400 V, 12 A NPN — the TO-220 that handles the heavy lift
The ST13009: This puts it in the class of high-voltage switching transistors for off-line power supplies, fluorescent lamp ballasts, and medium-power inverters where a single TO-220 part handles the primary-side switch. The 2.5 V saturation voltage at 3 A base current and 12 A collector current (Vce(sat) max @ Ib=3A, Ic=12A) tells you the conduction loss at full load: at 12 A, expect about 30 W of dissipation in the saturated state, which drives the heatsinking requirement. The DC current gain of 10 minimum at 8 A, 5 V (hFE min @ Ic=8A, Vce=5V) confirms this is a high-current, moderate-gain device — the base drive needs to be sized accordingly.
TO-220 package — will it survive the hot air?
Housed in a TO-220-3 through-hole package, the ST13009 is a rework-friendly part. The tab is the collector, and the pinout is standard: base, collector, emitter left to right with the tab facing away. The copper tab is large enough to sink heat from a soldering iron on the collector pin without lifting the pad, as long as the iron tip is clean and the dwell time stays under 5 seconds per joint. Mounting is through-hole, so the leads go into plated holes on the PCB. The tab is typically soldered to a copper pour for heatsinking or bolted to an external heatsink with a TO-220 mounting clip and thermal pad. The tube packaging keeps the leads straight for auto-insertion.