I wanna use a transformer to convert AC voltage. 220V AC ------ for example, 5V 30mA AC. Many people told me, this transformer will be huge big. because the main frequency is huge low But, I check something about the transformer design, still have no idea, how big it will be. (BTW, 50Hz main Fre is so low, I am not sure if the transformer could magnetize..., maybe need big Fe core....)

For my converting requirement, and take Piezo transformer or any other high-advanced transformer design (like pcb stack twisting transformer) for example (smaller, better). How large it will be ? Suprise me.

(I have no idea about the transformer design, I mean, how thick the conventional coil wire, etc. I just know the basic equations Vin x Iin = Vout x I out...some text book stuff, no experimental experience.)

I know this question sounds a little stupid...