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

STMicroelectronics BULK128

Name: BULK128
Brand: STMicroelectronics
SKU: BULK128
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BULK128

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: SOT-82

Datasheet:: BULK128.pdf

Description:: TRANS NPN 400V 4A SOT-82-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BULK128 from STMicroelectronics is a high-voltage fast-switching NPN power transistor in SOT-82 package, rated for V_CEO = 400 V, I_C = 4 A, and P_tot = 55 W at T_c = 25°C. It features cellular emitter structure with planar edge termination, enabling high switching speed (t_s = 0.6–1 µs, t_f = 0.1–0.4 µs) while maintaining wide RBSOA - optimized for electronic ballasts in fluorescent lighting systems.

For engineers reviewing the BULK128 datasheet, BULK128 pinout, BULK128 application, or BULK128 equivalent, key selection criteria include its 400 V sustaining voltage under inductive switching, 2.27 °C/W junction-to-case thermal resistance, and validated performance in low-cost SMPS and lamp ignition circuits requiring robust safe operating area and fast turn-off.

Technical Context

The BULK128 employs high-voltage multi-epitaxial planar technology to achieve simultaneous high breakdown voltage and fast switching. Its cellular emitter layout and planar edge termination suppress secondary breakdown and improve dynamic ruggedness.

It operates with DC current gain h_FE = 10–28 (I_C = 10 mA to 2 A, V_CE = 5 V), collector-emitter saturation voltage V_CE(sat) = 0.5–1.5 V across 0.5–4 A, and base-emitter saturation voltage V_BE(sat) = 1.1–1.3 V - supporting efficient drive in hard-switched topologies.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	400 V - Sustaining voltage with open base; defines maximum off-state blocking capability in lamp ballast and SMPS switch applications.
I_C	4 A continuous - Rated collector current at T_c = 25°C; supports 25–30 W fluorescent lamp drivers and sub-100 W flyback converters.
P_tot	55 W at T_c = 25°C - Total dissipation limit; requires heatsinking per R_thj-case = 2.27 °C/W for thermal management.
t_s/t_f (inductive)	0.6/0.1 µs typical - Storage/fall time under V_clamp = 200 V, enabling <100 kHz operation with low switching loss.
R_thj-case	2.27 °C/W - Junction-to-case thermal resistance; determines minimum heatsink size needed to maintain T_J ≤ 150°C.
h_FE	10–28 - DC current gain range across I_C = 10 mA to 2 A; enables stable base drive design without excessive overdrive.

Pinout & Package

SOT-82 is a 3-pin, single-ended, through-hole power package with integrated mounting flange. It provides low-inductance emitter connection and mechanical stability for high-current switching in compact ballast PCB layouts.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Emitter terminal	Low-inductance, flange-connected output node; primary current return path with direct thermal path to heatsink.
2 (Base)	Control input	Direct-drive base terminal; accepts 0.1–1 A peak base current for full saturation across operating range.
3 (Collector)	High-voltage switch node	Main power switching terminal; rated for 400 V blocking and 8 A pulsed current (t_P < 5 ms).

Key Features

Feature	Design Value
Cellular emitter structure	Enhances current uniformity and suppresses localized hot-spot formation during fast switching transients.
Planar edge termination	Improves voltage distribution at die periphery, extending RBSOA and enabling reliable 400 V inductive switching.
Wide RBSOA	Validated safe operating area up to 400 V × 4 A with 10 ms pulse width - critical for lamp ignition surge tolerance.
ECOPACK® compliance	Lead-free second-level interconnect meeting JEDEC JESD97; supports RoHS-compliant manufacturing and reflow profiles.

Applications

Fluorescent Lamp Ballast

Low-Cost SMPS

Use Scenario: High-frequency electronic ballast driving 36–40 W T8/T12 lamps with instant start and dimming support.

IC Role / Device Role / Timing Role: Main switching transistor in half-bridge resonant inverter stage; handles 25–65 kHz switching with 400 V clamp.

Use Value: Fast storage/fall times minimize switching loss during zero-voltage switching transitions, improving efficiency >85%.

Use Scenario: Primary-side switch in 20–60 W offline flyback converters for consumer adapters and industrial auxiliary supplies.

IC Role / Device Role / Timing Role: Hard-switched NPN power switch; operated with base drive circuit providing 0.2–1 A peak current.

Use Value: 2.27 °C/W R_thj-case allows compact heatsink integration, reducing board space vs. TO-220 alternatives.

Lamp Ignition Circuit

DC-DC Boost Converter

Use Scenario: High-voltage pulse generator for preheating and striking fluorescent tubes using resonant LC tank.

IC Role / Device Role / Timing Role: Switch controlling energy transfer into resonant capacitor; subjected to repetitive 400 V, 2–4 A pulses.

Use Value: Wide RBSOA and 150°C max junction temperature ensure reliability during repeated cold-start surges.

Use Scenario: Step-up converter in 12 V input → 48 V output LED driver for signage and architectural lighting.

IC Role / Device Role / Timing Role: Medium-voltage boost switch handling 400 V transient spikes during MOSFET body-diode recovery.

Use Value: V_CEO(sus) = 400 V sustains clamped inductive kickback without avalanche stress or degradation.

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
BU2508AX	V_CEO = 800 V, I_C = 8 A, slower t_s/t_f (3/0.5 µs), TO-220FP package	Higher voltage margin but larger footprint and higher drive requirement	Preferred where 800 V blocking is mandatory and board space permits TO-220
BDW93C	V_CEO = 100 V, I_C = 12 A, faster t_f (0.15 µs), same SOT-82 package	Lower voltage rating limits use to ≤100 V SMPS; unsuitable for ballast	Select only for low-voltage, high-current linear or switching regulators where V_CEO < 120 V suffices

Compared with BU2508AX and BDW93C, BULK128 uniquely balances 400 V blocking, SOT-82 compactness, and sub-microsecond switching - making it optimal for cost-sensitive, space-constrained fluorescent ballasts where 400 V is the design ceiling.

Availability

BULK128 is available at Aetrix Electronics and suitable for fluorescent lighting ballasts, low-cost switch-mode power supplies, and lamp ignition circuits requiring stable component supply despite its obsolete status - supported via legacy inventory and cross-qualified replacements.

Supply support for BULK128 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, digital, and mixed-signal ICs and discrete devices for industrial, automotive, and consumer markets.

BULK128 belongs to ST's high-voltage bipolar power transistor product line, engineered specifically for lighting control and medium-power switching applications demanding ruggedness, thermal efficiency, and cost-effective through-hole packaging.

FAQ

Is BULK128 still in active production?

No - STMicroelectronics has marked BULK128 as obsolete (as confirmed in Rev 2, June 2008 datasheet). However, Aetrix Electronics maintains legacy stock and supports design continuity through verified cross-references and technical documentation for existing builds.

What is the maximum safe operating frequency for BULK128 in a fluorescent ballast?

Based on measured t_s + t_f ≤ 1.2 µs (inductive load), BULK128 supports reliable operation up to 65 kHz in resonant half-bridge ballasts. Above this, switching losses rise significantly due to finite storage time and reduced duty-cycle margin.

Can BULK128 replace BU2508AX in a 400 V design?

Yes - BULK128 matches BU2508AX's 400 V V_CEO rating and offers superior switching speed and smaller SOT-82 footprint. However, BU2508AX's higher 8 A I_CM and 800 V V_CES make it unsuitable as a drop-in replacement where those margins are actively used.

Does BULK128 require a heatsink in 4 A continuous operation?

Yes - at I_C = 4 A and V_CE(sat) ≈ 1.5 V, conduction loss is ~6 W. With R_thj-case = 2.27 °C/W, even minimal case-to-ambient resistance exceeds thermal limits. A minimum 15 cm² aluminum heatsink is required to hold T_J ≤ 130°C at 25°C ambient.

BULK128 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: SOT-82

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:: 500mV @ 1A, 4A

Current - Collector Cutoff (Max):: 250µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 14 @ 2A, 5V

Power - Max:: 55 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: SOT-82-3

BULK128 FAQ

1.How can I place an order for BULK128 through Aetrix?

Please submit a Request for Quotation (RFQ) for BULK128 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 BULK128 reliable?

The price and inventory of BULK128 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BULK128 is usually 5 days.

3.What payment methods are accepted for BULK128?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BULK128 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BULK128?

BULK128 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BULK128 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 BULK128?

For technical support, including BULK128 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BULK128 requirements.

6.How does Aetrix verify that BULK128 is sourced from the original manufacturer or authorized distributors?

All BULK128 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 BULK128 meets industry standards.

7.What is the process for return or replacement of BULK128?

All BULK128 units undergo pre-shipment inspection (PSI). If there is an issue with BULK128, 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 BULK128 part is unused and in its original packaging.

Return procedure for BULK128:

1.Submit a request within 90 days.

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

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