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

STMicroelectronics BUL743

Name: BUL743
Brand: STMicroelectronics
SKU: BUL743
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BUL743

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: BUL743.pdf

Description:: TRANS NPN 500V 12A TO-220

Quantity:: RFQ Add To RFQ list

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Inventory:1,648

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Product details

Overview

BUL743 from STMicroelectronics is a high-voltage fast-switching NPN power transistor designed for primary-side switching in electronic ballasts and SMPS. It features V_CEO = 500 V, I_C = 12 A, P_tot = 100 W at T_c = 25 °C, t_s = 2.5–3.8 µs, and rugged avalanche capability (E_ar = 3 mJ), enabling reliable operation in 256 W fluorescent lamp ballasts without external Transil protection.

For engineers reviewing the BUL743 datasheet, BUL743 pinout, BUL743 application, or BUL743 equivalent, key selection criteria include its 500 V sustaining voltage under pulsed conditions, low V_CE(sat) (0.15 V @ 3 A / 0.6 A), fast resistive-load switching times, TO-220 thermal resistance (R_thj-case = 1.25 °C/W), and intrinsic ruggedness against secondary breakdown.

Technical Context

The BUL743 employs a diffused-collector planar structure with enhanced high-voltage design to achieve stable V_CEO(sus) = 500 V under 300 µs pulses and withstand high collector current during breakdown. Its ruggedness eliminates need for Transil clamping in lamp ballast converters.

It delivers DC current gain h_FE = 24–45 at I_C = 2 A / V_CE = 3 V and switching performance with t_s ≤ 3.8 µs and t_f ≤ 500 ns under defined resistive-load test conditions (V_CC = 125 V, I_B(on/off) = ±1.2 A).

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	500 V - Sustaining voltage under pulsed IB = 0 conditions, enabling direct use in 400 V DC bus SMPS
I_C	12 A - Continuous collector current rating at T_c = 25 °C, supports 256 W ballast output
V_CE(sat)	0.15 V @ 3 A/0.6 A - Low saturation voltage reduces conduction loss in hard-switched topologies
t_s/t_f	2.5–3.8 µs / 400–500 ns - Fast resistive-load switching enables >50 kHz operation in electronic ballasts
E_ar	3 mJ - Repetitive avalanche energy with L = 2 mH, C = 1.8 nF, allows unclamped inductive turn-off
R_thj-case	1.25 °C/W - Enables 100 W dissipation with modest heatsinking in TO-220 package
h_FE	24–45 @ I_C = 2 A - Sufficient DC gain for base-driven switching without excessive drive current

Pinout & Package

Supplied in TO-220 package (standard 3-lead, vertical mounting, isolated tab). Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector (tab-connected). The collector is electrically tied to the metal tab, requiring insulating mounting hardware when used on grounded heatsinks.

Pin/Terminal	Circuit Role	Design Meaning
Pin 1 (Emitter)	Current return path for collector current	Low-inductance emitter connection critical for stable high-speed switching and EMI control
Pin 2 (Base)	Control terminal for bipolar conduction	Requires active drive (±1.2 A peak) and negative turn-off bias (–5 V) for optimal t_s/t_f
Pin 3 (Collector / Tab)	Main power output node and thermal interface	Electrically connected to heatsink; isolation required if heatsink is not at collector potential

Key Features

Feature	Design Value
Intrinsic ruggedness	Withstands high I_C during breakdown without Transil clamping-reduces BOM count and layout area in lamp ballasts
Low dynamic parameter spread	Minimized lot-to-lot variation in t_s, t_f, and h_FE ensures consistent timing and drive requirements across production batches
High V_CEO(sus)	500 V pulsed sustaining voltage supports 400 V DC link designs with margin for line transients
Fast switching with low V_CE(sat)	Combines 0.15 V saturation and sub-4 µs storage time-enables high-efficiency, high-frequency operation in SMPS

Applications

Fluorescent Lamp Electronic Ballast

Off-line Switch Mode Power Supply

Use Scenario: Driving resonant LC tank in 8 × 32 W (256 W) fluorescent lamp system with 20–60 kHz operation.

IC Role / Device Role / Timing Role: Primary-side high-voltage switch controlling lamp current via half-bridge topology.

Use Value: Eliminates need for external Transil due to intrinsic avalanche ruggedness, reducing component count and cost.

Use Scenario: Main switch in 100–300 W offline flyback or forward converter powering industrial controls.

IC Role / Device Role / Timing Role: High-voltage NPN switch handling 400 V DC bus with forced commutation.

Use Value: 500 V V_CEO(sus) and 3 mJ E_ar allow safe unclamped inductive turn-off during overload events.

DC-DC Converter for Industrial Lighting

AC-DC Adapter with High-Voltage Input

Use Scenario: Step-down converter feeding LED drivers from rectified 277 V AC mains in commercial lighting.

IC Role / Device Role / Timing Role: Primary switch operating in quasi-resonant mode with ZVS-assisted turn-on.

Use Value: Low t_s (≤3.8 µs) and tight parameter spread ensure predictable dead-time control and efficiency stability.

Use Scenario: Universal-input (90–264 V AC) adapter delivering 12 V/10 A for PoE-powered devices.

IC Role / Device Role / Timing Role: High-current, high-voltage switching element in primary-side regulation circuit.

Use Value: 12 A I_C rating and 100 W P_tot support high-power density without derating at ambient temperatures up to 70 °C.

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage NPN switching applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BU508A	V_CEO = 1000 V, I_C = 8 A, t_s = 4 µs - higher voltage rating but lower current and slower switching	Suitable for 400–600 V DC bus where current demand ≤8 A and switching frequency <30 kHz	Prefer BU508A only when V_CEO margin >1000 V is mandatory and thermal budget permits higher R_thj-case
ST13007	V_CEO = 400 V, I_C = 8 A, t_s = 2.5 µs - lower voltage rating but faster switching and same package	Fits 277 V AC-derived 400 V bus systems with tighter timing constraints and lower power (<200 W)	Select ST13007 when V_CEO = 400 V suffices and faster t_s/t_f improves efficiency at >70 kHz.

Compared with BU508A and ST13007, BUL743 uniquely balances 500 V V_CEO, 12 A I_C, and sub-4 µs t_s-making it optimal for 256 W ballasts and 300 W SMPS where both voltage headroom and current capability are simultaneously critical.

Availability

BUL743 is available at Aetrix Electronics and suitable for electronic ballasts, off-line switch mode power supplies, and industrial DC-DC converters requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for BUL743 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, designing and manufacturing analog, digital, and mixed-signal ICs and discrete power devices for industrial, automotive, and consumer markets.

The BUL743 belongs to ST's high-voltage bipolar power transistor product line, engineered specifically for rugged, high-reliability switching in lighting and power conversion where Transil-free operation and tight parameter distribution are essential.

FAQ

Is BUL743 pin-compatible with BU2508AX or ST13007?

No. BUL743 uses standard TO-220 pinout (E-B-C), but BU2508AX has reversed emitter-collector orientation (C-B-E), and ST13007 shares E-B-C order yet differs in internal doping profile and safe operating area limits. Mechanical fit does not guarantee functional or thermal equivalence.

Can BUL743 replace BU508D in a 220 V AC input SMPS?

Only with circuit validation. BU508D specifies V_CEO = 1000 V and I_C = 12 A but lacks documented E_ar and t_s/t_f data. BUL743 offers verified 500 V V_CEO(sus) and 3 mJ E_ar, making it safer for 220 V AC-derived ~310 V DC bus-but requires checking SOA curves at actual operating V_CE and I_C.

What is the recommended base drive for reliable switching?

ST recommends I_B(on) = +1.2 A and I_B(off) = –1.2 A with V_BE(off) = –5 V for t_s ≤ 3.8 µs. A dedicated base driver IC (e.g., UCC3800 series) or complementary BJT pair with ≥2.5 A peak current capability is required to meet these specs reliably.

Does BUL743 require heatsinking in 100 W continuous operation?

Yes. With R_thj-case = 1.25 °C/W and P_tot = 100 W at T_c = 25 °C, junction temperature rises 125 °C above case. To maintain T_J ≤ 150 °C at ambient 50 °C, total thermal resistance (case-to-ambient) must be ≤ 0.25 °C/W-requiring a substantial heatsink with forced air or thermal interface material.

BUL743 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-220-3

Packaging:: Tube

Product Status:: Active

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 12 A

Voltage - Collector Emitter Breakdown (Max):: 500 V

Vce Saturation (Max) @ Ib, Ic:: 1.5V @ 2.5A, 10A

Current - Collector Cutoff (Max):: 250µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 24 @ 2A, 3V

Power - Max:: 100 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

BUL743 FAQ

1.How can I place an order for BUL743 through Aetrix?

Please submit a Request for Quotation (RFQ) for BUL743 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 BUL743 reliable?

The price and inventory of BUL743 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BUL743 is usually 5 days.

3.What payment methods are accepted for BUL743?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BUL743 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BUL743?

BUL743 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BUL743 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 BUL743?

For technical support, including BUL743 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BUL743 requirements.

6.How does Aetrix verify that BUL743 is sourced from the original manufacturer or authorized distributors?

All BUL743 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 BUL743 meets industry standards.

7.What is the process for return or replacement of BUL743?

All BUL743 units undergo pre-shipment inspection (PSI). If there is an issue with BUL743, 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 BUL743 part is unused and in its original packaging.

Return procedure for BUL743:

1.Submit a request within 90 days.

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

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