My guess is that you have to find the Vin that causes each diode to conduct

Agreed.
I think the question should read:
6.1. Indicate for which VIN values diode D1 conducts.
6.2. Indicate for which VIN values diode D2 conducts.

 

Agreed.
I think the question should read:
6.1. Indicate for which VIN values diode D1 conducts.
6.2. Indicate for which VIN values diode D2 conducts.

Yes it is, sorry for my english, i am from Portugal.

 

Agreed.
I think the question should read:
6.1. Indicate for which VIN values diode D1 conducts.
6.2. Indicate for which VIN values diode D2 conducts.

Yeah that sounds very good.

I did a full analysis and found that the output waveshape for each half cycle is a combination of two different sinusoidal half waves where each sinusoid is governed by the diode for that half cycle. One half sinusoid is of higher amplitude and one has a DC offset. It is an interesting waveshape i'll post at an appropriate time.

 

Yes it is, sorry for my english, i am from Portugal.

I studied some Brazilian Portuguese some years back but already forgot a lot of it. I even forgot how to spell "Portuguese" and had to look it up just now (ha ha).

Oh BTW for what it is worth, we usually capitalize the word "English".

Ok i'll give some starter hints.
First, open circuit R1 (or the input voltage) and set D2 to a DC voltage source of 0.8v with a 100 Ohm resistor in series with it and short out the 100 Ohm resistor and open circuit D1, then calculate the output voltage Vout. Now that you have that Vout, calculate the input voltage required to get that output voltage with both D2 and D1 open circuited. Does this make sense to you?

It appears to me that maybe you should start with a simpler diode circuit in order to get a little more familiar with the behavior of diodes that switch on and off based on the circuit voltages and or currents. Probably a single diode circuit would be best.

 

The fact that the problem specifies diode forward voltage drop and diode resistance indicates the diode operates as a switch, so there are 4 different circuits to analyze during the course of a single power cycle (actually only 2 since the polarities are symmetrical). When the forward voltage across the diode exceeds the specified Vd=0.8 V (the switching point), the diode open circuit is replaced by a voltage source of 0.8V in series with a resistor of the specified Rd. The question seems to be at what value of Vin does this switch occur, and what is the peak output voltage at the peak input voltage of 30V? Not too sure what relevance the frequency has.