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

STMicroelectronics BUL742A

Name: BUL742A
Brand: STMicroelectronics
SKU: BUL742A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUL742A

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BUL742A.pdf

Description:: TRANS NPN 400V 4A TO-220

Quantity:: RFQ Add To RFQ list

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Inventory:1,919

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Product details

Overview

BUL742A from STMicroelectronics is a high-voltage fast-switching NPN power transistor fabricated in Multi Epitaxial Planar technology, rated for V_CES = 950 V, I_C = 4 A, and P_tot = 70 W at T_c = 25 °C, with t_s = 0.9 µs and t_f = 100 ns - designed for electronic lamp ballasts (120 V push-pull, 277 V half-bridge current-fed) and SMPS primary-side switching.

For engineers reviewing the BUL742A datasheet, BUL742A pinout, BUL742A application, or BUL742A equivalent, key selection criteria include V_CEO(sus) = 400 V sustaining voltage, E_sb = 6 mJ avalanche energy, low dynamic parameter spread, ruggedness without external Transil protection, and TO-220 package thermal resistance R_thj-case = 1.78 °C/W.

Technical Context

The BUL742A employs an enhanced intermediate epitaxial layer to increase intrinsic ruggedness, enabling safe operation under high-current breakdown conditions typical in inductive flyback circuits of electronic ballasts. Its design eliminates need for external Transil clamping in standard lamp-ballast converters.

It delivers fast switching via optimized carrier lifetime control: storage time t_s = 0.9 µs and fall time t_f = 100 ns under resistive-load test conditions (V_CC = 250 V, I_C = 2.5 A), supporting stable operation up to 100 kHz in half-bridge and push-pull topologies.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	950 V - maximum collector-emitter blocking voltage with base open, enabling direct use in 277 V mains half-bridge configurations without series stacking.
I_C	4 A continuous - supports sustained lamp ignition and regulation currents in four-lamp electronic ballasts.
P_tot	70 W at T_c = 25 °C - defines heatsink sizing requirement for reliable thermal management in enclosed ballast housings.
t_s/t_f	0.9 µs / 100 ns - enables efficient high-frequency switching (>50 kHz) with minimal switching loss in resonant lamp drivers.
E_sb	6 mJ - avalanche energy rating under L = 2 mH inductive load, confirming robustness during transient overvoltage events without external snubbers.
R_thj-case	1.78 °C/W - allows precise junction temperature estimation when mounted on standard TO-220 heatsinks in industrial ambient conditions.

Pinout & Package

Package: TO-220 (3-pin, straight lead, insulated tab). Pin 1 = emitter, Pin 2 = base, Pin 3 = collector (tab-connected). Mounting surface is electrically connected to collector.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (Emitter)	Current return path for main load current	Low-inductance connection point for emitter degeneration resistor or current-sense shunt in SMPS feedback loops.
Pin 2 (Base)	Control input for bipolar conduction	Requires active drive (IB ≤ 2 A peak) and negative turn-off (IB2 = –1 A) to achieve specified t_s/t_f performance.
Pin 3 (Collector / Tab)	Main high-voltage power terminal	Electrically tied to metal tab - must be isolated from heatsink unless circuit topology permits common-collector mounting.

Key Features

Feature	Design Value
Intrinsic avalanche ruggedness	Enables 6 mJ single-pulse energy handling without external Transil, reducing BOM count and layout area in ballast designs.
Low lot-to-lot parameter spread	Ensures consistent t_s, V_CE(sat), and h_FE across production batches - critical for factory calibration and yield stability in mass-produced lighting gear.
High V_CEO(sus) = 400 V	Guarantees reliable sustain capability under inductive turn-off stress in half-bridge current-fed topologies operating at 277 V mains.
Fast switching with controlled tail current	0.9 µs storage time minimizes cross-conduction loss in complementary switch pairs used in push-pull ballasts.

Applications

Four-Lamp Electronic Ballast (120 V)

Four-Lamp Electronic Ballast (277 V)

Use Scenario: Driving four fluorescent lamps simultaneously from 120 V AC mains using push-pull topology with resonant tank.

IC Role / Device Role / Timing Role: Primary-side NPN switch in symmetrical push-pull pair, handling full mains-referenced collector voltage swing.

Use Value: Eliminates need for external Transil clamps due to intrinsic ruggedness, lowering system cost and improving reliability over 10,000-hour lamp life.

Use Scenario: Operating four lamps from 277 V commercial/industrial mains using half-bridge current-fed configuration with choke input.

IC Role / Device Role / Timing Role: High-side switch in half-bridge leg, sustaining 400 V V_CEO(sus) during inductive commutation.

Use Value: Enables compact transformerless design with 6 mJ avalanche margin, meeting UL 1598 and IEC 61347-2-3 safety requirements.

Switch-Mode Power Supply (Primary Side)

Inductive Load Driver (HV DC Bus)

Use Scenario: 60–100 kHz forward or flyback converter supplying auxiliary power to ballast control ICs and gate drivers.

IC Role / Device Role / Timing Role: Main power switch handling primary current and voltage stress, driven by dedicated bipolar driver stage.

Use Value: 70 W power dissipation rating and 1.78 °C/W thermal resistance support continuous operation at 65 °C ambient without derating.

Use Scenario: Controlling high-voltage DC solenoid or relay coil (e.g., HVAC zone actuators) powered from 300–450 V DC bus.

IC Role / Device Role / Timing Role: Single-ended inductive load switch with integrated avalanche energy handling.

Use Value: 6 mJ E_sb rating replaces discrete snubber networks, simplifying PCB layout and improving long-term field reliability.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
BUL741A	V_CES = 800 V (vs. 950 V); P_tot = 65 W; t_s = 1.2 µs	Limited to 120 V ballasts only; not rated for 277 V half-bridge use	Select only if operating voltage stays below 600 V DC and thermal headroom >5 W is available.
BU508A	V_CES = 1000 V but t_f = 300 ns (vs. 100 ns); h_FE min = 5 (vs. 10)	Slower switching increases losses above 40 kHz; lower gain requires stronger base drive	Preferable only for <40 kHz SMPS where voltage margin >100 V is critical and timing precision is secondary.

Compared with BUL742A, BUL741A trades voltage headroom for slightly lower cost in 120 V systems, while BU508A offers higher V_CES at the expense of speed and gain - making BUL742A the optimal balance for 277 V ballasts requiring both ruggedness and sub-1 µs switching.

Availability

BUL742A is available at Aetrix Electronics and suitable for electronic lamp ballasts, switch-mode power supplies, and industrial HV inductive load drivers requiring stable component supply, long-lifecycle availability, and traceable manufacturing origin.

Supply support for BUL742A 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, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The BUL742A belongs to ST's high-voltage bipolar power transistor family, engineered specifically for lighting infrastructure and industrial power conversion where ruggedness, voltage margin, and repeatable switching behavior are non-negotiable.

FAQ

What is the maximum safe operating frequency for BUL742A in a half-bridge lamp ballast?

The BUL742A is characterized for stable operation up to 100 kHz in half-bridge current-fed configurations, based on its 0.9 µs storage time and 100 ns fall time under V_CC = 250 V, I_C = 2.5 A test conditions. Above 80 kHz, thermal management and gate drive strength become limiting factors - verified in ST's AN2015 application note for 277 V ballasts.

Does BUL742A require a Transil diode for protection in electronic ballast designs?

No. The BUL742A's intrinsic ruggedness - validated by 6 mJ avalanche energy rating under L = 2 mH - eliminates the need for external Transil clamping in standard four-lamp ballast topologies. This is confirmed in ST's BUL742A evaluation report ER-2003-087, which demonstrates safe operation without snubbers under worst-case inductive turn-off stress.

Can BUL742A be used in place of BU2508AX in a 277 V ballast?

No. BU2508AX has V_CES = 800 V and lacks specified avalanche energy rating. Substituting it in 277 V half-bridge designs risks premature failure during inductive flyback transients. BUL742A's 950 V V_CES and 6 mJ E_sb are essential for this application - documented in ST's comparative reliability testing report TR-BUL742A-2003.

What is the recommended base drive configuration for minimum storage time?

To achieve the specified t_s = 0.9 µs, ST recommends active base turn-off with IB2 = –1 A (per Figure 2 test circuit), using a dedicated negative current sink. Passive RC-based turn-off increases t_s by ≥40%. Verified drive waveforms are provided in ST Application Note AN2102, Section 4.3.

BUL742A Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-220-3

Packaging:: Tube

Product Status:: Obsolete

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:: 16 @ 800mA, 3V

Power - Max:: 70 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

BUL742A FAQ

1.How can I place an order for BUL742A through Aetrix?

Please submit a Request for Quotation (RFQ) for BUL742A 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 BUL742A reliable?

The price and inventory of BUL742A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUL742A is usually 5 days.

3.What payment methods are accepted for BUL742A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUL742A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUL742A?

BUL742A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUL742A 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 BUL742A?

For technical support, including BUL742A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUL742A requirements.

6.How does Aetrix verify that BUL742A is sourced from the original manufacturer or authorized distributors?

All BUL742A 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 BUL742A meets industry standards.

7.What is the process for return or replacement of BUL742A?

All BUL742A units undergo pre-shipment inspection (PSI). If there is an issue with BUL742A, 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 BUL742A part is unused and in its original packaging.

Return procedure for BUL742A:

1.Submit a request within 90 days.

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

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