Lab 3 Rectifier Circuits

Transcription

1 ECET 242 Electronic Circuits Lab 3 Rectifier Circuits Page 1 of 5 Name: Objective: Students successfully completing this lab exercise will accomplish the following objectives: 1. Learn how to construct a full-wave rectifier using both center-tapped transformer and bridge configurations. 2. Learn how to filter rectified waves to generate a DC source from an AC source. 3. Learn how to measure ripple effects from a filtered power supply. Lab Report: A formal lab report will be required based on your combined results from labs 2, 3 and 4. Retain you results from this lab exercise and combine them with results from labs 2 and 4. The formal lab report will be due one week after lab 4 has been performed. Equipment: Oscilloscope, 2 kω resistor, 1N4004 silicon diodes (4), 1 µf capacitor, 100 µf capacitor, Digital Multimeter (DMM), Cadet II Lab Trainer Breadboard and Power Supply. Procedure 1: Center-tapped Transformer Rectifier 1. Turn on the oscilloscope. 2. Follow the basic setup for display and measurement of time-varying signals from Lab Examine the Cadet II lab trainer. Notice the red, yellow and blue terminals of the 12.6 V transformer output. The red and blue terminals are connected to the ends of the secondary winding of the transformer. The yellow terminal is connected to the center tap of the transformer. 4. Examine the bread boards on the Cadet II lab trainer. Notice that there are four vertical columns for power strips per breadboard. Connect the ends of the secondary windings (red and blue terminals) to the outer vertical columns of one of the breadboards. Connect the center tap (yellow terminal) to the inner vertical columns. 5. Set the ground reference to the center tap of the transformer secondary winding. To do this, use a connecting lead to connect the yellow terminal of the transformer to the ground (black) terminal of the lab trainer. 6. Using the oscilloscope, clip the CH1 probe first to the blue terminal, then to the red terminal to measure the peak-to-peak voltage (with respect to ground) on each half of the secondary winding. Make sure the switch on the CH 1 probe is set to x1. Record your measurements in Table 1 below. Table 1: Transformer winding voltages Quantity Description Measured Value V 1 (P-P) Voltage across left half of winding (Yellow to Red) V 1 (P) V 2 (P-P) V 2 (P) Peak value of sine wave of V 1 (P-P) Voltage across right half of winding (Yellow to Blue) Peak value of sine wave of V 2 (P-P) 7. Construct the center-tapped transformer full wave rectifier shown on page 911 of the textbook. Use a 2 kω resistor as R L.

2 Page 2 of 5 8. Using the oscilloscope, connect the CH 1 probe to measure and display the resistor voltage. The probe should be connected at the 3-way junction of the resistor and the two diodes. This is the load voltage of the rectifier. Figure 1: Load voltage of a center-tapped transformer full-wave rectifier 9. Using the oscilloscope, measure the peak voltage of the rectified waveform. To obtain an accurate measurement, be sure to zero out the waveform and adjust the vertical control to set the ground level to the x-axis. V L (P) = V Notice that the peak value of the load voltage is about 0.7 V lower than the peak value of the supply voltage. 10. Using the relationship: V dc = V L(P), calculate the average value of the rectified wave from the measured peak load voltage, V L (P). Calculated V L (dc) = V 11. Use a DMM to measure the average load voltage. Connect the DMM across the terminals of the resistor and measure the DC voltage. This is the average load voltage of the rectifier. Measured V L (dc) = V 12. Add a 1 µf capacitor in parallel with resistor and notice the effects. BE VERY CAREFUL TO NOTE THE POLARITY OF THE CAPACITOR. (polarized caps can explode in you are not careful!!) Connect the + side of the capacitor to the HIGH (+) side of the resistor and the side of the capacitor to the LOW (-) side of the resistor. This is the filtered load voltage of a rectifier.

3 Page 3 of 5 Figure 2: Load voltage of a center-tapped transformer full-wave rectifier with a 1 µf filter capacitor 13. Replace the 1 µf capacitor with a 100 µf capacitor. BE VERY CAREFUL TO NOTE THE POLARITY OF THE CAPACITOR. (polarized caps can explode in you are not careful!!) Connect the + side of the capacitor to the HIGH (+) side of the resistor and the side of the capacitor to the LOW (-) side of the resistor.this is the filtered load voltage of a rectifier. Figure 3: Load voltage of a center-tapped transformer full-wave rectifier with a 100 µf filter capacitor Procedure 2: Bridge Rectifier Circuit 14. Connect the bridge rectifier using four 1N4004 diodes and a 2 kω load resistor as shown on page 912 of the textbook. 15. Remove the ground reference from the windings of the transformer. Connect a new ground reference to the black ground connection on the trainer and wire to one of the vertical columns. Connect this column appropriately as the to the ground points of your bridge rectifier circuit. 16. Connect the oscilloscope to measure resistor voltage. 17. Adjust the oscilloscope view until you see the full rectified waveform.

4 Page 4 of 5 Figure 4: Load voltage of a bridge rectifier 18. Add a 1 µf capacitor in parallel with the load resistor. BE VERY CAREFUL TO NOTE THE POLARITY OF THE CAPACITOR. Measure the Ripple voltage of the load voltage. The ripple voltage is the peak-to-peak voltage of the waveform. V RPP = V Calculate the Percent ripple (peak-to-peak) where %Ripple = (V RPP / V P ) x 100%. %Ripple = % Figure 5: Load voltage of a bridge rectifier with a 1 µf filter capacitor 19. Replace the 1 µf capacitor with a 100 µf capacitor. BE VERY CAREFUL TO NOTE THE POLARITY OF THE CAPACITOR. The ripple voltage is the peak-to-peak voltage of the waveform. Sketch the load voltage waveform with the 100 µf capacitor installed.

5 Page 5 of 5 Figure 6: Load voltage bridge rectifier with a 100 µf filter capacitor Measure the Ripple voltage of the load voltage. Record your result below. V RPP = V Calculate the Percent ripple (peak-to-peak) where %Ripple = (V RPP / V P ) x 100%. %Ripple = % Calculate the theoretical ripple voltage using equations from the textbook. V Ripple = V (theoretical) Calculate the % error between the measured and theoretical ripple voltage. %Error = %