EECE 310 Exam, Spring 2008

American University of Beirut · Electronics · 1 page

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EECE 310 Exam, Spring 2008, page 1

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Test 3 (Oct 22, 2007) Two identical zener diodes are connected back-to-back and in series with a 1.5 V battery as shown. The diodes have VZ = 5.92 V at 30 mA and rZ = 4 . When conducting in the forward direction, they may be modeled by 0.7 V in series with 1 . If vI is the rectangular waveform shown, determine the upper and lower levels of vO. Solution: For the zener diode, Vz = Vz0 + 0.004IZ. Substituting Vz = 5.92 V and IZ = 30 mA, gives VZ0 = 5.8 V. During the positive phase of vI, the circuit will be as shown, where Vz0 + VD0 = 6.5 V, and rZ + rD = 5 . It follows that  0.04 A, and vO = 6.5 + 1.5 + 50.04 = 8.2 V. During the negative phase of vI, the circuit will be as shown. It follows that  0.1 A, and vO = 1.5 – 6.5 – 50.1 = – 5.5 V. t, s vI, V 10 -10 1 2 t, s vI, V 10 -10 1 2 + – 10 V + – vO 45  1.5 V 6.5 V 5  I + – 10 V + – vO 45  1.5 V 6.5 V 5  I + – 10 V + – vO 45  1.5 V 6.5 V 5  I + – 10 V + – vO 45  1.5 V 6.5 V 5  I + – vI + – vO 45  1.5 V + – vI + – vO 45  1.5 V