Semiconductor Fundamentals Unit 6 – Transistor Load Lines and Gain
Exercise 2 – Collector Current Versus Base Current
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to demonstrate the relationship of
collector current to base current by using a transistor circuit. You will verify your results with a
multimeter.
DISCUSSION
- The circuit used in this exercise has two voltage supplies: one biases the base and the other
supplies the collector current. - Vary base current by adjusting the potentiometer (R2).
- The base-emitter junction is forward biased and the base-collector junction is reverse biased.
- The emitter current is equal to the sum of the base and collector currents.
- The base region is thin and lightly doped compared to the collector and emitter. This
condition allows current to flow between the base and collector junction even when the
junction is reversed biased. - Dc current gain is the ratio of collector-base currents (IC/IB) when the transistor is operating
in the linear region and is represented by the symbols βDC or hFE. - Beta can be between 10 and 500 and will increase with changes in the operating temperature
of the transistor. The transistor used in this exercise has a beta of between 50 and 300. - Gain is the transistor property that allows a small base current to control a much larger
collector current. - Gain defines the degree to which a transistor amplifies small input signals into large output
signals.