ElectronicsQUICK REFERENCE
Transistors / MOSFETs
Switch a larger DC load with a low-side transistor circuit.
01N-channel MOSFET
- Connections
- Supply + → load → drain; source → GND; MCU GND → supply GND.
- Gate
- GPIO → small series resistor (~100 ohm) → gate; ~10 kohm gate-to-source pull-down.
- Selection
- Choose a logic-level part with RDS(on) specified at your actual 3.3 V or 5 V gate drive.
02NPN alternative
- Connections
- Load to collector; emitter to GND; base driven through a calculated resistor.
- Base resistor
- Estimate sufficient base current for saturation, then Rbase = (Vgpio − VBE) / Ibase. Respect GPIO limits.
- Dissipation
- Check current, voltage and thermal ratings; a small signal transistor cannot drive every motor.
03Inductive loads
- Flyback diode
- Across load: cathode at supply +, anode at transistor drain/collector.
- Power loss
- MOSFET conduction loss ≈ I² × RDS(on), plus switching loss.
- Startup
- Pull-down keeps the load off while GPIO floats at reset.