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Question:

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 the Zener diode?

0.5mA;6mA

1mA;8.5mA

0.5mA;8.5mA

1.5mA;8.5mA

Solution:

At VB=8V, IL = 6 × 10⁻³ / 4 = 1.5 × 10⁻³ A
IR = (8 - 6) × 10⁻³ / 1 = 2 × 10⁻³ A
∴ izener diode = IR - IL = 0.5 × 10⁻³ A
At VB=16V, IL = 1.5 × 10⁻³ A
IR = (16 - 6) × 10⁻³ / 1 = 10 × 10⁻³ A
∴ izener diode = IR - IL = 8.5 × 10⁻³ A