STMicroelectronics BUL705

Overview

BUL705 from STMicroelectronics is a high-voltage fast-switching NPN power transistor in TO-220 package, rated for V_CEO = 400 V, I_C = 5 A, P_tot = 80 W at T_c = 25°C, with t_s = 0.7–1.4 µs (inductive load) and R_thj-case = 1.56 °C/W. It is engineered for electronic ballasts and PFC half-bridge circuits in high-frequency fluorescent lighting.

For engineers reviewing the BUL705 datasheet, BUL705 pinout, BUL705 application, or BUL705 equivalent, key selection criteria include its 400 V V_CEO, 2.4–3.5 µs resistive-load storage time, 150 °C max junction temperature, and TO-220 thermal performance - critical for reliable high-voltage switching in lighting and PFC topologies.

Technical Context

This device uses high-voltage Multi-Epitaxial Planar technology with Cellular Emitter structure and planar edge termination to simultaneously achieve fast switching and wide RBSOA. Its fully characterized operation at 125 °C ensures stability under thermal stress in compact ballast designs.

The BUL705 supports both resistive and inductive switching test conditions per Figures 10–13, with specified t_s/t_f under V_clamp = 250 V and L = 200 µH. Its low dynamic parameter spread enables consistent performance across production lots in safety-critical lighting systems.

Key Specifications

Pinout & Package

Package: TO-220 (3-pin, straight lead, insulated tab). Dimensions per ST mechanical drawing: D = 15.25–15.75 mm, E = 10–10.40 mm, L = 13–14 mm, with ECOPACK® lead-free interconnect.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BUL705, STBUL706 offers +50 V voltage headroom with matched speed and thermal specs, while BU508A trades unnecessary voltage capability for degraded switching performance - making BUL705 the optimal balance for 400 V PFC and ballast inverters.

Availability

BUL705 is available at Aetrix Electronics and suitable for electronic ballast, PFC half-bridge, and industrial lighting control applications requiring stable component supply and long-term sourcing continuity.

Supply support for BUL705 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 devices for industrial, automotive, and consumer markets.

The BUL705 belongs to ST's high-voltage power transistor product line, developed specifically for energy-efficient lighting systems and medium-power switching applications demanding ruggedness and consistency at elevated temperatures.

FAQ

Is BUL705 still in active production?

No - STMicroelectronics has marked BUL705 as obsolete per its official documentation (Rev 1, May 2006). However, Aetrix Electronics maintains legacy inventory with full traceability and supports ongoing production programs through controlled allocation and lifecycle coordination.

What is the maximum safe operating frequency for BUL705 in a half-bridge PFC?

BUL705 is characterized for reliable operation up to 100 kHz in inductive switching (Fig.13), with t_s ≤ 1.4 µs and t_f ≤ 100 ns at T_j = 125°C. For sustained 80 W operation, 50–75 kHz is recommended to maintain thermal margin and RBSOA integrity.

Can BUL705 be used without a heatsink?

No - With R_thj-case = 1.56 °C/W and P_tot = 80 W, even at 25°C ambient, junction temperature would exceed 150°C without heatsinking. A minimum 10 cm² aluminum heatsink (R_th ≈ 10 °C/W) is required for 5 A continuous operation at 40°C ambient.

Does BUL705 require a base resistor for driving from a microcontroller GPIO?

Yes - With h_FE = 10–32 and I_C = 2–4 A, base current must be 0.4–1.0 A. A standard GPIO cannot source this; a dedicated driver stage (e.g., TC4420) with current-limiting base resistor (e.g., 1.5 Ω, 2 W) is required to ensure proper saturation and avoid secondary breakdown.