NPN Transistor (2N2222 / BC547)
A tiny electronic switch — a small base current controls a big load.
How it works
A transistor lets a small signal control a much larger current. Used as a switch, a little current into the base (through a resistor) turns on a much bigger current from collector to emitter — so one Arduino pin can drive a motor, a relay coil, or a whole strip of LEDs that the pin could never power directly.
For an NPN transistor: emitter to GND, the load between +V and the collector, and the controlling pin to the base through a resistor (~1 kΩ).
Pins
- Base
- Control — to a digital pin through a ~1kΩ resistor.
- Collector
- To the load (the load's other end goes to +V).
- Emitter
- To GND.
Ratings
- Example
- 2N2222 / BC547, ~500–800 mA
- Base resistor
- ~1 kΩ
Tips
- Always drive the base through a resistor.
- Switching a motor or relay? Add a flyback diode across the load.
- Pinout varies by package — check the part's datasheet.