Transistor Amplifier Circuits Unit 2 – Common Base Circuit
Exercise 1 – Common Base Circuit DC Operation
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to determine the dc operating
conditions of a common base (CB) transistor circuit by using a typical CB circuit. You will
verify your results with a multimeter.
DISCUSSION
- In common base amplifier circuits the base terminal is common to both the input and output
signals. - The voltage divider network provides the fixed dc base voltage required to forward bias the
base-emitter junction of the transistor. - The voltage divider equation can be used to calculate the base voltage (VB).
- VBE, base-emitter voltage, of a forward biased silicon transistor is approximately 0.6 V.
- The emitter voltage (VE) is the difference between the base voltage and the base-emitter
voltage. VE = VB - VBE - Ohm’s law is used to calculate both emitter current (IE) and collector current (IC).
- Collector current can be found in two other ways: First the collector current is approximately
equal to the emitter current. Second the collector current is the difference between the emitter
current and the base current. IC = IE − IB - Transistor characteristic curves and dc load lines are used to determine the Q (quiescent)
point, dc-point, or operating point of the transistor circuit. - Saturation occurs when the base-collector voltage is zero.