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

STMicroelectronics BULD741-1

Name: BULD741-1
Brand: STMicroelectronics
SKU: BULD741-1
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BULD741-1

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-251-3 Short Leads, IPAK, TO-251AA

Datasheet:: BULD741-1.pdf

Description:: TRANS NPN 400V 2.5A IPAK

Quantity:: RFQ Add To RFQ list

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Inventory:5,545

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Product details

Overview

BULD741-1 from STMicroelectronics is a high-voltage fast-switching NPN power transistor in DPAK (TO-252) package, rated for V_CEO = 400 V, I_C = 2.5 A, and P_TOT = 30 W at T_C = 25 °C. It delivers V_CE(sat) ≤ 0.5 V at I_C = 2 A / I_B = 0.6 A and t_f = 350–500 ns, enabling reliable operation in electronic ballasts and SMPS with high repetitive avalanche energy (E_AR = 5 mJ).

For engineers reviewing the BULD741-1 datasheet, BULD741-1 pinout, BULD741-1 application, or BULD741-1 equivalent, key selection criteria include V_CEO ≥ 400 V, t_f < 500 ns, R_thJC ≤ 4.16 °C/W, and ruggedness under unclamped inductive switching-critical for lamp ballast converters without external Transil protection.

Technical Context

This device uses high-voltage multi-epitaxial planar technology with an enhanced intermediate layer to improve intrinsic ruggedness and withstand high collector current during breakdown. Its design eliminates the need for external Transil clamping in typical lamp ballast converters.

It supports pulsed operation (duty cycle ≤1.5%, pulse width = 300 µs) and exhibits low dynamic parameter spread across lots. The transistor maintains V_CEO(sus) ≥ 400 V at I_C = 10 mA and delivers h_FE = 25–50 at I_C = 0.45 A / V_CE = 3 V, optimized for resistive-load switching with t_s = 2.5–3.5 µs and V_BE(sat) = 1.1–1.5 V.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	400 V - Sustains full-rated collector-emitter voltage with zero base current, enabling direct use in 400 V bus SMPS stages.
I_C	2.5 A continuous - Supports sustained output current in compact ballast drivers without thermal derating at T_C = 25 °C.
R_thJC	4.16 °C/W - Enables efficient heat transfer from junction to case, critical for surface-mount thermal management on PCBs.
t_f	350–500 ns - Ensures rapid turn-off in high-frequency switching (e.g., >30 kHz fluorescent ballasts), minimizing switching losses.
E_AR	5 mJ - Withstands repetitive unclamped inductive energy events (L = 2 mH, C = 1.8 nF), eliminating need for external snubbers or Transils.
V_CE(sat)	0.5–1.5 V at I_C = 2 A - Low saturation voltage reduces conduction loss and improves efficiency in high-current switching nodes.

Pinout & Package

DPAK (TO-252) type C package with exposed drain-connected tab (pin 2), standard three-terminal configuration: emitter (pin 1), base (pin 3), collector (tab/pin 2). Mounting requires soldering the tab to a large copper pour for thermal and electrical connection.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1	Emitter	Low-impedance current return path; referenced to ground in common-emitter configurations.
Pin 2 (Tab)	Collector	Exposed metal tab electrically connected to collector; must be thermally and electrically tied to heatsink or PCB copper.
Pin 3	Base	Current-controlled input node; requires precise drive (I_B = 0.6 A typical for I_C = 2 A) to ensure saturation.

Key Features

Feature	Design Value
Intrinsic ruggedness	Withstands high I_C during V_CE breakdown without external protection-enables simplified, cost-optimized ballast designs.
Low lot-to-lot parameter spread	Ensures consistent t_s, t_f, and h_FE across production batches-critical for volume-manufactured lighting systems.
High V_CEO(sus)	400–450 V sustaining voltage at I_C = 10 mA-guarantees stable blocking behavior under transient overvoltage conditions.
Fast switching speed	t_s = 2.5–3.5 µs and t_f = 350–500 ns-supports >30 kHz operation while maintaining low E_SW.

Applications

Fluorescent Lamp Ballast

AC-DC SMPS Primary Switch

Use Scenario: High-frequency resonant driver for T5/T8 fluorescent tubes operating at 25–65 kHz.

IC Role / Device Role / Timing Role: Main switching transistor in half-bridge topology, handling 400 V DC bus and delivering 0.7–2 A load current.

Use Value: Eliminates external Transil due to intrinsic avalanche ruggedness (E_AR = 5 mJ), reducing BOM count and board space.

Use Scenario: Primary-side switch in offline flyback or forward converters for industrial power supplies.

IC Role / Device Role / Timing Role: High-voltage NPN switch controlling energy transfer from 375 V rectified AC line to transformer primary.

Use Value: V_CEO = 400 V and R_thJC = 4.16 °C/W enable robust operation at 85–265 V_AC input with minimal heatsinking.

Inductive Load Driver

UV-C Disinfection Power Stage

Use Scenario: Driving high-inductance magnetic components (e.g., solenoids, relays) in factory automation controllers.

IC Role / Device Role / Timing Role: Unclamped inductive switch managing 200–400 V flyback transients with repetitive energy dissipation.

Use Value: Verified 5 mJ repetitive avalanche rating allows safe operation without snubber networks or clamping diodes.

Use Scenario: Power stage for pulsed UV-C LED drivers requiring high-voltage, short-duration current bursts.

IC Role / Device Role / Timing Role: Fast-turning NPN switch delivering 2 A pulses at 100–500 kHz into capacitive-resistive loads.

Use Value: t_f ≤ 500 ns and V_CE(sat) ≤ 0.5 V minimize switching loss and thermal stress during high-duty-cycle pulsing.

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
STN9360	V_CEO = 600 V, I_C = 2 A, t_f = 200 ns, R_thJC = 5.5 °C/W	Higher voltage margin but lower current and slower thermal response	Preferred where 600 V bus tolerance is required, but less suitable for 2.5 A continuous conduction.
BU508A	V_CEO = 1500 V, I_C = 8 A, t_f = 1.2 µs, TO-220 package	Higher voltage/current but significantly slower and through-hole mounted	Used in legacy linear ballasts; not drop-in due to package and speed mismatch.

Compared with STN9360 and BU508A, BULD741-1 uniquely balances 400 V blocking, 2.5 A current, sub-500 ns fall time, and DPAK thermal performance-making it optimal for modern compact, high-frequency fluorescent and SMPS designs where board space and thermal density matter.

Availability

BULD741-1 is available at Aetrix Electronics and suitable for electronic ballasts, AC-DC switch-mode power supplies, and inductive load drivers requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for BULD741-1 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, Switzerland, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

BULD741-1 belongs to ST's high-voltage bipolar power transistor product line, engineered specifically for rugged, high-frequency switching in lighting and power conversion where reliability under unclamped inductive stress is mandatory.

FAQ

What is the maximum allowable junction temperature for BULD741-1?

The absolute maximum operating junction temperature (T_J) is 150 °C, as specified in Table 1 of DS5049. Operation beyond this limit risks permanent degradation of h_FE, increased leakage, and reduced avalanche endurance. Thermal design must ensure T_J remains below 150 °C under worst-case ambient and power dissipation conditions.

Does BULD741-1 require a Transil or TVS for safe operation in ballast circuits?

No-BULD741-1 is specifically designed with intrinsic ruggedness to withstand high collector current during breakdown without external Transil protection. Its 5 mJ repetitive avalanche energy rating (E_AR) and enhanced intermediate layer eliminate the need for clamping devices in properly designed lamp ballast converters.

Can BULD741-1 be used in place of BULD741T4?

No-BULD741-1 is an obsolete order code explicitly removed in DS5049 Rev 3 (July 2022). BULD741T4 is the current production version with updated DPAK type C mechanical data and packaging specifications. BULD741-1 is no longer manufactured or supported by STMicroelectronics.

What is the recommended PCB footprint for the DPAK (TO-252) type C package?

The recommended footprint is defined in Figure 16 of DS5049 Rev 3, specifying pad dimensions including 5.15–5.65 mm (E1), 6.00–6.20 mm (D), and 4.70–5.00 mm (E), with thermal relief vias under the tab. Minimum copper area for the collector tab should exceed 200 mm² for optimal R_thJC performance.

BULD741-1 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-251-3 Short Leads, IPAK, TO-251AA

Packaging:: Tube

Product Status:: Obsolete

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:: 30 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: IPAK

BULD741-1 FAQ

1.How can I place an order for BULD741-1 through Aetrix?

Please submit a Request for Quotation (RFQ) for BULD741-1 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 BULD741-1 reliable?

The price and inventory of BULD741-1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BULD741-1 is usually 5 days.

3.What payment methods are accepted for BULD741-1?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BULD741-1 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BULD741-1?

BULD741-1 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BULD741-1 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 BULD741-1?

For technical support, including BULD741-1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BULD741-1 requirements.

6.How does Aetrix verify that BULD741-1 is sourced from the original manufacturer or authorized distributors?

All BULD741-1 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 BULD741-1 meets industry standards.

7.What is the process for return or replacement of BULD741-1?

All BULD741-1 units undergo pre-shipment inspection (PSI). If there is an issue with BULD741-1, 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 BULD741-1 part is unused and in its original packaging.

Return procedure for BULD741-1:

1.Submit a request within 90 days.

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

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