Department of Electrical Engineering, IIT Kanpur ESc 201: Introduction to Electronics

9th September, 2013

Home Assignment – 6

1. For the circuit shown in Fig. 1, using ideal diodes, find the voltage (V0) and current (I) indicated.

(a) (b)

I10 kΩ

10 kΩ

10 kΩ

10 kΩ

+15V +10V

Vo

(c) (d)

Fig. 1

2. For the circuit shown in Fig. 2, sketch the output voltage waveform with time. When diode conducts, voltage drop is 0.7 V and forward resistance is 50 Ω. In OFF state diode is open circuit. Assume )sin(15 tVi ω= V.

Fig. 2 Fig. 3

Department of Electrical Engineering, IIT Kanpur ESc 201: Introduction to Electronics

3. The Zener diodes used in Fig. 3 have the following characteristics: Forward drop = 0.7

V; Zener voltage = - 7 V; Rf (Forward Resistance) = 20 Ω ; Rz (Resistance in Zener region) = 10 Ω. Sketch the output waveform Vo with time.

4. (a) Determine VL, IL, IZ and IR for the voltage regulator network shown in Fig. 4 if RL = 180 Ω. (b) Repeat part (a) if RL = 470 Ω. (c) Determine the value of RL that will establish maximum power conditions in the Zener diodes. (d) Determine the minimum value of RL to ensure that the Zener diode in "ON" state.

220 Ω

RL VL

IL

+

-

+

-

IR Rs

20 V

IZ

VZ = 10 VPzmax = 400 mW

Fig. 4 Fig. 5

5. A Full Wave Rectifier is shown in Fig. 5. The center tapped transformer voltage is 35 V

rms, 50 Hz. A 160 µF capacitor is connected in the output to filter out the load voltage ripple. A load of 250 Ω is connected in parallel with filter capacitor. Assume that the cut-off voltage of diode is 0.7 V and forward biased resistance is zero.

(a) Plot the output voltage Vo and diode current iD at steady state. (b) Calculate the ripple voltage and maximum diode current. (c) Calculate the peak inverse voltage.

6. A Full Wave Bridge Rectifier is used to design a dc power supply that provides an

average dc output voltage of 15 V on which a maximum of ±1 V ripple is allowed. The rectifier feeds a load of 150 Ω. The rectifier is fed from the line voltage (120 V rms, 60 Hz) through a transformer. The diodes available have 0.7 V drop when conducting.

(a) Specify the rms voltage that must appear across the transformer secondary. (b) Find the required value of the filter capacitor. (c) Find the PIV rating of the diode.

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