80 V PNP for medium-current linear and switching stages
The BD140-16 is a PNP bipolar power transistor rated for 80 V collector-emitter breakdown and 1.5 A continuous collector current, housed in a TO-225AA (SOT-32) through-hole package. It is part of the BD140 series from STMicroelectronics, a complementary pair to the NPN BD135 series, and is commonly used in medium-voltage linear regulators, relay and solenoid drivers, audio output stages, and general-purpose switching up to a few amps.
1.25 W dissipation — heatsinking required above a few hundred mA
Maximum power dissipation is 1.25 W, which sets the thermal budget for the TO-225AA package. At 1.5 A collector current, the Vce(sat) of 500 mV at 50 mA base drive (Ib=50 mA, Ic=500 mA) gives a conduction loss of 0.25 W at that point — but at full rated current the drop will be higher, and the junction-to-ambient thermal resistance of the TO-225AA (typically around 100 °C/W without a heatsink) means continuous operation above a few hundred mA requires a clip-on or bolted heatsink.
DC current gain floor: hFE min 40 at 2 V, 150 mA
The minimum DC current gain is 40 at Vce=2 V and Ic=150 mA, which is the typical bias point for linear regulator pass elements and audio driver stages. This hFE floor means the base drive current needed for a 1 A load is at least 25 mA — within the output capability of most op-amps and driver ICs. The 100 nA collector cutoff current (ICBO) at 150 °C junction is low enough not to affect bias stability in most designs, though leakage doubles roughly every 10 °C rise.
Through-hole TO-225AA — board assembly fit
The 0.100-inch (2.54 mm) lead pitch is standard for stripboard and prototyping, and the package body is compatible with most TO-126 footprints. For production, the through-hole mounting means wave soldering or hand-soldering — no reflow profile needed, but the leads must be clinched or the part mechanically secured before solder. The tab is collector-connected, so if a heatsink is used, an insulating washer and thermal compound are required unless the heatsink is electrically floating.