EE 321 Lab
Prelab for Lab 5: DIODES AND RECTIFIER CIRCUITS

1) Consider the `superdiode' shown in Figure 2.

• If Vo is positive which way is current flowing in the load resistor? Where is the current coming from? Which way is current flowing in the diode? What voltage would you measure at the output of the op-amp?
• If Vo is negative, answer the above questions. Would you expect the output to go negative when the input does?
• When the input goes positive what do you expect Vo to do?
• When the input goes negative what do you expect Vo to do?

2) Consider the "bridge" rectifier of Figure 3.

• Sketch the current path thru the diodes during each half-cycle (first when the sine input is positive and then when it is negative). Indicate the voltage drop across each diode and resistor.
• Reverse any one diode and draw the current paths and find voltages as above. What would the result be if you did this in the lab?

3) Consider the 'ripple' voltage for a full wave rectifier as you will measure in part 8. There will be a 5 k load and a 10 uf capacitor. First draw a figure of the waveform as in Fir 3.42 in Sedra and Smith with correct time and voltage scales (Vin = 10 V p-p).

• Use three methods to find the ripple amplitude.
• First use dv/dt = i/C to find the voltage drop. Show that this gives a peak to peak ripple voltage of iT/C where T is the period of the rectified signal.
• Second use V = Vpeak e -t/tau as a function for the voltage drop. Show that this gives a peak to peak ripple voltage of Vpeak (1- e -t/tau)
• Third find a formula in the book.
• Reduce the load resistance to 100 ohms, and find the ripple voltage by the three methods. Which make sense, which don't?

Extra Credit - do this in the prelab so you can do the extra credit part of the lab. Analyze the extra credit circuit and show measured voltage is proportional to the average (not peak) of the absolute value of the input voltage. Find the constant of proportionality and complete the design.