350 V, 4 A Darlington in DPAK — load-switching workhorse
The STMicroelectronics STD901T is an NPN Darlington transistor rated for 350 V collector-emitter breakdown and 4 A continuous collector current, housed in a DPAK (TO-252-3) surface-mount package. The 35 W maximum power dissipation sets the thermal budget: at 2 A collector current with a 2 V saturation drop, the conduction loss is 4 W, leaving headroom for switching losses in a typical motor or solenoid drive at moderate frequency.
Vce(sat) is specified at 2 V maximum with 20 mA base current and 2 A collector current — the Darlington configuration trades a higher saturation voltage for the very high gain. The 100 µA collector cutoff current at rated Vce is the leakage floor; at elevated junction temperature (150 °C max) it will rise, but stays within the typical Darlington range for this voltage class.
Package and mounting — DPAK layout notes
The DPAK (TO-252-3) has two leads plus a tab — the tab is the collector.
ROHS3 compliant.