Pre-biased NPN for compact switching loads
The Toshiba RN1421TE85LF is an NPN pre-biased transistor in a S-Mini (SOT-23-3) package, integrating two 1 kΩ resistors — one in series with the base (R1) and one from base to emitter (R2). This eliminates two external passives from the BOM, saving board space and placement cost in high-volume designs.
200 mW power ceiling in a small footprint
Maximum power dissipation is 200 mW, which is the practical thermal limit for the SOT-23-3 body. At 800 mA Ic, the Vce(sat) of 250 mV at 50 mA means the on-state voltage drop is low, but the 200 mW ceiling still governs the duty cycle and ambient temperature range. For continuous conduction above 100 mA, check the junction temperature against the derating curve — the small package has limited copper area to sink heat.
Built-in resistors simplify base drive
With R1 = R2 = 1 kΩ, the base current is set by the input voltage divided across the resistor network, so the transistor turns on when the drive voltage exceeds roughly 0.7 V plus the drop across R2. The 300 MHz transition frequency makes it fast enough for low-frequency switching up to a few megahertz — think relay drivers, LED strings, or logic-level interface buffers. The minimum DC current gain of 60 at 100 mA, 1 V ensures adequate drive margin for most loads.