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

STMicroelectronics BUL741

Name: BUL741
Brand: STMicroelectronics
SKU: BUL741
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUL741

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BUL741.pdf

Description:: TRANS NPN 400V 2.5A TO-220

Quantity:: RFQ Add To RFQ list

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Inventory:1,210

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Product details

Overview

BUL741 from STMicroelectronics is a high-voltage fast-switching NPN power transistor in TO-220 package, rated for 1050 V V_CES, 2.5 A continuous collector current, and 60 W total dissipation at T_c = 25 °C. It delivers very high switching speed (t_s = 2.5–3.5 µs, t_f = 350–500 ns) and intrinsic ruggedness enabling 5 mJ repetitive avalanche energy without external Transil protection - used in electronic ballasts for fluorescent lighting and switch-mode power supplies.

For engineers reviewing the BUL741 datasheet, BUL741 pinout, BUL741 application, or BUL741 equivalent, key selection criteria include V_CES = 1050 V, I_C = 2.5 A, t_s/t_f timing performance, R_thJC = 2.08 °C/W, and avalanche energy rating - critical for reliable operation in high-voltage flyback and resonant lamp-ballast topologies.

Technical Context

The BUL741 employs high-voltage multi-epitaxial planar technology to achieve both high breakdown voltage and fast switching. Its extended intermediate layer enhances intrinsic ruggedness, allowing safe operation under high-current breakdown conditions without external clamping diodes.

It operates with DC current gain h_FE = 48–100 (at I_C = 0.1–0.45 A), V_CE(sat) = 0.15–1.5 V across load range, and supports resistive-load switching with defined storage/fall times under controlled IB(on)/IB(off) drive conditions.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	1050 V - enables direct use in 800 V DC bus applications without series stacking
I_C (continuous)	2.5 A - supports lamp-ballast output stages up to ~100 W with thermal margin
t_s / t_f	2.5–3.5 µs / 350–500 ns - reduces switching losses in 20–100 kHz SMPS and ballast circuits
E_AR	5 mJ (repetitive avalanche) - eliminates need for external Transil in standard flyback snubbers
R_thJC	2.08 °C/W - allows 60 W dissipation with ≤125 °C case-to-junction rise at 25 °C ambient
h_FE	48–100 - provides stable base drive design margin across production lots and temperature
V_CEO(sus)	400–450 V - defines minimum sustaining voltage under transient overvoltage conditions

Pinout & Package

Package: TO-220 (3-lead, straight lead, insulated tab). Pin assignment verified per Figure 1 and mechanical data in ST Doc ID 13406 Rev 3.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current sink terminal	Low-impedance return path; connected to ground or low-side reference in boost/flyback
2 (Collector)	High-voltage output node	Connected to primary winding of lamp-ballast transformer or SMPS inductor
3 (Base)	Control input	Receives TTL/CMOS-compatible drive; requires 0.14–0.6 A peak for full saturation

Key Features

Feature	Design Value
High-voltage capability	V_CES = 1050 V enables single-transistor designs for universal-input offline converters
Very high switching speed	t_s ≤ 3.5 µs and t_f ≤ 500 ns reduce turn-off losses in 50–100 kHz ballast drivers
Intrinsic ruggedness	Withstands 5 mJ repetitive avalanche without external protection - simplifies PCB layout and BOM
Low lot-to-lot parameter spread	Specified h_FE, V_CE(sat), and t_s/t_f variation ensures consistent drive design across manufacturing batches

Applications

Electronic Ballast for Fluorescent Lamps

Switch-Mode Power Supply (SMPS)

Use Scenario: Driving resonant LC tank in instant-start electronic ballast for T8/T5 lamps at 20–60 kHz.

IC Role / Device Role / Timing Role: Main switching transistor handling 400–1000 V DC link and delivering pulsed current to lamp filaments.

Use Value: Intrinsic avalanche ruggedness eliminates Transil clamp, reducing component count and improving reliability under lamp-strike transients.

Use Scenario: Primary-side switch in 30–60 W flyback converter for industrial control power rails.

IC Role / Device Role / Timing Role: High-voltage NPN switch operating in discontinuous conduction mode with fixed-frequency PWM.

Use Value: 1050 V V_CES accommodates reflected voltage spikes and line surges without derating or stacking.

DC-DC Converter for LED Drivers

Inductive Load Switching in Industrial Controls

Use Scenario: Constant-current switching stage in isolated LED driver for streetlight applications.

IC Role / Device Role / Timing Role: High-voltage switch controlling primary current in forward or flyback topology feeding constant-current secondary.

Use Value: 2.5 A I_C and 60 W P_tot support >50 W LED loads with conservative thermal design using TO-220 heatsink.

Use Scenario: Solenoid or relay driver in programmable logic controller (PLC) output module.

IC Role / Device Role / Timing Role: Robust NPN switch handling inductive kickback from 24–48 V DC coils with fast turn-off.

Use Value: 5 mJ repetitive avalanche energy absorbs coil energy without snubber network, reducing board space and cost.

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_CES = 1500 V, I_C = 12 A, slower switching (t_f ≈ 1 µs), higher P_tot = 125 W	Higher voltage/current headroom but larger footprint and greater drive requirement	Preferred where surge immunity >1200 V is required and board space permits TO-3P
ST13007	V_CES = 400 V, I_C = 8 A, faster t_f = 300 ns, lower V_CES limits to <300 V DC bus	Suitable only for low-line or DC-fed SMPS; not usable in universal AC-input ballasts	Select when operating below 350 V and prioritizing switching efficiency over voltage margin

Compared with BU508A and ST13007, BUL741 uniquely balances 1050 V capability, 2.5 A rating, and sub-microsecond switching - making it optimal for compact, cost-sensitive fluorescent ballasts and mid-power flyback supplies where V_CES margin and avalanche robustness are decisive.

Availability

BUL741 is available at Aetrix Electronics and suitable for electronic ballasts, switch-mode power supplies, LED drivers, and industrial solenoid controls requiring stable component supply and long-term manufacturability.

Supply support for BUL741 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The BUL741 belongs to ST's high-voltage bipolar power transistor product line, engineered specifically for energy-efficient, rugged switching in lighting and offline power conversion systems.

FAQ

What is the maximum safe operating voltage for BUL741 in continuous conduction?

The absolute maximum collector-emitter voltage with base open (V_CEO) is 400 V, but the device is rated for 1050 V under V_BE = 0 condition (V_CES). For continuous conduction, V_CEO = 400 V defines the safe DC blocking limit unless actively clamped or snubbed during transients.

Can BUL741 replace BU2508AX in a fluorescent ballast design?

No - BU2508AX has V_CES = 1500 V and different gain/saturation characteristics. BUL741 offers lower voltage rating (1050 V) and distinct switching timing; substitution requires revalidation of avalanche margin, drive strength, and thermal performance in the specific circuit.

Is BUL741 RoHS-compliant and halogen-free?

Yes - per ST Doc ID 13406 Rev 3, BUL741 is offered in ECOPACK®-compliant TO-220 packages meeting RoHS Directive 2011/65/EU and halogen-free requirements as defined in ST's ECOPACK® specifications.

Does BUL741 require a heatsink in typical ballast operation?

Yes - with P_tot = 60 W at T_c = 25 °C and R_thJC = 2.08 °C/W, even moderate power dissipation (>5 W) exceeds junction temperature limits without heatsinking. A minimum 15 cm² aluminum heatsink is recommended for continuous 2.5 A operation at ambient >40 °C.

BUL741 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-220-3

Packaging:: Tube

Product Status:: Active

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 2.5 A

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

Vce Saturation (Max) @ Ib, Ic:: 1.5V @ 600mA, 2A

Current - Collector Cutoff (Max):: 250µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 25 @ 450mA, 3V

Power - Max:: 60 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

BUL741 FAQ

1.How can I place an order for BUL741 through Aetrix?

Please submit a Request for Quotation (RFQ) for BUL741 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 BUL741 reliable?

The price and inventory of BUL741 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUL741 is usually 5 days.

3.What payment methods are accepted for BUL741?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUL741 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUL741?

BUL741 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUL741 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 BUL741?

For technical support, including BUL741 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUL741 requirements.

6.How does Aetrix verify that BUL741 is sourced from the original manufacturer or authorized distributors?

All BUL741 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 BUL741 meets industry standards.

7.What is the process for return or replacement of BUL741?

All BUL741 units undergo pre-shipment inspection (PSI). If there is an issue with BUL741, 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 BUL741 part is unused and in its original packaging.

Return procedure for BUL741:

1.Submit a request within 90 days.

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

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