Modern Physics 6 Question 4

4. The figure represents a voltage regulator circuit using a Zener diode. The breakdown voltage of the Zener diode is 6V and the load resistance is RL=4kΩ. The series resistance of the circuit is Ri=1kΩ. If the battery voltage VB varies from 8V to 16V, what are the minimum and maximum values of the current through Zener diode?

(Main 2019, 10 April II)

(a) 1.5mA,8.5mA

(b) 1mA,8.5mA

(c) 0.5mA,8.5mA

(d) 0.5mA,6mA

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Solution:

  1. In given voltage regulator circuit,

Zener breakdown voltage, VZ=6V

So, across RL, potential drop is always 6V.

So, current through load resistance is

iL=VZRL=64×103=1.5×103A

Now, when VB=8V

Potential drop across R1=86=2V

So, current through R1 is i1=VR1=21×103=2×103A

So, current through Zener diode is

iZ=i1iL=2×1031.5×103=0.5×103A=0.5mA

Similarly, when VB=16V

VR1=166=10Vi1=101×103=10×103A

Hence,

iZ=i1iL=10×1031.5×103=8.5×103A=8.5mA



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