EGR 240 Lab 10. June 7-8, 2006. Rev. A

EXPERIMENT: Transformers, Diodes, Capacitors, and Power Supplies

A. Line Voltage.

The lab instructor will measure the line voltage with the oscilloscope and the multimeter. Record the measured values.

Oscilloscope Vpk-pk ______V

Oscilloscope Vrms ______V

Oscilloscope Frequency ______Hz

Oscilloscope Period ______ms

Multimeter AC V ______V

B. Transformer.

Plug in a transformer and measure the output voltages with the oscilloscope and the multimeter. Set the multimeter to read AC. Record the measured values.

1.  Output A to center tap:

Oscilloscope Vpk-pk ______V

Oscilloscope Vrms ______V

Oscilloscope Frequency ______Hz

Oscilloscope Period ______ms

Multimeter AC V ______V

2.  Output B to center tap:

Oscilloscope Vpk-pk ______V

Oscilloscope Vrms ______V

Multimeter AC V ______V

3.  Output A to B (multimeter only):

Multimeter AC V ______V


C. Half-wave Rectifier.

  1. Using a transformer and a breadboard, build the circuit shown in Figure 1.

Figure 1. Half-wave Rectifier.

  1. Measure the output voltage across RL with the oscilloscope and the multimeter. Set oscilloscope CH 1 to DC and the multimeter to read DC. Record the measured values.

Oscilloscope DC Vpk ______V

Oscilloscope Vrms ______V

Multimeter DC V ______V

  1. Draw the waveform seen on the oscilloscope.

Volts/Division (vertical)

______

Time/Division (horizontal)

______

Oscilloscope Screen Layout


D. Full-wave Rectifier.

  1. Modify the circuit shown as shown in Figure 2.

Figure 2. Full-wave Rectifier.

  1. Measure the output voltage across RL with the oscilloscope and the multimeter. Record the measured values.

Oscilloscope DC Vpk ______V

Oscilloscope Vrms ______V

Multimeter DC V ______V

  1. Draw the waveform seen on the oscilloscope.

Volts/Division (vertical)

______

Time/Division (horizontal)

______

Oscilloscope Screen Layout

  1. Add a 1.0 μF filter capacitor as shown in Figure 3.

Figure 3. Full-wave Rectifier with Filter.

  1. Measure the output voltage across RL with the oscilloscope and the multimeter. Record the measured values.

Oscilloscope DC Vpk ______V

Oscilloscope Vrms ______V

Multimeter DC V ______V

  1. Draw the waveform seen on the oscilloscope.

Volts/Division (vertical)

______

Time/Division (horizontal)

______

Oscilloscope Screen Layout

  1. Replace the 1.0 μF filter capacitor with a 10 μF capacitor as shown in Figure 4.

Figure 4. Full-wave Rectifier with Filter.

  1. Measure the output voltage across RL with the oscilloscope and the multimeter. Record the measured values.

Oscilloscope DC Vpk ______V

Oscilloscope Vrms ______V

Multimeter DC V ______V

  1. Draw the waveform seen on the oscilloscope.

Volts/Division (vertical)

______

Time/Division (horizontal)

______

Oscilloscope Screen Layout


Answer questions 37 - 40 on the class website for the next lab:

37. What is your best estimate of the turns ratio, secondary to primary, of the transformer? To provide an output voltage of 1.0 V, what input voltage would be required? Assuming 100% efficiency, what primary input current will be drawn if the secondary current drawn by the load is 10 mA?

38. Explain the purpose of the diode in a half-wave rectifier. Why does the diode conduct for only half a cycle?

39. Why does the addition of a second diode provide output for a full cycle? What is the phase relationship between the output from the upper half and the lower half of a center-tapped transformer?

40. What happens to the ripple amplitude if the size of the filter capacitor is increased? What happens to the ripple amplitude if the load resistance RL is decreased?

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