Transistor Biasing

Lab is based on the fundamentals of a transistor biasing and the analysis of the circuit.

The goal of Transistor Biasing is to establish a known Q-point in order for the transistor to work efficiently and produce an undistorted output signal. In bipolar transistor circuits, the Q-point is represented by ( VCE, IC ) for the NPN transistors or ( VEC, IC ) for PNP transistors.

Please review the following videos before getting started with this lab:

1. Watch the video: "Video 3: Fundamentals of breadboard"
2. Watch the video: "Video 4: Basic electrical components"
3. Watch the video: "Video 5: Simple resistive circuit with NI myDAQ"

Materials and Equipment:

Materials:

• Hardware Parts (In the Toolbox):

o An NPN transistor: 2N3904
o Four resistors: 1 kΩ, 470Ω, 3 kΩ and 6 kΩ
o Jumper wires

Equipment:

• Hardware Equipment:

o Breadboard
o NI myDAQ Instrument device
o Screw Driver
o Screw Terminal connector
o USB Cable
o Multimeter with probes
o Multimeter from NI ELVISmx Instrument Launcher

Procedure:

*** This lab has to be implemented only in hardware (using NI myDAQ) ***

1. Analyze the circuit in the Figure 1 below to calculate the following values: V_BB, V_E, I_E, V_C and V_CE. Make sure to include 20% tolerance for each resistor in the calculations.

2. Construct the circuit shown in Figure 1 below on the breadboard using the transistor and two resistors (RCand RE).

Figure 1

3. Using the jumper wires, screw driver and screw terminal connector, connect the board to NI MyDAQ Instrument Device.

4. Use channel +15V pin out on the NI myDAQ Instrument Device to provide the supply voltage (VCC). Use channel AI0 to measure the required voltages: VBB, VE and VC and currents: IC and IE using the Multimeter.

5. Tabulate the data from step 1 and step 5.

6. Short the resistor R2 and calculate the values in steps 1.

7. Modify the circuit in Figure 1 to short the resistor R2 and measure the values in step 4.

Review questions:

1. Compare a calculated and measured values in the table. Discuss whether the values are the same of different. If they are different, provide the reasoning. And how to reduce this difference between calculated and measured values.

2. What happens when R2 is shorted? Why does the measured values change?

3. If the NPN transistor is replaced with a PNP transistor, how does the change in the transistor effect the current and voltage in the circuit?

Deliverables:

1. Analysis of the circuit and calculations of voltages: V_BB, V_E and V_C and currents: I_C and I_E.

2. Place your student ID card on the breadboard and take a picture of the circuit board and pin out on the NI myDAQ Instrument Device.

3. Take screenshots of the measurements obtained from function generator and Multimeter on the NI ELVISmx Instrument Launcher on your screen.