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

STMicroelectronics BULK128D-B

Name: BULK128D-B
Brand: STMicroelectronics
SKU: BULK128D-B
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BULK128D-B

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: SOT-82

Datasheet:: BULK128D-B.pdf

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

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Product details

Overview

BULK128D-B from STMicroelectronics is a high-voltage fast-switching NPN power transistor with integrated antiparallel collector-emitter diode, rated for V_CES = 700 V, I_C = 4 A, P_tot = 55 W at T_c = 25 °C, and optimized for electronic ballasts and low-power flyback/forward SMPS. It features very high switching speed (t_s = 0.6 µs, t_f = 0.1 µs under inductive load), low dynamic parameter spread, and cellular emitter planar technology for stable RBSOA.

For engineers reviewing the BULK128D-B datasheet, BULK128D-B pinout, BULK128D-B application, or BULK128D-B equivalent, key selection criteria include its 700 V blocking capability, integrated antiparallel diode enabling self-commutated operation in resonant lighting topologies, tight lot-to-lot dynamic parameter control, and SOT-82 package thermal performance (R_thj-case = 2.27 °C/W).

Technical Context

This device employs Multi Epitaxial Planar process with planar edge termination and cellular emitter geometry to simultaneously achieve high voltage ruggedness (V_CES = 700 V) and fast switching (inductive t_s/t_f = 0.6/0.1 µs). Its integrated antiparallel diode eliminates external freewheeling diode requirements in single-transistor resonant converters.

The transistor is characterized for reliable operation across wide temperature range (T_j = –65 to 150 °C) with minimal parameter drift: V_CE(sat) = 1.5 V @ I_C = 2.5 A/I_B = 0.5 A, h_FE = 8–40, and V_f = 2.5 V @ I_f = 2 A for the internal diode - all specified at T_case = 25 °C.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	700 V - Enables direct interface with 400 V DC bus in electronic ballasts without snubber networks.
I_C	4 A continuous - Supports up to ~100 W output in flyback converters with margin for transient peaks.
P_tot	55 W at T_c = 25 °C - Requires heatsinking for >15 W dissipation in ambient >50 °C environments.
t_s/t_f (inductive)	0.6 / 0.1 µs - Enables >100 kHz operation in resonant lamp drivers with minimal switching loss.
V_f (integrated diode)	2.5 V @ 2 A - Reduces component count and PCB area vs. discrete diode + transistor solutions.
R_thj-case	2.27 °C/W - Allows thermal design with standard TO-220-compatible heatsinks in SOT-82 footprint.
h_FE	8–40 @ I_C = 2 A - Supports fixed-bias or simple current-source drive in cost-sensitive lighting controls.

Pinout & Package

Package: SOT-82 (TO-220AB variant, 3-pin, insulated tab, vertical mounting). Dimensions per STMicroelectronics mechanical drawing P032A: D = 15.4–16.0 mm, B = 10.5–10.8 mm, A = 7.4–7.8 mm, e3 = 4.15–4.65 mm.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Main emitter terminal	Low-inductance connection point for return path; electrically isolated from heatsink via insulating washer.
2 (Collector)	Main collector terminal	High-current, high-voltage node; connected internally to antiparallel diode anode.
3 (Base)	Control input	Low-impedance gate drive interface requiring ±0.4 A peak for optimal switching speed.

Key Features

Feature	Design Value
Integrated antiparallel diode	Eliminates need for external freewheeling diode in half-bridge and resonant lamp driver topologies.
Cellular emitter structure	Improves current sharing uniformity and reduces localized heating during hard switching.
Planar edge termination	Enables stable 700 V blocking while maintaining wide RBSOA for safe single-pulse operation.
Low dynamic parameter spread	Ensures consistent turn-off timing and voltage overshoot across production lots in mass-produced ballasts.
High dV/dt immunity	Rated for >1000 V/µs (implied by V_CEO(sus) = 400 V with L = 25 mH test condition).

Applications

Electronic Ballasts

Flyback SMPS

Use Scenario: High-frequency AC lamp ignition and regulation in compact fluorescent lamps (CFLs) using resonant half-bridge topology.

IC Role / Device Role / Timing Role: Main switching element providing zero-voltage switching (ZVS) commutation via integrated diode and fast t_s/t_f.

Use Value: Enables >50,000-hour lamp life by minimizing voltage stress transients and eliminating external diode failure modes.

Use Scenario: Primary-side switch in universal-input (90–264 VAC), <100 W offline flyback converters for LED drivers and appliance power supplies.

IC Role / Device Role / Timing Role: High-voltage switching transistor handling reflected output voltage plus leakage spike (V_reflected + V_spike ≤ 650 V).

Use Value: 700 V V_CES rating allows direct use without clamping circuits, reducing BOM cost and layout complexity.

Forward Converters

DC-DC Resonant Modules

Use Scenario: Single-transistor forward converter in industrial control power modules requiring regulated 12–24 V outputs at 2–5 A.

IC Role / Device Role / Timing Role: Primary switch operating at 50–100 kHz with reset winding; leverages integrated diode for auxiliary reset path.

Use Value: Integrated diode simplifies transformer reset circuitry and improves efficiency by ~2% over discrete implementations.

Use Scenario: Half-bridge leg switch in isolated DC-DC resonant modules for telecom and server auxiliary supplies.

IC Role / Device Role / Timing Role: Fast-switching NPN with matched dynamic parameters enabling precise dead-time control and ZVS across temperature.

Use Value: Tight lot-to-lot parameter spread ensures consistent timing margins in synchronous rectified designs.

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
STB12NK60Z	600 V MOSFET (not bipolar); R_DS(on) = 0.65 Ω; no integrated diode; gate-driven.	Requires external diode and gate driver; lower conduction loss above 1 A but higher EMI risk due to dV/dt sensitivity.	Preferable for >100 kHz PWM designs where gate drive simplicity and efficiency outweigh diode integration needs.
BUL128D	Same die, SOT-32 package (non-insulated tab); identical electrical specs but different thermal path and mounting.	Limited to non-heatsinked or low-power applications (<15 W) due to higher R_thj-amb (80 °C/W vs. 2.27 °C/W case).	Select only when mechanical constraints prohibit SOT-82 mounting or when isolation is unnecessary.

Compared with STB12NK60Z and BUL128D, BULK128D-B uniquely combines integrated antiparallel diode, 700 V rating, and SOT-82 thermal performance-making it optimal for cost-sensitive, thermally constrained lighting and low-power SMPS where diode integration and robustness outweigh MOSFET efficiency gains.

Availability

BULK128D-B is available at Aetrix Electronics and suitable for electronic ballasts, flyback converters, forward converters, and resonant DC-DC modules requiring stable component supply across extended production lifecycles.

Supply support for BULK128D-B 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, specializing in power management, analog, microcontrollers, and automotive ICs.

BULK128D-B belongs to ST's high-voltage bipolar power transistor family, designed specifically for energy-efficient lighting and low-cost switch-mode power conversion in consumer and industrial equipment.

FAQ

Is BULK128D-B still in active production?

No - BULK128D-B is marked "Obsolete Product(s)" in the official STMicroelectronics datasheet (Rev. August 2001). However, Aetrix Electronics maintains legacy inventory with full traceability and supports long-term design continuity through controlled distribution and cross-reference guidance for drop-in alternatives.

Can BULK128D-B replace BUL128D in existing designs?

Yes, electrically - both share identical die characteristics, V_CES, h_FE, and switching performance. Mechanically, BULK128D-B uses SOT-82 (insulated tab), whereas BUL128D uses SOT-32 (non-insulated). Replacement requires verifying heatsink isolation and thermal interface compliance in the target PCB layout.

What is the role of the integrated antiparallel diode?

The integrated diode connects cathode to collector and anode to emitter, enabling bidirectional current flow during inductive turn-off. In resonant ballasts, it provides the freewheeling path for LC tank current, eliminating external diode count and parasitic inductance - critical for stable ZVS operation at 20–60 kHz.

Does BULK128D-B require base current limiting in linear applications?

Yes - base current must be limited to ≤2 A continuous (IBM = 4 A pulsed) to avoid bond wire failure. For switching use, typical drive is ±0.4 A peak with 10–100 ns rise/fall times. Fixed-resistor base drive is acceptable only if calculated to ensure I_B ≤ 0.2 × I_C at worst-case h_FE min (h_FE = 8).

BULK128D-B 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:: 1.5V @ 500mA, 2.5A

Current - Collector Cutoff (Max):: 250µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 8 @ 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

BULK128D-B FAQ

1.How can I place an order for BULK128D-B through Aetrix?

Please submit a Request for Quotation (RFQ) for BULK128D-B 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 BULK128D-B reliable?

The price and inventory of BULK128D-B are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BULK128D-B is usually 5 days.

3.What payment methods are accepted for BULK128D-B?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BULK128D-B transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BULK128D-B?

BULK128D-B orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BULK128D-B 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 BULK128D-B?

For technical support, including BULK128D-B datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BULK128D-B requirements.

6.How does Aetrix verify that BULK128D-B is sourced from the original manufacturer or authorized distributors?

All BULK128D-B 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 BULK128D-B meets industry standards.

7.What is the process for return or replacement of BULK128D-B?

All BULK128D-B units undergo pre-shipment inspection (PSI). If there is an issue with BULK128D-B, 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 BULK128D-B part is unused and in its original packaging.

Return procedure for BULK128D-B:

1.Submit a request within 90 days.

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

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