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

onsemi BUT12A

Name: BUT12A
Brand: onsemi
SKU: BUT12A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUT12A

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BUT12A.pdf

Description:: TRANS NPN 450V 8A TO-220-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BUT12A from Fairchild Semiconductor is an NPN silicon power transistor designed for high-voltage switching applications, with V_CBO = 1000 V, V_CEO = 450 V, I_C = 8 A (DC), P_C = 100 W at T_C = 25°C, and TO-220 package. It serves as a robust main switch in flyback converters, motor controls, and snubberless AC-switching circuits.

For engineers reviewing the BUT12A datasheet, pinout, applications, or equivalent options, key selection considerations include sustaining voltage under inductive load (V_CE(sus) = 400 V), fast switching performance (t_ON = 1 µs, t_F = 0.8 µs), saturation behavior (V_CE(sat) = 1.5 V @ 6 A/1.2 A), thermal capability (T_J = 150°C), and TO-220 mechanical compatibility.

Technical Context

The BUT12A operates as a high-voltage, medium-current NPN bipolar junction transistor optimized for hard-switched inductive loads. Its design emphasizes ruggedness under repetitive avalanche stress, with specified V_CE(sus) = 400 V at I_C = 100 mA and L = 25 mH, and guaranteed storage time (t_STG = 4 µs) and fall time (t_F = 0.8 µs) under defined test conditions.

It requires active base drive control - not self-commutating - with V_BE(sat) = 1.5 V at I_C = 6 A / I_B = 1.2 A, and supports pulsed collector current up to I_CP = 20 A (PW = 300 µs, duty cycle = 1.5%). Junction temperature must be limited to 150°C for reliable operation.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CBO	1000 V - Maximum reverse-biased collector-base voltage before breakdown; enables use in >800 V DC bus applications.
V_CEO	450 V - Rated collector-emitter blocking voltage with base open; defines safe operating voltage in switch-mode topologies.
I_C (DC)	8 A - Continuous collector current rating at T_C = 25°C; determines steady-state power handling with heatsinking.
P_C	100 W - Maximum collector dissipation at case temperature 25°C; sets thermal design baseline for TO-220 mounting.
V_CE(sat)	1.5 V @ 6 A / 1.2 A - Low saturation voltage reduces conduction loss in high-current switching stages.
t_F	0.8 µs - Fast fall time minimizes switching transition loss during turn-off in hard-switched converters.
T_J	150°C - Maximum allowable junction temperature; constrains thermal design margin under sustained load.

Pinout & Package

Package: TO-220 (single-ended, through-hole, insulated tab). Standard 3-lead configuration with electrically isolated collector tab for direct heatsink mounting.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Control input terminal	Receives forward base current to saturate transistor; requires ≥1.2 A drive for full 6 A collector conduction.
2 (Collector)	Main current output terminal	Connected to high-voltage rail or inductive load; electrically tied to metal tab for thermal path and voltage reference.
3 (Emitter)	Main current return terminal	Serves as low-side common node; carries full load current and must be routed with low-inductance layout.

Key Features

Feature	Design Value
High V_CBO	1000 V enables direct interface with 700–800 V rectified mains or industrial DC bus systems without series stacking.
Rugged V_CE(sus)	400 V sustaining voltage under 25 mH inductive load ensures reliable operation in flyback and snubberless AC-switching designs.
Fast switching	Combined t_ON + t_STG + t_F < 6 µs supports PWM frequencies up to ~100 kHz in hard-switched topologies.
TO-220 thermal interface	Insulated tab allows direct mounting to heatsink without isolation washer, simplifying thermal management in compact power modules.
High I_CP	20 A pulsed rating accommodates short-term surge currents during motor startup or fault transients.

Applications

Switch-Mode Power Supply (SMPS)	AC Motor Control
Use Scenario: Primary-side switch in 100–300 W offline flyback converters with universal AC input. IC Role / Device Role / Timing Role: Main high-voltage switching element commutating energy into transformer primary winding. Use Value: V_CEO = 450 V and V_CE(sus) = 400 V ensure margin against reflected voltage spikes in discontinuous conduction mode.	Use Scenario: Phase-leg switch in single-phase AC induction motor drives operating from 230 V AC mains. IC Role / Device Role / Timing Role: High-side or low-side power switch controlling current flow to motor windings. Use Value: 8 A DC rating and 100 W dissipation support continuous 1/3 HP motor loads with adequate heatsinking.
Snubberless AC Switching	Industrial Solenoid Driver
Use Scenario: Direct AC line switching in solid-state relays or lighting ballasts without external snubbers. IC Role / Device Role / Timing Role: Bidirectional switching device used with external diode network to handle AC half-cycles. Use Value: High V_CBO = 1000 V and controlled turn-off characteristics reduce need for RC snubbers in resistive/inductive loads.	Use Scenario: High-energy pulse driver for 24–48 V DC industrial solenoids requiring 5–10 A peak current. IC Role / Device Role / Timing Role: Fast-turn-on switch delivering controlled current pulses to solenoid coils. Use Value: t_ON = 1 µs and I_CP = 20 A enable precise, high-force actuation with minimal coil heating.

Switch-Mode Power Supply (SMPS)

AC Motor Control

Use Scenario: Primary-side switch in 100–300 W offline flyback converters with universal AC input.

IC Role / Device Role / Timing Role: Main high-voltage switching element commutating energy into transformer primary winding.

Use Value: V_CEO = 450 V and V_CE(sus) = 400 V ensure margin against reflected voltage spikes in discontinuous conduction mode.

Use Scenario: Phase-leg switch in single-phase AC induction motor drives operating from 230 V AC mains.

IC Role / Device Role / Timing Role: High-side or low-side power switch controlling current flow to motor windings.

Use Value: 8 A DC rating and 100 W dissipation support continuous 1/3 HP motor loads with adequate heatsinking.

Snubberless AC Switching

Industrial Solenoid Driver

Use Scenario: Direct AC line switching in solid-state relays or lighting ballasts without external snubbers.

IC Role / Device Role / Timing Role: Bidirectional switching device used with external diode network to handle AC half-cycles.

Use Value: High V_CBO = 1000 V and controlled turn-off characteristics reduce need for RC snubbers in resistive/inductive loads.

Use Scenario: High-energy pulse driver for 24–48 V DC industrial solenoids requiring 5–10 A peak current.

IC Role / Device Role / Timing Role: Fast-turn-on switch delivering controlled current pulses to solenoid coils.

Use Value: t_ON = 1 µs and I_CP = 20 A enable precise, high-force actuation with minimal coil heating.

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_CBO = 1500 V, V_CEO = 700 V, I_C = 8 A, slower t_F = 1.2 µs	Better voltage margin but higher switching loss; suited for lower-frequency (<50 kHz) HV supplies	Choose BU508A when higher V_CBO is critical and switching speed is secondary.
ST112	V_CBO = 1000 V, V_CEO = 450 V, I_C = 6 A, P_C = 75 W, TO-220	Lower current/power rating; identical voltage specs and pinout	Choose ST112 only for derated 6 A designs where thermal budget is constrained.

Compared with BUT12A, BU508A offers superior voltage headroom but sacrifices switching speed, while ST112 matches voltage specs and footprint but limits continuous current to 6 A and power to 75 W - both require re-evaluation of thermal and dynamic performance in the target circuit.

Availability

BUT12A is available at Aetrix Electronics and suitable for switch-mode power supplies, AC motor controllers, snubberless AC switching circuits, and industrial solenoid drivers requiring stable component supply across extended production lifecycles.

Supply support for BUT12A 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

Fairchild Semiconductor was a U.S.-based designer and manufacturer of analog and discrete semiconductors, acquired by ON Semiconductor in 2016. Known for rugged power devices and broad legacy product support.

The BUT12A belongs to Fairchild's high-voltage bipolar transistor family, engineered specifically for industrial-grade switching applications demanding high breakdown voltage, avalanche ruggedness, and TO-220 thermal reliability.

FAQ

What is the maximum collector-emitter voltage rating for BUT12A?

The BUT12A has a maximum collector-emitter voltage rating (V_CEO) of 450 V with the base open. This rating applies under DC conditions at T_C = 25°C and defines the upper limit for safe blocking operation in switching circuits. Exceeding this voltage risks avalanche breakdown or permanent damage. The BUT12A datasheet confirms this value in its Absolute Maximum Ratings table.

Does BUT12A support pulsed operation beyond its DC current rating?

Yes, the BUT12A supports pulsed collector current up to 20 A, specified under pulsed test conditions (pulse width = 300 µs, duty cycle = 1.5%). This allows short-duration overload handling - such as motor startup surges or solenoid actuation - without exceeding junction temperature limits. The BUT12A datasheet explicitly lists I_CP = 20 A in its Absolute Maximum Ratings section.

What is the saturation voltage of BUT12A at rated current?

The BUT12A exhibits a collector-emitter saturation voltage (V_CE(sat)) of 1.5 V when operated at I_C = 6 A and I_B = 1.2 A. This value reflects conduction loss under typical hard-saturation drive and directly impacts efficiency in high-current switching stages. The BUT12A datasheet specifies this parameter in its Electrical Characteristics table under "Collector-Emitter Saturation Voltage".

Is BUT12A pin-compatible with BUT12?

Yes, the BUT12A shares identical pinout (Base–Collector–Emitter), package (TO-220), and mechanical dimensions with the BUT12. However, the BUT12A offers improved voltage ratings: V_CBO = 1000 V vs. 850 V and V_CEO = 450 V vs. 400 V. The BUT12A can serve as a drop-in upgrade where higher voltage margin is required, provided thermal and drive conditions remain within spec.

What is the maximum junction temperature specification for BUT12A?

The BUT12A has a maximum junction temperature (T_J) rating of 150°C, as stated in its Absolute Maximum Ratings table. This limit governs thermal design - including heatsink sizing, ambient temperature, and PCB copper area - to prevent irreversible degradation. Operation above 150°C risks parametric shift or catastrophic failure. The BUT12A datasheet confirms this value under standard test conditions.

BUT12A 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):: 8 A

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

Vce Saturation (Max) @ Ib, Ic:: 1.5V @ 1.2A, 6A

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

BUT12A FAQ

1.How can I place an order for BUT12A through Aetrix?

Please submit a Request for Quotation (RFQ) for BUT12A 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 BUT12A reliable?

The price and inventory of BUT12A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUT12A is usually 5 days.

3.What payment methods are accepted for BUT12A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUT12A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUT12A?

BUT12A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUT12A 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 BUT12A?

For technical support, including BUT12A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUT12A requirements.

6.How does Aetrix verify that BUT12A is sourced from the original manufacturer or authorized distributors?

All BUT12A 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 BUT12A meets industry standards.

7.What is the process for return or replacement of BUT12A?

All BUT12A units undergo pre-shipment inspection (PSI). If there is an issue with BUT12A, 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 BUT12A part is unused and in its original packaging.

Return procedure for BUT12A:

1.Submit a request within 90 days.

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

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