Lab 6 Transistor Amplifiers

Transcription

1 ECET 242 Electronic Circuits Lab 6 Transistor Amplifiers Page 1 of 5 Name: Objective: Lab Report: Equipment: Students successfully completing this lab exercise will accomplish the following objectives: 1. Learn to construct a common-emitter amplifier circuit. 2. Analyze the amplifier circuit and conduct measurements to determine operating parameters. An informal lab report will be required for this lab. Include all collected data, typed responses to any discussion questions, and graphs generated using a computer-based application. The report will be due 1 week after the lab exercise is carried out. Dual power supply 2N3904 NPN transistor Resistors: 10 Ω, 470 Ω, 680 Ω, 680 Ω, 3 k Ω, and 2.2 k Ω Polarized capacitors: 100µF, 100µF and 22µF Breadboard Wire Jumper Kit Connecting leads Oscilloscope Digital Multimeter (DMM) Procedure 1: Measurements and Analysis 1. Select the resistor values shown in Table 1. Measure and record the actual values of each resistor in Table 1 also. Table 1: Measured Values of Amplifier Biasing Resistors Component Measured Value R C = 680 Ω R L = 680 Ω R E =470 Ω R 1 = 3 k Ω R 2 = 2.2 k Ω

2 Page 2 of 5 2. Construct the universal biasing circuit shown in Figure 1. Use the resistors selected in the previous step. Select capacitors as follows: C IN = 22 µf, C OUT = C E = 100 µf. V CC R 1 R C C OUT V C C IN V B R L V E R 2 RE CE Figure 1: Common Emitter Amplifier Circuit 3. Turn on the power supply and set the voltage to 20 V. Measure the transistor voltages and record your results below. V B = V C = V E = V C should be about 10 V. If it is not, then debug the circuit. Using Ohm s Law the measured voltages above, and the measured resistances in step 2, calculate the collector and emitter currents: I C = I E = Using the relation, I E = I C + I B, substitute the calculated currents above and calculate the base current: I B = 4. Pull out the transistor and measure the voltage at the base test point. V B with transistor removed = Calculate the percent change in V B between no transistor and transistor in. % change = 5. Have the instructor check your circuit.

3 Page 3 of 5 Procedure 2: Measurements and Analysis 6. Connect the audio generator to an voltmeter. Set the frequency to 1000 Hz. Adjust the attenuation for an voltage of 30 mv rms. 7. Insert the transistor back into the circuit. Connect a 10 Ω resistor in series with the audio generator in series with C IN. Measure the voltages v HI and v LOW on each side of the 10 Ω resistor. Use Ohm s Law to calculate the input current, i IN, and the input impedance, Z IN. v HI = mv rms i IN = µa rms v LOW = v IN = mv rms Z IN = kω 8. From the current divider rule, i R1 R2 = i IN x Z IN / (R 1 R 2 ), calculate the current in the (R 1 R 2 ) parallel combination. i R1 R2 = µa rms 9. From Kirchhoff s Current Law, i IN = i b + i R1 R2, calculate the base current. i b = µa rms 10. From Ohm s Law, v IN = i b x Z IN (base),calculate the impedance looking into the base current. Z IN (base) = Ω 11. Use the DMM to measure the output voltage, v OUT, on the high side of the load resistor, R L. The high side is connected to the capacitor, C OUT. Calculate the output current, i OUT, from Ohm s Law. v OUT = mv rms i OUT = ma rms 12. From Ohm s Law, v OUT = i RC R C, calculate the current in the collector resistor. i RC = ma rms 13. From Kirchhoff s Current Law, i C = i RC + i OUT, calculate the collector current. i c = ma rms 14. Calculate the current gain of the transistor: h fe = i c / i b = 15. From the measurements above, calculate the voltage gain, A v = v OUT / v IN, and the current gain, A i = i OUT / i IN and the power gain, A P = A v x A i. Record all results from these calculations and those above in Table 2 below. 16. Attach the channel 1 probe of the oscilloscope to the test point for v IN and attach the channel 2 probe of the oscilloscope to the test point for v OUT. Set up the oscilloscope to display channels 1 and Sketch v IN versus time and v OUT versus time on the same graph. On the left vertical axis of the sketch, indicate input voltage values at each major grid line. On the right vertical axis, indicate output voltage values at each major grid line. On the horizontal axis, indicate time values at each major grid line.

4 Page 4 of 5 Figure 2: Input voltage (v IN ) and outputvoltage (v OUT ) versus time 18. Using no measurements and only nominal component values, calculate the transistor voltages and currents for h fe = 150. Show calculations on the next page. Record your calculated values in column 2 of Table 2. Table 2: Measured versus Calculated Parameters for a Common Emitter Amplifier Parameter Symbol Measured or Calculated from Measured Values Calculated Units Base Voltage V B V Collector Voltage V C V Emitter Voltage V E V Base Current I B ma Collector Current I C ma Emitter Current I E ma Impedence Looking into Base Z IN(Base) Ω Input Impedence Z IN Ω Input Current i IN µa Base Current i b µa Collector current i c ma Current Gain of the Transistor Output Current Output Voltage Amplifier Voltage Gain Amplifier Current Gain Amplifier Power Gain h fe i OUT v OUT A v A i A P ma rms V rms

5 Calculations: Page 5 of 5