onsemi BUL44G

Overview

BUL44G from onsemi is a high-voltage NPN bipolar power transistor designed for switching-mode power supply (SMPS) and electronic light ballast applications. It features 400 V_CEO, 700 V_CES, 2.0 A continuous collector current, 50 W total device dissipation at T_C = 25°C, and optimized dynamic saturation behavior for efficient high-voltage switching.

For engineers reviewing the BUL44G datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, TO-220AB package details, thermal resistance values (R_JC = 2.5°C/W), switching timing data (t_off ≤ 2.5 µs at 125°C), and validated alternatives for SMPS flyback and ballast designs.

Technical Context

The BUL44G employs an application-specific die architecture optimized for 220 V line-operated switchmode power supplies and electronic light ballasts. Its design emphasizes low base drive requirements via high and flat DC current gain (h_FE ≥ 8.0 at I_C = 1.0 A, T_J = 125°C) and eliminates current tail during turn-off-removing the need for a coil in the base circuit.

It is fully characterized at 125°C with tight parametric distributions across lots and supports robust operation under inductive load conditions (V_clamp = 300 V, L = 200 µH). Thermal performance is defined by R_JC = 2.5°C/W and R_JA = 62.5°C/W, enabling reliable heat transfer in TO-220AB mounting configurations.

Key Specifications

Pinout & Package

Package: TO-220AB (Case 221A-09, Style 1), Pb-free, with collector connected to tab for direct heatsinking.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN bipolar power transistor applications.

Compared with MJE13005 and BU2508DF, the BUL44G delivers superior thermal performance (R_JC = 2.5°C/W), tighter h_FE consistency at full rated current, and faster turn-off under worst-case temperature-making it the preferred choice for cost-optimized, thermally constrained 220 V SMPS and electronic ballast designs.

Availability

BUL44G is available at Aetrix Electronics and suitable for compact fluorescent lamp ballasts, AC-DC adapters, and LED driver power stages requiring stable component supply, long-term lifecycle support, and RoHS-compliant manufacturing.

Supply support for BUL44G 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 supplier focused on energy-efficient innovation for automotive, industrial, cloud, and intelligent power systems.

The BUL44G belongs to onsemi's SWITCHMODE™ bipolar power transistor family, engineered specifically for high-reliability, high-efficiency switching in 220 V line-operated power supplies and electronic lighting ballasts.

FAQ

What is the maximum operating junction temperature for the BUL44G?

The BUL44G has a specified operating junction temperature range of −65°C to +150°C. Its thermal resistance R_JC = 2.5°C/W allows precise junction temperature estimation when mounted on a heatsink with known case temperature. For continuous operation in SMPS applications, thermal design must ensure T_J remains ≤ 150°C under worst-case ambient and load conditions. The BUL44G datasheet confirms full parameter characterization at 125°C, validating its suitability for high-temperature environments.

Does the BUL44G require a base turn-off coil in switching applications?

No, the BUL44G does not require a base turn-off coil. Its application-specific die design eliminates current tail during turn-off, enabling clean, coil-free base drive circuits. This feature is explicitly documented in the BUL44G datasheet under "Features" and confirmed by dynamic saturation voltage measurements showing rapid V_CE(dsat) decay within 1–3 seconds after IB removal. Engineers can simplify driver design and improve reliability by omitting the coil when using the BUL44G.

What is the safe operating area (SOA) limitation for inductive loads with the BUL44G?

The BUL44G specifies a reverse-biased safe operating area (RBSOA) for inductive loads, verified under clamped conditions up to 300 V with L = 200 µH. At T_C = 25°C, it supports 2 A at 100 V for 10 ms pulses, with derating applied per Figure 17 in the BUL44G datasheet. Second breakdown limits dominate at high voltage/low time, while thermal limits govern longer pulses. Designers must consult Figures 15 and 16 in the official BUL44G datasheet to ensure operation stays within both forward- and reverse-bias SOA boundaries.

Is the BUL44G pin-compatible with other TO-220AB NPN transistors like the MJE13005?

The BUL44G uses TO-220AB (Case 221A-09, Style 1) with pinout Base–Collector–Emitter–Collector, matching the mechanical footprint and lead spacing of MJE13005. However, it is not a drop-in replacement: the BUL44G offers superior thermal resistance (2.5 vs. 3.0°C/W), tighter h_FE distribution at full current, and faster turn-off (2.5 vs. 3.0 µs). PCB layout may be reused, but thermal and drive circuit validation is required before substitution. The BUL44G datasheet does not claim pin compatibility with MJE13005.

How does the BUL44G perform at elevated temperatures such as 125°C?

The BUL44G is fully characterized at 125°C, including h_FE (min 8.0 at I_C = 1.0 A), V_CE(sat) (max 0.6 V), and switching times (t_off ≤ 2.5 µs). Its guaranteed parameters at this temperature confirm stable operation in thermally demanding applications like enclosed CFL ballasts. Unlike many general-purpose transistors, the BUL44G maintains usable gain and low saturation voltage even at junction temperatures approaching 125°C-enabling reliable performance without derating in compact, convection-cooled designs.