READING:Floyd, Sections 2-2 through 2-4

OBJECTIVES:After performing this experiment, you will be able to:

1. Construct half-wave, full-wave, and bridge rectifier circuits, and compare the input and output voltage for each.

2. Connect a filter capacitor to each circuit in objective 1 and measure the ripple voltage and ripple frequency.

MATERIAL NEEDED:One 12.6 V AC center-tapped transformer with fused line cordFour diodes 1N4007 (or equivalent)Two 2.2 kΩ resistorsTwo 100µF capacitors

PROCEDURE:Do this experiment only under supervision.

Warning! In this experiment, you are instructed to connect a low-voltage (12.6V ac) transformer to the ac line. Be certain that you are using a properly fused and grounded transformer that has no exposed primary leads. Do not touch any connection in the circuit. At no time will you make a measurement on the primary side of the transformer. Have your connections checked by your instructor before applying power to the circuit.

1. Connect the half-wave rectifier circuit shown in Figure 2. Notice the polarity of the diode. The line indicates the cathode (negative) side. Connect the oscilloscope so that channel 1 is across the transformer secondary and channel 2 is across the load resistor. The oscilloscope should be set for LINE triggering throughout this experiment as the waveforms to be viewed will all be synchronized with the ac line voltage. View the ac voltage into the rectifier, V IN and load voltage, VLOAD, for this circuit and sketch them on Plot 1. Label voltages on your sketch.

Plot 1

Measure the input voltage to the diode, VIN, and the output peak voltage, VLOAD. Remember to convert the oscilloscope reading to rms voltage. Record the data in Table 1.

VIN VLOAD

2. The output isn’t very useful as a dc source because of the variations in the output waveform. Connect a 100µF capacitor (C1) in parallel with the load resistor (R1). Note the polarity of the capacitor. Measure the dc load voltage, VLOAD and the peak-to-peak ripple voltage, VRIPPLE, in the output. To measure the ripple voltage, switch the oscilloscope vertical input to AC COUPLING. This allows you to magnify the small ac ripple voltage without including the much larger dc level. Measure the peak-to-peak ripple voltage and the ripple frequency. The ripple frequency is the frequency at which the waveform repeats. Record all data in Table. 1.

Table 1 Half-Wave Rectifier Circuit

Without Filter Capacitor With Filter CapacitorsCRO Measured

DVM-AC Measured

2 x VIN(RMS) Computed

CRO MeasuredDVM-DC

MeasuredMeasured Ripple

FrequencyVIN (PEAK) VIN (rms) VIN (PEAK) VLOAD (PEAK) VLOAD (DC) VLOAD (dc) VRIPPLE

3. Disconnect power and change the circuit to the full-wave rectifier circuit shown in Figure 3. Notice that the ground for the circuit has changed. The oscilloscope ground needs to be connected as shown. Check your circuit carefully before applying power. Compute the expected peak output voltage. Then apply power and view the V IN and VLOAD waveforms. Sketch the observed waveforms on Plot 2.

Plot 2

Measure VIN (rms) and the peak output voltage (VLOAD) without a filter capacitor. Record the data in Table 2.

4. Connect the 100µF capacitor in parallel with the load resistor. Measure VLOAD, the peak-to-peak ripple voltage, and the ripple frequency as before. Record the data in Table 2.

Table 2 Full-Wave Rectifier Circuit

Without Filter Capacitor With Filter CapacitorsCRO Measured

DVM-AC Measured

2 x VIN(RMS) Computed

CRO MeasuredDVM-DC

MeasuredMeasured Ripple

FrequencyVIN (PEAK) VIN (rms) VIN (PEAK) VLOAD (PEAK) VLOAD (DC) VLOAD (dc) VRIPPLE

VIN VLOAD

5. Investigate the effect of the load resistor on the ripple voltage by connecting a second 2.2 kΩ load resistor in parallel with RL and C1 in the full-wave circuit in Figure 3. Measure the ripple voltage. What can you conclude about the effect of additional load current on the ripple voltage?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

6. Disconnect power and change the circuit to the bridge rectifier circuit shown in Figure 4. Notice that no terminal of the transformer secondary is at ground potential. The input voltage to the bridge, V IN, is not referenced to ground. The oscilloscope cannot be used to view both the input voltage and the load voltage at the same time. Check your circuit carefully before applying power. Compute the expected peak output voltage. Then apply power and use a voltmeter to measure V IN (rms). Use the oscilloscope to measure the peak output voltage (VLOAD) without a filter capacitor. Record the data in Table 3.

7. Connect the 100µF capacitor in parallel with the load resistor. Measure VLOAD, the peak-to-peak ripple voltage, and the ripple frequency as before. Record the data in Table 3.

Table 3 Bridge Rectifier Circuit

Without Filter Capacitor With Filter Capacitors2 x VIN(RMS)

ComputedDVM-AC

MeasuredDVM-DC Measured

VLOAD(DC) =0.636Vload(PEAK)

CRO Measured

DVM-DC Measured (Step#8)

Measured Ripple Frequency

VIN (PEAK) VIN(rms) VLOAD (DC) VLOAD (PEAK) VLOAD (DC) VLOAD (dc) VRIPPLE

8. Simulate an open diode in the bridge by removing one diode from the circuit. What happens to the load DC voltage? The ripple voltage? The ripple frequency?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

9. ZENER DIODE REGULATOR:1. Measure VRIN, VROUT (Ripple Voltage Vpk-pk)2. Calculate Rz

EVALUATION AND REVIEW QUESTIONS:

1. What advantage does a full-wave rectifier circuit have over a half-wave rectifier circuit?

2. Compare a bridge rectifier circuit with a full-wave rectifier circuit. Which has the higher output voltage? Which has the greater current in the diodes?

3. In step 3, you moved the ground reference to the center-tap of the transformer. If you wanted to look at the voltage across the entire secondary, you would need to connect the oscilloscope as shown in Figure 5 and subtract channel 2 from channel 1. (Some oscilloscopes do not have this capability). Why is it necessary to use two channels to view the entire secondary voltage?

4. Explain how you would measure the ripple frequency to determine if a diode was open in a bridge rectifier circuit.

RECTIFIERS

1. Dual Voltage Positive FW CT Bridge

2. Dual Voltage Positive/Negative FW CT

3. Dual Voltage Positive/Negative HW