onsemi BUX85

Overview

BUX85G from onsemi is an NPN silicon power transistor designed for high-voltage, high-speed switching in converters, inverters, switching regulators, and motor control systems. It delivers 2 A continuous collector current, sustains 450 Vdc (V_CEO(sus)), dissipates 50 W at T_C = 25 °C, and features a 4 MHz f_T bandwidth with 0.3–0.5 µs turn-on time.

For engineers reviewing the BUX85G datasheet, pinout, applications, or equivalent options, key selection criteria include its 450 V sustained blocking capability, TO-220 package thermal resistance (R_θJC = 2.5 °C/W), switching speed under 1 µs, and suitability for hard-switched SMPS and industrial motor drive stages.

Technical Context

The BUX85G operates as a single NPN bipolar junction transistor optimized for high-voltage linear and switching operation. Its 1000 V_CES rating enables robust transient tolerance, while its 4 MHz f_T and sub-microsecond switching times (t_on ≤ 0.5 µs, t_s ≤ 3.5 µs) support efficient operation in 20–100 kHz converter topologies.

It uses a TO-220 case (Style 1) with dual collector terminals (pins 2 and 4), base on pin 1, and emitter on pin 3 - enabling low-inductance mounting and direct heatsink coupling. Thermal design is supported by R_θJC = 2.5 °C/W and a maximum junction temperature of +150 °C.

Key Specifications

Pinout & Package

Package: TO-220 (Case 221A, Style 1), 4-pin variant with pins 2 and 4 both connected to the collector for enhanced current handling and thermal path redundancy.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJE13009 and BUL128D, the BUX85G offers optimal balance of 450 V sustain voltage, 2 A capability, and TO-220 thermal performance - making it preferred for 100–200 W industrial SMPS and motor control where board space and thermal management are constrained.

Availability

BUX85G is available at Aetrix Electronics and suitable for switch-mode power supplies, motor control systems, and DC-DC converters requiring stable component supply and long-term industrial availability.

Supply support for BUX85G 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

onsemi (formerly ON Semiconductor) is a global semiconductor manufacturer specializing in power management, analog, sensors, and discrete devices for automotive, industrial, and cloud power applications.

The BUX85G belongs to onsemi's high-voltage bipolar power transistor family, engineered for ruggedized switching in industrial power conversion and motor drive circuits where reliability under repetitive surge stress is critical.

FAQ

What is the maximum safe operating voltage for BUX85G in inductive switching?

The BUX85G is rated for V_CEO(sus) = 450 Vdc with I_C = 100 mAdc and L = 25 mH per Figure 1 test circuit. This is the guaranteed minimum sustaining voltage under inductive turn-off conditions. For reliable design, operate below 400 VDC nominal bus voltage to maintain margin against transients and temperature derating. The absolute maximum V_CES = 1000 Vdc applies only for non-repetitive surge events.

Does BUX85G require a heatsink in continuous 2 A operation?

Yes - the BUX85G dissipates up to 50 W at T_C = 25 °C, but junction temperature rises rapidly with power. At 2 A and V_CE(sat) ≈ 1.0 V, conduction loss alone is ~2 W; however, switching losses dominate above 20 kHz. To hold T_J ≤ 150 °C with >1 W average dissipation, a heatsink with ≤10 °C/W thermal resistance (including interface) is required. The TO-220 metal tab must be electrically isolated and thermally coupled.

What is the base drive requirement to fully saturate BUX85G at 1 A collector current?

The BUX85G achieves V_CE(sat) ≤ 1.0 V at I_C = 1 A with I_B = 200 mA (I_C/I_B = 5), per Electrical Characteristics table. Base-emitter saturation voltage is 1.1 Vdc under those conditions. A driver capable of sourcing ≥250 mA peak with <1 Ω source impedance is recommended to ensure fast turn-on and avoid quasi-saturation during high-dI/dt transitions.

Is BUX85G pin-compatible with other TO-220 NPN transistors like BD249 or MJE13005?

No - the BUX85G uses TO-220 Style 1 (pin 1 = Base, pin 2 = Collector, pin 3 = Emitter, pin 4 = Collector), whereas BD249 and MJE13005 are standard 3-pin TO-220 devices. The 4-pin configuration provides dual collector paths for lower inductance and improved thermal spreading, but requires PCB layout adaptation. Pin mapping is not interchangeable without redesign.

What does the "G" suffix in BUX85G signify?

Per onsemi's ordering information, the "G" suffix on BUX85G denotes Pb-free (lead-free) construction and RoHS compliance. It confirms that the device meets EU Directive 2011/65/EU requirements, with tin-based terminations and no intentional lead content. This affects soldering profile (higher liquidus temperature) and qualifies the part for environmentally regulated end equipment.