can anybody explain me the WORKING of a peak detector.

 

Hello,

Here is a page with an opamp peak-detector.
http://www.falstad.com/circuit/e-peak-detect.html
When you rightclick on a part in the schematic you can edit the values.

There are much more applets on this site.
http://www.falstad.com/circuit/e-index.html

Greetings,
Bertus