Transistor as a Switch and Amplifier

PHY-118 · Semester I · Physics

Sandboxintermediate15 minAvailable

Transistor switch & amplifierA tiny I_B controls a big I_C

How to play

Objective

Drive an NPN transistor with a small base current and watch a much larger collector current turn a load on and off - the electronic switch inside every CPU.

The idea

A tiny current into the base unlocks a much bigger current between collector and emitter. Below a threshold the transistor is OFF; above it, ON; between, it amplifies.

Try this

1Slowly raise the base current and watch the load brighten.
2Find the cutoff, active and saturation regions on the curves.
3Raise the supply voltage and watch saturation move.
4Flip the base drive and watch the transistor snap on and off.

Watch for

Cutoff: no base drive, no collector current - OFF.
Active: collector current is beta times the base current - amplification.
Saturation: the transistor can't pass more - fully ON.
Millions of these tiny switches form a CPU.