STMicroelectronics BUL742C

Overview

BUL742C from STMicroelectronics is a high-voltage fast-switching NPN power transistor in TO-220 package, rated for 1050 V V_CES, 4 A I_C, and 70 W P_TOT at T_C = 25 °C. It delivers 2.4 µs storage time and 350 ns fall time under resistive load switching conditions (I_C = 2 A, V_CC = 125 V), enabling robust operation in electronic ballasts for fluorescent lighting.

For engineers reviewing the BUL742C datasheet, BUL742C pinout, BUL742C application, or BUL742C equivalent, key selection criteria include V_CES = 1050 V, V_CEO(sus) = 400–450 V, t_s/t_f = 2.4 µs/350 ns, R_thJC = 1.79 °C/W, and avalanche energy rating of 6 mJ - all critical for high-reliability SMPS and lamp ballast designs.

Technical Context

This device uses high-voltage multi-epitaxial planar technology to achieve both high breakdown voltage and fast switching. Its intrinsic ruggedness-enabled by an increased intermediate layer-allows it to sustain high collector current during breakdown without external Transil protection, a key advantage over standard converters in lamp ballast applications.

The transistor supports repetitive avalanche operation with 6 mJ energy rating (L = 2 mH, C = 1.8 nF, V_BE(off) = −5 V) and exhibits low dynamic parameter spread across lots, ensuring consistent timing and thermal behavior in production-grade lighting and power supply systems.

Key Specifications

Pinout & Package

Package: TO-220 (standard through-hole, insulated tab, 3-pin vertical mount). Pin assignment verified per Figure 1 and Table 1 of STMicroelectronics Doc ID 9488 Rev 4.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BU508A and ST13007, BUL742C uniquely balances 1050 V blocking, 2.4 µs storage time, and 6 mJ avalanche energy - making it optimal for 20–60 kHz fluorescent ballasts where both voltage headroom and switching efficiency are simultaneously critical.

Availability

BUL742C is available at Aetrix Electronics and suitable for electronic ballasts, switch-mode power supplies, LED drivers, and induction heating inverters requiring stable component supply and long-term industrial availability.

Supply support for BUL742C 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.

The BUL742C belongs to ST's high-voltage bipolar power transistor product line, engineered specifically for energy-efficient lighting and industrial power conversion where reliability under repetitive avalanche stress is mandatory.

FAQ

What is the maximum safe operating voltage for BUL742C in continuous conduction mode?

The absolute maximum collector-emitter voltage with base open (V_CEO) is 400 V, but the device is rated for 1050 V V_CES when base is shorted to emitter. For continuous conduction, design must respect V_CEO(sus) = 400–450 V under pulsed conditions (I_C = 10 mA), confirmed in Table 4 of Doc ID 9488 Rev 4.

Does BUL742C require external Transil protection in fluorescent ballast circuits?

No. The BUL742C's intrinsic ruggedness-achieved via an increased intermediate layer-enables it to withstand high collector current during breakdown without external Transil clamping, as explicitly stated in the Applications section and validated by its 6 mJ repetitive avalanche energy rating.

Which package variants of BUL742C are offered, and what are their thermal differences?

ST offers BUL742C in TO-220 (R_thJC = 1.79 °C/W), TO-220FP (R_thJC = 4.17 °C/W), I²PAK (TO-262), and D²PAK (TO-263). Only TO-220 and D²PAK share identical R_thJC; TO-220FP has significantly higher thermal resistance due to its plastic-isolated footprint, limiting usable power to ~30 W.

Can BUL742C be used in avalanche mode for ZVS soft-switching topologies?

Yes. Its 6 mJ repetitive avalanche energy rating (tested with L = 2 mH, C = 1.8 nF, V_BE(off) = −5 V) confirms suitability for controlled avalanche operation in zero-voltage-switching resonant converters, provided peak current and duty cycle remain within SOA limits shown in Figure 2.