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

onsemi BUL44

Name: BUL44
Brand: onsemi
SKU: BUL44
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUL44

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BUL44.pdf

Description:: TRANS NPN 400V 2A TO-220

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BUL44 from onsemi is an NPN bipolar power transistor designed for high-voltage switching in offline switchmode power supplies and electronic light ballasts. It features a 700 V_CES, 400 V_CEO, 2.0 A continuous collector current, TO-220AB package, and optimized dynamic saturation behavior for efficient 220 V line-operated systems.

For engineers reviewing the BUL44 datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, thermal derating curves, switching timing under resistive/inductive loads, safe operating area (SOA) boundaries, and real-world design implications for ballast and SMPS flyback topologies.

Technical Context

The BUL44 is a ruggedized, high-voltage NPN power transistor with a state-of-the-art die engineered specifically for 220 V AC input switchmode applications. Its design emphasizes low base drive requirements via high and flat h_FE (min 8.0 at I_C = 1.0 A, T_J = 125°C), fast turn-off without tail current, and full characterization at 125°C ambient.

It supports both resistive and inductive load switching with guaranteed SOA up to 300 V clamp voltage and 1.0 A peak current under clamped inductive conditions. The device exhibits tight parametric distributions across lots and is Pb-free/RoHS compliant per its G suffix marking.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO(sus)	400 V - Sustains 400 V collector-emitter voltage at I_C = 100 mA with 25 mH inductive load, enabling reliable operation in 220 V AC rectified rails.
V_CES	700 V - Collector-base breakdown voltage defines maximum voltage stress during switching transitions and snubber recovery.
I_C (continuous)	2.0 A - Maximum continuous collector current at T_C = 25°C; derates linearly above 25°C at 0.4 W/°C.
V_CE(sat)	0.20–0.60 V - Saturation voltage range at I_C = 0.4–1.0 A and I_B = 40 mA–0.2 A, directly determining conduction loss in hard-switched topologies.
t_off	1.5–2.5 µs - Turn-off time under 300 V clamp, 0.4 A load, and I_B1/I_B2 = 40 mA/0.2 A, critical for minimizing switching loss at 20–100 kHz.
R_JC	2.5 °C/W - Junction-to-case thermal resistance enables direct heatsink mounting and predictable junction temperature rise under 50 W dissipation.
f_T	13 MHz - Current gain bandwidth confirms usable gain at high-frequency switching nodes, supporting stable base drive design.

Pinout & Package

Package: TO-220AB (Case 221A-09, Style 1), with collector connected to tab for direct heatsinking. Mounting hole centered on tab, lead pitch 2.54 mm.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Control input	Receives base current to saturate or cut off the transistor; requires external driver capable of delivering 0.2 A peak for 1 A collector switching.
2 (Collector)	Main power output	Connected to high-side switching node (e.g., primary winding of flyback transformer); electrically tied to metal tab for thermal path.
3 (Emitter)	Power return reference	Serves as common emitter node; must be routed with low-inductance path to minimize voltage spikes during turn-off.
4 (Collector)	Redundant collector connection	Second collector terminal for enhanced current handling and reduced thermal resistance; soldered to same internal die region as Pin 2.

Key Features

Feature	Design Value
High and flat h_FE at 125°C	Min 8.0 at I_C = 1.0 A ensures stable base drive margin across industrial temperature range without overdesigning driver stage.
No current tail during turn-off	Eliminates need for base coil or active pull-down circuitry, simplifying gate/base drive design and reducing component count.
Full 125°C characterization	All key parameters (V_CE(sat), t_on/t_off, SOA) validated at max operating junction temperature, enabling robust thermal design.
Tight lot-to-lot parametric spread	Enables consistent performance across production batches without requalification, critical for high-volume lighting and PSU manufacturing.
Pb-free / RoHS-compliant packaging	G-suffix confirms compliance with environmental regulations and compatibility with lead-free reflow profiles (TL = 260°C for 5 s).

Applications

Electronic Ballasts	AC-DC Flyback Converters
Use Scenario: High-frequency (20–60 kHz) resonant lamp ignition and regulation in compact fluorescent lamps (CFLs) and LED drivers. IC Role / Device Role / Timing Role: Primary-side power switch controlling energy transfer into resonant tank; operates in hard-switched mode with zero-voltage switching assistance. Use Value: Low V_CE(sat) and fast t_off reduce conduction and switching losses, improving ballast efficiency >85% while maintaining thermal stability at 125°C case temperature.	Use Scenario: Primary-side switching element in universal-input (85–265 V AC) offline flyback converters for consumer adapters and industrial power modules. IC Role / Device Role / Timing Role: Main power switch in discontinuous conduction mode (DCM) flyback; handles peak currents up to 5.0 A with 300 V clamp protection. Use Value: Guaranteed RBSOA up to 300 V and 1.0 A enables reliable operation under transient overloads and short-circuit conditions without secondary protection circuitry.
Inductive Load Drivers	Switchmode Power Supply (SMPS) Front-End
Use Scenario: Driving inductive solenoids, relays, or magnetic actuators in industrial control panels requiring 220 V AC line isolation. IC Role / Device Role / Timing Role: High-voltage interface between low-voltage logic controller and inductive load; absorbs back-EMF via clamping diode or RC snubber. Use Value: Verified reverse-bias SOA (RBSOA) allows sustained simultaneous high voltage/current during turn-off, preventing second-breakdown failure during inductive kick.	Use Scenario: Main switching transistor in 40–100 W open-frame SMPS used in printers, monitors, and point-of-sale terminals. IC Role / Device Role / Timing Role: Energy storage and transfer switch in single-transistor forward or flyback topology; rated for continuous 2.0 A DC and 5.0 A pulse operation. Use Value: 2.5 °C/W R_JC and 50 W P_D rating support compact heatsink designs while maintaining <125°C junction temperature under full-load, 40°C ambient conditions.

Electronic Ballasts

AC-DC Flyback Converters

Use Scenario: High-frequency (20–60 kHz) resonant lamp ignition and regulation in compact fluorescent lamps (CFLs) and LED drivers.

IC Role / Device Role / Timing Role: Primary-side power switch controlling energy transfer into resonant tank; operates in hard-switched mode with zero-voltage switching assistance.

Use Value: Low V_CE(sat) and fast t_off reduce conduction and switching losses, improving ballast efficiency >85% while maintaining thermal stability at 125°C case temperature.

Use Scenario: Primary-side switching element in universal-input (85–265 V AC) offline flyback converters for consumer adapters and industrial power modules.

IC Role / Device Role / Timing Role: Main power switch in discontinuous conduction mode (DCM) flyback; handles peak currents up to 5.0 A with 300 V clamp protection.

Use Value: Guaranteed RBSOA up to 300 V and 1.0 A enables reliable operation under transient overloads and short-circuit conditions without secondary protection circuitry.

Inductive Load Drivers

Switchmode Power Supply (SMPS) Front-End

Use Scenario: Driving inductive solenoids, relays, or magnetic actuators in industrial control panels requiring 220 V AC line isolation.

IC Role / Device Role / Timing Role: High-voltage interface between low-voltage logic controller and inductive load; absorbs back-EMF via clamping diode or RC snubber.

Use Value: Verified reverse-bias SOA (RBSOA) allows sustained simultaneous high voltage/current during turn-off, preventing second-breakdown failure during inductive kick.

Use Scenario: Main switching transistor in 40–100 W open-frame SMPS used in printers, monitors, and point-of-sale terminals.

IC Role / Device Role / Timing Role: Energy storage and transfer switch in single-transistor forward or flyback topology; rated for continuous 2.0 A DC and 5.0 A pulse operation.

Use Value: 2.5 °C/W R_JC and 50 W P_D rating support compact heatsink designs while maintaining <125°C junction temperature under full-load, 40°C ambient conditions.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MJE13005	V_CEO = 400 V, I_C = 4.0 A, but f_T = 4 MHz and no 125°C SOA validation; higher I_C but slower switching and less thermal margin.	More suitable for lower-frequency (<30 kHz), higher-current linear-regulated supplies than high-efficiency CFL ballasts.	Select MJE13005 only when peak current exceeds 2.0 A and switching frequency remains below 25 kHz.
BU2508DF	V_CEO = 800 V, I_C = 8.0 A, TO-220F package with insulated tab; higher voltage/current but larger footprint and higher V_CE(sat) (0.8 V typical).	Better suited for 380 V DC bus or three-phase rectified inputs where 700 V V_CES headroom is insufficient.	Choose BU2508DF only when system requires >600 V blocking capability or >4 A average current, accepting higher conduction loss and board space.

Compared with MJE13005 and BU2508DF, the BUL44 offers superior combination of 125°C-rated SOA, low dynamic saturation voltage, and optimized 20–100 kHz switching performance-making it the preferred choice for thermally constrained, high-efficiency 220 V line-operated ballasts and SMPS where reliability at elevated temperature is mandatory.

Availability

BUL44 is available at Aetrix Electronics and suitable for electronic ballasts, AC-DC flyback converters, and industrial inductive load drivers requiring stable component supply, long-term lifecycle continuity, and traceable sourcing for production programs.

Supply support for BUL44 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 specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and IoT applications.

The BUL44 belongs to onsemi's SWITCHMODE™ family of high-voltage bipolar transistors, engineered specifically for reliability and efficiency in 220 V line-operated switchmode power supplies and electronic lighting ballasts.

FAQ

What is the maximum junction temperature rating for the BUL44?

The BUL44 has a specified operating junction temperature range of −65°C to +150°C. Its electrical characteristics-including V_CE(sat), h_FE, and switching times-are fully characterized at 125°C, ensuring predictable performance under sustained industrial thermal conditions. The BUL44 must be mounted to a heatsink with sufficient thermal mass to maintain T_J ≤ 150°C under worst-case load and ambient conditions.

Does the BUL44 require a base coil for turn-off?

No, the BUL44 does not require a base coil for turn-off. Its die design eliminates current tail during switching transitions, enabling clean, fast turn-off using standard resistor-based or active base drive circuits. This feature reduces component count and improves reliability compared to legacy bipolar transistors that rely on base coils to force rapid carrier removal.

What is the safe operating area (SOA) limit for inductive loads with the BUL44?

The BUL44's reverse-bias safe operating area (RBSOA) is validated for clamped inductive switching up to 300 V and 1.0 A at T_C = 25°C, with derating applied above that temperature. Figure 16 in the official BUL44/D datasheet defines the exact V_CE–I_C boundary under clamped conditions, which must be respected to avoid second breakdown during turn-off of inductive loads like ballast transformers or solenoids.

Is the BUL44 pin-compatible with other TO-220AB NPN transistors?

The BUL44 uses standard TO-220AB pinout (Base–Collector–Emitter–Collector), matching mechanical and electrical layout of industry-standard NPN power transistors in the same package. However, electrical parameters-including V_CES, h_FE profile, and SOA-are unique to the BUL44 die. Direct substitution requires verification of switching speed, saturation voltage, and thermal limits in the target application.

What does the "G" suffix in BUL44G indicate?

The "G" suffix in BUL44G denotes a Pb-free, RoHS-compliant version of the BUL44, manufactured using lead-free terminations and packaging materials. It meets JEDEC J-STD-020 moisture sensitivity level (MSL) requirements and supports lead-free reflow soldering profiles with peak temperature up to 260°C for 5 seconds, as confirmed in the official onsemi BUL44/D datasheet.

BUL44 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: SWITCHMODE™

Package/Case:: TO-220-3

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 2 A

Voltage - Collector Emitter Breakdown (Max):: 400 V

Vce Saturation (Max) @ Ib, Ic:: 600mV @ 200mA, 1A

Current - Collector Cutoff (Max):: 100µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 14 @ 200mA, 5V

Power - Max:: 50 W

Frequency - Transition:: 13MHz

Operating Temperature:: -65°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

BUL44 FAQ

1.How can I place an order for BUL44 through Aetrix?

Please submit a Request for Quotation (RFQ) for BUL44 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 BUL44 reliable?

The price and inventory of BUL44 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUL44 is usually 5 days.

3.What payment methods are accepted for BUL44?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUL44 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUL44?

BUL44 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUL44 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 BUL44?

For technical support, including BUL44 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUL44 requirements.

6.How does Aetrix verify that BUL44 is sourced from the original manufacturer or authorized distributors?

All BUL44 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 BUL44 meets industry standards.

7.What is the process for return or replacement of BUL44?

All BUL44 units undergo pre-shipment inspection (PSI). If there is an issue with BUL44, 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 BUL44 part is unused and in its original packaging.

Return procedure for BUL44:

1.Submit a request within 90 days.

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

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