Assume that the conduction angle of the silicon diodes shown in the circuit of Figure P17.15 is
$$
\begin{aligned}
& \phi=23^{\circ} \\
& v_{s 1}(t)=v_{s 2}(t)=8 \cos \omega t \quad \mathrm{~V} \\
& \omega=377 \mathrm{rad} / \mathrm{s} \quad R_o=20 \mathrm{k} \Omega \\
& C=0.5 \mu \mathrm{~F}
\end{aligned}
$$
Determine the rms value of the ripple voltage.