Experiment 7 - The Transistor as a Switch

In the context of the term "transistor" inevitably the keywords "switch" and "amplifiers" come up. What does it mean? Here you look first at a electronic switch circuit.

Basically, in previous experiments you have used the transistor in a switch circuit. To illustrate this, expand the circuit from the experiment 2 by a potentiometer.

Switch circuit of a transistor. (Enlarge) Protect Base Never connect the base directly to +9 volts! It would result in the flow of an excessive current and immediately destroy the transistor. Therefore always protect the base by a resistor (R1)!

Circuit diagram of a switch circuit.

When turning the potentiometer P1, the LED lights up very brightly for a long time before she goes out relatively quickly. A small base current is sufficient to fully switch through the transistor. If the base current decreases below a certain level, the transistor shuts rapidly.