$9\mathrm{.}3$ A thyristor circuit is shown in Figure P$9\mathrm{.}3.$ The junction capacitance of thyristor is $C_{J2}=30pF$ and can be assumed to be independent of the off$-$state voltage. The limiting value of charging current to turn on the thyristor is $10$ mA and the critical value of $d\frac{v}{d}t$ is $500\frac{V}{}s.$ Determine the value of capacitance $C_s$ so that the thyristor cannot be turned on due to $d\frac{v}{d}t.$

FIGURE P$9\mathrm{.}3$