The George Washington University
 School of Engineering and Applied Science
 Department of Electrical and Computer Engineering
 ECE 20 - LAB
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:

a. transistor type

b. maximum power it can dissipate at 25⁰C

c. maximum collector current rating

d. maximum collector to emitter voltage rating

e. operating temperature range

f. minimum and maximum h_fe

g. the emitter to base breakdown voltage

h. h_ie @ I_C = 5 mA

i. h_fe @ I_C = 5 mA

j. h_oe @ I_C = 5 mA

k. h_re @ I_C = 5 mA

l. 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

a. Set the ohm meter to the 200 kW scale. Measure and record the forward biased 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.

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

c. (HW) Explain what your tests would indicate if either the base-emitter or base-collector pn junctions were good, open or shorted.

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

Plot I_B vs V_BE for different values of V_CE. 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".

4.-  I_B vs V_BE Measurements Using a Test Circuit

Fig # 1

Assemble the circuit shown in Figure # 1. Set V_CE = 1 V_DC and vary I_B from 5 to 50 mA in steps of 5 mA and record the value of V_BE for each step. Set V_CE = 10 V_DC and once again vary I_B from 5 to 50 mA in steps of 5 μA and record the value of 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).

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

a. Plot I_C vs V_CE for different values of I_B. 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".

b. Repeat part a) but for the value of b equal to 10. Compare your results with those obtained in a).

6.-  I_C vs V_CE Measurements Using a Test Circuit

Set I_B = 20 mA and vary V_CE from 0 to 2 V_DC in 0.2 V_DC steps then step V_CE from 2 V_DC to 10 V_DC in 2.0 V_DC steps. Set I_B = 40 mA and once again vary V_CE from 0 to 2 V_DC in 0.2 V_DC steps then step V_CE from 2 V_DC to 10 V_DC in 2.0 V_DC steps. 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).

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).

8.- (HW) Data Analysis

a. Interpret and review all the data that you have taken.

b. Determine h_ie, h_re, h_fe, and h_oe when V_CE = 5V and I_C = 5 mA from plots A and B.

c. Compare your results to the manufacture’s specifications.

d. Determine the values of g_m, r_p, r_e, and r_o in terms of the h parameters.

e. 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

f. Compare the values obtained in d) and e)