450 V / 4 A NPN power transistor in TO-220
The STMicroelectronics BUL1102E is an NPN silicon power transistor designed for medium-power switching and linear applications. Its 450 V collector-emitter breakdown voltage and 4 A continuous collector current rating place it squarely in the off-line power supply, motor drive, and lighting ballast space. Packaged in the industry-standard TO-220-3 through-hole case, it suits both new builds and legacy BOM maintenance where a proven bipolar switch is preferred over a MOSFET.
The 450 V Vce breakdown gives enough headroom for rectified 240 VAC rails (≈340 V DC) with margin for line transients. At 4 A collector current, the device handles loads like small motors, transformer primaries, or switching regulator inputs in the 50–150 W range. The 1.5 V saturation voltage at 2 A collector current means conduction loss of about 3 W at that operating point — factor that into heatsink sizing.
Thermal and package considerations
The 70 W maximum power dissipation is the absolute ceiling with infinite heatsink — real-world designs will derate significantly. The TO-220 package's metal tab must be bolted to a heatsink for any continuous current above about 1 A. The junction temperature rating of 150°C sets the thermal design limit; keep Tj below 125°C for reliability in industrial environments.
It is ROHS3 compliant, suitable for markets requiring the latest RoHS exemption updates.