# Understanding/analyzing a power supply circuit

simulate this circuit – Schematic created using CircuitLab

I'm having some problems with this exercise, it is given:

$$V_1=220V_{rms}/60Hz\\\frac{V_2}{V_1}=1/15\\C=0,5mF\\R_L=12V \text{ and }1200mW\\\text{Led: }I_F=15mA \text{ for }V_F=2V\\\text{Voltage Regulator: For }15V<V_i<27V \rightarrow V_0=12V$$

It askes for the graph of $V_i(t)$, the resistance $R_{Led}$ and the voltage amplitude in the capacitor. The diodes are ideal (0V drop) and despise the regulator consumption.

Now I'm having problems with the following:

1) What is the meaning of the two expression: $R_L=12V$ and $1200mW$, $\text{Led: }I_F=15mA \text{ for }V_F=2V$? For the resistor is it the power when the voltage is 12V? For I is it the current when $V_f=2V$? If it is it doesn't make much sense since $V_0=12V$ always. Could I just multiply by 6 to get current for 12V?

2) It seems that I have to calculate the voltage on the capacitor? If so (and even if don't), I know the formula for the voltage according to time ${\displaystyle V(t)=V_{0}(1-e^{-t/\tau })}$ (charging) but I've only applied to circuits with one resistance, how to do it in the circuit above? I imagine that would something more complex than calculating the equivalent resistance in parallel or series.

Excuse me my english and I appreciate any help I can get.