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The figure represents a voltage regulator circuit using a Zener diode. The breakdown voltage of the Zener diode is 6 \mathrm{~V}and the load resistance is \mathrm{R}_{\mathrm{L}}=4 \mathrm{k} \Omega. The series resistance of the circuit is R_i=1 \mathrm{k} \Omega. If the battery voltage V_B varies from 9 \mathrm{~V} to 17 \mathrm{~V}, what are the minimum and maximum values of the current through Zener diode?

Option: 1

\quad 0.5 \mathrm{~mA} ; 7 \mathrm{~mA}


Option: 2

\quad 0.5 \mathrm{~mA} ; 9.5 \mathrm{~mA}


Option: 3

\quad 1.5 \mathrm{~mA} ; 9.5 \mathrm{~mA}


Option: 4

\quad 1 \mathrm{~mA} ; 8.5 \mathrm{~mA}


Answers (1)

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\begin{aligned} & \text { At } \mathrm{V}_{\mathrm{B}}=9 \mathrm{~V} \\ & \mathrm{i}_{\mathrm{L}}=\frac{6 \times 10^{-3}}{4}=1.5 \times 10^{-3} \mathrm{~A} \\ & \mathrm{i}_{\mathrm{R}}=\frac{(9-6) \times 10^{-3}}{1}=3 \times 10^{-3} \mathrm{~A} \end{aligned}

\begin{aligned} & \therefore \mathrm{i}_{\text {zener diode }}=\mathrm{i}_{\mathrm{R}}-\mathrm{i}_{\text {load }} \\ & =1.5 \times 10^{-3} \mathrm{~A} \end{aligned}

\begin{aligned} & \text { At } \mathrm{V}_{\mathrm{B}}=17 \mathrm{~V} \\ & \mathrm{i}_{\mathrm{L}}=1.5 \times 10^{-3} \mathrm{~A} \\ & \mathrm{i}_{\mathrm{R}}=\frac{(17-6) \times 10^{-3}}{1}=11 \times 10^{-3} \mathrm{~A} \end{aligned}

\begin{aligned} & \therefore \mathrm{i}_{\text {zener diode }}=\mathrm{i}_{\mathrm{R}}-\mathrm{i}_{\mathrm{L}} \\ & =9.5 \times 10^{-3} \mathrm{~A} \end{aligned}

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