onsemi BUT12TU

Overview

BUT12TU from Fairchild Semiconductor is an NPN silicon power transistor designed for high-voltage switching applications, with 400 V V_CEO, 8 A continuous collector current, and 100 W collector dissipation at T_C = 25°C; used in flyback converters, motor control snubbers, and AC solid-state relays.

For engineers reviewing the BUT12TU datasheet, pinout, applications, or equivalent options, key selection factors include its 400 V sustaining voltage under inductive load (V_CEO(sus)), 1.5 V V_CE(sat) at 6 A/1.2 A drive, and TO-220 package thermal performance for industrial switching designs.

Technical Context

The BUT12TU operates as a ruggedized NPN bipolar junction transistor optimized for inductive switching, featuring a minimum 400 V collector-emitter sustaining voltage with 25 mH load and 100 mA current. Its fast switching times-1 µs turn-on, 4 µs storage, and 0.8 µs fall-support efficient operation in repetitive pulse applications up to 20 A peak.

It requires base drive capable of delivering 1.2 A for saturation at 6 A collector current, with V_BE(sat) = 1.5 V under that condition. Junction temperature must remain ≤150°C, and storage temperature range is –65°C to +175°C.

Key Specifications

Pinout & Package

Package: TO-220 (3-lead, straight lead, insulated tab). Mounting surface is electrically isolated from collector terminal.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BU508A and 2SD1047, the BUT12TU uniquely balances 400 V blocking, 8 A current, and sub-1 µs fall time-making it optimal for mid-voltage industrial switching where both voltage margin and conduction efficiency matter.

Availability

BUT12TU is available at Aetrix Electronics and suitable for AC solid-state relays, flyback converter switches, and inductive load snubbers requiring stable component supply across extended production lifecycles.

Supply support for BUT12TU 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 of analog and discrete semiconductors, acquired by ON Semiconductor in 2016; known for rugged power transistors and high-reliability industrial components.

The BUT12TU belongs to Fairchild's high-voltage NPN switching transistor family, engineered specifically for industrial control, power conversion, and electromagnetic actuator interfaces demanding sustained 400 V operation and robust SOA.

FAQ

What is the maximum continuous collector current rating for the BUT12TU?

The BUT12TU has a maximum continuous collector current (I_C) rating of 8 A at T_C = 25°C. This rating assumes adequate heatsinking and derates linearly above 25°C case temperature. At 100°C case temperature, the usable I_C drops to approximately 4.5 A per the device's thermal resistance curve. The BUT12TU also supports 20 A pulsed collector current under specified short-duration conditions.

Does the BUT12TU have a built-in base-emitter resistor or ESD protection?

No, the BUT12TU is a bare NPN bipolar transistor with no integrated base-emitter resistor or ESD protection diodes. External base current limiting and transient suppression must be implemented in the circuit design. This is consistent with all devices in the BUT12/12A family, as confirmed in the original Fairchild datasheet Rev. A1.

Can the BUT12TU replace the BUT12A in a 450 V application?

No-the BUT12TU is rated for 400 V V_CEO, while the BUT12A is rated for 450 V. Using the BUT12TU in a 450 V application exceeds its absolute maximum rating and risks premature breakdown. The BUT12A variant must be selected where 450 V blocking is required; the BUT12TU is strictly limited to ≤400 V DC or peak AC applications.

What is the thermal resistance from junction to case (R_θJC) for the BUT12TU?

The BUT12TU has a junction-to-case thermal resistance (R_θJC) of 1.5°C/W, derived from its 100 W power dissipation rating at T_C = 25°C and 150°C maximum junction temperature. This value is consistent across the BUT12/12A family and enables accurate heatsink sizing using standard thermal modeling methods.

Is the BUT12TU pin-compatible with other TO-220 NPN transistors like the MJE13009?

Yes-the BUT12TU uses standard TO-220 package pinout (1=Base, 2=Collector, 3=Emitter), matching MJE13009 and most 3-lead TO-220 NPN transistors. However, electrical parameters differ significantly: MJE13009 has V_CEO = 400 V but only 12 W P_C, making it unsuitable as a direct replacement in high-power applications where the BUT12TU's 100 W rating is essential.