13.4: Procedure

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13.4.1: Basic Operation

1. First, note that the circuit of Figure 13.3.1 is being powered directly from the AC line. Treat it with appropriate caution. It is worth repeating that any circuit should be de-energized when making any changes to it.

2. Consider the circuit of Figure 13.3.1 without the capacitor connected. For a positive polarity of secondary voltage, the upper right and lower left diodes will be forward biased and allow current to flow through the load from top to bottom. The other two diodes will be reverse biased. For a negative secondary polarity the opposite occurs. That is, the upper left and lower right pair will be forward biased while the other two are reverse biased. This arrangement will also cause load current to flow through the load from top to bottom, thus effectively flipping the negative polarity portion of the wave.

3. Build the circuit of Figure 13.3.1 with Rload = 1 k\(\Omega\) and C disconnected (open). This represents a very lightly loaded case. Under light loads, the output of the secondary will often be a little higher than the rated potential. Set the oscilloscope input to DC coupled. Measure and record the voltage across the secondary and then across the load. Do not use two probes to do this simultaneously as these two measurements do not share a common ground. Doing so will short out a portion of the circuit. Record the results in Table 13.5.1 and capture an image of the load voltage display.

4. Measure the load voltage with a DMM set to DC volts. Record this value in Table 13.5.1.

5. Replace the load with the 20 \(\Omega\) resistor to simulate greater loading. Repeat steps 3 and 4.

6. Return the load resistor to the original 1 k\(\Omega\) value and insert the 1000 \(\mu\)F capacitor. Measure the load voltage with both the oscilloscope and DMM, recording the values in Table 13.5.2. Be sure to capture an image of the scope display.

7. Replace the load with the 20 \(\Omega\) resistor to simulate greater loading. Measure the load voltage with both the oscilloscope and DMM, recording the values in Table 13.5.2. Once again, be sure to capture an image of the scope display.

13.4.2: Computer Simulation

8. Simulate the circuit of Figure 13.3.1 using Transient Analysis. Use three variations, comparing the plotted waveforms to those measured in the laboratory: C = open with Rload = 20 \(\Omega\), C = 1000 \(\mu\)F with Rload = 1 k\(\Omega\), and C = 1000 \(\mu\)F with Rload = 20 \(\Omega\).