thermal resistance R_thj-case = 1.5 °C/W.

Technical Context

This NPN bipolar junction transistor uses multiepitaxial mesa construction to achieve high breakdown voltage and fast switching performance. Its 450 V sustaining voltage (V_CEO(sus)) and 1 µs turn-on time support reliable operation in discontinuous conduction mode (DCM) flyback topologies with input voltages up to 265 VAC.

The device features low saturation voltage (1.5 V @ I_C = 2.5 A, I_B = 0.5 A) and moderate DC current gain (h_FE = 10–35), optimized for base-driven switching rather than linear amplification. Thermal design is enabled by its 1.5 °C/W junction-to-case resistance and TO-220 mechanical footprint.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	450 V - Sustaining voltage with open base; enables use in 230 VAC offline converters without snubber overdesign
I_C	5 A - Continuous collector current rating; supports output power up to ~25 W in flyback designs
V_CE(sat)	1.5 V @ 2.5 A/0.5 A - Low conduction loss reduces heat generation during on-state
t_on/t_s/t_f	1/4/0.8 µs - Fast switching minimizes transition losses in 65–100 kHz SMPS applications
R_thj-case	1.5 °C/W - Enables direct heatsink mounting for thermal management in compact power supplies
h_FE	10–35 - Moderate DC gain suitable for fixed-base-drive circuits with stable bias networks
T_j(max)	150 °C - Maximum junction temperature defines safe operating area under transient overload

Pinout & Package

TO-220 plastic package with vertical mounting orientation, integral metal tab (collector-connected), and three leads: emitter (pin 1), base (pin 2), collector (pin 3). Tab is electrically connected to collector and must be isolated from heatsink unless referenced to same potential.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (Emitter)	Current sink terminal	Low-impedance return path for collector current; requires low-inductance PCB routing in switching nodes
Pin 2 (Base)	Control input	Receives drive current to saturate or cut off transistor; needs series resistor to limit I_B ≤ 2 A peak
Pin 3 / Tab (Collector)	Main power terminal	Connected internally to metal tab; must be electrically isolated from heatsink unless system ground reference permits

Key Features

Feature	Design Value
High-voltage capability	450 V V_CEO(sus) supports universal-input (85–265 VAC) flyback converters without voltage derating
Fast switching speed	1 µs turn-on and 0.8 µs fall time reduce switching losses at 65–100 kHz operation
Low saturation voltage	V_CE(sat) = 1.5 V @ 2.5 A ensures <1.9 W conduction loss at full load
Robust thermal performance	R_thj-case = 1.5 °C/W allows 55 °C temperature rise at 83 W dissipation with minimal heatsink
Multiepitaxial mesa structure	Enables precise control of breakdown voltage and carrier lifetime for consistent switching behavior

Applications

AC/DC Adapter Power Stage

Flyback Converter Primary Switch

Use Scenario: 12 V/1 A wall adapter for consumer electronics with universal AC input.

IC Role / Device Role / Timing Role: Main power switch in primary-side DCM flyback topology, driven by UC3842 or similar PWM controller.

Use Value: 450 V rating eliminates need for external clamping in 265 VAC surge conditions; 1.5 V V_CE(sat) keeps conduction loss below 2 W at full load.

Use Scenario: Isolated 5 V/2 A auxiliary supply in industrial PLC power module.

IC Role / Device Role / Timing Role: Single-transistor switching element in self-oscillating or fixed-frequency flyback circuit.

Use Value: 1 µs t_on and 0.8 µs t_f enable efficient operation at 85 kHz, reducing transformer size and EMI filter complexity.

Forward Converter Primary Switch

Offline LED Driver Switch

Use Scenario: 24 V/3 A forward converter for telecom interface card power rail.

IC Role / Device Role / Timing Role: Primary-side switch synchronized with transformer reset winding and freewheeling diode.

Use Value: 5 A I_C rating supports peak currents up to 10 A (I_CM) during startup transients without secondary breakdown.

Use Scenario: Constant-current LED driver for streetlight retrofit with 176–265 VAC input.

IC Role / Device Role / Timing Role: High-side switch in buck-derived offline topology with passive PFC stage.

Use Value: 150 °C T_j(max) and 1.5 °C/W R_thj-case allow reliable operation in enclosed outdoor enclosures without active cooling.

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
BU2508AX	V_CEO = 800 V, I_C = 8 A, t_f = 0.5 µs, R_thj-case = 1.3 °C/W	Higher voltage margin and faster fall time; higher cost and larger die size	Preferred when designing for 305 VAC surge immunity or >100 kHz operation
2SD1885	V_CEO = 400 V, I_C = 3 A, V_CE(sat) = 1.2 V @ 1.5 A, R_thj-case = 2.0 °C/W	Lower voltage rating and power handling; lower saturation voltage at reduced current	Suitable for sub-15 W designs where board space limits heatsink area

Compared with BU2508AX and 2SD1885, the BUT11A offers balanced trade-offs: sufficient 450 V rating for standard 230 VAC systems, proven thermal performance in TO-220, and predictable switching behavior in established flyback reference designs-making it ideal for cost-sensitive, medium-power offline converters.

Availability

BUT11A is available at Aetrix Electronics and suitable for AC/DC adapters, flyback converters, forward converters, and offline LED drivers requiring stable component supply and long-term production continuity.

Supply support for BUT11A 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 power management, analog, microcontrollers, and automotive ICs.

The BUT11A belongs to ST's high-voltage bipolar transistor product line, engineered specifically for rugged, cost-effective switching in offline power conversion applications up to 30 W.

FAQ

Is BUT11A still in active production?

No-BUT11A is marked "Obsolete Product(s)" in ST's official datasheet revision dated March 2004. However, Aetrix Electronics maintains legacy inventory with full traceability and supports ongoing production runs for qualified industrial and medical devices under extended lifecycle agreements.

Can BUT11A replace BU2508AX in existing designs?

Not directly: BU2508AX has higher 800 V V_CEO and 8 A I_C, while BUT11A is rated for 450 V and 5 A. Substitution requires re-evaluation of voltage stress margins, thermal design, and gate/base drive strength-especially in 305 VAC surge or high-duty-cycle applications.

What is the recommended base drive for BUT11A in flyback applications?

A base current of 0.5 A (with 2 A peak capability) is specified for saturation at I_C = 2.5 A. Typical implementation uses a 10 Ω series resistor with ±12 V drive, ensuring t_on/t_f remain within datasheet limits while avoiding excessive base charge storage.

Does the metal tab of BUT11A connect to collector internally?

Yes-the TO-220 metal tab is electrically connected to the collector terminal (pin 3). When mounted to a heatsink, electrical isolation (e.g., mica washer + thermal paste) is mandatory unless the heatsink is referenced to the collector potential in the circuit layout.

BUT11A Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-220-3

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 5 A

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

Vce Saturation (Max) @ Ib, Ic:: 1.5V @ 500mA, 2.5A

Current - Collector Cutoff (Max):: 1mA

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

Power - Max:: 100 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220-3

BUT11A FAQ

1.How can I place an order for BUT11A through Aetrix?

Please submit a Request for Quotation (RFQ) for BUT11A 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 BUT11A reliable?

The price and inventory of BUT11A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUT11A is usually 5 days.

3.What payment methods are accepted for BUT11A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUT11A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUT11A?

BUT11A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUT11A 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 BUT11A?

For technical support, including BUT11A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUT11A requirements.

6.How does Aetrix verify that BUT11A is sourced from the original manufacturer or authorized distributors?

All BUT11A 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 BUT11A meets industry standards.

7.What is the process for return or replacement of BUT11A?

All BUT11A units undergo pre-shipment inspection (PSI). If there is an issue with BUT11A, 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 BUT11A part is unused and in its original packaging.

Return procedure for BUT11A:

1.Submit a request within 90 days.

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

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