Experiment 4 - Current gain of a Common Emitter Circuit

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

Use the circuit shown.

Measuring current in a common emitter circuit. (Enlarge)

Circuit diagram current measurement in a common emitter circuit.

Turn the potentiometer P1, until a current of approx. I_in = 0.01 mA flows into the base. At the same time you measure at the output a typical value of approx. I_out = 3.00 mA.

Turn P1 a little further until a current of approx. I_in = 0.02 mA flows into the base. Now you measure a typical value of approx. I_out = 1.50 mA at the output.

A change of only 0.01 mA into the base results in a fall of 1.50 mA at the output (inverting!). This corresponds to a gain h_he = 150.

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

                           

The current gain of a common emitter circuit is high.

And what about the voltage in a common emitter circuit...?