Download Electronic Devices and Circuits – EET2222

Electronic Devices and Circuits – EET2222
Lab 5 – Bipolar Transistor Biasing
Reading:
Floyd, Thomas L., Electronic Device, Sections 5-1 through 5-3.
Objectives: After completing this experiment, you will be able to:
1. Construct and analyze a base bias transistor circuit.
2. Select appropriate bias resistors for a specified bias circuit.
Summary
of Theory:
For a transistor to amplify signals, the base-emitter junction must be forward-biased and
the base-collector junction must be reverse-biased. Transistor biasing circuits use
external resistors to provide the specific dc voltages and currents needed for proper
quiescent (no signal) conditions for circuit operation. These conditions are said to
establish the operating point or Q-point of the transistor circuit.
We will investigate bias circuits for three basic bipolar transistor circuit configurations:
common-base bias, common-emitter bias, and common-collector bias.
Procedure:
Part I – Base Bias
1. Calculate the value of RB in the circuit in Figure 3 to obtain a VCE of 4.5 V and a
collector current of 2 mA. (Hint: use the curve tracer)
2. Obtain a resistor with the closest standard value to what you calculated in step 1 for
RB. Measure and record the resistance of both resistors for the circuit in Figure 1.
3. Connect the circuit in Figure 1 using a 2N2219A transistor. Measure and record IC,
IE, IB, VCB, VBE, VRc, and VCE. Calculate and draw the load line for this circuit. Insert
a dot to show the measured operating point of your circuit.
4. Change RC to 1 kΩ and repeat steps 2 & 3. Plot the load line and new operating
point on the same graph as the one used in step 3.
5. Change RC to 4.7 kΩ and repeat steps 2 & 3. Plot the load line and new operating
point on the same graph as the one used in step 3.
6. Restore RC to its original value and obtain a second 2N2219A transistor. Repeat
steps 8 & 9. Plot the load line and operating point on a different graph than the one
used in steps 3, 4, & 5.
Questions:
1. Describe how to use a DMM to determine if a transistor is operating properly.
2. How did changing RC in steps 4 & 5 change the load line and operating point of the
circuit in Figure 1. Why?
3. How did your results change when you used a second transistor in step 6? Why?
Figure 1
Figure 2