Experiment 1 - The Transistor Circuit

To understand how a transistor works, a simple circuit is enough.

Consider the circuit shown... Simple transistor circuit. (Enlarge) The circuit has the typical behavior of a transistor circuit...

Circuit diagram of a simple transistor circuit.

• If the push-button switch S1 is open, no voltage applies to the base and no current flows into the base. The transistor blocks and the LED1 remains dark.
• If you press S1, a small voltage applies to the base, and a small current flows through the base into the transistor. The transistor is switches through and the LED1 lights up.

A small current into the base of the transistor has the result that a much larger current flows through the transistor from the collector to the emitter. The base current is amplified!

However, this is not the only way of how a transistor can amplify current, or also voltage...