Rectifier Circuit, graph (output wave)

[calvert11]

Homework Statement

Sketch the output waveform:

http://img7.imageshack.us/img7/3774/recgraph.jpg
(The coloured lines I added myself)

Homework Equations

Nothing which applies, I think.

The Attempt at a Solution

The answer has already been provided. I just have a concept question.

The full rectifier circuit is active only where the input voltage is 4 or greater (marked in blue). But why 4?

Is it simply the sum of the 4 diode's threshold voltages (marked in red), that is, 1+1+1+1=4?

But only 2 diodes are active at a time (at each peak or valley of the input wave), right? So, why isn't it 1+1=2 instead?

Or am I on the wrong track entirely?

 

[berkeman]

Homework Statement

Sketch the output waveform:

http://img7.imageshack.us/img7/3774/recgraph.jpg
(The coloured lines I added myself)

Homework Equations

Nothing which applies, I think.

The Attempt at a Solution

The answer has already been provided. I just have a concept question.

The full rectifier circuit is active only where the input voltage is 4 or greater (marked in blue). But why 4?

Is it simply the sum of the 4 diode's threshold voltages (marked in red), that is, 1+1+1+1=4?

But only 2 diodes are active at a time (at each peak or valley of the input wave), right? So, why isn't it 1+1=2 instead?

Or am I on the wrong track entirely?

I believe it should be 2V in the + direction and 2V in the - direction. Is there a chance that is where they got the 4? It still shoule be shown as +/-2V on the triangle wave, though, not +4V. Was that picture part of the solution, or an interpretation of a written answer?