Motion and power
PN2222A NPN transistor
Switch a small load using a modest base current.
What it does
A base current permits a larger collector-to-emitter current. In a low-side switch, the transistor connects the load’s negative side to ground.
Connections and compatibility
Identify emitter, base, and collector from the exact manufacturer’s datasheet. Use a base resistor and a base-to-emitter pull-down; the example switches only a low-current LED.
Choosing one
A known NPN transistor with documented pin order is preferable to an unmarked bag. Similar part names and packages can have different lead arrangements.
Common mistakes
Never substitute lead order from a photograph. An inductive load needs a flyback path; a motor needs a current and thermal calculation.
Use it in a tutorial
- Transistors — Build a low-side transistor switch, then learn what changes when the load becomes a motor or relay.