assignment6

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

RL

11th Sept. 2014

Home Assignment-6

1. A single phase full wave rectifier is shown in the Figure 1. The transformer voltage is 35 V

rms,50 Hz to center tap. A 160µF 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. The diode

resistance and the transformer leakage reactance may be neglected.

a) Calculate the cut out angle (the angle at which a diode stops conduction).

b) Plot the output voltage V0 and diode current at steady state.

c) Approximating the load voltage to be represented by the piece wise linear curve, draw a

suitable Thevenin’s model for the rectifier circuit.

d) Calculate average load current through 250Ω resistor and % regulation.

C

D1

35V 50Hz

Vout

+

-

Figure 1


-V0 +

Vi

2. Determine the output waveform for the network of Figure 2. Assume the diodes are ideal.

Calculate the output dc level and required PIV of each diode.

10 V

ωt

Figure 2(a)

2K

2K 2K

Figure 2(b)

3. In the circuit shown in Figure 3, I is a dc current and Vi is a sinusoidal signal with small

amplitude (less than 10 mV) and a frequency of 100 kHz. Representing the diode by its small

- signal resistance rd, which is a function of I,

(a) Sketch the circuit for determining the sinusoidal output voltage V0, and the thus find the

phase shift between Vi and V0.

(b) Find the value of I that will provide a phase shift of -450 and

(c) Find the range of phase shift achieved as I is varies over the range of 0.1 to 10 times this

value

Assume n=1.

Vi


DC

C10 nF

I

Figure 3

4. The circuit in Figure 4 implements a complementary output rectifier. Sketch and clearly label

the waveforms of v0+

and v0-. Assume a 0.7 V drop across each conducting diode. If the

magnitude of the average of each output is to be 15V, find the required amplitude of the sine

wave across the entire secondary winding.

Figure 4

Vi

V0

V0+

V0-


V0

5. The Zener diode of Figure 5(a) is used in a certain application where the output voltage Vo is

used to drive a load RL, connected parallel to the zener as shown in Figure 5(b). Calculate the

following:

a) Range over which Vo will vary when the input voltage is varied from 10 to 12 volts.

b) Power rating required for the Zener diode.

Assume no load conditions for (a) and (b).

c) If Vi = 12 volts, find the range of load currents possible through RL for Vo > 6.2 volts.

I (mA)

10

-6.5 -6.2 -6 5 0.9

-5 0.7 0.8 V (Volts)

-10

Figure 5(a)

1K

10-12V

1K

Figure 5(b)

Vi RL


6. Determine the output voltage with reference to ground for the circuit shown in Figure 6(a) and

Figure 6(b), assuming that cut-in voltage of both diode and Zener diode is 0.7V and that Zener

voltage is 3V.

2V

1K

D1

D2

6V

4.7V

1K

D1D2

1K

Figure 6(a) Figure 6(b)

7. Design the power supply circuit shown in Figure 7 that will supply 10V to a load of 1000Ω with

ripple voltage less than 0.2V. As part of the design, determine transformer turns ratio, value of

capacitance, diode peak current and peak inverse voltage. Assume that input is 220V rms with a

frequency of 50Hz.

C D1

D2

Vs

N1 N2

0

50

J…

Fo

o…

Figure 7

V0 V0

V0

RL


8. In an unregulated DC power supply using center-tapped transformer, as shown in Figure 8 , we

need to develop Vo = 8V across a 10Ω load (RL), with no more than 2% ripple present in Vo.

Determine:

a) The transformer turns ratio N,

b) The value of the filter capacitor C, and

c) The minimum breakdown voltage and the minimum peak current ratings of the diodes D1 and D2

(both using a safety factor of 2).

Use first- order diode model with Vϒ = 0.6 V.

C

D1

D2

-

+ +

-

-

+

230 V50Hz

Center-tapped transformer

N:1

Figure 8

V0

RL


9. A simple diode clamping circuit is shown in Figure 9. Draw the input and output waveforms for a

sinusoidal input Vi, varying from -15V to +15V. Use second- order model for diodes D1 and D2 with

V(gamma1) = V(gamma2) = 0.6 V, rF1 = 30 ohm and rF2 = 20 ohm. Here V (gamma) denotes the cut

in voltage.

-+

+-

+ +

- -

Vi Vo

Figure 9

assignment6

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