AVR SX440 is a particular model of AVR (Automatic Voltage Regulator). In terms of working principle, this AVR is pretty same as any other AVR. If you would like to know the general principle of AVR, CR4 is not a forum to teach you such theory in detail.
__________________
"All my technical advices in this forum must be consulted with and approved by a local registered professional engineer before implementation" - Mohammed Samad (Linkedin Profile: http://www.linkedin.com/in/msamad)
Good Answers: