By regulating of the voltage its meant that to keep the voltage approximately constant. But in case of the AC voltage regulator, the voltage regulator will keep the rms value of the voltage constant.
Now how it can be done:
first of all it depend upon the percentage of the voltage variation you may want.
it can be done simply by inserting a zener diode in the circuit you like to use. some times it has been seen that some sensitive circuits requires that the elements that regulates the voltage to be even more sensitive then the tolerance of the zener diode.
then there are many different methods even pre constructed voltage regulators in the market. Otherwise if you want to design a circuit according to your special requirements you can take advantages form SCRs, Zener diodes, electromagnetic switches and many other elements. What I Mean is this that there is no only one specific method for this. there are many ways for doing this. But it depends upon the type of the elements you have in hand and the tolerance you require.
I expect they are all in a special "lazy" class somewhere in India or similar, all got the same homework, all went to CR4 instead of using their own brain a little!
We will see a lot more I am afraid of their type......
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"What others say about you reveals more about them, than it does you." Anon.
I think you had posted the question two days ago as a guest and you must have got the "'answer" . look for preveous threads if you are really serious for answers . As you are a member now you can see site indices "whos online" at right hand and see for answers , and be "kind" enough to put questions in comment format with nature of posting and how much you are aware with little detailing.......this will help you more.... thank you ..........
If you don't pay attention when you are supposed to be learning, you won't understand anything. Anyone can memorize and 'parrot' an answer - Hollywood and NYC are full of people who make their living at doing this. If you want to know the operation of an AVR you are going to have to learn it, then you will understand the principle of it and other SIMPLE constructs. Maybe you need to go back to the basics. Start with Ohm's Law, then go on to Basic Electricity and Electronics.
I hope that you aren't trying to design any consumer electronics at this point in your game. The score will end up looking like a cricket match with you on the losing end.