STMicroelectronics BUL741FP

Overview

BUL741FP from STMicroelectronics is a high-voltage fast-switching NPN power transistor in TO-220FP package, rated for 1050 V V_CES, 2.5 A I_C, and 30 W P_tot at T_c = 25 °C. It delivers very high switching speed (t_s = 2.5–3.5 µs, t_f = 350–500 ns) and intrinsic ruggedness enabling 5 mJ repetitive avalanche energy without external Transil protection-optimized for electronic ballasts and SMPS primary-side switching.

For engineers reviewing the BUL741FP datasheet, BUL741FP pinout, BUL741FP application, or BUL741FP equivalent, key selection criteria include V_CES = 1050 V, I_C = 2.5 A, t_f ≤ 500 ns, R_thJC = 4.17 °C/W, and TO-220FP thermal/mechanical compatibility with heatsink-mounting constraints in high-reliability lighting and converter designs.

Technical Context

This transistor uses high-voltage multi-epitaxial planar technology with an increased intermediate layer to enhance breakdown robustness during overvoltage transients. Its design enables sustained operation at V_CEO(sus) = 400–450 V with I_C = 10 mA while maintaining low V_CE(sat) = 0.5 V (IC = 2 A, IB = 0.6 A) and h_FE = 25–50 at I_C = 0.45 A.

The device exhibits tightly controlled dynamic parameter spread across lots, supporting consistent timing and energy handling in mass-produced fluorescent lamp ballasts. Its safe operating area (SOA) is characterized up to 1050 V and 5 A peak, with derating defined by R_thJC = 4.17 °C/W and T_J(max) = 150 °C.

Key Specifications

Pinout & Package

TO-220FP package: insulated flange, vertical mounting, 3-pin through-hole configuration with metal tab electrically connected to collector. Flange provides thermal path and mechanical anchoring; no isolation washer required due to built-in insulation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with STBUL741, BUL741FP trades 30 W thermal capacity for flange insulation and board-level safety compliance; versus BU508AF, it offers superior speed and smaller form factor at the cost of lower peak current rating.

Availability

BUL741FP is available at Aetrix Electronics and suitable for electronic ballasts, switch-mode power supplies, LED drivers, and AC-DC adapters requiring stable component supply with guaranteed long-term availability and ECOPACK® environmental compliance.

Supply support for BUL741FP 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.

BUL741FP belongs to ST's high-voltage power transistor product line, engineered specifically for energy-efficient, high-reliability lighting and power conversion systems operating directly from rectified AC mains.

FAQ

What is the maximum safe operating voltage for BUL741FP in continuous conduction mode?

The absolute maximum collector-emitter voltage with base open (V_CEO) is 400 V, but the sustaining voltage (V_CEO(sus)) is rated 400–450 V at I_C = 10 mA. For reliable continuous operation, design must stay below 400 V with appropriate derating for temperature and transient margins-never exceed 1050 V V_CES, which applies only under V_BE = 0 condition.

Can BUL741FP replace BUL741 in existing TO-220 layouts?

No-BUL741FP uses TO-220FP (insulated flange), while BUL741 uses standard TO-220 (conductive flange). Pinout is identical (E-B-C), but mechanical mounting differs: BUL741FP's flange is internally isolated from collector, eliminating need for insulating washers. PCB footprint and hole pattern are incompatible due to different flange cutouts and lead spacing per ST mechanical drawings.

Is avalanche energy rating tested per JEDEC JESD22-A115A?

Yes-the 5 mJ repetitive avalanche energy (E_AR) is measured under standardized conditions: L = 2 mH, C = 1.8 nF, V_BB(off) = −5 V, and is specified in Table 4 of the official datasheet (Doc ID 13406 Rev 3). This rating validates single-pulse ruggedness during lamp-strike events and confirms suitability for unclamped inductive switching.

What base drive current is required to achieve full saturation at 2 A collector current?

To achieve V_CE(sat) ≤ 0.5 V at I_C = 2 A, the datasheet specifies I_B = 0.6 A (h_FE ≈ 3.3). However, for reliable saturation across temperature and process variation, a minimum I_B of 0.8–1.0 A is recommended. Base drive must also include −5 V reverse bias during turn-off to ensure t_f ≤ 500 ns, per Figure 12 test circuit.