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

STMicroelectronics BULT118

Name: BULT118
Brand: STMicroelectronics
SKU: BULT118
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BULT118

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-225AA, TO-126-3

Datasheet:: BULT118.pdf

Description:: TRANS NPN 400V 2A SOT-32-3

Quantity:: RFQ Add To RFQ list

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Inventory:6,637

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Product details

Overview

BULT118 from STMicroelectronics is a high-voltage fast-switching NPN power transistor in SOT-32 (TO-126) package, rated for V_CEO = 400 V, I_C = 2 A, P_tot = 45 W at T_c = 25 °C, with t_r/t_f = 0.4/0.25 µs (resistive load), designed for electronic ballasts and low-power flyback converters.

For engineers reviewing the BULT118 datasheet, BULT118 pinout, BULT118 application, or BULT118 equivalent, key selection criteria include its 400 V sustaining voltage, 2 A continuous collector current, 0.5 V V_CE(sat) at I_C = 0.5 A / I_B = 0.1 A, fast switching performance under resistive/inductive loads, and SOT-32 thermal and mechanical compatibility in lighting and SMPS designs.

Technical Context

This device uses high-voltage multi-epitaxial planar technology with cellular emitter structure and planar edge termination to simultaneously achieve high dV/dt immunity and wide RBSOA. Its design targets reliable operation in repetitive hard-switching conditions typical of fluorescent lamp ballasts.

The BULT118 operates with pulsed base drive (duty cycle ≤1.5%, pulse width = 300 µs) and supports both resistive (t_r = 0.4 µs, t_f = 0.25 µs) and inductive (t_s = 0.8 µs, t_f = 0.16 µs) switching profiles, with V_CE(sat) tightly specified across I_C = 0.5–2 A and corresponding I_B.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	400 V - Maximum collector-emitter voltage with open base; defines safe operating limit in flyback clamp and ballast resonant circuits
I_C	2 A - Continuous DC collector current; sets maximum average power handling in linear or quasi-resonant topologies
P_tot	45 W at T_c = 25 °C - Total thermal dissipation capability; requires heatsinking for sustained >10 W operation
t_r/t_f	0.4/0.25 µs - Rise/fall times under resistive load; enables >1 MHz switching in low-power SMPS with minimal switching loss
V_CE(sat)	0.5 V @ I_C = 0.5 A, I_B = 0.1 A - Low saturation voltage reduces conduction loss and self-heating in ballast preheat phase
h_FE	10–50 - DC current gain range across I_C = 10 mA to 2 A; determines required base drive strength and driver stage sizing
T_J(max)	150 °C - Maximum junction temperature; constrains thermal design margin for sealed lamp housings and compact PCB layouts

Pinout & Package

SOT-32 (TO-126) package: molded plastic case with isolated metal tab (collector-connected), 3-pin through-hole configuration, intended for direct mounting to heatsink via tab screw hole.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Emitter terminal	Low-impedance return path; connected to ground or negative rail in common-emitter switch configurations
2 (Base)	Control input	Receives current-limited drive signal; requires ≥0.1 A peak for full saturation at I_C = 0.5 A
3 (Collector / Tab)	High-voltage output / Thermal interface	Carries switched high-voltage current; metal tab is electrically connected to collector and serves as primary heat path to heatsink

Key Features

Feature	Design Value
High-voltage capability	V_CEO = 400 V enables direct use in 230 VAC-fed electronic ballasts without auxiliary clamping networks
Very high switching speed	t_r/t_f = 0.4/0.25 µs minimizes transition losses in 20–100 kHz ballast and low-power SMPS operation
Wide RBSOA	Robust secondary breakdown margin supports inductive turn-off stress in flyback and forward converters
Cellular emitter + planar termination	Enables uniform current distribution and predictable switching behavior across production lots
ECOPACK® lead-free packaging	Complies with JEDEC JESD97; eliminates Pb in second-level interconnect while maintaining solderability and thermal reliability

Applications

Electronic Ballast

Flyback Converter

Use Scenario: Driving resonant LC network in 20–60 kHz instant-start fluorescent lamp ballasts.

IC Role / Device Role / Timing Role: Main switching transistor controlling lamp current via base-driven hard switching.

Use Value: 400 V V_CEO withstands lamp ignition spikes; 0.5 V V_CE(sat) reduces preheat-stage conduction loss by >30% vs. older 1.2 V devices.

Use Scenario: Primary-side switch in <50 W offline AC/DC adapters with universal input.

IC Role / Device Role / Timing Role: High-voltage NPN switch turning on/off transformer primary winding during each switching cycle.

Use Value: 0.8 µs storage time under inductive load ensures stable operation at 50–100 kHz with minimal tail current loss.

Forward Converter

Compact Lighting Driver

Use Scenario: Single-transistor forward topology powering LED arrays or control logic in industrial lighting fixtures.

IC Role / Device Role / Timing Role: Main power switch synchronizing with transformer reset and output rectification timing.

Use Value: Wide RBSOA prevents secondary breakdown during MOSFET gate-drive transformer reset transients.

Use Scenario: Dimmable CFL/LED retrofit lamp with integrated EMI filter and thermal foldback.

IC Role / Device Role / Timing Role: Fast-switching power transistor in half-bridge or single-ended resonant driver stage.

Use Value: Tight lot-to-lot h_FE spread ensures consistent dimming linearity and startup reliability across manufacturing batches.

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, t_r/t_f = 0.3/0.2 µs, TO-220 package	Higher voltage/current rating; larger footprint and thermal mass	Preferred where higher surge tolerance or >50 W output is required; requires PCB layout revision
BDW53C	V_CEO = 100 V, I_C = 12 A, P_tot = 90 W, TO-220 package	Lower voltage rating; unsuitable for 230 VAC mains-referenced topologies	Only viable in low-line (<120 VAC) or DC-fed applications; not drop-in compatible

Compared with BU2508AX and BDW53C, the BULT118 offers optimal balance of 400 V capability, 2 A current, and SOT-32 thermal/mechanical fit for space-constrained 20–40 W lighting and SMPS designs-neither over-specified nor voltage-limited.

Availability

BULT118 is available at Aetrix Electronics and suitable for electronic ballasts, flyback converters, and forward converters requiring stable component supply and legacy-compatible through-hole power transistors.

Supply support for BULT118 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.

The BULT118 belongs to ST's high-voltage bipolar power transistor product line, developed specifically for cost-sensitive, thermally constrained lighting and low-power SMPS applications where fast switching and rugged SOA are critical.

FAQ

Is the BULT118 still in active production?

No-the BULT118 is marked as Obsolete Product(s) in ST's official documentation (Rev 2, July 2008). It remains available through authorized legacy distributors and Aetrix Electronics' long-term inventory program with full traceability and extended lifecycle support for existing designs.

Can the BULT118 be used in place of a MOSFET in a flyback converter?

Yes, but with design adjustments: it requires sufficient base drive current (≥0.4 A peak for I_C = 2 A), exhibits higher conduction loss than modern superjunction MOSFETs, and lacks inherent body diode recovery benefits. Its advantage lies in ruggedness and lower gate-drive complexity in low-frequency (<100 kHz) implementations.

What is the thermal resistance from junction to case (R_θJC) for the BULT118?

The datasheet does not specify R_θJC directly. However, based on SOT-32 (TO-126) package geometry and P_tot = 45 W at T_c = 25 °C, typical R_θJC is ~1.1 °C/W. Derating follows the curve in Figure 3: linear reduction to zero at T_c = 125 °C.

Does the BULT118 require a base resistor, and how is its value calculated?

Yes-a series base resistor is mandatory to limit I_B. For I_C = 2 A and minimum h_FE = 8, I_B ≥ 250 mA is needed. With V_BE(sat) ≈ 1.3 V and driver supply = 12 V, R_B = (12 − 1.3) V / 0.25 A ≈ 43 Ω. A standard 39 Ω, 1 W resistor is recommended for reliability.

BULT118 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-225AA, TO-126-3

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 2 A

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

Vce Saturation (Max) @ Ib, Ic:: 1.5V @ 400mA, 2A

Current - Collector Cutoff (Max):: 250µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 10 @ 500mA, 5V

Power - Max:: 45 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: SOT-32-3

BULT118 FAQ

1.How can I place an order for BULT118 through Aetrix?

Please submit a Request for Quotation (RFQ) for BULT118 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 BULT118 reliable?

The price and inventory of BULT118 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BULT118 is usually 5 days.

3.What payment methods are accepted for BULT118?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BULT118 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BULT118?

BULT118 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BULT118 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 BULT118?

For technical support, including BULT118 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BULT118 requirements.

6.How does Aetrix verify that BULT118 is sourced from the original manufacturer or authorized distributors?

All BULT118 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 BULT118 meets industry standards.

7.What is the process for return or replacement of BULT118?

All BULT118 units undergo pre-shipment inspection (PSI). If there is an issue with BULT118, 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 BULT118 part is unused and in its original packaging.

Return procedure for BULT118:

1.Submit a request within 90 days.

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

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