El escenario
A robotics student needs to control a 12V DC gear motor from a microcontroller PWM output.
Qué hay en este dibujo
Lee las decisiones que hay detrás.
01TIP120 Darlington provides ~1000x current gain
MCU sinks only ~1 mA at base while collector switches up to 5 A.
02
4.7 kΩ base resistor limits Ib to ~2.6 mA, keeping the transistor in saturation.
03
1N4007 flyback diode clamps inductive kick from motor windings, protecting the BJT.
Replace TIP120 with an N-channel MOSFET (IRFZ44N + gate resistor) for better efficiency at higher currents.