EE 2212

EXPERIMENT 5

5 October 2017

Full Wave Bridge Rectifier and Precision Rectification Signal Processing Function

Diode-Bridge Full-Wave Rectifier

Ø Construct the circuit shown in Figure 1. Note that to provide a floating input from the signal generator which has one side grounded , we will use a transformer to provide isolation. There could be two styles of transformers in the bin. One plugs directly into the circuit board; note the “P” stands for primary. The second type has colored leads. Both are essentially the same. Review the overview of transformer operation as presented in our class.

Ø Do not monitor the input of the bridge with the oscilloscope because you will automatically ground (that is short circuit) one side of the circuit. Monitor the input on the signal generator side of the circuit. (Brown and blue transformer primary winding). Also observe how this floating input is modeled in SPICE. Refer to the SPICE demo in class last week.

Figure 1 Full-Wave Bridge Rectifier

Ø Start by setting the input Vs as a 10 volt peak-to-peak 100 Hz sinusoid. Same input as we used for the half-wave rectifier. You will also adjust the input voltage and observe the results. Observe and plot Vo(t) and the transfer characteristic, Vo vs Vs. Explain why this circuit would function as an “absolute value” extraction function circuit.

Ø Now use the three values of C from 1μF to 100 μF across the 1 kΩ resistor to illustrate and measure the change in ripple voltages by measuring Vo(t). Use the ”Measure” menu on the oscilloscope to measure the rms voltage of the output using dc and ac coupling. Explain the differences in these measurements and explain what these measurements are illustrating. Use your diode model and check your lab measurements using SPICE.

Ø Compare your full-wave rectifier results with SPICE simulations and the half-wave rectifier circuits studied in Experiment 4.

PRECISION RECTIFICATION-DIGITAL SIGNAL PROCESSING FUNCTION (DSP)

Precision rectification is used in DSP (Digital Signal Processing) applications where the “switch” and absolute value function needs to be implemented but there must be a minimization of the effect of the diode forward voltage. Can we design a circuit that negates the 0.7 volt forward voltage drop? Of course the answer is yes or why would we spend the time in the lab demonstrating this!

Measure the transfer characteristic, Vout as a function of Vin of the circuit shown in Figure 2(a). Pay particular attention to the effect of the diode offset voltage. Now construct the circuit shown in Figure 2(b). Use ±12 volts for the mA 741 operational amplifier. Measure the transfer characteristic and compare to the results in Figure 2(a). Justify the term “precision rectification” when applied to the circuit in Figure 2(b). Refer to Section 12.8 of the text, page 745, Figure 12.51 for additional information. Simulate in SPICE.

Figure 2 (a) and Figure 2(b)

More Good Stuff-The 10 Commandments (Sort of archaic prose but fun)