Experiment 7 - Current gain of a Common Collector Circuit

How strongly does a common collector circuit amplify a current? For this measure the current at the input and output of the common collector circuit.

Use the circuit shown.

Measuring current in a common collector circuit. (Enlarge)

Circuit diagram current measurement in a common collector circuit.

Turn the potentiometer P1, until a current of approx. I_in = 0.010 mA flows into the base. At the same time you measure at the output a typical value of approx. I_out = 2.50 mA.

Turn P1 a little further until a current of approx. I_in = 0.015 mA flows into the base. Now you measure a typical value of approx. I_out = 3.50 mA at the output.

A change of only 0.005 mA into the base results in a rise of 1.00 mA at the output. This corresponds to a gain h_he = 200.

The gain h_he can vary greatly in your experiments. Important however is the finding...

                           

The current gain of a common collector circuit is high.

And what about the voltage gain...?