The BUJ106A,127 is an NPN power bipolar junction transistor in a TO-220-3 through-hole package. It is rated for a 400 V collector-emitter breakdown voltage and a continuous collector current of 10 A. The maximum power dissipation is 80 W, and the operating junction temperature limit is 150°C. This part belongs to a family of high-voltage NPN bipolars designed for switching and linear applications in power supplies, lighting ballasts, and motor drives where a 400 V blocking rating is required.
Ratings that matter for the BOM
The 400 V Vceo is the headline spec — it tells you this transistor can handle rectified mains up to about 265 VAC with margin for transients. The 10 A continuous current rating is the load-handling ceiling, but the real-world limit in a switching circuit is set by the saturation voltage and thermal impedance. Vce(sat) is 1 V maximum at 1.2 A base current and 6 A collector current, which means conduction loss at 6 A is about 6 W — you need a heatsink that keeps the junction below 150°C. The DC current gain minimum is 14 at 500 mA and 5 V, so at higher currents the forced beta drops further and the base drive must deliver several hundred milliamps to keep the device saturated.
Package and mounting
The BUJ106A,127 comes in a TO-220-3 package, also referred to as TO-220AB. It is a through-hole device with the standard three-lead power-tab form factor. The metal tab is the collector, and the device is designed to be bolted to a heatsink. The shipping medium is listed as Bulk, which means it arrives in tubes or loose pieces, not tape and reel — factor that into your pick-and-place planning if you are hand-loading or using a tube feeder.