Darlington gain stage in a SOT-23
The ROHM 2SD2142KT146 is an NPN Darlington transistor rated for 30 V collector-emitter breakdown and 300 mA continuous collector current, packaged in a SOT-23-3 (SC-59) surface-mount case. The Darlington configuration delivers a minimum DC current gain of 10000 at 100 mA collector current and 5 V Vce, which means a microcontroller GPIO can switch a 300 mA load directly with less than 10 µA base drive — no external driver transistor needed. Transition frequency is 200 MHz, so it handles PWM and low-speed switching cleanly within the 200 mW power dissipation budget.
Vce(sat) and base drive budget
Saturation voltage is specified at 1.5 V maximum with 100 µA base current and 100 mA collector current. The 100 nA maximum collector cutoff current (ICBO) is tight enough for battery-powered circuits where off-state leakage matters.
The SOT-23-3 (SC-59) footprint is shared by thousands of small-signal transistors, so board layout reuse is straightforward. Maximum junction temperature is 150°C, and the 200 mW power limit is the practical ceiling for continuous operation in free air. For loads near 300 mA, check the pulse duty cycle against the thermal impedance of the board — the SOT-23 has limited copper to sink heat.