Fast AC-DC Converter

[ramonest]

Hi all, I was wandering through some datasheets when I saw an example schamatic of a "Fast AC-DC converter" on a OPAmp datasheet, and "fast half wave rectifier".  I can't understand how they work.
Maybe I should understand it but I don't because I've been slacking too much during summer or maybe I'm just an idiot...
I'd really apreciate some help undertanding these.

[ebclr]

It's a active full wave rectifier.

Negative cicles goes to ground positive cicles pass with a gain near 1, the second stage is nothing more than a adder and "pseudo active capacitor" or low pass filter

The adder will add the ac plus one half cicle inverted with double amplitude ( note r3 = 1/2 r6 ) and this will make a full wave rectifier

[ramonest]

Got it thanks! What aplications might it have?

[CJay]

Measurement circuits, it eliminates the diode drop. also known, I think, as a precision rectifier or super diode.

https://en.wikipedia.org/wiki/Precision_rectifier

[ramonest]

Ok thank you very much! You guys take less time to answer that the time my professor would need to decide to answer smoething nonrelated...
Hope you don't mind an idiot asking some more dumb questions in the future.

[David Hess]

The thing which makes these "fast", and they are not that fast, is that A1 does not have to recover from saturation.  Slower precision rectifier designs allow the operational amplifier to saturate on alternate cycles and operational amplifiers, even fast ones, recover from saturation slowly.