EL - 200

Electronic Devices

Lab #4: Bipolar Transistor Circuits

Andrew Buettner

March 6, 2003

• Objective

The objective of this lab is to use a curve tracer to measure transistor parameters. Another objective of this lab is to construct and test base bias and voltage divider bias circuits. Then to observe the effect of b on the operating point of the test circuits.

• Equipment Used

  1) Trainer #:

  2) Multimeter #:

  3) Curve Tracer #:

  4) Transistor Type: 2N3904

  5) Additional components of the EL - 200 Lab kit

• Procedure

  I) Part A: Setting up the Curve Tracer

  1) Set the peak voltage range switch to "low (20V)," and the comparison switch to the center position.

  2) Power the curve tracer and warm it up for about 5 minutes.

  3) Insert one transistor into each socket of the tester.

  4) Set the tester to the following settings:

  i) Dissipation limiting resistance = 1K

  ii) Steps / sec = 240

  iii) Steps / family = mid range

  iv) Step control = .01mA / step

  v) Both Polarity controls to NPN (+)

  vi) Horizontal sensitivity = 2V / div

  vii) Vertical Sensitivity = 2mA / div

  viii) Collector sweep peak volts fully counter clockwise

  ix) Base step = repetitive

  5) Switch the transistor switch to `A' and increase the peak voltage until a good reading can be taken. If needed, fine tune the intensity and focus.

  6) Adjust the controls so the trace is on the lowest division of the screen.

  7) Hold the zero current - zero volts switch in the zero current position and further adjust the the position controls to set the trace aligns with the bottom horizontal.

  8) Use the step zero control to further make the first trace coincide with the lowest division and to ensure that each step is an increment of 10mA.

  9) Adjust the steps / family so that it is accurate for at least six traces

  10) Increase the peak volts so that at least the first three traces extend the full width of the display.

  II) Part B: Recording Information from the Curve Tracer

  1) Using the display from the tracer, determine I_C at V_CE = 10V, and I_B = 20mA

  2) Compute b for that point

  3) Record I_C for each I_B step at V_CE = 2V and V_CE = 10V, use the data to prepare a graph for the transistor

  4) Set the transistor switch to the `B' position

  5) Repeat steps 1 through 3

  III) Part C: Bias Circuits:

  a: Base Bias Circuit

  1) Assemble the following circuit:

  2) Record V_RB, V_RC, and V_CE

  3) Record I_B, I_C, and b

  4) Repeat steps 2 and 3 using transistor 2

  b: Voltage Divider Bias Circuit

  1) Assemble the following circuit:

  2) Record V_RC and V_C

  3) Record I_C

  4) Repeat Steps 2 and 3 using transistor 2

• Data

  1) Table 1: Part B: Table of I_C values for I_B and V_CE for Transistor 1

  I_B

  VCE	10mA	20mA	30mA	40mA	50mA	60mA
  2V	0mA	1.5mA	2.6mA	4.2mA	5.6mA	6.4mA
  10V	0mA	1.5mA	2.6mA	4.4mA	5.6mA	6.5mA

  2) Table 2: Part B: Table of I_C values for I_B and V_CE for Transistor 2

  I_B

  VCE	10mA	20mA	30mA	40mA	50mA	60mA
  2V	0mA	1.6mA	2.9mA	4.5mA	5.9mA	7.2mA
  10V	0mA	1.6mA	3.0mA	4.6mA	6.1mA	7.3mA

  3) Table 3: Data from Part III, a

  	VRB	VRC	VCE	IB	IC	b
  Transistor #1	11.28V	3.330V	8.67V	34.2mA	4.06mA	119
  Transistor #2	11.29V	3.61V	8.39V	34.2mA	4.40mA	129

  4) Table 4: Data from Part III, b

  	VRC	VC	IC
  Transistor #1	5.15V	6.48V	7.90mA
  Transistor #2	5.22V	6.75V	8.23mA

  5) Diagram 1: Schematic 1, Enlarged View

  
  6) Diagram 2: Schematic 2, Enlarged View

  

  7) Diagram 3: Graph of Transistor 1:

  
  

  8) Diagram 4: Graph of Transistor 2:

  
  

• Answers to Lab Questions

  1) Q: Use the data obtained from part B to graph the transistors:

  A:

  2) Q: Draw the load lines and show the Theoretical and actual Q points on the graph for circuit 2.

  A:

  3) Q: Compare the theoretical Q point and experimental Q point values

  A: In both circuits, the Q points are extremely close, but they are not exact.

  4) Q: Plot the load line and Q points for circuit 3.

  A:

  5) Q: Compare the theoretical Q points and the experimental Q points.

  A: The Q points for transistor 2 are much closer than they are for transistor 1 but they seem closer together than they are for schematic 1.

  6) Q: Compare the operating stability of the two circuits.

  A: From the data shown, it appears that circuit 2 has a more stable operation than circuit 1 because the actual Q points and the calculated Q points are closer together.

• Conclusions

  From this lab it can be seen that the effects of a different b can be lessened by the construction of the circuit that uses the transistor.

• Attachments

A) Original Handout

B) Original Lab Data

C) Calculations