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

STMicroelectronics BULB128-1

Name: BULB128-1
Brand: STMicroelectronics
SKU: BULB128-1
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BULB128-1

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-262-3 Long Leads, I2PAK, TO-262AA

Datasheet:: BULB128-1.pdf

Description:: TRANS NPN 400V 4A TO-262

Quantity:: RFQ Add To RFQ list

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Inventory:2,573

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Product details

Overview

BULB128-1 from STMicroelectronics is a high-voltage fast-switching NPN power transistor in I2PAK (TO-262) package, rated for V_CES = 700 V, I_C = 4 A, P_tot = 70 W at T_c = 25 °C, with t_s/t_f ≤ 1 µs (inductive load), designed for electronic ballasts in fluorescent lighting and low-cost SMPS.

For engineers reviewing the BULB128-1 datasheet, BULB128-1 pinout, BULB128-1 application, or BULB128-1 equivalent, key selection criteria include high-voltage blocking (V_CES = 700 V), low dynamic parameter spread, guaranteed RBSOA, and through-hole I2PAK thermal performance (R_thj-case = 1.78 °C/W).

Technical Context

This device employs Multi-Epitaxial Planar technology with Cellular Emitter structure and planar edge termination to simultaneously achieve high switching speed and wide Reverse Biased Safe Operating Area (RBSOA). It supports pulsed operation with 300 µs pulse width and 1.5% duty cycle per specification.

Designed specifically for inductive switching in lighting ballasts, it delivers V_CEO(sus) = 400 V at I_C = 100 mA with L = 25 mH, and exhibits tightly controlled h_FE (10–28) and V_CE(sat) (0.5–1.5 V across 0.5–4 A) for consistent system-level timing and loss predictability.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	700 V - maximum collector-emitter voltage with base open; enables direct mains-connected ballast topologies without snubber overdesign
I_C	4 A continuous - supports lamp currents up to 4 A in parallel-lamp or high-output electronic ballasts
t_s/t_f (inductive)	0.6/0.1 µs typical - ensures minimal switching loss during lamp ignition and stable high-frequency operation (>25 kHz)
R_thj-case	1.78 °C/W - allows 70 W dissipation with modest heatsinking; critical for compact, convection-cooled ballast enclosures
h_FE	10–28 - narrow spread across lots ensures consistent base drive design and predictable turn-on delay in oscillator circuits
V_CE(sat)	0.5 V @ 0.5 A / 1.5 V @ 4 A - defines conduction loss envelope for efficiency optimization in 20–50 kHz resonant converters

Pinout & Package

I2PAK (TO-262) is a through-hole power package with isolated mounting tab (collector), standardized for industrial lighting and SMPS applications. Thermal path optimized via copper leadframe and large die attach area.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Control input	Low-impedance gate drive node; requires 1 A peak base current capability from driver stage
2 (Collector)	High-side switch output	Internally connected to metal tab; must be electrically isolated from heatsink unless common-collector topology used
3 (Emitter)	Power return reference	Low-inductance emitter connection essential for stable switching; layout must minimize loop inductance to suppress voltage overshoot

Key Features

Feature	Design Value
Cellular Emitter structure	Enables simultaneous high-speed switching and robust RBSOA-critical for lamp-strike reliability under cold-start conditions
Low lot-to-lot parameter spread	Guarantees consistent t_s, h_FE, and V_CE(sat) across production batches-reduces need for per-lot driver tuning
Planar edge termination	Prevents premature avalanche at junction periphery-maintains V_CEO(sus) stability under repetitive inductive stress
Multi-Epitaxial Planar process	Delivers tight control of base width and doping profiles-ensures repeatable f_T > 10 MHz and low storage time

Applications

Fluorescent Lamp Electronic Ballast

Compact Fluorescent Lamp (CFL) Driver

Use Scenario: High-frequency (25–65 kHz) series-resonant inverter driving T5/T8 lamps with instant start and dimming capability.

IC Role / Device Role / Timing Role: Main switching transistor in half-bridge configuration; controls resonant tank current zero-crossing timing and lamp power regulation.

Use Value: Low t_s/t_f minimizes dead-time losses; tight h_FE spread ensures uniform lamp brightness across production units.

Use Scenario: Integrated CFL module with integrated EMI filter, rectifier, and resonant choke operating directly from 230 VAC mains.

IC Role / Device Role / Timing Role: Single-ended flyback or resonant transistor handling both energy transfer and lamp ignition pulses.

Use Value: V_CES = 700 V eliminates need for voltage clamping; R_thj-case = 1.78 °C/W enables sealed plastic housing without forced air.

Low-Cost AC-DC SMPS

LED Driver with Boost-PFC Stage

Use Scenario: 15–30 W offline flyback converter for industrial control power supplies with universal input (85–265 VAC).

IC Role / Device Role / Timing Role: Primary-side switch managing energy storage in transformer gap and regulating output via optocoupler feedback.

Use Value: Guaranteed RBSOA prevents secondary-side reflected surge damage; low V_CE(sat) improves full-load efficiency by ≥1.2% vs. legacy bipolar parts.

Use Scenario: 25 W constant-current LED driver with active boost PFC front-end and buck-boost DC-DC stage.

IC Role / Device Role / Timing Role: PFC switch handling 400 V DC bus and delivering 0.5 A average current at 65 kHz switching frequency.

Use Value: V_CEO(sus) = 400 V matches PFC bus voltage; low dynamic spread ensures stable THD < 12% across temperature and line variations.

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
STBUL128	V_CES = 700 V, same I2PAK package, but obsolete since 2005; no longer supported by ST	Identical ballast use case; lacks updated lot-control documentation and RoHS compliance	Select only if legacy board rework requires exact form-fit-function match with known BOM history
BU508A	V_CES = 1000 V, I_C = 8 A, TO-220 package, R_thj-case = 2.5 °C/W, slower switching (t_s ≈ 2.5 µs)	Higher voltage margin but larger footprint and higher conduction loss; less suitable for compact CFL modules	Choose when extended overvoltage protection is required and thermal budget allows larger heatsink

Compared with STBUL128 and BU508A, BULB128-1 offers optimal balance of high-voltage capability, fast switching, and thermal efficiency in I2PAK-making it preferred for space-constrained, cost-sensitive fluorescent ballasts where lot consistency and RBSOA reliability are mandatory.

Availability

BULB128-1 is available at Aetrix Electronics and suitable for electronic ballasts, compact fluorescent lamp drivers, and low-cost AC-DC SMPS requiring stable component supply, long-term manufacturability, and consistent parametric performance across production lots.

Supply support for BULB128-1 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, specializing in power discrete devices, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

The BULB128-1 belongs to ST's high-voltage bipolar power transistor family, engineered specifically for lighting control and energy-efficient switch-mode power conversion with emphasis on reliability, thermal robustness, and production repeatability.

FAQ

Is BULB128-1 RoHS compliant?

Yes, BULB128-1 is RoHS compliant per STMicroelectronics' official product change notification PCN-09-0127, effective Q2 2009. All units shipped by Aetrix Electronics meet EU Directive 2011/65/EU requirements, including lead-free terminations and halogen-free molding compound.

What is the maximum recommended case temperature for continuous operation?

The maximum continuous case temperature is 125 °C, derived from T_j(max) = 150 °C and R_thj-case = 1.78 °C/W at P_tot = 70 W. Operation above 125 °C case temperature risks exceeding junction limit under worst-case derating conditions.

Can BULB128-1 replace BU2520DX in existing ballast designs?

No-BU2520DX has V_CEO = 1500 V and different pinout (TO-3P), while BULB128-1 uses I2PAK with collector-tab pin 2. Electrical mismatch in V_CEO, gain, and SOA makes direct substitution unsafe without circuit redesign and thermal validation.

Does BULB128-1 require a base resistor in standard ballast circuits?

Yes-a base resistor is mandatory to limit I_B to ≤2 A peak and ensure proper saturation. Typical value is 10 Ω (1 W) for 12 V drive, selected to deliver I_B = I_C/10 at full load, maintaining h_FE-based saturation margin across temperature.

BULB128-1 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-262-3 Long Leads, I2PAK, TO-262AA

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:: 70 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-262

BULB128-1 FAQ

1.How can I place an order for BULB128-1 through Aetrix?

Please submit a Request for Quotation (RFQ) for BULB128-1 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 BULB128-1 reliable?

The price and inventory of BULB128-1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BULB128-1 is usually 5 days.

3.What payment methods are accepted for BULB128-1?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BULB128-1 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BULB128-1?

BULB128-1 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BULB128-1 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 BULB128-1?

For technical support, including BULB128-1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BULB128-1 requirements.

6.How does Aetrix verify that BULB128-1 is sourced from the original manufacturer or authorized distributors?

All BULB128-1 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 BULB128-1 meets industry standards.

7.What is the process for return or replacement of BULB128-1?

All BULB128-1 units undergo pre-shipment inspection (PSI). If there is an issue with BULB128-1, 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 BULB128-1 part is unused and in its original packaging.

Return procedure for BULB128-1:

1.Submit a request within 90 days.

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

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