## ENGR 2010 (Section 02) – Assignment 7 Due: Wednesday November 25th, 11:59 pm Points: 20 Prof. Lei Reading: Sections 6.2-6.3 of Nilsson and Riedel, Electric Circuits, 9th Edition Submit electronic solutions (i.e. using Microsoft Word or a scanned copy of your written work) to the following problems on Blackboard. To receive credit, you must show work indicating how you arrived at each final answer. Problem 1 Consider the RC circuit on the right. and suppose that Vs(t) is a time-varying voltage input shown at the bottom. a) Suppose VC(0) = 0V. Plot VR(t) and VC(t) from 0ms to 300ms. Show your work in obtaining VR(t) and VC(t). b) Suppose the capacitance value is changed to 2μF, and VC(0) = 0V. Plot VR(t) and VC(t) from 0ms to 300ms. Show your work in obtaining VR(t) and VC(t). c) Explain how VC(t) qualitatively compares with Vs(t), and how VR(t) qualitatively compares with Vs(t). d) Explain how the capacitance value affects VC(t). t Vs(t) 1V -1V 50ms 100ms 150ms 200ms 250ms + – Vs(t) 100000 Ohms 1 uF + – VC(t) + – VR(t) 0ms 300ms Note: Capacitors are often used to protect against sudden changes in a voltage value, which could damage electronic components. Here, Vs(t) undergoes many sudden changes, but VC(t) undergoes less change. Problem 2 Using PSpice, perform two transient analysis simulations – one for the circuit in part (a), and one for the circuit in part(b) of problem 1 – to verify that your plots in problem 1 are correct. For each simulation, plot the traces for VR(t) and VC(t). Hint: You may need to perform arithmetic operations between simulation traces. Take a screenshot of your constructed circuits and the simulation traces for VR(t) and VC(t), which you will submit onto Blackboard. t Vs(t) 1V -1V 50ms 100ms 150ms 200ms 250ms + – Vs(t) 100000 Ohms 1 uF + – VC(t) + – VR(t) 0ms 300ms 1 uF or 2 uF Problem 3 Consider the Resistor-Diode circuit on the right, and suppose that Vs(t) is a time-varying voltage input shown at the bottom. Suppose that for the diode to turn on, it needs 0.7V between the positive and negative terminals. a) Plot VR(t) and VD(t) from 0ms to 300ms b) Explain how VD(t) qualitatively compares with Vs(t), and how VR(t) qualitatively compares with Vs(t). t Vs(t) 1V -1V 50ms 100ms 0ms 150ms 200ms 250ms 300ms + – Vs(t) 100000 Ohms + – VD(t) + – VR(t) Problem 4 Using PSpice, perform a transient analysis simulation for the circuit in problem 3 – to verify that your plots in problem 3 are correct. For the simulation, plot the traces for VR(t) and VD(t). To create the diode in PSpice, use the Dbreak component. After placing the component on the page, highlight the component, and edit the Pspice model (Edit -> PSpice Model) and set Rs to 0. Hint: You may need to perform arithmetic operations between simulation traces. Take a screenshot of your constructed circuit and the simulation traces for VR(t) and VD(t), which you will submit onto Blackboard. Note that your simulation trace plots may not be exactly the same as those from Problem 3, since the PSpice diode model has a turn-on voltage that’s not exactly 0.7V. t Vs(t) 1V -1V 50ms 100ms 0ms 150ms 200ms 250ms 300ms + – Vs(t) 100000 Ohms + – VD(t) + – VR(t) Problem 5 (Bonus: 5 points) In the circuit from problem 1 (shown on the right), write several sentences to explain why VC(t) is often referred to as the “low-pass filtered” output, and VR(t) is often referred to as the “high-pass filtered” output. You will need to look up the definitions for “low-pass” and “high-pass” filters. Examining your plots for VC(t) and VR(t) will help. t Vs(t) 1V -1V 50ms 100ms 150ms 200ms 250ms + – Vs(t) 100000 Ohms 1 uF + – VC(t) + – VR(t) 0ms 300ms

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