Experiment 10 - The Darlington Pair

In the last experiment, you saw that a very weak signal at the base of a transistor, can barely be amplified. However, the amplification can be increased significantly by a combination of two transistors.

Take the circuit from the last experiment and leave the potentiometers P1 and resistor R1 unaltered. You know that you have a very weak signal.

Build the circuit shown that now contains two transistors. If you re-connected the battery, the LED will light up brightly again! Darlington pair of two transistors. (Enlarge) This circuit is known as a "Darlington Pair".

Circuit diagram of the Darlington pair.

Over the next three experiments, you take a look at another class of transistor applications.