The voltage regulator shown in Figure P15.79 is a variable voltage, 0 to \(5 \mathrm{~A}\) power supply. The transistor parameters are \(\beta=80\) and \(V_{B E}(\mathrm{on})=0.7 \mathrm{~V}\). The op-amp has a finite open-loop gain of \(A_{O L}=5 \times 10^{3}\). The zero-current Zener voltage is \(V_{Z O}=5.6 \mathrm{~V}\) and the Zener resistance is \(r_{z}=12 \Omega\).

(a) For \(I_{Z}=12 \mathrm{~mA}\), find \(R_{1}\).

(b) Determine the range of output voltage as the potentiometer \(R_{3}\) is varied.

(c) If the potentiometer is set such \(x=1\), determine the load regulation. Assume \(R_{o}\) of the op-amp is zero.

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V+= 25 V V+ = 25 V R ww + Vz Figure P15.79 (1-x) R2 = 1 10 -Vo R3 = 2 k RL ww ww R = 1 kQ