A voltage regulator is to have a nominal output voltage of \(10 \mathrm{~V}\). The specified Zener diode has a rating of \(1 \mathrm{~W}\), has a \(10 \mathrm{~V}\) drop at \(I_{Z}=25 \mathrm{~mA}\), and has a Zener resistance of \(r_{z}=5 \Omega\). The input power supply has a nominal value of \(V_{P S}=20 \mathrm{~V}\) and can vary by \(\pm 25\) percent. The output load current is to vary between \(I_{L}=0\) and \(20 \mathrm{~mA}\).

(a) If the minimum Zener current is to be \(I_{Z}=5 \mathrm{~mA}\), determine the required \(R_{i}\).

(b) Determine the maximum variation in output voltage.

(c) Determine the percent regulation.