i want to build a powersupply but i don't know which and what type of transformer i'm gonna used.

i have this schematic and still don't have 3.3v
http://imageshack.us/photo/my-images/862/powersupplyp.jpg/

 

What for, a PC or for project testing?

 

It would help if you gave more info about your application. How much current is required for each voltage? What are the tolerances for each supply?

Why is there a battery? Do you require survival during momentary brown outs?

The transformer selection is critical. It's output voltage will determine how much power each regulator dissipates under load.

Power supplies are NOT brain-dead simple designs to do.

 

I did one of these yesterday. Here's the basic layout. Just leave out the "5.1 kit".
Edit: This one uses a low dropout regulator. If you want to go old school, raise the transformer to 25.2 V center tapped (you can get 'em at Radio Shack).
We await more details from you.

 

A computer power supply will supply these and more.... plus it will only run you a few dollars , spend less time and effort on the power supply and have more time to spend on projects to power off of it.