The diode in the next figure is considered ideal (i.e. works as a simple switch, being turned ON when $U_D \geq 0$ and OFF when $U_D < 0$). What is the voltage $U_S$ across $R_S$?
I've assumed that the diode is OFF and replaced it with an open circuit. The conditions are: $U_D > 0, I_D = 0$. I think I should be applying KVL now to find the voltage, but I'm not sure how. Also, I've also taken into consideration using Thevenin's Theorem, but I get stuck at a point where I need to find $I_D$ in order to calculate $U_S$. However, I think the assumed states method is better in this case. Could you give me an idea on how to continue this?