EE 461G Introduction to Electronics

Homework # 4 Due September 21, 1999

Review for exam 1. Your are responsible for Chapter 3 in Sedra and Smith, sections 3.1, 3.2, 3.3.4, 3.10, 3.11, 3.12, 3.13, 3.14, and 3.16. Your are responsible for knowing how to use B2 spice and in particular on how to determine tend and tstep. Your are also responsible for knowing the material from circuits 1 and 2. In particular know how to solve a first order system (an RC circuit is an example) for both transient and steady state.

Problem 1

The input voltage to a circuit is a 1kHz, 10V rms sine wave. The output is a 1kHz 5Vrms sine wave at 45 degrees lagging. Sketch the waveforms on a common scale as you would see them on an oscilloscope.

  1. Label the peak value of the input.
  2. Label the peak value of the output.
  3. Label the period.
  4. Label the time delay between the input and output.
  5. Is this circuit capacitive or inductive?

Problem 2

  1. Draw the diode schematic symbol and label the anode and the cathode.
  2. Label the direction of easy current flow.
  3. Draw the characteristic curve of a diode with a 0.7 forward bias voltage and a reverse breakdown voltage of 15 V.
  4. On your drawing label the three regions of diode operation, forward bias, reverse bias, and reverse breakdown.

Problem 3

Diodes can be used to create logic gates such as "and" and "or" gates. For the circuits above what is the output voltage and the current in the resistor for the input voltages in the table below? Assume the diode forward drop is 0.7 V when the diode is forward biased.

a) Fill in the table below for circuit a)

b) Fill in the table below for circuit b)
 

Va

Vb

Vo

IR
         

i)

0 V

0 V

    

ii)

0 V

5 V

    

iii)

5 V

0 V

    

iv)

5 V

5 V

    

c) What is the minimum reverse breakdown voltage (voltage rating) the diodes must have?

Problem 4

Io = 250 mA, F = 10,000 Hz, L = 1.0 mH

The current source is a sine wave that is stepped on at t equal to zero. The initial current in the inductor is 0 A. The diode is ideal with a 0.7 V drop when it is forward biased.

a) Carefully draw I(t) for one cycle numerically labeling both the vertical and horizontal axis.

b) Draw the above circuit during the first quarter cycle of the current input replacing the diode with its appropriate equivalent circuit.

c) Compute the inductor current and inductor voltage during the first quarter cycle. Give expressions in terms of L, w, and Io and find the numerical value of the largest value of the inductor voltage. At what value of t is the inductor voltage a maximum? 10 points

d) At what inductor voltage and time does the diode change states (form on to off or off to on)? Give numerical values.

Problem 5

You are to design a voltage regulator with a 15Vdc output that can work from no load to a full load of 5W. The input voltage is 25V.

  1. What is the no load resistance value?
  2. What is the full load output current and load resistance value?
  3. What is the minimum current in the Zener diode at full load and the maximum current in the Zener diode at no load?
  4. What is the maximum value of Rreg?
  5. What is the power dissipated in the Zener diode at full load and no load?
  6. If the input voltage drops to 20V and Rreg is the value you calculated in part d), what is the maximum load for which the regulator still regulates?