I can't figure out how those 110/220v transformer work. Like the ones in cell phone chargers. Say for example, if the primary voltage is 110v, the secondary will be 24v. But if the primary is connected to 220v, the secondary should be 48v. Are the stages after the secondary designed for up to 48v? These are the ones without 110v/220v select switch like in the back of a desktop PC SMPS. I am trying to design a linear 24V, 3A DC power supply. I couldn't find a small enough transformer. Everything I found was big(toroidal - 10cm dia and 5cm height) and heavy(1Kg). But the transformers in DC adapters like laptop have small form factor.