PNP medium-power switch in SOT-223
The STN790A is a PNP bipolar junction transistor from STMicroelectronics rated for 30 V collector-emitter breakdown and 3 A continuous collector current. It comes in a SOT-223 surface-mount package, which is a three-lead plus tab design that reflows easily and can be hand-soldered with a fine-tip iron or hot air. The 100 MHz transition frequency makes it suitable for medium-speed switching and linear regulation up into the low-MHz range.
What the 3 A and 30 V ratings mean for your circuit
The 3 A collector current is the continuous DC limit; pulsed operation can go higher if the junction temperature stays within the 150 °C maximum. At 3 A the saturation voltage is 700 mV typical, which gives a conduction loss around 2.1 W — that exceeds the 1.6 W package power limit, so in practice you derate the current or use pulse-width modulation to keep the average dissipation under the thermal ceiling. The 30 V VCEO is the collector-emitter breakdown with the base open; for inductive loads add a snubber or clamp diode to keep the flyback voltage below that limit.
Rework and footprint notes
SOT-223 is one of the more forgiving surface-mount packages for rework. The tab is the collector and provides both electrical connection and thermal path.
Lifecycle and procurement status
ROHS3 compliant.