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

STMicroelectronics BULD742CT4

Name: BULD742CT4
Brand: STMicroelectronics
SKU: BULD742CT4
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BULD742CT4

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-252-3, DPAK (2 Leads + Tab), SC-63

Datasheet:: BULD742CT4.pdf

Description:: TRANS NPN 400V 4A DPAK

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BULD742CT4 from STMicroelectronics is a high-voltage fast-switching NPN power transistor in DPAK package, rated for V_CEO = 400 V, I_C = 4 A continuous, P_tot = 45 W at T_c = 25°C, with t_s = 2.4–3.5 µs and t_f = 350–500 ns. It enables rugged operation in electronic ballasts and switch-mode power supplies without external Transil protection due to intrinsic breakdown robustness.

For engineers reviewing the BULD742CT4 datasheet, BULD742CT4 pinout, BULD742CT4 application, or BULD742CT4 equivalent, key selection criteria include V_CES = 1050 V capability, R_thj-case = 2.78 °C/W thermal resistance, V_CE(sat) ≤ 0.6 V at I_C = 3.5 A, h_FE = 25–50 at I_C = 0.8 A, and E_AR = 6 mJ repetitive avalanche energy under defined test conditions.

Technical Context

This device uses ST's high-voltage Multi-Epitaxial Planar process to achieve both high breakdown voltage (V_CES = 1050 V) and fast switching (t_s/t_f < 4 µs/500 ns). Its extended intermediate layer provides inherent ruggedness during overvoltage transients, eliminating need for external clamping diodes in lamp-ballast converters.

It operates with DC current gain h_FE of 48–100 at low I_C, dropping to 25–50 at 0.8 A, and maintains V_CE(sat) ≤ 1.5 V up to I_C = 3.5 A with I_B = 1 A - enabling efficient hard-switched topologies in 400 V-class SMPS and ballast drivers.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	1050 V - supports primary-side switching in offline 400 V AC-input SMPS without derating
I_C (continuous)	4 A - sustains full-load current in 150–200 W electronic ballasts and auxiliary SMPS stages
R_thj-case	2.78 °C/W - enables 45 W dissipation with ≤125°C junction rise above 25°C case temperature
t_s/t_f	2.4–3.5 µs / 350–500 ns - ensures clean turn-off in 20–50 kHz resonant ballast and flyback converters
E_AR	6 mJ - withstands repetitive inductive switching surges in unclamped flyback or forward converters
V_CE(sat)	≤0.6 V @ I_C=3.5 A, I_B=1 A - limits conduction loss to <2.1 W at rated current
h_FE	25–50 @ I_C=0.8 A - supports stable base drive design with moderate gate driver current demand

Pinout & Package

Package: DPAK (TO-252), surface-mount, single-ended power transistor with exposed drain pad for thermal conduction. Dimensions per ST mechanical drawing: D = 6.0–6.2 mm, E = 6.4–6.6 mm, H = 9.35–10.1 mm, L = 1.0 mm, e1 = 4.4–4.6 mm.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Emitter terminal	Low-impedance return path; connected directly to PCB ground plane for minimal loop inductance
2 (Base)	Control input	Receives current-driven signal; requires 1 A peak for full saturation at 3.5 A collector load
3 (Collector)	High-voltage output	Connected to primary winding or bus rail; handles 1050 V blocking and 8 A pulsed current

Key Features

Feature	Design Value
Intrinsic avalanche ruggedness	6 mJ repetitive energy rating without external snubbers or Transil diodes
Low dynamic parameter spread	Consistent t_s, t_f, and h_FE across production lots ensures predictable timing in mass-produced ballasts
High V_CES capability	1050 V rating allows direct use in 400 V AC rectified rails with margin for line surges
ECOPACK® lead-free packaging	DPAK meets JEDEC JESD97; RoHS-compliant second-level interconnect with marked environmental category

Applications

Electronic Ballast Control

SMPS Primary Switch

Use Scenario: High-frequency (20–65 kHz) resonant driver for T5/T8 fluorescent lamps with dimming and end-of-life detection.

IC Role / Device Role / Timing Role: Main switching transistor in half-bridge inverter stage; handles 400 V DC bus and 3.5 A peak load current.

Use Value: Eliminates need for external Transil clamping due to built-in avalanche energy handling (6 mJ), reducing BOM count and board space.

Use Scenario: Primary-side switch in 100–200 W offline flyback converter for industrial control power supplies.

IC Role / Device Role / Timing Role: Hard-switched NPN transistor operating at 50 kHz with 400 V blocking and 4 A continuous current.

Use Value: Low R_thj-case (2.78 °C/W) enables compact heatsinking; V_CE(sat) ≤ 0.6 V minimizes conduction loss at full load.

Inductive Load Driver

DC-DC Converter Stage

Use Scenario: High-side switch driving solenoids or relays in HVAC control modules with 300–400 V supply rails.

IC Role / Device Role / Timing Role: Rugged NPN switch sustaining 8 A pulsed collector current (t_P < 5 ms) and 1050 V off-state voltage.

Use Value: Withstands inductive kickback without external protection, simplifying circuit layout and improving reliability in harsh environments.

Use Scenario: Step-down switching element in isolated 48 V-to-12 V DC-DC converter for telecom shelf management.

IC Role / Device Role / Timing Role: Fast-switching NPN transistor in forward converter primary side, operating at 100 kHz with 400 V bus.

Use Value: Fast t_f (≤500 ns) reduces switching losses; h_FE stability across temperature supports consistent base drive design.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
STBULD742CT4	Tape-and-reel variant with identical electrical specs and DPAK package; same marking, different packaging code	No functional difference; intended for automated SMT placement vs. bulk handling	Select based on assembly line requirements, not performance or fit
BU508AF	Lower V_CES = 1000 V, higher I_C = 8 A, slower t_f = 1.2 µs, no specified E_AR	Suitable for higher-current but lower-frequency (<20 kHz) SMPS where avalanche robustness is less critical	Prefer BULD742CT4 when fast switching and guaranteed avalanche energy are required

Compared with STBULD742CT4 (identical die, different packaging), and BU508AF (higher current but slower, no avalanche rating), BULD742CT4 uniquely balances 1050 V blocking, sub-µs fall time, and 6 mJ repetitive avalanche energy - making it optimal for compact, high-reliability 20–50 kHz ballast and SMPS designs.

Availability

BULD742CT4 is available at Aetrix Electronics and suitable for electronic ballasts, switch-mode power supplies, and inductive load drivers requiring stable component supply, long-lifecycle support, and RoHS-compliant DPAK packaging.

Supply support for BULD742CT4 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.

BULD742CT4 belongs to ST's high-voltage bipolar power transistor product line, engineered specifically for rugged, high-frequency switching in lighting and power conversion systems where reliability under transient stress is critical.

FAQ

What is the maximum safe operating voltage for BULD742CT4 in continuous DC blocking?

The absolute maximum V_CES rating is 1050 V with V_BE = 0, verified per ST's datasheet Table 2. For reliable long-term operation, ST recommends limiting V_CE to ≤80% of V_CES (i.e., 840 V) under steady-state conditions, especially at elevated junction temperatures above 100°C.

Can BULD742CT4 replace BU2508DF in a 25 kHz electronic ballast design?

No - BU2508DF has V_CEO = 1500 V and different gain/saturation characteristics. BULD742CT4's V_CEO = 400 V and V_CES = 1050 V make it unsuitable as a drop-in replacement; its base drive and SOA differ significantly. Use only if circuit re-verification confirms safe operation within its 400 V sustained and 1050 V pulse limits.

Does BULD742CT4 require a heatsink in a 45 W dissipation scenario?

Yes - with R_thj-case = 2.78 °C/W, dissipating 45 W at T_c = 25°C raises junction temperature by 125°C, reaching 150°C (T_Jmax). To maintain margin, a heatsink must reduce case temperature or add forced airflow; typical designs use ≥10 cm² copper pour plus thermal vias or an external finned heatsink.

Is the DPAK package of BULD742CT4 compatible with standard TO-252 footprints?

Yes - BULD742CT4 uses industry-standard DPAK (TO-252) mechanical dimensions per ST's drawing: D = 6.0–6.2 mm, E = 6.4–6.6 mm, e1 = 4.4–4.6 mm. It mates with IPC-7351B "TO252_DPAK" land patterns and is compatible with standard SMT reflow profiles for lead-free assembly.

BULD742CT4 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-252-3, DPAK (2 Leads + Tab), SC-63

Packaging:: Tape & Reel (TR)

Product Status:: Active

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 4 A

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

Vce Saturation (Max) @ Ib, Ic:: 1.5V @ 1A, 3.5A

Current - Collector Cutoff (Max):: 250µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 25 @ 800mA, 3V

Power - Max:: 45 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: DPAK

BULD742CT4 FAQ

1.How can I place an order for BULD742CT4 through Aetrix?

Please submit a Request for Quotation (RFQ) for BULD742CT4 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 BULD742CT4 reliable?

The price and inventory of BULD742CT4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BULD742CT4 is usually 5 days.

3.What payment methods are accepted for BULD742CT4?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BULD742CT4 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BULD742CT4?

BULD742CT4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BULD742CT4 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 BULD742CT4?

For technical support, including BULD742CT4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BULD742CT4 requirements.

6.How does Aetrix verify that BULD742CT4 is sourced from the original manufacturer or authorized distributors?

All BULD742CT4 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 BULD742CT4 meets industry standards.

7.What is the process for return or replacement of BULD742CT4?

All BULD742CT4 units undergo pre-shipment inspection (PSI). If there is an issue with BULD742CT4, 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 BULD742CT4 part is unused and in its original packaging.

Return procedure for BULD742CT4:

1.Submit a request within 90 days.

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

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