50 V, 100 mA continuous collector rating
The RN2907,LF(CT: Minimum DC current gain of 80 at 10 mA, 5 V ensures consistent switching performance across the batch; the 200 MHz transition frequency keeps switching losses negligible at typical PWM frequencies below 100 kHz. Power dissipation is limited to 200 mW total — in a 25 °C ambient the US6 package's thermal resistance means each transistor should stay below 100 mW continuous when both are on simultaneously, or the junction temperature climbs past the safe operating area.
What the 10 kOhm base resistor means for the BOM
The 10 kOhm R1 sets the base current when the drive voltage is applied — at 5 V logic, the base sees roughly (5 V - 0.7 V) / 10 kOhm ≈ 430 µA, which with a minimum hFE of 80 supports a collector current of about 34 mA, well within the 100 mA rating. The 47 kOhm R2 across base-emitter provides a guaranteed off-state: with the drive at 0 V, the resistor pulls the base to emitter, keeping collector cutoff below 500 nA — critical for preventing leakage-driven loads in battery-powered or high-impedance circuits.