STMicroelectronics BUL49D

Overview

BUL49D from STMicroelectronics is a high-voltage fast-switching NPN power transistor in TO-220 package, rated for 850 V V_CES, 5 A continuous collector current, and 80 W total dissipation at T_c ≤ 25°C. It delivers 450 V V_CEO(sus) under pulsed conditions and achieves 0.6 V V_CE(sat) at I_C = 4 A / I_B = 0.8 A, enabling use in electronic transformers for halogen lamps and low-power flyback converters.

For engineers reviewing the BUL49D datasheet, BUL49D pinout, BUL49D application, or BUL49D equivalent, key selection criteria include its 850 V blocking capability, sub-1 µs fall time (100 ns inductive load), rugged 150°C junction rating, and verified performance in unclamped inductive switching at 450 V without snubber.

Technical Context

The BUL49D employs ST's high-voltage multi-epitaxial planar process to achieve simultaneous high breakdown voltage and fast switching-evidenced by 0.6 µs storage time and 100 ns fall time under inductive load conditions. Its V_CEW of 450 V at I_C = 8 A with V_BB = −2.5 V confirms snubberless operation capability in flyback topologies.

Thermal design is enabled by R_thj-case = 1.56 °C/W (TO-220), supporting 80 W dissipation at case temperature ≤25°C. The device exhibits tight parameter spread across lots, with h_FE ranging 10–60 (I_C = 10 mA to 7 A) and guaranteed V_(BR)EBO ≥10 V at I_E = 10 mA.

Key Specifications

Pinout & Package

Package: TO-220 (standard through-hole, 3-pin, vertical mounting). Pin assignment confirmed per Figure 1 and Table 1: Pin 1 = Collector, Pin 2 = Base, Pin 3 = Emitter. Mounting tab is electrically connected to collector.

Key Features

Applications

Equivalent & Alternatives

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

Compared with STBUL49DFP, BUL49D offers 2.3× higher power dissipation and direct collector-tab connection for simplified thermal design; versus BU508A, it delivers 12× faster fall time and 50% lower saturation voltage-critical for high-frequency, high-efficiency lamp drivers.

Availability

BUL49D is available at Aetrix Electronics and suitable for electronic transformers for halogen lamps, flyback converters, and forward converters requiring stable component supply with long-term industrial availability and JEDEC-compliant lead-free packaging.

Supply support for BUL49D 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, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The BUL49D belongs to ST's high-voltage bipolar power transistor product line, engineered specifically for rugged, high-frequency switching in lighting ballasts and offline SMPS-prioritizing voltage endurance, switching speed, and lot-to-lot consistency.

FAQ

What is the maximum safe operating voltage for BUL49D in continuous DC blocking?

The absolute maximum V_CES is 850 V with base open, validated per Table 2. For reliable long-term operation, ST recommends limiting V_CE to ≤750 V in continuous DC blocking applications to maintain >15% safety margin against transients and temperature derating. This aligns with typical design practices for halogen transformer primary switches fed from 400 VDC bus.

Can BUL49D replace BU2508AX in a 35 kHz halogen lamp driver?

No-BU2508AX has 1500 V V_CEO and different gain/saturation characteristics. BUL49D's 450 V V_CEO(sus) and 850 V V_CES are sufficient for 400 VDC bus applications, but its h_FE profile (10–60) and 0.6 V V_CE(sat) differ significantly from BU2508AX. Direct substitution requires revalidation of base drive and thermal design.

Is the metal tab of BUL49D electrically connected to any internal terminal?

Yes-the metal tab is internally connected to the collector (Pin 1), as confirmed in Figure 1 and mechanical drawings. This requires electrical isolation from the heatsink unless the collector node is referenced to chassis ground. Insulating pads or shoulder washers must be used if the heatsink is grounded elsewhere in the circuit.

What is the recommended gate/base drive for reliable saturation at 4 A collector current?

Per Table 4, 0.8 A peak base current is required to achieve V_CE(sat) ≤ 0.6 V at I_C = 4 A. A base resistor of ≤10 Ω (with 8 V drive) or dedicated transistor driver (e.g., ULN2003) is recommended. Fast turn-off requires negative base drive (−5 V) or active pull-down to minimize storage time, as shown in Figure 13 test circuit.