EECE 310 Homework 3 with Solution, Fall 2007

American University of Beirut DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING EECE 310 – Electronics Fall 2007 – 2008 Homework 3 1. Consider the waveform shown below. t vs(t) (Volts) Vmax -Vmax T 2T The waveform is superimposed on a 9 V DC source, and applied to a circuit consisting of a 1 KΩ resistor and a (conducting) diode. Find the value of Vmax for which small-signal analysis is applicable, if the variation in the diode voltage is limited to +/– 10 mV. Assume that the diode drops a voltage of 0.7 V when conducting, and that n = 1.7. Provide a plot of the total diode current, as derived from DC and small-signal analyses. 2. Repeat Problem 2, parts (a) and (b) in Homework 2 using the following model for the conducting diodes: VD0 = 0.68 V, rD = 30 Ω. 3. Design a Zener voltage regulator to provide a regulated voltage of around 9 V. The available 9.1 V, ½ W Zener is specified to have a drop of 9.1 V at a test current of 16 mA. At this value of current rZ is specified to be 6.25 Ω. The value of IZK for the Zener diode is 3 mA. The unregulated supply varies between 12 V and 15 V. The regulator is required to supply a load that dissipates 10 to 300 mW at 9 V. a. Find VZ0 for the Zener diode. b. Calculate the range of values for the resistor R in the circuit. c. Using a value of R that is close, to the nearest standard resistor value, to the upper range: i. Find the change in load voltage that corresponds to the 12-to-15 V variation in the unregulated supply voltage. Assume that the load current is constant. ii. Find the change in load voltage that corresponds to the full change in load current. Assume that the supply voltage is fixed. iii. What is the maximum current that the Zener diode should be able to conduct? What is the Zener power dissipation under this condition?