The George Washington University
 School of Engineering and Applied Science
 Department of Electrical and Computer Engineering
 ECE 20 - Spring 2003
Experiment # 4

Bipolar Junction Transistors
Testing & Characteristic

Equipment:
You must make up a complete equipment list and have your instructor review it before you start.

Components:

• Q1 - 2N3904 NPN Transistor
• R1 - 100 KW

Objectives:

• To use an ohm meter to determine the forward and reverse resistance of transistor pn junctions
• To use the diode test function of the Keithley Model 175 to measure transistor pn junction characteristics
• To obtain several transistor characteristic curves by plotting the information taken from a transistor test circuit
• To obtain the IV Characteristic Curves for a transistor by using a Tektronix Model 571 Curve Tracer
• To determine the h parameters (h_ie, h_re, h_fe and h_oe) of a Transistor
• To verify manufacturer specifications

1.-  (HW) Transistor specifications, ratings and symbols

Refer to the specifications for the 2N3904 and find the following information.  The specification (in PDF format) can be accessed HERE.

1. transistor type
2. maximum power it can dissipate at 25⁰ Celcius
3. maximum collector current rating
4. maximum collector to emitter voltage rating
5. operating temperature range
6. minimum and maximum h_fe
7. the emitter to base breakdown voltage
8. h_ie @ I_C = 5 mA
9. h_fe @ I_C = 5 mA
10. h_oe @ I_C = 5 mA
11. h_re @ I_C = 5 mA
12. V_BE @ V_CE = 1.0 V and I_C = 5 mA

• Place all this information in Data Table A - 2N3904 Specifications & Ratings.

• Identify the base, collector and emitter pins of the 2N3904. Draw a pin out diagram of this device and call it Figure A - Pin Out Diagram of 2N3904.

• Draw and label the electrical symbols for a NPN and PNP transistor. Place this information in Figure B - Types of Transistors & Their Electrical Symbols.

2.-  Static Measurements

1. (HW) From experiment #1, what would you think the forward-biased Resistance values are for base-emitter junction and the base-collector junction of Q₁ ?

2. Set the ohm meter to the 200 kW scale. Measure and record the forward bias resistance of the base-emitter junction and the base-collector junction in Q₁. Set the ohm meter to its highest scale and measure and record the reverse bias resistance of both junctions in Q₁. Place this information in Data Table B - 2N3904 Characteristics.

3. (HW)How do you make sure that the base-emitter or base-collector pn junctions were working properly using Keithley Model 175.

4. Test both pn junctions of Q₁ with the diode test function of the Keithley Model 175. Measure and record the forward and reverse biased readings of Q₁ of both of these junctions. Include this information also in Data Table B.

3.- (HW) I_B vs V_BE for different values of V_CE with ORCAD

Plot I_B vs V_BE for different values of V_CE. Use Figure #1 for the circuit.  This plot is a SPICE parametric DC sweep. The ranges for I_B and V_BE are 50 mA and 1Volt. V_CE should vary from 0 to 10 Volts with 1 Volt increments. Label this plot "Plot A - ORCAD I_B vs V_BE".
Hint: NS3904 can be obtained from "bipolar.olb" library in ORCAD.  You must do DC sweep with primary sweep varying V_BE and secondary Sweep varying V_CE.  IB should be in y axis.

4.-  I_B vs V_BE Measurements Using a Test Circuit

Fig # 1

Assemble the circuit shown in Figure # 1.
a)  Set V_CE = 1 V_DC and vary I_B from 5 to 50 mA in steps of 5 mA and record the values of I_B and V_BE  for each step.

b)  Set V_CE = 10 V_DC and once again vary I_B from 5 to 50 mA in steps of 5 mA and record the value of  I_B and V_BE for each step.

Place all this information in Data Table # 1 - Base Characteristics. Plot I_B vs. V_BE in Graph # 1 - 2N3904 Base Characteristics (be sure to annotate the V_CE lines for V_CE = 1V and V_CE = 10V).

5.- (HW) I_C vs V_CE for different values of I_B with ORCAD

1. Plot I_C vs V_CE for different values of I_B. Use Figure #1 for the circuit.  This plot is a SPICE parametric DC sweep. The ranges for I_C and V_CE are 10 mA and 10 Volts. I_B should vary from 0 to 50 mA with 5 mA increments. Label this plot "Plot B- ORCAD I_C vs V_CE".

2. Repeat part a) but for the value of b equal to 10. Why there is a difference in the graph when you change b value?

Hint: To change b value, follow these steps:
1.  Highlight NS3904 in the circuit
2.  Click on Edit
3.  Click on PSpice Model.
4.  b is called "BF" in the model.
5.  Change the BF value to 10

Hint: NS3904 can be obtained from "bipolar.olb" library in ORCAD.  You must do DC sweep with primary sweep varying V_CE and secondary Sweep varying V_BE.  I_C should be in y axis.

6.-  I_C vs V_CE Measurements Using a Test Circuit

Using circuit of Figure #1:
a)  Set I_B = 20 mA and vary V_CE from 0 to 2 V_DC in 0.2 V_DC steps. Then vary V_CE from 2 V_DC to 10 V_DC in 2.0 V_DC steps.   Record the value of  I_C and V_CE for each step.

b)  Set I_B = 40 mA and vary V_CE from 0 to 2 V_DC in 0.2 V_DC steps. Then vary V_CE from 2 V_DC to 10 V_DC in 2.0 V_DC steps.
record the value of  I_C and V_CE for each step.

Place all this information in Data Table # 2 - IV Characteristic Data. Plot I_C vs. V_CE in Graph # 2 - 2N3904 Characteristic Curves (be sure to annotate the I_B lines for I_B = 20 mA and IB = 40 mA).

7.-   I_C vs V_CE Measurements Using a Curve Tracer

Obtain a copy of a family of 10 curves for the 2N3904 from the Tektronix Model 571 Curve tracer. Set I_C to be no greater than 10 mA, V_CE to be no greater than 10 V and I_B to step 10 times in 5 mA steps (be sure to annotate the I_B lines).  Label this plot as "Plot C - I_C vs V_CE Measurements Using a Curve Tracer"

8.- Data Analysis

1. Determine h_ie, h_re, h_fe, and h_oe when V_CE = 5V and I_C = 5 mA from Graph #1 and Graph #2.

Hint:  Use the handout that will be given in class to find those values.

2. Compare your results to the manufacture’s specifications.
3. Determine the values of g_m, r_p, r_e, and r_o in terms of the h parameters.
4. Determine the values of g_m, r_p, and r_e from the following formulas:

g_m= I_C / V_T
r_p= V_T / I_B
r_e= V_T / I_E

6. Compare the values obtained in c) and d)