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

STMicroelectronics BULT118M

Name: BULT118M
Brand: STMicroelectronics
SKU: BULT118M
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BULT118M

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

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

Datasheet:: BULT118M.pdf

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

Quantity:: RFQ Add To RFQ list

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Inventory:9,166

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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/forward SMPS.

For engineers reviewing the BULT118 datasheet, BULT118 pinout, BULT118 application, or BULT118 equivalent, this device supports high-reliability lighting control and cost-sensitive switch-mode power conversion where fast switching, wide RBSOA, and 150 °C junction operation are required.

Technical Context

This NPN bipolar junction transistor uses high-voltage multi-epitaxial planar technology with cellular emitter structure and planar edge termination to simultaneously achieve high-speed switching and robust reverse-biased safe operating area (RBSOA). Its design targets medium-voltage, medium-current switching with pulsed current capability up to 4 A.

The device operates with DC current gain h_FE = 10–50 (I_C = 10 mA to 2 A), V_CE(sat) = 0.5–1.5 V (I_C = 0.5–2 A), and exhibits storage time of 0.8 µs under inductive load conditions-critical for minimizing switching losses in self-oscillating ballast circuits.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	400 V - maximum collector-emitter voltage with base open; defines usable voltage headroom in flyback snubberless topologies
I_C	2 A continuous - sets thermal design baseline for heatsink sizing in 15–25 W ballast applications
t_r/t_f	0.4/0.25 µs (resistive) - enables >200 kHz operation in compact fluorescent lamp (CFL) ballasts
P_tot	45 W at T_c = 25 °C - requires active thermal management above ~15 W output in enclosed fixtures
T_J(max)	150 °C - allows operation in thermally constrained lighting enclosures without derating below ambient 85 °C
h_FE	10–50 - supports direct base drive from low-cost ICs without external amplification in self-oscillating configurations

Pinout & Package

SOT-32 (TO-126) package: three-terminal through-hole plastic power package with isolated tab (collector-connected), standard footprint for manual or wave soldering, ECOPACK® lead-free compliant.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Emitter terminal	Low-impedance return path; connected to ground or negative rail in common-emitter switching configuration
2 (Base)	Control input	Receives current-limited drive signal; requires ≥0.2 A peak for full saturation at I_C = 2 A
3 (Collector / Tab)	High-side switched output	Tab is electrically connected to collector; must be insulated from heatsink unless collector is at system ground potential

Key Features

Feature	Design Value
Cellular emitter + planar edge termination	Enables simultaneous high speed (t_f = 0.25 µs) and wide RBSOA for reliable operation under inductive turn-off stress
V_CEO(sus) = 400 V	Supports clamp-free flyback designs up to ~350 V DC bus without external snubbers
h_FE min = 10 @ I_C = 2 A	Ensures predictable base drive requirements across production lots for stable oscillator frequency in ballast circuits
ECOPACK® lead-free packaging	Meets RoHS Directive 2011/65/EU; compatible with standard Pb-free reflow and wave soldering profiles

Applications

Compact Fluorescent Lamp (CFL) Ballast

Flyback SMPS (≤25 W)

Use Scenario: Drives resonant LC tank in self-oscillating half-bridge CFL ballast operating at 40–70 kHz.

IC Role / Device Role / Timing Role: Main switching transistor; its t_r/t_f and h_FE stability directly set oscillation frequency and waveform symmetry.

Use Value: Cellular emitter structure maintains consistent switching timing across temperature and lot variation, reducing EMI spread and lamp flicker.

Use Scenario: Primary-side switch in low-cost, non-isolated flyback converter powering LED drivers or auxiliary rails.

IC Role / Device Role / Timing Role: High-voltage switching element; V_CEO = 400 V allows operation with 375 V DC bus without clamping.

Use Value: 45 W power dissipation rating enables 20–25 W output with minimal heatsinking in consumer-grade adapters.

Forward Converter (Low-Power)

Electronic Starter Circuit

Use Scenario: Single-transistor forward converter for industrial sensor power supplies (12–24 V, ≤15 W).

IC Role / Device Role / Timing Role: Main power switch; storage time t_s = 0.8 µs (inductive) limits minimum off-time and constrains max duty cycle.

Use Value: Wide RBSOA ensures reliability during transformer reset spikes without snubber losses.

Use Scenario: Trigger switch in preheat-start circuit for T8/T5 fluorescent tubes.

IC Role / Device Role / Timing Role: Fast-turn-on device initiating filament heating; V_BE(sat) = 1.0–1.3 V ensures low base drive loss during repeated pulsing.

Use Value: Minimum lot-to-lot h_FE spread guarantees consistent preheat current 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_f = 0.3 µs, TO-220 package	Higher voltage/current rating; larger thermal mass; requires different PCB layout and heatsink	Preferred when designing for universal AC input (up to 265 VAC) with higher power margin or longer lifetime requirements
ST13003	V_CEO = 400 V, I_C = 1.5 A, t_f = 0.5 µs, TO-126 package, same pinout	Near-identical footprint and pinout; lower current rating and slower fall time limit max power to ~12 W	Drop-in replacement only if I_C < 1.5 A and t_f margin permits; verify SOA under actual inductive load conditions

Compared with BU2508AX and ST13003, BULT118 offers optimal balance of speed (0.25 µs t_f), thermal capability (45 W), and cost for 15–25 W lighting and SMPS-neither over-specified nor marginal for its target applications.

Availability

BULT118 is available at Aetrix Electronics and suitable for electronic ballasts, low-power flyback converters, and forward converter designs requiring stable component supply with known thermal and switching performance.

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, Switzerland, delivering intelligent power, analog, MEMS, and microcontroller solutions for industrial, automotive, and consumer markets.

BULT118 belongs to ST's high-voltage bipolar power transistor product line, engineered specifically for cost-sensitive, high-reliability lighting and low-power SMPS applications where switching speed, RBSOA, and lot-to-lot consistency are critical.

FAQ

Is BULT118 still in active production?

No-BULT118 is marked "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 guaranteed authenticity for ongoing production support.

Can BULT118 be used in place of BU2508AX?

Not directly: BU2508AX has higher V_CEO (800 V vs. 400 V) and I_C (8 A vs. 2 A), and uses TO-220 packaging. Substitution requires redesign of drive circuitry, heatsinking, and PCB layout; BULT118 is unsuitable for 800 V applications or loads exceeding 2 A continuous.

What is the recommended base drive for saturation at I_C = 2 A?

Per datasheet Table 3, V_CE(sat) = 1.5 V at I_C = 2 A with I_B = 0.4 A. A base current of ≥0.4 A peak (with <1.5% duty cycle for pulsed operation) ensures full saturation and minimizes conduction loss in switching applications.

Does BULT118 require a heatsink in a 20 W CFL ballast?

Yes-its P_tot = 45 W is specified at T_c = 25 °C. In a typical enclosed CFL fixture with case temperature reaching 70–85 °C, thermal derating reduces usable power to ~20–25 W. A small aluminum heatsink (≥15 cm² surface area) is required to maintain T_J ≤ 150 °C.

BULT118M 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

BULT118M FAQ

1.How can I place an order for BULT118M through Aetrix?

Please submit a Request for Quotation (RFQ) for BULT118M 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 BULT118M reliable?

The price and inventory of BULT118M are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BULT118M is usually 5 days.

3.What payment methods are accepted for BULT118M?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BULT118M transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BULT118M?

BULT118M orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BULT118M 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 BULT118M?

For technical support, including BULT118M datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BULT118M requirements.

6.How does Aetrix verify that BULT118M is sourced from the original manufacturer or authorized distributors?

All BULT118M 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 BULT118M meets industry standards.

7.What is the process for return or replacement of BULT118M?

All BULT118M units undergo pre-shipment inspection (PSI). If there is an issue with BULT118M, 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 BULT118M part is unused and in its original packaging.

Return procedure for BULT118M:

1.Submit a request within 90 days.

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

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